combats a controlled fire on the mobile aircraft firefighting training device May 2, 2006.]]

Firefighting is the act of extinguishing fires. A firefighter fights these fires to prevent destruction of life, property and the environment. Firefighting is a highly technical skill that requires professionals who have spent years training in both general firefighting techniques and specialized areas of expertise.

History

n firefighters in action, 1930s]] Firefighting is believed to have originated during the Roman invasion of Britain in AD43. These organised teams would use buckets and syringes to douse a fire.

United Kingdom

Prior to the Great Fire of London, in 1666, some parishes in the UK had begun to organise rudimentary firefighting. After much of London was destroyed the first insurance against fire was introduced by a man named Nicholas Barbon. To reduce the cost Barbon formed his own Fire Brigade. Eventually there were many other such companies. Then at the start of the 1800s, those with insurance were given a badge or mark to attached to their properties. Only those with such a badge would have a fire extinguished. Other buildings with no coverage or under a different company were left to burn.

In 1833 companies in London merged to form The London Fire Engine Establishment.

Steam powered appliances were first introduced in the 1850s, allowing a greater quantity of water to be guided onto a fire.

The steam powered appliances were replaced in the early 1900s with the invention of the internal combustion engine.

Firefighters' duties

Firefighters' goals are to save life, property and the environment. A fire can rapidly spread and endanger many lives; however, with modern firefighting techniques, catastrophe is usually, but not always, avoided. To prevent fires from starting, a firefighter's duties include public education and conducting fire inspections.

Because firefighters are often the first responders to people in critical conditions, firefighters provide many other valuable services to the community they serve, such as:

Emergency medical services, as technicians or as licensed paramedics, staffing ambulances;

Hazardous materials mitigation (HAZMAT);

Vehicle Rescue/Extrication;

Search and rescue;

Community disaster support.

Fire Risk Assessments

In addition, firefighters also service in specialized fields, such as:

Aircraft/airport rescue;

Wildland fire suppression;

Shipboard and military fire and rescue;

Tactical paramedic support ("SWAT medics");

Tool hoisting;

High Angle Rope Rescue;

Swiftwater Rescue.

In the US, firefighters also serve the Federal Emergency Management Agency (FEMA) as urban search and rescue (USAR) team members.

Hazards caused by fire

The primary risk to people in a fire is smoke inhalation (breathing in smoke; the more common cause of death in a fire rather than burns). The risks of smoke include:

suffocation due to the fire consuming or displacing all of the oxygen from the air;

poisonous gases produced by the fire;

aspirating heated smoke that can burn the inside of the lungs.

Firefighters carry self-contained breathing apparatus (SCBA; an open-circuit positive pressure compressed air system) to prevent smoke inhalation. These are not oxygen tanks; they carry compressed air. SCBA usually hold 30 to 45 minutes of air, dependent upon the size of the tank and the rate of consumption during strenuous activities.

Obvious risks stem from the effects of heat. Even without contact with the flames (conduction), there are a number of comparably serious risks: burns from radiated heat, contact with a hot object, hot gases (e.g., air), steam and hot and/or toxic smoke. 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.

The heat can make pressurised gas cylinders and tanks explode, producing what is called a BLEVE (boiling liquid expanding vapor explosion). Some chemical products such as ammonium nitrate fertilizers can also explode. Explosions can cause physical trauma or potentially serious blast or shrapnel injuries.

Heat causes human flesh to burn as fuel, causing potentially severe medical problems. Depending upon the heat of the fire, burns can occur in a fraction of a second.

Additional risks of fire include the following:

smoke can obscure vision, potentially causing a fall, disorientation, or becoming trapped in the fire;

structural collapse.

According to a University News Bureau Life Sciences article reported by News Editor Sharita Forest and photographed by L. Brian Stauffer, from the website of the University of Illinois at Urbana-Champaign,: "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 apparently 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 identify the specific risks and the 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 spot the seat of the fire.

The "reading" of the fire is the analysis by the firefighters of the forewarnings of a thermal accident (flashover, backdraft, 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.

Ideally, part of reconnaissance is to consult an existing preplan for the building. This provides knowledge of existing structures, firefighter hazards, and can include strategies and tactics.

Science of extinguishment

Fire elements

There are four elements needed to start and sustain a fire and/or flame. These elements are classified in the “fire tetrahedron” and are: #Reducing agent (fuel) #Heat #Self-sustained chemical chain reaction #Oxidizing agent (oxygen)

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 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. A chain reaction is a series of reactions that occur in sequence with the results of each individual reaction being added to the rest. This happens in the science of fire, but is self-sustaining in that it continues without interruption. 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.

is used to fight a wildfire]] A fire can be extinguished or put out by taking away any of the four components of the tetrahedron.

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 away, 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 activate 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

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

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.

Keep in mind that 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.

Appendix: 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 :$V\_v\; =\; 3571\; \backslash cdot\; V\_w$ 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): :$V\_v\; =\; 1723\; \backslash cdot\; V\_w$ 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 :$V\_v\; =\; 0.286\; \backslash cdot\; V\_r$ 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).

{| class='wikitable' | Amount of water required to suppress the fire volume computation |- ! rowspan="2" | Area of the room ! rowspan="2" | Volume of the room V_r ! colspan="2" | Amount of liquid water V_w |- ! 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

Outline of firefighting – structured list of firefighting topics, organized by subject area

References

Category:Active fire protection Category:Wildland fire suppression

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