"ipment in the factory used to convey steam, air, refrigerant or any hazardous substance, and each part and fitting of, and attachment to, every pipe, pump, compressor and other equipment is ???(a) of good construction, sound material and adequate strength;(b) free from patent defects; and(c) properly maintained.Gas plants35.???(1) Every gas plant shall be of sound construction and properly maintai" . . . . .