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Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
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5
Working with Chemicals

   

5.A INTRODUCTION

 

81

   

5.B PRUDENT PLANNING

 

81

   

5.C GENERAL PROCEDURES FOR WORKING WITH HAZARDOUS CHEMICALS

 

82

   

5.C.1 Personal Behavior

 

82

   

5.C.2 Minimizing Exposure to Chemicals

 

82

   

5.C.2.1 Avoiding Eye Injury

 

82

   

5.C.2.2 Avoiding Ingestion of Hazardous Chemicals

 

82

   

5.C.2.3 Avoiding Inhalation of Hazardous Chemicals

 

83

   

5.C.2.4 Avoiding Injection of Hazardous Chemicals

 

83

   

5.C.2.5 Minimizing Skin Contact

 

83

   

5.C.2.6 Clothing and Protective Apparel

 

83

   

5.C.3 Housekeeping

 

84

   

5.C.4 Transport of Chemicals

 

84

   

5.C.5 Storage of Chemicals

 

84

   

5.C.6 Disposal of Chemicals

 

84

   

5.C.7 Use and Maintenance of Equipment and Glassware

 

85

   

5.C.8 Handling Flammable Substances

 

85

   

5.C.9 Working with Scaled-up Reactions

 

86

   

5.C.10 Responsibility for Unattended Experiments and Working Alone

 

86

   

5.C.11 Responding to Accidents and Emergencies

 

86

   

5.C.11.1 General Preparation for Emergencies

 

86

   

5.C.11.2 Handling the Accidental Release of Hazardous Substances

 

87

   

5.C.11.3 Notification of Personnel in the Area

 

87

   

5.C.11.4 Treatment of Injured and Contaminated Personnel

 

87

   

5.C.11.5 Spill Containment

 

88

   

5.C.11.6 Spill Cleanup

 

88

   

5.C.11.7 Handling Leaking Gas Cylinders

 

88

   

5.C.11.8 Handling Spills of Elemental Mercury

 

89

   

5.C.11.9 Responding to Fires

 

89

   

5.D WORKING WITH SUBSTANCES OF HIGH TOXICITY

 

90

   

5.D.1 Planning

 

90

   

5.D.2 Experiment Protocols Involving Highly Toxic Chemicals

 

90

   

5.D.3 Designated Areas

 

91

   

5.D.4 Access Control

 

91

   

5.D.5 Special Precautions for Minimizing Exposure to Highly Toxic Chemicals

 

91

   

5.D.6 Preventing Accidents and Spills with Substances of High Toxicity

 

92

   

5.D.7 Storage and Waste Disposal

 

93

   

5.D.8 Multihazardous Materials

 

93

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
×
Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
×

5.A INTRODUCTION

Prudent execution of experiments requires not only sound judgment and an accurate assessment of the risks involved in laboratory work, but also the selection of appropriate work practices to reduce risk and protect the health and safety of the laboratory workers as well as the public and the environment. Chapter 3 provides specific guidelines to enable laboratory workers to evaluate the hazards and assess the risks associated with laboratory chemicals, equipment, and operations. Chapter 4 demonstrates how to control those risks when managing the inventory of chemicals in the laboratory. How the protocols outlined in Chapter 3 are put to use in the execution of a carefully planned experiment is the subject of Chapter 5.

Chapter 5 presents general guidelines for laboratory work with hazardous chemicals rather than specific standard operating procedures for individual substances. Hundreds of thousands of different chemicals are encountered in the research conducted in laboratories, and the specific health hazards associated with most of these compounds are generally not known. Also, laboratory work frequently generates new substances of unknown properties and unknown toxicity. Consequently, the only prudent course is for laboratory personnel to conduct their work under conditions that minimize the risks due to both known and unknown hazardous substances. The general work practices outlined in this chapter are designed to achieve this purpose.

Specifically, section 5.C describes basic prudent practices that should be employed in all laboratory work with chemicals. These guidelines are the standard operating procedures for all work conducted in laboratories where hazardous chemicals are stored or are in use.

In section 5.D, additional special procedures are presented for work with highly toxic substances. How to determine when these additional procedures are necessary is discussed in detail in Chapter 3, section 3.C. Section 5.E gives detailed special procedures for work with chemicals that pose risks due to biohazards and radioactivity; section 5.F, flammability; and section 5.G, reactivity and explosibility. Special considerations for work with compressed gases are the subject of section 5.H.

Chapter 6 provides precautionary methods for handling laboratory equipment commonly used in conjunction with hazardous chemicals. Chapters 3, 5, and 6 should all be consulted before working with hazardous chemicals.

Four fundamental principles underlie all of the work practices discussed in this chapter:

  • Plan ahead. Determine the potential hazards associated with an experiment before beginning it.

  • Minimize exposure to chemicals. Do not allow laboratory chemicals to come in contact with skin. Use laboratory hoods and other ventilation devices to prevent exposure to airborne substances whenever possible.

  • Do not underestimate risks. Assume that any mixture of chemicals will be more toxic than its most toxic component. Treat all new compounds and substances of unknown toxicity as toxic substances.

  • Be prepared for accidents. Before beginning an experiment, know what specific action to take in the event of the accidental release of any hazardous substance. Know the location of all safety equipment and the nearest fire alarm and telephone, and know what telephone numbers to call and whom to notify in the event of an emergency. Be prepared to provide basic emergency treatment. Keep your co-workers informed of your activities so that they can respond appropriately.

5.B Prudent Planning

The risk associated with an experiment should be determined before the laboratory work begins. The hypothetical question that should be posed before an experiment is, ''What would happen if... ?" For the possible contingencies, preparations should be made to take the appropriate emergency actions. The worker should know the location of emergency equipment and how to use it. He or she should be familiar with emergency procedures and should know how to obtain help in an emergency. Any special safety precautions that may be required should be addressed before the experiment is begun. The consequences of loss of electrical power or water pressure should also be considered.

The physical and health hazards associated with chemicals should be determined before working with them. This determination may involve consulting literature references, Laboratory Chemical Safety Summaries (LCSSs), Material Safety Data Sheets (MSDSs), or other reference materials (see also Chapter 3, section 3.B) and may require discussions with the laboratory supervisor and consultants such as safety and industrial hygiene officers. Every step of the waste minimization and removal processes should be checked against federal, state, and local regulations. Production of mixed chemical-radioactive-biological waste (see Chapter 7, section 7.C.1.3) should not be considered without discussions with environmental health and safety experts.

Many of the general practices applicable to working

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
×

with hazardous chemicals are given elsewhere in this volume (as discussed in Chapter 2). The reader is referred to Chapter 4, section 4.C, for detailed instructions on the transport of chemicals; Chapter 4, section 4.E on storage; Chapter 6 for information on use and maintenance of equipment and glassware; and Chapter 7 for information on disposal of chemicals.

5.C GENERAL PROCEDURES FOR WORKING WITH HAZARDOUS CHEMICALS

5.C.1 Personal Behavior

Professional standards of personal behavior are required in any laboratory:

  • Avoid distracting or startling other workers.

  • Do not allow practical jokes and horseplay at any time.

  • Use laboratory equipment only for its designated purpose.

  • Do not allow visitors, including children and pets, in laboratories where hazardous substances are stored or are in use or hazardous activities are in progress.

  • If children are permitted in laboratories, for example, as part of an educational or classroom activity, ensure that they are under the direct supervision of qualified adults.

  • Make sure that teaching materials and publicity photographs show people wearing appropriate safety gear, in particular, eye protection.

5.C.2 Minimizing Exposure to Chemicals

Precautions should be taken to avoid exposure by the principal routes, that is, contact with skin and eyes, inhalation, and ingestion, which are discussed in detail in Chapter 3, section 3.C.

5.C.2.1 Avoiding Eye Injury

Eye protection should be required for all personnel and visitors in all locations where chemicals are stored or used. Eye protection is required whether or not one is actually performing a chemical operation. Visitor safety glasses should be made available at the entrances to all laboratories.

Researchers should assess the risks associated with an experiment and use the appropriate level of eye protection:

  • Safety glasses with side shields provide the minimum protection acceptable for regular use. Safety glasses must meet the American National Standards Institute (ANSI) standard Z87.1-1989, Standard for Occupational and Educational Eye and Face Protection, which specifies a minimum lens thickness, certain impact resistance requirements, and so on.

  • Safety splash goggles or face shields should be worn when carrying out operations in which there is any danger from splashing chemicals or flying particles. These thin shields do not provide protection from projectiles, however.

  • Goggles are preferred over regular safety glasses to protect against hazards such as projectiles, as well as when working with glassware under reduced or elevated pressures (e.g., sealed tube reactions), when handling potentially explosive compounds (particularly during distillations), and when employing glassware in high-temperature operations.

  • Because goggles offer little protection to the face and neck, full-face shields should be worn when conducting particularly hazardous laboratory operations. In addition, glassblowing and the use of laser or ultraviolet light sources require special glasses or goggles.

Ordinary prescription glasses do not provide adequate protection against injury. Prescription safety glasses and goggles can be obtained.

Contact lenses offer no protection against eye injury and cannot be substituted for safety glasses and goggles. It is best not to wear contact lenses when carrying out operations where chemical vapors are present or a chemical splash to the eyes or chemical dust is possible because contact lenses can increase the degree of harm and can interfere with first aid and eye-flushing procedures. If an individual must wear contact lenses for medical reasons, then safety glasses with side shields or tight-fitting safety goggles must be worn over the contact lenses.

5.C.2.2 Avoiding Ingestion of Hazardous Chemicals

Eating, drinking, smoking, gum chewing, applying cosmetics, and taking medicine in laboratories where hazardous chemicals are used should be strictly prohibited. Food, beverages, cups, and other drinking and eating utensils should not be stored in areas where hazardous chemicals are handled or stored. Glassware used for laboratory operations should never be used to prepare or consume food or beverages. Laboratory refrigerators, ice chests, cold rooms, ovens, and so forth should not be used for food storage or preparation. Laboratory water sources and deionized laboratory water should not be used for drinking water.

Laboratory chemicals should never be tasted. A pipet bulb or aspirator should be used to pipet chemi-

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
×

cals or to start a siphon; pipetting should never be done by mouth. Hands should be washed with soap and water immediately after working with any laboratory chemicals, even if gloves have been worn.

5.C.2.3 Avoiding Inhalation of Hazardous Chemicals

Toxic chemicals or compounds of unknown toxicity should never be smelled. Procedures involving volatile toxic substances and operations involving solid or liquid toxic substances that may result in the generation of aerosols should be conducted in a laboratory hood. Dusts should be recognized as potentially contaminated and hazardous. Hoods should not be used for disposal of hazardous volatile materials by evaporation. Such materials should be treated as chemical waste and disposed of in appropriate containers in accord with institutional procedures.

The following general rules should be followed when using laboratory hoods:

  • For work involving hazardous substances, use only hoods that have been evaluated for adequate face velocity and proper operation. Hood operation should be inspected regularly, and the inspection certified in a visible location.

  • Keep reactions and hazardous chemicals at least 6 inches behind the plane of the hood sash.

  • Never put your head inside an operating laboratory hood to check an experiment. The plane of the sash is the barrier between contaminated and uncontaminated air.

  • On hoods where sashes open vertically, work with the hood sash in the lowest possible position. On hoods where sashes open horizontally, position one of the doors to act as a shield in the event of an accident in the hood. When the hood is not in use, keep the sash closed to maintain laboratory airflow.

  • Keep hoods clean and clear; do not clutter with bottles or equipment. If there is a grill along the bottom slot or a baffle in the back of the hood, clean them regularly so they do not become clogged with papers and dirt. Allow only materials actively in use to remain in the hood. Following this rule will provide optimal containment and reduce the risk of extraneous chemicals being involved in any fire or explosion. Support any equipment that needs to remain in hoods on racks or feet to provide airflow under the equipment.

  • Report suspected hood malfunctions promptly to the appropriate office, and make sure they are corrected. Post the name of the individual responsible for use of the hood in a visible location. Clean hoods before maintenance personnel work on them.

(See Chapter 8, section 8.C, for more information on hoods.)

5.C.2.4 Avoiding Injection of Hazardous Chemicals

Solutions of chemicals are often transferred in syringes, which for many uses are fitted with sharp needles. The risk of inadvertent injection is significant, and vigilance is required to avoid that accident. Needles must be properly disposed of in "sharps" containers. Use special care when handling solutions of chemicals in hypodermic syringes.

5.C.2.5 Minimizing Skin Contact

Wear gloves whenever handling hazardous chemicals, sharp-edged objects, very hot or very cold materials, toxic chemicals, and substances of unknown toxicity. The following general guidelines apply to the selection and use of protective gloves:

  • Wear gloves of a material known to be resistant to permeation by the substances in use. Wearing the wrong type of glove can be more hazardous than wearing no gloves at all, because if a chemical seeps through, the glove can hold it in prolonged contact with the wearer's hand.

  • Inspect gloves for small holes or tears before use.

  • Wash gloves appropriately before removing them. (Note: some gloves, e.g., leather and polyvinyl alcohol, are water-permeable.)

  • In order to prevent the unintentional spread of hazardous substances, remove gloves before handling objects such as doorknobs, telephones, pens, and computer keyboards.

  • Replace gloves periodically, depending on the frequency of use and their permeation and degradation characteristics relative to the substances handled.

(For more information, see OSHA Personal Protective Equipment Standard (29 CFR 1910.132-138) regarding hand protection.)

5.C.2.6 Clothing and Protective Apparel

Long hair and loose clothing or jewelry must be confined when working in the laboratory. Unrestrained long hair, loose or torn clothing, and jewelry can dip into chemicals or become ensnared in equipment and moving machinery. Clothing and hair can catch fire. Sandals and open-toed shoes should never be worn in a laboratory in which hazardous chemicals are in use.

It is advisable to wear a laboratory coat when work-

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
×

ing with hazardous chemicals. This is particularly important if personal clothing leaves skin exposed. Apparel giving additional protection (e.g., nonpermeable laboratory aprons) is required for work with certain hazardous substances. Because many synthetic fabrics are flammable and can adhere to the skin, they can increase the severity of a burn. Therefore, cotton is the preferred fabric.

5.C.3 Housekeeping

There is a definite correlation between orderliness and level of safety in the laboratory. In addition, a disorderly laboratory can hinder or endanger emergency response personnel. The following housekeeping rules should be adhered to:

  • Never obstruct access to exits and emergency equipment such as fire extinguishers and safety showers.

  • Clean work areas (including floors) regularly. Properly label (see Chapter 3, section 3.B.4) and store (see Chapter 4, section 4.E) all chemicals. Accumulated dust, chromatography adsorbents, and other chemicals pose respiratory hazards.

  • Secure all compressed gas cylinders to walls or benches.

  • Do not store chemical containers on the floor.

  • Do not use floors, stairways, and hallways as storage areas.

5.C.4 Transport of Chemicals

Chemicals being transported outside the laboratory or between stockrooms and laboratories should be in break-resistant secondary containers. Secondary containers commercially available are made of rubber, metal, or plastic, with carrying handle(s), and are large enough to hold the contents of the chemical containers in the event of breakage. When transporting cylinders of compressed gases, the cylinder should always be strapped in a cylinder cart and the valve protected with a cover cap. When cylinders must be transported between floors, passengers should not be in the elevator.

5.C.5 Storage of Chemicals

The accumulation of excess chemicals can be avoided by purchasing the minimum quantities necessary for a research project. All containers of chemicals should be labeled properly. Any special hazards should be indicated on the label. For certain classes of compounds (e.g., ethers as peroxide formers), the date the container was opened should be written on the label. Peroxide formers should have the test history and date of discard written on the label as well. Only small quantities (less than 1 liter (L)) of flammable liquids should be kept at workbenches. Larger quantities should be stored in approved storage cabinets. Quantities greater than 1 L should be stored in metal or break-resistant containers. Large containers (more than 1 L) should be stored below eye level on low shelves. Hazardous chemicals and waste should never be stored on the floor.

Refrigerators used for storage of flammable chemicals must be explosion-proof, laboratory-safe units. Materials placed in refrigerators should be clearly labeled with water-resistant labels. Storage trays or secondary containers should be used to minimize the distribution of material in the event a container should leak or break. It is good practice to retain the shipping can for such secondary containers.

All chemicals should be stored with attention to incompatibilities so that if containers break in an accident, reactive materials do not mix and react violently.

(See Chapter 4, section 4.E, and Chapter 7, section 7.C.1.2, for more information.)

5.C.6 Disposal of Chemicals

Virtually every laboratory experiment generates some waste, which may include such items as used disposable labware, filter media and similar materials, aqueous solutions, and hazardous chemicals. The overriding principle governing the handling of waste in prudent laboratory practice is that no activity should begin unless a plan for the disposal of nonhazardous and hazardous waste has been formulated. Application of this simple rule will ensure that the considerable regulatory requirements for waste handling are met and that unexpected difficulties, such as the generation of a form of waste (e.g., chemical-radioactive-biological) that the institution is not prepared to deal with, are avoided.

Each category of waste has certain appropriate disposal methods. In choosing among these methods, several general principles apply, but local considerations can strongly influence the application of these rules:

  • Hazardous or flammable waste solvents should be collected in an appropriate container pending transfer to the institution's central facility or satellite site for chemical waste handling or pickup by an outside disposal agency.

  • Waste solvents can usually be mixed for disposal, with due regard for the compatibility of the compo-

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
×

nents. Sometimes halogenated and nonhalogenated wastes must be segregated for separate handling.

  • The container used for the collection of liquid waste must be appropriate for its use. Glass bottles are impervious to most chemicals but present a breakage hazard, and narrow necks can cause difficulty in emptying the bottles. The use of plastic (e.g., polyethylene jerrycans) or metal (galvanized or stainless steel) safety containers for the collection of liquid waste is strongly encouraged and, indeed, required for flammable liquids.

  • Galvanized steel safety cans should not be used for halogenated waste solvents because they tend to corrode and leak. Flame arresters in safety cans can easily become plugged if there is sediment and may need to be cleaned occasionally.

  • Waste containers should be clearly and securely labeled as to their contents and securely capped when not in immediate use.

  • Aqueous waste should be collected separately from organic solvent waste. Some laboratories may be served by a wastewater treatment facility that allows the disposal of aqueous waste to the sanitary sewer if it falls within a narrow range of acceptable waste types. Thus, solutions of nonhazardous salts or water-miscible organic materials may be acceptable in some localities. Solutions containing flammable or hazardous waste, even if water-miscible, are almost never allowed, and water-immiscible substances must never be put down the drain. Aqueous waste for nonsewer disposal should be collected in a container selected for resistance to corrosion. Glass should not be used for aqueous waste if there is danger of freezing. Depending on the requirements of the disposal facility, adjustment of the pH of aqueous waste may be required. Such adjustment requires consideration of the possible consequences of the neutralization reaction that might take place: gas evolution, heat generation, or precipitation.

  • Solid chemical waste, such as reaction by-products, or contaminated filter or chromatography media, should be placed in an appropriately labeled container to await disposal or pickup. Unwanted reagents should be segregated for disposal in their original containers, if possible. If original containers are used, labels should be intact and fully legible. Every effort should be made to use, share, or recycle unwanted reagents rather than commit them to disposal. (See Chapter 4, sections 4.D and 4.E, for a discussion of labeling alternatives.)

  • Nonhazardous solid waste can be disposed of in laboratory trash or segregated for recycling. Institutional policy should be consulted for these classifications. (See Chapter 7 for further information regarding disposal, and check the appropriate LCSS to determine toxicity.)

5.C.7 Use and Maintenance of Equipment and Glassware

Good equipment maintenance is essential for safe and efficient operations. Laboratory equipment should be inspected and maintained regularly and serviced on schedules that are based on both the likelihood of and the hazards from failure. Maintenance plans should ensure that any lockout procedures cannot be violated.

Careful handling and storage procedures should be used to avoid damaging glassware. Chipped or cracked items should be discarded or repaired. Vacuum-jacketed glassware should be handled with extreme care to prevent implosions. Evacuated equipment such as Dewar flasks or vacuum desiccators should be taped or shielded. Only glassware designed for vacuum work should be used for that purpose.

Hand protection should be used when picking up broken glass. Small pieces should be swept up with a brush into a dustpan. Glassblowing operations should not be attempted unless proper annealing facilities are available. Adequate hand protection should be used when inserting glass tubing into rubber stoppers or corks or when placing rubber tubing on glass hose connections. Cuts from forcing glass tubing into stoppers or plastic tubing are the most common kind of laboratory accident and are often serious. Tubing should be fire polished or rounded and lubricated, and hands should be protected with toweling and held close together to limit movement of glass should it fracture. The use of plastic or metal connectors should be considered.

(Refer to Chapter 6 for more discussion.)

5.C.8 Handling Flammable Substances

Flammable substances present one of the most widespread hazards encountered in the laboratory. Because flammable materials are employed in so many common laboratory operations, basic prudent laboratory practice should always assume the presence of fire hazard unless a review of the materials and operations in the laboratory verifies the absence of significant hazard. For example, simple operations with aqueous solutions in a laboratory where no flammable organic liquids are present involve no appreciable fire hazard. In all other circumstances, the risk of fire should be recognized and kept to a minimum.

For a fire to start, an ignition source, fuel, and oxidizer must be present. Prudent laboratory practice in avoiding fire is based on avoiding the presence of one of these components. The flammability and explosive characteristics of the materials being used should be

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
×

known. Solvent labels, LCSSs, or other sources of information can be consulted to learn the flash point, vapor pressure, and explosive limit in air of each chemical handled. While all flammable substances should be handled prudently, the extreme flammability of some materials requires additional precautions.

To ensure that laboratory workers respond appropriately, they should be briefed on the necessary steps to take in case of a fire. The laboratory should be set up in such a way that the locations of fire alarms, pull stations, fire extinguishers, safety showers, and other emergency equipment are marked and all laboratory personnel alerted to them (see section 5.C.11 below). Exit routes in case of fire should be reviewed. Fire extinguishers in the immediate vicinity of an experiment should be appropriate to the particular fire hazards. Proper extinguishers must be used because fires can be exacerbated by use of an inappropriate extinguisher. Telephone numbers to call in case of an accident should be readily available.

(Refer to Chapter 3, section 3.B, for further information.)

5.C.9 Working with Scaled-up Reactions

Scale-up of reactions from those producing a few milligrams or grams to those producing more than 100 g of a product may represent several orders of magnitude of added risk. The attitudes, procedures, and controls applicable to large-scale laboratory reactions are fundamentally the same as those for smaller scale procedures. However, differences in heat transfer, stirring effects, times for dissolution, and effects of concentration and the fact that substantial amounts of materials are being used introduce the need for special vigilance for scaled-up work. Careful planning and consultation with experienced workers to prepare for any eventuality are essential for large-scale laboratory work.

Although it is not always possible to predict whether a scaled-up reaction has increased risk, hazards should be evaluated if the following conditions exist:

  • The starting material and/or intermediates contain functional groups that have a history of being explosive-e.g., N-N, N-O, N-halogen, O-O, and O-halogen bonds-or that could explode to give a large increase in pressure.

  • A reactant or product is unstable near the reaction or work-up temperature. A preliminary test consists of heating a small sample in a melting point tube.

  • A reaction is delayed; that is, an induction period is required.

  • Gaseous by-products are formed.

  • A reaction is exothermic. What can be done to provide cooling if the reaction begins to run away?

  • A reaction requires a long reflux period. What will happen if solvent is lost owing to poor condenser cooling?

  • A reaction requires temperatures below 0 °C. What will happen if the reaction warms to room temperature?

In addition, thermal phenomena that produce significant effects on a larger scale may not have been detected in smaller-scale reactions and therefore could be less obvious than toxic and/or environmental hazards. Thermal analytical techniques should be used to determine whether any process modifications are necessary.

(See sections 5.D.1 and 5.G.1 and Chapter 4, section 4.B, for more information.)

5.C.10 Responsibility for Unattended Experiments and Working Alone

Generally, it is prudent to avoid working alone at the bench in a laboratory building. Individuals working in separate laboratories outside of working hours should make arrangements to check on each other periodically, or ask security guards to check on them. Experiments known to be hazardous should not be undertaken by a worker who is alone in a laboratory. Under unusually hazardous conditions, special rules may be necessary.

Laboratory operations involving hazardous substances are sometimes carried out continuously or overnight with no one present. It is the responsibility of the worker to design these experiments so as to prevent the release of hazardous substances in the event of interruptions in utility services such as electricity, cooling water, and inert gas. Laboratory lights should be left on, and signs should be posted identifying the nature of the experiment and the hazardous substances in use. If appropriate, arrangements should be made for other workers to periodically inspect the operation. Information should be posted indicating how to contact the responsible individual in the event of an emergency.

(See also Chapter 3, section 3.A.)

5.C.11 Responding to Accidents and Emergencies

5.C.11.1 General Preparation for Emergencies

All laboratory personnel should know what to do in case of an emergency. Laboratory work should not

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
×

be undertaken without knowledge of the following points:

  • How to report a fire, injury, chemical spill, or other emergency to summon emergency response;

  • The location of emergency equipment such as safety showers and eyewashes;

  • The location of fire extinguishers and spill control equipment; and

  • The locations of all available exits for evacuation from the laboratory.

The above information should be available in descriptions of laboratory emergency procedures and in the institution's Chemical Hygiene Plan. Laboratory supervisors should ensure that all laboratory workers are familiar with all of this information.

Inappropriate action by individuals inadequately trained in emergency procedures can make the consequences of an emergency worse. Laboratory workers should be aware of their level of expertise with respect to use of fire extinguishers and emergency equipment, dealing with chemical spills, and dealing with injuries. They should not take actions outside the limits of their expertise but instead should rely on trained personnel.

Names and telephone numbers of responsible individuals should be posted on the laboratory door.

5.C.11.2 Handling the Accidental Release of Hazardous Substances

Experiments should always be designed so as to minimize the possibility of an accidental release of hazardous substances. Experiments should use the minimal amounts of hazardous compounds practical, and such materials should be transported properly, using break-resistant bottles or secondary containers. Personnel should be familiar with the properties (physical, chemical, and toxicological) of hazardous substances before working with them. A contingency plan to deal with the accidental release of each hazardous substance should be in place. The necessary safety equipment, protective apparel, and spill control materials should be readily available. In the event of a laboratory-scale spill, the following general guidelines for handling it should be followed in the indicated order:

  1. Notify other laboratory personnel of the accident and, if necessary, evacuate the area (see section 5.C.11.3).

  2. Tend to any injured or contaminated personnel and, if necessary, request help (see section 5.C.11.4).

  3. Take steps to confine and limit the spill if this can be done without risk of injury or contamination (see section 5.C.11.5).

  4. Clean up the spill using appropriate procedures (see section 5.C.11.6). Dispose of contaminated materials properly, according to the procedures described in Chapter 7, section 7.B.8.

(See Chapter 6, section 6.F.2, for more information on emergency procedures.)

5.C.11.3 Notification of Personnel in the Area

Other nearby workers should be alerted to the accident and the nature of the chemicals involved. In the event of the release of a highly toxic gas or volatile material, the laboratory should be evacuated and personnel posted at entrances to prevent other workers from inadvertently entering the contaminated area. In some cases (e.g., incidents involving the release of highly toxic substances and spills occurring in nonlaboratory areas), it may be appropriate to activate a fire alarm to alert personnel to evacuate the entire building. The proper authorities should be called on for emergency assistance.

5.C.11.4 Treatment of Injured and Contaminated Personnel

If an individual is injured or contaminated with a hazardous substance, tending to him or her generally takes priority over implementing the spill control measures outlined in section 5.A.11.5 below. It is important to obtain medical attention as soon as possible by calling the posted number.

For spills covering small areas of skin, follow these procedures:

  1. Immediately flush with flowing water for no less than 15 minutes.

  2. If there is no visible burn, wash with warm water and soap, removing any jewelry to facilitate clearing of any residual materials.

  3. Check the Material Safety Data Sheet (MSDS) to see if any delayed effects should be expected.

  4. Seek medical attention for even minor chemical burns.

  5. Do not use creams, lotions, or salves.

Take the following steps for spills on clothes:

  1. Do not attempt to wipe the clothes.

  2. Quickly remove all contaminated clothing, shoes, and jewelry while using the safety shower.

  3. Seconds count, so do not waste time because of modesty.

  4. Take care not to spread the chemical on the skin or, especially, in the eyes.

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
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  1. Use caution when removing pullover shirts or sweaters to prevent contamination of the eyes; it may be better to cut the garments off.

  2. Immediately flood the affected body area with warm water for at least 15 minutes. Resume if pain returns.

  3. Get medical attention as soon as possible.

  4. Discard contaminated clothes or have them laundered separately from other clothing.

For splashes into the eye, take these steps:

  1. Immediately flush with tepid potable water from a gently flowing source for at least 15 minutes.

  2. Hold the individual's eyelids away from the eyeball, and instruct him or her to move the eye up and down and sideways to wash thoroughly behind the eyelids.

  3. Use an eyewash. If one is not available, place the injured person on his or her back and pour water gently into the eyes for at least 15 minutes.

  4. Follow first aid by prompt treatment by a member of a medical staff or an ophthalmologist who is acquainted with chemical injuries.

5.C.11.5 Spill Containment

Every laboratory in which hazardous substances are used should have spill control kits tailored to deal with the potential risk associated with the materials being used in the laboratory. These kits are used to confine and limit the spill if such actions can be taken without risk of injury or contamination. A specific individual should be assigned to maintain the kit. Spill control kits should be located near laboratory exits for ready access. Typical spill control kits might include these items:

  • Spill control pillows. These commercially available pillows generally can be used for absorbing solvents, acids, and caustic alkalis, but not hydrofluoric acid.

  • Inert absorbents such as vermiculite, clay, sand, kitty litter, and Oil Dri®. Paper is not an inert material and should not be used to clean up oxidizing agents such as nitric acid.

  • Neutralizing agents for acid spills such as sodium carbonate and sodium bicarbonate.

  • Neutralizing agents for alkali spills such as sodium bisulfate and citric acid.

  • Large plastic scoops and other equipment such as brooms, pails, bags, and dust pans.

  • Appropriate personal protective equipment, warnings, barricade tapes, and protection against slips or falls on wet floor during and after cleanup.

5.C.11.6 Spill Cleanup

Specific procedures for cleaning up spills vary depending on the location of the accident, the amount and physical properties of the spilled material, the degree and type of toxicity, and the training of the personnel involved. Outlined below are some general guidelines for handling several common spills:

  • Materials of low flammability that are not volatile or that have low toxicity. This category of hazardous substances includes inorganic acids (e.g., sulfuric and nitric acid) and caustic bases (e.g., sodium and potassium hydroxide). For cleanup, appropriate protective apparel, including gloves, goggles, and (if necessary) shoe coverings should be worn. Absorption of the spilled material with an inert absorbent and appropriate disposal are recommended. The spilled chemicals can be neutralized with materials such as sodium bisulfate (for alkalis) and sodium carbonate or bicarbonate (for acids), absorbed on Floor-Dri ® or vermiculite, scooped up, and disposed of according to the procedures detailed in Chapter 7, section 7.B.8.

  • Flammable solvents. Fast action is crucial when a flammable solvent of relatively low toxicity is spilled. This category includes petroleum ether, pentane, diethyl ether, dimethoxyethane, and tetrahydrofuran. Other workers in the laboratory should be alerted, all flames extinguished, and any spark-producing equipment turned off. In some cases the power to the laboratory should be shut off with the circuit breaker, but the ventilation system should be kept running. The spilled solvent should be soaked up with spill absorbent or spill pillows as quickly as possible. These should be sealed in containers and disposed of properly. Nonsparking tools should be used in cleanup.

  • Highly toxic substances. The cleanup of highly toxic substances should not be attempted alone. Other personnel should be notified of the spill, and the appropriate safety or industrial hygiene office should be contacted to obtain assistance in evaluating the hazards involved. These professionals will know how to clean up the material and may perform the operation.

5.C.11.7 Handling Leaking Gas Cylinders

Leaking gas cylinders constitute hazards that may be so serious as to require an immediate call for outside help. Workers should not apply extreme tension to close a stuck valve. Personal protective equipment should be worn. The following guidelines cover leaks of various types of gases:

  • Flammable, inert, or oxidizing gases. The cylinder

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
×

should be moved to an isolated area, away from combustible material if the gas is flammable or an oxidizing agent, and signs should be posted that describe the hazards and state warnings. Care should be taken when moving leaking cylinders of flammable gases so that accidental ignition does not occur. If feasible, leaking cylinders should always be moved into laboratory hoods until exhausted.

  • Corrosive gases. Corrosive gases may increase the size of the leak as they are released, and some corrosives are also oxidants, flammable, and/or toxic. The cylinder should be moved to an isolated, well-ventilated area, and suitable means used to direct the gas into an appropriate chemical neutralizer. If there is apt to be a reaction with the neutralizer that could lead to a "suck-back" into the valve (e.g., aqueous acid into an ammonia tank), a trap should be placed in the line before starting neutralization. Signs should be posted that describe the hazards and state warnings.

  • Toxic gases. The same procedure should be followed for toxic gases as for corrosive gases, but for the protection of personnel, a special warning should be given for the added hazard of exposure. The cylinder should be moved to an isolated, well-ventilated area, and suitable means used to direct the gas into an appropriate chemical neutralizer. Signs should be posted that describe the hazards and state warnings. Appropriate personal protective equipment should be worn. (See also section 5.D.6.)

5.C.11.8 Handling Spills of Elemental Mercury

Mercury spills can be avoided by using supplies and equipment that do not contain mercury. However, most mercury spills do not pose a high risk. The initial response to a spill of elemental mercury should be to isolate the spill area and begin the cleanup procedure. Those doing the cleanup should wear protective gloves. The cleanup should begin with collecting the droplets. The large droplets can be consolidated by using a scraper or a piece of cardboard, and the pool of mercury removed with a pump or other appropriate equipment. A standard vacuum cleaner should never be used to pick up mercury. If a house vacuum system is used, it can be protected from the mercury by a charcoal filter in a trap. For cleaning up small mercury droplets, a special vacuum pump may be used, or the mercury may be picked up on wet toweling, which consolidates the small droplets to larger pieces, or picked up with a piece of adhesive tape. Commercial mercury spill cleanup sponges and spill control kits are available. The common practice of using sulfur should be discontinued because the practice is ineffective and the resulting waste creates a disposal problem. The mercury should be placed in a thick-wall high-density polyethylene bottle and transferred to a central depository for reclamation. After a mercury spill the exposed work surfaces and floors should be decontaminated by using an appropriate decontamination kit.

5.C.11.9 Responding to Fires

Fires are one of the most common types of laboratory accidents. Accordingly, all personnel should be familiar with general guidelines (as stated below) to prevent and minimize injury and damage from fires. Handson experience with common types of extinguishers and proper choice of extinguisher should be part of basic laboratory training.

(See also Chapter 6, section 6.F.2.)

The following should be noted:

  • Preparation is essential! Make sure all laboratory personnel know the locations of all fire extinguishers in the laboratory, what types of fires they can be used for, and how to operate them correctly. Also ensure that they know the location of the nearest fire alarm pull station, safety showers, and emergency blankets.

  • Even though a small fire that has just started can sometimes be extinguished with a laboratory fire extinguisher, attempt to extinguish such fires only if you are confident that you can do it successfully and quickly, and from a position in which you are always between the fire and an exit to avoid being trapped. Do not underestimate the danger from a fire, and remember that toxic gases and smoke may present additional hazards. Notify trained professionals.

  • Fires in small vessels can usually be put out by covering the vessel loosely. Never pick up a flask or container of burning material.

  • Extinguish small fires involving reactive metals and organometallic compounds (e.g., magnesium, sodium, potassium, and metal hydrides) with Met-L-X® or Met-L-Kyl® extinguishers or by covering with dry sand. Because these fires are very difficult to extinguish, sound the fire alarms before you attempt to extinguish the fire.

  • In the event of a more serious fire, evacuate the laboratory and activate the nearest fire alarm. Upon their arrival, tell the fire department and emergency response team what hazardous substances are in the laboratory.

  • If a person's clothing catches fire, have him or her immediately drop to the floor and roll. Dousing with water from the safety shower can be effective. Use fire blankets only as a last resort because they tend to hold in heat and to increase the severity of burns. Remove contaminated clothing quickly, douse the person with water, and place clean, wet, cold cloth on burned areas. Wrap the injured person in a blanket to avoid shock, and get medical attention promptly.

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
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5.D WORKING WITH SUBSTANCES OF HIGH TOXICITY

Individuals who are working with highly toxic chemicals, as identified in Chapter 3, section 3.C, should be thoroughly familiar with the general guidelines for the safe handling of chemicals in laboratories (see section 5.C). They should also have acquired through training and experience the knowledge, skill, and discipline to carry out safe laboratory practices consistently. But these guidelines alone are not sufficient when handling substances that are known to be highly toxic and chemicals that, when combined in an experimental reaction, may generate highly toxic substances or produce new substances with the potential for high toxicity. Additional precautions are needed to set up multiple lines of defense to minimize the risks posed by these substances. As discussed in section 5.B, preparations for handling highly toxic substances must include sound and thorough planning of the experiment, understanding the intrinsic hazards of the substances and the risks of exposure inherent in the planned processes, selecting additional precautions that may be necessary to minimize or eliminate these risks, and reviewing all emergency procedures to ensure appropriate response to unexpected spills and accidents. Each experiment must be evaluated individually because assessment of the level of risk for work with any substance depends on how the substance will be used. Therefore, it would not be prudent for the planner to rely solely on a list of "highly toxic" chemicals to determine the level of the risk; under certain conditions, even chemicals not on these lists may become highly toxic.

In general, the guidelines in section 5.C reflect the minimum standards for handling hazardous substances. They should become standard practice when highly toxic substances are handled in the laboratory. For example, it is always preferable to avoid working alone in laboratories. However, when highly toxic materials are being handled, it is essential that more than one person be present and that all people working in the area be familiar with the hazards of the experiments being conducted and with the appropriate emergency response procedures. Personal protective equipment to safeguard the hands, forearms, and face from exposure to chemicals, while desirable in most circumstances, is essential in handling highly toxic materials. Good housekeeping creates an intrinsically safer workplace and should be maintained scrupulously in areas where highly toxic substances are handled. Source reduction is always a prudent practice, but in the case of highly toxic chemicals it may mean the difference between working with toxicologically dangerous amounts of materials and working with quantities that can be handled safely with routine practice. Similarly, emergency response planning and training become very important when working with highly toxic compounds. Additional hazards from these materials (e.g., flammability and high vapor pressures) can complicate the situation, making operational safety all the more important.

5.D.1 Planning

Careful planning needs to precede any experiment involving a highly toxic substance whenever the substance is to be used for the first time or whenever an experienced user carries out a new protocol that increases substantially the risk of exposure. Planning should include consultations with colleagues who have experience in handling the substance safely and in protocols of use. Experts in the institution's environmental health and safety program are a valuable source of information on the hazardous properties of chemicals and safe practice. They also need to be consulted for guidance regarding those chemicals that are regulated by federal, state, and local agencies or by institutional policy. Training and documentation requirements may have to be incorporated into the experiment plan.

Effective planning is always guided by two principles: substitution of highly toxic substances with less toxic alternatives whenever appropriate and use of the smallest amount of material that is practicable for the conduct of the experiment. Other important factors to be considered in determining the need for additional safeguards are the likelihood of exposure inherent in the proposed experimental process, the toxicological and physical properties of the chemical substances being used, the concentrations and amounts involved, the duration of exposure, and known toxicological effects. It is also important to plan for careful management of the substances throughout their life cycle—from acquisition and storage through destruction or safe disposal.

5.D.2 Experiment Protocols Involving Highly Toxic Chemicals

Experiment plans that involve the use of highly toxic substances or high-risk protocols should be considered carefully, and experienced personnel or an appropriate source should be consulted about the risk. An experiment plan that describes the additional safeguards that will be used for all phases of the experiment from

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
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acquisition of the chemical to its final safe disposal should be in place before the experiment begins. The amounts of materials used and the names of the people involved in the laboratory work should be included in the written summary and recorded in the laboratory notebook.

The planning process may determine that area monitoring and/or medical surveillance is necessary for ensuring the safety of the experimenters. Such a determination is likely to be made only when there is reason to believe that exposure levels for the substances planned to be used in an experiment could exceed OSHA-established regulatory action levels or similar guidelines established by other authoritative organizations. It would be prudent to review the amounts of material to be used, the toxicological properties of the substances, the opportunity for and duration of exposure, and plans for waste disposal for any experiment plans involving highly hazardous chemicals.

5.D.3 Designated Areas

Most experimental procedures involving highly toxic chemicals, including their transfer from storage containers to reaction vessels, should be confined to a designated work area in the laboratory. This area, which could be a hood or glove box, a portion of a laboratory, or the entire laboratory module, should be recognized by everyone in the laboratory or institution as a place where special precautions, laboratory skill, and safety discipline are required. Conspicuous signs should clearly indicate which areas are designated. It is not necessary to restrict the use of a designated area to the handling of highly toxic chemicals as long as laboratory personnel are aware of the nature of the substances being used and of the precautions that are necessary, and have been trained appropriately for emergency response. It may also be prudent to post relevant Laboratory Chemical Safety Summaries (LCSSs) outside the laboratory door.

The laboratory supervisor should determine which procedures need to be confined to designated areas. The general guidelines (section 5.C) for handling hazardous chemicals in laboratories may be sufficient for procedures involving low concentrations and small amounts of highly toxic chemicals, depending on the experiment, the reagents, and their toxicological and physical properties.

5.D.4 Access Control

Only persons who are directly involved in the laboratory work and who have been advised of the special precautions that may apply should have access to laboratories where highly toxic chemicals are handled. Administrative procedures or even physical barriers may be required to prevent unauthorized personnel from entering these laboratories.

The use of locks and barricades may be appropriate to limit access to unattended areas where large amounts of highly toxic materials are being handled routinely or stored. However, it is important that locks not prevent emergency exits from the laboratory or hinder entrance for emergency response. Locks are generally more appropriate for securing storage areas and unattended laboratories than for preventing access to laboratories in which toxic chemicals are being actively used.

Some long experiments involving highly toxic compounds may require unattended operations. In such cases, securing the laboratory from access by untrained personnel is essential. These operations should also include fail-safe backup options such as shutoff devices in case a reaction overheats or pressure builds up. Additionally, equipment should include interlocks that shut down experiments by turning off devices such as heating baths or reagent pumps, or that close solenoid valves if cooling water stops flowing through an apparatus or if airflow through a fume hood becomes restricted or stops. An interlock should be constructed carefully in such a way that if a problem develops, it places the experiment in a safer mode and will not reset even if the hazardous condition is reversed. Protective devices should include alarms that indicate their activation. Security guards and untrained personnel should never be asked or allowed to check on the status of unattended experiments involving highly toxic materials. Warning signs on locked doors should list the trained laboratory workers who can be contacted in case an alarm sounds within the laboratory.

5.D.5 Special Precautions for Minimizing Exposure to Highly Toxic Chemicals

The practices listed below help build the necessary multiple lines of defense to enable laboratory work with highly toxic chemicals to be conducted safely:

  1. Procedures involving highly toxic chemicals that can generate dust, vapors, or aerosols must be conducted in a hood, glove box, or other suitable containment device. Hoods should be checked for acceptable operation prior to conducting experiments with toxic chemicals. If experiments are to be ongoing over a significant period of time, the hood should be rechecked at least quarterly for integrity of flow. Hoods in continuous or long-term use with toxic materials

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
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should be equipped with flow-sensing devices that can show at a glance or by an audible signal whether they are performing adequately. When toxic chemicals are used in a glove box, it should be operated under negative pressure, and the gloves should be checked for integrity and appropriate composition before use. Any effluent from these reactions should be reactively or chemically scrubbed and/or cleaned with HEPA (high-efficiency particulate air) filters prior to discharge into the hood atmosphere. Hoods should not be used as waste disposal devices, particularly when toxic substances are involved. In order to offer maximum protection, hoods should be operated with sashes closed whenever possible, and experiments involving toxic materials should be shielded further. Monitoring equipment might include both active and passive devices to sample laboratory working environments. (See Chapter 8, section 8.C, for detailed discussion on hoods and environmental control.)

  1. When working with toxic liquids or solids, it is critical that gloves be worn to protect the hands and forearms. These gloves must be carefully selected to ensure that they are impervious to the chemicals being used and are of appropriate thickness to allow reasonable dexterity while also ensuring adequate barrier protection. Double gloves can provide a multiple line of defense and are likely to be appropriate for many situations with highly toxic chemicals. When risks from toxicity are only one facet of working with a given chemical or experimental apparatus, it is important to find a glove or combination of gloves that addresses all of the hazards present.

    When using gloves, it is important to exercise proper hygiene. Reusable gloves should be washed and inspected before and after each use. Gloves that might be contaminated with toxic materials should not be removed from the immediate area (usually a hood) in which the chemicals are located. They should never be worn when handling common items such as doorknobs, elevator buttons, handles, or switches on common equipment. Other types of personal protective equipment, such as aprons of reduced permeability and disposable laboratory coats, can offer additional safeguards when working with large quantities of toxic materials.

  2. Face and eye protection is also essential in preventing ingestion, inhalation, and skin absorption of toxic chemicals in the case of unexpected events. Safety glasses with side shields are a minimum standard for all laboratory work. When using toxic substances that could generate vapors, aerosols, or dusts, additional levels of protection, including full-face shields and respirators, are appropriate, depending on the degree of hazard represented. Transparent explosion shields in hoods offer additional protection from splashes. Medical supervision or surveillance may be warranted when using some toxic substances, particularly when large quantities of chemicals are involved or experiments are conducted with smaller quantities over an extended period of time. Medical certification may also be required if respirators are worn.

  3. Equipment used for the handling of highly toxic chemicals should be suitably isolated from the general laboratory environment. Laboratory vacuum pumps used with these substances should be protected by high-efficiency scrubbers or HEPA filters and vented into an exhaust hood. Motor-driven vacuum pumps are recommended because they are easy to decontaminate (decontamination should be conducted in a designated hood).

  4. Good laboratory hygiene should never be compromised in laboratories where highly toxic chemicals are handled. After using toxic materials the laboratory worker should wash his or her face, hands, neck, and arms. Equipment (including personal protective equipment such as gloves) that might be contaminated must never be removed from the environment reserved for handling toxic materials without complete decontamination. When possible, laboratory equipment and glassware should be chosen with an eve toward the ease of cleaning and decontamination. Mixtures that contain toxic chemicals or substances of unknown toxicity must never be smelled or tasted.

  5. Transportation of very toxic chemicals from one location to another should be planned carefully, and handling of these materials outside the specially designated laboratory area should be minimized. When these materials are transported, the full complement of personal protective equipment appropriate to the chemicals in question should be worn, and the samples should be carried in unbreakable secondary containers.

5.D.6 Preventing Accidents and Spills with Substances of High Toxicity

Emergency response procedures must cover highly toxic substances because such procedures provide the last line of defense in working with these chemicals. Spill control and appropriate emergency response kits should be nearby, and laboratory workers should be trained in their proper use. To avoid their being contaminated or made inaccessible in an emergency, these kits should not be located within the immediate area where highly toxic substances are handled. Spill control absorbents, impermeable ground covers (to prevent the spread of contamination while conducting emergency response), warning signs, emergency barriers, first aid supplies, and antidotes should be in these kits. The contents of the kits should be validated before starting experiments. Safety showers, eyewashes, and

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
×

fire extinguishers should be readily available nearby. Self-contained impermeable suits, a self-contained breathing apparatus, and cartridge respirators may also be appropriate for spill response preparedness, depending on the physical properties and toxicity of the materials being used (see section 5.C.2.3).

Experiments conducted with highly toxic chemicals should be carried out in work areas designed to contain accidental releases (see also section 5.D.3). Hood trays and other types of secondary containers should be used to contain inadvertent spills, and careful technique must be observed to minimize the potential for spills and releases.

All toxicity and emergency response information about the highly toxic chemicals being used should be readily available both before and during experimentation and should be located outside the immediate work area to ensure accessibility in emergencies. All laboratory workers who could potentially be exposed must be properly trained to participate in first aid or emergency response operations. In some cases the frequency with which highly toxic chemicals are used or the quantities involved might make formal emergency response drills warranted. Such ''dry runs" may involve medical personnel as well as emergency cleanup crews.

(See also sections 5.C.11.5 and 5.C.11.6.)

5.D.7 Storage and Waste Disposal

Highly toxic chemicals should be stored in unbreakable secondary containers. If the materials are volatile or could react with moisture or air to form volatile toxic compounds, these secondary containers should be placed in a ventilated environment under negative pressure. All containers of highly toxic chemicals should be labeled clearly with chemical composition, known hazards, and warnings for handling. Chemicals that can combine to make highly toxic materials (e.g., acids and inorganic cyanides, which can generate hydrogen cyanide) should not be stored together in the same secondary container. A list of highly toxic compounds, their locations, and contingency plans for dealing with spills should be displayed prominently at any storage facility. Access to areas where highly toxic compounds are stored should be restricted to workers who are familiar with the risks they pose and who have been trained to handle these chemicals. Highly toxic chemicals that have a limited shelf life need to be tracked and monitored for deterioration in the storage facility. Those that require refrigeration should be stored in a ventilated refrigeration facility.

Procedures for disposal of highly toxic materials should be established before experiments begin, preferably before the chemicals are ordered. The procedures should address methods for decontamination of all laboratory equipment that contacts (or could contact) highly toxic chemicals. Waste should be accumulated in clearly labeled, impervious containers that are stored in unbreakable secondary containers. Volatile or reactive waste should always be covered to minimize release to the hood environment in which it is being handled.

It is the responsibility of the experimenter and the laboratory supervisor to ensure that waste is disposed of in a manner that renders it innocuous. This may involve pretreatment of the waste either before or during accumulation. In other circumstances, prudence might dictate that highly toxic compounds never be moved from an enclosed environment and might suggest in-laboratory destruction as the safest and most effective way of dealing with the waste. Regulatory requirements may have an impact on this decision (see Chapter 9). If waste cannot be rendered harmless in the laboratory, then accumulation in closed, impervious containers within secondary containment systems is prudent. The choice of methods for final disposal must ensure that these chemicals are completely destroyed or rendered harmless in some manner.

5.D.8 Multihazardous Materials

Some highly toxic materials present additional hazards because of their flammability (see Chapter 3, sections 3.D.1 and 3.D.4; see also section 5.F), volatility (see sections 5.E and 5.G.6), explosibility (see Chapter 3, section 3.D.3; see also section 5.G.4), or reactivity (see Chapter 3, section 3.D.2; see also section 5.G.2). These materials warrant special attention to ensure that risks are minimized and that plans to deal effectively with all potential hazards and emergency response are implemented. (Tables 3.9 and 3.14 give information regarding incompatible chemicals and substances requiring extreme caution.)

5.E WORKING WITH BIOHAZARDOUS AND RADIOACTIVE MATERIALS

5.E.1 Biohazardous Materials

For even the most experienced laboratory worker, a careful review of the publication Biosafety in Microbiological and Biomedical Laboratories (U.S. DHHS, 1993) should be a prerequisite for beginning any laboratory activity involving a microorganism. It defines four levels of control that are appropriate for safe laboratory work with microorganisms that present occupational risks ranging from no risk of disease for normal healthy individuals to high individual risk of life-threatening

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
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disease, and it recommends guidelines for handling specific agents. The four levels of control, referred to as biosafety levels 1 through 4, describe microbiological practices, safety equipment, and features of laboratory facilities for the corresponding level of risk associated with handling a particular agent. The selection of a biosafety level is influenced by several characteristics of the infectious agent, the most important of which are the severity of the disease, the documented mode of transmission of the infectious agent, the availability of protective immunization or effective therapy, and the relative risk of exposure created by manipulations used in handling the agent.

Biosafety level 1 is the basic level of protection appropriate only for agents that are not known to cause disease in normal, healthy humans. Biosafety level 2 is appropriate for handling a broad spectrum of moderate-risk agents that cause human disease by ingestion or through percutaneous or mucous membrane exposure. Hepatitis B virus, human immunodeficiency virus (HIV), and salmonellae and toxoplasma spp. are representative of agents assigned to this biosafety level. Extreme precaution with needles or sharp instruments is emphasized at this level. A higher level of control may be indicated when some of these agents, especially HIV, are grown and concentrated.

Biosafety level 3 is appropriate for agents with a potential for respiratory transmission and for agents that may cause serious and potentially lethal infections. Emphasis is placed on the control of aerosols by containing all manipulations. At this level, the facility is designed to control access to the laboratory and includes a specialized ventilation system, such as a biological safety cabinet, that minimizes the release of infectious aerosols from the laboratory. The bacterium Mycobacterium tuberculosis is an example of an agent for which this higher level of control is appropriate. Exotic agents that pose a high individual risk of life-threatening disease by the aerosol route and for which no treatment is available are restricted to high containment laboratories that meet biosafety level 4 standards. Worker protection in these laboratories is provided by the use of physically sealed glove boxes or fully enclosed barrier suits that supply breathing air.

Several authoritative reference works are available that provide excellent guidance for the safe handling of infectious microorganisms in the laboratory, one of which is Biosafety in the Laboratory—Prudent Practices for the Handling and Disposal of Infectious Materials (NRC, 1989). Standard microbiological practices described in these references are consistent with the prudent practices used for the safe handling of chemicals.

Practices that are most helpful for preventing laboratory-acquired infections are as follows:

  • Wear protective gloves and a laboratory coat or gown.

  • Wash hands after infectious material is handled, after gloves are removed, and before leaving the laboratory.

  • Perform procedures carefully to reduce the possibility of creating splashes or aerosols.

  • Contain in biological safety cabinets operations that generate aerosols.

  • Use mechanical pipetting devices.

  • Promptly decontaminate work surfaces after spills of infectious materials and when procedures are completed.

  • Never eat, drink, smoke, handle contact lenses, apply cosmetics, or take or apply medicine in the laboratory.

  • Wear eye protection.

  • Take special care when using "sharps," that is, syringes, needles, Pasteur pipets, capillary tubes, scalpels, and other sharp instruments.

  • Keep laboratory doors closed when experiments are in progress.

  • Use secondary leak-proof containers to move or transfer cultures.

  • Decontaminate infectious waste before disposal.

5.E.2 Radioactive Materials

Prudent practices for working with radioactive materials are similar to those needed to reduce the risk of exposure to toxic chemicals (section 5.C has similar information) and to biohazards:

  • Know the characteristics of the radioisotopes that are being used, including half-life, types and energies of emitted radiations, the potential for exposure, how to detect contamination, and the annual limit on intake.

  • Protect against exposure to airborne and ingestible radioactive materials.

  • Never eat, drink, smoke, handle contact lenses, apply cosmetics, or take or apply medicine in the laboratory, and keep food, drinks, cosmetics, and tobacco products out of the laboratory entirely so that they cannot become contaminated.

  • Do not pipet by mouth.

  • Provide for safe disposal of waste radionuclides and their solutions.

  • Use protective equipment to minimize exposures.

  • Use equipment that can be manipulated remotely, as well as shielding, glove boxes, and personal protective equipment, including gloves, clothing, and respirators, as appropriate.

  • Plan experiments so as to minimize exposure by reducing the time of exposure, using shielding against exposure, increasing your distance from the radiation,

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
×

and paying attention to monitoring and decontamination.

  • Keep an accurate inventory of radioisotopes.

  • Record all receipts, transfers, and disposals of radioisotopes.

  • Record surveys.

  • Check workers and the work area each day that radioisotopes are used.

  • Minimize radioactive waste.

  • Plan procedures to use the smallest amount of radioisotope possible.

  • Check waste materials for contamination before discarding.

  • Place only materials with known or suspected radioactive contamination in appropriate radioactive waste containers.

  • Do not generate multihazardous waste (combinations of radioactive, biological, and chemical waste) without first consulting with the designated radiation and chemical safety officers.

(See Chapter 7 for more information on waste and disposal.)

5.F WORKING WITH FLAMMABLE CHEMICALS

All laboratory personnel should know the properties of chemicals they are handling as well as have a basic understanding of how these properties might be affected by the variety of conditions found in the laboratory. As stated in section 5.B, Laboratory Chemical Safety Summaries (LCSSs) or other sources of information should be consulted for further information such as vapor pressure, flash point, and explosive limit in air. The use of flammable substances is common, and their properties are also discussed in Chapter 3, section 3.D.

General prudent practices include minimizing the amounts used, storing chemicals properly, keeping appropriate fire extinguishing equipment readily available, physically separating flammable materials from other operations and sources of ignition, properly grounding static sources of ignition, and using the least hazardous alternative available.

Ignition sources should be eliminated from any area where flammable substances are handled. Open flames, such as Bunsen burners, matches, and smoking tobacco, are obvious ignition sources. Gas burners should not be used as a source of heat in any laboratory where flammable substances are used. Less obvious ignition sources include gas-fired space heating or water-heating equipment and electrical equipment, such as stirring devices, motors, relays, and switches, which can all produce sparks that will ignite flammable vapors. Because the location of this equipment is often fixed, operations with flammable substances may have to be carried out elsewhere.

Even low-level sources of ignition, such as hot plates, steam lines, or other hot surfaces, can provide a sufficiently energetic ignition source for the most flammable substances in general laboratory use, such as diethyl ether and carbon disulfide (see Chapter 3, section 3.D.1.3). Flammable substances that require low-temperature storage should be stored only in refrigerators designed for that purpose. Ordinary refrigerators are a hazard because of the presence of potential ignition sources, such as switches, relays, and, possibly, sparking fan motors, and should never be used for storing chemicals. When transferring flammable liquids in metal containers, sparks from accumulated static charge must be avoided by grounding.

Fire hazards posed by water-reactive substances such as alkali metals and metal hydrides, pyrophoric substances such as metal alkyls, strong oxidizers such as perchloric acid, and flammable gases such as acetylene require procedures beyond the standard prudent practices for handling chemicals described here (see sections 5.C and 5.D) and should be researched in LCSSs or other references before work begins. In addition, emergency response to incidents involving these substances must take their special hazards into account.

5.F.1 Flammable Materials

The basic precautions for safe handling of flammable materials include the following:

  • Handle flammable substances only in areas free of ignition sources. Besides open flames, ignition sources include electrical equipment (especially motors), static electricity, and, for some materials (e.g., carbon disulfide), even hot surfaces. Check the work area for flames or ignition sources before using a flammable substance. Before igniting a flame, check for the presence of a flammable substance.

  • Never heat flammable substances with an open flame. Preferred heat sources include steam baths, water baths, oil and wax baths, salt and sand baths, heating mantles, and hot air or nitrogen baths.

  • Ventilation by diluting the vapors until they are no longer flammable is one of the most effective ways to prevent the formation of flammable gaseous mixtures. Use appropriate and safe exhaust whenever appreciable quantities of flammable substances are transferred from one container to another, allowed to stand in open containers, heated in open containers, or handled in any other way. In using dilution techniques, make certain that equipment (e.g., fans) used to pro-

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
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vide dilution is explosion proof and that sparking items are located outside the air stream.

  • Keep containers of flammable substances tightly closed at all times when not in use.

  • Use only refrigeration equipment certified for storage of flammable materials.

  • Use the smallest quantities of flammable substances compatible with the need, and, especially when the flammable liquid must be stored in glass, purchase the smallest useful size bottle.

5.F.2 Flammable Liquids

Flammable liquids burn only when their vapor is mixed with air in the appropriate concentration. Therefore, such liquids should always be handled so as to minimize the creation of flammable vapor concentrations. Dilution of flammable vapors by ventilation is an important means of avoiding flammable concentrations. Containers of liquids should be kept closed except during transfer of contents. Transfers should be carried out only in fume hoods or in other areas where ventilation is sufficient to avoid a buildup of flammable vapor concentrations. Spillage or breakage of vessels or containers of flammable liquids or sudden eruptions from nucleation of heated liquid can result in a sudden release of vapor, which will produce an unexpected quantity of flammable vapor.

Metal lines and vessels discharging flammable liquids should be grounded properly and also grounded to discharge static electricity. For instance, when transferring flammable liquids in metal equipment, avoid static-generated sparks by grounding and the use of ground straps. Development of static electricity is related closely to the level of humidity and may become a problem on very cold, dry winter days. When nonmetallic containers (especially plastic) are used, the contact should be made directly to the liquid with the grounding device rather than to the container. In the rare circumstance that static electricity cannot be avoided, all processes should be carried out as slowly as possible to give the accumulated charge time to disperse, or should be handled in an inert atmosphere.

Note that vapors of many flammable liquids are heavier than air and capable of traveling considerable distances along the floor. This possibility should be recognized, and special note should be taken of ignition sources at a lower level than that at which the substance is being used. Close attention should be given to nearby potential sources of ignition.

5.F.3 Flammable Gases

Leakage or escape of flammable gases can produce an explosive atmosphere in the laboratory. Acetylene, hydrogen, ammonia, hydrogen sulfide, propane, and carbon monoxide are especially hazardous. Acetylene, methane, and hydrogen have very wide flammability limits, which adds greatly to their potential fire and explosion hazard. Installation of flash arresters on hydrogen cylinders is recommended. Prior to introduction of a flammable gas into a reaction vessel, the equipment should be purged by evacuation or with an inert gas. The flush cycle should be repeated three times to reduce residual oxygen to about 1%.

(See section 5.H for specific precautions on the use of compressed gases.)

5.F.4 Catalyst Ignition of Flammable Materials

Palladium or platinum on carbon, platinum oxide, Raney nickel, and other hydrogenation catalysts should be filtered carefully from hydrogenation reaction mixtures. The recovered catalyst is usually saturated with hydrogen, is highly reactive, and, thus, inflames spontaneously on exposure to air. Especially for large-scale reactions, the filter cake should not be allowed to become dry. The funnel containing the still-moist catalyst filter cake should be put into a water bath immediately after completion of the filtration. Use of a purge gas (nitrogen or argon) is strongly recommended for hydrogenation procedures so that the catalyst can then be filtered and handled under an inert atmosphere.

5.G WORKING WITH HIGHLY REACTIVE OR EXPLOSIVE CHEMICALS

An explosion results when a material undergoes rapid reaction that results in a violent release of energy. Such reactions can occur spontaneously or be initiated and can produce pressures, gases, and fumes that are hazardous. Highly reactive and explosive materials used in the laboratory require appropriate procedures. In this section, techniques for identifying and handling potentially explosive materials are discussed.

5.G.1 Overview

Light, mechanical shock, heat, and certain catalysts can be initiators of explosive reactions. Hydrogen and chlorine react explosively in the presence of light. Examples of shock-sensitive materials include acetylides, azides, organic nitrates, nitro compounds, perchlorates, and many peroxides. Acids, bases, and other substances can catalyze the explosive polymerizations. The catalytic effect of metallic contamination can lead to explosive situations. Many metal ions can catalyze the violent decomposition of hydrogen peroxide.

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
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Many highly reactive chemicals can polymerize vigorously, decompose, condense, and/or become self-reactive. The improper handling of these materials may result in a runaway reaction that could become violent. Careful planning is essential to avoid serious accidents. When highly reactive materials are in use, emergency equipment should be at hand. The apparatus should be assembled in such a way that if the reaction begins to run away, immediate removal of any heat source, cooling of the reaction vessel, cessation of reagent addition, and closing of laboratory hood sashes are possible. Evacuation of personnel until the reaction is under control is advisable. A heavy, transparent plastic explosion shield should be in place to provide extra protection in addition to the hood window.

Highly reactive chemicals can lead to reactions with rates that increase rapidly as the temperature increases. If the heat evolved is not dissipated, the reaction rate can increase until an explosion results. Such an event must be prevented, particularly when scaling up experiments. Sufficient cooling and surface for heat exchange should be provided to allow control of the reaction. It is also important that the concentrations of the solutions used not be excessive, especially when a reaction is being attempted or scaled up for the first time. Use of too highly concentrated reagents has led to runaway conditions and to explosions. Particular care must also be given to the rate of reagent addition versus its rate of consumption, especially if the reaction is subject to an induction period.

Large-scale reactions with organometallic reagents and reactions that produce flammables as products and/or are carried out in flammable solvents require special attention. Active metals, such as sodium, magnesium, lithium, and potassium, are a serious fire and explosion risk because of their reactivity with water, alcohols, and other compounds containing acidic OH. These materials require special storage, handling, and disposal procedures. Where active metals are present, Class D fire extinguishers that use special extinguishing materials such as a plasticized graphite-based powder or a sodium chloride-based powder (Met-L-X®) are required.

Some chemicals decompose when heated. Slow decomposition may not be noticeable on a small scale, but on a large scale with inadequate heat transfer, or if the evolved heat and gases are confined, an explosive situation can develop. The heat-initiated decomposition of some substances, such as certain peroxides, is almost instantaneous. In particular, reactions that are subject to an induction period can be dangerous because there is no initial indication of a risk, but after the induction a violent process can result.

Oxidizing agents may react violently when they come in contact with reducing materials, trace metals, and sometimes ordinary combustibles. These compounds include the halogens, oxyhalogens, and peroxyhalogens, permanganates, nitrates, chromates, and persulfates, as well as peroxides (see also section 5.G.3). Inorganic peroxides are generally considered to be stable. However, they may generate organic peroxides and hydroperoxides in contact with organic compounds, react violently with water (alkali metal peroxides), or form superoxides and ozonides (alkali metal peroxides). Perchloric acid and nitric acid are powerful oxidizing agents with organic compounds and other reducing agents. Perchlorate salts can be explosive and should be treated as potentially hazardous compounds. "Dusts"—suspensions of oxidizable particles (e.g., magnesium powder, zinc dust, carbon powder, or flowers of sulfur) in the air—constitute a powerful explosive mixture.

Scale-up of reactions can create difficulties in dissipation of heat that are not evident on a smaller scale. Evaluation of observed or suspected exothermicity can be achieved by differential thermal analysis (DTA) to identify exothermicity in open reaction systems; differential scanning calorimetry (DSC), using a specially designed sealable metal crucible, to identify exothermicity in closed reaction systems; or syringe injection calorimetry (SIC) and reactive systems screening tool (RSST) calorimetry to determine heats of reaction on a microscale and small scale. (For an expanded discussion of identifying process hazards using thermal analytical techniques, see Tuma (1991).) When it becomes apparent that an exotherm exists at a low temperature and/or a large exotherm occurs that might present a hazard, large-scale calorimetry determination of exothermic onset temperatures and drop weight testing are advisable. In situations where formal operational hazard evaluation or reliable data from any other source suggest a hazard, review or modification of the scale-up conditions by an experienced group is recommended to avoid the possibility that an individual might overlook a hazard or the most appropriate procedural changes.

Any given sample of a highly reactive material may be dangerous. Furthermore, the risk is associated not with the total energy released, but rather with the remarkably high rate of a detonation reaction. A highorder explosion of even milligram quantities can drive small fragments of glass or other matter deep into the eye. It is important to use minimum amounts of hazardous materials with adequate shielding and personal protection.

Not all explosions result from chemical reactions. A dangerous, physically caused explosion can occur if a hot liquid is brought into sudden contact with a lower-boiling-point one. The instantaneous vaporization of the lower-boiling-point substance can be hazardous to

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
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personnel and destructive to equipment. The presence or inadvertent addition of water to the hot fluid of a heating bath is an example of such a hazard. Explosions can also occur when warming a cryogenic material in a closed container or overpressurizing glassware with nitrogen (N2) or argon when the regulator is incorrectly set. Violent physical explosions have also occurred when a collection of very hot particles is suddenly dumped into water. For this reason, dry sand should be used to catch particles during laboratory thermite reaction demonstrations.

5.G.2 Reactive or Explosive Compounds

Occasionally, it is necessary to handle materials that are known to be explosive or that may contain explosive impurities such as peroxides. Since explosive chemicals might be detonated by mechanical shock, elevated temperature, or chemical action with forces that release large volumes of gases, heat, and often toxic vapors, they must be treated with special care.

The proper handling of highly energetic substances without injury demands attention to the most minute detail. The unusual nature of work involving such substances requires special safety measures and handling techniques that must be understood thoroughly and followed by all persons involved. The practices listed in this section are a guide for use in any laboratory operation that might involve explosive materials.

Work with explosive (or potentially explosive) materials generally requires the use of special protective apparel (e.g., face shields, gloves, and laboratory coats) and protective devices such as explosion shields, barriers, or even enclosed barricades or an isolated room with a blowout roof or window (see Chapter 6, sections 6.F.1 and 6.F.2). Before work with a potentially explosive material is begun, the experiment should be discussed with a supervisor or an experienced co-worker, and/or the relevant literature consulted (see Chapter 3, sections 3.B.2, 3.B.5, and 3.B.6). A risk assessment should be carried out.

Various state and federal regulations cover the transportation, storage, and use of explosives. These regulations should be consulted before explosives (and related dangerous materials) are used or generated in the laboratory. Explosive materials should be brought into the laboratory only as required and then in the smallest quantities adequate for the experiment (see Chapter 4, section 4.B). Insofar as possible, direct handling should be minimized. Explosives should be segregated from other materials that could create a serious risk to life or property should an accident occur.

5.G.2.1 Personal Protective Apparel

When explosive materials are handled, the following items of personal protective apparel are needed:

  • Safety glasses that have solid side shields or goggles should be worn by all personnel, including visitors, in the laboratory.

  • Full-length shields that fully protect the face and throat should be worn whenever the worker is in a hazardous or exposed position. Special care is required when operating or manipulating synthesis systems that may contain explosives (e.g., diazomethane), when bench shields are moved aside, and when handling or transporting such systems. In view of the special hazard to life that results from severing the jugular vein, extra shielding around the throat is recommended.

  • Heavy leather gloves should be worn if it is necessary to reach behind a shielded area while a hazardous experiment is in progress or when handling reactive compounds or gaseous reactants. Proper planning of experiments should minimize the need for such activities.

  • Laboratory coats should be worn at all times in explosives laboratories. The coat should be made of flame-resistant material and should be quickly removable. A coat can help reduce minor injuries from flying glass as well as the possibility of injury from an explosive flash.

5.G.2.2 Protective Devices

Barriers such as shields, barricades, and guards should be used to protect personnel and equipment from injury or damage from a possible explosion or fire. The barrier should completely surround the hazardous area. On benches and hoods, a 0.25-inch-thick acrylic sliding shield, which needs to be screwed together in addition to being glued, can effectively protect a worker from glass fragments resulting from a laboratory-scale detonation. The shield should be in place whenever hazardous reactions are in progress or whenever hazardous materials are being stored temporarily. However, such shielding is not effective against metal shrapnel. The laboratory hood sash provides a safety shield only against chemical splashes or sprays, fires, and minor explosions. If more than one hazardous reaction is carried out, the reactions should be shielded from each other and separated as far as possible.

Dry boxes should be fitted with safety glass windows overlaid with 0.25-inch-thick acrylic when potentially explosive materials capable of detonation in an inert atmosphere are to be handled. This protection is adequate against most internal 5-g detonations. Protec-

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
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tive gloves should be worn over the rubber dry box gloves to provide additional protection. Other safety devices that allow remote manipulation should be used with the gloves. Detonation of explosives from static sparks can be a considerable problem in dry boxes, so adequate grounding is essential, and an antistatic gun is recommended.

Armored hoods or barricades made with thick (1.0 inch) polyvinylbutyral resin shielding and heavy metal walls give complete protection against detonations not in excess of the acceptable 20-g limit. These hoods are designed to contain a 100-g explosion, but an arbitrary 20-g limit is usually set because of the noise level in the event of a detonation. Such hoods should be equipped with mechanical hands that enable the operator to manipulate equipment and handle adduct containers remotely. A sign, such as

CAUTION: NO ONE MAY ENTER AN ARMORED HOOD FOR ANY REASON DURING THE COURSE OF A HAZARDOUS OPERATION

should be posted.

Miscellaneous protective devices such as both long-and short-handled tongs for holding or manipulating hazardous items at a safe distance and remote control equipment (e.g., mechanical arms, stopcock turners, labjack turners, remote cable controllers, and closed-circuit television monitors) should be available as required to prevent exposure of any part of the body to injury.

5.G.2.3 Evaluating Potentially Reactive Materials

Potentially reactive materials must be evaluated for their possible explosive characteristics by consulting the literature and considering their molecular structures. The presence of functional groups or compounds listed in sections 5.C.9 or 5.G.6 indicates a possible explosion hazard. New compounds can be screened for explosiveness by cautious heating and hammering of very small samples. Highly reactive chemicals should be segregated from materials that might interact with them to create a risk of explosion. Highly reactive chemicals should not be used past their expiration date.

5.G.2.4 Determining Reaction Quantities

When a possibly hazardous reaction is attempted, small quantities of reactants should be used. When handling highly reactive chemicals, it is advisable to use the smallest quantities needed for the experiment. In conventional explosives laboratories, no more than 0.1 g of product should be prepared in a single run. During the actual reaction period, no more than 0.5 g of reactants should be present in the reaction vessel. This means that the diluent, the substrate, and the energetic reactant must all be considered when determining the total explosive power of the reaction mixture. Special formal risk assessments should be established to examine operational and safety problems involved in scaling up a reaction in which an explosive substance is used or could be generated.

5.G.2.5 Conducting Reaction Operations

The most common heating devices are heating tapes and mantles and sand, water, steam, wax, silicone oil, and air (or nitrogen) baths. These should be used in such a way that if an explosion were to occur the heating medium would be contained. Heating baths should consist of nonflammable materials. All controls for heating and stirring equipment should be operable from outside the shielded area. (See Chapter 6, section 6.C.5, for further information.)

Vacuum pumps should carry tags indicating the date of the most recent oil change. Oil should be changed once a month, or sooner if it is known that the oil has been exposed to reactive gases. All pumps should either be vented into a hood or trapped. Vent lines may be Tygon, rubber, or copper. If Tygon or rubber lines are used, they should be supported so that they do not sag, causing a trap for condensed liquids. (See Chapter 6, section 6.C.2, for details.)

When potentially explosive materials are being handled, the area should be posted with a sign such as

WARNING: VACATE THE AREA AT THE FIRST INDICATION OF [the indicator for the specific case]. STAY OUT. CALL [responsible person] AT [phone number].

When condensing explosive gases, the temperature of the bath and the effect on the reactant gas of the condensing material selected must be determined experimentally (see Chapter 6, section 6.D). Very small quantities should be used because detonations may occur. A taped and shielded Dewar flask should always be used when condensing reactants. Maximum quantity limits should be observed. A dry ice solvent bath is not recommended for reactive gases; liquid nitrogen is recommended. (See also Chapter 3, section 3.D.3.1.)

5.G.3

Organic Peroxides

Organic peroxides are a special class of compounds whose unusually low stability makes them among the

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
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most hazardous substances commonly handled in laboratories, especially as initiators for free-radical reactions. Although they are low-power explosives, they are hazardous because of their extreme sensitivity to shock, sparks, and other forms of accidental detonation. Many peroxides that are handled routinely in laboratories are far more sensitive to shock than most primary explosives (e.g., TNT), although many have been stabilized by the addition of compounds that inhibit reaction. Nevertheless, even low rates of decomposition may automatically accelerate and cause a violent explosion, especially in bulk quantities of peroxides (e.g., benzoyl peroxide). These compounds are sensitive to heat, friction, impact, and light, as well as to strong oxidizing and reducing agents. All organic peroxides are highly flammable, and fires involving bulk quantities of peroxides should be approached with extreme caution.

Precautions for handling peroxides include the following:

  • Limit the quantity of peroxide to the minimum amount required. Do not return unused peroxides to the container.

  • Clean up all spills immediately. Solutions of peroxides can be absorbed on vermiculite or other absorbing material and disposed of harmlessly according to institutional procedures.

  • The sensitivity of most peroxides to shock and heat can be reduced by dilution with inert solvents, such as aliphatic hydrocarbons. However, do not use aromatics (such as toluene), which are known to induce the decomposition of diacyl peroxides.

  • Do not use solutions of peroxides in volatile solvents under conditions in which the solvent might be vaporized because this will increase the peroxide concentration in the solution.

  • Do not use metal spatulas to handle peroxides because contamination by metals can lead to explosive decomposition. Magnetic stirring bars can unintentionally introduce iron, which can initiate an explosive reaction of peroxides. Ceramic, Teflon, or wooden spatulas and stirring blades may be used if it is known that the material is not shock-sensitive.

  • Do not permit smoking, open flames, and other sources of heat near peroxides. It is important to label areas that contain peroxides so that this hazard is evident.

  • Avoid friction, grinding, and all forms of impact near peroxides, especially solid peroxides. Glass containers that have screw-cap lids or glass stoppers should not be used. Polyethylene bottles that have screw-cap lids may be used.

  • To minimize the rate of decomposition, store peroxides at the lowest possible temperature consistent with their solubility or freezing point. Do not store liquid peroxides or solutions at or lower than the temperature at which the peroxide freezes or precipitates because peroxides in these forms are extremely sensitive to shock and heat.

  • If a container of peroxide-forming material is past its expiration date, and there is a risk that peroxides may be present, open it with caution and dispose of it according to institutional procedures (see section 5.G.3.2).

  • Test for the presence of peroxides if there is a reasonable likelihood of their presence and the expiration date has not passed (see section 5.G.3.1).

(Also refer to Chapter 7, section 7.D.2.5.)

5.G.3.1 Peroxide Detection Tests

The following tests can detect most (but not all) peroxy compounds, including all hydroperoxides:

  • Add 1 to 3 milliliters (mL) of the liquid to be tested to an equal volume of acetic acid, add a few drops of 5% aqueous potassium iodide solution, and shake. The appearance of a yellow to brown color indicates the presence of peroxides. Alternatively, addition of 1 mL of a freshly prepared 10% solution of potassium iodide to 10 mL of an organic liquid in a 25-mL glass cylinder should produce a yellow color if peroxides are present.

  • Add 0.5 mL of the liquid to be tested to a mixture of 1 mL of 10% aqueous potassium iodide solution and 0.5 mL of dilute hydrochloric acid to which has been added a few drops of starch solution just prior to the test. The appearance of a blue or blue-black color within a minute indicates the presence of peroxides.

  • Peroxide test strips, which turn to an indicative color in the presence of peroxides, are available commercially. Note that these strips must be air dried until the solvent evaporates and then exposed to moisture for proper operation.

None of these tests should be applied to materials (such as metallic potassium) that may be contaminated with inorganic peroxides.

5.G.3.2 Disposal of Peroxides

Pure peroxides should never be disposed of directly but must be diluted before disposal. Small quantities (25 g or less) of peroxides are generally disposed of by dilution with water to a concentration of 2% or less, after which the solution is transferred to a polyethylene

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
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bottle containing an aqueous solution of a reducing agent, such as ferrous sulfate or sodium bisulfite. The material can then be handled as a waste chemical; however, it must not be mixed with other chemicals for disposal. Spilled peroxides should be absorbed on vermiculite or other absorbent as quickly as possible. The vermiculite-peroxide mixture can be burned directly or may be stirred with a suitable solvent to form a slurry that can be treated according to institutional procedures. Organic peroxides should never be flushed down the drain.

Large quantities (more than 25 g) of peroxides require special handling. Each case should be considered separately, and handling, storage, and disposal procedures should be determined by the physical and chemical properties of the particular peroxide (see also Hamstead, 1964).

Peroxides can be formed during storage of some materials in air, and a peroxide present as a contaminant in a reagent or solvent (e.g., 1,4-dioxane) can be very hazardous and change the course of a planned reaction. Especially dangerous are ether bottles that have evaporated to dryness. Excluding oxygen by storing potential peroxide-formers under an inert atmosphere (N2 or argon) or under vacuum greatly increases their safe storage lifetime. In many instances, it is possible to purchase the chemical stored under nitrogen in septum-capped bottles. In some cases, stabilizers or inhibitors (free-radical scavengers that terminate the chain reaction) are added to the liquid to extend its storage lifetime. Because distillation of the stabilized liquid removes the stabilizer, the distillate must be stored with care and monitored for peroxide formation. Furthermore, HPLC-grade solvents generally contain no stabilizer, and the same considerations apply to their handling.

(Also see Chapter 3, section 3.D.3.2; for disposal information, see Chapter 7, section 7.D.2.5.)

5.G.4 Explosive Gases and Liquefied Gases

A substance is more concentrated in the form of a liquefied gas than in the vapor phase and may evaporate extremely rapidly. Contact with liquid oxygen, in particular, may introduce extreme risk. Liquefied air is almost as dangerous as liquid oxygen because the nitrogen boils away, and as it does, it leaves an increasing concentration of oxygen. Other cryogenic liquids, such as nitrogen and helium, if they have been open to air, may have absorbed and condensed enough atmospheric oxygen to be very hazardous. When a liquefied gas is used in a closed system, pressure may build up, so that adequate venting is required. Relief devices are required to prevent this dangerous buildup of pressure. If the liquid is flammable (e.g., hydrogen), explosive concentrations in air may develop. Because flammability, toxicity, and pressure buildup may become serious when gases are exposed to heat, gases should be stored only in specifically designed and designated areas (see Chapter 8, section 8.E).

5.G.5 Hydrogenation Reactions

Hydrogenation reactions are often carried out under pressure with a reactive catalyst and so require special attention. Along with observation of the precautions for the handling of gas cylinders and flammable gases, additional attention must be given to carrying out hydrogenation reactions at pressures above 1 atm. The following precautions are applicable:

  • Make sure that the autoclave, pressure bottle, or other apparatus is appropriate for the experiment. Most preparative hydrogenations of substances such as alkenes can be carried out safely in a commercial hydrogenation apparatus using a heterogeneous catalyst (e.g., Pt and Pd) under moderate (<80 psi H2) pressure.

  • Review the operating procedures for the apparatus, and inspect the container before each experiment. Glass reaction vessels are subject to scratches or chips that render them unsuitable for use under pressure. Never fill the vessel to capacity with the solution; filling it about half full (or less) is much safer.

  • One of the most important precautions to be taken with any reaction involving hydrogen is to remove as much oxygen from the solution as possible before adding hydrogen. Failure to do this could result in an explosive oxygen-hydrogen (O2/H2) mixture. Normally, the oxygen in the vessel is removed by pressurizing the vessel with inert gas (N2 or argon), followed by venting the gas. If available, vacuum can be applied to the solution. Repeat this procedure of filling with inert gas and venting several times before the hydrogen or other high-pressure gas is introduced.

  • Do not approach the rated safe pressure limit of the bottle or autoclave, with due regard to increased pressure upon heating. A limit of 75% of the rating in a high-pressure autoclave is advisable, but if this limit is exceeded accidentally, replace the rupture disk upon completion of the experiment.

  • Monitor the pressure of the high-pressure device periodically as the heating proceeds to avoid too high a pressure in case of unintentional overheating.

  • Purge the system of hydrogen by repeated "rinsing" with inert gas at the end of the experiment to avoid producing hydrogen-oxygen mixtures in the presence of the catalyst during work-up. Handle cata-

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
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lyst that has been used in the reaction with special care because it can be a source of spontaneous ignition upon contact with air.

(Also see section 5.C.)

5.G.6 Reactive or Explosive Materials Requiring Special Attention

The following list is not intended to be all-inclusive. Further guidance on reactive and explosive materials should be sought from pertinent sections of this book (see Chapter 3, sections 3.D.2 and 3.D.3) and other sources of information (note sources included in Chapter 3, section 3.B).

Acetylenic compounds can be explosive in mixtures of 2.5 to 80% with air. At pressures of 2 or more atmospheres, acetylene (C2H2) subjected to an electrical discharge or high temperature decomposes with explosive violence. Dry acetylides detonate on receiving the slightest shock. Acetylene must be handled in acetone solution and never stored alone in a cylinder.

Aluminum chloride (AlCl3) should be considered a potentially dangerous material. If moisture is present, there may be sufficient decomposition to form hydrogen chloride (HC1) and build up considerable pressure. If a bottle is to be opened after long storage, it should first be completely enclosed in a heavy towel.

Ammonia (NH3) reacts with iodine to give nitrogen triiodide, which detonates on touch. Ammonia reacts with hypochlorites to give chlorine. Mixtures of NH3 and organic halides sometimes react violently when heated under pressure. Ammonia is combustible. Inhalation of concentrated fumes can be fatal.

Azides, both organic and inorganic, and some azo compounds can be heat- and shock-sensitive. Azides such as sodium azide can displace halide from chlorinated hydrocarbons such as dichloromethane to form highly explosive organic polyazides; this substitution reaction is facilitated in solvents such as dimethyl sulfoxide (DMSO).

Carbon disulfide (CS2) is both very toxic and very flammable; mixed with air, its vapors can be ignited by a steam bath or pipe, a hot plate, or a light bulb.

Chlorine (C12) is toxic and may react violently with hydrogen (H2) or with hydrocarbons when exposed to sunlight.

Chromium trioxide—pyridine complex (CrO3 C5H5N) may explode if the CrO3 concentration is too high. The complex should be prepared by addition of CrO3 to excess C5H5N.

Diazomethane (CH2N2) and related diazo compounds should be treated with extreme caution. They are very toxic, and the pure gases and liquids explode readily even from contact with sharp edges of glass. Solutions in ether are safer from this standpoint. An ether solution of diazomethane is rendered harmless by drop wise addition of acetic acid.

Diethyl, diisopropyl, and other ethers, including tetrahydrofuran and 1,4-dioxane and particularly the branched-chain type of ethers, sometimes explode during heating or refluxing because the presence of peroxides has developed from air oxidation. Ferrous salts or sodium bisulfite can be used to decompose these peroxides, and passage over basic active alumina can remove most of the peroxidic material. In general, however, old samples of ethers should be disposed of after testing, following procedures for disposal of peroxides (see Chapter 7, section 7.D.2.5).

Dimethyl sulfoxide (DMSO), (CH3)2SO, decomposes violently on contact with a wide variety of active halogen compounds, such as acyl chlorides. Explosions from contact with active metal hydrides have been reported. Dimethyl sulfoxide does penetrate and carry dissolved substances through the skin membrane.

Dry benzoyl peroxide (C6H5CO2)2 is easily ignited and sensitive to shock. It decomposes spontaneously at temperatures above 50 °C. It is reported to be desensitized by addition of 20% water.

Dry ice should not be kept in a container that is not designed to withstand pressure. Containers of other substances stored over dry ice for extended periods generally absorb carbon dioxide (CO2) unless they have been sealed with care. When such containers are removed from storage and allowed to come rapidly to room temperature, the CO2 may develop sufficient pressure to burst the container with explosive violence. On removal of such containers from storage, the stopper should be loosened or the container itself should be wrapped in towels and kept behind a shield. Dry ice can produce serious burns, as is also true for all types of dry-ice-cooled cooling baths.

Drying agents, such as Ascarite® (sodium hydroxide-coated silica), should not be mixed with phosphorus pentoxide (P2O5) because the mixture may explode if it is warmed with a trace of water. Because the cobalt salts used as moisture indicators in some drying agents may be extracted by some organic solvents, the use of these drying agents should be restricted to drying gases.

Dusts that are suspensions of oxidizable particles (e.g., magnesium powder, zinc dust, carbon powder, and flowers of sulfur) in the air can constitute powerful explosive mixtures. These materials should be used with adequate ventilation and should not be exposed to ignition sources. When finely divided, some solids, including zirconium, titanium, Raney nickel, lead

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
×

(such as prepared by pyrolysis of lead tartrate), and catalysts (such as activated carbon containing active metals and hydrogen), can combust spontaneously if allowed to dry while exposed to air and should be handled wet.

Ethylene oxide (C2H4O) has been known to explode when heated in a closed vessel. Experiments using ethylene oxide under pressure should be carried out behind suitable barricades.

Halogenated compounds, such as chloroform (CHCl3), carbon tetrachloride (CC14), and other halogenated solvents, should not be dried with sodium, potassium, or other active metal; violent explosions usually result. Many halogenated compounds are toxic. Oxidized halogen compounds—chlorates, chlorites, bromates, and iodates—and the corresponding peroxy compounds may be explosive at high temperatures.

Hydrogen peroxide (H2O2) stronger than 3% can be dangerous; in contact with the skin, it can cause severe burns. Thirty percent H2O2 may decompose violently if contaminated with iron, copper, chromium, or other metals or their salts. Stirring bars may inadvertently bring metal into a reaction and should be used with caution.

Liquid nitrogen-cooled traps open to the atmosphere condense liquid air rapidly. Then, when the coolant is removed, an explosive pressure buildup occurs, usually with enough force to shatter glass equipment if the system has been closed. Hence, only sealed or evacuated equipment should be so cooled.

Lithium aluminum hydride (LiAlH4) should not be used to dry methyl ethers or tetrahydrofuran; fires from reaction with damp ethers are often observed. The reaction of LiAlH4 with carbon dioxide has reportedly generated explosive products. Carbon dioxide or bicarbonate extinguishers should not be used for LiAlH4 fires; instead such fires should be smothered with sand or some other inert substance.

Nitrates, nitro and nitroso compounds may be explosive, especially if more than one nitro group is present. Alcohols and polyols can form highly explosive nitrate esters (e.g., nitroglycerine) from reaction with nitric acid.

Organometallics are hazardous because some organometallic compounds burn vigorously on contact with air or moisture. For example, solutions of t-butyl lithium can cause ignition of some organic solvents on exposure to air. The pertinent information should be obtained for a specific compound.

Oxygen tanks should be handled with care because serious explosions have resulted from contact between oil and high-pressure oxygen. Oil or grease should not be used on connections to an O2 cylinder or gas line carrying O2.

Ozone (O3) is a highly reactive and toxic gas. It is formed by the action of ultraviolet light on oxygen (air), and, therefore, certain ultraviolet sources may require venting to the exhaust hood. Ozonides can be explosive.

Palladium (Pd) or platinum (Pt) on carbon, platinum oxide, Raney nickel, and other catalysts present the danger of explosion if additional catalyst is added to a flask in which an air-flammable vapor mixture and/ or hydrogen is present. The use of flammable filter paper should be avoided.

Parr bombs used for hydrogenations should be handled with care behind a shield, and the operator should wear goggles and a face shield.

Perchlorates should be avoided insofar as possible. Perchlorate salts of organic, organometallic, and inorganic cations are potentially explosive and have been set off either by heating or by shock.

Perchlorates should not be used as drying agents if there is a possibility of contact with organic compounds or of proximity to a dehydrating acid strong enough to concentrate the perchloric acid (HClO4) (e.g., in a drying train that has a bubble counter containing sulfuric acid). Safer drying agents should be used.

Seventy percent HClO4 can be boiled safely at approximately 200 °C, but contact of the boiling undiluted acid or the hot vapor with organic matter, or even easily oxidized inorganic matter, will lead to serious explosions. Oxidizable substances must never be allowed to contact HClO4. This includes wooden benchtops or hood enclosures, which may become highly flammable after absorbing HClO4 liquid or vapors. Beaker tongs, rather than rubber gloves, should be used when handling fuming HClO4. Perchloric acid evaporations should be carried out in a hood that has a good draft. The hood and ventilator ducts should be washed with water frequently (weekly; but see also section 8.C.7.5) to avoid danger of spontaneous combustion or explosion if this acid is in common use. Special perchloric acid hoods are available from many manufacturers. Disassembly of such hoods must be preceded by washing of the ventilation system to remove deposited perchlorates.

Permanganates are explosive when treated with sulfuric acid. If both compounds are used in an absorption train, an empty trap should be placed between them and monitored for entrapment.

Peroxides (inorganic) should be handled carefully. When mixed with combustible materials, barium, sodium, and potassium peroxides form explosives that ignite easily.

Phosphorus (P) (red and white) forms explosive mixtures with oxidizing agents. White phosphorus should be stored under water because it ignites spontaneously in air. The reaction of phosphorus with aqueous

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
×

hydroxides gives phosphine, which may either ignite spontaneously or explode in air.

Phosphorus trichloride (PC13) reacts with water to form phosphorous acid with HCl evolution; the phosphorous acid decomposes on heating to form phosphine, which may either ignite spontaneously or explode. Care should be taken in opening containers of PCl3, and samples that have been exposed to moisture should not be heated without adequate shielding to protect the operator.

Potassium (K) is much more reactive than sodium; it ignites quickly on exposure to humid air and, therefore, should be handled under the surface of a hydrocarbon solvent such as mineral oil or toluene (see Sodium). Potassium can form explosive peroxides on contact with air. If this happens, the act of cutting a surface crust off the metal can cause a severe explosion.

Residues from vacuum distillations have been known to explode when the still was vented suddenly to the air before the residue was cool. Such explosions can be avoided by venting the still pot with nitrogen, by cooling it before venting, or by restoring the pressure slowly. Sudden venting may produce a shockwave that can detonate sensitive materials.

Sodium (Na) should be stored in a closed container under kerosene, toluene, or mineral oil. Scraps of sodium or potassium should be destroyed by reaction with n-butyl alcohol. Contact with water should be avoided because sodium reacts violently with water to form hydrogen (H2) with evolution of sufficient heat to cause ignition. Carbon dioxide, bicarbonate, and carbon tetrachloride fire extinguishers should not be used on alkali metal fires. Metals like sodium become more reactive as the surface area of the particles increases. Prudence dictates using the largest particle size consistent with the task at hand. For example, use of sodium ''balls" or cubes is preferable to use of sodium "sand" for drying solvents.

Sodium amide (NaNH2) can undergo oxidation on exposure to air to give sodium nitrite in a mixture that is unstable and may explode.

Sulfuric acid (H2SO4) should be avoided, if possible, as a drying agent in desiccators. If it must be used, glass beads should be placed in it to help prevent splashing when the desiccator is moved. To dilute H2SO4, the acid should be added slowly to cold water. Addition of water to the denser H2SO4 can cause localized surface boiling and spattering on the operator.

Trichloroethylene (Cl2CCHCl) reacts under a variety of conditions with potassium or sodium hydroxide to form dichloroacetylene, which ignites spontaneously in air and detonates readily even at dry ice temperatures. The compound itself is highly toxic, and suitable precautions should be taken when it is used.

5.G.7 Chemical Hazards of Incompatible Chemicals

When transporting, storing, using, or disposing of any substance (see Chapter 4, and section 5.C), utmost care must be exercised to ensure that it cannot accidentally come into contact with an incompatible substance (see Chapter 3, section 3.D). Such contact could result in a serious explosion or the formation of substances that are highly toxic or flammable or both. Oxidizing agents and reducing agents should be separated from one another so that no contact is possible in the event of an accident. These reagents can also pose a risk upon contact with the atmosphere. Storage should be appropriate for the chemical under consideration. Glass systems that are to be evacuated should be taped to prevent danger of flying glass on implosion.

5.H WORKING WITH COMPRESSED GASES

5.H.1 Chemical Hazards of Compressed Gases

Compressed gases expose the worker to both chemical and physical hazards. Such hazards and the equipment required for the safe use of compressed gases are discussed in Chapter 6, section 6.D.

Safe storage, monitoring for leaks, and proper labeling are essential for the prudent use of compressed gases. If the gas is flammable, flash points lower than room temperature compounded by rapid diffusion throughout the laboratory present the danger of fire or explosion. Additional hazards can arise from the reactivity and toxicity of the gas, and asphyxiation can be caused by high concentrations of even inert gases such as nitrogen. An additional risk of simple asphyxiants is head injury resulting from falls following rapid loss of oxygen from the brain. Death can also occur after asphyxiation if oxygen levels remain too low to sustain life. Finally, the large amount of potential energy resulting from the compression of the gas makes a highly compressed gas cylinder a potential rocket or fragmentation bomb. On-site chemical generation of a gas should be considered as an alternative to use of a compressed gas if relatively small amounts are needed. Monitoring compressed gas inventories and disposal or return of gases not in current or likely future use are advisable to avoid the development of hazardous situations.

5.H.2 Specific Chemical Hazards of Select Gases

Workers are advised to consult the Laboratory Chemical Safety Summary (LCSS) and the Material Safety Data Sheet

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
×

(MSDS)for specific gases. Certain hazardous substances that may be supplied as compressed gases are listed below:

Boron halides are powerful Lewis acids and hydrolyze to strong protonic acids. Boron trichloride (BCl3) reacts with water to give HCl, and its fumes are corrosive, toxic, and irritating to the eyes and mucous membranes.

Chlorine trifluoride (ClF3) in liquid form is corrosive and very toxic. It is a potential source of explosion and causes deep, penetrating burns on contact with the body. The effect may be delayed and progressive, as in the case of burns caused by hydrogen fluoride.

Chlorine trifluoride reacts vigorously with water and most oxidizable substances at room temperature, frequently with immediate ignition. It reacts with most metals and metal oxides at elevated temperatures. In addition, it reacts with silicon-containing compounds and thus can support the continued combustion of glass, asbestos, and other such materials. Chlorine trifluoride forms explosive mixtures with water vapor, ammonia, hydrogen, and most organic vapors. The substance resembles elemental fluorine in many of its chemical properties and handling procedures, which include precautionary steps to prevent accidents.

Hydrogen selenide (H2Se) is a colorless gas with an offensive odor. It is a dangerous fire and explosion risk and reacts violently with oxidizing materials. It may flow to ignition sources. Hydrogen selenide is an irritant to eyes, mucous membranes, and pulmonary system. Acute exposures can cause symptoms such as pulmonary edema, severe bronchitis, and bronchial pneumonia. Symptoms also include gastrointestinal distress, dizziness, increased fatigue, and a metallic taste in the mouth.

Methyl chloride (CH3Cl) has a slight, not unpleasant odor that is not irritating and may pass unnoticed unless a warning agent has been added. Exposure to excessive concentrations of CH3Cl is indicated by symptoms similar to those of alcohol intoxication, that is, drowsiness, mental confusion, nausea, and possibly vomiting.

Methyl chloride may, under certain conditions, react with aluminum or magnesium to form materials that ignite or fume spontaneously with air, and contact with these metals should be avoided.

Phosphine (PH3) is a spontaneously flammable, explosive, poisonous, colorless gas with the foul odor of decaying fish. The liquid can cause frostbite. Phosphine is a dangerous fire hazard and ignites in the presence of air and oxidizers. It reacts with water, acids, and halogens. If heated, it will form hydrogen phosphides, which are explosive and toxic. There may be a delay between exposure and the appearance of symptoms.

Silane (SiH4) is a pyrophoric, colorless gas that ignites spontaneously in air. It is incompatible with water, bases, oxidizers, and halogens. The gas has a choking, repulsive odor.

Silyl halides are toxic, colorless gases with a pungent odor that are corrosive irritants to the skin, eyes, and mucous membranes. When silyl halides are heated, toxic fumes can be emitted.

Suggested Citation:"Working with Chemicals." National Research Council. 1995. Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. Washington, DC: The National Academies Press. doi: 10.17226/4911.
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This volume updates and combines two National Academy Press bestsellers--Prudent Practices for Handling Hazardous Chemicals in Laboratories and Prudent Practices for Disposal of Chemicals from Laboratories--which have served for more than a decade as leading sources of chemical safety guidelines for the laboratory.

Developed by experts from academia and industry, with specialties in such areas as chemical sciences, pollution prevention, and laboratory safety, Prudent Practices for Safety in Laboratories provides step-by-step planning procedures for handling, storage, and disposal of chemicals. The volume explores the current culture of laboratory safety and provides an updated guide to federal regulations. Organized around a recommended workflow protocol for experiments, the book offers prudent practices designed to promote safety and it includes practical information on assessing hazards, managing chemicals, disposing of wastes, and more.

Prudent Practices for Safety in Laboratories is essential reading for people working with laboratory chemicals: research chemists, technicians, safety officers, chemistry educators, and students.

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