Diving instructor killed – incorrect valve threads

The Dutch Labour Inspectorate (Nederlandse Arbeidesinspectie) reports an incident in which a diving instructor was killed. The incident is reported here (in Dutch).

What happened

During a dive, the valve came loose from the diving cylinder and fatally hit the diving instructor; a cylinder with internal thread G3/4 was used, which was fitted with a valve with external thread M25x2.

What was the cause

Threads on the diving cylinder and the mounted valve were incompatible. In this case, the screw thread of the valve was slightly smaller than that of the screw thread in the diving cylinder. The result was that there was an increased risk that the valve will come loose from the cylinder when at pressure.

Members are advised to follow the guidance contained within IMCA D 064 Guidance on diving cylinder and valve thread compatibility. The Dutch Labour Inspectorate (Nederlandse Arbeidesinspectie) notes that despite various (international) publications about the prevention of such incidents, these situations unfortunately continue to occur.

Members may wish to refer to:

• Pillar valve failure (2009, investigation revealed that the cylinder (Luxfur S50 brand) had an imperial thread and the pillar valve (MDE 232 bar) which failed had a metric thread)
• Diver injury during air cylinder recharging (2010, root cause was that the pillar valve had an external metric thread of M25x2 whilst the cylinder had a Whitworth imperial thread of 1 inch (25.4 mm))
• High potential Near-miss: Incompatible pillar valve assembly (2013)
• Injuries due to failure of diver’s emergency gas cylinder (2014, the inner thread on the HP cylinder was not compatible with the outer thread of the pillar valve)
• Injuries due to failure of divers emergency gas cylinder – use of incompatible threads (2016)
• Bailout cylinder and pillar valve compatibility failure (2017)