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Private Box 302-372
North Harbour 0751

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Types of Fire Extinguishers

 

There are many different types of Fire Extinguishers; you will need to select the most suitable one for the type(s) of fire you anticipate. Different types of Fire Extinguishers are usually identifiable by their colour. However the manufacturing standards recently changed so that now all standards approved Fire Extinguishers are red, where they were previously different colours depending on type

Portable Fire Extinguishers are manufactured in accordance with AS 1841 currently under review

Water

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. 

Foam
(previously blue, now red with a blue band or label) Foam is suitable for use on Class A and B fires. Foam cools and creates a blanket to smother the fire. It is dangerous to use these Fire Extinguishers on live electrical equipment and hot cooking oil and fat fires as the foam is approximately 94% water.

                                               
Fighting a petrol fire with a foam extinguisher

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. full 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. 

full 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 labelled AFFF/ATC or Alcohol Resistant AFFF, which gives airport operators and firefighters the impression that the foam is okay for airport use. 

Wet Chemical
(previously oatmeal, now red with an oatmeal band or label) Wet chemical Fire Extinguishers are specifically designed for use on Class F fires however they are suitable for Class A fires also. The wet chemical physically reacts with the oil/fat creating blanket to extinguish the fire. It is dangerous to use these Fire Extinguishers on live electrical equipment
 

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. 

Dry Powder
(previously red or white, now red with a white band or label) Powder physically absorbs fuel molecules into the surface of the powder and also smothers the fire. There are three main types of powder commonly referred to: mono-ammonium phosphate based (ABE); sodium/potassium bicarbonate based (BE); and specialised powders for Class D fires. Mono-ammonium phosphate based: Suitable for use on Class A, B, C and E fires. Not effective on class F fires. Most common powder available. Sodium/Potassium bicarbonate: Suitable for use on Class B, C, E and F fires, Not very effective on Class A fires. Specialised powders for Class D fires are available and are usually designed for a specific metal such as lithium, sodium, magnesium etc.

Note Prior to standard changes in the 1990’s ABE, BE was commonly referred to as ABC and BC. 

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 2, 5, 6, 10 and 20-pound capacities. 

Carbon Dioxide
(red, now red with a black band or label) Carbon Dioxide or CO2 is suitable for use on Class B and E fires. It is not very effective on other classes of fire and may be dangerous if used on Class F fires. Its major advantage is that it is a naturally occurring gas that does not require cleaning up after use.

                                              
Carbon dioxide extinguisher

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. 

Vaporising Liquid
(previously yellow or red, now red with a yellow band) There are many different types of vaporising liquids in the market today, Halon, BCF, Cleanguard, FM200, NAF PIII… many of these are ozone depleting and/or global warming and not available in New Zealand for these reasons. Halon and BCF are no longer allowed to be imported (except for special situations) or manufactured and it is illegal to discharge them unless to control a fire.  

Note that Fire Extinguishers not manufactured to New Zealand or Australian standards may be different colours and have different rating and classification systems that may cause confusion and a potentially dangerous situation.  

Portable fire extinguishers come in a range of sizes and weights, take in to consideration the person who is likely to be carrying it. It is recommended that the Fire Extinguisher you buy has a pressure gauge and is approved by Standards Australia or Standards New Zealand.  

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 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 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.  

Short Notes:  

Graphite based dry powders generally quite effective on fires involving high melting point metals such as, Zirconium, titanium and sodium potassium.

Sodium bicarbonate-base dry chemical designed to suppress fires on most metal alkyls (pyrophoric liquids that ignite on contact with air) Such as triethylaluminium. 

Sodium chloride based dry powder is used on most class D fires involving metals such as magnesium.

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