Stels

STEL stands for Short-Term Exposure Limit. It is a workplace air concentration limit intended to protect workers from acute health effects when they may experience brief peaks of exposure to hazardous substances. STEL values are typically defined for a 15-minute period and are used alongside longer-term limits such as TLVs or PELs to manage both peak and chronic risks.

In practice, a STEL represents the maximum concentration to which a worker can be exposed for any 15-minute interval without adverse health effects. To manage job tasks, many guidelines specify that no more than a certain number of 15-minute exposures to the STEL should occur in a work shift (commonly up to four times per day), and there must be a minimum gap between such exposures (often at least 60 minutes). The goal is to limit peak concentrations while still allowing normal workflow, as long as overall daily exposure remains within the applicable long-term limits.

STEL values are issued by organizations such as the American Conference of Governmental Industrial Hygienists (ACGIH) as part of their TLV framework, and they may be adopted by national or regional safety regulators. The exact numeric STEL for a given substance depends on the substance’s toxicology and measurement methods, and STELs vary by jurisdiction and update cycle. STELs are not universal ceilings; they are one element of a broader exposure-management strategy that also includes TLV-TWAs, PELs, engineering controls, and personal protective equipment.

Limitations of STELs include variation by substance and regulatory origin, possible updates that change values, and the need for accurate sampling methods to measure short-term concentrations. They are intended as practical guides for protecting workers from acute effects rather than comprehensive risk assessments.