Firefighters put out fires by selecting an extinguishing medium that matches the burning material and hazard, then applying that medium through equipment capable of delivering it in the required form and quantity.
Water remains the most common medium for many ordinary-combustible fires, but it is not appropriate for every hazard. Foam, dry chemical, carbon dioxide, wet chemical, Class D agents, water mist, and engineered fixed-system agents all solve different fire problems.
The useful question is therefore not simply what firefighters use, but which extinguishing medium and delivery method fit the specific fire.
What Extinguishing Agents Do Firefighters Use?
Fire classification varies between jurisdictions. Under the U.S. system, the main classes are A, B, C, D, and K.
Water and Water-Based Agents
Water is primarily used on Class A ordinary combustibles such as wood, paper, cloth, and many common solid materials. Its main suppression mechanism is cooling.
Standard water application is not appropriate for energized electrical equipment, combustible metals, or many flammable-liquid situations unless the specific firefighting method and equipment are designed for that hazard.
Foam
Firefighting foam can be used for selected Class A and Class B hazards. In flammable-liquid applications, the foam layer can separate fuel vapors from the flame and help control vapor release.
Foam selection depends on the fuel involved and the foam formulation. A foam suitable for one liquid hazard should not be assumed suitable for every flammable liquid.
Dry Chemical
Dry chemical agents interrupt flame chemistry and are used in portable extinguishers and fixed systems.
The fire classes covered depend on the formulation and rating. ABC multipurpose dry chemical and BC dry chemical are not interchangeable descriptions.
Dry chemical also leaves agent residue, which matters where contamination or cleanup is a concern.
Carbon Dioxide
CO₂ is used for appropriate Class B and energized-electrical hazards. It is electrically non-conductive and does not leave extinguishing-agent residue.
Because CO₂ can create a hazardous atmosphere by reducing oxygen concentration, enclosed-space applications require appropriate system design and personnel safeguards.
Wet Chemical
Wet chemical agents are associated particularly with Class K commercial-cooking hazards involving hot cooking oils and fats. The agent and appliance protection system should be selected for the specific cooking hazard.
Class D Agents
Combustible-metal fires require agents matched to the specific metal. A generic water, foam, CO₂, or multipurpose extinguisher should not be assumed suitable for a Class D fire.
Engineered Fixed-System Agents
Clean agents, inert gases, aerosols, water mist, dry chemical, CO₂, and other fixed-system technologies can protect defined hazards or enclosures. Selection depends on the fuel, enclosure, occupancy, equipment sensitivity, required suppression mechanism, and applicable system design requirements.
How Are Extinguishing Agents Delivered?
Portable Fire Extinguishers
Portable extinguishers store a defined agent and allow early manual application to a fire within the extinguisher’s rated capability.
Hose, Nozzle, and Monitor Systems
Water or foam can be supplied through pumps, hose, nozzles, and monitors. Required flow, pressure, stream pattern, reach, and operator control depend on the incident and equipment configuration.
Foam Proportioning and Application Equipment
Foam systems combine water and foam concentrate at the required proportion before the finished foam is applied through suitable discharge equipment.
Fixed Fire-Suppression Systems
A fixed system stores or generates its extinguishing medium and releases it through an engineered distribution or discharge arrangement. Detection, control, alarms, interlocks, enclosure conditions, and discharge design can be as important as the agent itself.
How Do Firefighters Choose What to Use?
Selection starts with the hazard:
- What material is burning?
- Is electrical equipment still energized?
- Is the fire in an open area or enclosed space?
- Are people present?
- Will water or agent residue damage critical equipment?
- Is cooling required after flame suppression?
- Can the agent reach the fuel effectively?
- Is there a risk of re-ignition?
- What firefighting system or equipment is already available at the site?
Cooling, oxygen reduction, fuel isolation, and chemical flame inhibition are different suppression mechanisms. The correct method depends on which mechanism can safely control the specific fire.
For a separate discussion of combustion fundamentals, see The 3 Elements of the Fire Triangle.
For firefighting hand tools and forcible-entry equipment, see What Tools Do Firefighters Use?.