An occupational exposure limit (OEL) is the highest concentration of a gas, vapour or dust in the air at a workplace that is considered acceptable over a defined period of exposure. In the United Kingdom the legal figures are called Workplace Exposure Limits and are published by the Health and Safety Executive in the EH40 list. The older Dutch term MAC value (maximum accepted concentration) and the German MAK value describe the same idea; in the Netherlands the term was formally replaced by “limit value” in 2007.
How a limit is expressed
- Long term exposure limit (8 hour time weighted average) — the average exposure over a working day
- Short term exposure limit (usually 15 minutes) — for substances where even a brief peak is harmful
- Skin notation — for substances that are also absorbed through the skin, so inhalation is not the only route
What counts is the air the worker actually breathes, measured in the breathing zone.
Why this matters on site
The important exposures on a building site are not exotic; they are everyday.
- Respirable crystalline silica — released when cutting, grinding, routing or drilling concrete, blockwork, brick, stone and tiles. Prolonged exposure causes irreversible lung damage
- Wood dust — especially hardwood dust, which is classed as carcinogenic
- Asbestos — governed by its own, far stricter regime, with a survey duty and licensed removal for higher risk work
- Vapours from solvents, adhesives, coatings and isocyanates
What you actually do about it
The order of control measures is fixed: deal with the source first, personal protection last.
- Substitute — choose a low dust or solvent free product
- Control at source — on tool dust extraction or water suppression. For silica dust this is by far the biggest single improvement
- Ventilate and separate — do not let others keep working in an enclosed space while dust is being generated
- Respiratory protection — the final layer, with the correct filter class and a face fit tested mask. A beard makes a tight fitting mask largely useless
Related terms
- Health and safety
- Asbestos
- Confined space
- Emissions
- Mechanical ventilation
- Indoor climate
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