In the field of occupational toxicology for the pharmaceutical industry, it is quite common to see the numerical value for an occupational exposure limit (OEL) or OHC assignment change over the course of product development. New data, longer studies, and more human experience with the compound all have the potential to cause the OEL or OHC to change. In addition, once the product is on the market, there may be adverse events reported that were not observed in the clinical development of the product.

In most cases, as the data gets more comprehensive, the numerical OEL value goes higher in value and the exposure control band assignment goes down (i.e. from an exposure control band 3 to an exposure control band 2); however, while rare, occasionally the numerical OEL will decrease in value such that the OHC goes up (i.e. OHC from 2 to 3). In these cases it is often a challenging risk communication issue for the EHS professional because employees will be asking questions such as “Was I over-exposed?” or “Will I be harmed?” This is where it is important that an environmental, health and safety professional in the pharmaceutical industry have a strong understanding of the underlying concepts and assumptions behind occupational exposure limits. These concepts include the following:

• Most OELs assume long-term exposure. With the exception of short-term exposure limits (STELs) and ceiling limits, OELs assume that a worker will be potentially exposed to a compound for 8-hours per day, 5-days per week, for an entire working lifetime (approximately 40 years). If you were to look back several decades where most people would have lifetime jobs doing the same thing, this was a valid assumption. However, in today’s dynamic work environment, most people switch jobs and careers much more rapidly.
• OELs are not bright lines between safe and unsafe. The majority of OELs use the uncertainty factor (now called adjustment factors) method for determining the OEL value. In most cases these OELs are protective over a wide range of airborne concentrations.
• The starting point for determining an OEL is at the very bottom of the dose-response curve. When using the adjustment factor method for determining an OEL the occupational toxicologist is typically tasked with finding what is called the “point of departure (PoD).” As defined by the EPA, “A 'point of departure' (POD) marks the beginning of extrapolation to lower doses. The POD is an estimated dose (usually expressed in human-equivalent terms) near the lower end of the observed range, without significant extrapolation to lower doses.” In other words, the PoD is near the very bottom of the dose-response curve where the slightest response was observed. Once the PoD is selected, then the occupational toxicologists applies the adjustment factors to even further lower the acceptable dose.
• OELs assume that there was no benefit from personal protective equipment worn. The numerical value of the OEL is based solely on the inherent toxicology of the compound and makes no adjustment for respiratory protection worn or engineering controls used (that’s part of the risk assessment process).

So if the numerical OEL goes down, or your ECB goes up, should you panic? Well the answer is no; but you should gain an understanding as to why the OEL or OHC has changed and make the appropriate adjustments to your operations and activities.

As always, if you have any questions regarding potent compound safety or occupational toxicology, please contact us at Affygility Solutions.

Published March 29, 2018

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