Residual capacity of a damaged water mist system

Navies have been facing budget reductions over the past decade. Since crew size is a major cost driver, this has led to efforts to reduce manning on board naval ships. Traditionally, damage control and firefighting were manpower intensive operations. To enable crewing level reductions without compromising the ability to deal with damage and firefighting requires both the introduction of new technologies and changes in how damage control and firefighting are carried out. Newly built warships are being fitted with more fixed firefighting systems, in particular water mist systems. The design of these systems is based on requirements and applications in civilian (commercial shipping) environments where the possibility of damage to piping infrastructure or pumps arising from battle damage was not taken into account. This paper describes the results of an experimental program that investigated the influence of fragment holes in water mist system piping on the system’s firefighting efficiency. A test chamber of 7.5 × 7.5 x 2.4 m³ was equipped with a four-nozzle high pressure water mist system. Systematically, the water flow to 1, 2 and 4 of the water mist nozzles was altered by damage to the water feed line piping. The systems performance against a 1.3 MW diesel pool fire was evaluated by evaluating compartment gas temperatures and time to extinguishment. Pressure drops in the system and water loss through the fragment holes were measured. The research has both provided insight into the physical phenomena behind water mist fire extinguishment and the residual fire suppression capacity of damaged water mist systems. The paper also highlights practical suggestions for design of water mist systems when considering battle damage. Over all, the capability of the water mist system evaluated showed good resilience against pressure drops and water loss through moderately sized fragment holes. This research was carried out as part of a collaborative research project involving the Canadian Department of National Defence and the Swedish and Netherlands’ Ministries of Defence.