Which of the following is a STEL guideline regarding frequency?

• A. There must be more than 60 minutes between excursions.
• B. STEL can be exceeded once per week.
• C. Less than 15 minutes in duration.
• D. No more than 4 times per work day.

Answer: (D)

Short-term exposure limits are meant to prevent acute effects from brief spikes in concentration. The rule for how often you can exceed this limit in a single workday is that it should not happen more than four times. This frequency cap ensures that occasional peaks do not translate into a pattern of repeated high exposures, giving time for recovery between spikes. The 60-minute spacing between exceedances is related but separate, focusing on separating those peaks rather than limiting the total number per day. Exceeding once per week is too infrequent to reflect typical exposure scenarios, and limiting duration to less than 15 minutes focuses on how long a single exceedance lasts, not how often they occur. Therefore, no more than four exceedances per workday is the correct frequency guideline.