Extinguishing agent
Extinguishing agents have the task of combustible materials taking into account their fire rating to and prevailing environmental conditions (such as personal hazard or room size) Delete . They are used for fire fighting by the fire brigades or in automatic fire extinguishing systems or are available for self-help in portable fire extinguishers or mobile fire extinguishing devices.
Every extinguishing agent has a main extinguishing effect and possible secondary effects . The wrong choice of extinguishing agent can have fatal consequences. So react some chemicals with water . Chemical extinguishing agents sometimes break down molecules at high temperatures and form new compounds . Possible consequences are a risk of explosion or acid formation .
water
The extinguishing agent water is suitable for fire class A. The extinguishing agent has advantages over other extinguishing agents: it is inexpensive, non- toxic , pH- neutral, non- corrosive , mostly available in sufficient quantities and easy to pump.
Water must not in burning metals are used because the enormous heat would chemically split the water - the contained oxygen would fire explosively fan and the hydrogen burn; Under certain circumstances, the mixture of hydrogen with atmospheric oxygen can lead to the formation of highly explosive oxyhydrogen gas (the generally accepted view that the main danger is oxyhydrogen formation is not applicable. Instead: hot light metal = reducing agent → splitting of water molecules → exothermic redox reaction light metal + Oxygen ).
In the event of a chimney fire , water would evaporate under high pressure due to the very limited space in the chimney (1 liter of water results in 1,700 liters of water vapor ) and destroy the chimney. In the event of fires involving fats and oils with temperatures above 100 ° C, it should be noted that water evaporates immediately on contact and the burning oil is carried away and splashed. The resulting oil mist has a large surface area, which means that the oxygen in the air can attack it and it burns like an explosion (“ fat explosion ”). The electrical conductivity of water carries the risk of coming into contact with high voltage and receiving an electric shock .
Main extinguishing effect: cooling.
Secondary extinguishing effect: suffocation
Water with additives
Wetting agent / water
A wetting agent is an additive to the extinguishing water to reduce the surface tension of the water. The finished mixture is called "network water". Foam agents are normally used as wetting agents - they are then simply dosed lower and no air is added. Usual multigrade foaming agents, which are mixed in with 3% to produce foam, can e.g. B. can be used as a wetting agent in a range of approx. 0.5 - 1%.
Wetting agents are added in order to improve the penetration of the extinguishing agent into the burning material or to make it possible in the first place by reducing the surface tension. This should also be used to reach deep or hidden embers , such as those that occur in humus soil in the forest or in chip bunkers .
In recent times it has become more and more popular that fires in buildings for which pure water was previously used can also be fought more efficiently through the use of wetting agents. Extinguishing water damage caused by draining extinguishing water can be reduced if the water penetrates the fire material in a targeted manner and does not mainly flow away due to the surface tension.
Occasionally the term "light water" is used for network water. However, “Light Water” is a brand name of the 3M company for an AFFF foam agent that used to be very popular . The confusion of terms may arise from the fact that AFFF can also be applied as a non-foamed foam concentrate-water mixture in liquid fires, which is also possible for B. was or is often the case with built-in compact extinguishing systems in smaller vehicles (e.g. "poly" extinguishing system in VRW ). The principle of action in this application is different, however, the "network effect" only comes into play with solid fuels.
Gel builder
If a high adhesive strength and a higher viscosity of the extinguishing water appear necessary, gel formers can be added. These additives are usually based on superabsorbents and can be supplied as a powder or emulsion . Gel formers should, for example, achieve good results in so-called "DSD fires" (fires of stored packaging waste) and enable the creation of an airtight barrier layer for bulk goods that is significantly more stable than a foam carpet , lasts longer and releases significantly less water into the fire. The water consumption is considerably lower in certain fire scenarios.
If extinguishing gel is used, less water can be used for one bolt position. In the outdoor area without the risk of water damage, this is particularly useful when the much cheaper water is not available in sufficient quantities or the type of development hinders its use in sufficient quantities.
Extinguishing gel is attractive in almost all cases in which water can only be transported with great difficulty and at high costs, because you have to use helicopters, for example. If the transport costs are significantly higher than the additional costs for the gel agent, in view of the water hazard class 1 it can be justifiable and reasonable to give the water a higher extinguishing effect in this way.
Retardants
Retardants are additives to the extinguishing water that are mainly used to fight vegetation fires with aircraft. They should, for example, reduce evaporation, increase the boiling point and, through their orange-red (contrasting to plant green) color, make the areas on which the extinguishing agent has already been applied more recognizable. Many of these agents are based, at least in large part, on salts from the artificial fertilizer industry. Some of these salts react when exposed to heat with the surface of the organic material and thereby reduce the flammability of the surface.
Salts
Salts are also used in handheld fire extinguishers . They increase the boiling point of the water and thus the extinguishing power.
Extinguishing foam
Extinguishing foam is an extinguishing agent that is created by adding a foam agent to the water and then adding air. Extinguishing foam has a suffocating effect by placing an airtight layer over the combustible material . Depending on the ratio of the water-foam concentrate-air mixture, three types are distinguished:
| designation | Expansion rate |
| Heavy foam | up to 20 (practically relevant only from ≈ 4) |
| Middle foam | 20 to 200 |
| Lightweight foam | over 200 |
Main extinguishing effect: "suffocation" (here: sticking effect through separation)
Secondary extinguishing effect: cooling
- Compressed air foam
The compressed air foam process (also referred to as CAFS: C ompressed A ir F oam S ystem) differs by the type of delivery of the required for foaming air . As the name suggests, the air is fed into the water / foam mixture as compressed air. This takes place in the fire engine or, in the case of stationary systems, on a pump or a foam compound admixer , the foam is conveyed completely ready through the hoses to the nozzle . With conventional methods, the air would only be absorbed at the foam nozzle . Occasionally, the CAFS system is also used in fire extinguishers or other portable fire extinguishers. The foaming takes place either at the upper end of the riser pipe or in a mixing chamber located at the same point with the aid of the propellant gas.
Dry powder
Extinguishing powders are mixtures of very finely divided solid chemicals that prevent combustion . The prevention takes place either by suffocation ( fire classes A + D) and / or inhibition ( fire class B + C). There are three types:
| designation | Suitable for fire class | Extinguishing effect |
|---|---|---|
| ABC powder | A, B, C - everything (except grease and metal fire) | Inhibition (flames), suffocation (embers) |
| BC powder | B, C - liquids (except fat) and gases | Inhibition |
| D powder | D - metal fire | Suffocation |
Inert gases
The extinguishing effect of argon , nitrogen and carbon dioxide (in principle not an inert gas and therefore not suitable for fires of fire class D) is achieved by displacing the oxygen in the air. This is referred to as the sticking effect , which occurs when the specific limit value required for combustion is not reached. In most cases, the fire goes out when the oxygen level is reduced to 13.8% by volume. For this purpose, the existing air volume only needs to be displaced by about a third, which corresponds to an extinguishing gas concentration of 34% by volume. In the case of incendiary substances that require considerably less oxygen for combustion , an increase in the extinguishing gas concentration is necessary, for example ethyne , carbon monoxide and hydrogen . Since the extinguishing gases argon and carbon dioxide are heavier than the ambient air, they penetrate the flooding area particularly quickly and thoroughly. Mixtures of the aforementioned gases, such as Inergen, are also used to improve the extinguishing properties .
carbon dioxide
Carbon dioxide is suitable for fighting fires of fire classes B and, when used in stationary extinguishing systems, C. Due to its physical properties, carbon dioxide is also used as the only extinguishing gas in fire extinguishers and fire extinguishers . In stationary fire extinguishing systems , carbon dioxide is liquefied under pressure in high-pressure steel cylinders or stored cooled at −20 ° C in large low-pressure containers. Due to the liquid storage, significantly larger extinguishing agent stocks can be kept in a space-saving manner. Since carbon dioxide is harmful to health at high concentrations, the professional associations prescribespecial protective measures if a limit value of more than 5% by volume is exceeded.
Carbon dioxide is mainly used as an extinguishing agent in electrical and electronic systems because, unlike all water-based extinguishing agents and most powders, it is not electrically conductive. The extreme cold, however , destroys magnetic data carriers - for example hard disk drives and their contents. When using it, it is particularly important to ensure that carbon dioxide is a breath poison .
Carbon dioxide cannot be used to extinguish burning light metals - for example ( alkali and alkaline earth metals ) - because it is decomposed into oxygen and carbon (or carbon monoxide ) ( redox reaction ).
On older carbon dioxide extinguishers, the term carbon dioxide extinguisher is sometimes also found.
Main extinguishing effect: suffocation
( secondary extinguishing effect: cooling down - practical but hardly relevant)
argon
Argon is a noble gas obtained from the ambientair that is stored in compressed gas form in high-pressure steel cylindersas an extinguishing agent for stationary fire extinguishing systems . The maximum operating pressure is 300 bar. Argon is not poisonous. However, when building up the required extinguishing concentration, especially in connection with a fire incident, there may be a risk from fire gases and lack of oxygen. It is 0.93% by volume in the atmosphere. Its density in relation to air is 1.38: 1. Due to its higher weight and its high inertia ("real" inert gas), argon can act against nitrogen in individual cases - e.g. B. as extinguishing gas for metal fires - offer advantages.
Note: In the event of a high extinguishing concentration, there may be a risk to persons due to a lack of oxygen.
Main extinguishing effect: suffocation
nitrogen
Nitrogen is a colorless, odorless and tasteless gas that is 78.1% by volume in the atmosphere. Its density in relation to air is 0.967: 1. As an extinguishing agent for stationary fire extinguishing systems , nitrogen is compressed in gaseous form and stored in high-pressure steel cylinders. At an ambient temperature of +15 ° C, the maximum operating pressure is currently 300 bar. Nitrogen is not toxic. However, when building up the required extinguishing concentration, in particular in connection with a fire incident, a hazard from fire gases and lack of oxygen can arise.
In recent years nitrogen has also been used more and more in expansion joint or silo fires . In this case, the liquid gas from tankers, as used for industrial deliveries, is delivered at a temperature of −190 ° C and brought in liquid at the scene of the fire.
In the case of silos, nitrogen has the advantage over carbon dioxide that it does not escape as snow, but changes completely from the liquid state to the gaseous state. In the case of silos, the gaseous nitrogen can more easily seep through the stored goods and does not lead to clumping as with carbon dioxide. The oxygen content is reduced to below 7%, which suffocates a possible smoldering fire in the silo, and the silo can then be cleared safely.
Note: In the event of a high extinguishing concentration, there may be a risk to persons due to a lack of oxygen.
Main extinguishing effect: suffocation
Aerosol extinguishing agent
Aerosol fire extinguishers and extinguishing systems work with a solid, aerosol-forming compound which, when activated, turns into a rapidly expanding, dry extinguishing aerosol based on potassium compounds. Aerosol extinguishing systems are said to have positive properties. The extinguishing principle is similar to that of a powder extinguisher, except that the propellant gas is only generated when triggered by a pyrotechnic charge, whereby the extinguishing agent is also created and released in a finely distributed manner.
Halons (chemically active extinguishing gases or liquid gases)
After the remaining halons 1211 ( bromochlorodifluoromethane ) and 1301 ( bromotrifluoromethane ) have largely disappeared from the market (apart from aircraft fire extinguishers) due to the Montreal Protocol , some companies (e.g. DuPont , 3M , Great Lakes Chemical Corporation) have today again “new” halons for fire-fighting purposes in the program, which should be problem-free with regard to their ozone- damaging effect (ODP). At least some of these halons have already received EU approval. These are in particular the halons
- Trifluoromethane (HFC-23, Halon 1300, brand name Trigon )
- Pentafluoroethane (HFC-125, Halon 2500)
- 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea, Halon 3700, brand names: FM-200 (DuPont Corporation), FE-227 (DuPont Corporation), Solkaflam 227 (Solvay Fluor GmbH))
- 1,1,1,3,3,3-hexafluoropropane (HFC-326fa, Halon 3600)
- Chlorotetrafluoroethane (HCFC-124, Halon 2410)
- as well as the substances below
Extinguishing effect
Halons ( halogenated hydrocarbons ) extinguish by disrupting the combustion process by leading to a chain termination reaction ( homogeneous inhibition ). In contrast to asphyxiation with inert gases and CO 2, this process requires significantly less extinguishing agent volume. Not to be forgotten, however, is their, in some cases, extremely strong effect as a greenhouse gas in relation to CO 2 . Decomposition to toxic by-products is also possible or likely , especially with longer pre-burning times of fire class A.
Novec 1230
The extinguishing agent 3M Novec 1230 ( ISO marking FK-5-1-12, used in the system types: Minimax MX 1230, SAPPHIRE, Kidde KD1230, Siemens Sinorix 1230) is a colorless, almost odorless liquid with the chemical formula CF 3 CF 2 C (O) CF (CF 3 ) 2 . Strictly speaking, it is not a halon, but a fluorinated ketone (perfluorinated ethyl isopropyl ketone ). The extinguishing effect of the Novec 1230 used in stationary fire extinguishing systems is not based on homogeneous inhibition , as is the case with a halon , but on the extraction of heat from the flame. This is due to the significantly higher heat capacity compared to air. The molecule has no electrical conductivity and is therefore suitable for erasing electrical and electronic systems, such as server rooms. With a global warming potential (CO 2 equivalent) of 1, it has the lowest value of all currently permitted chemical extinguishing agents and disintegrates within a few days under solar radiation.
Halon 1211 and 1301
Due to their environmentally damaging effects, the Halons 1211 ( bromochlorodifluoromethane , BCF, Freon 12B1, formula CF 2 ClBr) and 1301 ( bromotrifluoromethane , BTM, Freon 13B1, formula CF 3 Br) , which were previously very common, are prohibited by the Montreal Protocol and are now only used as extinguishing agents in Exceptional cases for military applications, approved as an extinguishing agent in racing and aviation. Halon 1211 was mainly used in hand-held fire extinguishers, Halon 1301 mainly in stationary extinguishing systems.
Emergency extinguishing agents
The term "emergency extinguishing agent" refers to substances, mixtures or objects that actually serve other purposes, but can also be used as extinguishing agents. Different emergency extinguishing agents are used in different contexts.
- In metal fires can cement powder or dry road salt are used.
- In the event of vegetation fires , locally available soil material (sand or earth) is often used.
- In the event of small fires in the kitchen and household , a wet, wrung-out towel is recommended .
Historical extinguishing agents
Fire water
Extinguishing water has always been the only, but above all the most widely available extinguishing agent. Before the establishment of fire brigades in the localities, in the event of a fire, all able-bodied residents had to rush to the scene of the fire with buckets filled with extinguishing water and line up in double rows to the extinguishing water pond : "The bucket flew through the hands long chain in competition." Later, the fire departments wooden pressure syringes were used, but these had to be continually filled with extinguishing water that was brought in with buckets. Then the fire engines , which could also suck in the water , prevailed . The later construction of the central water supply with the installation of hydrants made water transport much easier.
Chemical extinguishing agents
First attempts with chemical extinguishing agents were made in the middle of the 19th century . To extinguish or suppress an outbreak of fire in small, lockable rooms, so-called "Buchersche fire extinguisher cans" were used, which, through their content (8 parts saltpeter , 4 parts sulfur and 1 part coal ) worked towards the formation of sulphurous or carbonic gas , which prevent ignited objects from burning away. These cans were either stored in the pubs concerned and then acted automatically after they had ignited if a fire broke out, or they were thrown into the pubs at the time of the fire, but the latter closed again (Morgenstern Karl: About facilities and protective measures to safeguard against danger for the life and health of workers employed in commercial establishments, Volume 1: General. A, furnishing of work rooms… B, steam boilers,… C, motors,… D, Transmissions, Leipzig 1883, page 29).
The "Innsbrucker Nachrichten" of December 19, 1856 reported on the experiences with this still primitive extinguishing agent :
- "On the 13th. M., the announced rehearsal was made with Bucher's fire extinguishing cans in Würzburg. Brushwood etc. was piled up in a mess booth; this was set on fire, and when everything was burning properly and the fire was already breaking through the roof of the booth, three cans were made one after the other; every 5 pounds thrown in. Immediately thick smoke came from the cracks and openings of the booth, which dampened the fire for a few seconds, but was not able to completely suffocate it, whereupon it burned away with renewed strength and was finally extinguished by a syringe. In spite of this unsatisfactory success, no definite judgment about the suitability of that fire extinguishing agent can be made from this sample; Because the booth not only had various openings, but also expanded when the boards began to shrink due to the heat, all the joints of the same, so that a strong draft had to arise inside, while that extinguishing agent is initially only intended for closed rooms. In addition, when the water was used, the last can had not yet burst. Yesterday's trial showed that much, however, that in the event of a decent fire, good syringes and a capable fire-fighting team will not be dispensed with in the future either. [...] "
Halons
Before 1980, halons were mostly much more poisonous than they are today; in particular:
Carbon tetrachloride
Carbon tetrachloride ( Tetra, Halon 1400) Tetra was a widely used extinguishing agent in hand-held fire extinguishers until the middle of the 20th century. By adding 6% trichlorethylene, frost resistance of down to −35 ° C could be achieved, which was particularly important for on-board fire extinguishers. This mixture could also be enriched with the solid hexachloroethane (still called "hexachlorethylene" at the time), which remained after the more volatile tetra had evaporated, only evaporated at 185 ° C and thus ensured lasting extinguishing success. This addition had proven particularly useful for wooden radio towers, since conductive extinguishing agents were out of the question there.
bromide
Bromide (the names are historically determined and can therefore contradict the current nomenclature) was used as a name for various bromine hydrocarbons used as extinguishing agents. As a rule, they were more powerful than Tetra, but at least some of them were also more narcotic:
Methyl bromide (CH 3 Br, bromomethane ) had a very good extinguishing effect, but the jet atomized and evaporated very quickly, so that it was later often mixed with higher-boiling substances. In addition, methyl bromide is very toxic, resulting in some injuries and deaths.
Methylene bromide (CH 2 Br 2 , dibromomethane ).
Ethylene bromide (C 2 H 4 Br 2 , dibromoethane ) was offered in a mixture with methyl bromide and depending on the manufacturer Ardexin or mini Maxin mentioned.
Ethyl bromide (C 2 H 5 Br).
Monochloromonobromomethane (Halon 1011) as a technical mixture of ≈80% monochlorobromomethane, ≈10% methylene chloride (CH 2 Cl 2 ) and ≈10% methylene bromide (CH 2 Br 2 ), at the time very often sold and used under the name CB . Pure monochloromonobromomethane was very expensive to produce and therefore appeared uneconomical. CB was very advanced in that it did not contain methyl bromide and could be handled without pressure. Also was CB safer than Tetra and bromide, as it is not in the formation of phosgene or bromophosgene could come. In the GDR from 1956 a similar mixture with a comparable effect was produced under the name Pyrexin (later Emixin ). While 500 g of carbon dioxide or 560 g of Tetra were required per m³ of fire space, 260 g of Minimaxin and only 232 g of Exmixin were sufficient for the successful extinguishing of the fire.
Iodocarbons
Iodohydrocarbons have an excellent extinguishing effect, but were never important because of their exorbitantly high price (in the 1950s about a factor of 10 compared to bromohydrocarbons).
Fluorocarbons
Fluorocarbons dichlorodifluoromethane (CCl 2 F 2 ) and dichlorodifluoroethane (C 2 Cl 2 F 2 ) were patented as fire extinguishing agents as early as the first half of the 20th century. Little is known about its actual use, however. The same applies to chlorobromoiodofluoromethane (CClBrIF) and dibromodifluoromethane (CBr 2 F 2 ).
literature
- Andreas Pfeiffer: Extinguishing agents in fire fighting . Springer Verlag, 1st edition 2016. ISBN 978-3-658-12971-2
- Roy Bergdoll, Sebastian Breitenbach: Die Roten Hefte, Issue 1 - Burning and Extinguishing . 18th edition. Kohlhammer, Stuttgart 2019, ISBN 978-3-17-026968-2 .
Web links
Individual evidence
- ↑ World of Miracles : Firesorb - With a miracle gel against large fires (broadcast on July 4, 2010).
- ↑ a b Inerting - what is it? In: Brand Aus, monthly magazine of the Lower Austrian Fire Brigade Association , issue 10/2010.
- ↑ Inerting in the event of fire (silo fires) ( Memento from September 6, 2009 in the Internet Archive ) on Messer Austria, accessed on October 27, 2010.
- ↑ The chemistry school: aerosol extinguishing agents
- ^ The chemistry school: Aerosol extinguishing systems
- ↑ according to the information provided by a supplier of the aerosol extinguishing agents ( PDF ).
- ↑ 3M : 3M ™ Novec ™ 1230 Fire Protection Fluid ( Memento from September 27, 2011 in the Internet Archive )
- ↑ Fire extinguisher guide accessed on December 15, 2017
- ^ Franz-Josef Sehr : The fire extinguishing system in Obertiefenbach from earlier times . In: Yearbook for the Limburg-Weilburg district 1994 . The district committee of the Limburg-Weilburg district, Limburg-Weilburg 1993, p. 151-153 .