Protect employees by understanding and applying Occupational Exposure Limits (OELs)

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Working with solvents implies potential exposure to evaporative emissions. To help you assess acceptable employee exposure, every chemical we produce is assigned a specific Occupational Exposure Limit (OEL). The OEL is listed on each product's Material Safety Data Sheet.

It's important to the health of your employees and your customers' employees to understand about OELs and the Vapor Hazard Ratio, which is a formula you can apply to manage exposure to solvents.

Unless otherwise noted, OELs are based on an 8-hour day and 40-hour week. OELs factor in work pattern and describe the airborne concentration below which it is generally accepted that workers may be repeatedly exposed day after day without adverse effects. While OELs are useful in assessing the inhalation hazard of a material, they are not an index of the toxicity inherent in the specific material.

OELs for hydrocarbon fluids
The best-known OELs are the Threshold Limit Values (TLVs) set by the American Conference of Governmental Industrial Hygienists (ACGIH). In most EU countries, OELs are available for single components only. European Solvents Industry Group (ESIG) member companies producing hydrocarbon solvents developed OELs based on the well-established Reciprocal Calculation Procedure (RCP). Using this calculation procedure together with guidance values for groups of specific hydrocarbon components enables OELs to be calculated for commercial products including complex substances and mixtures.

RCP-OELs and TLVs are set based on a review of the scientific data including toxicological, epidemiological, clinical and industrial hygiene evidence.

Risk potential
Toxicity alone is not adequate to assess the actual risk potential of a solvent exposure. Other factors that affect the risk potential include:

  • Vapor pressure
  • Natural and mechanical ventilation
  • Manner of usage, handling procedures and protective clothing 

The potential for exposure by inhalation depends on the ability of the material to evaporate and generate an airborne concentration. The potential for exposure is determined by the vapor pressure of the material.

Vapor Hazard Ratio (VHR) is one tool used to compare the potential of different solvents to generate vapor under a given set of conditions and to relate that potential to the OEL. 
VHR = Equilibrium Vapor Concentration (at 20°C / 68°F) divided by the OEL . The lower the ratio the lower the potential risk.

Two ways to reduce the Vapor Hazard Ratio

  • When products have a similar OEL, choose the material of lowest volatility (lowest equilibrium vapor concentration).
  • When products have similar volatility, choose the material with a higher OEL.