Abstract : While the Halon 1301 fire suppression systems installed in machinery spaces are very effective, environmental regulations have essentially prohibited the use of these systems for future ships. A high-pressure water mist system was developed as an environmentally friendly alternative for conventional Halon 1301 systems. Outlined in NSTM Chapter 555, Section 10 are procedures for dealing with an out-of-control class B fire in a machinery space protected with Halon 1301. Some of these procedures are unnecessary when water mist is used, since water mist can discharge for an extended period of time and offer continuous protection, the need to wait 15 minutes before entering the space is eliminated, and the affected space ventilation can be used during attack team entry. Also, due to the high thermal capacity of water, the potential exposure to hazardous post- fire conditions and the likelihood of fire spread are significantly reduced.