Last edited 05 Aug 2018

Workplace exposure limits

Some workplace processes involve the use of substances that could cause harm. The Control of Substances Hazardous to Health Regulations 2002 (COSHH) require that employers prevent or reduce workers' exposure to such substances.

Workers might be exposed by:

  • Inhalation.
  • Ingestion.
  • Contact with the skin.
  • Contact with the eyes.
  • Skin puncture.

COSHH stipulates that the control of hazardous substance exposure will only be regarded as being adequate if it falls below the necessary workplace exposure limit (WEL). The regulations place a duty on employers to prevent or control exposure to within the particular WEL.

WEL values are approved by the Health and Safety Commission (HSC), which acts on the advice of the Advisory Committee on Toxic Substances (ACTS). They are expressed as a time weighted average (TWA). There are two variations of WEL:

  • Long-term exposure limit (LTEL): The maximum exposure over an 8-hour period. This is intended to protect the workforce from contaminants which, over a long period of time, may cause ill health.
  • Short-term exposure limit (STEL): The maximum exposure over a 15-minute reference period. This is intended to protect the workforce from peak exposure incidents which might result in immediate and acute ill health.

A document published by the Health and Safety Executive (HSE) contains the list of WELs for use with COSHHEH40/2005 Workplace exposure limits.

Since there are a large number of chemical compounds used in construction, there will be some that are not included on this list of WELs, perhaps due to a lack of information about them. However, this does not mean that they are therefore safe. They should be controlled to a level at which the workforce could be exposed for a long period of time without experiencing any adverse health effects.

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