Fire Fighting

Fire-Fighting Strategy

Fire fighting strategy involves the following basic procedures: arriving at the scene of the fire as rapidly as possible; assessing the nature of the fire by determining its intensity and extent, the type and abundance of fuel, the danger of entering the fire area, and the most effective techniques for extinguishing the fire; locating and rescuing endangered persons; containing the fire by protecting adjacent areas; ventilating the fire area to allow for the escape of heat and toxic gases; and, finally, extinguishing the fire.

Fire-Fighting Personnel

In most cities, firefighters are trained members of government-supported organizations, such as fire departments. Elsewhere, fire-fighting organizations are primarily composed of volunteers, or “vols.” Fire-fighting organizations also help design and implement fire-prevention programs, which may include such measures as building codes requiring fire alarms, regularly located fire-extinguishing equipment, internal fire walls to help contain a fire, sprinkler systems, the use of fire-retardant construction materials, and safe electrical wiring. Educating the public about fire safety and fire-prevention practices is an important part of all fire-prevention programs.

Fire-Fighting Apparatus

Fire-fighting vehicles have evolved into highly specialized equipment. Ladder trucks provide access to buildings as much as 100 ft (30 m) high; snorkel trucks enable firefighters to douse fires from above. In addition, modern fire apparatus includes rescue trucks, mobile laboratories, searchlight cars, double-ended tunnel engines, smoke ejectors, high-pressure spray trucks, foam trucks, and even coffee wagons. For fires of long duration there are tank trucks to bring extra fuel to the pumpers. The modern diesel pump delivers about 2,000 gal per min (8,000 liters per min) through lightweight hose 1 in. (2.5 cm) to 2.5 in. (6.3 cm) in diameter, reinforced with artificial fibers. A fireboat, not limited to hydrant supply, can deliver as much as 10,000 gal per min (40,000 liters per min). Airports have specially equipped crash trucks, and refineries have chemical applicators.

The commonly seen metal cylinder with a short hose attached is the soda-and-acid extinguisher; inside it, above a solution of soda and water, is a container of acid. When the extinguisher is inverted, the acid mixes with the solution and reacts with the soda to generate carbon dioxide; gas pressure then forces the solution out of the hose. A foam extinguisher is a cylinder containing water, sodium bicarbonate, an agent (often licorice powder) for strengthening the foam, and an inner container of aluminum sulfate powder. Mixed together, these ingredients form a foam of carbon dioxide bubbles. A carbon dioxide extinguisher consists of a tank of liquid carbon dioxide under pressure. When released, the carbon dioxide forms flakes that vaporize and blanket the fire.

Extinguishing Fires

For a fire to occur, there must be available oxygen, a supply of fuel, and enough heat to kindle the fuel. Therefore, the three basic ways of extinguishing fire are to smother it, to cut off the fuel supply, or to cool it below the flammability temperature. Fires are classified into four types: those in solids, e.g., wood, paper, and cloth; those in flammable liquids, e.g., gasoline, alcohol, oils, lacquers, and paints; those in electrical apparatus; and those in flammable metals such as magnesium. These are called, respectively, class A, B, C, and D fires.

Characteristics of Extinguishing Substances

Certain dry materials that melt and coat the burning material, thus excluding air, are useful against all classes of fire. In certain cases inert gases such as argon or nitrogen are used to fight fires in materials that would react dangerously with water or with other extinguishing agents; sodium and water, for example, is a dangerous combination.

Water, although supplanted somewhat by other materials, is still the most common substance used for quenching class A fires, which are the most common types of fire; water both cools and helps smother the fuel. Buckets of water are the simplest equipment for fighting small fires in solids. More effective are fire extinguishers capable of directing a stream of water. Wetting agents called detergents make water more penetrating, especially for such objects as cotton bales and mattresses.

Class B fires cannot be fought with water unless it is sprayed in a fine mist, for flammable liquids will usually float on water and spread. Foam is most often used to suffocate class B fires, particularly oil fires.

Since both water and foam conduct electricity, neither can be used against class C fires unless a fog nozzle, which produces tiny droplets that burst into a smothering blanket of steam, is employed. Halogen compounds and carbon dioxide are effective agents in fighting class C fires and are also used against flammable liquids and small fires in solids. Halogen compounds such as carbon tetrachloride turn into a vapor that settles over a fire, smothering it. Unfortunately, most halogen vapors are both toxic and corrosive; but for enclosed spaces where water damage would be as disastrous as fire damage, it is the agent of choice. In any case, nearly all professional firefighters today are equipped with oxygen tanks. Dry-chemical extinguishing agents, such as fine sodium bicarbonate, can be used on class B and C fires but are especially effective against class B fires.

Special Equipment and Techniques

Buildings are protected against fire most effectively by protective sprinkler systems. In most sprinkler systems, water circulates through overhead pipes whose outlets are normally closed; at high temperatures the outlets open, spraying water on the fire. Most large buildings also provide water for fire fighting through a standpipe system with hose connections on each floor. Forest and brush fires are fought by making a firebreak and by covering the fire with extinguishing substances. A narrow strip is cut and cleared in front of the fire down to mineral soil. Embers flying into the strip are put out, while water and other fire-extinguishing substances are spread from land-based vehicles or are dropped on the fire from the air. Oil-field fires demand multiple approaches: water streams, fogs, foams, and explosives may all be used simultaneously to quench a fire and prevent its reignition.

History of Fire Fighting

Ancient Rome is known to have had a fire department consisting by the 1st cent. of approximately 7,000 paid firefighters. These fire brigades not only responded to and fought fires, but also patrolled the streets with the authority to impose corporal punishment upon those who violated fire-prevention codes. The inventor Ctesibius of Alexandria devised the first known fire pump c.200 B.C. but the idea was lost until the fire pump was reinvented about A.D. 1500. The only equipment available to fight the London fire in 1666 were two-quart hand syringes and a similar, slightly larger syringe; it burned for four days. Elsewhere in Europe and in the American colonies fire fighting equipment was equally rudimentary. The London fire stimulated the development of a two-person operated piston pump on wheels.

In 1648, Governor Peter Stuyvesant of New Amsterdam (New York City) was the first in the New World to appoint fire inspectors with the authority to impose fines for fire code violations. Boston imported (1679) the first fire engine to reach America. For a long time the ten-person pump devised by the English inventor Richard Newsham in 1725 was the most widely used. The inventor Thomas Lote of New York built (1743) the first fire engine made in America. About 1672 leather hose and couplings for joining lengths together were produced; though leather hose had to be sewn like a fine boot, fabric and rubber-treated hose did not come into general use until 1870. A steam fire engine was built in London in 1829, but the volunteer fire companies of the day were very slow to accept it. When a group of insurance companies in New York had a self-propelled engine built in 1841, the firefighters so hindered its use that the insurance companies gave up the project. Finally, in Cincinnati, Ohio, the public forced a steam engine on the firefighters.

The aerial ladder wagon appeared in 1870; the hose elevator, about 1871. Gasoline engines were at first used either as pumping engines or as tractors to pull apparatus. In 1910 the two functions were combined, one engine both propelling the truck and driving the pump. Modern equipment is usually diesel powered, and multiple variations of the basic fire engine enable firefighters to respond to many types of emergency situations.

Bibliography

See P. R. Lyons, Fire in America (1976); C. V. Walsh and L. Marks, Firefighting Strategy and Leadership (2d ed. 1976); J. Robertson, Introduction to Fire Prevention (1989).

A repair locker hose team aboard USS John F. Kennedy (CV 67) combats a controlled fire on the mobile aircraft firefighting training device May 2, 2006.

Firefighting is the act of extinguishing destructive fires. A firefighter fights these fires and prevents destruction of life, property and the environment. Firefighting is a highly technical profession which requires years of training and education in order to become proficient.

Historically, physicists created a graphical representation detailing the three elements of fire (fire triangle). In recent years, one more point has been added, creating the fire tetrahedron. The four elements needed to sustain combustion are:

• fuel, oxidizer, heat and a chemical chain reaction.

To extinguish a fire, it is necessary to remove one or more of the three components of combustion. Removing any of these will not allow combustion to continue. Firefighters work by

• Limiting exposure of fuel that may be ignited by nearby flames or radiant heat
• Containing and extinguishing the fire
• Removing debris and extinguishing all hidden fires to prevent rekindling

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 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 basic life support as emergency medical technicians or advanced life support as licensed paramedics.

Risks of a fire

Firefighters arrive at the scene.

A burning building casts off clouds of smoke.

The primary risk to people in a fire is smoke inhalation (breathing in smoke); most of those killed in fires die from this, not from burns. The risks of smoke include:

• suffocation due to the fire consuming or displacing all the oxygen from the air;
• poisonous gases produced by the fire;
• aspirating heated smoke that can burn the inside of the lungs.

As an example, plastics inside a car can generate 200,000 m³ of smoke at a rate of 20-30 m³/sec.^{[citation needed]}. Firefighters carry self-contained breathing apparatus (SCBA) (an open-circuit positive pressure compressed air system) to prevent smoke inhalation.

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 severe medical problems. Depending upon the heat of the fire, burns can occur in a fraction of a second. A first degree burn (on the skin surface) is extremely painful. A second degree burn is a burn into the skin, and can cause shock, infections, and dehydration and if left untreated often results in death. Second degree burns compromise nerve tissue and are not painful. Third degree burns leave muscles and internal organs exposed from completely destroyed skin. If the person survives the shock and exposure to germs, medical treatment is extremely difficult.

Additional risks of firefighting encompass the following:

• vision can be obscured by the smoke: a person inside the building may not be able to see, can fall, or become disoriented and lost; becoming trapped and killed by the smoke or fire.
• the building can collapse on its occupants.

Reconnaissance and reading the fire

The first step of the operations 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 spot 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;
• the presence of soot on the windows, which usually means that combustion is incomplete and thus there is a lack of air
• smoke goes in and out from the 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 vaporises with a hiss.

Suppressing the fuel and the energy

The first method is to remove fuel for the fire by, for example, cutting off the domestic gas supply and moving combustible objects from the path of the fire. When the activation energy is still present, it is also useful to switch it off; this will not stop a fire, but will help in controlling a starting fire and will prevent a new fire from occurring.

The first action is thus to cut off the domestic gas and electricity, and switch off working machines (motors). It is also important to turn off ventilation and air conditioning, as they supply oxygen which supports combustion and can dangerously change the behaviour of the fire.

Use of water

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 vapour displaces the oxygen (the volume of water vapour is 1,700 times greater than liquid water); leaving the fire with not enough combustive agent to continue, and it dies out.
• the vaporization of water absorbs the heat; it cools the smoke, air, walls, objects in the room, etc., 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 extinction is thus a combination of "asphyxia" 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 by pressurized fire hydrant, pumped from water sources such as lakes or rivers, delivered by tanker truck, or dropped from aircraft tankers in fighting forest fires.

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 can be surrounded by the flames. But there might be a big risk of expansion.

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) 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 breathing in smoke or poisonous gases.

Closed volume fire

Until the 1970s, fires were usually attacked while they declined, so the same strategy as 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 of 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. This activation of the fire, and the mixing of the gases produced by the water flow, can create a flashover.

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 endanger the lives of people, including firefighters. The volume must be cooled before the seat is treated. This strategy originally of Swedish (Mats Rosander & Krister Giselsson) origin, was further adapted by London Fire Officer Paul Grimwood following a decade of operational use in London's busy west-end district between 1984-94 (www.firetactics.com) and termed three-dimensional attack, or 3D attack.

Use of a diffused spray was first proposed by Chief Lloyd Layman of Parkersburg, West Virginia Fire Department, at the Fire Department Instructor's Conference (FDIC) in 1950 held in Memphis, Tennessee, U.S.A.

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;
• the pressure of the gas drops when it cools (law of ideal gases), 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 ("pencilling").

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 sinister, and to reduce the smoke. When the flow is too small, the cooling is not sufficient, 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 gallons).

French fire-fighters used an alternative method in the 1970s: they sprayed 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 new fire.

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. hydrocarbon (gasoline, oil, alcohol, etc.); a burning layer can then spread and extend;
• in case of a pressurised gas tank, it is necessary to avoid heat shocks that may damage the tank: the resulting decompression may produce a BLEVE.

It is then necessary to asphyxiate the fire. This can be done in two 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.

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 positive pressure ventilation.

Paul Grimwood introduced the concept of tactical ventilation in the 1980s to encourage a more well 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 service and are now referred to throughout revised Home Office training manuals (1996-97).

Paul 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'.

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.

Categorizing fires

Fires are sometimes categorized as "one alarm", "two alarm", "three alarm" or even "four alarm". There is no standard definition. 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[1][2].

Appendix : Calculation of 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 which 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 which should not actually 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 us call:

• V_r the volume of the room,
• V_v the volume of vapour required,
• V_w 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^[3]

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):^[4]

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^[5]

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).

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.

References

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

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