How will the OEL change if I reduce the exposure time?

We often get asked the question, "How will the OEL change if I reduce the exposure time?"

Before asking this question, it's important to review the definition of occupational exposure limit; which is as follows:

"An occupational exposure limit (OEL) is the maximum average airborne concentration of an active pharmaceutical ingredient (API) or a hazard chemical to which nearly all workers can be exposed to for 8-hours per day, 5-days per week, for an entire working lifetime (which is estimated to be 40 years). Unless otherwise specified, it is a time-weighted average (TWA) over the 8-hour work shift."

The OEL is based solely on the toxicology of the compound. Reducing exposure time doesn't change the OEL, but does change the time-weighted average airborne concentration for the day. For short batch-type activities this needs to be verified through industrial hygiene monitoring.