Twin Agent Unit

A mobile fire-extinguishing system that uses a combination of AFFF and dry powder has been developed and approved for shipboard use. The twin agent unit (TAU) is mounted on a movable tractor (figs. 5-38 and 5-39). The TAU is used primarily to rescue pilots. It is operated by one person and is extremely effective. Very large fires, including gasoline fires on aircraft carriers, have been put out in less than 1 minute with the TAU.

The TAU uses AFFF and PKP. When the PKP has interrupted the chemical reaction and slowed down combustion, the AFFF is applied. AFFF floats on the surface of the fuel and prevents reflash. Using AFFF to prevent a reflash is very important because PKP gives no reflash protect ion.

The TAU has a sphere containing 200 pounds of PKP and a cylinder containing 80 gallons of AFFF in solution. A nitrogen cylinder is also installed on the TAU. The nitrogen is used to pressurize both the PKP sphere and the AFFF cylinder. The nitrogen cylinder should be fully charged to 2,400 psi when the unit is first put into operation. The pressure regulator on the nitrogen cylinder is preset to reduce the pressure to 230 psi for the PKP sphere and for the AFFF cylinder. The two rubber discharge hoses have a working-pressure rating of 400 psi. They are 1 inch in diameter for AFFF and 3/4 inch in diameter for PKP. The two hoses are married together for easy handling. The twin pistol-grip

Figure 5-38.-Twin agent unit (view 1).

Figure 5-39.-Twin agent unit (view 2).

nozzles are joined together; one nozzle is operated with one hand and the other with the other hand. This allows selection of the agent desired and also makes for easy handling.

A separate valve is used to allow each agent to flow into its hose line. A 100-foot hose allows rapid running out to the fire areas. A relief valve is not provided for the sphere. The sphere must be bled through the hose. Relief valves are provided for the AFFF tank and the pressure regulator.

The TAU requires some preventive maintenance. Drain the PKP hose after each use to prevent clogging of the unit. Check the nitrogen cylinder to verify that it has the proper pressure; each nitrogen cylinder supplied for the TAU has a gauge attached. Have the cylinders recharged whenever their pressure drops to 1,500 psi. Note that the TAU does NOT require lubrication.

Observe the following safety precautions when using the TAU:

Use only nitrogen to pressurize the TAU. NEVER use oxygen or any other compressed gas.

When preparing to use the TAU, make sure that all of the fill caps are airtight and that they are not cross threaded. Also, be sure that all hose connections are tight.

When preparing to refill the unit or to secure it, be sure that the PKP sphere and the AFFF cylinder are depressurized before removing the fill caps. Do NOT stand over the fill caps when you remove them. Do NOT stand in front of the pressure relief valve when you release pressure.