Fire tetrahedron
The fire tetrahedron represents the addition of a chemical chain reaction component to the three already present in the fire triangle. Once a fire has started, the resulting exothermic chain reaction maintains the fire and allows it to continue until at least one element of the fire is blocked. Foam can be used to deprive a fire of essential oxygen. Water can be used to lower the temperature of the fuel below its flash point and to remove or disperse the fuel. Halon can be used to scavenge free radicals and create an inert gas barrier while directly attacking the chemical reaction that causes fire.
In the same way, as soon as one of the four elements of the tetrahedron is removed, combustion stops.
Oxidizer
Some chemicals, such as fluorine gas, perchlorate salts such as ammonium perchlorate, or chlorine trifluoride, act as oxidizing agents, sometimes more powerful than oxygen itself. A fire started by reaction with these oxidizers can be very difficult to extinguish until the oxidizer is exhausted; this leg of the fire triangle cannot be broken by normal means (that is, depriving it of air will not suffocate it).
In some cases, such as some explosives, the oxidizer and fuel are the same (for example, nitroglycerin, an unstable molecule that has the oxidizing parts in the same molecule as the oxidizing parts).
The reaction is initiated by activating energy, in most cases heat. A few examples include friction, as in the case of matches, heat from an electrical wire, a flame (spread of fire), or a spark (from a lighter or any electrical starting device). There are also many other ways to obtain sufficient activation energy, including electricity, radiation, and pressure, all of which will result in an increase in temperature. In most cases, the release of heat ensures that the reaction is self-sustaining and contributes to the development of a chain reaction. The temperature at which a liquid produces enough vapor to produce a flammable mixture with self-sustaining combustion is called its flash point.
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Putting out the fire
To stop the combustion reaction, one of the three elements of the fire triangle must be removed.
Without sufficient heat, a fire cannot start and cannot continue. Heat can be removed by applying a substance that reduces the amount of heat available for the fire reaction. This is often water, which absorbs heat for a phase change from water to steam. Injecting sufficient amounts and types of powder or gas into the flame reduces the amount of heat available for the fire reaction in the same way. Scraping the embers from a burning structure also removes the heat source. Turning off the power during an electrical fire eliminates the source of the ignition.
Without fuel, the fire will stop. Fuel can be removed naturally, such as when the fire has consumed all combustible material, or by manual, mechanical, or chemical removal of fuel from the fire. Fuel separation is an important factor in wildfire suppression and is the basis of most basic tactics such as controlled burns. The fire stops because the lower concentration of fuel vapor in the flame results in less energy release and a lower temperature. Thus, removing fuel reduces heat.
Without sufficient oxygen, a fire cannot start and cannot continue. When the oxygen concentration decreases, the combustion process slows down. Oxygen can be denied to a fire using a carbon dioxide fire extinguisher, a fire blanket or water.
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Water can have two different roles. In the case of solid fuels, solid fuels produce pyrolysis products when exposed to heat, usually radiation. This process is stopped by the use of water, since water evaporates more easily than the fuel pyrolyses. In this way, energy is removed from the surface of the fuel, and it cools, and pyrolysis stops, eliminating the supply of fuel to the flame. In firefighting this is called surface cooling.
Water cannot be used on certain types of fires:
Since these reactions are well studied, it has been possible to create special water additives that will:
Water-based additives are typically designed to combat multiple categories of fires (Class A + Class B or even Class A + Class B + Class F), which means better global performance and the ease of use of a single extinguisher on many different types of fires (or fires associated with several different classes of materials).
Multi-level fire triangles for forest fires
At the smallest scale, the combustion triangle, individual fuel particles ignite once at a critical temperature, and the fire transfers energy to its immediate surroundings. Fire events range from a few seconds to several days, and their effects are tracked on a quadrant scale. The largest scale, on the contrary, describes the fire mode concept.
Global climate change is the driving force behind many of the factors that form the wildfire and fire regime triangles. For example, with respect to fire regime, a particular vegetation type will support a characteristic fire in terms of frequency, intensity, seasonality, and biological effects; changing vegetation type will affect changes in fire regime.
Fire triangle
A fire is the spontaneous spread of fire through combustible material. Fire fighting is the process of eliminating combustion conditions. In order to effectively eliminate spontaneously spreading combustion, it is necessary to know the laws of this process. The “Fire Triangle” was invented in order to form a visual and universal model with which you can predict the development of the situation and determine the procedure for extinguishing.
What is the "triangle of fire"?
Combustion is the process of oxidation of a combustible material, which occurs with the release of:
When fuel is completely burned, only gaseous products are formed. In case of incomplete combustion, coals, ash, and soot remain.
The “Fire Triangle” concentrates 3 conditions for the occurrence and spontaneous spread of fire. This:
This model combines into a single system the factors necessary for the existence of a fire. Oxygen is the main oxidizing agent in the atmosphere that can start a fire. Heat is an elevated temperature that is a factor in the combustion of a material. Fuel is understood as any material that can burn, that is, oxidize in the presence of oxygen and high ambient temperatures. Only organic matter, i.e., high molecular weight compounds of carbon and hydrogen, can burn under such conditions.
Thus, on each side of the combustion triangle, the conditions of not only the spread of the fire, but also the occurrence of the fire are usually presented as a factor.
Triangle elements
This simple model should be considered not only statically, but also dynamically. Combustion and fire, despite the different content of these concepts, are a process with constantly changing parameters.
The “combustion triangle” shows the unity and immutability of factors, despite constantly changing parameters. Three elements are always necessary for ignition, combustion and fire - a combustible substance, which is the basis of the process, an oxidizing agent (a substance that determines the course of a chemical reaction) and temperature (the condition for the speed of the process).
Warmth, temperature
Spontaneous combustion of organic matter is a rare phenomenon. It occurs only if the decay products of organic matter move from an anaerobic environment to an aerobic environment.
For example, peat placed from the depths of the earth into the open air begins to rapidly oxidize. With an abundance of oxygen, oxidation occurs so rapidly that rising temperature becomes a catalyst. The result is fire. Peat located in places of its natural formation does not ignite because it does not have enough oxygen to do so.
A similar process develops when storing fine coal in large piles. Small pieces of coal oxidize slowly at first. However, gradually the temperature in the coal pile rises, which leads to the outbreak of fire.
Spontaneous combustion is not possible in haystacks or forest floors of leaves, grass and wood. The fact is that the decomposition of dead organic matter under these conditions occurs under the influence of bacteria and fungi. Natural oxidation here is so weak that without microorganisms, dead organic matter retains its structure for thousands of years.
For a fire to occur, a temperature in the area of contact with flammable material requires an average of +200...+600°C. However, this does not mean that dry leaves, paper or woolen fabrics placed in a hot oven will catch fire without contact with the flame. In order for them to catch fire, they need to be set on fire. Fires in nature are formed only due to the fact that the fire source comes into contact with fuel. The forest burns from lightning, a falling meteorite, a volcanic eruption, a match, a spark, and in rare cases from the spontaneous combustion of peat and coal.
The temperature factor also manifests itself as a fire spreads. There is a drying and warming effect. For a fire spreading in a wooden structure, air temperature and humidity do not matter. A fire can spread even in the rain if the flame temperature is high enough.
Fuel
Each combustible material has its own combustion characteristics. Liquid petroleum products ignite quickly and burn completely in a short time. For the formation of a fire based on solid organic matter, environmental conditions consisting of humidity, distances between units of combustible material, oxygen availability, and combustion temperature are of great importance.
For example, a dry leaf easily ignites, but a fire is formed only if there is a distance from one leaf to another sufficient to transfer the flame. Fires are rapidly developing in the dry steppe with tall grass and coniferous forest. Cereal stalks burn well because they contain a lot of cellulose. In this case, the distance between the stems is such that the flame easily transfers from one blade of grass to another.
Coniferous trees catch fire easily due to their resinous trunks and the presence of essential oils in the needles. At the same time, the temperature develops so high that neighboring trees dry out even as the fire front approaches.
Oxygen
The main condition for the role of air as an oxidizing agent is its concentration. For example, it is difficult to burn a thick stack of paper. Only the outer leaves and edges of the stack are burned. This occurs because there is little air in the center of tightly packed sheets.
During a fire, wind is of great importance because it constantly mixes the air, blowing away the released carbon dioxide and delivering new portions of oxygen. This principle is the basis for the method of extinguishing fires in nature, such as an oncoming fire. If the wind allows, then dry grass is set on fire opposite the edge of the fire. As a result, the fire ceases to exist due to 2 factors - a decrease in oxygen concentration and the elimination of flammable material.
The use of foam from fire extinguishers also helps to stop the flow of oxygen to the burning material.
Firefighting Basics
The “Fire Triangle” is the basis for the formation of firefighting tactics and strategies. All techniques of modern firefighters are based on influencing one or another fire factor. Flooding a fire with water affects two factors at once - it reduces the temperature of the object and makes it difficult to deliver oxygen to the combustible material.
You can put out a burning small object by knocking down the flame or covering it with something that can create insulation between the burning organic matter and the air. For example, a blanket thrown over a person's burning clothing prevents the penetration of oxygen to the burning object. Since the flame emits mainly carbon dioxide and water vapor, combustion stops due to the lack of oxygen.
Thus, the “triangle” is a model that allows you to constantly compare the parameters of fire factors. It is necessary to take into account these factors in their dynamics not only for the effective organization of fire fighting. This must also be done when improving technical fire extinguishing means.
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