46 CFR 148.285: Metal sulfide concentrates.

(a) When information given by the shipper under § 148.60 of this part indicates that the metal sulfide concentrate may generate toxic or flammable gases, the appropriate gas detection equipment from §§ 148.415 and 148.420 of this part must be on board the vessel.

(b) No cargo hold containing a metal sulfide concentrate may be ventilated.

(c) No person may enter a hold containing a metal sulfide concentrate unless—

(1) The atmosphere in the cargo hold has been tested and contains sufficient oxygen to support life and, where the shipper indicates that toxic gas(es) may be generated, the atmosphere in the cargo hold has been tested for the toxic gas(es) and the concentration of the gas(es) is found to be less than the TLV; or

(2) An emergency situation exists and the person entering the cargo hold is wearing the appropriate self-contained breathing apparatus.