Workplace Air Sampling

Thousands of workers each year contract occupational diseases through breathing in dust, fumes or other airborne contaminants in the workplace.  Many of these people die or become permanently disabled and are unable to work as a result of these conditions.

In Britain, the COSHH Regulations are designed to protect workers from exposure to hazardous substances and introduce a variety of controls aimed at reducing employee exposure.  One of these controls introduces Workplace Exposure Limits (WEL’s) for hazardous substances.

Workplace Exposure Limits for hazardous substances in the air are published by the HSE in their EH40 document which is updated annually. The list of WEL’s has legal status under the COSHH Regulations and the limits should be compared with the actual exposure levels measured in the workplace, to check whether exposure is being adequately controlled.

Workplace Exposure Limits are concentrations of hazardous substances in the air, averaged over a specified period of time and referred to as a time weighted average (TWA).  Two time periods are used: long-term (8 hours) and short-term (15 minutes).  Where a substance has been assigned a WEL, adequate control has been achieved if the airborne concentration of the substance is below the limit.  The WEL must not be exceeded. There are some particularly hazardous substances where compliance with the WEL is not sufficient and the exposure to these must be reduced to as low a level as is reasonably practical.  Examples of these are substances that can cause asthma or cancer.

HSE has produced a guidance document HS(G) 173 “Monitoring Strategies for Toxic Substances”, designed to help with the design and implementation of an inhalation monitoring strategy.  This guidance is supplemented by a range of other documents that explain the actual procedures to be used for the measurement of personal exposure to each particular contaminant – these are called MDHS (Methods for Determining Hazardous Substances) notes.

Measuring employee personal exposure to hazardous substances in air should only be carried out by competent personnel.  It may include the use of personal sampling equipment, chemical indicator tubes, smoke tubes and air velocity meters.  Where samples are collected for laboratory analysis, a United Kingdom Accrediation Service (UKAS) accredited laboratory should be used to guarantee the accuracy of the results.

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