Fire Extinguishers - Theory and Types

Introduction

A fire extinguisher is a hand held or cart mounted pressurized container. Cylindrical in shape, it utilizes an agent to put out or control small fires. A fire extinguisher is considered to be an active fire protection device. As opposed to a smoke detector (fire prevention device), which is stationary and used to alert.

To be effective, the following criteria must be met:

•The extinguisher must be used with the correct class of fire
•It must be in good working order and inspected annually
•It must be easily accessible
•The user must be trained to use it correctly.

The following article will discuss:

• Types of fire
• Extinguisher theory
• Types of fire extinguishers.

Types of Fire

All fire extinguishers have a label on the canister. This conveys to the user the type of fire with which that particular extinguisher must be used. It is very important to recognize what type of fire you are dealing with in order to determine which extinguisher is appropriate. Using the wrong extinguisher for the application can result in acceleration of the fire and serious injury. Table 1 below explains the different types of fires and classes of fire extinguishers.

Table 1

Some extinguishers are only suitable for one class of fire others can fight two or even three classes. Unfortunately, no extinguisher will fight all classes of fire.

Fire Extinguisher Theory

All types of extinguishers employ one common principle, which is to remove one of the elements of the fire tetrahedron (see figure A below) in order to stop the progress of the fire.

Figure A

Types of Fire Extinguishers

There are two main categories of fire extinguishers:

•Stored pressure
•Cartridge operated

Stored pressure fire extinguishers

These extinguishers are the most common type. They contain the expellant and the agent within the same chamber. This type of fire extinguisher is immediately ready-to-use because it has already been pressurized and therefore there is no need to do so before use.

Cartridge operated fire extinguishers

This type of extinguisher differs from the stored pressure type, in that the expellant is stored in a separate cartridge this is attached to the side of the large vessel, containing the agent. Some important features are the cartridge cover, hose, carrying handle, fill cap, and label.

This type is not as common and is largely used in industrial applications. The expellant gas, typically carbon dioxide, is protected by a cartridge cover and must be punctured prior to use.

The main benefit of the cartridge type extinguisher is that it can be recharged; which allows the operator to return to the fire in a relatively short time.

Within these two categories of extinguishers, there are also different types of extinguishers, including:

•Water
•Foam
•Carbon Dioxide
•Dry Chemical
•Wet Chemical
•Clean Agent
•Dry Powder
•Water Mist

Table 2

Table 2- explains the class of fire with which each extinguisher can be used and the method with which the fire is extinguished (refer to figure A).