Ruptured acetylene hose: Fire

What happened?

A subcontractor was preparing to use an oxy-acetylene torch on the back deck of a vessel. The oxygen and acetylene cylinders were located on the quayside with the hoses rigged to the vessel. On lighting the torch, a ‘pop’ sound was heard, and a small fire was observed from a rupture of the acetylene hose just ahead of the flash-back arrestor.

What went wrong?

The actual cause of this incident could not be established. However, flash-back can occur when a flammable mixture remains in the blowpipe or hoses when the torch is lit. Ignition can travel towards the cylinder but is normally stopped by the flash-back arrestor, which prevents decomposition of the acetylene or an explosion.

What actions were taken?

Our member took the following actions:

  • Regularly check the condition of oxygen and acetylene hoses and ensure they are replaced as required in any planned maintenance system (PMS) or supplier instructions;
  • Keep torches in good condition to avoid turbulent gas flow and so reduce the risk of flash-back;
  • As a minimum there should be a non-return valve at the torch end of each hose and a pressure or temperature variation activated flash-back arrestor at the cylinder end;
  • Only use regulators, flash-back arrestors, hoses and blowpipes which are designed for either acetylene or oxygen and are clearly marked and manufactured to the correct standard;
  • Ensure that flash-back arrestors are being replaced at least every 12-months;
  • Welding gas hoses should be correctly connected, and jubilee clips should never be used;
  • For cutting and purging operations the oxygen and acetylene hoses should be separately purged to remove any flammable mixtures before lighting the blowpipe;
  • Monitor and confirm the subcontractor’s compliance to the above requirements.

What lessons were learned?

Our member gave the following advice to crew for what to do if a flash-back occurs and it is safe to do so:

  • Immediately close the oxygen nozzle valve and then the acetylene nozzle valve (NB: this is the opposite of the normal closing down sequence);
  • Close both oxygen and acetylene cylinder valves;
  • If the flame cannot be put out at once, evacuate the area and raise the alarm. For onshore sites or for a vessel which is alongside alert the emergency services;
  • Once the situation is secured, the equipment must be quarantined until it can be fully examined for damage and either confirmed safe for reuse or safely disposed of;
  • Never attempt to move or vent a cylinder but monitor for any heat generation;
  • If a hotspot is detected on the acetylene cylinder evacuate the area, raise the alarm and where appropriate, notify the emergency services, if safe to do so apply cooling water.