The fire and fire classes

The decisive element of the fire is the flame that develops in an uncontrolled way in time and in space.
Combustion is a chemical reaction between a body fuel and a combustive agent.

The fuel

È la sostanza in grado di bruciare, in condizioni ambientali normali esso può essere allo stato solido (legno, carta, carbone, ecc. ) , liquido ( petrolio, benzina, alcool, ecc) gassoso
(acetylene, fuel gas, hydrogen, etc.)

The combustive agent

che interviene in un incendio è l’ossigeno presente nell’aria.
Il rischio d’incendio, quindi esiste in tutti i locali.

Flash temperature

È la minima temperatura alla quale il combustibile sviluppa vapori in quantità sufficienti a formare con l’aria una miscela infiammabile.

The range and the flammability limits

The fuel must be present in fixed proportions so that the fuel mixture combustive agent result flammable gaseous state. For every combustible substance exists a range of values, expressed in % by volume of flammable substance in air or in grams of the substance in 1 m3 of air. This field is defined flammable range. Below or above these limits the flammable gas present in the mixture with the combustion gases can not give rise to a combustion.

The ignition temperature

It is the minimum temperature at which the flammable mixture starts to burn spontaneously and continues in combustion without supply heat.

The trigger

It is the element which, in contact with the flammable mixture, starts the combustion reaction. It may be formed from any source of heat:

    • open flames, for example. welding operations
    • incandescent particles (charcoal) from an existing outbreak
    • spark of electrical origin
    • sparks of electrostatic
    • sparks from impact or friction
    • increase in temperature due to the compression of the gas
    • chemical reactions
    • overheating moving parts

The fire

it can be represented with a triangle whose three sides are made up of fuel, comburent, heat source. In the absence of one of the three elements, fire does not exist.


The greatest danger to people in case of fire may be:

    • due to the flame
    • due to the heat, the hot gases of combustion and not, can cause dehydration
    • resulting from the lack of oxygen: the oxygen concentration, due to the combustion, may fall below the limit of normality.
      To decrease gradually associate, movement difficulties, low capacity assessment, collapse and asphyxiation.
    • Toxicity: the gases produced in a combustion can be toxic as in relation to the materials involved as in relation to the amount of oxygen present in the site of the fire. At 1st place for the number of victims is the carbon dioxide (CO2), poison gas at high concentrations. Among other gases known to the toxicity remembers hydrogen sulfide, hydrogen cyanide, nitrogen oxide, ammonia, sulfur dioxide, etc..2), gas asfissiante ad elevate concentrazioni. Tra gli altri gas noti per la tossicità si ricorda l’idrogeno solforato, l’acido cianidrico, l’ossido di azoto, l’ammoniaca, l’anidride solforosa, ecc.
    • the presence of fumes: the phase in which the gases of combustion drag solid or liquid particles that make it opaque. Smoking produces an irritating effect on the eyes and the respiratory tract, reduces the visibility and power of attorney panic.
    • traumatic effects: when the fire is associated with an explosion, the resulting pressure waves can cause trauma in subjects exposed.

Fire classes

It is necessary to ensure the protection of people:

    • respecting the number and size of exits regulations and checking that the exits are always free
    • ensuring that the fire resistance of structures is adequate
    • contain any flammable materials and products in special cabinets
    • inform and train workers and employees in fire prevention, systematically inform new recruits on devices with extinction and first aid (location, terms of use) and carry out regular exercises.
    • maintain the efficiency of all fire fighting equipments: fire extinguishers, hoses, plant and so on.

CLASS A - Fires of combustible solids, flammable and incandescent

Material to be protected - ordinary combustibles such as wood, paper, fabric, plastic, and most kinds of trash

Extinguishing agent - ABC powder; Water; Foam

CLASS B - Fires of liquid materials for which you need a hedge effect and choking

Material to be protected - Alcohols, ethers, paints and solvents, mineral oils and fuels, vehicles

Extinguishing agent - ABC powder; Foam;Carbon dioxide(CO2)2)

CLASS D - chemicals spontaneously combustible in the presence of air, inactive in the presence of water or foam with the formation of hydrogen and explosion hazard

Material to be protected - Alkylated aluminum, barium peroxide, sodium, magnesium, and manganese, potassium, aluminum powder, potassium peroxide

Extinguishing agent - D powder, Carbon dioxide

CLASS E - Fire of electrical equipment under voltage

Material to be protected - ransformers, alternators, panels and switches, electric motors, telephone systems

Extinguishing agent - Carbon dioxide2)

CLASS F - Fires involving cooking hobs

Material to be protected - Kitchens, canteens, restaurants and working with presence of animal and vegetable fats

Extinguishing agent - Foam class F