were attributable to fuel explosions in voids or so-called dry bays. As a result, the military services joined in an effort to improve the survivability of jet aircraft and helicopters. This led to development and experimentation with a variety of approaches that addressed fire extinguishing in several areas, including engine nacelles/bays, dry bays, fuel tanks, occupied spaces, and ground and ship flight decks. Technologies considered were (1) solid foams, powders, and inert gas generators for dry bays; (2) solid foams and inert gases for fuel tank ullage areas; (3) halon 1301 for engine nacelles and bays; (4) portable halon bottles, principally 1301, for occupied areas; and (5) AFFF and halon 1211 for crash fire fighting and small fires incident to engine start.
The adoption of halons 1301 and 1211 was the culmination of fleeting military involvement with halons over the years. In the 1920s non-fluorinated halon agents were tried experimentally in engine nacelle extinguishers, but their use was abandoned by the U.S. military in favor of the non-corrosive CO2. Despite their relatively high inhalation toxicity, systems using halon 104, 1001, and 1011 were developed during World War II and employed by the British and Germans in military aircraft. The use of these agents expanded into the civil sector after the war. In the United States, however, it was only after development of fluorinated halons (1301, 1211) that CO2 was replaced in Air Force and Navy aircraft by these new highly effective, less toxic, and non-corrosive agents. And since they had already gained some acceptance in U.S. civil aviation as well as in various civil ground applications, the military quickly adopted them to meet the variety of needs cited above.
Fire at sea has always posed a special danger. In warships, the fire hazard is exacerbated by the threat of explosive weapon warheads and propellants. Throughout its history the Navy has dealt with fire protection challenges by exacting the most from existing fire fighting systems through organization and training as well as by exploiting new technologies. The exploitation of dry chemical powders and aqueous film-forming foam as well as the introduction of specialized naval fire fighting systems are examples of the constant improvement sought by the Navy in the safety and survivability of its vessels, aircraft, and crews. Employing halons for machinery space and aviation fire extinguishing applications is an example of adopting new technology to improve fire protection.
The principal fire threats in machinery spaces are the combustible liquid pool and pressurized spray fire. The most hazardous type of incident, and one that absolutely requires a gas-phase fire suppressant, is the three-dimensional spray or cascading fire. These fires arise from fuel or lubricant pipe or fitting leaks, human error, or mechanical damage. Leaks can vary in scale from less than 1 to greater than 50 gallons per minute. Pressurized spray fires generally occur in fuel, lubricating oil, or hydraulic fluid system piping. Pressures range from 10 to 1000 psi. Non-pressurized cascading fuel fires often involve sounding tubes, gravity storage tanks, and fuel piping that transit the space servicing other areas such as aviation fuel systems. In general, a spray or cascading fuel fire will also produce a pool fire.
A release of fuel or lubricating oil can be quickly ignited by hot surfaces (steam pipes or boiler fronts), electrical arcing or shorts, welding operations, and mechanical sources (friction, sparking, and so on, related to equipment failure). The intensity of these fires can easily approach 50-MW power equivalent. The fire growth time scale is on the order of several seconds, so that very large fires, high temperatures, and fatal concentrations of carbon monoxide (CO) can occur in 30 seconds or less. Since there is insufficient oxygen to maintain a large fire, the power level will decrease with time, and higher CO production will occur.
The size and growth rate of these three-dimensional fires preclude safe reliance on manual firefighting in closed spaces. Clearly, manual fire fighting against a large machinery space fire is not the approach of choice because of the rapidity with which the space becomes untenable due to heat, smoke,