15. Every part of the gas system must—
(a)so far as is practicable, be so located and protected as not to be exposed to accidental damage;
(b)be soundly and properly constructed of materials which are compatible with one another and with the gas used or likely to be used and which are capable of withstanding the loads or stresses likely to be met in operation; and
(c)be so designed and constructed that the number of joints is kept to a minimum, and that leakage of gas is unlikely to occur.