The European community through the CEN (European Committee for Standardisation) has produced a standard that defines fire classes according to the nature of the fuel. The standard is one of the first standards drawn up by CEN, indicating the importance and necessity of defining what the dangers of fire may be. The standard has undergone changes and updates over the years as a result of the technological evolution of both fuels and the technologies used to fight fires with fire extinguishers. The EN 2 standard currently in force is the October 2004 edition where the previous edition (October 1992) has been updated with the addition of Annex A1. The EN 2 October 2004 edition entered the UNI national standard body on April 2005.
The standard defines 5 fire classes; it does not define a fire class for fires with a risk due to electrical fuels, furthermore, the fire classes are used to determine the extinguishing capability of fire extinguishers by means of specific tests carried out in accordance with EN 3. Fire extinguishers, with the exception of those with a powder and carbon dioxide extinguishing agent, will therefore have to undergo an additional test to verify their suitability on live electrical equipment. This suitability will be shown on the fire extinguisher's marking label without any pictorial pictograms.
The first fire class defined by the standard is Class A. This fire class represents the most common and most everyday fire hazard.
To this fire class belong all solid combustible materials, usually organic in nature, that produce embers when burnt.
The most common and widespread materials are wood, paper, textiles, coal, leather, rubber and similar flammable substances.
Combustion, in this case, may occur with moving open flames or without (i.e., producing glowing embers).
Several parameters influence combustion:
The extinguishing test defined according to EN 3 part 7 for this fire class is represented by a firebox with wood where the length of the firebox itself represents the fire class according to the diagram below:
| Fire type designation | Number of 50 cm wooden beams per layer | Fire length in cm |
|---|---|---|
| 5 A | 5 | 50 |
| 8 A | 8 | 80 |
| 13 A | 13 | 130 |
| 21 A | 21 | 210 |
| 27 A | 27 | 270 |
| 34 A | 34 | 340 |
| 43 A | 43 | 430 |
| 55 A | 55 | 550 |
The extinguishing agents that are most effective on this type of fire class are those that have their main extinguishing action through cooling by reducing the temperature of the fuel: water, water with additives for class A, foaming agents, polyvalent powder.
Fire class B represents fires originating from highly flammable liquids such as petrol, hydrocarbons, alcohols, solvents, fats and mineral oils.
In this case, the combustible material has a volume but no form of its own, so its expansion must be contained. Using a direct water jet to extinguish it may be counterproductive, as the impact of the jet on the liquid may only increase the length and width of the ignited area.
The extinguishing test defined according to EN 3 part 7 for this class of fire is represented by a fire with highly flammable liquid inside a circular metal vessel. The different size of the metal receptacle gives an indication of the standardised fire class according to the volume of liquid inside it as shown in the table below:
Fire type designation | Volume of combustible liquid in litres | Container dimensions, diameter in mm |
|---|---|---|
| 21 B | 21 | 910 |
| 34 B | 34 | 1200 |
| 55 B | 55 | 1500 |
| 70 B | 70 | 1700 |
| 89 B | 89 | 1900 |
| 113 B | 113 | 2120 |
| 144 B | 144 | 2400 |
| 183 B | 183 | 2710 |
| 233 B | 233 | 3000 |
The fire-extinguishing agents that are most effective on this type of fire class are those that have their main extinguishing action by suffocation; also by cooling, the action is sufficient to contain the fire principle: foam, chemical powder, CO2.
Fire class C represents fires that can develop in the presence of a leakage of butane, propane, methane, G.P.L., hydrogen, acetylene.
By nature, gas has no shape, volume or surface area, which is why flammable gases in air are very dangerous: they have a high probability of flame propagation and the risk of causing an explosion is high.
Therefore, when acting on this type of fire, it is necessary above all to attempt to block the escape of gas by obstructing its flow (by means of the valve or by closing any leak); given the complexity of the operation, it may be necessary to wait for the competent authorities or for employees with emergency management skills to come to the rescue.
In this case, there is no test according to current standards to determine the suitability of the fire extinguisher or other equipment for this specific fire class, but it is only possible to indicate class C for powder fire extinguishers that have passed at least the test required for fire class B.
If you are facing a class C fire, you can use water, either a fractioned jet or a nebulised jet, to cool the hoses or gas cylinders; as for fire extinguishers, you can use powder extinguishers (if they have the appropriate certification) and CO2 extinguishers.
In this case, the extinguishing action is based on the principle of separating the combustible material from the air.
The metals that can burn are mainly light alkaline metals such as aluminium, potassium, magnesium, sodium and manganese, but peroxides and chlorates also fall into this class.
These fires usually develop in a metalworking company, on construction sites, warehouses, construction areas or in places and premises with similar characteristics.
All fires developed from metals cannot be extinguished with most class A and B fire extinguishers: the most common control and extinguishing media, including water, generate violent reactions with this type of fire, and may lead to the release of smoke and toxic vapours.
EN 3 Part 7 does not provide a fire classification for this class of fire.
This sector was introduced by the latest revision of EN 2 and includes fires developed from combustible oils and fats, whether vegetable or animal, which tend to be used in kitchen laboratories or in a catering establishment (e.g. school canteens or factories).
These oils are to be distinguished from the mineral oils of class B on account of their different chemical formula.
The extinguishing substances for this class are effective due to their chemical action; they produce negative catalysis, i.e. an interruption of the positive catalysis chemical reactions that support combustion processes.
The extinguishing test defined according to EN 3 part 7 for this fire class is represented by a fire with edible vegetable oil inside a rectangular-shaped metal vessel. The different size of the metal container gives an indication of the standardised fire class based on the volume of liquid inside, as shown in the table below:
| Fire type designation | Volume of combustible liquid in litres |
|---|---|
| 5 F | 5 (+1 -0) |
| 25 F | 25 (+1 -0) |
| 40 F | 40 (+1 -0) |
| 75 F | 75 (+1 -0) |
The extinguishing agents that are most effective on this type of fire class are those whose main extinguishing action is by suffocation: foam.
Any other type of extinguishing agent is considered dangerous for this type of fire class.
