Laboratory Chemical Exposure Assessment

Chemical exposures in the workplace must be maintained below acceptable levels, referred to as Occupational Exposure Limits, please see the Occupational Exposure Limits section below for more information. Chemical exposures in the laboratory are generally well managed due to engineering controls (e.g. chemical fume hoods) and work practice controls (following the group’s Laboratory Safety Plan and Standard Operating Procedures).

Sometimes laboratory tasks may require work outside of a chemical fume hood, be impractical in a fume hood, or there may be a concern that an engineering control is not effective for the method. In these cases, chemical exposure may need to be evaluated further. Please contact DRS at 217-333-2755 or to discuss performing a Laboratory Chemical Exposure Assessment if there are concerns for the chemicals used in your lab.

DRS will work with the laboratory to perform an assessment and determine if an Occupational Exposure Limit may be exceeded routinely. This will include reviewing the materials used and determining the best method for controlling exposure using the Hierarchy of Controls. DRS and the laboratory can often solve potential exposure concerns by adding additional engineering controls or implementing improved work practice techniques.

If the chemical exposure assessment shows that an Occupational Exposure Limit may be exceeded after improvements are implemented, or where improvements are not feasible, air sampling may be required to determine the level of exposure.

Occupational Exposure Limits

Occupational Exposure Limits (OELs) are workplace standards designed to protect workers from adverse exposures. These values are generally Time Weighted Average (TWA) concentrations, based on an 8-hour work day, or a 15 minute Short Term Exposure Limit (STEL). These can be regulatory limits established by OSHA, or voluntary guidelines published by professional organizations.

Many chemicals have an Action Level. These are 8-hour Time Weighted Averages that initiate additional requirements, such as exposure monitoring and medical surveillance. Some substances have a Ceiling Value (C). These are concentrations that cannot be exceeded at any time during the workday. The formula for calculating TWA exposures can be found here.

Permissible Exposure Limits (PELs)

Permissible Exposure Limits (PELs) are OELs published by OSHA. Employers are required to limit workplace exposures below the published PEL, STEL, and Ceiling Values. These were adopted in 1970 by OSHA from the 1968 Threshold Limit Values (TLVs) published by the American Conference of Governmental Industrial Hygienists (ACGIH) and have largely remained unchanged.

OSHA has published Permissible Exposure Limits (PELs) for several hundred chemicals, along with substance specific standards (e.g. benzene, formaldehyde, lead, etc.) in OSHA Standards 29 CFR 1910.1000 through 1910.1052. The Action Level of certain chemicals indicates a level below the PEL, but where additional requirements are specified.

Threshold Limit Values (TLVs)

Threshold Limit Values (TLVs) are established by ACGIH, which is a professional, scientific organization that annually updates TLVs based on current research. These consist of 8-hour TWA TLVs, TLV-STELs, and Ceiling Values.

Recommended Exposure Limits (RELs)

The National Institute for Occupational Safety and Health (NIOSH) is part of the Centers for Disease Control and Prevention (CDC) and was established to research occupational health and safety issues. They make recommendations for health and safety standards for OSHA. NIOSH publishes Recommended Exposure Limits (RELs) for hundreds of chemicals. These are generally 10 hour TWAs, along with Ceiling Values and STELs. These values are maintained in the NIOSH Pocket Guide to Chemical Hazards.


The University is required to maintain exposures below the PELs. OSHA recognizes the PELs are out of date and other recommended limits are more prudent guidelines. The University is committed to the health and safety of all personnel and exposures will be controlled below the lowest published occupational exposure limit.

In addition to the OSHA PELs, ACGIH TLVs, and NIOSH RELs, other chemical exposure recommendations exist that are used as guidelines.

Occupational Exposure Limit Sources

Safety Data Sheets: Section 8 of the SDS can be referenced for OELs. More information regarding Safety Data Sheets can be found here.

OSHA’s Lists of PELs

OSHA’s Annotated Tables – These lists include TLVs and RELs for chemicals in Z-1, Z-2, or Z-3. It does not include any TLVs or RELs for chemicals outside of Table Z-1, Z-2, or Z-3. See the NIOSH and ACGIH links below for the full lists of TLVs and RELs.

NIOSH Pocket Guide to Chemical Hazards


    Last Updated: 7/28/2021