Acetylene cylinders may be encountered at domestic garages and many other commercial locations. As imported acetylene cylinders may not conform to relevant UK regulatory standards, personnel attending an incident involving cylinders must carry out a risk assessment and consider the possibility of incorrect or lack of colour markings. The incident commander should use as many sources of information as possible to verify that the contents of the cylinder match the colour coding. These may include:
- Confirmation with the owner, occupier or operative
- Any documentation available
- Site-specific risk information (SSRI)
- Visual information, for example, the shape of a cylinder or a cylinder connected to an oxygen cylinder or strapped to a welding trolley etc. N.B. although a common configuration for cutting and welding, other fuel types may also be encountered for example oxy-propane.
The following signs can indicate possible heating:
- Visible bulge in the shell – personnel should treat the cylinder with extreme caution as this indicates a greatly increased likelihood of catastrophic failure
- Burnt cylinder labels
- Melted plastic rings around the cylinder valve
- Blistered or burnt cylinder paintwork
- Surface steam when water is applied
- Pressure relief devices (if fitted) that are operating (N.B. the operation of a pressure relief disc or fusible plug with gas burning off or leaking indicates an increased likelihood of catastrophic failure and should not be regarded as a sign of safety)
Witnesses may be able to confirm:
- Whether a cylinder has suffered direct flame contact and, if so, the severity and duration
- Whether a flash back has occurred (and not a backfire, which produces a single cracking or ‘popping’ sound)
If thermal imaging or scanning is used for assessing a fire involving an acetylene cylinder, the source of heat inside the cylinder may be protected by the insulation effects of the internal mass of the cylinder.
The cooling procedure detailed in control measure Cool pressurised gas containers: Acetylene should be followed when the acetylene cylinder has been sufficiently heated for decomposition to be initiated (i.e. above 350C – this is normally only achieved by direct flame contact).