Classes of Fire and fire Extinguishers

7/30/2019 Classes of Fire and fire Extinguishers

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Presented By:Adebayo Johnson

17th December 2012


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Criteria cover installations for Class A, B, C,D, and K hazards

The selection, inspection, maintenance,recharging, and testing of portable fireextinguishing equipment.

Includes a list of obsolete fire extinguishersthat should be removed from service
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Portable fire extinguishers are classified to indicate

their ability to handle specific classes and sizes offires.

Labels on extinguishers indicate the class andrelative size of fire that they can be expected to

handle. Colour coding also indicate content and type of

extinguisher


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In order to choose the right type fire extinguisher,

you must know what type of fire you areattempting to control.

CAUTION

If you are not sure, your best course of action is toleave the area and activate the fire alarm.


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The National Fire Protection Association

(NFPA) has divided fires into four types,determined by the materials or fuel beingburned.

There is also a newest class.making them

five There are three major types.based on

occurrence Extinguishers are labeled as to which of the

four types of fire they are effective incontrolling.


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A Class A fire is the most common type of fire. This fire is fueled by common materials such aswood, paper, rubber, plastics or cloth. This type of fire leaves an ash behind after burning andhas an ember flame. To extinguish this type of fire, the temperature has to be brought downusing water or a general-use fire extinguisher.

A Class B fire is fueled by flammable and combustible liquids. A flammable liquid must beburning at room temperature in order to be a Class B fire, and a combustible liquid must beheated to its flammable point to be classified as Class B. Some flammable and combustibleliquids included in this classification are petroleum, tars, oil-based paints, oil, alcohols,lacquers, solvents and flammable gases. Water may not always extinguish these types of fires,and it is best to use a layer of foam from a Class B fire extinguisher.

A Class C fire is a fire that can be classified as an A or B fire, but that involves electricalequipment as well. These types of fires cannot be extinguished with water or Class A/B fireextinguishers. Carbon dioxide or a dry chemical agent fire extinguisher must be used on thistype of fire.

A Class D fire is characterized by combustible metals. These metals can include potassium,magnesium, titanium, Zirconium or lithium. Automobiles contain most of these types ofcombustible metals. A Class D fire burns at an exceptionally high temperature, and when water

is used on these types of fires it can actually break down into hydrogen and oxygen and fuelthe fire further. Special powders such as sodium chloride, dry sand or salt can extinguish thistype of fire.

Class K is the newest NFPA classification of fire. This classification includes appliances involvedin cooking that ignite using a combustible medium such as cooking oil, other fats andalcohols.


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There are two main types of fire extinguishers: stored pressure andcartridge-operated.

Have the expellant stored in the same chamber as the firefightingagent itself. Depending on the agent used, different propellants areused. With dry chemical extinguishers, nitrogen is typically used; waterand foam extinguishers typically use air.Stored pressure fire extinguishers are the most common type.

These extinguishers contain the expellant gas in a separate cartridgethat is punctured prior to discharge, exposing the propellant to theextinguishing agent.Not common; they are used primarily in areas such as industrialfacilities, where they receive higher-than-average use.

They have the advantage of simple and prompt recharge, allowing anoperator to discharge the extinguisher, recharge it, and return to thefire in a reasonable amount of time.Use compressed carbon dioxide instead of nitrogen, although nitrogencartridges are used on low temperature.


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water fire extinguishers discharge a stream of water onto the fire, lowering the temperature ofthe burning material to below ignition point.

They are good for Type A Fires only. You cannot use a water extinguisher for a Type B fire asflammable liquids are lighter than water and will float on the surface of the water. This willsimply aid in the spread of the fire. You cannot use a water extinguisher on a Type C fire,(electrical fire), because you run the risk of receiving an electrical shock. Water is an electricalconductor. As the water spreads out, the chance of electrocution increases.

There are special water mist extinguishers that work well on a Type A & C fires. Suchextinguishers are ideal for Class A fires where a potential Class C hazard exists. The mistingnozzle provides safety from electric shock and reduces the scattering of burning materials.

A CO2 extinguisher is not a good choice for a Type A fire, (wood, paper, cloth), because of theforce of the CO2 gas being expelled from the extinguisher. When this type of extinguisher isused on a wood, paper or cloth fire, the burning items are blown around the room by the forceof the CO2 gas, thereby aiding the spread of the fire. Secondly, a Type A fire will usually re-

ignite as soon as the CO2 gas dissipates.The CO2 extinguisher works well on flammable liquids or an electrical fire Types B or C fires.So, you will often find a CO2 fire extinguisher next to precious electrical equipment, fromswitchgear to mobile discos.

In most office, workplace, factory or warehouse situations, the best combination is to have awater additive or foam unit alongside your CO2 extinguisher, for maximum fire fighting ability.


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The multipurpose dry chemical extinguisher for Type A, B, or C fires is most common.

They have the most range of compatibility with items and are good for most types of fires.

A Type BC fire extinguishers contain sodium or potassium bicarbonate and a Type ABC fire

extinguishers contain ammonium phosphate. They have an advantage over CO2 extinguishers

in that they leave a blanket of non-flammable material on the extinguished material whichreduces the likelihood of re-ignition. However, they make quite a mess and the fine powder

will irritate the throat and lungs.

The contents of these cylinders can pack down over time and when a person goes to use them

they may not fire (work). If this happens, turn the cylinder over and rap it sharply on the top to

loosen the compacted powder inside. Then try firing the cylinder again. If the cylinder will not

fire leave the area immediately. All fire extinguishers have fire ratings stamped on them. You

should familiarise yourself with this rating. For example, a dry chemical cylinder may have 2A,

10 BC stamped on it; this means that the contents of the cylinder are enough to fight 2 square

meters of a Type A fire or 10 square meters of a Type B or C fire. Higher numbers mean more

firefighting power.

Flammable solids (alkyllithiums, Grignards and diethylzinc) require a Class D extinguisher..

Type D fires burn at high temperatures and the metals will react violently with water, air,and/or other chemicals. This type of fire requires special metal/sand extinguishers. They work

by simply smothering the fire with powdered copper metal or sodium chloride (NaCl). The type

of class D extinguisher depends upon the type of flammable metals you have; you will require

the copper extinguishing medium for lithium and lithium alloy metals; the sodium chloride

extinguisher works better for fires involving magnesium, sodium, potassium, uranium and

powdered aluminum.


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After removing the fire extinguisher from its mount, twist the pin in order to breakthe plastic seal and then pull the pin out of the handle.

Approach the fire with the extinguisher pointed at the base of the fire.

Squeeze the handle and continue to aim at the base of the fire. Sweep the extinguisher from side to side, still aiming at the base of the fire. After

the fire appears to be out or your extinguisher has been fully discharged, backaway from the fire and seek safety outside of the building.


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P - Pull the PinA - Aim at the base of the fireS - Squeeze the handle

S - Sweep from side to side

CAUTION: Extinguishers will work for

approximately 30 seconds. If you have not put thefire out by that time, leave the area immediately.


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www.uncg.edu/sft/ 2.html

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Classes of Fire and fire Extinguishers