How is a fire extinguisher chosen?
The fire extinguisher is chosen according to the type of extinguishing agent and its field of application.
The suitability of the extinguishing agent on a given type of fire depends greatly on the origins of the fire principle and the material that is causing the fire.
The European standard EN 2 helps us understand which extinguisher is best to use according to the fire classification that determines the type of fire extinguishers. See in-depth study dedicated to the page "The Fire Classes".
It consists of mixtures of chemicals combined together with sodium or potassium bicarbonate, monoammonium phosphate (MAP) and various additives for maintaining fluidity.
Powders can be divided into two main categories:
Multi-purpose: suitable for fire class A, B and C ratings
Bivalents: powders based on sodium or potassium bicarbonate specifically for extinguishing fire classes B and C or specific classes (fire class D)
The effects of powder extinguishing agent in extinguishing are as follows:
The reference standard for powder extinguishing agents that can be used in fire extinguishers is EN 615.
Suitable for classes A, B and C, it is the only one that covers three categories and is often the most economical means. The average powder extinguisher has an operating range of -30°C to +60°C.
Usually the extinguishing powder comes out of the device with high pressure, this makes it more difficult to extinguish the fire. Shortly after use, a dense cloud forms, obstructing the view and making it more difficult to reach the escape route. Because it cannot be used specifically during extinguishment, the dust spreads over a very large area and leaves behind a lot of dirt, which moreover results in very high cleaning costs.
Most common and widespread extinguishing substance, it can be used on electrical equipment if the dielectric test is passed as per EN 3/7.
The effects of water in extinguishing are as follows:
It is a clean and environmentally friendly extinguishing agent. It is used in environments where the fire risk is low such as offices or environments with similar use (schools, kindergartens, etc...). Purchase costs are low and disposal costs are lowered.
Only suitable for fire class A. Operating range of +5°C to +60°C.
A mixture of water and foaming additives of various kinds, it is particularly suitable for class A and B fireplaces.
The effects of foam in quenching are as follows:
Suitable for fire classes A and B. It is suitable in a multitude of environments: warehouses with large quantities of paper, cardboard and plastic materials, environments such as offices and for private use.
At the time of use it can be applied very specifically to the ignited object thus limiting contamination of the surrounding environment, also lowering cleaning costs.
These specific foams cannot be used in fires derived from animal oils and fats. The average foam extinguisher operates at temperatures between +5°C and +60°C, some models are approved with a frost-resistant foam for use in temperatures down to -30°C.
Mixture of water and foaming additives of various kinds. They are specifically for hearths that originate from animal or vegetable oils and fats, so they are used on cooking appliances in kitchens. Suitable on classes A, B and F.
The effects of foam in quenching are as follows:
Fire extinguishers with this type of extinguishing agent must also be mandatorily tested for use on energized electrical equipment.
The fire extinguisher for oils and fats of animal or vegetable origin is the only device that possesses fire classes A, B and F, thus embracing the greatest range of use than any other model (warehouses, offices, stores, private, kitchens etc..). The extinguishing medium can be used in a very controlled manner, thus avoiding any major contamination and lowering the cost of restoring environments. Can also be used on live electrical equipment.
The average operating range is from +5°C to +60°C.
Carbon dioxide is an inert and dielectric gas, in the quenching phase its effects are as follows:
The useful distance of the jet is about 2 to 3 meters and disperses into the surrounding air.
Suitable for fire class B the CO2 fire extinguisher works by displacing oxygen and thus smothers flames. CO2 has the advantage of evaporating in a short time without leaving a residue, so it is mainly used in areas with sensitive equipment. On average it has an operating range of -30°C to +60°C.
In too small and unventilated rooms, displacement of oxygen can be dangerous to the life of the operator operating the extinguisher, therefore, it is always essential to calculate the volume of the room in advance and accordingly choose the right size extinguisher (2kg or 5kg CO2). Carbon dioxide escapes from the hose at temperatures as low as -78°C, so it should not be directed toward people or animals.
Clean Agents are new generation eco-friendly chemical gases. These gases have rapid fire extinguishing capacity and are environmentally friendly. During their delivery, the gas mixes homogeneously with the air in the room to be protected in order to achieve the ideal concentration to suppress flames. They are in liquid form with a high molecular weight and are therefore able to be stored in a smaller volume. The most common and widespread Clean Agents are: FK 5-1-12; Novec and chemical gas mixtures.
In the quenching phase, its effects are as follows:
Suitable for fire classes A and B. They are classified as “clean agents”; have ozone depletion potential (ODP) of zero; global warming potential (GWP) of one; atmospheric lifetime (ALT) of five days.
The margin of safety with respect to oxygen displacement for the operator who goes to use the extinguisher is greatly increased compared to CO2. It can also be used on live electrical equipment. It is used to protect valuable products and machinery as it leaves no residue after discharge and does not create thermal shock. Average temperature of use between -30°C and
+60°C.
In rooms that are too small and unventilated, oxygen displacement can be life-threatening for the operator operating the extinguisher, therefore, it is always critical to calculate the volume of the room in advance before going to use the extinguishing equipment.
| Extinguishing type | |||||
FIRE CLASSES | Powder | CO2 | Water | Foam | Clean Agent | |
Solid Materials | A | YES | NO | YES | YES | YES |
Liquid Materials | B | YES | YES | NO | YES | YES |
Gas | C | YES | YES | YES(1) | NO | NO |
Metals(2) | D | YES | NO | NO | NO | NO |
Oils of Plant or Animal Origin | F | NO | NO | NO | YES | NO |
For fires arising from electrical material, the suitability of the device according to dielectric test provided by EN 3/7 standard shall be verified
Notes: The indications in the Table are general: make sure that the fire classes for which the extinguisher is intended appear on the fire apparatus.
Extinguishing agents are several, each one extinguishes fire in a different way and it is more or less effective according to the kind of fuel that caused the fire that has to be extinguished.
CARBON DIOXIDE
Carbon dioxide is suitable for class B and C fires, does not damage electrical appliances and it is effective in enclosed spaces. It cools down and suffocates the fuel. While carbon dioxide is inside the fire extinguisher, it is at the liquid state, and it becomes “dry ice” as soon as it is expelled. It sublimates quickly, so it leaves no trace. It should not be used on class A or D fires (so, in general, on fire generated by solid fuel) and, obviously, not on appliances that could be damaged by thermal shocks (carbon dioxide reaches -75°C inside fire extinguishers). If possible, do not direct it on human beings, as the extremely low temperature could cause frostbites and it could lead to death by suffocation, as it removes oxygen.
FOAM
Foam suffocates and cools down fuels. There are different types of foam used as extinguishing agents.The most common is AFFF (aqueous film forming foam), that is a water solution of foaming agents. It is particularly effective on class A and B fires, thanks to the film it creates that isolates fuel from oxygen and, at the same time, lowers the temperature. It should be mentioned that AFFF is mainly made of water, so, unless the fire extinguisher has passed the dielectric test, it should not be used on electrical appliances. It is not advisable to use it on class C and D fires.
DRY CHEMICAL AND DRY POWDER
Basically, when dry chemical or dry powder come into contact with heat, they release inert gases which create incombustible residues. The composition of dry chemical may extensively vary, every mixture is more or less effective on different fire classes. The most common mixture, and the one with the broader spectrum, is the multi-purpose dry chemical, whose main component is monoammonium phosphate. It is also called ABC dry chemical, because it is possible to extinguish any class of fire with it, with the exception of class D fires. Standard ABC dry chemical contains 40% monoammonium phosphate, while dry chemical used for an enhanced fire suppression may contain up to 90% monoammonium phosphate.
