Terry Winograd

The technical of the crayonnage ( combination attack in English) is a technique used by the firemen to cool the Fumée S at the time of a Incendie in closed medium or semi-close (for example in a building).

This technique consists in drawing letters in the air with a diffuse jet. The drawing of the letters lasts from one to two seconds. It was introduced by Keith Royer and Floyd W. “Bill” Nelson of the Fire Service Extension of the University of Iowa into the Années 1950.

Principle of the crayonnage

Smoke represents the principal danger: in addition to their asphyxiating and plugging character, they cart heat and fuel, and are thus likely to start a fire elsewhere in the building, or to cause a thermal Accident.

The maximum collecting of heat is obtained with a diffuse jet (cloud of droplets, like a Brouillard). Generated vapor form an inert gas sky which cannot take fire any more.

During the fire, the atmosphere is laminated: the air is hot with the ceiling and cold close to the ground. The diffusion of a too long jet by a lance puts the masses of air moving: the hot air goes down and can come to burn the speakers or the victims. In addition, the watering of the ceiling or the walls is likely to generate a quantity of vapor likely to attack the people; on the contrary, to cool smoke involves its contraction (according to the law of the Perfect gas S) and avoids the vapor return. This contraction makes smoke less mobile.

The respect of the stratification thus forces to cool all the layers at the same time, other than the ceiling and of the walls.

One can use two techniques: to make short impulses with the ceiling, or the crayonnage. The disadvantage of the impulses is that generates water hammers which can damage the hydraulic material (Fire hose, connection, Pompe).

These techniques are usable only for moderate volumes: if the ceiling is too high (case of a large warehouse), the diffuse jet cannot reach the high layers.

Implementation of the technique

The technique is carried out with a flow of 500 L/min.

The lance holder makes a jet runs to the ceiling in order to test the heat of smoke (see the article Lecture of fire ). If water falls down in the form of droplets, the binomial can progress, or, if it is vis-a-vis fire, carry out the extinction. If water evaporates, then it is necessary in priority to cool smoke, by crayonnage.

If the thermal intensity is strong, the lance holder draws “Z” because it is the letter whose layout is longest. It observes then and generally does not have any more but to make completions, in lower flow. With a lower thermal intensity, one will make a “O” whose layout is shorter or “T” for which the opening of the lance will be only one second.

False friend

The English term to indicate the crayonnage is combination attack (litt. attacks combined). The term pencilling (litt. crayonnage…) indicate a parabolic attack.

Let us note however that the combination attack is regarded with the the United States as an indirect method, i.e. a method of attack since outside, because of the risk of generation of vapor if water touches the walls, whereas in France, it is used when the carrier of lance is inside the room on fire.

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