391. Where a chain is used in a shaft to suspend a conveyance or a work platform, the chain shall:(1) be of alloyed heat-treated steel and bear the letter “A” on each link to so indicate;
(2) have a safety factor of at least 10 after taking into consideration its possible inclination;
(3) be checked at least once a month and be discarded if:(a) the chain or any part thereof has stretched by 3% or more of its length;
(b) a link is worn in one place through 10% or more of its diameter;
(c) a link is cracked, misshapen or damaged.