Occupational Exposure Limit, or OEL, are legally enforceable thresholds that define the maximum concentration of a specific chemical to which a worker may be exposed over a defined period. These limits are established to prevent both short-term and long-term adverse health effects resulting from chemical exposure.
OEL
Occupational Exposure Limit
Why OELs are Significant in the Workplace
Occupational Exposure Limits (OELs) are critical tools in protecting worker health and safety. They provide quantitative benchmarks for evaluating an employee’s exposure to hazardous substances in the workplace. By comparing measured exposures to established OELs, employers and safety professionals can determine whether control measures are needed to reduce exposure and prevent harm.
Maintaining exposures below OELs helps minimize the risk of adverse health effects, including respiratory illnesses, chemical sensitization, and both short- and long-term impacts on physical and mental well-being. OELs are also instrumental in ensuring regulatory compliance and fostering a safer, healthier work environment.
Exposure Guidelines and Regulatory Limits
Regulated Standard - OSHA 29 CFR 1910.1000 – Air Contaminants
- These standards are federally enforced and legally required to be followed. They establish Permissible Exposure Limits (PELs) for various air contaminants in the workplace to protect employee health and safety. Employers are mandated to ensure exposures do not exceed these limits.
Recommended Standard - ACGIH TLV Chemical Substances
- The Threshold Limit Values (TLVs) established by the American Conference of Governmental Industrial Hygienists (ACGIH) are not legally enforceable, but they are widely recognized as best practice guidelines.
Key Occupational Exposure Limit Definitions
PELs – Permissible Exposure Limits
OSHA-enforced limits that define the maximum allowable concentration of a substance an employee can be exposed to over a specified time period, intended to prevent both short-term and long-term health effects.
TWAs – Time-Weighted Averages
Average exposure limits calculated over a standard work shift (e.g., 8, 10, or 12 hours). Sampling data collected over shorter durations can be adjusted to estimate full-shift exposure.
TLVs – Threshold Limit Values
Exposure limits recommended by ACGIH, representing concentrations believed to be safe for nearly all workers during a typical workday and workweek. These are advisory and not legally enforceable but are widely used in industry best practices.
ECELs – Existing Chemical Exposure Limits
Limits established under the EPA’s Toxic Substances Control Act (TSCA) for specific chemicals, identifying concentrations that should not be exceeded during a defined exposure period to prevent adverse health effects.
STELs – Short-Term Exposure Limits
The maximum concentration an employee may be exposed to for a short duration, typically 15 minutes, without suffering from irritation, chronic or irreversible tissue damage, or narcosis.
Ceiling Limits
Absolute exposure limits that must never be exceeded at any time during the workday. These are critical for chemicals that pose immediate danger at high concentrations.
Action Levels
OSHA- and NIOSH-recognized concentrations that, when reached or exceeded, require the implementation of exposure monitoring, medical surveillance, or chemical management plans.
Table 1. Common Hazardous Materials Used at UK by Time-Weighted Average (TWA) Exposure Limits
| PARAMETER | OSHA PEL TWA | ACGIH TLV TWA | EPA ECEL TWA |
| Formaldehyde | 0.75 ppm | 0.1 ppm | *N/A |
| Xylene | 100 ppm | 20 ppm | *N/A |
| Methylene Chloride | 25 ppm | 50 ppm | 2 ppm |
| Respirable Dust (general) | 5 mg/m³ | *N/A | *N/A |
| Lead and other metals | Review Table Z-1 | Refer to ACGIH TLVs & BEIs | *N/A |
* Note: “N/A” indicates no exposure limit has been established by that agency for the parameter
Table 2. Common Hazardous Materials Used at UK by Short-term OEL
| PARAMETER | OSHA PEL STEL | ACGIH TLV STEL | EPA STEL |
| Formaldehyde | 2 ppm | 0.3 ppm | *N/A |
| Xylene | *N/A | *N/A | *N/A |
| Methylene Chloride | 125 ppm (ceiling) | *N/A | 16 ppm |
| Respirable Dust (general) | *N/A | *N/A | *N/A |
| Lead and other metals | Review OSHA Table Z-1 | Refer to ACGIH TLVs & BEIs | *N/A |
*Note: There is currently no defined STEL for some parameters. "N/A" indicates that no STEL has been established by the respective organization.
Contact
General Inquiries
Email: OHS@uky.edu