What is the Short-Term Exposure Limit (STEL) used for in evaluating chemical exposure?

• A. A 60-minute exposure limit that should not be exceeded.
• B. A 10-minute exposure limit under special conditions.
• C. A 15-minute exposure limit; intended to control peak exposures.
• D. A daily exposure limit averaged over 24 hours.

Answer: (D)

The key idea is that STEL is about brief, high-concentration peaks that could cause acute harm. It sets a limit for a short exposure period, typically 15 minutes, to cap those peak concentrations and prevent immediate health effects from transient spikes. This concept is used alongside the longer-term time-weighted average to evaluate overall risk, because a daily average can miss dangerous short-term peaks. In practice, you apply the 15-minute limit to any quarter-hour block and, depending on the substance, manage how many peak exposures occur in a day and ensure enough time between them.