Fire and Classification of Fire

 

Fire and Classification of Fire

Introduction

                This is The Fire Triangle. Actually, it's a tetrahedron, because there are four elements that must be present for a fire to exist. There must be oxygen to sustain combustion, heat to raise the material to its ignition temperature, fuel to support the combustion and a chemical reaction between the other three elements.

Remove any one of the four elements to extinguish the fire.

The concept of Fire Protection is based upon keeping these four elements separate.

Types of Fires

Not all fires are the same. Per NFPA 10 National Fire Protection Association, burning may be classified into one or more of the following fire classes and your fire protection specialist will select the right fire extinguisher size and agent for the hazard.

Classification of Fire:-

Class A

Class A fires are fires in ordinary combustibles such as wood, paper, cloth, rubber, and many plastics.

Class B

Class B fires are fires in flammable liquids such as gasoline, petroleum greases, tars, oils, oil-based paints, solvents, alcohols. Class B fires also include flammable gases such as propane and butane. Class B fires do not include fires involving cooking oils and grease.

Class C

Class C fires are fires involving energized electrical equipment such as computers, servers, motors, transformers, and appliances. Remove the power and the Class C fire becomes one of the other classes of fire.

 

 

Class D

Class D fires are fires in combustible metals such as magnesium, titanium, zirconium, sodium, lithium, and potassium.

Class K

Class K fires are fires in cooking oils and greases such as animal and vegetable fats.

            Some types of fire extinguishing agents can be used on more than one class of fire. Others have warnings where it would be dangerous for the operator to use on a particular fire extinguishing agent.

Types of Fire Extinguishers

Water and Foam

                Water and Foam fire extinguishers extinguish the fire by taking away the heat element of the fire triangle. Foam agents also separate the oxygen element from the other elements.

Water extinguishers are for Class A fires only - they should not be used on Class B or C fires. The discharge stream could spread the flammable liquid in a Class B fire or could create a shock hazard on a Class C fire.

Carbon Dioxide

                Carbon Dioxide fire extinguishers extinguish fire by taking away the oxygen element of the fire triangle and also be removing the heat with a very cold discharge.

            Carbon dioxide can be used on Class B & C fires. They are usually ineffective on Class A fires.

Dry Chemical

                Dry Chemical fire extinguishers extinguish the fire primarily by interrupting the chemical reaction of the fire triangle.

            Today's most widely used type of fire extinguisher is the multipurpose dry chemical that is effective on Class A, B, and C fires. This agent also works by creating a barrier between the oxygen element and the fuel element on Class A fires.

            Ordinary dry chemical is for Class B & C fires only. It is important to use the correct extinguisher for the type of fuel! Using the incorrect agent can allow the fire to re-ignite after apparently being extinguished successfully.

Wet Chemical

                Wet Chemical is a new agent that extinguishes the fire by removing the heat of the fire triangle and prevents re-ignition by creating a barrier between the oxygen and fuel elements.

Wet chemical of Class K extinguishers were developed for modern, high efficiency deep fat fryers in commercial cooking operations. Some may also be used on Class A fires in commercial kitchens.

Clean Agent

                Halogenated or Clean Agent extinguishers include the halon agents as well as the newer and less ozone depleting halocarbon agents. They extinguish the fire by interrupting the chemical reaction and/or removing heat from the fire triangle.

            Clean agent extinguishers are effective on Class A, B and C fires. Smaller sized handheld extinguishers are not large enough to obtain a 1A rating and may carry only a Class B and C rating.

Dry Powder

                Dry Powder extinguishers are similar to dry chemical except that they extinguish the fire by separating the fuel from the oxygen element or by removing the heat element of the fire triangle.

However, dry powder extinguishers are for Class D or combustible metal fires, only. They are ineffective on all other classes of fires.

Water Mist

                Water Mist extinguishers are a recent development that extinguish the fire by taking away the heat element of the fire triangle. They are an alternative to the clean agent extinguishers where contamination is a concern.

            Water mist extinguishers are primarily for Class A fires, although they are safe for use on Class C fires as well.

Cartridge Operated Dry Chemical

                Cartridge Operated Dry Chemical fire extinguishers extinguish the fire primarily by interrupting the chemical reaction of the fire triangle.

            Like the stored pressure dry chemical extinguishers, the multipurpose dry chemical is effective on Class A, B, and C fires. This agent also works by creating a barrier between the oxygen element and the fuel element on Class A fires.

            Ordinary dry chemical is for Class B & C fires only. It is important to use the correct extinguisher for the type of fuel! Using the incorrect agent can allow the fire to re-ignite after apparently being extinguished successfully.

The Rules for Fighting Fires

Just remember the three A's

ACTIVATE the building alarm system or notify the fire department by calling 911. Or, have someone else do this for you.

ASSIST any persons in immediate danger, or those incapable on their own, to exit the building, without risk to yourself.

Only after these two are completed should you ATTEMPT to extinguish the fire.

Note: - Only fight a fire if:

·         The fire is small and contained

·         You are safe from toxic smoke

·         You have a means of escape

·         Your instincts tell you it's OK

 

Fire Extinguisher Use

It is important to know the locations and the types of extinguishers in your workplace prior to actually using one.

Fire extinguishers can be heavy, so it's a good idea to practice picking up and holding an extinguisher to get an idea of the weight and feel.

Take time to read the operating instructions and warnings found on the fire extinguisher label. Not all fire extinguishers look alike.

Practice releasing the discharge hose or horn and aiming it at the base of an imagined fire. Do not pull the pin or squeeze the lever. This will break the extinguisher seal and cause it to lose pressure.

When it is time to use the extinguisher on a fire, just remember PASS!

Pull the pin.

Aim the nozzle or hose at the base of the fire from the recommended safe distance.

Squeeze the operating lever to discharge the fire extinguishing agent.

Starting at the recommended distance, Sweep the nozzle or hose from side to side until the fire is out. Move forward or around the fire area as the fire diminishes. Watch the area in case of re-ignition.

 

Fire Extinguisher Inspection

                Like any mechanical device, fire extinguishers must be maintained on a regular basis to ensure their proper operation. You, the owner or occupant of the property where the fire extinguishers are located, are responsible for arranging your fire extinguishers' maintenance.

Fire extinguishers must be inspected or given a "quick check" every 30 days. For most extinguishers, this is a job that you can easily do by locating the extinguishers in your workplace and answering the three questions below.

Is the extinguisher in the correct location?

Is it visible and accessible?

Does the gauge or pressure indicator show the correct pressure?

Fire Extinguisher Maintenance

                In addition, fire extinguishers must be maintained annually in accordance with local, state, and national codes and regulations. This is a thorough examination of the fire extinguisher's mechanical parts, fire extinguishing agent, and the expellent gas. Your fire equipment professional is the ideal person to perform the annual maintenance because they have the appropriate servicing manuals, tools, recharge materials, parts, lubricants, and the necessary training and experience.

 

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