WES (Workplace Exposure Standard)
A WES sets the maximum airborne concentration of a hazardous substance a worker can be exposed to. It's a key threshold in confined space and hazmat work.
Ask Chalkline about this →WES stands for Workplace Exposure Standard. It is the maximum airborne concentration of a hazardous substance to which a worker may be repeatedly exposed during a working day without adverse health effects. WES values are set by Safe Work Australia and published in the Workplace Exposure Standards for Airborne Contaminants document.
WES values come in two forms: Time Weighted Average (TWA) is the maximum average concentration over an 8-hour shift; Short-Term Exposure Limit (STEL) is the maximum concentration over any 15-minute period. Both must be respected where hazardous airborne contaminants are present.
In confined space work, atmospheric monitoring must confirm that toxic contaminants remain below their WES before and during entry. For example, hydrogen sulfide (H2S) in a sewer pit must not exceed its WES for the entrant to proceed safely. Where the WES cannot be maintained through ventilation or other controls, respiratory protective equipment (RPE) matched to the specific contaminant is required.
WES values are published by Safe Work Australia and reviewed periodically. The current table is available at safeworkaustralia.gov.au.
Also known as: occupational exposure standard (OES, older terminology)
Category: WHS / hazardous substances
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Last updated: 2026-05-10. Verified: 2026-05-10. Quarterly review for currency.