Fire extinguisher Guide, Meaning , Facts, Information and Description
A fire extinguisher is a device used to put out a fire, often in an emergency situation. They consist of a pressurised container of chemicals that when discharged can put out a fire. It is important to familiarise yourself with the use of fire extinguishers in your vicinity, as improper or untimely use may be counterproductive.
Classification
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In the United States, the National Fire Protection Agency has created five classes of fire extinguishers, A, B, C, D, and K.
- Class A extinguishers are used for putting out fires of general combustibles such as wood or paper. These usually contain a foam-like mixture of water and carbon dioxide. The symbol is a triangle around the letter A.
- Class B extinguishers are intended for use on liquids or grease and are distinguished by a square around the letter B.
- Class C extinguishers are used on electrical fires. Their mixture is non-conducting to prevent zapping the user.
- Class D extinguishers are used on fires of flammable metals and certain other exotic chemicals. They are designated with a star around the letter D. These are rarely encountered and much more expensive than class A, B, or C extinguishers. Class D extinguishers have to specialised to the particular hazard and require special operator training.
- Class K extinguishers are used in Kitchens and environments with the high probability of grease fires. These are rarer because the category has only existed since 1998, so many kitchens are still equipped with Class B extinguishers.
Other countries may have broadly similar systems which differ in detail. For example in Australia, the classes are:
- Class A: Same as US class A.
- Class B: Same as US class B.
- Class C: Flammable gases.
- Class D: Same as US class D.
- Class E: Same as US class C.
- Class F: Same as US class K.
| Type | pre-1997 | current |
|---|---|---|
| Water | Solid red | |
| Foam | Solid blue | Red with a blue band |
| Powder | Red with a white band | |
| Carbon dioxide | Red with a black band | |
| Vapourising liquid (not halon) | Red with a yellow band | |
| Halon | Solid yellow | — |
| Wet chemical | Solid oatmeal | Red with an oatmeal band |
A fire extinguisher may emit a solid, liquid, or gaseous chemical.
Similarly water sprayed on an electrical fire may cause the operator to receive an electric shock. (However, if the power can be reliably disconnected and a carbon dioxide or halon extinguisher is not available, clean water will actually cause less damage to electrical equipment than will either foam or dry powders.)
This is an Article on Fire extinguisher. Page Contains Information, Facts Details or Explanation Guide About Fire extinguisher Chemistries
Water
Water is the most common chemical for class A fires and is quite effective as one would imagine. Most water based extinguishers also contain traces of other chemicals to prevent the extinguisher rusting. Some also contain wetting agents which help the water penetrate deep into the burning material and cling better to steep surfaces. Water works to extinguish a fire by simply cooling it below the ignition point, although large amounts of water can also exclude oxygen. However, water will merely exacerbate other fire classes. For instance, water sprayed over burning liquid petroleum merely spreads the flames around.Foams
Foams are commonly used on class B fires, and are also effective on class A fires. These are mainly water based, with a foaming agent so that the foam can float on top of the burning liquid to exclude oxygen. Ordinary foams are designed to work on nonpolar flammable liquids such as petrol (gasoline), but may break down too quickly in polar liquids such as alcohol or glycol. Facilities which handle large amounts of flammable polar liquids use a specialised "alcohol foam" instead. Alcohol foams must be gently "poured" across the burning liquid. If the fire cannot be approached closely enough to do this, they should be sprayed onto an adjacent solid surface so that they run gently onto the burning liquid. Ordinary foams work better if "poured" but it is not critical.Dry Powder
For classes B and C, a dry powder is used. There are two main dry powder chemistries in use:
Both types of powders can also be used on class C fires, but provide a significant cleanup and corrosion problem that is likely to make the electrical equipment unsalvageable.Wet potassium salts
Most class K extinguishers contain a solution of potassium acetate, sometimes with some potassium citrate or potassium bicarbonate. The extinguishers spray the agent out as a fine mist. The mist acts to cool the flame front, while the potassium salts saponify the surface of the burning cooking oil, producing a layer of foam over the surface. This solution thus provides a similar blanketing effect to a foam extinguisher, but with a greater cooling effect. The saponification only works on animal fats and vegetable oils, so class K extinguishers cannot be used for class B fires. The misting also helps to prevent splashing the blazing oil.Carbon dioxide
Carbon dioxide also works on classes B and C and works by displacing the less dense oxygen. This can be problematic in enclosed occupied spaces as we need oxygen too! Although carbon dioxide is exhaled in our own breath, in the high concentrations required to extinguish deep seated fires it is one of the most toxic extinguishing agents used. Carbon dioxide is especially popular on electrical fires because, being a gas, it does not leave any residues which might further harm the damaged equipment. (Carbon dioxide can also be used on class A fires when it is important to avoid water damage, but in this application the gas concentration must usually be maintained longer than is possible with a hand-held extinguisher.)Halons
Halons are very versatile extinguishers. They will extinguish any type of fire except class D and are highly effective even at quite low concentrations. They are the only fire extinguishing agents that are quite suitable for discharge in aircraft (carbon dioxide is too toxic in confined spaces, and other materials pose a corrosion hazard to the aircraft). They work by breaking the chemical reaction of the fire. Halons are chlorofluorocarbons and are being phased out for more environmentally-friendly alternatives. Halon fire extinguishers may cost upwards of 800 USD due to production and import restrictions.Fluorocarbons
Recently Dupont has begun marketing several nearly saturated fluorocarbons under the trademarks FE-13, FE-25, FE-36, FE-227, and FE-241. These materials are claimed to have all the advantageous properties of halons, but lower toxicity, and zero ozone depletion potential. They require about 50% greater concentration for equivalent fire quenching.Specialised materials for Class D
Class D fires involve extremely high temperatures and highly reactive fuels. For example, burning magnesium metal breaks water down to hydrogen gas and causes an explosion; breaks halon down to toxic phosgene and fluorophosgene and may cause a rapid phase transition explosion; and continues to burn even when completely smothered by nitrogen gas or carbon dioxide (in the latter case, also producing toxic carbon monoxide). Consequently, there is no one type of extinguisher agent that is approved for all class D fires; rather, there are several common types and a few rarer ones, and each must be compatibility approved for the particular hazard being guarded. Additionally, there are important differences in the way each one is operated, so the operators must receive special training. Some example class D chemistries include:
See also