What does the excursion limit average (also called STEL) represent?

The excursion limit average, or short-term exposure limit (STEL), specifically refers to the average concentration of a substance in the air over a short duration, typically 15 minutes, where exposure should not exceed certain levels to prevent adverse health effects. STEL values are established for substances to provide a safeguard against acute exposure risks that can lead to serious health impacts when individuals are exposed to high concentrations over a short period.

When identifying that the excursion limit average reflects an average concentration over a defined short-term period, it’s important to clarify that it is measured over a 15-minute time frame and allows for some fluctuation in concentration during that time. Therefore, the correct understanding of the STEL is that it focuses on preventing excessive exposure peaks that could occur during brief exposures, thus promoting health and safety in environments where such hazardous materials may be present.