Set fire to

The term fire was borrowed by the French language from the 16th century from the Latin “incendium” ( flashover ), derived from “incendere” ( to light ). It indicates a violent fire, a flashover which is propagated at a building, a house, a forest, etc the fire is a reaction of Combustion not controlled in time and space.

The fire, called Fire commonly, is particularly destroying for the human activities and nature: Dwelling S, places of work, warehouses, Vehicle S, cultures, Forests, historic buildings…

The taking into account of the fire hazard resulted in creating first-aid organizations (firemen, Civil protection). They developed and improved means of Lutte against the fire to fight the fire.

Origin of the fires

The major part of the fires has human origins (imprudence, ill will, cause technical…). The natural causes most frequent are the lightning and fermentation (peat bogs…). The causes of the fires can also be energy: sparks, chemical reactions, short-circuit…

After the voluntary acts, one estimates that nonthe respect of prohibition to smoke and the incidents of electric origin constitute the major part of the starting risks of fire.

Dangers of a fire

Part of the principal dangers to which a person close to a fire exposes itself are related to high heat. Even apart from the flames, one exposes oneself to the risk of Brûlure due mainly to the Fumée S heats, but also to the radiation Infrarouge, the contact with heated objects, the heated air, or to the steams produced by watering. To secure burns the firemen are equipped with fireproofed protective clothing and helmets slowing down the progression of heat towards the skin.

The other risks are primarily respiratory. Indeed fire consumes the Dioxygène Air, essential to survival and can thus involve a Asphyxie. Moreover fire releases from the fine particles (commonly called smoked) which can come to burn the interior of the lungs, and often from pollutant gases being able to cause poisonings. As example, the plastics contained in a car can generate 200 000 m of smoke at intervals from 20 to 30 cubic meters a second. This is why the firemen carry a Breathing apparatus isolating.

Heat can cause Explosion S of bottles of gas and tanks, as well as certain products like the ammonitrés Engrais . These explosions can cause traumatism by fall (nobody reversed), projection of glares, like from caused overpressure ( blast ).

In interior, it is necessary to add two risks:

the obscuration of the vision by smoke: one does not see where one goes, and one can thus make a fall or lose oneself;
the risk of collapse of the structure.

Lastly, let us note that firemen are regularly victims of road accidents while going towards their barracks when they are called, in particular night (conjunction of the stress, tiredness, road negligence of the safety regulations).

Propagation of a fire

A fire develops in several phases during which its temperature will rise. According to its environment, it will extend and decline.

Blossoming

The meeting of the elements of the triangle of fire, i.e. a Combustible , a Combustive (in general the Dioxygène of the Air) and a energy of activation (Heat, naked flame, spark) sufficient will make it possible the Combustion to start.

At this stage, the heat emission is moderate, the not very abundant Fumée S (called sometimes wrongly Aérosol, this term indicating makes a liquid mixture/gas of them whereas smoke is a solid mixture/gas)

Growth

Combustion produces heat (exothermic Réaction), fire maintains and increases the energy of activation. If the fuel and the combustive one are available in sufficient quantities, the fire extends in an exponential way . It is estimated that to extinguish a dry fire being born, it is necessary:

water glass during the first minute,
a water bucket during the second minute,
a water cistern at the end of the third minute.

In the case of a fire in a closed volume (for example a fire of dwelling), one estimates that the temperature of the air reached 600 °C at the end of five minutes; in a stair-well, it can reach 1 200 °C in same time.

Thermal phenomena and fast progressions of fire

Under certain conditions, it can occur a fast progression of fire (PRF) by thermal Phénomènes . The independent factor supporting the appearance of these phenomena is the flow of air feeding fire:

fire fed in air: Flashover generalized flash;

fire deprived of air: Explosion of smoke.

However, the phenomena are more complex. The Anglo-Saxons distinguish two types of explosion of smoke, the backdraft and the smoke explosion , and consider the possibility of an explosion with a fed fire ( high presses backdraft ).
These phenomena can occur for very reduced volumes, such as for example a metal container of dustbins.

Fire made up

It is the moment or fire is with strongest of him same. At this time it cannot grow any more and will follow its phase of decline then.

Decline

Decline made when fire ceases growing. Fire gradually will drop in intensity then to enter in slow combustion jusqua what it lacks fuel and dies out.

Modes of propagation

Radiation

It is about a mode of remote propagation which can be done in the vacuum. It is the phenomenon which makes that when one is vis-a-vis a fire, the exposed side is hot whereas the opposite side is cold.

The frequency of the radiation located is in the Infrarouge (IR). The power of the radiation is function of:

the temperature (the radiation increases with the power fourth temperature)
the distance (the radiation decreases with the square of the distance)
the nature of the particles constituting smoke, in particular soots

Convection

The Convection is a transport of hot gas. A hot gas goes up: the Densité of a gas decreases with heat, the Poussée of Archimedes thus causes the rise in this mass. When this mass reaches a cold obstacle (for example a ceiling), it transfers its heat to him, cools and falls down, it thus has a movement of “bearing”, similar to the movement of water carried with boiling in a pan.

In the case of a fire, the Fumée S follow the same ascending behavior. They can traverse important distances and transfer their heat to a combustible material which would be on their way. One frequently quotes the case of fires of cellar whose smoke borrows the stair-well, saves the intermediate stages and accumulates in the roofs before setting them ablaze. If smoke contains unburnt particles because of an incomplete combustion, their accumulation in a distant point can lead to an explosive resumption of the hearth.

To fight against the accumulation of smoke and to limit their dangerous character, of the systems of Désenfumage (Trap door S, Opening S or Extractor S) can be established in a building. Failing this, one of the first action of the firemen will be to practice a high opening, with the requirement by breaking the roof, a pane or a wall. The doors firebreak limit the propagation of smoke and thus that of the fire. They protect the people against the intoxication by smoke.

Conduction

The thermal Conduction is the mode of transfer of heat caused by a difference in temperature between two areas of the same medium or between two mediums in contact without appreciable displacement of molecules. This spontaneous transfer of heat of an area of high temperature towards an area of lower temperature obeys the law known as of Fourier.

Thus, the handle of a metal spoon which exceeds of an ebullient dish will warm up until becoming extreme. At the time of a fire, this same phenomenon can transport important quantities of energy of one part to the other of a building. Metallic materials (structural members, rails, conduits, concrete-reinforcing steels…) have a conductivity particularly high.

Projection

Ignited or incandescent objects can travel in the air, either carried by the wind if they are light (for example sheets of tree or paper, ashes), or to be projected by an explosion. These objects can create new distant hearths.

Thermal power

Several values make it possible to approach the quantity of energy released during a fire:

the calorific value of a fuel: expressed in kJ/kg or kJ/m ³, it is the maximum quantity of heat which the unit of mass or volume for a complete combustion can release;

the calorific load : expressed in kJ for a zone, it is the total quantity of heat which can release the whole of fuels present in a given space (a part for example);

the calorific potential : in kJ/m ² (for a zone), it is the calorific load brought back to surface on the ground of space considered;

the input rating : in kJ/kg/s or W/kg, it is the quantity of heat produced by a unit of time for the combustion of the unit of mass of a fuel.

The Chaleur released by second (thermal power) at the time of a fire primarily depends on the calorific potential on the objects. Here as an indication some powers:

an upholstered chair: 500 K W (0,5 M W);
small convenient: 1,8 MW;
a settee three places: 3,5 MW;
two twin beds in pine: 4,5 MW;
power released at the time of a Flashover generalized flash: 3-10 MW (7 MW on average).

This is to be compared with the absorbable thermal power by a diffused water jet:

0,5 MW with 40 L/min;
2 MW with 150 L/min;
6 MW with 500L/min.

Protective clothing (textile fireproofed) of the firemen, as for them, guarantees in 2005 a protection against a heat flow of 40 kW/m ², that is to say 0,04 MW/m ².

Large famous fires

Arsons

A case of arson is the voluntary act to put fire in the intention to destroy a good or to kill out of the individuals. Means of revenge, the case of arson is also the work of people reached of psychiatric disorders or Pyromane S. the cases of arson are also for a long time a current practice during military or social confrontations.

Mobiles

Intention to harm
Pyromania
Swindle the insurances
Property developers

Scientific police

August 1st

Folklore

the fire in Rio is a famous song of Maurice Tézé (words) and Gerard Gustin (music), interpreted by Sacha Distel.

See too

External bonds

articles of the site Urgencies Online

Intoxication with smoke of fire
Intoxication with CO (Carbon monoxide)

Files Firemen - Documentation
Speak-Firemen the Community Internet of the sappers firemen
Photo-Fireman photo Album of the firemen
virtual Center of intervention

the fire of dwelling, an article of the European Center of prevention of risks (CEPR)
Attentionaufeu.fr, a site of prevention in French dedicated completely to the question of the domestic fires.
Safety of the goods and installation-Safety fire-pages of the gate of the risk-IUT Bordeaux 1 EPD HSE
Site of François Calay: Testimony and account of a badly burned person.
Gate of the risk - pages of fire protection and its thermodynamic phenomena technical Documents on the fire, combustion, the explosion and zones ATEX
Gerald Home Page - a personal site dedicated to protection fire
''' All Safety ''' - the prevention sets fire to in ERP

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