Which exposure value allows for a maximum of four repeated 15-minute exposures with a 60-minute rest period?

• A. TLV-TWA
• B. TLV-C
• C. TLV-STEL
• D. PEL

Answer: (C)

The correct answer relates to the TLV-STEL, which stands for Threshold Limit Value - Short Term Exposure Limit. This exposure value is specifically designed to monitor short-term exposures to hazardous materials. It allows workers to be exposed to a chemical agent for a maximum of 15 minutes, provided that there are no more than four such exposures in a workday, followed by a minimum rest period of 60 minutes.

This approach is important for protecting workers' health, as it recognizes that short bursts of exposure may occur in certain work environments, but limits the frequency and duration to minimize the risk of adverse effects. The TLV-STEL is established to ensure that workers can experience these limited exposures without experiencing toxic effects or serious health risks.

Other exposure values, such as TLV-TWA (Time Weighted Average), are meant for average concentrations to which workers can be exposed over a longer period, usually an entire 8-hour workday, while PEL (Permissible Exposure Limit) is a legal limit set by regulatory agencies. TLV-C (Ceiling) indicates an exposure limit that should not be exceeded at any time. Therefore, the TLV-STEL's structure is uniquely suited for allowing multiple brief exposures with specific resting times in between.