Fire kits

Good to READ

Fundamentals of High Pressure

In all fires, particularly forest fires, there are 2 major problems:

• The distance
• The lack of water

Le CRITICAL FLOW (CFR): is defined by the minimum flow of water necessary to extinguish a fire sufficiently in a given area.

In the near future, solutions will have to be found to reduce the "critical flow" as much as possible during forest fires and for this we will have to find extinguishing methods which will save scarce water and cover great distances. with an ever lower weight and volume of equipment in short time.

Over the years, new technologies have been developed to allow intervention with the least amount of water possible depending on the extinguishing capacity and with an ever lower weight and volume of equipment. High-performance equipment can now vary distances in less time and with less weight.

Simple physical case study

Studies were carried out in the 1930s by the Paris Fire Brigade.

The case involved the contact surface of a drop of water:
If a drop of water with a radius of 1 mm is divided into drops with a radius of 0,01 mm, then the total cooling surface will increase from 6 m to 600 m and the number of drops will be 1,9 trillion drops.

Comparison of extinction at low pressure (7 Bar) and high pressure (40 Bar) according to the 1999 “Svensson and Lundstrom” study.

CONCLUSION : The high pressure offers greater water savings, less critical flow and stability of fixing the drop of water in front of the fuel by capillary system.

For extinguishing 1000 m2 of surface, high pressure uses 50% less water than low pressure.

Principles of extinguishing efficiency with high pressure water and / or foam

• Efficiency due to the increase in the heat exchange surface
The cooling capacity increases as a function of the heat exchange surface of the droplets. By increasing the pressure on the water, it is divided into drops of smaller caliber, but this requires multiplying the contact surface.

• Efficiency by heat absorption
Extinguishing can be done by spraying water to absorb a large amount of heat. Water requires a heat quantity of 573 Kcal (2395 KJ) in order for the liquid vapor state to be carried out. Traditional systems produce relatively small water droplets large with small cooling areas. In the PRC, only a small percentage of water is evaporated and used for extinction. For this reason, large quantities of water are required to exceed the critical value.
If the pressure of the extinguishing agent is increased so that the drops of water are only half the previous diameter, the consumption of the extinguishing agent and the extinction times will be reduced by half or even lower speeds.

• Efficiency due to asphyxiation

The tendency to spread during vaporization is another characteristic of water which allows it to increase its extinguishing capacity. Thus at 100 °, a single liter of water turns into 1700 liters of steam.
Naturally, by increasing the temperature, the amount of steam increases; indeed, at 260 °, this is what happens: 1 liter of water turns into 2400 liters of steam and 6500 liters (into 4200 liters)
The principle that steam contributes to the extinction of combustion is smothering.

The fractionated water occupies the space surrounding the fire, depriving it of the oxygen essential for its combustion and preventing its reactivation.
The condensed steam also makes it possible to eliminate part of the gases and fumes during combustion present in closed rooms. (By comparing water at 100 bars with water at 40 bars of pressure, at 100 bars a curtain of water mist is created 3 times larger than at 40 bars, and with a similar consumption.

• Effectiveness by impact
Extinguishing can be done through the vaporization of water to absorb a large amount of heat. For the liquid state to “vapor” stage to be carried out, the water needs an amount of heat equal to 573 Kcal (2395 KJ).
Traditional systems produce relatively large water droplets with small cooling surfaces. In the PRC, only a small percentage of the water is evaporated and used for extinction. For this reason, large quantities of water are required to exceed the critical value.
If the pressure of the extinguishing agent is increased so that the drops of water are only half the previous diameter, the consumption of the extinguishing agent and the extinction times will be reduced by half or even lower speeds.