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17 May 2006 - HSE Advice on Gas Analysis of
Diving Cylinders
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Following an incident in which two people were injured when a
gas cylinder valve ejected during analysis of a diving cylinder, the Health and
Safety Executive (HSE) have issued precautionary advice to anyone involved in
such tasks, in order to reduce the risk of further accidents.
A Draeger rebreather, four litre, steel cylinder, which had been
charged with Nitrox analysis was being carried out in a dive shop, when the
incident occurred.
Fitted to the cylinder, was a charging adaptor, supplied by the
customer. The cylinder had no "boot", which would have allowed the
cylinder to stand erect, thus the person about to carry out the analysis having
to hold the cylinder upright in one hand.
To allow the necessary low flow of gas release for the analysis,
the cylinder valve, as it was being opened, created an unexpected increase in
gas flow, which in turn caused a violent rotation of the cylinder.
The unexpected rotation of the cylinder injured the hand of the
person holding it, resulting in the release of the cylinder from his grasp and
causing the cylinder to spin out of control into the shop.
One customer in the shop tried to stop the cylinder from hitting
his son by stopping it with his foot and in the process of doing so was also
injured.
The valve, still fitted with the charging adaptor, was then
ejected from the cylinder, causing the cylinder to continue uncontrollably out
of the shop travelling a further 20 meters before coming to rest outside the
shop premises.
The valve, dislodged from the cylinder, travelled out of control
for approximately 3 meters inside the shop.
Analysis by scientific and engineering specialists has failed to
provide a conclusive result as to why there was an increase in gas flow, or what
caused the ejection of the cylinder valve.
The HSE, in order to reduce the risk of similar accidents
occurring, have issued precautionary advice to anyone involved in gas cylinder
analysis as follows:
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When a charging adaptor is fitted to the cylinder, there is a
possibility that if struck it will affect the torque applied between the
cylinder and cylinder valve. To reduce the probability of this happening
charging adaptors should only be fitted immediately before charging and removed
immediately afterwards.
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Charging adaptors which are used with pure oxygen or oxygen
enriched (oxygen greater than 21 per cent) gases should be suitable for use with
oxygen. In order to maintain their 'fit for oxygen' status when not in use they
should be stored to maintain that status - for example, placed in a clean
transparent bag, which can be sealed closed and then placed in a second similar
bag.
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When carrying out any checks that require the cylinder valve to
be opened the cylinder should be secured in a manner that allows both hands of
the checker to be free. One hand to operate the valve and the other to hold any
test equipment and does not allow the cylinder to fall over or be dropped.
The HSE have many leaflets and guidance sheets on diving
cylinders etc available from their website, all of which can be accessed by
clicking the following:
Information about health and safety at work
Article by Alexandra Johnston
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