Firefighting

Not to be confused with a firefight, which is a battle with firearms.

Firefighters at a major fire involving an abandoned convent in Canada, 2006

Firefighting in Jyväskylä, Finland

Firefighting is the act of extinguishing fires. A firefighter suppresses and extinguishes fires to protect lives and prevent the destruction of property and the environment. Firefighters may provide many other valuable services to their communities including emergency medical services.

Firefighting demands a professional approach and many firefighters achieve a high degree of technical skill as a result of years training in both general firefighting techniques and developing specialist expertise in particular fire and rescue operations such as aircraft/airport rescue; Wilderness fire suppression; and Search and rescue.

One of the major hazards associated with firefighting operations is the toxic environment created by combustible materials, the four major hazards being smoke, the oxygen deficient atmosphere, elevated temperatures, and toxic atmospheres. Additional risks of fire include falls and structural collapse that can exacerbate the problems entailed in this toxic environment. To combat some of these risks, firefighters carry self-contained breathing apparatus.

The first step of a firefighting operation is a reconnaissance to search for the origin of the fire and identification of the specific risks and any possible casualties.

Fires can be extinguished by water, fuel removal, or chemical flame inhibition.

In the US, fires are sometimes categorized as "one alarm", "all hands", "two alarm", "three alarm" (or higher) fires. There is no standard definition for what this means quantifiably, though it always refers to the level response by the local authorities. In some cities, the numeric rating refers to the number of fire stations that have been summoned to the fire. In others, the number counts the number of "dispatches" for additional personnel and equipment.

History

Bulgarian firefighters in action, 1930s

The earliest known firefighters were in the city of Rome. In 6 A.D. , emperor Augustus made the Corps of Vigils to protect Rome after a disastrous fire. The Corps of Vigils consisted of 7000 people. They were equipped with buckets and axes, and they fought fires and served as police.

Old Tactics and Tools

In 4th century B.C. , an Alexandrian Greek named Ctesibuis made a double force pump called a 'siphona'. As water rose in the chamber, it compressed the air inside which forced the water to eject in a steady stream through a pipe and nozzle.

In the 16th century, syringes were also used as firefighting tools, the larger ones being mounted on wheels but a traditional method that survived was the bucket brigade, two lines formed between the water source and the fire, in one typically men would pass along the full buckets of water to the fire while in the other women and children would pass back the empty buckets to be refilled.

In the 17th century, 'fire engines' were being made, notably in Amsterdam and in 1721 Richard Newsham made a popular fire engine that was essentially a rectangular box on wheels filled using a bucket brigade to fill a reservoir while hand-powered pumps supplied sufficient water pressure to douse fires at a distance.

Ancient Rome

Ancient Rome did not have municipal firefighters. Instead, private individuals would rely upon their slaves or supporters to take action, not only forming bucket brigades or attempting to smother smaller fires but also demolishing or razing nearby buildings to slow the spread of the fire. However, there is no mention of fires being extinguished, rather they were contained and burned themselves out. Ancient Rome did not have an organized firefighting force until the Vigiles were formed in the reign of Augustus.

United Kingdom

Prior to the Great Fire of London in 1666, some parishes in the UK had begun to organize rudimentary firefighting. After the Great Fire Nicholas Barbon introduced the first fire insurance. In order to reduce insurance costs Barbon also formed his own fire brigade, and other companies followed suit.

By the start of the 1800s, insured buildings were identified with a badge or mark, indicating that they were eligible. (Buildings with no coverage, or insurance with a different company, were left to burn unless they were adjacent to an insured building, in which case it was often in the insurance company's interest to prevent the fire from spreading.) In 1833, these companies in London merged to form The London Fire Company Establishment.

Steam powered apparatuses were first introduced in the 1850s, allowing a greater quantity of water to be directed onto a fire, and in the early 1930s these were superseded by versions powered internal combustion engine.

In World War II, the Auxiliary Fire Service and later the National Fire Service were established to supplement local fire services. At that time there was no countrywide standard for firefighting terms, procedures, ranks or equipment (such as hose couplings). After WWII, firefighting terms, procedures, ranks, and equipment were standardized.

United States

As early as January of 1608, a fire destroyed many of the colonists' provisions and lodgings in Jamestown, Virginia. Boston, New York, and Philadelphia were all plagued by fires, and volunteer fire brigades formed soon after that.

In 1736, Benjamin Franklin founded the Union Fire Company in Philadelphia, which became the standard for volunteer fire organizations. Two tools were critical to these firefighters: salvage bags and bed keys. Salvage bags were used to save valuables, and bed keys were used to break down the wooden frame of a bed to safely remove it from the fire.

The first American attempt at fire insurance failed after a large fire in Charlestown, Massachusetts in 1736. Later in 1740, Benjamin Franklin organized the Philadelphia Contributionship to provide fire insurance, which was more successful. The Contributionship adopted "fire marks" to easily identify insured buildings. Firefighting started to become formalized with rules to provide buckets, ladders, hooks, and the formation of volunteer companies. The chain of command was also established.

Firefighter duties

A firefighter's goals are to save lives, property and the environment.

A fire can rapidly spread and endanger many lives but with modern firefighting techniques, catastrophe is usually, but not always, avoided.

To prevent fires from starting, a firefighter's duties may include public education about fire safety and conducting fire inspections of locations for their adherence to local fire codes.

Aerial video of Firefighting

Firefighter skills

Firefighting requires skills in combating, extinguishing, and preventing fires, answering emergency calls, operating and maintaining fire department equipment and quarters and extensive training in performing firefighting and rescue activities. Firefighters must also have (or be able to acquire) knowledge of department organizations, operations, and procedures and the district or city street system they must negotiate to perform their duties.

They must meet the minimum physical fitness standards and must be able to learn various firefighting and rescue duties within a reasonable test period including first responder assistance to people in critical conditions, provide many other valuable services to the community they serve in addition to firefighting:

• Emergency medical services, as technicians or as licensed paramedics, staffing ambulances;
• Vehicle rescue/extrication;
• Defensive Hazardous materials mitigation (HAZMAT);
• Community disaster support.
• Fire risk assessments

Conduct of firefighters

There are very strict and specific rules that firefighters have to follow when on duty:

• No firefighter should do any action that will lower the respect of the public or local government.
• They should not report for duty under the influence of any intoxicating liquor, drug, or compound.
• There should be no horseplay or rough housing in or around any fire department facility.

Basically, firefighters are expected to use common sense and exercise sound judgement when it comes to behavior.

Specialized skills

There are specialized areas of fire and rescue operations that are considered special operations. These areas may require firefighters to attend schools and classes for subject-specific training.

A hose team training to fight an aircraft fire aboard a US aircraft carrier, 2006

• Aircraft/airport rescue
• Building collapse
• Cold-water rescue
• Confined space rescue
• High-angle rope rescue
• Offensive Hazardous materials technician (HAZMAT)
• Search and rescue
• Shipboard and military fire and rescue
• Swift water rescue
• Tactical paramedic support ("SWAT medics")
• Tool hoisting
• Trench rescue
• Wildland fire suppression

Shift hours

Firefighters usually follow a 24-hour shift schedule. Some fire departments work eight or 12-hour shifts, but the 24-hour shift is more common. Australian firefighters work a 10/14 shift, in which the day shift works 10 hours and the night shift works 14 hours. Firefighting personnel will be split up into alternating shifts. Usually, the shifts are 24 hours, which are followed by two days off. The shift personnel will arrive ready to complete a regular tour of duty. The next oncoming shift will report for roll call at a specified time. While on shift, the firefighter is to remain at the fire station unless relieved or assigned other duties somewhere else. Everyone is expected to keep their protective clothing on until after roll call. Finally, no one will be excused from duty except in the case of an extreme emergency.

Fire warden

A fire warden poster, circa 1940s.

In fire fighting, there are also people designated as fire wardens, also known as the chief officer. The duties vary, some may ensure evacuation of that part of the building for which they are responsible. Another type of warden is one who has responsibility for fire control in a particular area, directs a crew in the suppression of forest fires, or is a fire patrolman in a logging area.

The chief officer is the person that is in charge of his firefighters during fires or emergencies, expected to command and control the situation while effectively combating a fire or other emergency. They must be able to evaluate the firefighter, use sound judgement when deciding when it is time to pull out his firefighters from the fire, and react calmly in emergency situations. The chief officer must direct the activities of a fire department and must supervise all firefighting and rescue activities. In addition the chief officer must have extensive knowledge of the city, the location of the streets, the location of the fire hydrants and fire alarm boxes, and where the principal buildings are; have knowledge of explosives; hazardous chemicals; the combustion qualities of materials in buildings, homes and industrial plant.

Hazards caused by fire

Structure fire in Grand Rapids, Michigan, US

One of the major hazards associated with firefighting operations is the toxic environment created by combusting materials. The four major hazards associated with these situations are as follows:

• Smoke, which is becoming increasingly dangerous due to the rise in synthetic household materials.
• Oxygen deficient atmosphere, 21% O₂ is normal, 19.5% O₂ is considered oxygen deficient.
• Elevated temperatures
• Toxic atmospheres

To combat these potential effects, firefighters carry self-contained breathing apparatus (SCBA; an open-circuit positive pressure system) to prevent smoke inhalation. These are not oxygen tanks (oxygen is an powerful accelerant that would represent a grave risk when combined with virtually anything combustible in the presence of fire) but work using compressed air in a similar manner to SCUBA diving gear. A firefighters SCBA usually hold 30 to 45 minutes of air, depending upon the size of the tank and the rate of consumption during strenuous activities.

Obvious risks are associated with the immense heat: even without direct contact with the flames (direct flame impingement or conductive heat), radiant heat can create serious burns from a great distance. There are a number of comparably serious heat-related risks: burns from hot gases (e.g., air), steam and hot and/or toxic smoke. Accordingly, firefighters are equipped with personal protective equipment (PPE) that includes fire-resistant clothing (Nomex or polybenzimidazole fiber (PBI)) and helmets that limit the transmission of heat towards the body. No PPE, however, can completely protect the user from the effects of all fire conditions.

Heat can make flammable liquid contained in tanks explode violently producing what is called a BLEVE (boiling liquid expanding vapor explosion). Some chemical products such as ammonium nitrate fertilizers can also explode, potentially causing physical trauma from blast or shrapnel injuries. Sufficient heat causes human flesh to burn as fuel, or the water within to boil, causing potentially severe medical problems.

Depending upon the heat of the fire, burns can occur in a fraction of a second.

Main article: Burn

Additional risks of fire include the following:

• smoke can obscure vision, potentially causing a fall, disorientation, and becoming trapped in the fire;
• structural collapse.

According to one article "Three hours of fighting a fire stiffens arteries and impairs cardiac function in firefighters" according to a new study by Bo Fernhall, a professor in the department of kinesiology and community health in the College of Applied Health Sciences and Gavin Horn, director of research at the Illinois Fire Service Institute. The conditions (observed in healthy male firefighters) are "also apparent found in weightlifters and endurance athletes..."

Reconnaissance and reading the fire

The first step of a firefighting operation is a reconnaissance to search for the origin of the fire (which may not be obvious for an indoor fire, especially when there are no witnesses), and identification of the specific risks and any possible casualties. Any fire occurring outside may not require reconnaissance; on the other hand, a fire in a cellar or an underground car park with only a few centimeters of visibility may require a long reconnaissance to identify the seat of the fire.

The "reading" of the fire is the analysis by the firefighters of indications of thermal events such as flashover, backdraft or smoke explosion), which is performed during the reconnaissance and the fire suppression maneuvers.

The main signs are:

• Hot zones, which can be detected with a gloved hand, especially by touching a door before opening it;
• Soot on windows, which usually means that combustion is incomplete and thus there is a lack of air;
• Smoke going in and out around a door frame, as if the fire breathes, which usually means a lack of air to support combustion;
• Spraying water on the ceiling with a short pulse of a diffused spray (e.g., cone with an opening angle of 60°) to test the heat of the smoke:
  • When the temperature is moderate, the water falls down in drops with a sound of rain,
  • When the temperature is high, it vaporizes with a hiss — the sign of a potentially extremely dangerous impending flashover

Ideally, part of reconnaissance is to consult an existing pre-plan for the building, providing knowledge of existing structures, firefighter hazards, and can include the most appropriate strategies and tactics.

Science of extinguishment

See also: Fire Chemistry and Physical properties of wildfires

A fire helicopter is used to fight a wildfire

Fire elements

There are four elements needed to start and sustain a fire and/or flame. These elements are classified in the “fire tetrahedron” are

• A reducing agent (fuel)
• Heat,
• Oxidizing agent (oxygen)
• Chemical Reaction

The reducing agent, or fuel, is the substance or material that is being oxidized or burned in the combustion process. The most common fuels contain carbon along with combinations of hydrogen and oxygen.

Heat is the energy component of the fire tetrahedron. When heat comes into contact with a fuel, it provides the energy necessary for ignition, causes the continuous production and ignition of fuel vapors or gases so that the combustion reaction can continue, and causes the vaporization of solid and liquid fuels.

The resulting self-sustained chemical chain reaction is a complex reaction that requires a fuel, an oxidizer, and heat energy to come together in a very specific way. An oxidizing agent is a material or substance that when the proper conditions exist will release gases, including oxygen. This is crucial to the sustainment of a flame or fire.

A fire can be extinguished by taking away any of the four components of the tetrahedron.

One common method to extinguish a fire is to use water: the first way that water extinguishes a fire is by cooling, which removes heat from the fire, made possible through water’s ability to absorb massive amounts of heat by converting water to water vapor. Without heat, the fuel cannot keep the oxidizer from reducing the fuel to sustain the fire. The second way water extinguishes a fire is by smothering the fire. When water is heated to its boiling point, it converts to water vapor. When this conversion takes place, it dilutes the oxygen in the air with water vapor, thus removing one of the elements that the fire requires to burn. This can also be done with foam.

Another way to extinguish a fire is fuel removal: this can be accomplished by stopping the flow of liquid or gaseous fuel; by removing solid fuel in the path of a fire; or by allowing the fire to burn until all the fuel is consumed, at which point the fire will self-extinguish.

One final extinguishing method is chemical flame inhibition. This can be accomplished through dry chemical or halogenated agents that interrupt the chemical chain reaction and stop flaming. This method is effective on gas and liquid fuels because they must flame to burn.

Sound waves have been successfully used in a device by two George Mason University senior engineering students, Viet Tran and Seth Robertson, but this is still awaiting patent (2015).

Use of water

USMC firefighters neutralize a fire during a training exercise

A firefighting aircraft dumping water on a forest fire in South Africa.

Often, the main way to extinguish a fire is to spray with water. The water has two roles:

• in contact with the fire, it vaporizes, and this vapor displaces the oxygen (the volume of water vapor is 1,700 times greater than liquid water, at 1,000 °F (540 °C) this expansion is over 4,000 times); all this leaves the fire with insufficient combustive agent to continue, and it dies out.
• the vaporization of water absorbs the heat; it cools the smoke, air, walls and objects that could act as further fuel, and thus prevents one of the means that fires grow, which is by "jumping" to nearby heat/fuel sources to start new fires, which then combine.

The extinguishment is thus a combination of "asphyxia" (cutting off the oxygen supply) and cooling. The flame itself is suppressed by asphyxia, but the cooling is the most important element to master a fire in a closed area.

Water may be accessed from a pressurized fire hydrant, pumped from water sources such as lakes or rivers, delivered by tanker truck, or dropped from water bombers, aircraft adapted as tankers in fighting forest fires. An armoured vehicle (firefighting tank) may be used where access to the area is difficult.

Open air fire

For fires in the open, the seat of the fire is sprayed with a straight spray: the cooling effect immediately follows the "asphyxia" by vapor, and reduces the amount of water required. A straight spray is used so the water arrives massively to the seat without being vaporized before. A strong spray may also have a mechanical effect: it can disperse the combustible product and thus prevent the fire from starting again.

The fire is always fed with air, but the risk to people is limited as they can move away except in the case of wildfires or bushfires where they risk being easily surrounded by the flames.

Spray is aimed at a surface, or object: for this reason, the strategy is sometimes called two-dimensional attack or 2D attack.

It might be necessary to protect specific items (house, gas tank, etc.) against infrared radiation, and thus to use a diffused spray between the fire and the object.

Breathing apparatus is often required as there is still the risk of inhaling smoke or poisonous gases.

Closed volume fire

Until the 1970s, fires were usually attacked while they declined, so the same strategy that was used for open air fires was effective. In recent times, fires are now attacked in their development phase as:

• firefighters arrive sooner;
• thermal insulation of houses confines the heat;
• modern materials, especially the polymers, produce a lot more heat than traditional materials (wood, plaster, stone, bricks, etc.).

Additionally, in these conditions, there is a greater risk of backdraft and flashover.

Spraying of the seat of the fire directly can have unfortunate and dramatic consequences: the water pushes air in front of it, so the fire is supplied with extra oxygen before the water reaches it. The most important issue is not the flames, but control of the fire, i.e., the cooling of the smoke that can spread and start distant fires, and that endangers the lives of people, including firefighters.

The volume must be cooled before the seat is treated. This strategy originally of Swedish origin (Mats Rosander & Krister Giselsson), was further adapted by London Fire Officer Paul Grimwood following a decade of operational use in the busy West End of London between 1984 and 1994 and termed three-dimensional or 3D attack.

Use of a diffused spray was first proposed by Chief Lloyd Layman of the Parkersburg Fire Department, at the Fire Department Instructors Conference (FDIC) in 1950 held in Memphis. Using Grimwood's modified 3D attack strategy, the ceiling is first sprayed with short pulses of a diffused spray:

• it cools the smoke, thus the smoke is less likely to start a fire when it moves away;
• cooler gas become more dense (Charles's law), thus it also reduces the mobility of the smoke and avoids a "backfire" of water vapour;
• it creates an inert "water vapour sky", which prevents roll-over (rolls of flames on the ceiling created by the burning of hot gases).

Only short pulses of water must be sprayed, otherwise the spraying modifies the equilibrium, and the gases mix instead of remaining stratified: the hot gases (initially at the ceiling) move around the room and the temperature rises at the ground, which is dangerous for firefighters.

An alternative is to cool all the atmosphere by spraying the whole atmosphere as if drawing letters in the air ("penciling").

The modern methods for an urban fire dictate the use of a massive initial water flow, e.g. 500 L/min for each fire hose. The aim is to absorb as much heat as possible at the beginning to stop the expansion of the fire, and to reduce the smoke. When the flow is too small, the cooling is insufficient and the steam that is produced can burn firefighters (the drop of pressure is too small and the vapor is pushed back).

Although it may seem paradoxical, the use of a strong flow with an efficient fire hose and an efficient strategy (diffused sprayed, small droplets) requires a smaller amount of water: once the temperature is lowered, only a limited amount of water is necessary to suppress the fire seat with a straight spray. For a living room of 50 m² (60 square yards), the required amount of water is estimated as 60 L (15 gal).

French firefighters used an alternative method in the 1970s: spraying water on the hot walls to create a water vapour atmosphere and asphyxiate the fire. This method is no longer used because it was risky; the pressure created pushed the hot gases and vapour towards the firefighters, causing severe burns, and pushed the hot gases into other rooms where they could start a fires.

Asphyxiating a fire

In some cases, the use of water is undesirable:

• some chemical products react with water and produce poisonous gases, or even burn in contact with water (e.g., sodium);
• some products float on water, e.g., hydrocarbons (gasoline, oil, alcohol, etc.); a burning layer can then spread and extend;
• in case of a pressurised fuel tank, it is necessary to avoid heat shocks that may damage the tank: the resulting decompression may produce a BLEVE;
• electrical fires where water would act as a conductor.

It is then necessary to asphyxiate the fire. This can be done in different ways:

• some chemical products react with the fuel and stop the combustion;
• a layer of water-based fire retardant foam is projected on the product by the fire hose, to keep the oxygen in air separated from the fuel;
• using carbon dioxide, halon, or sodium bicarbonate;
• in the case of very small fires, and in the absence of other extinguishing agents, literal blanketing of the flames can eliminate oxygen flow to the fire. A simple, and usually effective, way to put out a stove-top pan whose contents have become ignited is to put a lid on the pan and leave it there.

Tactical ventilation or isolation of the fire

One of the main risks of a fire is the smoke: it carries heat and poisonous gases, and obscures vision. In the case of a fire in a closed location (building), two different strategies may be used: isolation of the fire, or ventilation.

Paul Grimwood introduced the concept of tactical ventilation in the 1980s to encourage a better thought-out approach to this aspect of firefighting. Following work with Warrington Fire Research Consultants (FRDG 6/94) his terminology and concepts were adopted officially by the UK fire services, and are now referred to throughout revised Home Office training manuals (1996–97). Grimwood's original definition of his 1991 unified strategy stated that, "tactical ventilation is either the venting, or containment (isolation) actions by on-scene firefighters, used to take control from the outset of a fire's burning regime, in an effort to gain tactical advantage during interior structural firefighting operations."

Ventilation affects life safety, fire extinguishment, and property conservation by 'pulling' fire away from trapped occupants when properly used.

In most cases of structural firefighting a 4x4 foot opening is cut into the roof directly over the fire room. This allows hot smoke and gases to escape through the opening returning the conditions of the room to normal. It is important that ventilation is coordinated with interior fire attack as the opening of a ventilation hole will give the fire air. It may also "limit fire spread by channeling fire toward nearby openings and allows fire fighters to safely attack the fire" as well as limit smoke, heat, and water damage.

Positive pressure ventilation (PPV) consists of using a fan to create excess pressure in a part of the building; this pressure will push the smoke and the heat out of the building, and thus secure the rescue and fire fighting operations. It is necessary to have an exit for the smoke, to know the building very well to predict where the smoke will go, and to ensure that the doors remain open by wedging or propping them.

The main risk of this method is that it may accelerate the fire, or even create a flashover, e.g., if the smoke and the heat accumulate in a dead end.

Hydraulic ventilation is the process of directing a stream from the inside of a structure out the window using a fog pattern. This effectively will pull smoke out of room. Smoke ejectors may also be used for this purpose.

Categorising fires

USA

Main article: Multiple-alarm fire

In the US, fires are sometimes categorised as "one alarm", "all hands", "two alarm", "three alarm" (or higher) fires. There is no standard definition for what this means quantifiably, though it always refers to the level response by the local authorities. In some cities, the numeric rating refers to the number of fire stations that have been summoned to the fire. In others, the number counts the number of "dispatches" for additional personnel and equipment.

Alarms are generally used to define the tiers of the response by what resources are used.

Example:

Structure fire response draws the following equipment:

• 3 Engine/Pumper Companies
• 1 Truck/ladder/aerial Company
• Heavy Rescue

This is referred to as an Initial Alarm or Box Alarm.

Working fire request (for the same incident)

• Air/Light Units
• Other specialized rescue units
• Chief Officers/Fireground Commanders (if not on original dispatch)

Note: This is the balance of a First Alarm fire.

Second and subsequent Alarms:

• 2 Engine Companies
• 1 Truck Company

The reason behind the "Alarm" is so the Incident Commander doesn't have to request each apparatus with the dispatcher. He can say "Give me a second alarm here", instead of saying "Give me a truck company and two engine companies" along with requesting where they come from.

Categorization of fires varies between each fire department. A single alarm for one department may be a second alarm for another. Response always depends on the size of the fire and the department.

Calculating the amount of water required to suppress a fire in a closed volume

In the case of a closed volume, it is easy to compute the amount of water needed. The oxygen (O₂) in air (21%) is necessary for combustion. Whatever the amount of fuel available (wood, paper, cloth), combustion will stop when the air becomes "thin", i.e. when it contains less than 15% oxygen. If additional air cannot enter, we can calculate:

• The amount of water required to make the atmosphere inert, i.e., to prevent the pyrolysis gases to burn—this is the "volume computation"
• The amount of water required to cool the smoke, the atmosphere—this is the "thermal computation"

These computations are only valid when considering a diffused spray that penetrates the entire volume. This is not possible in the case of a high ceiling: the spray is short and does not reach the upper layers of air. Consequently, the computations are not valid for large volumes such as barns or warehouses: a warehouse of 1,000 m² (1,200 square yards) and 10 m high (33 ft) represents 10,000 m³. In practice, such large volumes are unlikely to be airtight anyway.

Volume computation

Fire needs air; if water vapour pushes all the air away, the fuel can no longer burn. But the replacement of all the air by water vapour is harmful for firefighters and other people still in the building: the water vapour can carry much more heat than air at the same temperature (one can be burnt by water vapour at 100 °C (212 °F) above a boiling saucepan, whereas it is possible to put an arm in an oven—without touching the metal!—at 270 °C (520 °F) without damage). This amount of water is thus an upper limit that should not be reached.

The optimal, and minimum, amount of water to use is the amount required to dilute the air to 15% oxygen: below this concentration, the fire cannot burn.

The amount used should be between the optimal value and the upper limit. Any additional water would just run on the floor and cause water damage without contributing to fire suppression.

Let:

• V_r be the volume of the room,
• V_v be the volume of vapour required,
• V_w be the volume of liquid water to create the V_v volume of vapour,

then for an air at 500 °C (773 K, 932 °F, best case concerning the volume, probable case at the beginning of the operation), we have

$V_v = 3571 \cdot V_w$

and for a temperature of 100 °C (373 K, 212 °F, worst case concerning the volume, probable case when the fire is suppressed and the temperature is lowered):

$V_v = 1723 \cdot V_w$

For the maximum volume, we have:

$V_v = V_r$

considering a temperature of 100 °C. To compute the optimal volume (dilution of oxygen from 21 to 15%), we have

$V_v = 0.286 \cdot V_r$

for a temperature of 500 °C. The table below show some results, for rooms with a height of 2.70 m (8 ft 10 in).

Amount of water required to suppress the fire volume computation
Area of the room	Volume of the room Vr	Amount of liquid water Vw
		maximum	optimal
25 m² (30 yd²)	67.5 m³	39 L (9.4 gal)	5.4 L (1.3 gal)
50 m² (60 yd²)	135 m³	78 L (19 gal)	11 L (2.7 gal)
70 m² (84 yd²)	189 m³	110 L (26 gal)	15 L (3.6 gal)

Note that the formulas give the results in cubic meters, which are multiplied by 1,000 to convert to liters.

Of course, a room is never really closed, gases can go in (fresh air) and out (hot gases and water vapour) so the computations will not be exact.

Notes

^ indeed, the mass of one mole of water is 18 g, a liter (0.001 m³) represents one kilogram i.e. 55.6 moles, and at 500 °C (773 K), 55.6 moles of an ideal gas at atmospheric pressure represents a volume of 3.57 m³.

^ same as above with a temperature of 100 °C (373 K), one liter of liquid water produces 1.723 m³ of vapour

^ we consider that only V_r - V_v of the original room atmosphere remains (V_v has been replaced by water vapour). This atmosphere contains less than 21% of oxygen (some was used by the fire), so the remaining amount of oxygen represents less than 0.21·(V_r-V_v). The concentration of oxygen is thus less than 0.21·(V_r-V_v)/V_r, and we want this fraction to be 0.15 (15%).

See also

• Glossary of firefighting—list of firefighting terms and acronyms, with descriptions
  • Glossary of firefighting equipment—expansion of Glossary of firefighting
  • Glossary of wildfire terms—expansion of Glossary of firefighting
• Index of firefighting articles—alphabetical list of firefighting articles
• List of fire departments
• Outline of firefighting—structured list of firefighting topics, organized by subject area

External links

• CDC - NIOSH Fire Fighter Fatality Investigation and Prevention Program