The Health and Safety Executive (HSE) has issued precautionary advice to dive shop owners and any other people carrying out gas analysis on diving cylinders after an incident at a dive shop where two people were injured after a valve was ejected from a cylinder.

The incident happened during gas analysis of a Draeger rebreather four-litre steel cylinder, which had been charged with Nitrox. A charging adaptor had been supplied by the customer and was still fitted to the cylinder valve. The cylinder did not have a 'boot' that would have allowed it to stand upright unsupported. Instead, the person carrying out the gas analysis held the cylinder upright with one hand.

As the cylinder valve was opened to allow a low flow of gas for analysis there was an unexplained increase in flow causing the cylinder to rotate violently, injuring the hand of the person holding it. As a result, he let go and the cylinder spun off into the shop. A member of the public was injured trying to stop the spinning cylinder with his foot, as he tried to stop it hitting his son. At this point the valve, still fitted with the charging adaptor, was ejected from the cylinder. The cylinder flew out of the dive shop and travelled a further 20 metres before coming to rest outside. The valve travelled about three metres within the shop.

Despite being analysed by scientific and engineering specialists, it is still not clear why there was an increase in gas flow or what caused the cylinder valve to be ejected.

However, HSE is issuing precautionary advice to reduce the risk of a similar incident happening. In particular, 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.

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.

Furthermore, 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. i.e. 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.

Note to Editor

1 The relevant Local Authority normally enforces safety at dive shops. However, due to the nature of the incident, it was agreed that HSE would lead the investigation.

2 Nitrox is a generic term for oxygen/nitrogen gas mixes with an oxygen content greater than 21 per cent. The cylinder in question contained 40% oxygen.

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