Some protection against gas cylinders overheating can be achieved by ensuring
that any gas cylinder locker or housing has a fire resistance of 30 minutes.
There are several accepted ways of achieving this fire resistance for cylinder
lockers or cylinder housings:

• they must be constructed of metal at least 0.9mm (0.03ins) thick, with
  continuously welded or brazed joints
• they must be made of fibre reinforced plastics (FRP) of minimum thickness
  5mm (0.2ins)
• they must be made of materials with a fire resistance of 30 minutes, in
  accordance with BS 476-20. [7.4]