Dry powder
When powder is called dry chemical (very finely divided powdered solids ) for fire fighting .
General
Extinguishing powder is available for fire classes B and C (so-called normal extinguishing powder and high-performance extinguishing powder ), A, B and C (so-called ABC powder or fire extinguishing powder) and D (so-called metal fire extinguishing powder, metal fire powder, or M powder).
Colloquially, the word component “delete” is often left out, so that we are talking about BC powder, for example.
In addition to the main components - which differ depending on the type - extinguishing powder contains additives for better flowability and for hydrophobing . In the past, alkali and alkaline earth stearates were used for waterproofing, whereas nowadays silicon-based aggregates are more commonly used.
use
Drying powders were developed in the 20th century. Extinguishing powder is most widely used in hand-held fire extinguishers . Fire brigades also keep extinguishing powder - often in larger containers of 250 kg or 750 kg. In the case of large (works) fire brigades, in particular, there are also vehicles that transport extinguishing powder in larger quantities as the primary extinguishing agent (see TroLF or SLF ). Extinguishing powder is also used in stationary systems , where it is necessary to suddenly extinguish flames. Mobile powder extinguishers with a capacity of 50 kg are also used, especially in companies.
Caution is advised when using extinguishing foam in combination : many powders decompose the foam quickly and permanently. For use with foam, there are special foam-compatible extinguishing powders, which are often marked with the abbreviation “SV” (for “foam compatible”).
Extinguishing powders are basically available in a wide variety of colors. B. on the type allow. Usually these are distinguishing features that make different products in a manufacturer's range easier to distinguish. There are white extinguishing powders and those in pastel shades (yellow, light blue, pink) through to intense colors (e.g. deep blue-violet).
ABC extinguishing powder
ABC powder was developed in the 1950s as a universal extinguishing agent for all more frequently occurring fire classes. It is the only extinguishing agent that covers fire classes A, B and C. In addition, it can be stored well and has a high extinguishing effect.
It is found in most handheld fire extinguishers . Theoretically, ABC powder could also be used in stationary systems and larger mobile containers, but BC extinguishing powder is mostly used there, since such systems are usually used with the focus on fire fighting of fire classes B and C.
ABC powder mainly consists of finely ground ammonium dihydrogen phosphate and ammonium sulfate .
The extinguishing effect of the ABC extinguishing powder is based on the anti-catalytic extinguishing effect in flames (fire classes B, C, partly also A) ; in the case of ember fires of fire class A, the melting extinguishing powder also creates a suffocating sintered layer on the hot material.
BC extinguishing powder
The original extinguishing powder based on sodium hydrogen carbonate (baking soda) is now often referred to as the standard extinguishing powder . There are also extinguishing powder based on potassium sulfate and so-called high - performance extinguishing powder , which are mostly based on potassium hydrogen carbonate (e.g. Purple K ).
BC extinguishing powders have no noteworthy extinguishing effect against fires of fire classes A and D. In the case of fires of fire class D (metal fires), the powder may even decompose. Fires of fire class F Edible fat fires can u. May be briefly extinguished, but protection against re-flashing after the extinguishing agent concentration in the ambient air has decreased is not guaranteed.
BC extinguishing powder is practically only stored and used in larger quantities where there are special risks of fire classes B and C, for example in the chemical and petrochemical industry, or where fire protection is to be ensured in the case of risks that are not precisely known (for example the so-called triple fire protection in Use of dangerous goods by fire services). Extinguishing powder, which is used by public fire brigades in so-called “powder balls” or other mobile powder extinguishing systems, is mostly BC powder.
The extinguishing effect of the BC extinguishing powder is achieved through the anti-catalytic extinguishing effect .
D-extinguishing powder
D-extinguishing powder (also: metal fire powder, metal fire extinguishing powder, M powder) are the only standardized extinguishing agents for metal fires . As a rule, they consist mainly of finely ground alkali chlorides (often sodium chloride ). A special feature is the high reaction and temperature stability.
D-Powder is used in portable fire extinguishers weighing 12 kg, mobile extinguishers weighing 50 kg or larger containers. The application is very soft and pressureless with a special powder spray, in order to be able to carefully cover any metal melt that may be present with an airtight layer that is supposed to bake together to form a sintered layer.
Extinguishing tactics when extinguishing with powder
When extinguishing it should be noted that the tactics for extinguishing differ depending on the fire class :
- Fires of fire class A are extinguished by a powder layer that is as closed as possible on the fire material. It is advisable to dispense the powder in short, soft bursts of powder in order to avoid the formation of a floating powder cloud as far as possible.
- Flame fires of fire classes B and C require a complete intimate mixing of the flames with the powder cloud. Therefore, the flame must be completely enveloped with the powder cloud - which requires a certain distance from the burning material so that the powder cloud can develop. An interruption of the application can endanger the success of the deletion. With fire class B, the following risk of re-ignition is greater than, for example, when using foam, since the powder does not separate the fire from the surrounding atmospheric oxygen.
- Fires of fire class C are usually only extinguished if this cannot be avoided - otherwise the unburned gas escaping inevitably creates an explosive atmosphere in many cases.
- When extinguishing fires on electrical systems, the prescribed minimum clearances must be observed; corresponding instructions can be found on the fire extinguisher. The distance for common household and car voltages below 1000 volts is usually 1 meter.
Side effects
Extinguishing agent damage occurs mainly because the powder is carried far beyond the source of the fire by the resulting powder cloud of extinguishing salts and settles in practically every crack and corner.
Due to its properties as a salt mixture, these deposits in connection with (air) moisture can lead to severe corrosion damage. This corrosion damage sometimes only occurs after several weeks or months, depending on the humidity and the amount of extinguishing powder.
Another disadvantage of powder as an extinguishing agent is the resulting cloud of powder and the resulting obstruction of view. For this reason, use in closed rooms is only possible to a limited extent, and attention should always be paid to the crowds and possible escape routes.