One of the most important tools in the OEHS toolkit is the concept of Occupational Exposure Limits, commonly refered to as OELs for short. These values represent the admissible level of exposure to chemical, physical or biological hazards at which most workers are not likely to develop adverse health effects. These exposure levels are defined for a predetermined length of time (usually 8 hours) and are based on the assumption that workers experience long-term repeated exposure.

There are many OELs in existence, each developed to serve a different purpose, but in general it is helpful to categorize OELs based on two main characteristics:

1. The agency that published them, and
2. The type of exposure they are meant to characterize.

Below we describe the importance of these two principle characteristics and how they should be interpreted.

NOTE: OELs are developed as guidelines to be used and interpreted by health and safety professionals such as industrial hygienists. They are not meant to represent a clear line between safe and dangerous conditions and should not be used or interpreted by anyone who is not trained in the discipline of industrial hygiene or occupational health.

OELs by Agency

There are many professional organizations and agencies around the world dedicated to the study of the effects of workplace contaminants on worker health. Some of these organizations will use the chemical and physical acharacteristics of these contaminants, the results from experimental studies on animals and people, and other toxicological and epidemiological data to develop OELs for different contaminants.

Some of the agencies that publish OELs are regulatory bodies, such as OSHA in the United States, the HSE in the UK, or the DFG in Germany. In those cases, the OELs are regulatory limits that are legally enforceable in their respective countries. Some agencies, such as NIOSH or the ACGIH, are not regulatory bodies, and can only go as fas as recommending exposure limits and other guidelines that they have determined are protective of most workers. The regulatory bodies of some countries may adopt these recommendations as legally binding standards, such as is the case in Canada, Japan and Mexico.

In the following table we display some of the most well known OELs, accompanied by their country of origin and scope of application.

Although the ACGIH is not a regulatory body, their TLVs and their accompanying documentation are widely recognized as the most authoritative OELs around the world based on their rigorous standards for publication.

It is also important to note that although OSHA is a regulatory body in the United States, the agency has acknowledged the outdated and inadecuate nature of their OELs for the purpose of protecting worker health. Therefore, OSHA recommends that “employers consider using the alternative occupational exposure limits” such as ACGIH TLVs, NIOSH RELs or the Cal/OSHA PELs for the purpose of creating a healthy workplace.

OELs by Exposure Type

Since exposures come in different forms and can last for varying durations of time, most agencies will develop OELs for different scenarios in order to account for the circumstances in which they occur and the acute toxicity of the contaminants in question. For the most part, these OELs can be divided into four main categories:

STEL and Ceiling limits are generally higher than TWA limits, and correspond to the threshold level at which the contaminant may induce:

• irritation,
• sensitization,
• central nervous system depression, or
• chronic or irreversable damage to worker health.

Some contaminants do not have a published STEL or Ceiling limit, but may still cause adverse health effects as a result of acute exposures. In these cases, the ACGIH provides guidelines that industrial hygienists may use to adjust TWA limits for evaluating short term exposures where short term limits are not available. These guidelines are known as Peak Limits and should only be used and interpreted by a person trained in the discipline of industrial hygiene.

For a convenient and visual summary of the different kinds of OELs discussed above, check out our publication “[Infographic] Occupational Exposure Limits”.

Monitoring OELs

Companies can verify that their workers’ exposure to hazardous agents is below their corresponding OELs through monitoring. To do this, a qualified professional such as an industrial hygienist measures the magnitude of worker exposure through different mechanisms, depending on the agent being evaluated, and can involve measuring the concentration of a substance in the air, measuring the intensity of noise, determining the acceleration of vibration, or calculating shifts in core body temperature of exposed personel.

The results of monitoring are vital indicators of workers’ risk of experiencing adverse health effects as a result of their exposure. However, carrying out periodic monitoring activities and interpreting the results that are derived from them can be a complex task. With Bernardino OEHS, you can count on a team of experienced professionals to take care of it for you. From hazard recognition to the delivery of results with actionable recommendations, we have your back.

Contact one of our experts today and let us help you build a healthier, more productive workplace.

References

American Conference of Governmental Industrial Hygienists. 2024 TLVs and BEIs Based on the Documentation of the Threshold Limit Values for Chemical Substances and Physical Agents & Biological Exposure Indices.

American Conference of Governmental Industrial Hygienists. “TLV/BEI Guidelines.”

Canadian Center for Occupational Health and Safety. “Ocupational Exposure Limits.”

OSHA. “Permissible Exposure Limits—Anotated Tables.”

UK Health and Safety Executive. “Workplace Exposure Limits.”