Exposure Limits: ACGIH TLVs® and OSHA PEL Explained

May 7th, 2025 | Posted in Air Cleaners

In a previous blog we discussed some of the aspects of monitoring for occupational exposures to airborne contaminants.  The focus of that blog was a screening technique that measures “Particulates Not Otherwise Classified (PNOC) as a surrogate for coolant mist generated by machining operations. We also noted that the OSHA  Permissible Exposure Limit (PEL) for PNOC is 5 mg/m3.   This raises the question: “What is an OSHA PEL?” What does that term mean?

In this blog by AQE, we explain the purpose and origin of OSHA PEL limits, how they differ from other standards, and why understanding them is critical to managing workplace air quality.

What is an OSHA PEL?

An OSHA PEL is set by the Occupational Safety and Health Administration and carries the force of law in the United States; they are federal regulations.  There is a rather complex process by which these PELs are established and OSHA must justify them based on scientific studies defining exposure concentrations and epidemiological outcomes.  These exposure limits are based on sound research and the recommendations of the National Institutes for Occupational Safety and Health (NIOSH).

The Role of the General Duty Clause

Section 5(a)(1) of the Occupational Safety and Health Act (the “General Duty Clause”) requires an employer to furnish to its employees: “employment and a place of employment which are free from recognized hazards that are causing or are likely to cause death or serious physical harm to his employees…” An OSHA PEL is the metric used to determine whether an occupational exposure is sufficiently great to constitute a recognized health hazard.  OSHA has established PELS for approximately 500 substances.  These PELs are to be found in the Z tables of the Air Contaminants Standard, 29 CFR 1910.1000.  You can view the OSHA PEL Annotated Tables for more specific information. Click on the ”Z Tables” to review the lists.

Outdated OSHA PELs

The same OSHA web page as above contains this statement:states, “OSHA recognizes that many of its permissible exposure limits (PELs) are outdated and inadequate for ensuring protection of worker health.”  That disconnect has evolved since the PELS were established in 1970; 55 years ago.  We’ve learned a lot in the last 55 years. OSHA notes, “Industrial experience, new developments in technology, and scientific data clearly indicate that in many instances these adopted limits are not sufficiently protective of worker health.”

Because the regulatory promulgation process is slow and difficult, OSHA has not been able to update the PELs to keep them current with a current scientific understanding of health effects and what constitutes an acceptable (minimum health risk) exposure.

ACGIH and TLVs^®

The American Conference of Governmental Industrial Hygienists (ACGIH), which is a scientific organization rather than a government organization, has been able to maintain a more current list of hazardous substances and appropriate exposure limits. The ACGIH exposure limits are called Threshold Limit Values^® or TLVs^®. Even though the TLVs® do not carry the force of law, as do the OSHA PELs, the TLVs^® constitute a “recognized standard of care.”

Recognizing the values of the TLVs^®, OSHA notes, “OSHA’s Hazard Communication standard (1910.1200 Appendix D) requires that safety data sheets list not only the relevant OSHA PEL but also the ACGIH^® TLV^® and any other exposure limit used or recommended by the chemical manufacturer, importer, or employer preparing the safety data sheet.”

In the 2025 Guide to Occupational Exposure Values published by the ACGIH over 2,000 substances are listed with TLVs^® and, where they exist, PELS. (One should note that three other sets of exposure standards are also listed in the Guide to Occupational Exposure Values but these are not discussed here as they are not commonly used by the layperson.)

Two Commonly Used Exposure Standards

What this boils down to is that there are two commonly used sets of exposure standards:

• OSHA PELs which carry the force of law
• ACGIH TLVs^® which are NOT legal requirements but are recognized standards of care

It is considered prudent practice to use whichever of the two is more protective when determining if an intervention, such as air cleaning or respirators, is called for.

Important Considerations

In either case, neither the OSHA PELs nor the TLVs^® represent a fine line between a hazardous exposure and a non-hazardous exposure. There is substantial variation in individual susceptibility to health hazards. Consequently, these exposure limits do not guarantee that there will be zero health effects for a specific individual at that level. Rather, the assumption is that nearly all workers may be repeatedly exposed at or below these exposure limits without adverse health effects. Because ANY exposure to a hazardous substance is not a good thing, prudent practice dictates minimizing exposures even if they are below the PELs or TLVs^®. Air cleaning is a good way to accomplish this goal.