fires on board several ships induced a review of both equipment and fire fighting tactics. A variety of technical approaches were considered that would make possible quick evacuation of a machinery space, followed by remote actuation of the fire extinguishing system. After a rigorous selection process and substantial testing in the early 1970s, halon 1301 was chosen as the optimum total flooding agent for ''abandon-the-machinery-space'' fires.

The first halon systems were installed in aircraft carriers and mine craft in 1978. A policy was established calling for installation of halon in new-construction ships, such as the FFG-7 class frigates, and selective retrofitting into older vessels began on an age-selective basis. The original twin-agent AFFF/PKP reels were retained in engine rooms for small-fire application, but with the PKP side deactivated. Engine rooms also were equipped with AFFF bilge flooding systems. And although the principal reason for acquiring halon 1301 systems was to fight machinery space fires, halon 1301's attraction as a very effective, non-toxic agent resulted in its being substituted for CO2 in other spaces where flammable liquids were stored.

This introduction of halon to the Navy followed its earlier acceptance for total space flooding applications in the civil community. Thus, because of a confluence of events—availability and civil acceptance of halon 1301, an urgent Navy need for a better agent, and top-level support—halon became the agent of choice for coping with fuel spray fires in confined spaces. Use of halon enabled the Navy to adopt a casualty-reducing tactic of (1) taking the man out of the loop initially by abandoning the fire scene, (2) remotely actuating the halon 1301 flooding system, and (3) reentering the space when the fire was extinguished to deal with any minor residual flare-ups.

Halon 1211 has only limited application aboard ship. It replaced PKP in fire trucks aboard aviation ships in the late 1980s for fighting three-dimensional fires. The agent is also used in mine craft (MSCs) and air cushion landing craft (LCAC), and there are a few hand-held bottles to be found in certain other ship classes.

Aircraft

Fires in aircraft have been a major concern since the inception of powered flight in the early 1900s. The very nature of aircraft—being airborne, carrying large amounts of flammable liquids, containing potential ignition sources—makes them inherently vulnerable to loss if fire should break out. Hence, fire prevention is a major consideration in aircraft design, as are fire extinguishing systems tailored for the specific plane and its anticipated operating environment. Since most fires start in inaccessible areas, particularly in military tactical aircraft, extinguishing them must depend on automatic or remote activation of extinguishing systems. And as mentioned above, combat aircraft have the additional challenge of coping with damage that may be inflicted by enemy antiaircraft artillery and missiles.

Early combat loss experience in World War II highlighted the vulnerability of tactical aircraft to loss by fire and explosion. Self-sealing fuel tanks were installed to reduce the probability of leakage if hit, with the resultant fumes causing explosions in void (dry bay) areas. Additionally, attention was paid to placement of fuel lines and shielding components. CO2 fire extinguishing systems were installed in the nacelles of multiengine aircraft, as they were in civil airliners of the time.

The introduction of jet aircraft into the Navy in the 1950s was accompanied by a change in strategic emphasis toward nuclear warfare. Attack aircraft were designed to fly long ranges, while designers tried to exact maximum speed and altitude performance from fighters. In the quest for performance, the vulnerability of planes to combat damage, including fire and explosion, was accorded low priority during aircraft design. Even in the case of rotor craft that fly slowly at low altitude, little attention was paid to measures that might reduce vulnerability to loss if the helicopter was struck by enemy projectiles or small missiles.

During the Vietnam War the United States suffered combat losses totaling 5000 aircraft—2500 fixed-wing jets and 2500 helicopters. As losses mounted during the course of the conflict, studies were initiated to see what might be done to lower loss rates, an effort that continued after the war. The analysis revealed that fuel fires and explosions accounted for 50% of the losses and that half of these



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