PREVENTING THE SPREAD OF FIRE

Preventing the spread of a fire is a vital part of shipboard fire fighting. It is a job that must be undertaken simultaneously with the job of fire extinguishment. A fire that is properly contained so that it cannot spread is well on the way to being controlled.

Various techniques may be used to keep a fire from spreading. Sometimes it is possible to set up a fire barrier of fireproof materials. In many situations you will have to establish fire barriers by keeping combustible materials in the area cooled with water. When particularly dangerous combustible materials such as gasoline or explosives are located nearby, you should remove them from the fire area. The bulkheads, decks, and overheads adjacent to a fire should be cooled with water to prevent the spread of fire by conduction or radiation. This cooling will also help to keep the structures from being weakened and distorted by the heat of the fire. Sometimes it may be necessary to fill adjacent compartments with CO2 to keep the fire from spreading to combustibles in those compartments.

One of the most important phases of preventing the spread of fire has to do with the correct operation and maintenance of the ship's ventilation systems. The question of whether or not to secure the ventilation system during firefighting operations depends upon the particular circumstances existing at the time. It is important to remember, however, that any ventilation system can provide a means by which a fire can rapidly spread from one compartment to another, or from one area of the ship to another.

The danger of a fire spreading through the ventilation system is particularly great if there is dirt or dust in the duct work, on the screens, or in any other part of the ventilation system. Therefore, it is very important to make sure that the ventilation systems are inspected regularly and cleaned as often as necessary. A regular ventilation system cleaning schedule should be established and followed aboard ship. Vent ducts, heaters, screens, grease filters, flame arrestors, laundry filters, and all other parts of the ventilation systems must be kept clean. Vacuum cleaners, brushes, and low-pressure compressed air may be used to loosen and remove dirt from ducts, vents, heaters, and screens. Flame arrestors, grease filters, and laundry filters may

be washed with a dishwashing compound and then rinsed with warm water.

OVERHAULING THE FIRE

After a fire has been extinguished, it must be overhauled. This is done to make sure that it will not start burning again (reflash). The general procedures for overhauling a fire include breaking up the combustible materials with a fire axe or a fire rake and cooling the fire area with water or fog. Since many fires can flare up again after they appear to be out, it is necessary to set a reflash watch after a fire has been extinguished.

DESMOKING

After a fire has been definitely extinguished and overhauled, it is usually necessary to desmoke the compartments involved. This is done by natural or forced ventilation. However, before any ventilation is undertaken, you must observe the following precautions:

1. Be SURE that the fire has actually been extinguished, and that the atmosphere tests for oxygen and explosive gases are completed and acceptable results obtained.

2. Investigate the ventilation systems to the affected areas to be sure they are free of burning or smoldering materials.

3. Have fire parties and equipment standing by the blower and controller of the ventilation systems.

4. Obtain permission from the engineer officer to open ventilation system closures and to start the blowers required to desmoke the compartments involved.

You need to decide whether to use exhaust systems or supply systems for desmoking. If supply systems are used to ventilate interior spaces, smoke and fumes are usually forced into adjacent spaces. Spaces directly open to the weather can be cleared by supply systems without any particular problem.

Portable electric or pneumatic (air) ventilating blowers can be used for desmoking, although they are not as efficient or convenient as installed ventilating systems. However, when explosive vapors or fumes are present, it may be dangerous to use installed ventilation systems. Under these circumstances, portable ventilating blowers are usually used. The following portable ventilating blowers are available for use in the Navy.

. The Red Devil blower is an axial-flow type blower and is fitted with a noncollapsible hose that is 8 inches in diameter. The rated capacity of this blower is 500 cubic feet per minute with about 200 feet of 8-inch hose attached. This blower is driven by an explosion-proof electric motor; that is, the motor is explosion proof when it leaves the factory. It may or may not be explosion proof after is has been overhauled or mishandled during previous usage. Therefore, if these motors have been overhauled, mishandled, or suspected of not being explosion proof, they should NOT be used where the presence of explosive vapors is suspected. . The A3/4T air-turbine driven centrifugal

type of blower is fitted with an 8-inch noncollapsible hose. This blower, which was developed to handle air that contains explosive vapors, is driven by compressed air supplied at a pressure not to exceed 80 psi. This blower has a rated capacity of 750 cubic feet per minute with about 100 feet of 8-inch hose attached.