718 Fire Prevention Plans

ISO Fire Extinguisher Classes

The International Organization for Standardization (ISO) classifies extinguishers according to the type of fires they control. Below is a list of all ISO fire extinguisher classifications and uses:

Class A Extinguishers: Used for ordinary solid combustible materials such as wood, paper, cardboard, textiles, and some plastics. These fires typically produce glowing embers and are most effectively controlled by cooling the burning material below its ignition temperature. Class A fires are the most common type encountered in buildings and are commonly addressed with water, foam, or ABC dry chemical extinguishers.

Class B Extinguishers: Used on flammable or combustible liquids including gasoline, diesel fuel, oils, solvents, paints, and alcohols. These fires spread across the surface of the liquid fuel and require extinguishment methods that suppress vapors and separate the fuel from oxygen. Cooling alone is usually ineffective, and agents such as foam, carbon dioxide, or dry chemical are typically used.

Class C Extinguishers: Used for flammable gases such as propane, butane, methane, natural gas, and hydrogen. These fires cannot be safely extinguished unless the gas supply is shut off, as the fuel source will continue to feed the fire. Fire control focuses on isolating or stopping the gas flow, with extinguishers primarily used to control flames during shutdown.

Class D Extinguishers: Used combustible metals such as magnesium, sodium, potassium, lithium metal, and titanium. These fires burn at extremely high temperatures and can react violently with water or conventional extinguishing agents. Safe control requires specialized, metal-specific dry powder extinguishers designed to absorb heat and isolate the burning metal from oxygen.

Class F Extinguishers: Used on high-temperature cooking oils and fats, most commonly found in commercial kitchen operations. These oils burn at temperatures significantly higher than typical flammable liquids, and the use of incorrect extinguishing agents can cause splashing or flare-ups. Extinguishment relies on wet chemical agents that cool the fire and create a soapy foam layer through saponification, sealing the surface and preventing re-ignition.

Class L Extinguishers:  The 2026 publication of the International Organization for Standardization (ISO) BS ISO 3941:2026 introduced Class L as a dedicated fire class for fires involving lithium-ion (Li-ion) cells and batteries where no metallic lithium is present.

Lithium-ion fires are characterized by the serious risk of thermal runaway, intense internal heat generation, release of toxic gases, and a high likelihood of re-ignition even after visible flames are suppressed. Effective control requires specialized extinguishing agents that provide sustained cooling and encapsulation, such as AVD, water-based cooling systems, or other lithium-ion-specific suppression technologies.

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