When long-term experiments involving highly toxic compounds require unattended operations, securing the laboratory from access by untrained personnel is essential. These operations should also include failsafe 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 laboratory chemical hood becomes restricted or stops. An interlock should be constructed 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 personnel to be contacted in case an alarm sounds within the laboratory.
6.D.5 Special Precautions for Minimizing Exposure to Highly Toxic Chemicals
The practices listed below help establish the necessary precautions to enable laboratory work with highly toxic chemicals to be conducted safely:
1. Conduct procedures involving highly toxic chemicals that can generate dust, vapors, or aerosols in a laboratory chemical hood, glovebox, or other suitable containment device. Check hoods 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 proper operation and be equipped with flow-sensing devices that show at a glance or by an audible signal whether they are performing adequately. When toxic chemicals are used in a glovebox, it should be operated under negative pressure, and the gloves should be checked for integrity and appropriate composition before use. Consider if reactive or toxic effluents may be generated by the procedure. If so, scrubbing may be necessary. If dusts or aerosols are generated, consider using high-efficiency particulate air (HEPA) filters prior to discharge to the atmosphere. Hoods should not be used as waste disposal devices, particularly when toxic substances are involved. To offer maximum protection, they should be operated with sashes at their proper level whenever possible. Monitoring equipment might include both active and passive devices to sample laboratory working environments. The experimenter must ensure that the hood exhaust will not present a hazard to anyone outside the immediate laboratory environment. For instance, rooftop access may need to be eliminated during certain operations or, when rooftop access is required, work with highly toxic materials must not be allowed. (See Chapter 9, section 9.C, for detailed discussion on laboratory chemical hoods and environmental control.) When available, alarmed detection devices are another engineering control that should be used for highly toxic materials. Air dispersion modeling may be necessary to determine if exhaust ventilation will affect nearby air intakes or other sensitive receptors.
2. Gloves must be worn when working with toxic liquids or solids to protect the hands and forearms. Select gloves carefully to ensure that they are impervious to the chemicals being used and are of correct thickness to allow reasonable dexterity while also ensuring adequate barrier protection. (See section 6.C.2.6.1 for more information on gloves.)
3. Face and eye protection is necessary to prevent ingestion, inhalation, and skin absorption of toxic chemicals. 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 certification, training, and fit-testing are required if respirators are worn.
4. Equipment used for the handling of highly toxic chemicals should be isolated from the general laboratory environment. Consider venting laboratory vacuum pumps used with these substances via high-efficiency scrubbers or an exhaust hood. Motor-driven vacuum pumps are recommended because they are easy to decontaminate (decontamination should be conducted in a designated hood).
5. Always practice good laboratory hygiene where highly toxic chemicals are handled. After using toxic materials, trained laboratory personnel should wash their face, hands, neck, and arms. Equipment (including PPE such as gloves) that might be contaminated must never be removed from the environment reserved for handling toxic materials without complete decontamination. Choose laboratory equipment and glassware that are easy to clean and decontaminate. Work