46 CFR §151.50-55

1. (a)Ventilation (cargo tank):
   1. (1)Cargo tank ventilation shall be provided to maintain the concentration of H2S below one-half of its lower explosive limit throughout the cargo tank vapor space for all conditions of carriage; i.e., below 1.85 percent by volume.
   2. (2)Where mechanical ventilation systems are used for maintaining low gas concentrations in cargo tanks, an alarm system shall be provided to give warning if the system fails.
   3. (3)Connections shall be provided to enable sampling of the atmosphere over the cargo in each cargo tank for analysis.
   4. (4)The ventilation system shall be designed and arranged to preclude the depositing of sulfur within the system.
2. (b)Void spaces:
   1. (1)Openings to void spaces adjacent to cargo tanks shall be designed and fitted to prevent the entry of water, sulfur or cargo vapors.
   2. (2)Connections shall be provided to enable sampling and analyzing vapors in void spaces.
3. (c)Temperature controls shall be provided in accordance with § 151.20-10 and applicable sections of Subpart 151.40 of this part. Heat transfer media shall be steam, and alternate media will require specific approval of the Commandant.