Laboratory chemicals should never be tasted. A pipet bulb, aspirator, or mechanical device must be used to pipet chemicals or to start a siphon. To avoid accidental ingestion of hazardous chemicals, 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.

6.C.2.4 Avoiding Inhalation of Hazardous Chemicals

Only in certain controlled situations should any laboratory chemical be sniffed.1 In general, the practice is not encouraged. Toxic chemicals or compounds of unknown toxicity should never be deliberately sniffed. Conduct all procedures involving volatile toxic substances and operations involving solid or liquid toxic substances that may result in the generation of aerosols in a laboratory chemical hood. Air-purifying respirators are required for use with some chemicals if engineering controls cannot control exposure. Significant training, along with a medical evaluation and respirator fit, are necessary for the use of respirators. For further guidance on the use of respirators with specific chemicals refer to Chapter 7, section 7.F.2.4 of this book, the OSHA Respiratory Protection Standard (29 CFR § 1910.134), and ANSI Standard Z88.2-1992.

Laboratory chemical 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 according to institutional procedures and government regulations. (See Chapter 8 for information on waste handling.)

6.C.2.4.1 General Rules for Laboratory Chemical Hoods

Detailed information regarding laboratory ventilation can be found in Chapter 9. The information here is intended to provide a brief overview. These general rules should be followed when using laboratory chemical hoods:

   Before using a laboratory chemical hood, learn how it operates. They vary in design and operation.

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

   Review the MSDS and the manufacturer’s label before using a chemical in the laboratory or hood. Observe the permissible exposure limit, threshold limit value, the primary routes of exposure, and any special handling procedures described within the document. Confirm that the experimental methods and available engineering controls are capable of controlling personnel exposure to the hazardous chemicals being used.

   Keep reactions and hazardous chemicals at least 6 in. (15 cm) behind the plane of the sash, farther if possible.

   Never put your head inside an operating 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 sash in the lowest possible position. Where sashes open horizontally, position one of the doors to act as a shield in the event of an accident. When the hood is not in use, the sash should be kept at the recommended position to maintain laboratory airflow.

   Keep laboratory chemical 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, clean it regularly so it does not become clogged with papers and dirt. Allow only materials actively in use to remain in the hood. Following this rule provides optimal containment and reduces the risk of extraneous chemicals being involved in any fire or explosion. Support any equipment in hoods on racks or feet to provide airflow under the equipment.

   Do not remove the airfoil, alter the position of inner baffles, block exterior grills, or make any other modifications without the approval of the appropriate staff.

   Report suspected laboratory chemical hood malfunctions promptly to the appropriate office, and confirm that the problems are corrected.

   If working in a glovebox, check the seals and pressures on the box before use.

Post the name of the individual responsible for the hood in a visible location. Clean hoods before maintenance personnel work on them.

(See Chapter 9, section 9.C, for more information on laboratory chemical hoods.)


1In a controlled instructional setting, students may be told to sniff the contents of a container. In such cases, the chemical being sniffed should be screened ahead of time to ensure that it is safe to do so. If instructed to sniff a chemical, gently waft the vapors toward your nose using a folded sheet of paper. Do not directly inhale the vapors.

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