# Fire classification

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System of categorizing fire

Demonstration of using the wrong suppressant on a grease fire

**Fire classification** is a system of categorizing [fires](/source/Fire) with regard to the type(s) of [combustible](/source/Combustion) material(s) involved, and the form(s) of suitable extinguishing agent(s).[1] Classes are often assigned letter designations, which can differ somewhat between territories.

## Standards

- [International (ISO)](/source/International_Organization_for_Standardization): ISO 3941 Classification of fires

- [Australia](/source/Australia): AS/NZS 1850

- [Europe](/source/Europe): DIN EN2 Classification of fires

- [United States](/source/United_States): NFPA 10 Chapter 5.2.1-5.2.5

## Materials and hazards

### Flammable solids: Class A (US/EU/AU)

Fires involving ordinary flammable [solids](/source/Solid) fall under **Class A**. This includes [wood](/source/Wood), [paper](/source/Paper), [fabric](/source/Fabric), [rubber](/source/Rubber), and some types of [plastics](/source/Plastic). Such fires may be extinguished by water, wet chemical suppression, or dry chemical powder.[2][3]

### Flammable liquids: Class B (US/EU/AU)

A carbon dioxide [fire extinguisher](/source/Fire_extinguisher) rated for flammable liquids and gases

Fires involving flammable [liquids](/source/Liquid) or liquefiable solids fall under **Class B**[note 1]. Examples may include [petrol/gasoline](/source/Gasoline), [oil](/source/Petroleum), [paint](/source/Paint), some [waxes](/source/Wax) & plastics, though cooking fats and oils are explicitly excluded (discussed and categorised separately below).

A solid stream of water should never be used to extinguish this type of fire because it can cause the fuel to scatter, spreading the flames.[5] The most effective way to extinguish a liquid fire is by inhibiting the chemical chain reaction of the fire, which can be done by dry chemical or [Halon](/source/Halomethane) extinguishing agents.[6] Smothering with [CO2](/source/CO2) or foam is also effective. Halon has fallen out of favor in recent times (except for aircraft fire extinguishing systems) because it is an [ozone-depleting](/source/Ozone_depletion) material (the [Montreal Protocol](/source/Montreal_Protocol) declares that Halon should no longer be used). Chemicals such as [FM-200](/source/FM-200) are now the recommended halogenated suppressant.[7]

1. **[^](#cite_ref-5)** Under the European and Australian systems, flammable liquids designated Class B require flash points no more than 93 °C (199 °F).[4]

### Flammable gases: Class B (US) / Class C (EU/AU)

Fires involving flammable [gases](/source/Gas) fall under **Class C** in the European/Australian system, and **Class B** (along with flammable liquids) in the US system.[8][6][9] This can include [natural gas](/source/Natural_gas), [hydrogen](/source/Hydrogen), [propane](/source/Propane), and [butane](/source/Butane).

Due to the nature of the fuel, these fires can be difficult to extinguish. The most effective techniques for the control of a flammable gas fire are to stop the flow of fuel (by turning off any gas taps or valves) or to displace the supply of oxygen.[3] Control of fires involving flammable gases where the gas source cannot be controlled must be carefully managed. If the flames are extinguished, but the gas continues to leak, an explosive atmosphere may be created, and the gas may find a source for reignition outside of the originally affected area. Strategies employed to manage these fires may include trying to direct or contain the fire to prevent the ignition of other fuels whilst work is done to control the fuel supply.[1]

### Combustible metals: Class D (US/EU/AU)

Fires involving combustible [metals](/source/Metal) fall under **Class D**.[9] This especially concerns [alkali metals](/source/Alkali_metal) like [lithium](/source/Lithium), [potassium](/source/Potassium) and [sodium](/source/Sodium), [alkaline earth metals](/source/Alkaline_earth_metal) such as [magnesium](/source/Magnesium), and [group 4 elements](/source/Group_4_element) such as [titanium](/source/Titanium) and [zirconium](/source/Zirconium).[2]

Metal fires represent a unique hazard because people are often unaware of the characteristics of these fires and are not properly prepared to fight them.[2] It is also not always clear what type of metal is burning. Certain metals [catch fire in contact with air or water](/source/Pyrophoricity) (for example, [sodium](/source/Sodium)), which exacerbates this risk. Monolithic masses of combustible metals do not usually represent great fire risks because heat is conducted away from hot spots so efficiently that the heat of combustion cannot be maintained. In consequence, significant heat energy is required to ignite a contiguous mass of combustible metal. Generally, metal fires are a hazard when the metal is in the form of [swarf](/source/Swarf) which combusts more rapidly than larger blocks due to the increased [surface-area-to-volume ratio](/source/Surface-area-to-volume_ratio).[6] Metal fires can be ignited by the same ignition sources that would start other common fires.[6]

Special care must be taken when extinguishing metal fires. Water and other common firefighting agents can exacerbate them.[6] The [National Fire Protection Association](/source/National_Fire_Protection_Association) recommends that metal fires be fought with dry powder extinguishing agents that work by smothering and heat absorption.[6] Different metals require different extinguishing agents and for a particular metal, agents cannot necessarily be substituted for one another. The most common agents are [sodium chloride](/source/Sodium_chloride) granules and [graphite](/source/Graphite) powder. In recent years,[*[when?](https://en.wikipedia.org/wiki/Wikipedia:Manual_of_Style/Dates_and_numbers#Chronological_items)*] powdered [copper](/source/Copper) has also come into use. These *dry powder* extinguishers should not be confused with those that contain *dry chemical* agents. The two are not the same, and only dry powder should be used to extinguish a metal fire. Using a dry chemical extinguisher in error, in place of dry powder, can be ineffective or actually increase the intensity of a metal fire.[6] Lacking a specialist extinguisher, [sand](/source/Sand) may in some cases provide a sufficient alternative, though notably sand may contain moisture which could result in a rapid, hazardous release of steam.[10]

### Electrical fires: Class C (US) / Class E (AU) / Unclassified (EU)

"Electrical fire" redirects here; not to be confused with [Electric fire](/source/Electric_fire_(disambiguation)).

Road damage from an electrical fire caused by energized fallen power line caused by [Hurricane Maria](/source/Hurricane_Maria) in [Puerto Rico](/source/Puerto_Rico)

Fires involving the danger of [electrical](/source/Electrical) hazards fall under **Class E** under the Australian system, and **Class C** under the US system.[3] The European system previously assigned this **Class E**, but no longer has a specific classification for electrical fires, instead focussing on the ignited fuel type.

Electrical fires can result from the likes of faulty electrical equipment or wiring[6] (for instance loose or corroded connections; deteriorated insulation; [electrical arcing](/source/Electric_arc)), overheating electrical components (possibly due to improper system or product design), or unintentional contact of electrical or electronic components with flammable materials. These fires can be a severe hazard to firefighters using water or other conductive agents, which upon contact with electrical sources can establish a conductive path through the firefighter to [Earth](/source/Ground_(electrical)). Such [electric shocks](/source/Electrical_shocks) have caused many firefighter deaths.[6]

Electrical fires may be fought in the same way as an ordinary combustible fire, but water, foam, and other conductive agents should not be used due to the dangers just described. Instead an extinguishing agent specifically rated for electrical fires should be used. [Carbon dioxide](/source/Carbon_dioxide) (CO2), NOVEC 1230, [FM-200](/source/FM-200), dry chemical powder extinguishers, and even baking soda are especially suited to extinguishing this sort of fire.[5] [PKP](/source/Purple-K) should be a last resort solution due to its corrosive tendencies.

Once electricity is shut off to the equipment involved, it will generally become an ordinary combustible fire.[5]

### Grease fires (cooking): Class F (EU/AU) / Class K (US)

Laboratory simulation of a [chip pan fire](/source/Chip_pan#Fire_hazard): a beaker containing wax is heated until it catches fire. A small amount of water is then poured into the beaker. The water vaporizes instantly (*[slopover](/source/Boilover#Related_phenomena)*), expanding to 1700 times its volume,[5][*[AI-retrieved source](https://en.wikipedia.org/wiki/Template:AI-retrieved_source/doc)*] ejecting a plume of burning liquid wax into the air.

Fires involving [cooking oils](/source/Cooking_oil) and [fats](/source/Fat) (greases) fall under **Class F** under the European and Australian systems, and **Class K** under the US system.[3][8] Though such fires are technically a subclass of the flammable liquid/gas class(es), the special characteristics of these types of fires, namely the higher flash point, are considered important enough to recognize them separately.

Some special extinguishers designed for this use smother the fire by turning the oil into a foam. As with Class B fires, a solid stream of water should never be used to extinguish this type because it can cause the fuel to scatter, spreading the flames.[6] Commercial kitchens may have a fire suppression system built into exhaust hoods to release an extinguishing agent onto stove tops, releasing automatically with a fusible link or manually using a pull station.[8]

If a [fire blanket](/source/Fire_blanket) is used to extinguish burning liquids the liquid can soak into the blanket. A hot liquid might then lead to the self-ignition of the blanket.[3] A blanket must therefore only be used if it does not act as a [wick](/source/Capillary_action) or if it is heavy enough to cool the liquid down below [autoignition temperature](/source/Autoignition_temperature). Preferably a lid or a similar solid item should be used to seal the burning container off from the surrounding atmosphere.[4]

### Lithium-ion cells and batteries: Class L (EU)

Fires involving lithium-ion cells and batteries, where no lithium metal is present. Class L fires are electrochemical fires. This category has been introduced into ISO 3941:2026.[11] Condensed aerosol suppression (such as Stat-X), aqueous vermiculite dispersion (AVD), F-500 encapsulator agent (F-500 EA).[12][13][14]

## Comparison

Comparison of letter codes in different regional standards.

Type of fire Class Australia Europe United States Flammable solids A A A Flammable liquids, excluding cooking fats and oils B B B Flammable gases C C B Combustible metals D D D Electrical fires E[a] Unclassified (formerly E[a]) C Grease fires (cooking fats and oils) F F K Lithium-ion cells and batteries N/A L N/A

1. ^ [***a***](#cite_ref-class-e_17-0) [***b***](#cite_ref-class-e_17-1) Technically there is no such thing as a "Class E" fire, as electricity itself does not burn. However, it is considered a dangerous and very deadly complication to a fire, therefore using the incorrect extinguishing method can result in serious injury or death. Class E, however generally refers to fires involving the danger of electricity, therefore a bracketed "(E)" is denoted on various types of extinguishers suitable for such scenarios.[15]

## See also

- [Fire control](/source/Fire_control)

- [Fire extinguisher](/source/Fire_extinguisher)

## References

1. ^ [***a***](#cite_ref-:2_1-0) [***b***](#cite_ref-:2_1-1) *Fire Detection and Suppression Systems* (Third ed.). Stillwater, OK: International Fire Service Training Association. 2005. p. 9. [ISBN](/source/ISBN_(identifier)) [0-87939-267-3](https://en.wikipedia.org/wiki/Special:BookSources/0-87939-267-3). [OCLC](/source/OCLC_(identifier)) [62785313](https://search.worldcat.org/oclc/62785313).

1. ^ [***a***](#cite_ref-IFSTA-10_2-0) [***b***](#cite_ref-IFSTA-10_2-1) [***c***](#cite_ref-IFSTA-10_2-2) *Fire Detection and Suppression Systems* (Third ed.). Stillwater, OK: International Fire Service Training Association. 2005. p. 10. [ISBN](/source/ISBN_(identifier)) [0-87939-267-3](https://en.wikipedia.org/wiki/Special:BookSources/0-87939-267-3). [OCLC](/source/OCLC_(identifier)) [62785313](https://search.worldcat.org/oclc/62785313).

1. ^ [***a***](#cite_ref-:0_3-0) [***b***](#cite_ref-:0_3-1) [***c***](#cite_ref-:0_3-2) [***d***](#cite_ref-:0_3-3) [***e***](#cite_ref-:0_3-4) ["Choosing and using fire extinguishers"](https://web.archive.org/web/20190530154609/https://www.usfa.fema.gov/prevention/outreach/extinguishers.html). *U.S. Fire Administration*. December 12, 2017. Archived from [the original](https://www.usfa.fema.gov/prevention/outreach/extinguishers.html) on May 30, 2019. Retrieved May 30, 2019.

1. ^ [***a***](#cite_ref-:6_4-0) [***b***](#cite_ref-:6_4-1) ["Flammable and combustible liquids"](https://www.worksafe.qld.gov.au/safety-and-prevention/hazards/hazardous-chemicals/specific-hazardous-chemicals/flammable-and-combustible-liquids#:~:text=The%20globally%20harmonised%20system%20for%20the%20classification,to%20the%20ADG%20code%20packing%20group%20I-III.). *WorkSafe*. March 23, 2025. Retrieved March 23, 2025. In the European/Australian system, flammable liquids are designated "Class B" having flash points no more than 93°C.

1. ^ [***a***](#cite_ref-:7_6-0) [***b***](#cite_ref-:7_6-1) [***c***](#cite_ref-:7_6-2) [***d***](#cite_ref-:7_6-3) ["Classes of Fires & Fire Extinguishers - Safety | UCLA Health"](https://www.uclahealth.org/safety/ambulatory-safety/ambulatory-fire-and-life-safety-program/classes-fires-fire-extinguishers?utm_source=chatgpt.com). *www.uclahealth.org*. Retrieved April 12, 2025.

1. ^ [***a***](#cite_ref-:3_7-0) [***b***](#cite_ref-:3_7-1) [***c***](#cite_ref-:3_7-2) [***d***](#cite_ref-:3_7-3) [***e***](#cite_ref-:3_7-4) [***f***](#cite_ref-:3_7-5) [***g***](#cite_ref-:3_7-6) [***h***](#cite_ref-:3_7-7) [***i***](#cite_ref-:3_7-8) [***j***](#cite_ref-:3_7-9) ["NFPA 10 Standard Development"](https://www.nfpa.org/codes-and-standards/nfpa-10-standard-development/10). *www.nfpa.org*. Retrieved March 31, 2025.

1. **[^](#cite_ref-8)** ["Wollongong Extinguisher Service-Australia. For Fire Extinguishers"](https://web.archive.org/web/20080508224118/http://www.fireservice.com.au/extinguisher.html). May 8, 2008. Archived from [the original](http://www.fireservice.com.au/extinguisher.html) on May 8, 2008. Retrieved March 23, 2025.

1. ^ [***a***](#cite_ref-:5_9-0) [***b***](#cite_ref-:5_9-1) [***c***](#cite_ref-:5_9-2) ["AS/NZS 1841.1:2007 4"](http://www.top-safefire.com/uploadfile/2013092821213983579.pdf) (PDF). Retrieved March 31, 2025.

1. ^ [***a***](#cite_ref-:4_10-0) [***b***](#cite_ref-:4_10-1) Standards, European. ["BS EN 2:1992 Classification of fires"](https://www.en-standard.eu/bs-en-2-1992-classification-of-fires/). *www.en-standard.eu*. Retrieved March 31, 2025.

1. **[^](#cite_ref-:11_11-0)** ["Extinguishers For Metals"](https://www.fireextinguisherguide.co.uk/types-of-fire-extinguishers/extinguishers-for-metals-2/). June 1, 2025. Retrieved June 1, 2025.

1. **[^](#cite_ref-:12_12-0)** ["ISO 3941:2026 Classification of fires"](https://www.iso.org/standard/88174.html). February 2, 2026. Retrieved February 2, 2026.

1. **[^](#cite_ref-13)** ["Testing of Aerosol Fire Extinguishing Agent for Li-ion Battery Fires"](https://hillerfire.com/resources/dnv-gl-lithium-battery-testing-report-for-stat-x/).

1. **[^](#cite_ref-14)** ["AVD"](https://firesys.com.au/wp-content/uploads/2023/09/AVD-Fire-Brochure-June-2023.pdf) (PDF).

1. **[^](#cite_ref-15)** ["Lithium Ion Battery Fire extinguisher: Australian guide"](https://www.fireextinguisheronline.com.au/blog/post/lithium-ion-battery-fire-extinguishers-a-guide). *www.fireextinguisheronline.com.au*. Retrieved March 2, 2026.

1. **[^](#cite_ref-16)** New South Wales Rural Fire Service VF - (2005) Village Firefighter Manual, pg 16.

## External links

- [Classification of Portable Fire Extinguishers](https://web.archive.org/web/20080401035246/http://www.osha.gov/doc/outreachtraining/htmlfiles/extmark.html), [Occupational Safety and Health Administration](/source/Occupational_Safety_and_Health_Administration)

- [Evacuation Plans and Procedures eTool](https://www.osha.gov/SLTC/etools/evacuation/portable_about.html), [Occupational Safety and Health Administration](/source/Occupational_Safety_and_Health_Administration)

- [Information on Fire Extinguishers](http://www.firesafe.org.uk/html/fsequip/exting.htm), The Fire Safety Advice Centre

- [Australian Fire Classes](https://futurafire.com/fire-class/), Futura Fire – Australia

- [For Fire Extinguishers](https://web.archive.org/web/20080508224118/http://www.fireservice.com.au/extinguisher.html), Wollongong Extinguisher Service-Australia

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