A first fire extinguisher classification divides them on the basis of the weight of the extinguishing agent contained in the tank, a feature that also affects the minimum duration of operation of the extinguisher itself, normally measured with the valve fully open.
Thus we can distinguish portable extinguishers, with a mass up to 20 kg, designed to be carried and used by hand by one operator during a fire principle. Wheeled fire extinguishers, with a mass exceeding 20 kg, transported on wheels and necessarily used by two operators, especially in the case of fires already developed.
A further classification of the extinguishers is based on the extinguishing agent present inside the tank and, consequently, on the extinguishing capacity of the extinguishers themselves in relation to the classification of fire classes as sanctioned by the Committee for Standardization (CEN).
The water extinguisher was probably the first portable device designed to shut down the principles of fire, recently back in vogue from the ecological problems connected to the use of other chemical compounds. Firefighter Recruitment NSW places emphasis on knowledge of these aspects and must pass the firefighting aptitude test.
The tank of this type of fire extinguisher contains about 90% water, while the rest of the volume is made up of film and additives that act both for cooling and for extinguishing.
It has a permanent pressurization system and the extinguishing agent is dispensed by advanced mechanism in order to produce greater heat exchange and greater heat absorption. In Italy it is forbidden to use it on electrical equipment, which is why it is mandatory to apply the relevant danger symbol on the prescribed label.
Powder fire extinguisher
In this type of fire extinguisher, the tank contains a fire-extinguishing powder composed of various mixed chemicals, subdivided into two main categories: ABC powder, generally made of ammonium sulfate and phosphate, able to extinguish multiple types of fire (wood, paper, coal, flammable liquids and gases). BC powder, mainly consisting of sodium bicarbonate and specific for fires of flammable liquids and gases.
The chemical powders extinguish the fire by acting as an inhibitor of the material that is not yet combusted, suffocating the flame and immediately breaking down the combustion temperature through an endogenous action.
It contains halogenated hydrocarbons, commonly called Halons, which act in the combustion reaction by subtracting oxygen, with consequent extinguishing of the fire as an extinguishing agent.
Following the adoption of international protocols aimed at banning the use of stratospheric ozone-depleting substances harmful to the environment, the halons have been replaced by hydrochlorofluorocarbons (HCFC) and hydrofluorocarbons (HFCs), which have an index of impoverishment of the ozone layer close to “0”.