CLASSES AND SUITABILITY OF PORTABLE FIRE EXTINGUISHERS

 CLASSES AND SUITABILITY OF PORTABLE FIRE EXTINGUISHERS

These are also called as first aid fire extinguishers; these are expected to deal with initial small fires, the initial small fires if dealt properly, promptly and effectively would stop small fires from getting spread to other areas and prevent the small fire to transform into larger fires. They are very valuable in the early stages of fire. The fully charged portable fire extinguisher should not be more than 17 kg. 

There are two types of portable fire extinguishers based on how the extinguishing medium is discharged or expelled on to the fire 

1.      Stored pressure fire extinguishers: These are easily the most common type where the expellantgas and agent are stored in the same cylinder.  The different extinguishing media or agents used in the fire extinguisher may require different propellants.  Dry chemical extinguishers typically use nitrogen or dry air as a means of propelling the agent onto the fire.  Water and foam extinguishers typically use air.

2.     Cartridge-operated  fire extinguishers: In a cartridge-operated extinguisher, the cylinder has just powder/agent inside, for expellant/ gas and there is a separate pressure cartridge that has to be activated to pressurize the extinguisher and push the powder with force 

 

Hence a proper selection, installation, maintenance, testing and functional understanding of portable fire extinguishers are very much required to make sure that portable fire extinguishers are correctly and timely operated in times of emergency and suitable for the intended function.  

The effectiveness of the fire extinguishers plays a vital role in timely suppression of smaller fires, for which they should 

·       Easy to operate (Simple steps of operation) 

·       Immediately available and put into use (Instant operation)

·       Easy to carry or push (either portable or wheel)

·       Adequate distance covered by the contents (Adequate throw)

·       Sufficient quantity of fire extinguishing content as per rating 

·       Shelf life (Storage stability of the fire extinguishing contents)

·       Knowledge and operation of fire extinguishers

·       Having similar control devices for different types of fire extinguishers to have ease of operation

·       Training on usage directed for all employees regularly

 

 

CLASSES OF FIRE 

No fire extinguisher is effective on all types of fire, depending upon the source and nature of contents that are under fire a quick decision to be taken for selecting the right type of fire extinguisher for the right type of fire.  To understand the type of fire and the required fire extinguisher to be used, fires are grouped under four (4) types, these are: 

A.    Class A fires — Fires involving solid combustible materials of organic nature such as wood, paper, rubber, plastics, etc., where the cooling effect of water is essential for the extinction of fires.

 

B.    Class B fires — Fires involving flammable liquids or liquefiable solids or the like where a blanketing effect is essential. 

C.     Class C fires — Fires involving flammable gases under pressure including liquefied gases, where it is necessary to inhibit the burning gas at a fast rate with inert gas, powder or vaporizing liquid for extinguishment. 

D.    Class D fires — Fires involving combustible metals, such as magnesium, aluminium, zinc, sodium, potassium, etc., when the burring metals are reactive to water and watercontaining agents and in certain cases carbon dioxide, halogenated hydrocarbons and ordinary dry powders. These fires require special media and techniques to extinguish

Electric fires – Electric fires are not categorized as separate class, but where energized electrical equipment is involved in a fire, the electric equipment to be de-energized, then only the extinguishers suitable for the class of fire risk involved can be used safely only after confirming the non-conductivity of the extinguishing media

 

SUITABILITY OF PORTABLE/FIRST-AID FIRE EXTINGUISHERS

TYPE OF FIRE EXTINGUISHER	SUITABILITY FOR TYPES OF FIRES
	A	B	C	D
Water type fire extinguisher	YES	NO	NO	NO
Mechanical foam type	YES	YES	NO	NO
Dry powder  (BC/ABC  type)	YES	YES	YES	NO
Dry powder for metal fires	NO	NO	NO	YES
Carbon dioxide gas	NO	YES	YES	NO
Clean agent/Halon gas type	YES	YES	YES	NO

 

OTHER GENERAL SAFETY USAGEGUIDELINES CONCERNING FIRE EXTINGUISHERS:

·       The use of water, foam and powder fire extinguishers contaminates the area and sensitive electrical equipment, control instruments and electronic equipment can get damaged by the spread of extinguishing media on this sensitive equipment, to prevent such incidents from happening only carbon dioxide or clean agent type extinguishers should be used.

·       Mechanical foam extinguisher with alcohol-resistant foam should be used for fires involving polar solvents and other water-miscible flammable liquids. (When Alcohol resistant foam is used on a polar solvent fuel fire, the polar solvent fuel tries to absorb water from the foam blanket and break the foam blanket, but in alcohol-resistant foam, the polymer precipitates out forming the foam layer and a physical membrane/barrier between the fuel surface and foam blanket is formed which protect the foam blanket that is generated from destruction by the alcohol fuel)

·       Dry powder fire extinguishers when used to confined spaces, can reduce the visibility due to powder, escape and emergency action plans to be carefully carried out while using dry powder extinguishers. Dry powder, being a quick knockdown agent, is ideal for tackling ‘running’ or ‘three-dimensional’ fires involving flammable liquids.

·       Dry powder of different types (BC/ABC/ D) of powder should be avoided as it can cause a chemical reaction resulting in a dangerous pressure build-up in the container which can be observed within few weeks.

·       Whenever fire extinguishers are placed near places which are highly subject to corrosive atmospheres or coming in contact with corrosive fluids, special protection to the provided for those fire extinguishers from getting corroded or damaged.

·       Clean agent type fire extinguisher will have low toxicity in the free state, but when used on fires they are liable to produce toxic decomposition products. Hence, when used in extinguishing fires in confined unventilated rooms, closets, etc., the occupants should immediately vacate such spaces even before these extinguishers are used and also it is advisable to take the same precaution when carbon dioxide extinguishers are used under similar circumstances.

·       While replacing components or parts, it should be ensured that only the appropriate /standard components specified by the manufacturer or equivalents are to be used.

HSE Notes by PJ Mohan

Sr.Faculty, NIFS