What is the workplace exposure limit (WEL) for isocyanates?

In the UK, the Workplace Exposure Limit (WEL) for isocyanates is set at:

• 0.02 mg/m³ (8-hour time-weighted average)

• 0.07 mg/m³ (15-minute short-term exposure limit)

These limits apply to all isocyanates, measured as NCO group — which refers to the part of the molecule that causes health effects.

The short-term limit is especially important in spray applications or short bursts of high exposure. Exceeding these limits can increase the risk of workers developing asthma, sensitisation, or other respiratory issues.

Keep in mind that the WEL is the maximum allowable concentration — not a safe zone. Sensitised individuals may react at levels well below the limit, so controls should aim to reduce exposure as much as reasonably possible.