Sampling tubes are sometimes used to extend the reach of gas detection devices and/or to allow detection at an increased distance from the user. Following a recent incident where a gas detector failed to detect the presence of a flammable vapour the HSE have released a safety alert highlighting the risk of misleading gas detection readings associated with the use of sampling tubes with pumped gas detectors.
In this particular case the mistaken belief that there was no flammable vapour present lead to hot work being carried out which caused an explosion resulting in a fatal injury.
Investigations found that while there were errors in the selection and set-up of the gas detector, the most significant contributor to the failure of the gas detector was the adsorption of the flammable vapour on the surface of the sample tube before it could reach the gas detector.
The HSE are reminding users to ensure that any gas detection systems are suitable for their intended purpose. In particular they are recommending that in the case of gas detectors that will be used with a sample tube, at least the first function check (‘bump test’) for a new intended use and/or a new sampling configuration be conducted using the combination of the gas detector and its sample tube and the substance of interest, where practicable. This is of particular importance if the substance of interest is not the substance used to calibrate the system.
Full details of the safety alert can be found on the HSE’s website at: https://www.hse.gov.uk/safetybulletins/failure-to-detect-dangerous-gas.htm?utm_source=hse.gov.uk&utm_medium=refferal&utm_campaign=dangerous-gas-safety-alert&utm_term=safety-alerts&utm_content=news-page
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