Fire fighting foam

Extinguishing foam is of special foam, which largely of filling gas ( usually air ), water and a foaming agent, is. Due to its composition it is also called air foam. Extinguishing foam - usually by a fire department - used as fire extinguishing agents for combating fires of class A (solids) or B ( liquids).

  • 4.1 Heavy Foam
  • 4.2 Medium Foam
  • 4.3 Lightweight foam
  • 4.4 Network Water
  • 6.1 Strahlrohrverschäumter foam
  • 6.2 Compressed air foam
  • 7.1 classic admixture
  • 7.2 Pumpenvormischung 7.2.1 first straight-ahead method
  • 7.2.2 second shunt procedure

Historical

1877 developed the Englishman John Henry Johnson, a foam manufacturing process, which was based on a chemical reaction. For this he received British Patent No. 560 over a fire extinguisher. An aqueous solution was treated with saponin. This solution was allowed to act on sodium aluminum sulfate. The water formed in the reaction of carbon dioxide brought the solution to foam. The foam production by this method was cumbersome and there were only very limited quantities are made of extinguishing agent. Nevertheless, the method was further developed in the 1930s.

The air foam method until today almost unchanged Applied goes back to the Berlin Patent Attorney Clemens Wagner. This invented in 1923, the air - foam lance, which became known as Comet tube then. He converted his idea that you could use normal air for foam generation instead of a stick gas such as carbon dioxide. In 1932, Wagner patented his invention.

1928 experimented Dr. Wilhelm Friedrich in Berlin with foam. He developed a foaming agent that has made it possible to produce foam by the foaming agent -water mixture is sprayed by a lance.

Extinguishing effect (s)

Extinguishing foam has, depending on the type (see next section ), different quenching effects. For each type of foam is made here between the main and the secondary quenching effects.

  • As release -effect refers to the fact that a closed foam fire blanket is separated from the surrounding atmosphere and so removes the need for the combustion oxygen.
  • While the foam insert and foam is destroyed. This creates tiny water droplets absorb the heat and evaporate. This cooling effect deprives the fire energy (heat).
  • Applied as a foam blanket on flammable liquids will prevent the liquid releases gases. The masking effect, preventing the emergence of an explosive vapor-air or gas / air mixtures.
  • Especially high expansion foam (see below) is used to flood rooms. This crowding-out effect both flammable gases and oxygen from spaces can be pressed out.
  • As a gas / water mixture passes foam only very slightly heat. This one uses the insulating effect, in which the foam prevents the spread of fire by radiation.

Terms

Foam expansion

The expansion ratio ( VZ ) is the ratio ( the ratio ) between the volume of the finished foam and the volume of the original water-foam mixture. The expansion ratio depends on the foam lance used and can not be changed.

Proportioning

The induction rate ( ZR ) indicates how large the proportion foam concentrate in the water-foam mixture. At a 3% admixture in 100 liters of water-foam mixture are so 3 liters of foam concentrate. The induction rate is set at the proportioner, usually values ​​from 1 % to 6 % are possible. The induction rate to be set is specified by the manufacturer of the foaming agent. In general, however, that the foam is more stable the higher the induction rate.

Destruction rate

The destruction rate indicates how high the proportion of extinguishing foam is that is destroyed upon impact directly on the fire. This can be caused in addition to the heat of the fire, for example, chemical reaction with the fuel. In the calculation of required quantities of foam is expected usually with destruction rates of 50 %, in some cases (as in very hot oil fires ) this but may be up to 70%.

Water half-life

The water half-life ( WHZ ) indicates the time in which half of the liquid originally present in the foam ( foam and water ) has leaked. The leakage of the liquid leads to an increasing drying of the foam with decreasing quenching effect.

Foams

When the fire brigade fighting foams are classified mainly according to expansion ratio into three categories: foam, foam agent and lightweight foam.

Water-foam mixture can also be used non- foamed to achieve better wetting at solid fires. The foam medication is dosed lower than for use as a foam, then one speaks of network water.

Heavy foam

Low expansion foam is a relatively wet foam, with which you can achieve good casting distances. It is used for fires involving solids or liquids ( fire classes A and B). The main effects that contribute to firefighters, here are the cooling effect and the separation effect. Expansion foam can also conditionally "stick" on vertical surfaces remain (depending on foaming agents, foaming, and not least the structure of the surface ).

Low expansion foam is also partly still used preventively as foam carpet at emergency landings at airports to prevent fires caused by sparks.

Medium Foam

Due to the higher expansion ratio of the foam agent is significantly lighter than heavy foam and can (if the foam can not flow off ), up to 5 feet high piled. Its adhesion to surfaces is small, thus it can be used for venting of objects. In addition to the displacement effect include cutting and subordinate cooling effect to the extinguishing effects of the central foam.

Lightweight foam

This type of foam can not be thrown, because it is so light that it is already being blown away by the wind. The main field of application is therefore in enclosed spaces. Moreover, in contrast to previous foams for light, a special foam generator for producing necessary.

The main extinguishing effect applies the displacement effect. In addition, the foam when exposed to heat decays very fast to very fine water droplets and thus acts a cooling effect.

Mains water

The feed water is a special feature, because it is true ( here used as a wetting agent) of water and foaming agent, but is delivered as such foams over multi-purpose or Nozzles (so no fighting foam ). The foaming agent addition, the surface tension of water is lowered, allowing the mixture to better and deeper in ( burning ) objects - such as Paper or textile bales - penetrate.

Foaming agent

The foam agents are either already in the car or later mixed by a proportioner to the clear water.

When firefighters different foaming agents are used:

  • More with foams ( MBS) can be all foam types (heavy, medium and light foam) produce.
  • Aqueous film forming foams ( AFFF, also called " A3F " written, Eng. aquatious for film- forming foam) form in addition between foam and burning liquid in a steam tight, aqueous liquid film. Some of them, however, are prohibited for environmental hazards.
  • Class A foam foams ( ClAFSM ) are widely used in the USA, Germany, however, only on the rise. ClAFSM were developed as a wetting and foaming agents for Class A fires, especially for vegetation fires. A big advantage is that they only 0.1 % to 1.0% of the extinguishing water must be added depending on the application, so they are very economical to use.
  • To be lost to the significance of the protein foaming agent. With the protein foaming agents made ​​from animal raw materials can be produced only foam, but it includes an unmatched adhesion.
  • Fluoroprotein foaming agent (FPS ) and film forming fluoro protein foam agents ( FFFP ) come closer to Werkfeuerwehren used.

The demands placed on foam agent for heavy, medium and light foam for use on non-polar liquids and heavy foam for use on polar liquids are specified in DIN EN 1568.

Occasionally, the term " foam concentrate " used. Since, however, concentrates before use must be diluted, this term is incorrect.

Foaming techniques

Strahlrohrverschäumter foam

As " Strahlrohrverschäumter foam " refers to any foam, the air until the foam lance ( or light foam generator ) is added. In the tube so only a mixture of water and foam concentrate is encouraged.

Compressed air foam

When compressed air foam ( "DLS " or " CAFS " for " Compressed Air Foam System " ), the foam is sponsored ready generated and compressed by the hoses of water, foaming agent, and air already in the car. The procedure itself dates back to the 1930s, was heavily into oblivion, but experienced in Germany just coming back from the U.S., a very controversial Renaissance.

The structure of the compressed air foam is much more homogeneous than that of the conventional air foam, it is similar to the consistency of shaving cream and adheres to vertical surfaces. Thus, it is possible to delete not only in the literal sense, but also for example walls lather precaution to protect it. The expansion ratio of the compressed air foam, depending on the setting of the system of between about 4 and 15 and thus in the area of heavy foam within the meaning of air foam, but the quenching effect is based on an expansion ratio of 15 due to the different structure, as opposed to air foam to tend to the separation -and the cooling effect.

A manufacturing method for the water / foaming agent mixture

The foaming agent solution to the fighting foam can be produced when using the conventional Z / Zr proportioner ( DIN inductors ) according to various methods:

Classical mixing

In the classical method is the proportioner between the manifold and the beam pipe. Proportioner and foam lance here are matched in their flow directly to each other.

The problem with this method, firstly, that there is high pressure losses in the proportioner (according to DIN 14384 up to 38 % loss of pressure are permissible) and between proportioner and foam lance, a maximum pressure difference of 2 may prevail bar, otherwise the proportioner no longer works reliably. Meanwhile, there are also firemen, connect the proportioner directly to the pump outlet. This has the advantage that one need not carry as far as the foaming agent. In addition, you can use this to add foaming agents, as wetting agents.

Pumpenvormischung

The proportioner is how the term " Pumpenvormischung " says installed upstream of the pump. This can be achieved at the discharge fitting long casting distances, because it is constructed only in the pump to the water-foam mixture of pressure.

The main disadvantage is the contamination of the pump.

First straight-ahead method

The straight method uses two series-connected pumps, between which / are or admixers is built into the hose line. The problem of the traditional method with the maximum pressure difference of 2 bar between proportioner and spray lance is eliminated. The total capacity of this structure remains from the proportioner dependent, by the depending on the type (Z2, Z4, Z8 ), only a certain amount of water (200 l / min 400 l / min 800 l / min) flow. This can be circumvented by several foam inductor are connected in parallel between the two pumps.

Second shunt procedure

This method is a further development of the straight-ahead method which operates with only one pump and a proportioner. At the pump, a foam inductor is connected to an outlet, which provides its mixture in the ring closure via a claw back into the pump. Another outlet supplies the mixture to the beamlines.

Through the swirling in the pump achieves a very good mixing of extinguishing water and foaming agent. The engineer at the pump, however, must pay attention to pressure equality of two tributaries to the pump ( as a guide for the pump pressure should be approximately 4 bar above the hydrant pressure, which corresponds to the pressure loss in the proportioner ). If it does not achieve optimum mixing and at worst not produce foam.

The effective mixing at the discharge valves can be represented by the formula

Calculate.

Stationary foam extinguishing systems

Stationary foam extinguishing systems Fire extinguishing systems, which according to the classical Zumischverfahren in which, after the pump proportioner is used to work. The EN 13565-2 regulates in Europe the design, installation, commissioning and operation of heavy -, medium- or high-expansion foam fire extinguishing systems.

In the fixed foam extinguishing systems, the foam at the outlet of the duct system through special sprinkler nozzles, foam jet, foam pourer or high expansion foam generators can be delivered. For sprinkler systems with fire extinguishing nozzles they are uniformly distributed in the space to be protected. Foam systems are preferably used there, is where to expect flammable liquids, such as in fuel depots or transfer stations. In industrial plants, or airports, for example, in hangars also often called monitors are used for selective deletion with foam. In these systems, the foam occurs under high pressure from the gun of the monitor, so as to achieve long ranges.

Foam extinguishers

Foam fire extinguishers are working in part with separate foam and water supplies. After activating the extinguisher CO2 pushes out the foaming agent from a cartridge into the container with water and then the water-foam mixture from the fire extinguisher, where it is finally foamed.

There are also foam extinguishers, which already contain a pre- foam agent and water mixture.

(Solids) and B (liquids ) as well as special grease fire extinguishers in addition to the fire class F ( grease fires) are foam extinguishers manufactured for fire classes A.

Hazards and Safety

Working with foam agent can only be done eye protection. Foam agents are usually classified as water hazard class 2, which is why a Löschwasserrückhaltung should be established to prevent material from entering drains or open waters.

In areas where foam is used, may be taken only with self-contained breathing, as in a fall in the foam no longer breathing is otherwise possible.

In electrical installations, no foam may be used as long as the system is not activated.

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