Piping
Piping conveying gas or flammable liquid
should be, as far as practicable, of rigid metal.
Any necessary flexible piping should consist
of material suitable for the gas or liquid being
conveyed; it should be adequately reinforced to
resist crushing and withstand the maximum
internal pressure to which it may be subjected.
Any connections to the flexible piping should
be of an approved pattern (i.e. screwed or
otherwise secured with a patent design device
to prevent accidental disconnection). If in
doubt you should seek advice from a competent person.