The Health and Safety Executive has issued an important Safety Alert which is for the attention of anyone in the chemical processing and production sector who is involved in specifying and selecting devices for measuring concentrations of flammable and toxic gases.

In a recent incident, a gas detector failed to detect the presence of a flammable vapour. Hot work proceeded in the belief that there was no flammable vapour present. The subsequent explosion resulted in a fatal injury.

The investigation found that a significant contributor to the failure to detect the flammable vapour was it being adsorbed on the inner surface of the sample tube. This meant that no flammable vapour reached the detector before the test was completed and a false conclusion that the work area was free of flammable vapour.

Sampling tubes are sometimes used to extend the reach of the detection device and/or to allow detection at an increased distance from the user.

This incident has highlighted the importance of selecting the correct systems for gas detection and verifying the effectiveness of the detection system.

This safety alert is to highlight the risk of adsorption if an unsuitable sample tube is used.

See the full HSE Safety Alert for a detailed report on the incident, links to the relevant legislation and to the relevant reference documents.