what three elements must be present to start or maintain a fire?

Model for agreement the ingredients for fires

The fire triangle or combustion triangle is a simple model for agreement the necessary ingredients for most fires.^[1]

The triangle illustrates the three elements a fire needs to ignite: heat, fuel, and an oxidizing agent (usually oxygen).^[2] A burn down naturally occurs when the elements are present and combined in the correct mixture.^[3] A burn can be prevented or extinguished by removing whatever one of the elements in the fire triangle. For example, covering a fire with a fire blanket blocks oxygen and can extinguish a fire. In large fires where firefighters are called in, decreasing the corporeality of oxygen is not usually an option considering there is no effective manner to make that happen in an extended area.^[4]

Fire tetrahedron [edit]

Not to be confused with NFPA 704, also called the burn down diamond.

The fire tetrahedron represents the addition of a component in the chemical chain reaction, to the 3 already present in the burn triangle. In one case a burn has started, the resulting exothermic chain reaction sustains the fire and allows it to go on until or unless at least 1 of the elements of the burn down is blocked. Foam can be used to deny the fire the oxygen it needs. H2o tin be used to lower the temperature of the fuel below the ignition indicate or to remove or disperse the fuel. Halon can exist used to remove free radicals and create a barrier of inert gas in a straight attack on the chemic reaction responsible for the fire.^[5]

Combustion is the chemical reaction that feeds a fire more rut and allows information technology to continue. When the fire involves burning metals like lithium, magnesium, titanium,^[6] etc. (known as a class-D fire), it becomes even more of import to consider the energy release. The metals react faster with h2o than with oxygen and thereby more energy is released. Putting water on such a fire results in the fire getting hotter or even exploding. Carbon dioxide extinguishers are ineffective against certain metals such as titanium.^[6] Therefore, inert agents (e.g. dry sand) must be used to pause the chain reaction of metallic combustion.

In the same way, equally presently as i of the four elements of the tetrahedron is removed, combustion stops.

Oxidizer [edit]

The oxidizer is the other reactant of the chemic reaction. In most cases, it is the ambient air, and in particular one of its components, oxygen (O_two). By depriving a burn down of air the fire tin can be extinguished, such equally when covering the flame of a pocket-size candle with an empty drinking glass. To the opposite, if air is blown over a wood burn down (as with bellows), the burn down is activated past the introduction of more air.

Some chemicals, such as fluorine gas, perchlorate salts such as ammonium perchlorate, or chlorine trifluoride, human action every bit oxidizers, sometimes more powerful ones than oxygen itself. A fire based on a reaction with these oxidizers tin can be very difficult to put out until the oxidizer is exhausted; that leg of the fire triangle cannot exist broken by normal ways (i.e., depriving information technology of air will not smother information technology).

In sure cases such as some explosives, the oxidizer and combustible are the same (e.g., nitroglycerin, an unstable molecule that has oxidizing parts in the aforementioned molecule every bit the oxidizeable parts).

Reaction is initiated by an activating energy — in about cases, information technology is rut. Several examples include friction, every bit in the case of matches, heating an electrical wire, a flame (propagation of fire), or a spark (from a lighter or from whatsoever starting electrical device). There are besides many other ways to bring sufficient activation energy including electricity, radiation, and pressure level, all of which volition lead to a temperature rise. In almost cases, heat production enables cocky-sustainability of the reaction, and enables a chain reaction to abound. The temperature at which a liquid produces sufficient vapor to get a flammable mix with cocky-sustainable combustion is called its flash-indicate.

Extinguishment of the fire [edit]

To end a combustion reaction, 1 of the three elements of the fire triangle must be removed.

Without sufficient heat, a fire cannot begin, and it cannot continue. Heat tin be removed by the awarding of a substance which reduces the amount of heat available to the fire reaction. This is often water, which absorbs heat for stage alter from water to steam. Introducing sufficient quantities and types of powder or gas in the flame reduces the amount of heat bachelor for the burn reaction in the same style. Scraping embers from a called-for construction also removes the heat source. Turning off the electricity in an electric burn removes the ignition source.

Without fuel, a burn down will stop. Fuel tin exist removed naturally, every bit where the fire has consumed all the burnable fuel, or manually, by mechanically or chemically removing the fuel from the fire. Fuel separation is an important factor in wildland fire suppression, and is the basis for most major tactics, such equally controlled burns. The fire stops considering a lower concentration of fuel vapor in the flame leads to a subtract in free energy release and a lower temperature. Removing the fuel thereby decreases the estrus.

Without sufficient oxygen, a fire cannot begin, and it cannot continue. With a decreased oxygen concentration, the combustion process slows. Oxygen can exist denied to a burn using a carbon dioxide burn extinguisher, a burn coating or h2o.

Role of water in fire-fighting [edit]

The water can have two different roles. In the case of a solid flammable, the solid fuel produces pyrolyzing products nether the influence of heat, commonly radiations. This process is halted by the awarding of water, since water is more easily evaporated than the fuel is pyrolyzed. Thereby free energy is removed from the fuel surface and it is cooled and the pyrolysis is stopped, removing the fuel supply to the flames. In fire fighting, this is referred to as surface cooling.

In the gas phase, i.e. in the flames or in the smoke, the combustible can not exist separated from the oxidizer, and the only possible action consists of cooling down. In this instance, water droplets are evaporated in the gas stage, thereby lowering the temperature and adding water vapour making the gas mixture non combustible. This requires aerosol of a size less than about 0.ii mm. In burn fighting, this is referred to every bit gas cooling or smoke cooling.

Cases also be where the ignition factor is not the activation energy. For case, a smoke explosion is a very violent combustion of unburned gases contained in the smoke created by a sudden fresh air input (oxidizer input). The interval in which an air/gas mix can burn is express by the explosive limits of the air. This interval can be very pocket-size (kerosene) or large (acetylene).

Water cannot be used on certain type of fires:

• Fires where live electricity is present – as h2o conducts electricity it presents an electrocution hazard.
• Hydrocarbon fires – every bit information technology will only spread the fire considering of the difference in density/hydrophobicity. For case, adding h2o to a burn down with an oil source will cause the oil to spread, since oil and h2o do not mix.
• Metallic fires – equally these fires produce huge amounts of energy (up to seven.550 calories/kg^{[ disputed – hash out ]} for aluminium) and water tin can as well create fierce chemical reactions with called-for metal (peradventure even serving every bit an additional oxidizing amanuensis).

Since these reactions are well understood, information technology has been possible to create specific water-additives which will allow:

• A better heat absorption with a college density than h2o.
• Carrying complimentary radical catchers on the burn.
• Carrying foaming agents to enable water to stay on the surface of a liquid fire and prevent gas release.
• Conveying specific reactives which will react and modify the nature of the burning fabric.

Water-additives are by and large designed to be effective on several categories of fires (course A + class B or fifty-fifty form A + course B + course F), meaning a ameliorate global performance and usability of a single extinguisher on many different types of fires (or fires that involve several different classes of materials).

Multi-calibration fire triangles for wildland fires [edit]

Multi-scale fire triangles describing the elements of wildland burn at the scale of the flame, a wildfire, and a burn regime. Adapted from Moritz et al. (2005) Wildfire, complexity, and highly optimized tolerance. Proceedings of the National University of Sciences 102, 17912-17917.

In the context of wildland fire, the burn down triangle tin can be scaled up to apply to sympathize burn spread over landscapes (scales of days and several kilometres) and recurrence of fire over time (scales of decades and hundreds of kilometres).^[7] Thus, while heat is important to ignite a flame, topography is important for aiding fire spread especially by preheating upslope fuels, and ignitions sources are of import to help explicate recurrence on longer time scales. Similarly, while oxygen is relevant to sustain a flame, weather and associated winds feed oxygen into a spreading fire, and the longer-term design of conditions is summarized as climate. Lastly, fuels is the term to describe what burns in a single flame to the range of materials burnt in a spreading wildfire, but fuels vary over larger space and fourth dimension scales in what is called vegetation.

At the smallest scale, the combustion fire triangle, individual fuel particles are ignited once at a critical temperature, and fire transfers free energy to the nearest environs. Combustion events range on the scale of several seconds to a couple of days and their effects are monitored at the quadrant scale. The largest scale, in contrast, describes the fire government concept. Global climate change drives many of the factors involved in the 'wildfire' and the 'burn regime' triangles. For example, with respect to the fire regime, a particular vegetation blazon will back up a feature fire in terms of recurrence, intensity, seasonality and biological effects; a alter in vegetation type will have implications for a changing fire regime.

Run across likewise [edit]

• Glossary of firefighting terms
• Fire classes

Notes [edit]

1. ^ The Fire Triangle Archived 2012-04-06 at the Wayback Machine, Hants Fire brigade, accessed June 2009
2. ^ "Wildland Burn down Facts: There Must Be All Three". National Park Service . Retrieved 30 August 2018.
3. ^ IFSTA, 2008 p. 88.
4. ^ "What is a burn illuminate shape? triangle". FireRescue1 . Retrieved 2017-02-14 .
5. ^ "The Fire Tetrahedron (A pyramid)". Data about the Fire Triangle/Tetrahedron and Combustion. Safelincs Ltd. Retrieved 30 August 2012.
6. ^ ^{a b} http://www.titanium.com/titanium/tech_manual/tech16.cfm Archived 2009-01-26 at the Wayback Machine Titanium MSDS
7. ^ Moritz, Max A.; Morais, Marco East.; Summerell, Lora A.; Carlson, J. M.; Doyle, John (2005-12-13). "Wildfires, complication, and highly optimized tolerance". Proceedings of the National Academy of Sciences of the Us of America. 102 (l): 17912–17917. doi:10.1073/pnas.0508985102. ISSN 0027-8424. PMC1312407. PMID 16332964.

References [edit]

• Essentials of Fire Fighting and Fire Department Operations (fifth ed.). International Burn down Service Training Clan. 2008.

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Source: https://en.wikipedia.org/wiki/Fire_triangle