Halon 1301 is installed and used in fixed flooding  systems  for  extinguishing  flammable liquid fires. Halon 1211 is not used in total flooding systems. Its lower volatility, plus a high liquid density, permits the agent to be sprayed as a liquid and therefore propelled into the fire zone to a greater extent than is possible with other gaseous agents. Halon 1211 will replace Purple- K-Powder (PKP) in twin-agent systems installed on  mobile  fire-fighting  apparatus  on  aircraft carriers. • Steam. Steam smothers a fire by reducing the concentration of oxygen or the gaseous phase of the fuel in the air to the point that combustion stops. As long as the steam blanket is maintained, it will prevent reignition. Since steam is a vapor when applied, it provides little cooling. Additionally, steam condenses when its supply is shut off. Its volume decreases rapidly and combustible vapors and air rush in to replace it. A fire can reflash if it has not been completely extinguished and cooled. The temperature of steam itself is high enough to ignite many liquid fuels. Steam is hazardous to personnel because the heat it carries can inflict severe burns. • Dry Chemical Extinguishing Agent. PKP is a dry chemical principally used as a fire- extinguishing agent for flammable liquid fires. It is used in portable extinguishers and handheld hose-line systems aboard ship. Various additives are mixed with PKP base materials to improve their storage, flow, and water-repellency characteristics. The most com- monly used additives are silicones, which coat the particles of PKP to make them free flowing and resistant to the caking effect of moisture and vibration. When PKP is applied to fire, the dry chemical extinguishes the flame by breaking the combus- tion chain. PKP does not have cooling capability. When PKP is applied, an opaque cloud is formed in the combustion areas. This cloud limits the amount of heat that can be radiated back to the heart of the fire. Less fuel vapor is produced because of reduced radiant heat. PKP attacks the chain reaction required to sustain a fire. It is believed that PKP reduces the ability of the molecular fragments to recombine, thereby breaking the chain reaction. PKP is primarily used to extinguish flammable liquid fires but can also be used on electrical fires (class C). PKP is highly effective in extinguishing both flammable liquid pool fires and oil spray fires. Although PKP can be used on electrical fires, it will leave a residue that may be hard to clean. PKP can be used in the galley for fighting fires on such items as the cooking hood, ducts, and ranges. WARNING The ingredients presently used in PKP are nontoxic. However, the discharge of large quantities of PKP may cause temporary breathing difficulty during and immediately after discharge and may seriously interfere with visibility. The following is a list of limitations for PKP use. 1. 2. 3. 4. 5. 6. PKP is not effective on materials that con- tain oxygen. PK should not be used in installations where relays and delicate electrical contacts are present. PKP is not effective on combustible metals and may cause a violent reaction. Where moisture is present, PKP may com- bine with the moisture to corrode or stain surfaces on which it settles; when possible, PKP should be removed from all surfaces. PKP does not produce a lasting inert at- mosphere above the surface of a flammable liquid; consequently, its use will not result in permanent extinguishment if ignition sources such as hot metal surfaces or persistent electrical arcing are present. PKP  is  not  effective  on  fires  involving ordinary combustibles (class A). However, it can be used to knock down a flaming fire, keeping it under control, until hose lines are advanced to the scene. Aqueous Potassium Carbonate. Aqueous potassium carbonate (APC) is used aboard ships for extinguishing burning cooking oil and grease in deep fryers and galley ventilation exhaust ducts. An APC solution consists of 42.2 percent K₂CO₃ and 57.8 percent water. Alkaline solutions such as APC are often used in combating liquid grease fires  involving  unsaturated  animal  fat  and 7-13