(a) Smoking, open flames or devices that might ignite an explosive mixture shall not be permitted in the immediate vicinity of the holder.

(b) During the progress of minor construction or maintenance work on holders, all customary safety rules prevailing in the plant, as well as those hereinbefore described, shall be rigidly adhered to. On work of the foregoing nature, experienced men shall be employed under direct and competent supervision, and all crews shall consist of at least two men.

(c) All procedures recommended by the American Gas Association for the purging, operation and maintenance of gasworks equipment and apparatus, including mains, are to be followed.