46 CFR §108.451

1. (a)Except as provided in paragraph (b) of this section, each cylinder of a CO2 system must be outside each space protected by the system and in a location that would be accessible if a fire occurred in any space protected by the system.
2. (b)A CO2 system that has a CO2 supply of 136 kilograms (300 pounds) or less may have one or more cylinders in the space protected by the system if the space has a heat detection system to activate the system automatically in addition to the remote and manual controls required by this subpart.
3. (c)Each space that contains cylinders of a CO2 system must be ventilated and designed to prevent an ambient temperature of more than 54 °C. (130 °F.)
4. (d)Each cylinder in a CO2 system must be securely fastened, supported, protected from damage, in an accessible location, and capable of removal from that location.
5. (e)Each unit must have a means for weighing cylinders of a CO2 system.
6. (f)A cylinder in a CO2 system may not be mounted in a position that is inclined more than 30° from a vertical position, except that a cylinder having flexible or bent siphon tubes may be mounted in a position that is inclined up to 80° from the vertical. The bottom of each cylinder when mounted must be at least 5 centimeters (2 inches) from the deck.
7. (g)If a cylinder does not have a check valve on its independent cylinder discharge, it must have a plug or cap to close the outlet when the cylinder is moved.