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A fire extinguisher is an Active Fire Protection device to put out fires, often in an emergency situation. They consist of a pressurized container of chemicals that when discharged can put out a Fire . It is important to familiarize yourself with the use of fire extinguishers in your vicinity, as improper or untimely use may be counterproductive. HISTORY The first version of the modern fire extinguisher was invented in the United Kingdom by Captain George William Manby in 1816 , consisting of a copper vessel of 3 Gallon s (13.6 Litre s) of pearl ash ( Potassium Carbonate ) solution under Compressed Air pressure. The late 19th Century saw the invention of the Soda-Acid extinguisher where a cylinder contained 1 or 2 gallons of water that had Sodium Bicarbonate mixed in it. Suspended in the cylinder was a vial containing concentrated Sulfuric Acid . The vial of acid was broken by one of two means depending on the type of extinguisher. One means involved the use of a plunger that broke the acid vial, while the second involved the release of a lead bung that held the vial closed. Once the acid was mixed with the bicarbonate solution, Carbon Dioxide gas would be expelled and this would in turn pressurize the water. The pressurized water was forced from the canister through a nozzle or short length of hose. Around 1912 Pyrene pioneered the Carbon Tetrachloride or CTC extinguisher, where the liquid was expelled from a Brass or Chrome container by handpump, usually of 1 imperial Quart (1.1 L) or 1 imperial Pint (0.6 L) capacity but also made in up to 2 imperial gallon (9 L) size, onto a fire. The CTC vapourised and extinguished the flames by chemical reaction. This extinguisher was suitable for liquid and electrical fires and was popular in motor vehicles for the next 60 years. The vapour and combustion by-products were highly toxic and deaths did occur from using these extinguishers in confined spaces. CONSTRUCTION General A fire extinguisher is usually made using the following components :
One of the most common types of fire extinguishers, a portable stored pressure type, is shown in the picture. The shape, proportions and details may vary according to the model, but the components are as above. Bottle Bottle characteristics vary according to the use of the extinguisher. Basically, there are two classes of bottles :
CLASSIFICATION .]] Europe Three classes are defined according to the European Standard (EN 3):
In addition to this, some other categories appear from time to time
Classes A and B are designated by a number, expressing the capability of that particular model to extinguish a specified fire, thus defining a ''fire class'' as :
The standard rating for class A and B range from 5 to 233 according to the Fibonacci Sequence : 5, 8, 13, 21, 34, 55, 89, (113), 144, (168), 233. Values 113 (= 89 + 34) and 168 (= 113 + 55) are not part of the Fibonacci sequence, but were used in the past, and remain valid. Ratings 5 and 8 are used only for class A fires. Thus, a 13A 168B fire class extinguisher, if properly used by a professional, will put out fires both from a wood stack 1.3 metre long and from a circular basin containing 168 litre of liquid, water below and ''n''-heptane floating on water. Class C has no numerical rating; according to EN3 standards, the fulfilment of the gas extinguishing test is shown by a C after the designation of fire classes A and B; in the above example, a '''13A 168 B C''' extinguisher will also put out a flame created by LPG in standard test conditions. (The LPG flame, mind you, is put out, but the LPG flow is not discontinued, so putting out the flame may be more dangerous than letting it burn). Class D is not covered by EN3. Class E has been deleted in EN3; a dielectric test is performed if required by the manufacturer, and the capability of operating on live electrical equipment without electrocuting hazard is now shown by a pictogram. A good 6 kg dry powder extinguisher will rate 21A 233B C fire class; a 5 kg carbon dioxide will rate '''89B'''. A 1 kg extinguisher for cars or small leisure boats rates '''34B C''' or, if multi-purpose, '''8A 34B C''' (passing C-class test is dubious for small extinguishers). United States The National Fire Protection Association has created five classes of fire extinguishers, A, B, C, D, and K.
United States ratings In the US, extinguishers also receive ratings for Class A and B fires.
Fire extinguishers are often designed to combat more than one class of fire. Commonly available are A (water), BC (carbon dioxide), and ABC (dry chemical). MARKINGS Australia United Kingdom Before 1997, UK Fire Extinguishers were also colour coded but slightly differently: Continental Europe (CEN countries other than UK) No colour coding imposed : All extinguishers shall be signal red ( RAL 3000). Recently, some voluntary color coding has appeared, however different from the UK National Addendum to EN 3. United States Fire extinguishers in the US are not color coded, though most Class D extinguishers are colored yellow. Extinguishers are marked with symbols, formerly with colored geometric symbols, though pictograms are now used. Some extinguishers use both the old symbols and modern pictograms. No official pictogram exists for Class D extinguishers, though training manuals sometimes show a drill press with shavings burning underneath. CHEMISTRIES A fire extinguisher may emit a solid, liquid, or gaseous chemical. Water Water is the most common chemical for class A fires and is quite effective as one would imagine. Water has a great effect on cooling the fuel surfaces and thereby reducing the pyrolysis rate of the fuel. The gaseous effect is minor for extinguishers, but water fog nozzles used by fire brigades creates water droplets small enough to be able to extinguish flaming gases as well. The smaller the droplets, the bigger the gaseous effect. 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 may or may not help extinguishing class B fires. It depends on whether or not the liquid's molecules are Polar Molecule s. If the liquid that is burning is polar (such as alcohol), there won't be any problem. If the liquid is Nonpolar (such as large Hydrocarbons , like Petroleum ), the water will merely spread the flames around. Similarly, water sprayed on an electrical fire (US: Class C, UK: Class E) will probably 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). Special spray nozzles, equipped with tiny rotating devices called ''spiracles'' will replace the continuous water jet with a succession of droplets, greatly increasing the Resistivity of the jet. These shall however be used by skilled personnel, since improper handling of the nozzle may restore continuity of the water jet. Foams fire with a foam extinguisher]] Foam s 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 and break the interaction between the flames and the fuel surface. 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. A "protein foam" was used for fire suppression in aviation crashes until the 1960s development of "light water", also known as "Aqueous Film-Forming Foam" (or AFFF ). Carbon dioxide (later sodium bicarbonate) extinguishers were used to knock down the flames and foam used to prevent re-ignition of the fuel fumes. "Foaming the runway" can reduce friction and sparks in a crash landing, and protein foam continued to be used for that purpose, although FAA regulations prohibited reliance upon its use for suppression. Dry Powder ("Dry Chemical" in the US) For classes B and C, a dry powder is used. There are two main dry powder chemistries in use:
BC Powder has a slight Saponification effect on cooking oils & fats due to its alkalinity & sometimes used to be specified for kitchens prior to the invention of Wet Chemical extinguishers. Where an extremely fast knockdown is required potassium bicarbonate ( Purple K ) extinguishers are used. A particular blend also containing Urea ( Monnex ) decrepitates upon exposure to heat increasing the surface area of the powder particles and providing very rapid knockdown.
Both types of powders can also be used on electrical fires, but provide a significant cleanup and corrosion problem that is likely to make the electrical equipment unsalvageable. Wet potassium salts ('Wet Chemical') Most class F (class K in the US) 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 F extinguishers cannot be used for class B fires. The misting also helps to prevent splashing the blazing oil. Carbon dioxide Carbon Dioxide (CO2) also works on classes B and C/E and works by suffocating the fire. Carbon dioxide will not burn and displaces air. Carbon dioxide can be used on electrical fires because, being a gas, it does not leave 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.) Carbon dioxide extinguishers have a horn on the end of the hose. Due to the extreme cold of the carbon dioxide that is expelled from an extinguisher, it should not be touched. Halons Halon s are very versatile extinguishers. They will extinguish most types of fire except class D & K/F and are highly effective even at quite low concentrations (less than 5%). Halon is a poor extinguisher for Class A fires, a nine pound Halon extinguisher only receives a 1-A rating and tends to be easily deflected by the wind. They are the only fire extinguishing agents that are quite suitable for discharge in Aircraft (as other materials pose a Corrosion hazard to the aircraft). The major extinguishing effect is by disturbing the thermal balance of the flame, and to a small extent by inhibiting the chemical reaction of the fire. Halons are Chlorofluorocarbon s causing damage to the Ozone Layer and are being phased out for more environmentally-friendly alternatives. Halon fire extinguishers may cost upwards of 800 US dollars due to production and import restrictions. Halon extinguishers used to be widely used in vehicles and computer suites. It is mildly toxic in confined spaces, but to a far less extent than its predecessors such as carbon tetrachloride, chlorobromomethane and methyl bromide. Since 1992 the sale and service of Halon extinguishers has been made illegal in Canada except for in a few rare cases. In the UK and Europe Halons were made illegal at the end of 2003, except for certain specific aircraft and Law Enforcement uses. This appears to be at least partially in response to the Montreal Protocol and effort by the United Nations Environment Programme ( UNEP ) to combat release of quantities of harmful chemicals into the atmosphere. Fluorocarbons Recently, Dupont has begun marketing several nearly saturated Fluorocarbon s under the Trademark s 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:
MAINTENANCE To operate safely and effectively, extinguishers should be subject to regular maintenance by a competent person and most countries in the world require this maintenance as part of fire safety legislation. Lack of maintenance can lead to an extinguisher not discharging when required, or worse still, rupturing when pressurised. Deaths have occurred, even in recent times, from corroded extinguishers exploding. There is no all-encompassing fire code in the United States. Generally, most municipalities (by adoption of the International Fire Code ) require inspections every 30 days to ensure the unit is pressurized and unobstructed (done by an employee of the facility) and an annual inspection by a qualified technician. Also, a 5 yearly hydraulic pressure testing for all types of extinguisher is required. Through electronic monitoring of fire extinguishers the 30 day inspection can be eliminated. In the UK, three types of maintenance are required:
Recommended locations in houses It is recommended that houses have a fire extinguisher accessible on every floor, especially in the Kitchen . For each room it important to choose a fire extinguisher of the type appropriate to the fire risk. SEE ALSO
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