Which value indicates the maximum allowable exposure for 15 minutes, not to be exceeded repeatedly?

The value that indicates the maximum allowable exposure for 15 minutes, not to be exceeded repeatedly, is the Threshold Limit Value - Short Term Exposure Limit (TLV-STEL). This limit is specifically designed to protect workers from exposures to hazardous substances that could occur over short durations, typically a 15-minute period, during which it is permissible to exceed the time-weighted average exposure limit.

The TLV-STEL is pertinent in environments where short-term spikes in exposure can happen and warrants specific limits to safeguard against acute health risks associated with those short-term exposures. It is important for ensuring that any exposure that exceeds the average over more extended periods does not pose a significant risk to health when averaged out over time.

In contrast, the other values listed serve different purposes. The TLV-TWA (Time-Weighted Average) represents the average exposure over an 8-hour workday, which does not focus on short-term exposures but rather on chronic exposure levels. PEL (Permissible Exposure Limit) refers to limits established by regulations that can get more specific and structured as either short-term or long-term limits but may not explicitly limit short intervals the way TLV-STEL does. REL (Recommended Exposure Limit), provided by the National Institute for Occupational