Description Of A Class A StoredPressure Fire

Extinguisher Essay, Research Paper

Introduction ? General Description

A fire extinguisher is a portable or movable apparatus used to put out a small fire by directing onto it a substance that cools the burning material, deprives the flame of oxygen, or interferes with the chemical reactions occurring in the flame. Water performs two of these functions: its conversion to steam absorbs heat, and the steam displaces the air from the vicinity of the flame. Many simple fire extinguishers, therefore, are small tanks equipped with hand pumps or sources of compressed gas to propel water through a nozzle. The water may contain a wetting agent to make it more effective against fires in upholstery, an additive to produce a stable foam that acts as a barrier against oxygen, or an antifreeze. Carbon dioxide is a common propellant that is used in store-pressure extinguishers, brought into play by removing the locking pin of the cylinder valve containing the liquefied gas; this method has superseded the process, used in the soda-acid fire extinguisher, of generating carbon dioxide by mixing sulfuric acid with a solution of sodium bicarbonate.

Numerous agents besides water are used; the selection of the most appropriate one depends primarily on the nature of the materials that are burning. Secondary considerations include cost, stability, toxicity, ease of cleanup, and the presence of electrical hazard.

Small fires are classified according to the nature of the burning material. Class A fires involve wood, paper, and the like; Class B fires involve flammable liquids, such as cooking fats and paint thinners; Class C fires are those in electrical equipment; Class D fires involve highly reactive metals, such as sodium and magnesium. Water is suitable for putting out fires of only one of these classes (A), though these are the most common. Fires of classes A, B, and C can be controlled by carbon dioxide, halogenated hydrocarbons such as halons, or dry chemicals such as sodium bicarbonate or ammonium dihydrogen phosphate. Class D fires ordinarily are combated with dry chemicals.

Four main parts make up the exterior of the fire extinguisher: the ring, the operating lever, the outer can, and the nozzle.

Description of Parts and Their Function

Ring. This thin metal rod with a circular end is found between the operating lever and the handle. Pulling the ring will unlock the operating lever and allows you to discharge the extinguisher.

Operating Lever. The lever is located at the very top of the extinguisher. After the pin is pulled, squeezing the lever down to the handle will discharge the extinguishing agent. Releasing the lever will stop the discharge.

Outer Can. The outer can is the cylindrical ?body? of the extinguisher. Just inside the outer can, in a thin layer, is the gas cartridge. When the lever is squeezed, the open valve

releases the carbon dioxide from the gas cartridge to the space above the water. The pressure of the carbon dioxide forces down the inner can, which in turn causes water to drive up the siphon tube and out the nozzle. When the lever is released, the release valve is activated. This valve disconnects the siphon tube, allowing no water to travel to the nozzle.

Nozzle. The nozzle is a tube from which the water leaves the extinguisher. When squeezing the operating lever, the nozzle should be held firmly to ensure proper aim.

Conclusion and Operating Description

When faced with a fire, keep your back to an exit and stand six to eight feet away from the fire. Follow the four-step PASS procedure:

1. Pull the Pin. This will allow you to operate the extinguisher.

2. Aim Low. This is where the fuel is.

3. Squeeze the Lever. This releases the pressurized extinguishing agent

in the extinguisher.

4. Sweep from Side to Side until the fire is completely extinguished. Start

using the extinguisher from the safe distance away, then move forward.

Once the fire is out, keep an eye on the fire in case it re-ignites.

You should always test the extinguisher briefly, to ensure that it operates correctly, before taking it to the fire. If you are in a position where there is a high fire risk (e.g. working with flammable materials or heat), then you should arrange to attend a hands-on fire extinguisher training program.

Fire extinguishers may go unused for many years, but they must be maintained in a state of readiness. For this reason, periodic inspection and servicing are required, and that responsibility rests with the owner. Fire department inspectors check at periodic intervals to see that extinguishers are present where required by law and that they have been serviced within the specified time period.