A fire extinguisher is an active fire protection device used to extinguish or control a fire, often in emergency situations. Typically, a fire extinguisher consists of a handheld cylindrical pressure vessel containing an agent which can be discharged to extinguish a fire.
The typical steps for operating a fire extinguisher (described by the acronym "PASS") are the following:
P - Pull the safety pin
A - Aim the nozzle at the base of the fire, from a safe distance (about six feet away)
S - Squeeze the handle
S - Sweep the extinguisher from side to side while aiming at the base of the fire
There are various types of extinguishers, which are used for different types of fires; using the wrong type can worsen the fire hazard, but using the right one can better the situation.
The modern fire extinguisher was invented by British Captain George William Manby in 1818Insert non-formatted text here; it consisted of a copper vessel of 3 gallons (13.6 litres) of pearl ash (potassium carbonate) solution contained within compressed air.
The soda-acid extinguisher was invented in the 19th century, which contained a cylinder of 1 or 2 gallons of water with sodium bicarbonate mixed into it. A vial was suspended in the cylinder containing concentrated sulphuric acid. Depending on the type of extinguisher, the vial of acid could be broken in one of two ways. One used a plunger to break the acid vial, while the second released a lead bung that held the vial closed. Once the acid was mixed with the bicarbonate solution, carbon dioxide gas was expelled and thereby pressurize the water. The pressurized water was forced from the canister through a nozzle or short length of hose.
Around 1912 Pyrene invented the carbon tetrachloride or CTC extinguisher, which expelled the liquid from a brass or chrome container by a handpump; it was usually of 1 imperial quart (1.1 L) or 1 imperial pint (0.6 L) capacity but was also available in up to 2 imperial gallon (9 L) size. The CTC vapourised and extinguished the flames by chemical reaction. The 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 could cause death in confined spaces.
Internationally there are several accepted classification methods for hand-held fire extinguishers. Each classification is useful in fighting fires with a particular group of fuel.
In Australia, yellow (Halon) fire extinguishers are illegal to own or use on a fire, unless an essential use exemption has been granted.
According to the standard BS EN 3, fire extinguishers in the United Kingdom as all throughout Europe are red RAL 3000, and a band or circle of a second color covering at least 5% of the surface area of the extinguisher indicates the contents. Before 1997, the entire body of the fire extinguisher was colour coded according to the type of extinguishing agent.
The UK recognizes six fire classes. Class A fires involve organic solids such as paper and wood. Class B fires involve flammable liquids. Class C fires involve flammable gases. Class D fires involve metals, Class E fires involve live electrical items and Class F fires involve cooking fat and oil. Fire extinguishing capacity is rated by fire class using numbers and letters such as 13A, 55B. EN 3 does not recognize a separate E class - this is an additional feature requiring special testing (dielectric test per EN3-4) and NOT passing this test makes it compulsory to add a special label (pictogram) indicating the inability to isolate the user from a live electric source.
There is no official standard in the United States for the color of fire extinguishers, though they are typically red, except for Class D extinguishers, which are usually yellow. Extinguishers are marked with pictograms depicting the types of fires that the extinguisher is approved to fight. In the past, extinguishers were marked with colored geometric symbols, and some extinguishers still use both symbols. No official pictogram exists for Class D extinguishers, though training manuals sometimes show a drill press with shavings burning underneath. The types of fires and additional standards are described in NFPA 10: Standard for Portable Fire Extinguishers.
The Underwriters Laboratories rate fire extinguishing capacity in accordance with UL/ANSI 711: Rating and Fire Testing of Fire Extinguishers. The ratings are described using numbers preceding the class letter, such as 1-A:10-B:C. The number preceding the A multiplied by 1.25 gives the equivalent extinguishing capability in gallons of water. The number preceding the B indicates the size of fire in square feet that an ordinary user should be able to extinguish. There is no additional rating for class C, as it only indicates that the extinguishing agent will not conduct electricity, and an extinguisher will never have a rating of just C.
A fire extinguisher may emit a solid, liquid, or gaseous chemical.
Water is the most common chemical for class A fires and if available in sufficient volume can be quite effective. Water extinguishes flame by cooling the fuel surfaces and thereby reduces the pyrolysis rate of the fuel. The effectiveness against the combustion sustaining effect of burning gases is minor for extinguishers, but water fog nozzles used by fire departments create water droplets small enough to be able to extinguish flaming gases as well. The smaller the droplets, the greater the effectiveness water has against burning gases.
Most water based extinguishers also contain traces of other chemicals to prevent the extinguisher from rusting. Some also contain surfactants which help the water penetrate deep into the burning material and cling better to steep surfaces.
Water may or may not help extinguish class B fires. It depends on whether or not the liquid's molecules are polar molecules. If the liquid that is burning is polar (such as alcohol), then water can be an effective means of extinguishment. If the liquid is nonpolar (such as large hydrocarbons, like petroleum or cooking oils), the water will merely spread the flames around.
Similarly, water sprayed on an electrical fire (UK: Class E, US: Class C) increases the likelihood that the operator will receive an electric shock. However, if the power can be reliably disconnected and a carbon dioxide or halon extinguisher is not available, clean water actually causes less damage to electrical equipment than will either foam or dry powders. Special spray nozzles called fog nozzles, equipped with tiny rotating devices called spiracles replace the continuous water jet with a succession of droplets, greatly increasing the resistivity of the jet. These should however be used by skilled personnel, since these complex nozzle assemblies may be difficult to use effectively without training. --Water extinguishers have a 2 1/2 gallon capacity.
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 and break the interaction between the flames and the fuel surface. 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 continue to be used for that purpose, although FAA regulations prohibit reliance upon its use for reduction of the risk of ignition in gear up landing.
AFFF in concentrations less than 3% is not acceptable to the FAA for use on airports. The 1% concentrate that is available should not be used in ARFF applications because of the difficulty in consistently providing an accurate mixture. Any attempt to use 1% foam would necessitate the installation of a computer-controlled system and each load would have to be checked carefully.
There are other means of proportioning but they are not accurate at low percentage proportioning settings. Experience and testing have shown there is no consistency between different loads. Also, at low concentration, there is no room for error on the fire ground. If a mixture is discharged on the lean side, the result is plain water being applied to a fuel fire. An overly rich mixture can also be a problem, because concentrate is consumed at higher than the designed rate.
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 specialized "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.
The FAA does not approve the use of alcohol type foams in ARFF vehicles on airports and FAA Best Practices Part 139 does not provide for substituting Aqueous Film Forming Foam (AFFF) with alcohol type foams.
Alcohol type foams are typically used by city and industrial fire departments because they are effective on both hydrocarbons, such as gasoline, and polar solvents such as alcohol. Most fire department will only carry only one type of foam on their trucks if they use alcohol type foams.
These foams are labeled AFFF/ATC or Alcohol Resistant AFFF, which gives airport operators and firefighters the impression that the foam is okay for airport use.
For classes B and C, a dry chemical powder is used. There are two main dry powder chemistries in use:
* BC powder is either sodium bicarbonate or potassium bicarbonate, finely powdered and propelled by carbon dioxide or nitrogen. Similarly to almost all extinguishing agents the powders acts as a thermal ballast making the flames too cool for the chemical reactions to continue. Some powders also provide a minor chemical inhibition, although this effect is relatively weak. These powders thus provide rapid knockdown of flame fronts, but may not keep the fire suppressed. Consequently, they are often used in conjunction with foam for attacking large class B fires. BC extinguishers are often kept in small vehicles since they provide good knockdown of a rapidly flaring class B fire, from a small package. BC Powder has a slight saponification effect on cooking oils & fats due to its alkalinity and 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.
* ABC powder is monoammonium phosphate and/or ammonium sulphate. As well as suppressing the flame in the air, it also melts at a low temperature to form a layer of slag which excludes the gas and heat transfer at the fuel surface. For this reason it can also be effective against class A fires. ABC powder is usually the best agent for fires involving multiple classes. However it is less effective against three-dimensional class A fires, or those with a complex or porous structure. Foams or water are better in those cases.
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. Dry chemical extinguishers typically come in 2½, 5, 6, 10 and 20-pound capacities (and 30-pound Amerex High preformace models).
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 (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 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). Halon fire-suppression systems are also incorporated into some armored fighting vehicles, such as the M1 Abrams tank. 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 chlorofluorocarbons 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 due to environmental concerns except for in a few rare cases, as per the Montreal Protocol.
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.
Like Halon, phosphorus tribromide is a flame chemistry poison, marketed under the brand name PhostrEx. PhostrEx is a liquid which needs a propellant, such as compressed nitrogen and/or helium, to disperse onto a fire. As a fire extinguisher, PhostrEx is much more potent than Halon, making it particularly appealing for aviation use as a lightweight substitute. Unlike Halon, PhostrEx reacts quickly with atmospheric moisture to break down into phosphorous acid and hydrogen bromide, neither of which harms the earth's ozone layer.
High concentrations of PhostrEx can cause skin blistering and eye irritation, but since so little is needed to put out flames this problem is not a significant risk, especially in applications where dispersal is confined within an engine compartment. Any skin or eye contact with PhostrEx should be rinsed with ordinary water as soon as practical. PhostrEx is not especially corrosive to metals, although it can tarnish some. The U.S. EPA and FAA both approved PhostrEx, and the substance will find its first major use in Eclipse Aviation's jet aircraft as an engine fire suppression system.
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.
Class D fires involve extremely high temperatures and highly reactive fuels. For example, burning magnesium metal breaks water down to hydrogen gas and excites the fire; 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:
* Granulated sodium chloride and graphite applied by a shaker, scoop or shovel. Suitable for sodium, potassium, magnesium, titanium, aluminium, and most other metal fires.
* Powdered graphite, applied with a long handled scoop, is preferred for fires in fine powders of reactive metals, where the blast of pressure from an extinguisher may stir up the powder and cause a dust explosion. Graphite both smothers the fire and conducts away heat.
* Finely powdered copper propelled by compressed argon is the currently preferred method for lithium fires. It smothers the fire, dilutes the fuel, and conducts away heat. It is capable of clinging to dripping molten lithium on vertical surfaces. Graphite can also be used on lithium fires but only on a level surface.
* Other materials sometimes used include powdered sodium carbonate, powdered dolomite and argon gas.
* As a very poor last resort dry sand may be used to smother a metal fire if nothing else is available, applied with a long-handled shovel to avoid the operator receiving flash burns. Sand is, however, notorious for collecting moisture, and even the smallest trace of moisture may result in a steam explosion, spattering burning molten metal around.
Fire extinguishers are typically fitted in buildings at an easily-accessible location, such as against a wall in a high-traffic area. They are also often fitted to motor vehicles, water and aircraft - this is required by law in many juristictions, for identified classes of vehicles. Under NFPA 10 all commercial vehicles must carry at least one fire extinguisher (size/UL rating depending on type of vechical and cargo(ie. fuel tanker typically must have a 20lb. when most others can carry a 5lb.).
Most countries in the world require regular fire extinguisher maintenance by a competent person to operate safely and effectively, as part of fire safety legislation. Lack of maintenance can lead to an extinguisher not discharging when required, or rupturing when pressurized. 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. Hydrostatic pressure testing for all types of extinguishers is also required, generally every five years for water and CO2 models up to every 12 years for dry chemical models.
Recently the National Fire Protection Association and ICC voted to allow for the elimination of the 30 day inspection requirement so long as the fire extinguisher is monitored electronically. According to NFPA, the system must provide record keeping in the form of an electronic event log at the control panel. The system must also constantly monitor an extinguisher’s physical presence, internal pressure and whether an obstruction exists that could prevent ready access. In the event that any of the above conditions are found, the system must send an alert to officials so they can immediately rectify the situation. Electronic monitoring can be wired or wireless.
In the UK, three types of maintenance are required:
* Basic Service: All types of extinguisher require a basic inspection annually to check weight, correct pressure (using a special tool, not just looking at the gauge) & for signs of damage or corrosion; (the powder used in Dry Powder type fire extinguishers tend to settle, the technician is unable to physical confirm this and is forced to open the extinguisher) Tests conducted by SABS in South Africa have proven that by adding "powder indicators" steel balls would give the technician or owner the opportunity to first shake the dry-powder fire extinguisher to physically hear/feel the movement of the indicating balls thus confirming the condition of the powder. These indicators can be further used to test the different types of powders presently available.
* Extended Service: Water, Wet Chemical, Foam & Powder extinguishers require every five years a more detailed examination including a test discharge of the extinguisher & recharging if satisfactory;
* Overhaul: CO2 extinguishers, due to their high operating pressure, are subject to pressure vessel safety legislation and must be hydraulic pressure tested & date stamped every 10 years.