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Fire Classifications for Fire Extinguishers

Australian Standard AS/NZS 1850 sets out requirements for the classification, performance testing and rating of fire extinguishers. This article explores the classification system (class) for fire extinguishers.

CEO, Firewize
17 Nov, 2020
Portable Fire Extinguisher Classifications Class A, B, C, D, E, F

Australian Standard AS/NZS 1850:2009 covers the classification, rating and performance testing of fire extinguishers.

The Standard was originally developed to define a system of classification and rating of fire extinguishers. This classification system also defines a method of test in order to determine if an extinguisher can be given a rating appropriate to the class of fire.

The ultimate classification and rating of an extinguisher or its recommended use is based on its fire extinguishing potential, as determined by the appropriate tests.

Six Classifications of Fire Extinguishers

Fires may be categorised in one of six classes;

  1. Class A - Combustible Materials
  2. Class B - Flammable Liquids
  3. Class C - Flammable Gasses
  4. Class D - Combustible Metals
  5. Class E - Electrical Equipment
  6. Class F - Cooking oil, fat, grease & heated waxes

Class A - Combustible Materials

A Class A fire is one that involves carbonaceous solids. A carbonaceous solid is one where the primary chemical element is carbon that serves as the base fuel.  Carbonaceous solids commonly found around the home, workshop or workplace include cardboard, timber, cloth, dry garden clippings, etc.

Almost every type of fire extinguisher can be used with a Class A fire however Carbon Dioxide fire extinguishers are less effective than the other types.

Class B - Flammable Liquids

A Class B fire is one that involves flammable liquids. The globally harmonised system ("GHS") for the classification and labelling of chemicals GHS defines a flammable liquid as a liquid having a flash point of not more than 93°C.

A flammable liquid is classified in one of four categories for this class according to the following table:

GHS Category Criteria
1 Flash point <23°C and initial boiling point < 35oC
2 Flash point <23°C and initial boiling point > 35°C
3 Flash point >23°C and < 60°C
4 Flash point >60°C and < 93°C

A service station, workshop, garden shed or paint store are some of the most common locations that a member of the public might come into contact with flammable and combustible liquids on a regular basis.

Class C - Flammable Gasses

A Class C fire is one that involves flammable gasses. There are 9 classes of dangerous goods, and Division 2.1 - defines a Flammable Gas as material that is a gas at 20ºC or below and 101.3 kPa of pressure (ambient temperature and pressure), i.e. the material has a boiling point of 20ºC at sea level and:

  • Is ignitable when in a mixture of 13 percent or less by volume with air.
  • Or has a flammability range with air of at least 12% regardless of the lower limit. 

Class D - Combustible Metals

A Class D fire is one that involves combustible metals. A combustible metal is defined as any metal composed of distinct particles or pieces, regardless of shape, size or chemical composition that will burn.

The following is a list of combustible metals that require a Class D fire extinguisher:

  • calcium
  • cerium
  • cesium
  • lithium
  • lutetium
  • magnesium and magnesium alloys
  • neodymium
  • phosphorus
  • potassium
  • potassium-sodium alloys
  • rubidium
  • sodium
  • strontium
  • aluminum (powder)
  • beryllium (powder)
  • nickel catalyst (Raney)
  • titanium (powder)
  • zinc (powder)
  • zirconium (powder)
  • aluminum phosphide
  • calcium carbide
  • gallium arsenide
  • gallium phosphide
  • lithium aluminum deuteride
  • lithium aluminum hydride
  • lithium aluminum hydride bis(tetrahydrofuran)
  • lithium amide
  • lithium borohydride
  • lithium-6 deuteride
  • lithium hydride
  • lithium tetraphenylborate tris(1,2-dimethoxyethane)
  • lithium tri-tert-butoxyaluminohydride
  • magnesium hydride
  • phosphorus pentasulfide
  • potassium hydride
  • Red-Al
  • sodium aluminum hydride
  • sodium bis(2-methoxyethoxy)aluminum hydride in toluene
  • sodium borohydride
  • sodium borohydride cobalt-doped
  • sodium borohydride on alumina
  • sodium hydride
  • zinc phosphide

Class E - Electrical Equipment

A Class E fire is one that involves electrical equipment. Electrical equipment includes any machine powered by electricity. It usually consists of an enclosure, a variety of electrical components, and often a power switch.

More specifically, electrical equipment refers to the individual components of an electrical distribution system. These components may involve:

  • Electric switchboards
  • Distribution boards
  • Circuit breakers and disconnects
  • Transformers
  • Electricity meters

The National Construction Code ("NCC") requires a Class A(E) or Class (E) fire extinguisher adjacent to an emergency services switchboard is one which sustains emergency equipment operating in the emergency mode.

Class F - Cooking oils and fats

A Class F fire is one that involves cooking oils and fats. Technically a fire fires involving cooking oils and fats are actually a type of fire caused by flammable liquids or gases at high temperatures. These type of fires differ from conventional fires because they burn at incredibly high temperatures.

Cooking oil and fat fires are a major cause of fires and loss in the home. Kitchen fires triggered by cooking oil or fats cause the fastest-spreading destruction of any kind of fire.

The ideal type of fire extinguisher for burning oils and fat fires is a "wet chemical" fire extinguisher.  A wet chemical fire extinguisher is red in colour with a beige band around the extinguisher cylinder.

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