85. Door characteristics: These doors shall, in addition, possess the following characteristics:(a) have cables or chains having a safety factor of at least 5;
(b) have counterweights covered with guards and solidly attached and heavy enough to avoid any excessive effort in operating the doors;
(c) be equipped with devices allowing locking them in the open position during loading and unloading;
(d) be provided with pulleys of appropriate diameter to prevent excessive wearing of cables;
(e) be so constructed and hung that they cannot become disengaged from their carriers or hangers.