In the regulatory framework of theOccupational Safety and Health Administration (OSHA), specifically under standards such as29 CFR 1910.1001(Asbestos), anexcursion limitis a specific type ofShort-Term Exposure Limit (STEL). While the primary Permissible Exposure Limit (PEL) is typically calculated as an 8-hour Time-Weighted Average (TWA), the excursion limit is designed to protect workers from high-intensity, short-duration spikes in exposure that could be harmful even if the 8-hour average remains below the PEL.
Technically, OSHA defines an excursion limit as a maximum concentration to which a worker can be exposed over a specific short period—usually30 minutes.1For example, in the asbestos standard, the excursion limit is 1.0 fiber per cubic centimeter of air (1 f/cc) as averaged over a sampling period of 30 minutes. This is functionally a STEL, though "STEL" is more commonly associated with 15-minute intervals in other chemical standards. TheTLV(Option C) is a term used by the American Conference of Governmental Industrial Hygienists (ACGIH) and is not an enforceable OSHA legal limit, although OSHA often uses TLV data when establishing its PELs.2
For aCertified Emergency and Disaster Professional (CEDP), monitoring for excursion limits is vital during disaster cleanup and industrial response. During activities like debris removal or structural demolition, particulate levels can fluctuate wildly. A TWA might suggest an environment is safe, but "excursions" during peak activity can cause acute respiratory distress or long-term damage. Therefore, safety plans must include real-time air monitoring and the use of theAssigned Protection Factor (APF)of respirators to ensure that even during these peak "excursion" periods, the worker’s intake remains within safe biological limits.
