Firefighting

Firefighting is the work of controlling and extinguishing fires, together with the rescue and protection tasks that go with it. A glossary published by the US Nuclear Regulatory Commission treats it as fire suppression, either manual, with hoses, portable extinguishers or manually operated fixed systems, or automatic, by systems using water, Halon or carbon dioxide. Besides attacking the fire, fire services search for and rescue occupants, protect property and limit harm to the environment. Early action matters: an automatic extinguishing system generally intervenes while the fire is still in its growth stage, so the fire cannot become fully developed. A fire service that arrives after flashover, by contrast, may have no effect on the fire itself. Tactics differ between countries and situations; the Dutch fire service, for example, prefers to fight building fires from outside and attacks from inside only when an exterior attack fails and this can be done safely.

Who fights fires and what they aim for

Many fires are fought first by the people who discover them. In the decision process that Bryan describes, an occupant who has recognised a fire chooses between flight, leaving the building, and fight, fetching an extinguisher or raising the alarm. In a British study of 2,193 people at 952 fires, 14.9 % made fighting the fire their first action. In a US study of residential fires the share was 10.4 %, and in both studies men were more often active in fighting the fire. The Australian handbook to the Fire Safety Verification Method (print version 1.1, 2020) notes that many smouldering and small flaming fires are dealt with by occupants and never reported. Estimates of how often design fires occur are therefore commonly based on reported fires, ignoring suppression by occupants.

At industrial sites, trained staff and private fire brigades take part as well. The US glossary describes a fire watch: people trained to recognise fire hazards, to use fire extinguishers and to follow the proper notification procedures. At US nuclear power plants, the fire brigade operates fixed systems by hand, removes fuel sources, switches off electrical systems and uses portable extinguishers and hose streams. The International Fire Engineering Guidelines (2005 edition) include such private brigades, for example the brigade of an industrial complex, in their analysis of fire service intervention.

The aims of firefighting go beyond putting out flames. According to the guidelines, fire services are commonly responsible for search and rescue, containing and extinguishing the fire and protecting property. They also protect the environment and the community, for example from contaminated firefighting water running off a chemical warehouse. Control means that the fire is kept from growing, for instance by wetting nearby combustibles and cooling the hot gases under the ceiling, while extinguishment is the complete suppression of all burning material. An attack can be offensive, applying water to the fire, or defensive, using hose streams to protect adjoining property, or both.

How fires are put out

Extinguishing mechanisms work by separating the fuel from the flame, removing or diluting the oxygen, cooling the fuel or the flame, or interfering with the chemistry of combustion. Several of them often act at once. Water on a burning solid cools the solid, so that it releases less flammable gas, and cools the flame, so that less heat reaches the fuel. Steam can keep oxygen away in some confined conditions, and a fog of fine droplets can block heat radiation. Water is the most common extinguishing agent because it is widely available, cheap and able to absorb a great deal of heat. Fleming gives 9,280 Btu for one US gallon of water heated from 21 °C and turned into steam at 100 °C, which is about 2.6 MJ for every litre.

Firefighting objectives and mechanisms must match the incident. Based on Iqbal and Salley (2004), p. B-15 and Fleming (2002), p. 4-72.

Water does not suit every fire. It is inappropriate for certain water-reactive materials, with which it can produce heat, flammable or toxic gases or explosions. Most hydrocarbon fuels are lighter than water and do not mix with it, so they float on the water and keep burning. On hot oil or fat, water can sink below the surface, turn to steam and throw out burning oil in a boilover. In the US classification of fires, water must never be used on Class D fires, which involve combustible metals such as magnesium, sodium and lithium.

Foam is the main alternative to water, used mostly on burning liquids. Firefighting foam consists of air-filled bubbles made from water mixed with a foam concentrate, typically at 1, 3 or 6 percent. It floats on the fuel and forms a layer that keeps air out and stops the fuel from evaporating, so the fire goes out once the whole surface is covered. Low-expansion foam works well on a pool of liquid but much less well on running fuel or a pressurised spray, where an extra agent such as dry chemical is used. Heat breaks foam down, so it must be applied fast enough and in large enough amounts to keep a layer over the fuel. A ruptured foam blanket can let the fire burn back and put firefighters at risk.

Dry chemical powders probably act mainly on the chemistry of the flame, and they also absorb heat, block radiation and, in one type, coat the burning surface. They leave residue that needs thorough cleaning and can corrode equipment. In a 2001 fire at the Point Beach nuclear plant in the United States, the fire brigade discharged about 32 kg of dry chemical from three extinguishers without success. The fire was finally put out with 57 to 76 L of water, and white dust covered large parts of the containment building. Gaseous agents such as Halon 1301 put out visible flames almost at once, but glowing combustion inside a solid fuel can continue and re-ignite when air is let back in.

Manual firefighting: extinguishers, hoses and water

A Fire extinguisher is one of the means of manual suppression named in the US glossary, alongside hoses and manually operated fixed systems. In the United States, its rating combines a number for relative effectiveness with a letter for each class of fire on which it has proved effective. Class A covers ordinary combustibles such as wood and paper, B flammable liquids and gases, and C fires involving energised electrical equipment. Class D covers combustible metals and K cooking oils and fats. Dry chemical agents are safe on electrical fires as far as electric shock is concerned, but they can damage delicate equipment.

Hose lines need a water supply that the fire service can reach. A Fire hydrant provides water to the pumpers of the fire department. In tall buildings, Dry and wet risers carry water to outlets on the floors, so firefighters can connect their hoses near the fire instead of laying them from the street. In New York City, supplying extra water to a building's fire protection systems is a routine fire department operation. Reaching the hydrants, inlets and fire floor is a matter of fire service access, which New Zealand's Verification Method C/VM2 (second edition, 2025) covers in its scenario for firefighting operations.

The water flow must match the size of the fire. The Netherlands Institute for Public Safety (NIPV) gives rules of thumb for cooling capacity. A high-pressure jet of 125 L/min is generally sufficient for a fire of up to about 2.5 MW, and a low-pressure jet of 450 L/min for up to about 10 MW. For comparison, Van Rossum gives about 2.5 MW for an average living-room sofa and a peak of 8.5 MW for a car. He notes that such heat release data help the fire service judge whether a fire can still be fought with the flow its vehicle delivers at low, medium or high pressure.

Time is often decisive. In an aircraft fuel spill fire, the aluminium skin of the aircraft can burn through in about 1 minute. The cabin becomes unsurvivable once the windows melt out after about 3 minutes. Airport rescue and firefighting vehicles are designed to reach an incident on the airport within 2 to 3 minutes. Once there, they must apply agent to control the fire within 1 minute, a critical time recognised by US and international aviation and fire protection bodies.

Automatic systems and the fire service

Automatic sprinklers often act long before firefighters can. Human response, from discovery of the fire to the travel of the fire brigade, usually takes much longer than the time sprinklers need to control a fire in its early stages. Sprinklers are designed to control a fire, but they often put it out, because the wetted materials around it can no longer heat up to their ignition temperature. Even where sprinklers do not suppress a fire, their cooling can protect the structure until the fire is extinguished by other means.

Manual and automatic firefighting both depend on the water supply. Sprinkler systems fail when a supply valve is closed, a water tank is empty, a fire pump does not start or loses its power, or the pipes and heads are blocked or corroded. At World Trade Center 7, the sprinklers on the lower 20 floors depended on one automatic fire pump and on the city main. After the collapse of WTC 1, the fire department could not provide firefighting or supplementary water to the building. In the SFPE Handbook, Siu warns that many fire risk studies for nuclear power plants ignore the reliance of automatic and manual suppression on a common water supply, which can make their results non-conservative.

Manual and automatic suppression have different dependencies. Based on Iqbal and Salley (2004), pp. F-25–F-26 and 10-1–10-2.

Risk studies of US nuclear power plants estimate from past events how long manual firefighting takes. For all fire types together, NUREG/CR-6850 (2005) gives a probability of 0.46 that a fire is still burning after 10 minutes of manual suppression, and 0.10 after 30 minutes. These curves leave out the time to detect the fire and the response time of the fire brigade. Both must be subtracted from the time before damage occurs to find the time that is actually available for suppression.

Tactics: inside or outside, offensive or defensive

Firefighting tactics weigh the chance of success against the risk to firefighters. The International Fire Engineering Guidelines note that a shortage of water or of firefighters for an interior attack can change the strategy from offensive, fighting the fire, to defensive. The defensive aim is to stop the fire spreading to adjoining buildings.

The Dutch fire service arranges its tactics in a quadrant model. The goal is either to prevent fire growth or to extinguish the seat of the fire, and the attack is made either from inside or from outside the building. Firefighters prefer to fight a fire from outside, and they carry out an interior attack only in a small room or building when an exterior attack fails and it can be done safely. A smoke-filled space is entered only if the benefits outweigh the risks, and reducing material damage is not a reason to take risks.

The Dutch basic principles start with taking time to stop and think, followed by a reconnaissance from outside, for example with a thermal imaging camera. Three questions then decide the type of attack: is it known where the fire is, can it be reached from outside, and is there enough cooling capacity. If the fire cannot be found, reached and cooled from outside, large buildings are fought defensively and considered beyond saving. In a small building an offensive interior attack may still be possible, with control of the doors, the building kept closed where possible and water on the fire as quickly as possible.

An interior attack also needs a short route through smoke and enough cooling capacity, and the commanding officer on site makes the final decision. Van Rossum stresses the same point for engineering studies: a positive result does not mean that the fire service will attack from inside, because that decision always rests with the fire service on site. The Australian handbook, summarising limits from the Fire Brigade Intervention Model, adds that search and rescue cannot be carried out in a room that has reached flashover.

Ventilation, backdraft and smoke explosions

Firefighters also change the ventilation of a burning building. Positive pressure ventilation uses fans to blow fresh air into an enclosure, creating a pressure difference that drives the existing air and combustion products out through an exit opening. It is used to influence the degree of ventilation, to assist firefighting and to influence the burning itself.

Ventilation can alter both visibility and combustion conditions. Based on Iqbal and Salley (2004), p. F-46 and Van Rossum (2027), §4.9.

Adding air is risky when a fire is short of oxygen. In a ventilation-controlled fire the oxygen supply limits the burning, so unburnt pyrolysis gases can build up, and mixed with oxygen they form a flammable mixture that needs only ignition energy. A Backdraft is the explosive ignition of such gases when fresh air suddenly enters, for example when a door is opened, and it can produce a large fireball or a jet of flame. Van Rossum describes it as a dangerous phenomenon for the fire service.

A smoke explosion is a different event. It is the very rapid burning of flammable gases that are already reasonably premixed with air within their explosion limits, set off by a spark, by glowing particles or by self-ignition. The Dutch basic principles favour keeping a building closed where possible, which they call anti-ventilation, and controlling the doors during an interior attack.

Ventilation, smoke control and sprinklers also affect one another. The NIPV study notes that smoke and heat removal can raise the chance of a successful interior attack in indoor car parks. Building ventilation systems that keep running during a fire, or that recirculate air, can themselves spread smoke through the building. Sprinkler sprays can also cool the heat-sensitive links of downstream sprinklers and smoke vents and delay their opening, effects known as sprinkler skipping and vent skipping.

Firefighting in building design and regulation

The International Fire Engineering Guidelines state that evacuation analysis should not rely on fire service intervention, although the needs of fire services must not be discounted. In New Zealand, C/VM2 (second edition, 2025) sets out a design scenario for firefighting operations. It sets requirements for access, water supply, information for firefighters and structural stability. For large unsprinklered firecells near a boundary, it sets limits for the moment when firefighters first apply water. The radiation at 1.5 m above the floor may then not exceed 4.5 kW/m², and the smoke layer must be at least 2 m above the floor. That moment may be taken as 1,200 s, or 1,000 s with a fire alarm connected directly to a remote receiving centre.

In Australia, the Fire Safety Verification Method Standard 2022 includes a fire brigade intervention scenario, assessed with the Fire Brigade Intervention Model, that applies to buildings within 50 km road travel of a fire station. The 2020 handbook shows how a design fire may be cut short by occupants, by sprinklers, or by fire brigade suppression before or after flashover. The design fire is then modified for the automatic or fire brigade intervention that applies to the scenario.

In the Netherlands, an equivalent solution under the 2012 Building Decree cannot take credit for a fire service attack. The NIPV study stresses that the fire service has an obligation of best efforts rather than of result. Some Dutch design curves do include firefighting: the car fire curve in the car park standard NEN 6098, as described by Van Rossum, reflects the extinguishing action of the fire service.

Limits and common misconceptions

Putting out the visible flames does not always end a fire. Glowing combustion inside solids can survive a gaseous agent and re-ignite when air returns, and a damaged foam blanket can let a liquid fire burn back. Battery packs of electric vehicles can catch fire again shortly after the flames are out. They therefore need continuous cooling and temperature monitoring, for example in a water-filled immersion container.

More agent is not automatically better. Water can spread a burning liquid that floats on it, and repeated discharges of dry chemical at Point Beach left residue across the containment building without putting the fire out. In enclosed spaces, dry chemical can also impair breathing and reduce visibility. Firefighting itself exposes firefighters to heat, flame, smoke, explosion and structural collapse, as one of the US definitions of fire suppression states.

Engineering models cannot promise what firefighters will find. The International Fire Engineering Guidelines note that the effect of fire service activities does not lend itself easily to quantification, so many aspects rest on qualitative judgement. C/VM2's limits apply only at the moment firefighters first apply water, and operations after that depend on the conditions they face at the time.

See also

• Hose reel
• Rollover
• Electric vehicle fire
• Critical water application rate

References

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• Australian Building Codes Board. (2022). Fire Safety Verification Method Standard 2022.
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