The essence of the processes of combustion and explosion. Reasons for the fire. Combustion and spontaneous combustion Causes and conditions of spontaneous combustion
Combustion- a chemical oxidation reaction, accompanied by the release of a large amount of heat and usually glow.
For the occurrence and continuation of combustion, the presence of a combustible substance, an oxidizing agent (usually atmospheric oxygen, as well as chlorine, fluorine, iodine, bromine, nitrogen oxides) and an ignition source (ignition) is necessary.
In addition, it is necessary that the combustible substance be heated to a certain temperature and be in a certain quantitative ratio with the oxidizing agent, and the ignition source would have sufficient energy.
Typically, the oxidizing agent in the combustion process is oxygen gas in the air.
Burning stops if any of the conditions that caused it are violated. So, for example, when extinguishing a tree with water, it cools below the ignition temperature, when extinguishing burning liquids with foams, the flow of fuel vapor into the combustion zone stops.
combustible substances are combustible gases (gg), flammable liquids (lvzh), flammable liquids (gzh), combustible dusts (gp).
Sources of ignition(ignition) can be an open flame, an electrical and mechanical spark, a heated body (radiant energy), etc. Some substances can ignite spontaneously. This is the ability of a substance to ignite spontaneously at normal, natural ambient temperature with little or no heat input from the outside.
Ignition can also occur in the absence of an ignition source if, during the oxidation process, the rate of heat release exceeds the rate of heat removal. This phenomenon is called spontaneous combustion.
Spontaneous combustion- this is a phenomenon of a sharp increase in the rate of exothermic reactions, leading to the combustion of a substance in the absence of an ignition source.
Spontaneous combustion accompanied by the appearance of a flame is called self-ignition.
Distinguish:
1. Thermal spontaneous combustion (due to self-heating of a material, such as coal, when stored in piles)
2. chemical
3. microbiological (cotton, moistened hay, peat, sawdust - as a result of the vital activity of organisms) piled or stacked sawdust, wood chips, freshly prepared charcoal, straw, raw cotton, fossil coals, peat, oiled cloth, etc. The main reason for the spontaneous combustion of these substances is their ability to oxidize due to biological and chemical processes at low temperatures.
In the event of a chemical fire, three groups of substances are distinguished:
1. Substances that ignite spontaneously when exposed to air. This group includes: heaps or piles of sawdust, wood chips, freshly prepared charcoal, straw, raw cotton, fossil coals, peat, oiled cloth, etc. The main reason for the spontaneous combustion of these substances is their ability to oxidize due to biological and chemical processes at low temperatures.
2. Substances that cause combustion when exposed to water. This group includes: potassium, sodium, calcium carbide, alkali metal carbides, quicklime, sodium hydrosulfide, etc.
3. Substances that ignite spontaneously when mixed with each other. This group includes oxidizers. Thus, compressed oxygen causes spontaneous combustion of mineral oils.
Chemical called spontaneous combustion, resulting from the chemical interaction of substances.
Substances that ignite spontaneously on contact with water. This group of materials includes potassium, sodium, rubidium, cesium, calcium carbide and alkali metal carbides, alkali and alkaline earth metal hydrides, calcium and sodium phosphides, silanes, quicklime, sodium hydrosulfide, etc.
Alkali metals - potassium, sodium, rubidium and cesium - interact with water with the release of hydrogen and a significant amount of heat:
2Na + 2H 2 O \u003d 2NaOH + H 2 2K + 2H 2 O \u003d 2KOH + H 2.
The released hydrogen spontaneously ignites and burns together with the metal only if the piece of metal is larger than a pea in volume. The interaction of these metals with water is sometimes accompanied by an explosion with splashing of molten metal. The hydrides of alkali and alkaline earth metals (KH, NaH, CaH 2) behave in the same way when interacting with a small amount of water:
NaH + H 2 O \u003d NaOH + H 2.
When calcium carbide reacts with a small amount of water, so much heat is released that, in the presence of air, the resulting acetylene ignites spontaneously. With a lot of water, this does not happen. Alkali metal carbides (for example, Na 2 C 2, K 2 C 2) explode on contact with water, and the metals burn out, and carbon is released in a free state:
2Na 2 C 2 + 2H 2 O + O 2 \u003d 4 NaOH + 4C.
Calcium phosphide Ca 3 P 2, when interacting with water, forms hydrogen phosphide (phosphine):
Ca 3 P 2 + 6H 2 O \u003d 3Ca (OH) 2 + 2PH 3.
Phosphine pH 3 is a combustible gas, but is not capable of spontaneous combustion. Together with PH 3, a certain amount of liquid P 2 H 4 is released, which is capable of spontaneous combustion in air and can cause ignition of PH 3.
Silanes, i.e. silicon compounds with various metals, for example Mg 2 Si, Fe 2 Si, under the action of water, emit hydrogen silicon, which ignites spontaneously in air:
Mg 2 Si + 4H 2 O \u003d 2 Mg (OH) 2 + SiH 4
SiH 4 + 2O 2 \u003d SiO 2 + 4H 2 O.
Barium peroxide and sodium peroxide, although they interact with water, do not form combustible gases. Combustion can occur if peroxides are mixed or in contact with combustible substances.
Calcium oxide (quicklime), reacting with a small amount of water, heats up to glow and can ignite combustible materials in contact with it.
Sodium hydrosulfite, being wet, is vigorously oxidized with the release of heat. As a result of this, spontaneous combustion of sulfur occurs, which is formed during the decomposition of hydrosulfite.
Substances that ignite spontaneously on contact with oxidizing agents. Many substances, mostly organic, are capable of spontaneous combustion when mixed or in contact with oxidizing agents. Oxidizing agents that cause spontaneous combustion of such substances include compressed oxygen, halogens, nitric acid, sodium and barium peroxide, potassium permanganate, chromic anhydride, lead dioxide, nitrate, chlorates, perchlorine
you, bleach, etc. Some of the mixtures of oxidizing agents with combustible substances are capable of spontaneous combustion only when exposed to sulfuric or nitric acids or upon impact and low heating.
Compressed oxygen causes spontaneous combustion of substances (mineral oil) that do not spontaneously ignite in oxygen at normal pressure.
Chlorine, bromine, fluorine and iodine are extremely actively combined with some combustible substances, and the reaction is accompanied by the release of a large amount of heat, and the substances ignite spontaneously. So, acetylene, hydrogen, methane and ethylene mixed with chlorine spontaneously ignite in the light or from the light of burning magnesium. If these gases are present at the time of the release of chlorine from any substance, their spontaneous combustion occurs even in the dark:
C 2 H 2 + Cl 2 + 2HCl + 2C
CH 4 + 2Cl 2 = 4HCl + C, etc.
Do not store halogens together with flammable liquids.
It is known that turpentine, distributed in any porous substance (in paper, fabric, cotton), ignites spontaneously in chlorine. Diethyl ether vapors can also ignite spontaneously in a chlorine atmosphere:
C 2 H 5 OS 2 H 5 + 4Cl 2 \u003d H 2 O + 8HCl + 4C.
Red phosphorus instantly ignites spontaneously when in contact with chlorine or bromine.
Not only halogens in the free state, but also their compounds react vigorously with some metals. Thus, the interaction of ethane tetrachloride C 2 H 2 Cl 4 with metallic potassium occurs with an explosion
C 2 H 2 Cl 4 + 2K = 2KSl + 2HCl + 2C.
A mixture of carbon tetrachloride CCl 4 or carbon tetrabromide with alkali metals explodes when heated to 70 0 C.
Nitric acid, decomposing, releases oxygen, therefore it is a strong oxidizing agent capable of causing spontaneous combustion of a number of substances.
4НNO 3 \u003d 4NO 2 + O 2 + 2H 2 O.
In contact with nitric acid, turpentine and ethyl alcohol ignite spontaneously.
Plant materials (straw, flax, cotton, sawdust and shavings) ignite spontaneously if they are exposed to concentrated nitric acid.
In contact with sodium peroxide, the following combustible and flammable liquids are capable of spontaneous combustion: methyl, ethyl, propyl, butyl, isoamyl and benzyl alcohols, ethylene glycol, diethyl ether, aniline, turpentine and acetic acid. Some liquids spontaneously ignite with sodium peroxide after introducing a small amount of water into them. This is how acetic ethyl ether (ethyl acetate), acetone, glycerin and isobutyl alcohol behave. The beginning of the reaction is the interaction of water with sodium peroxide and the release of atomic oxygen and heat:
2Na 2 O 2 + H 2 O \u003d 2NaOH + O.
Atomic oxygen at the moment of release oxidizes the combustible liquid, and it ignites spontaneously. Aluminum powder, sawdust, coal, sulfur and other substances mixed with sodium peroxide instantly ignite spontaneously when a drop of water enters them.
A strong oxidizing agent is potassium permanganate KMnO 4 . Its mixtures with solid combustible substances are extremely dangerous. They ignite spontaneously from the action of concentrated sulfuric and nitric acids, as well as from impact and friction. Glycerin C 3 H 5 (OH) 3 and ethylene glycol C 2 H 4 (OH) 2 ignite spontaneously in a mixture with potassium permanganate a few seconds after mixing.
Chromic anhydride is also a strong oxidizing agent. Upon contact with chromic anhydride, the following liquids ignite spontaneously: methyl, ethyl, butyl, isobutyl and isoamyl alcohols; acetic, butyric, benzoic, propionic aldehydes and paraldehyde; diethyl ether, ethyl acetate, amyl acetate, methyldioxane; acetic, pelargonic, nitrilacrylic acids; acetone.
Mixtures of saltpeter, chlorates, perchlorates are capable of spontaneous combustion when exposed to sulfuric, and sometimes nitric acid. The cause of spontaneous combustion is the release of oxygen under the action of acids. When sulfuric acid reacts with Berthollet salt, the following reaction occurs:
H 2 SO 4 + 2KClO 3 \u003d K 2 SO 4 + 2HClO 3.
Perchloric acid is unstable and, when formed, decomposes with the release of oxygen:
2HClO 3 \u003d 2HCl + 3O 2.
Questions for self-control
1. What temperature is called the self-heating temperature?
2. Write down the formula for calculating the self-heating temperature.
3. What substances are called pyrophoric?
4. What spontaneous combustion is called thermal?
5. What substances are capable of thermal spontaneous combustion?
6. What spontaneous combustion is called microbiological?
7. What substances are capable of chemical spontaneous combustion?
4. combustion of mixtures of gases and vapors with air
However, there is the process of ignition of materials without an ignition source, i.e. selffire, which can be of the following types: thermal, chemical And microbiological.
thermal spontaneous combustion is expressed in the accumulation of heat by the material, during which the material self-heats. The self-heating temperature of a substance or material is an indicator of its fire hazard. For most combustible materials, this indicator lies in the range from 80 to 150°C. Long smoldering before the start of the fiery
th burning is a distinguishing characteristicbehavior of thermal spontaneous combustion processes, which are detected by the long-lasting and persistent smell of smoldering material.
Chemical spontaneous combustion immediately manifests itself in fiery combustion, which is typical when organic substances are combined with acids, vegetable and technical oils. Oils and fats, in turn, are capable of spontaneous combustion in an oxygen environment.
In practice, the combined processes of spontaneous combustion are most often manifested: thermaland chemical.
Fire dynamics
Assessing the dynamics of the development of a fire, several of its main phases can be distinguished:
1st phase (up to 10 minL - initial stage, includes the transition of ignition to fire in a time of approximately 1-3 minutes. and the growth of the combustion zone within 5-6 minutes. In this case, there is a predominantly linear spread of fire along combustible substances and materials, which is accompanied by abundant smoke emission. During this phase, it is very important to ensure that the room is isolated from outside air, as in some cases, self-extinguishing of the fire occurs in a sealed room.
2nd phase - stage of volumetric developmentra, takes 30^40 minutes. It is characterized by a rapid combustion process with a transition to volumetric combustion, the process of flame propagation occurs remotely due to the transfer of combustion energy to other materials.
After 15-20 min. the glazing is destroyed, the oxygen supply increases sharply, the maximum values are reached by the temperature (up to 800-900 ° C) and the burnout rate. Stabilization of a fire at its maximum values occurs for 20-25 minutes. and continues for another 20-30 minutes. In this case, the bulk of combustible materials burn out.
3rd phase - fire extinguishing stage, those. afterburning in the form of slow smoldering, after which the fire stops.
Analyzing the dynamics of the development of a fire,certain conclusions can be drawn:
1. Technical fire safety systems (alarms and automatic fire extinguishing) must work until the maximum burning intensity is reached, or better -
in the early stages of a fire. This will allow the head of the educational institution to have a margin of time in order to organize measures to protect people.
2. Fire departments arrive, as a rule, in 10-15 minutes. after the call, i.e. after 15-20 min. after the outbreak of a fire, when it takes on a volumetric shape and maximum intensity.
Fire extinguishing agents
There is a classification of fires according to the characteristics of a combustible medium, and it is of great practical importance when choosing the types of primary fire extinguishing agents:
Class A- combustion of solids (wood, paper, textiles, plastics);
Class B- combustion of liquid substances;
Class C- combustion of gases;
Class D - combustion of metals and metal-containing substances;
Class E- burning electrical installations.
The designated classes of fires suggest appropriate ways to extinguish them. For example, in buildings and structures, fire extinguishing agents.
The cessation of combustion (extinguishing method) is carried out on the basis of the following well-known principles:
"- cooling of reacting substances;
»-» isolation of reacting substances from the combustion zone;
»-* dilution of reactants to non-flammable concentrations;
»-» chemical inhibition of the combustion reaction.
In practice, the designated principles of cessation of combustion are usually implemented in a complex manner.
When extinguishing a fire, it is conditionally possible to distinguish periods of its localization and liquidation.
A fire is considered contained when:
No threat to people and animals;
There is no threat of explosions and collapse;
Fire development is limited;
The possibility of its elimination by the available forces and means is provided.
A fire is considered extinguished when:
Burning stopped;
Prevention of its occurrence is provided.
The indicated signs of localization and elimination of a fire must be known to officials of educational institutions in order to make the right decisions in case of fire.
To the main fire extinguishing agentsrelate:
Water and its solutions;
Chemical and air-mechanical foams;
Water and its solutions has received the greatest use due to availability, low cost and efficiency with the dominant principle of cooling to stop combustion. But it must be borne in mind that it is impossible:
■* Extinguish live electrical installations with water;
■» use water to extinguish burning oil products;
** use water to extinguish chemicals that react with it.
However, water has a high surface tension, which makes it difficult to wet solids, especially fibrous ones. This property of water should be taken into account when used on a fire in educational institutions of an internal fire water supply. To reduce the shortcomings of water as the main fire extinguishing agent, various additives are added to it.
Powder fire extinguishing compositions have a diverse mechanism for stopping combustion, high efficiency and are able to stop burning of almost any class. This determines their widespread use in fire extinguishers. But they have a tendency to caking, so they require periodic shaking as part of fire extinguishers. They can also be used to extinguish electrical installations under voltage.
Dioxide carbon (CO 2) - its solid fraction, when used in fire extinguishers, immediately passes into gas, bypassing the liquid phase. Implements several mechanisms to stop burning, very effective. It is recommended to use for extinguishing electrical installations under voltage, although it is able to stop the burning of almost all combustible materials, with the exception of metallic sodium and potassium, magnesium and its alloys.
The listed fire extinguishing agents are the main ones when used in educational institutions, although fire departments widely use various foams with unique properties.
The problem of determining the required stakequality of primary fire extinguishing equipmenthundred, but it is necessary to keep in mind somestanding.
Processing equipment is completed with fire extinguishers in accordance with the requirements of passports for this equipment or the relevant fire safety rules.
It is recommended to select the type and calculate the required number of fire extinguishers depending on their fire extinguishing capacity, the maximum area of the premises, and the fire class of combustible substances.
In public buildings and structures, at least two hand-held fire extinguishers must be placed on each floor.
If there are several small rooms of the same fire hazard category, the number of necessary fire extinguishers is determined taking into account the total area of \u200b\u200bthese rooms.
Thus, the “Fire Safety Rules in the Russian Federation” PPB 01-03 recommend using either four OP-5 powder fire extinguishers or two OP-10, or four OU-2, or two OU-5 for public buildings with an area of 800 m 2. It is preferable, in our opinion, to use fire extinguishers OP-5 as the most effective in terms of protected areas, with additional placement of fire extinguishers OU-2 (OU-5) in computer classes, i.e. where. There are electrical installations under voltage. This approach does not reduce the recommendations of the "Fire Safety Rules in the Russian Federation", but only strengthens them, based on the characteristics of educational institutions.
Pyrokinesis is a parapsychological term that refers to the ability to cause fire or a significant increase in temperature at a distance with the power of thought. A being capable of pyrokinesis is called a pyrokinetic, capable of influencing matter with the power of thought. In addition, cases of unexpected and inexplicable spontaneous combustion of people, when a living body turns into a handful of ashes, are also considered pyrokinesis.
Cases in history
Interestingly, flammable material near the victim (bed linen, clothing or paper) was untouched.
So, in the 18th century, the mysterious death of Countess Bandi from Casena occurred. All that was left of her was her head, three fingers, and both legs in a pile of ash that was 4 feet from the bed. There were no signs of fire on the floor or on the bed.
In the second half of the 19th century, physicians also began to write about pyrokinesis. One of them, an assistant professor at the University of Aberdeen, read the work of colleagues and became convinced that about half of the doctors consider spontaneous human combustion to be quite possible.
So, in the report of a certain Dr. Berthall to the Medical and Surgical Society there is a message about a woman who, on August 1, 1869, burned down in her apartment. According to an eyewitness, the body looked like it had been in a smelting furnace. However, everything around was intact, only the floor burned a little - just in the place where the corpse was. The victim did not utter a single scream, did not call for help, since the residents of neighboring apartments did not hear anything.
Even in the middle of the 20th century, the belief that a person could burn out from drunkenness was very strong. Colonel O. Arkhipov in the military-historical essay "In the Bryansk Forests" tells about a strange incident, which he personally witnessed. During the Great Patriotic War, at one of the field airfields, a sick soldier was loaded into the back of an old lorry to be sent to the infirmary. They said that he drank something obscene, called "chassis" - a liquid that was intended to fill the shock absorbers. And along the way, in front of the accompanying soldiers, the body of the victim suddenly flared up with a blue flame. When the driver braked sharply, everyone jumped out of the body and rushed in all directions, and after some time they found the charred corpse of a fellow traveler in the truck. The strangest thing was that the overcoat on which he was lying did not catch fire. The incredible case was written off as "spontaneous combustion by ingestion of a flammable liquid".
Types of ignition
Over the past three centuries, pyrokinesis, including in the presence of witnesses, overtook hundreds of people, regardless of their gender and whether they were drunkards or teetotalers during their lifetime. It is rather difficult to derive any regularity in the selectivity of objects for spontaneous combustion. Pyrokinesis is ubiquitous and merciless in any setting. Therefore, specialists can only register fresh facts and systematize where it manifested itself once again. The American popular science magazine Discovery reports that over the past 12 years, the number of cases of pyrokinesis has almost doubled. Two types of ignition are noted: turning the victim into ashes and sintering it into a charred mass. In some cases, some part of the body is not touched by the flames. It has been established that during the spontaneous combustion of human bodies, the temperature of the fire reached 3000 °C.
spontaneous combustion of people. cases
1905, winter - in England there were three strange fires. In the small village of Batlocks Het (Hampshire), the charred corpses of the Kylie spouses were found in one of the houses. It is interesting that neither the furniture, nor the curtains, nor the carpet, on which the elderly married couple suddenly caught fire, was touched by the fire. In Lincolnshire, a farmer died in a similar fire, along with about 300 geese and chickens. And a few days later, an elderly woman suddenly caught fire nearby.
Billy Peterson (USA) burst into flames while parking his car in a Detroit car park. When rescuers removed his charred body, it was discovered that the temperature in the car was so high that the parts on the instrument panel were completely melted.
1956 - 19-year-old Mabel Andrews was dancing with her friend Billy Clifford on one of the dance floors in London and suddenly burst into flames. Although Clifford and those around him tried to help her, she died on the way to the hospital. According to Billy, there were no sources of fire nearby, and it seemed to him that the fire was coming out directly from her body.
1969 - Dora Metzel, sitting in her car on one of the streets of Luxembourg, suddenly ignited, burned to the ground in a matter of seconds. Several people tried to help her, but to no avail. But when it was over, it turned out that the interior trim and seats of the car, unlike the case with Peterson, were not damaged.
1996 - a naked girl jumped out of a motel room in Brisbane (Australia) with a wild cry. After she woke up, she said that she came here for the weekend with her boyfriend. She went to bed, her boyfriend went to take a bath. And when he came out of there and lay down next to her, he suddenly caught fire and a minute later turned into dust.
Still, according to one curious version, the culprit of pyrokinesis is a special pyrobacteria that "eats" the sugar that is contained in the human body and produces volatile combustible substances - for example, alcohol. Then pyrokinesis can be explained as the combustion of an "alcoholized" organism from an imperceptible, random spark. This bacterium has not yet been discovered, and exists only in the form of a complex computer model.
Harugi Ito from Japan put forward a version that the cause of pyrokinesis is a change in the flow of time. In the normal state, the human body produces and radiates a certain amount of heat into space, but if, for some reason, the physical processes occurring in nature suddenly slow down sharply inside, and their speed remains constant on the surface of the skin, then the generated heat simply does not have time to radiate into space and incinerates a person.
Candidate of Technical Sciences A.Stekhin offers his own version. According to him, pyrokinesis is cold plasma combustion. “Three-quarters of a person consists of liquid formations, that is, of water. Free radicals in its molecules are able to "take away" energy. It can be either solar energy or biological energy. In exceptional cases, it is released and bursts out in a stream of quanta. Moreover, the external temperature of the body does not exceed 36 ° C, and the internal temperature reaches 2000 ° C, which explains the paradox mentioned in written sources: the body burns to ashes, while shoes, clothes, bedding, etc. remain intact.
Finally, a number of scientists adhere to a very fantastic point of view, arguing that the source of energy in a living cell is a thermonuclear reaction. Under certain conditions, unknown energy processes appear in the cells of the body, similar to those occurring during the explosion of an atomic bomb. Such self-destructive processes do not go beyond the body and are not reflected in the molecules of neighboring matter - for example, on clothes or car upholstery.
French scientist Jacques Millon has been solving pyrokinesis for many years. At first, he encountered this phenomenon in psychiatric hospitals, where they kept patients accused of attempting to commit suicide by self-immolation. But, as it turned out, patients completely denied even the very thought of suicide. They talked about the unexpected spontaneous combustion of the body, described their feelings and.
Having taken up the study of this problem closely, Monsieur Milon received two additional educations (physics and field physics) and put forward his own version of pyrokinesis, based on the existence of a pyropole. It is known that in nature there are various types of fields - electric, magnetic, gravitational and, finally, a biofield. Moreover, all types of fields interact with each other, and the energy shell of a living being remains the most mysterious. Scientists to this day cannot explain why a healthy person's body temperature fluctuates by 0.5 ° C during the day or why a sudden fever occurs during nervous stress.
There is another type of field in nature - the so-called pyropole, capable of heating protein matter. But not any, but only matter with a powerful biofield, that is, the human body. Then the diurnal temperature fluctuations are the result of pyropole fluctuations around its average level. And fever during nervous stress, the so-called thermoneurosis, is the result of the interaction of the pyropole with the weakened biofield of the subject. It is also known that the electric and magnetic field of the Earth from time to time inexplicably gives out a powerful surge of its energy in a limited area of space.
The pyropole behaves in exactly the same way, which, during flashes, throws out narrow beams of energy, similar to discharges of invisible lightning. Such extremes are deadly for humans. A person caught in an invisible beam flares up and burns out instantly. And the more powerful the biofield, the more tasty bait an individual becomes for the burning forces of nature. In turn, the pyropole does not act on inanimate objects (clothes, shoes, bed, car, etc.). It, like a fire brought to a puddle of alcohol on the table, burns out the alcohol, and the table area does not even heat up.
Spontaneous combustion is the result of self-heating of substances, i.e. spontaneous process ending in smoldering or fiery combustion.
The occurrence of spontaneous combustion is influenced by the heat of combustion, thermal conductivity, specific surface and bulk density of the substance, as well as the conditions of heat exchange with the external environment.
Self-heating of a substance can be caused by various reasons. It can be initiated by microbiological processes occurring in the nutrient medium, exposure to high temperature, and release of heat as a result of chemical reactions.
In order for the process of self-heating to end with spontaneous combustion, it is necessary that the substance has the ability to oxidize and that the conditions necessary for the accumulation of heat are formed.
The physical essence of the processes of spontaneous combustion and self-ignition is the same and the conditions for self-acceleration of the reaction are the same. The main difference between them is that spontaneous combustion occurs at an ambient temperature equal to or greater than the auto-ignition temperature, and self-ignition occurs at an ambient temperature less than the auto-ignition temperature, and for this process to occur, the fuel must be heated from the outside. Based on the causes of spontaneous combustion of substances, three mechanisms of this process are distinguished - microbiological, thermal and chemical, as well as their various combinations.
Microbiological processes of spontaneous combustion are the main cause of spontaneous combustion of substances of plant origin, such as under-dried hay, sawdust, dry leaves, cotton.
Microbiological processes also explain the spontaneous combustion of milled peat. The vital activity of bacteria and fungi in the throat can begin already at 10 - 18 ° C and ends at 70 ° C. The nutrient medium for bacteria is water-soluble substances formed as a result of the decay of plants.
Under-dried materials are especially prone to spontaneous combustion, since moisture and heat contribute to the vital activity of microorganisms. The low thermal conductivity of plant materials also leads to heating. At a temperature exceeding 75 "C, microorganisms, as a rule, die, but the temperature increase does not stop, since at 70 ° C some organic substances are able to char. The resulting porous coal adsorbs gases and dads and the self-heating process continues. At 200 ° C C begins to decompose fiber, which is part of vegetable oils, which leads to further intensification of oxidation and the occurrence of spontaneous combustion.
Thermal self-ignition is inherent in dispersed substances with a highly developed surface, capable of adsorbing oxygen and reacting with it, while the heat exchange of substances with the external environment is not intense.
It is known that fossil coals (brown and hard coal) stored in heaps or stacks are prone to spontaneous combustion. The reason for spontaneous combustion is the ability of coals to oxidize and adsorb vapors and gases at low temperatures.
Self-heating of coal that occurs in stacks occurs first throughout the entire volume of the stack, excluding the top layer (30 - 50 cm). With an increase in temperature, the self-heating process acquires a nesting character. Up to 60 °C, the temperature rises very slowly - intensive ventilation prevents its increase. However, starting from 60 °C, the rate of self-heating increases sharply. This temperature is considered critical for coal.
Spontaneous combustion of coals is also facilitated by an increase in the degree of their grinding and the presence of impurities - pyrite and moisture.
In chemical spontaneous combustion, an increase in the rate of a chemical reaction with increasing temperature is of great importance. Insufficient heat removal contributes to the heating of the material as a result of the occurrence of oxidative processes and, accordingly, the achievement of critical conditions for the occurrence of combustion or smoldering.
Spontaneously combustible chemicals can be divided into three main groups.
More on the topic of spontaneous combustion:
- 5.4. The cost of reproduction and payment for natural resources
- 5.3. Comparative economic evaluation of natural resources
- 4.3. The main directions of scientific and technological progress and their impact on environmental protection and rational nature management
