Failure to detect dangerous gas/vapour due to incorrect specification of sample tube

Health and Safety Executive - Safety alert

Department Name:
Chemicals, Explosives and Microbiological Hazards Division (CEMHD)

Bulletin No:
CEMHD1 – 2020

Issue Date:
10 September 2020

Target Audience:

  • Personnel specifying and selecting devices for measuring concentrations of flammable and toxic gases
  • Chemical processing and production

Key Issues:
This safety alert highlights the risk of misleading gas detection readings associated with the use of sampling tubes with pumped gas detectors. 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.

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.

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

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



Action required

Relevant legal documents


Further Information

Health and Safety Executive
Chemicals, Explosives and Microbiological Hazards Division
Redgrave Court
Merton Road
Bootle, Merseyside, L20 7HS

General note

Please pass this information to a colleague who may have this product/equipment or operate this type of system/process.