What can be cooked from squid: quick and tasty

Flammable and flammable liquids differ in terms of their flash point. Flash point is the temperature of a liquid at which vapors above the surface of a liquid can ignite from exposure to an open fire. Flammable liquids have a flash point not higher than 61 ° C, flammable liquids - above 61 ° C.

Types of flammable and combustible liquids

Flammable liquids are of three categories: especially dangerous (first category), constantly dangerous (second category), and dangerous at elevated air temperatures (third category). Flash point of especially dangerous flammable liquids is -13оС. Characteristic feature especially dangerous flammable liquids is the need for certain conditions for their transportation, because if the storage vessel is not sealed, liquid vapors can quickly spread and ignite at a distance from the vessel. These liquids include acetone, some types of gasoline, ether, petroleum ether, diethyl ether, hexane, isopentane, cyclohexane.

Flammable liquids of the second category have a flash point from -13 to + 23оС. Such liquids have the ability to ignite at room temperature when their vapors are combined with air. These are liquids such as ethyl alcohol, benzene, methyl acetate, ethyl acetate, ethylbenzene, octane, toluene, isooctane, lower alcohols, dioxolanes and dioxanes.

Flammable liquids of the third category are flammable liquids with a flash point from +23 to + 60 ° C. Such liquids will only ignite if there is a source of fire in the immediate vicinity. These include the following liquids: turpentine, solvent, white alcohol, xylene, cyclohexanone, amyl acetate, butyl acetate, chlorobenzene.

Flammable liquids have the property of self-combustion at a flash point above 61 ° C. Flammable liquids include fuel oil, oils (vaseline, castor), diesel fuel, glycerin, ethylene glycol, hexyl alcohol, hexadecane, aniline. Such liquids can be stored in open containers and reservoirs (for example, in barrels), including on outdoors... When working with flammable and flammable liquids, remember the need to comply with fire safety rules for storage, transportation and use.

Class B fires

• Materials that, if ignited, can lead to Class B fires, are divided into three groups:
• flammable and combustible liquids,
• paints and varnishes,
• flammable gases.
• Let's consider each group separately.

Flammable and flammable liquids

Flammable liquids are liquids with a flash point of up to 60 ° C and below. Flammable liquids are liquids with a flash point exceeding 60 ° C. Flammable liquids include acids, vegetable oils and lubricants with a flash point exceeding 60 ° C.

Flammability characteristics:

It is not the flammable and combustible liquids themselves that burn and explode when mixed with air and ignited, but their vapors. Upon contact with air, the evaporation of these liquids begins, the rate of which increases when the liquids are heated. To reduce the risk of fire, they should be stored in closed containers. When using liquids, care should be taken to minimize exposure to air.

Explosions of flammable vapors most often occur in a confined space, such as a container, tank. The force of the explosion depends on the concentration and nature of the vapor, the amount of the vapor-air mixture and the type of container in which the mixture is located.

Flash point is the generally accepted and most important factor, but not the only factor in determining the hazard posed by a flammable or combustible liquid. The hazardousness of a liquid is also determined by its flash point, flammability range, evaporation rate, reactivity when contaminated or under the influence of heat, density and diffusion rate of vapors. However, when a flammable or combustible liquid burns for a short period of time, these factors have little effect on the flammability characteristics.

The combustion and flame propagation rates of various flammable liquids differ slightly from each other. The burnout rate of gasoline is 15.2 - 30.5 cm, kerosene - 12.7 - 20.3 cm of layer thickness per hour. For example, a layer of gasoline 1.27 cm thick will burn out in 2.5 - 5 minutes.

Combustion products

During the combustion of flammable and combustible liquids, in addition to the usual combustion products, some specific combustion products characteristic of these liquids are formed. Liquid hydrocarbons usually burn with an orange flame and produce thick clouds of black smoke. Alcohols burn with a clear blue flame, emitting a small amount of smoke. The combustion of some terpenes and ethers is accompanied by violent boiling on the surface of the liquid, their quenching is significant difficulty... Burning petroleum products, fats, oils and many other substances produces acrolein, a highly irritating toxic gas.

Flammable and combustible liquids of all types are transported by tankers as bulk cargo, as well as in portable containers, including placing them in containers.

Each vessel carries a large amount of flammable liquids in the form of fuel oil and diesel fuel, which are used to prop up the vessel and generate electricity. Fuel oil and diesel fuel are especially dangerous if they are heated before being fed to the injectors. If there are cracks in the pipelines, these fluids leak out and are exposed to ignition sources. Significant spreading of these fluids results in a very severe fire.

Other locations where flammable liquids are available include galleys, various workshops and rooms where lubricating oils are used or stored. In the engine room, residual oil and diesel fuel can be found on and under the equipment in the form of residues and films.

Extinguishing

In the event of a fire, quickly shut off the source of flammable or combustible liquid. Thus, the flow of combustible substances to the fire will be suspended, and people engaged in fighting the fire will be able to use one of the following methods of extinguishing the fire. For this purpose, a foam layer is used that covers the burning liquid and prevents the flow of oxygen to the fire. In addition, steam or carbon dioxide may be supplied to areas where combustion occurs. By turning off the ventilation, the oxygen supply to the fire can be reduced.

Cooling. It is necessary to cool tanks and areas under the influence of a fire using a spray or compact jet of water from the fire main.

Slowing down the spread of the flame . For this, fire extinguishing powder must be applied to the burning surface.

Due to the fact that there are no identical fires, it is difficult to establish a single method of extinguishing them. However, when extinguishing fires associated with the combustion of flammable liquids, it is necessary to be guided by the following.

1. In case of slight spreading of the burning liquid, powder or foam fire extinguishers or a spray of water.

2. In case of significant spreading of the burning liquid, powder fire extinguishers should be used with the support of fire hoses to supply foam or a spray jet. Equipment exposed to fire should be protected with a water jet

3. When spreading a burning liquid over the surface of the water, it is necessary first of all to limit the spreading. If you succeed in this, you need to create a layer of foam that covers the fire. In addition, you can use a large volume spray jet.

4. To prevent flue gas from escaping from inspection and metering hatches, use foam, powder, high-speed or low-speed water spray, blown horizontally across the opening until it can be closed.

5. To fight fires in cargo tanks, a deck foam extinguishing system and (or) a carbon dioxide extinguishing system or a steam extinguishing system, if available, should be used. For heavy oils, water mist can be used.

6. To extinguish a fire in the galley, it is necessary to use carbon dioxide or powder fire extinguishers.

7. If liquid fuel equipment is on fire, use foam or water spray.

Paints and varnishes

The storage and use of most paints, varnishes and enamels, except for those that are water-based, are associated with a high fire hazard. The oils in oil paints are not themselves flammable liquids (linseed oil, for example, has a flash point above 204 ° C). But paints usually contain flammable solvents, the flash point of which can be as low as 32 ° C. All other components of many paints are also flammable. The same applies to enamels and oil varnishes.

Even after drying, most paints and varnishes remain flammable, although their flammability is significantly reduced by evaporation of solvents. The flammability of a dry paint actually depends on the flammability of its base.

Flammability characteristics and combustion products

Liquid paint burns very intensely and produces a lot of thick black smoke. Burning paint can spread, so that a fire associated with burning paints resembles burning oils. Due to the formation of dense smoke and the release of toxic fumes when extinguishing burning paint in an enclosed space, use breathing apparatus.

Paint fires are often accompanied by explosions. Since paints are usually stored in tightly closed cans or drums with a capacity of up to 150 - 190 liters, a fire in the storage area can easily cause the drums to heat up, causing these containers to burst. The dyes contained in the drums instantly ignite and explode when exposed to air.

Normal location on board

Paints, varnishes and enamels are stored in painters' rooms located fore or aft under the main deck. Painting rooms should be made of steel or completely sheathed with metal. These areas can be serviced by a fixed carbon extinguishing system or other approved system.

Extinguishing

Insofar as liquid paints contain solvents with a low flash point; water is not suitable for extinguishing burning paints. To extinguish a fire associated with the burning of a large amount of paint, it is necessary to use foam. Water can be used to cool the surrounding surfaces. If small amounts of paint or varnish ignite, you can use carbon dioxide or dry powder extinguishers. You can use water to extinguish dry paint.

Flammable gases. In gases, molecules are not bound to each other, but are in free motion. As a result, the gaseous substance does not have its own form, but takes the form of the container in which it is enclosed. Most solids and liquids, if their temperature rises enough, can be converted to gas. This term "gas" means the gaseous state of a substance under the conditions of the so-called normal temperatures (21 ° C) and pressure (101.4 kPa).

Any gas that burns at normal oxygen levels in the air; called flammable gas. Like other gases and vapors, flammable gases only burn when their concentration in the air is within the flammability range and the mixture is heated to the ignition temperature. Typically, flammable gases are stored and transported on board ships in one of the following three states: compressed, liquefied and cryogenic. Compressed gas is a gas that, at normal temperature, is completely gaseous in a pressurized container. Liquefied gas is a gas that, at normal temperatures, is partly liquid and partly gaseous in a pressurized container. Cryogenic gas is gas that is liquefied in a container at well below normal temperatures at low and medium pressures.

Major dangers

The dangers posed by the gas in the container are different from those that arise when it leaves the container. Let's consider each of them separately, although they can exist simultaneously.

Dangers of limited scope. When a gas is heated in a limited volume, its pressure increases. In the presence of a large amount of heat, the pressure can rise so much that it will cause gas leakage or rupture of the container. In addition, contact with fire can reduce the strength of the container material, which also contributes to its rupture.

To prevent explosions of compressed gases, safety valves and fusible links are installed on tanks and cylinders. As the gas expands in the container, the safety valve opens, resulting in a decrease in internal pressure. The spring-loaded device will close the valve again when the pressure has dropped to a safe level. A melt metal insert can also be used, which will melt at a certain temperature. The insert plugs the hole usually found in the upper part of the container body. The heat generated by the fire threatens the container containing the compressed gas, causes the insert to melt and allows the gas to escape through the hole, thereby preventing pressure build-up in the insert that leads to an explosion. But since such a hole cannot be closed, gas will escape until the container is empty.

An explosion can occur in the absence of safety devices or if they do not work. An explosion can also be caused by a rapid increase in pressure in the container, when the safety valve is unable to release the pressure at a rate that would prevent the build-up of pressure capable of causing an explosion. Tanks and cylinders can, in addition, explode if their strength decreases as a result of contact of flames with their surfaces. The impact of flame on the walls of the container, which are above the level of the liquid, is more dangerous than contact with the surface that is in contact with the liquid. In the first case, the heat emitted by the flame is absorbed by the metal itself. In the second case, most of the heat is absorbed by the liquid, but this also creates a dangerous situation, since the absorption of heat by the liquid can cause a dangerous, although not so rapid increase in pressure. Spraying the surface of the container with water prevents a rapid increase in pressure, but does not guarantee the prevention of an explosion, especially if the flame also affects the walls of the container.

Capacity rupture. Compressed or liquefied gas has a large amount of energy held back by the container in which it is located. When a container ruptures, this energy is usually released very quickly and violently. Gas escapes, and the container or its elements scatter.

Ruptures of containers containing liquefied flammable gases under the influence of fires are not uncommon. This type of destruction is called a boiling liquid expanding vapor explosion. In this case, as a rule, the upper part of the container is destroyed, in the place where it comes into contact with the gas. The metal stretches, becomes thinner and breaks along its length.

The force of the explosion depends mainly on the amount of evaporating liquid during the destruction of the container and the mass of its elements. Most explosions occur when the container is 1/2 to about 3/4 full of liquid. A small container without insulation can explode after a few minutes, and a very large container, even if it is not cooled with water, takes only a few hours. Uninsulated containers containing liquefied gas can be protected against explosion by supplying water to them. A water film must be supported in the top of the container where the vapors are.

Dangers associated with gas escaping from a confined volume. These hazards depend on the properties of the gas and where it leaves the container. All gases, except oxygen and air, are hazardous if they displace the air required for breathing. This is especially true for odorless and colorless gases such as nitrogen and helium, as there are no signs of their appearance.

Toxic or poisonous gases are life-threatening. If they go outside near a fire, then they block access to the fire for people who are fighting with it, or force them to use breathing apparatus.

Oxygen and other oxidizing gases are non-flammable, but they can cause inflammable substances to ignite at temperatures below normal.

Skin contact with the gas causes frostbite, which can be serious with prolonged exposure. In addition, when exposed to low temperatures, many materials, such as carbon steel and plastics, become brittle and degrade.

Flammable gases escaping from the container pose a risk of explosion and fire, or both. The escaping gas explodes when it accumulates and mixes with air in a confined space. The gas will burn without exploding if the gas-air mixture accumulates in an amount insufficient for an explosion, or if it ignites very quickly, or if it is in an unlimited space and can be scattered. Thus, when flammable gas escapes onto the open deck, a fire usually occurs. But when a very large amount of gas escapes, the surrounding air or the ship's superstructure can so limit its dispersion that an explosion will occur, called an open air explosion. This is how liquefied non-cryogenic gases, hydrogen and ethylene explode.

Properties of some gases.

The most important properties of some flammable gases are discussed below. These properties explain the varying degrees of the hazards that arise in the case of the accumulation of gases in a limited volume or during their spreading.

Acetylene. This gas is transported and stored, as a rule, in cylinders. For safety reasons, a porous filler is placed inside the acetylene cylinders - usually diatomaceous earth, which has very small pores or cells. In addition, the aggregate is impregnated with acetone, a flammable material that readily dissolves acetylene. Thus, acetylene cylinders contain significantly less gas than it seems. Several fuse-links are installed in the upper and lower parts of the cylinders, through which the gas escapes into the atmosphere if the temperature or pressure in the cylinder rises to a dangerous level.

The release of acetylene from the cylinder can be accompanied by an explosion or fire. Acetylene ignites more easily than most flammable gases and burns more quickly. This increases explosions and makes ventilation difficult to prevent explosion. Acetylene is only slightly lighter than air, so it mixes easily with air when it leaves the container.

Anhydrous ammonia. It consists of nitrogen and hydrogen and is used mainly for the production of fertilizers, as a refrigerant and a source of hydrogen required for the thermal treatment of metals. It is a fairly toxic gas, but its inherent pungent odor and irritating effect serve as a good warning of its appearance. Strong leaks of this gas caused the rapid death of many people before they could leave the area of ​​its appearance.

Anhydrous ammonia is transported in trucks, rail tank cars and barges. It is stored in cylinders, tanks and cryogenic in insulated containers. Explosions of expanding vapors of a boiling liquid in uninsulated cylinders containing anhydrous ammonia are rare due to the limited flammability of the gas. If such explosions do occur, they are usually associated with fires of other combustible substances.

Anhydrous ammonia can explode and burn on its way out of a cylinder, but its high LEL and low calorific value greatly reduce this hazard. The release of large quantities of gas when used in refrigeration systems, as well as storage when unusually high pressure may cause an explosion.

Ethylene. It is a gas composed of carbon and hydrogen. It is usually used in the chemical industry, for example, in the manufacture of polyethylene; in smaller quantities it is used for fruit ripening. Ethylene has a wide flammability range and burns quickly. While non-toxic, it is an anesthetic and asphyxiant.

Ethylene is transported in a compressed form in cylinders and in a cryogenic state in insulated trucks and rail tank cars. Most ethylene cylinders are protected against overpressure by bursting discs. Ethylene cylinders used in medicine may have fusible links or combined safety devices. Safety valves are used to protect the tanks. Cylinders can be destroyed by fire, but not the expanding vapor of a boiling liquid, since there is no liquid in them.

When ethylene leaves the cylinder, explosion and fire are possible. This is facilitated by the wide flammability range and the high combustion rate of ethylene. In a number of cases, associated with the release of large amounts of gas into the atmosphere, explosions occur.

Liquefied natural gas. It is a mixture of substances consisting of carbon and hydrogen, the main component of which is methane. It also contains ethane, propane and butane. Liquefied natural gas used as a fuel is non-toxic, but it is an asphyxiant.

Liquefied natural gas is transported in a cryogenic state on gas carriers. Stored in insulated containers protected from overpressure by safety valves.

The release of liquefied natural gas from a cylinder into a closed room can be accompanied by an explosion and fire. Test data and experience show that LNG explosions do not occur in the open air.

Liquefied petroleum gas

This gas is a mixture of substances consisting of carbon and hydrogen. Industrial LPG is typically propane or normal butane, or a mixture of these with small amounts of other gases. It is non-toxic, but it is an asphyxiant. It is used mainly as fuel in cylinders for domestic needs.

Liquefied petroleum gas is transported in the form of liquefied gas in uninsulated cylinders and tanks on trucks, rail tank cars and gas carriers. In addition, it can be transported by sea in a cryogenic state in heat-insulated containers. Stored in cylinders and insulated tanks. Relief valves are commonly used to protect LPG tanks from overpressure. Some cylinders have fusible links and sometimes safety valves and fusible links together. Most of the containers can be destroyed by explosions of expanding vapors of a boiling liquid.

The release of liquefied petroleum gas from the container can be accompanied by an explosion and fire. Since this gas is mainly used indoors, explosions are more frequent than fires. The risk of explosion is exacerbated by the fact that from 3.8 liters of liquid propane or butane, 75 - 84 m 3 of gas are obtained. An explosion may occur if large quantities of LPG are released into the atmosphere.

Normal location on board

Liquefied flammable gases such as liquefied petroleum and natural gases are transported in bulk on tankers. In cargo ships, flammable gas cylinders are carried on deck only.

Extinguishing

Fires involving flammable gases can be extinguished with extinguishing powders. For some types of gases, carbon dioxide and freons should be used. In case of fires caused by the ignition of flammable gases, a great danger for people fighting the fire is the high temperature, as well as the fact that the gas will continue to escape even after the fire has been extinguished, and this can cause a renewal of the fire and an explosion. Powder and sprayed water jet create a reliable heat shield, while carbon dioxide and freons cannot create a barrier to thermal radiation generated during gas combustion.

It is recommended that the gas be allowed to burn until its flow cannot be shut off at the source. No attempt should be made to extinguish a fire unless the gas flow is interrupted. As long as the flow of gas to the fire cannot be stopped, the efforts of people fighting the fire should be directed towards protecting the surrounding combustible materials from: ignition by a flame or the high temperature that occurs during a fire. For these purposes, compact or spray water jets are usually used. As soon as the flow of gas from the container stops, the flame should go out. But if the fire was extinguished before the end of the gas outflow, it is necessary to monitor the prevention of ignition of the escaping gas.

A fire associated with the burning of liquefied flammable gases, such as LPG and natural gas, can be controlled and extinguished by creating a dense foam layer on the surface of the spreading combustible.

Class B fires are combustion of liquid substances that can be soluble in water (alcohols, acetone, glycerin) and insoluble (gasoline, oil, fuel oil).

Just like solids, flammable liquids give off vapors when they burn. The vaporization process differs only in speed - for liquids it happens much faster.

The hazard level of flammable liquids depends on the flash point - the lowest temperature of a condensed substance at which vapors above it can flare up under the influence of an ignition source, but combustion does not occur after its elimination. Also, the hazard of flammable liquids is influenced by the flash point, flammability range, evaporation rate, reactivity under the influence of heat, density and diffusion rate of vapors.

Flammable liquids are considered to be liquids with a flash point of up to 61 ° C (gasoline, kerosene), combustible - with a flash point above 61 ° C (acids, vegetable and lubricating oils).

Class B fires

A class B fire can result from the combustion of the following materials:

• paints and varnishes;
• flammable and flammable liquids;
• liquefied solids (paraffins, stearins).

1. Varnishes, paints, enamels. Liquids on water based less dangerous than oil. The flash point of the oils contained in paints, varnishes and enamels is quite high (about 200 ° C), but the flammable solvents contained in them flare up much earlier - at a temperature of 32 ° C.

Paints burn well, producing a lot of thick black smoke and toxic gases. When paints or varnishes ignite, the containers in which they are located often explode.

It is impossible to extinguish paints, varnishes and enamels with water due to the low flash point. Water can only be used to cool the surrounding objects or extinguish dry paint.

The burning of paints and varnishes is suppressed with foam, in some cases - carbon dioxide or dry powder fire extinguishers.

1. Flammable and flammable liquids. Their combustion is accompanied by the release of non-standard combustion products characteristic of just such liquids.

Alcohols burn with a blue transparent fire with a small amount of smoke.

Combustion of liquid hydrocarbons is characterized by an orange flame and the formation of thick, dark smoke.

Esters and terpenes burn while boiling on their surface.

In the process of burning petroleum products, oils and fats, a poisonous irritating gas, acrolein, is released.

Extinguishing flammable and combustible liquids is not easy, and each fire has its own characteristics and sequence of suppression. First, you need to shut off the ingress of liquid into the fire.

The surrounding objects and containers with burning liquids should be cooled with water. There are several ways to extinguish a class B fire:

• a foam or powder fire extinguisher or a sprayed stream of water can cope with a small fire;
• in the case of a large spread of flammable liquid, it is better to use dry powder fire extinguishers in conjunction with fire hoses to supply foam;
• if the liquid burns on the surface of the water, then first you need to limit its spreading, and then cover the flame with foam or a powerful water jet;
• when extinguishing equipment operating on liquid fuel, spray water or foam must be used.

Paraffins and other similar refined products. Putting them out with water is strictly prohibited and dangerous. Small fires can be suppressed with carbon dioxide fire extinguishers. Large fires - with foam.

Combustion of liquids.

All flammable liquids are capable of evaporating, and their combustion occurs only in the vapor phase located above the surface of the liquid. The amount of vapor depends on the composition and temperature of the liquid. Combustion of vapors in air is possible only at a certain concentration.

The lowest temperature of a liquid at which the concentration of its vapors in a mixture with air ensures the ignition of the mixture from an open ignition source without subsequent stable combustion is called the flash point. At the flash point, stable combustion does not occur, since at this temperature the concentration of the mixture of liquid vapors with air is not stable, which is necessary for such combustion. The amount of heat released during the flash is not enough to continue burning, and the substance is not yet sufficiently heated. In order to ignite a liquid, you need not a short-term, but a long-term ignition source, the temperature of which would be higher than the autoignition temperature of a mixture of vapors of this liquid with air.

In accordance with GOST 12.1.004-76, a combustible liquid (GZH) is understood as a liquid that can burn independently after removing the ignition source and has a flash point above + 61 ° C (in a closed crucible) or + 66 ° C (in an open crucible).

A highly flammable liquid (FL) is a liquid that can burn independently after removing the ignition source and has a flash point no higher than + 61 ° C (in a closed crucible) or + 66 ° C (in an open crucible).

The flash point is the lowest temperature at which a liquid becomes especially dangerous in terms of fire, therefore, its value is taken as the basis for the classification of flammable liquids according to their degree fire hazard... The fire and explosion hazard of liquids can also be characterized by the temperature limits of ignition of its vapors.

The temperature of the liquid at which the concentration of saturated vapors in the air in a closed volume is capable of igniting when exposed to an ignition source is called the lower temperature limit of ignition. The temperature of the liquid at which the concentration of saturated vapors in the air in a closed volume can still ignite when exposed to an ignition source is called the upper temperature limit of ignition.

The temperature limits of ignition of some liquids are given in table. 29.

Table 29 The temperature limits of ignition of some liquids: acetone, gasoline A-76, benzene, tractor kerosene, ethyl alcohol.

The temperature limits indicate in which temperature range the liquid vapors will form combustible mixtures with air.

Combustion is a complex physical and chemical process of interaction of a combustible substance and an oxidizer, characterized by a self-accelerating chemical excess and accompanied by the release of a large amount of heat and radiant energy.

For the onset and development of the combustion process, a combustible substance, an oxidizer and an ignition source are required, which initiates the reaction between the fuel and the oxidizer. Combustion is distinguished by a variety of types and characteristics. Depending on the state of aggregation of combustible substances, combustion can be homogeneous and heterogeneous. With homogeneous combustion, the components of the combustible mixture are in the same state of aggregation (more often in gaseous form). Moreover, if the reacting components are mixed, then the combustion of the premixed mixture occurs, which is sometimes called kinetic (since the combustion rate in this case depends only on the kinetics of chemical transformations). If the gaseous components are not mixed, then diffuse combustion occurs (for example, when a flow of combustible vapors enters the air). The combustion process is limited by the diffusion of the oxidant. Combustion characterized by the presence of a phase separation in the combustible system (for example, the combustion of a liquid and solid materials) is heterogeneous. Combustion is also differentiated by the speed of flame propagation, and depending on this factor, it can be deflagration (within a few m / s), explosive (tens and hundreds of m / s) and detonation (thousands of m / s). In addition, combustion is laminar (layer-by-layer propagation of the flame front along the fresh combustible mixture) and turbulent (mixing of the flow layers with increased speed burnout).

As a rule, fires are characterized by heterogeneous diffuse combustion, and the rate of combustion depends on the diffusion of atmospheric oxygen in the environment. The emergence and development of fires significantly depends on the degree of fire hazard of substances. One of the criteria for the fire hazard of solid, liquid and gaseous substances is the autoignition temperature, i.e. the ability of a substance to ignite spontaneously.

For the initiation of an endogenous fire, it is necessary to have a substance that can quickly oxidize when low temperatures as a result of which spontaneous combustion may occur. This property of the substance is called chemical activity to spontaneous combustion. As a result of oxidation and heat accumulation, self-heating turns into ignition.

Ignition is a qualitatively new process different from self-heating, characterized by high oxidation rates, heat release and light emission. Self-heating and self-ignition is generated by separate small nests, and therefore, it is very difficult to detect it.

Spontaneous combustion occurs due to the accumulation of heat inside the substance and does not depend on the influence of an external heat source.

All substances, according to their danger in relation to spontaneous combustion, can be divided into four groups:

* substances that can spontaneously ignite on contact with air at ordinary temperatures ( vegetable oils, drying oil, oil paints, primers, lignite and bituminous coals, white phosphorus, aluminum and magnesium powder, soot, etc.);

* substances that can ignite spontaneously at elevated ambient temperatures (50 ° C and above) and as a result of external heating to temperatures close to the temperatures of their ignition and self-ignition (films of nitrolacs, pyroxylin and nitroglycerin powders, vegetable semi-drying oils and drying oils made from them, turpentine etc.);

* substances, the contact of which with water causes the combustion process (alkali metals, carbides of alkali metals, calcium carbide, aluminum, etc.);

* substances that cause spontaneous combustion of flammable substances in contact with them (nitric, magnesium, hypochlorous, chloride and other acids, their anhydrides and salts; sodium, potassium, hydrogen peroxides, etc.; gases - oxidizing agents - oxygen, chlorine, etc.).

The most important characteristic of solid bulk materials is the degree of their flammability.

All materials, regardless of the field of application, are divided into three groups:

* Fireproof materials, which, under the influence of fire or high temperature, do not ignite, do not smolder or char.

* Flame retardant materials, which, under the influence of fire or high temperature, ignite, smolder or char and continue to burn or smolder in the presence of a fire source, and after removing the fire source, combustion and smoldering cease.

* Combustible materials, which, when exposed to fire or high temperature, ignite or smolder and continue to burn or smolder after removal of the fire source.

Some chemical substances, combustible and lubricants in certain concentrations and conditions are capable not only of ignition from heat sources, but also of an explosion.

The fire hazard of substances (gaseous, liquid, solid) is determined by a number of indicators, the characteristics and quantity of which depend on the state of aggregation of the given substance.

Fire hazard criteria for solid, liquid and gaseous substances are: flash point, ignition and self-ignition temperature, flame spread index, oxygen index, smoke production coefficient, indicator of toxicity of combustion products, etc.

One of the criteria for the fire hazard of flammable liquids is the flash point.

Flash point of vapor A combustible liquid is the minimum temperature of the liquid at which, under normal pressure, the liquid releases vapor over its free surface in an amount sufficient to form a mixture with the surrounding air that flares up when an open flame is brought to it.

For flammable liquids(Flammable liquids) include liquids that can burn independently after removing the ignition source and have a flash point of no higher than 61 °? in a closed crucible and 66 ° C in an open crucible.

For flammable liquids(ГЖ) include liquids that can burn independently after removing the ignition source and have a flash point above 61 °? in a closed crucible and 66 ° C in an open crucible.

Ignition temperature is called the minimum temperature at which a liquid heated under certain conditions ignites when a flame is brought to it and burns for (at least) 5s. The flash point is more dangerous than the flash point, since the vapors and liquid, if ignited, continue to burn after the flame has been removed.

At construction works, especially when preparing mastics, painting works, it is necessary to clearly know the degree of flammability of nearby materials and structures, properly organize control to prevent fires and provide the necessary amount of extinguishing agents.

Depending on the type of combustible material, fires are divided into classes: A, B, C and D (Fig. 4.2.1.).

Fires are accompanied by dangerous and harmful phenomena that must be taken into account in the design and construction of buildings and structures, in the conduct of work. From point of view fire safety it is very important to make the right planning decision, to offer protection building structures, provide the necessary escape routes.

Explosion is a kind of burning and is characterized by extremely fast processes physical and chemical conversions of combustible substances with the formation of huge amounts of thermal energy, practically without heat dissipation into the environment.

There are two concentration limits for the explosiveness of substances.

The minimum concentration of gas, vapor or dust in a mixture with air that can ignite or explode is calledlower flammable limit (LP).

The highest concentration of gases or vapors in the air, at which ignition or explosion is still possible (further, with an increase in concentration, ignition or explosion is considered impossible)n calledupper flammable limit (VP).

Explosion differs from combustion by an even greater speed of fire propagation. So, the speed of propagation of a flame in an explosive mixture located in closed pipe, 2000 - 3000 m / s. Combustion of a mixture at such a rate is called detonation... The appearance of detonation is explained by the compression, heating and movement of the unburned mixture ahead of the flame front, which leads to acceleration of flame propagation and the appearance of a shock wave in the mixture. Air shock waves formed during the explosion of a gas-air mixture have a large energy reserve and propagate over considerable distances. While driving, they destroy structures and can cause accidents. The assessment of the danger of air shock waves for people and various structures is carried out according to two main parameters - pressure in the front of the shock wave? P and compression f. The compression phase is understood as the time of action of excess pressure in the wave. When φ? 11 ms, a pressure of 0.9-113 Pa is considered safe for people. Calculations of safe distances for people with a potential explosion threat are carried out only by the pressure in the shock front, since in explosions, f is always many times greater than 11 ms.