Chapter 11: Airborne Exposure Limits

Airborne Exposure Limits

Many chemicals used in laboratories have significant volatility at room temperature. Consequently, inhalation is generally the most likely route of chemical exposure for laboratory workers. Although airborne exposure limits have been established for many chemicals, these exposure limits are not a strict delineation between safe and unsafe conditions. Nevertheless, exposure to an airborne chemical at a concentration that is below the established exposure limit is generally considered safe. It should be pointed out that many established airborne exposure limits do not take into consideration carcinogenic or reproductive end points, and thus may not provide an adequate level of safety with respect to these toxicological effects.

There are two primary sets of exposure limits used in the United States, the OSHA Permissible Exposure Limits (PELs), and the Threshold Limit Values (TLVs) established by the American Conference of Industrial Hygienists (ACGIH). The OSHA PELs are regulatory exposure limits that are legally enforceable (OSHA will issue a citation if an overexposure occurs), while the ACGIH TLVs are recommended limits. Since TLVs are not regulatory limits, they are revised (based on new information) much more frequently than are PELs and are generally considered to more accurately reflect current knowledge pertaining to the health effects of chemical exposures. Although the OSHA PELs are the regulatory exposure limits, it is recommended that personal exposures be maintained below the lower of the PEL or TLV. Other airborne exposure limits, to include Recommended Exposure Limits (RELs) established by the National Institute for Occupational Safety and Health, may also be used in some circumstances.

Availability of Published Exposure Limits

PELs and TLVs can be found in Safety Data Sheets (SDSs) or they can be obtained from EH&S. Additionally, the OSHA PELs are published in the OSHA regulation, “Air Contaminants.” Many chemicals used in research laboratories do not have established exposure limits, and good laboratory safety practices that minimize exposure to all chemicals should be routinely implemented.

Exceeding Exposure Limits

Exposure limits are most likely to be exceeded when performing operations outside of a lab hood, especially when using highly volatile chemicals, large volumes of chemicals, or chemicals with low exposure limits (for example, less than 50 ppm). Air monitoring is necessary to accurately quantify chemical exposure (see next section, Air Monitoring).

Workers should be familiar with the odor and/or visual characteristics of the chemicals they work with as these characteristics can sometimes be used to detect the presence of chemicals in the laboratory. Do not use chemical odor and/or visual characteristics as a means of determining that inhalation exposure limits are not being exceeded as sometimes these characteristics are only detected at concentrations far above that which is considered safe. For example, the odor threshold (the concentration at which a chemical can be detected by its odor) of acetonitrile is 1160 ppm, while the exposure limit is 40 ppm!

Air Monitoring

Air monitoring is necessary to quantitatively determine the concentration of airborne chemicals. This information is used to estimate risk to personnel, assess the efficiency of laboratory hoods and other exposure control equipment, and to verify regulatory compliance. To ensure that the air monitoring accurately represents personnel exposure, it must be conducted in accordance with regulatory requirements and accepted professional practice. EH&S is responsible for performing chemical air monitoring at UNR and has several direct-reading monitors that can be used to measure the air concentration of many chemicals at near real time. Additionally, air samples can be collected for more detailed laboratory analysis. Generally, consistent use of the good laboratory practices outlined in this manual will keep chemical exposures below established exposure limits; however, if you feel that air monitoring is warranted in your laboratory, contact the University Chemical Hygiene Officer.