FIRE TACTICS

LECTURE NOTES

Topic: Fire and its development

Arkhangelsk, 2015

Literature:

2. Federal law dated July 22, 2008 N 123 Federal Law “Technical regulations on fire safety requirements.”

3. Terebnev V.V., Podgrushny A.V. Fire tactics - M.: - 2007

I'M WITH. Pozik. RTP Directory. Moscow. 2000

5. Ya.S. Pozik. Fire tactics. Moscow. Stroyizdat. 1999

6. M.G.Shuvalov. Basics of firefighting. Moscow. Stroyizdat. 1997

Study questions:

1. Question General concept of the combustion process. Conditions necessary for combustion (combustible substance, oxidizer, ignition source) and its cessation. Combustion products. Complete and incomplete combustion. Brief information about the nature of combustion of solid combustible materials, flammable and combustible liquids, gases, flammable mixtures of vapors, gases and dusts with air

2. Question

General concept of the combustion process. Conditions necessary for combustion (combustible substance, oxidizer, ignition source) and its cessation. Combustion products. Complete and incomplete combustion. Brief information about the nature of combustion of solid combustible materials, flammable and combustible liquids, gases, flammable mixtures of vapors, gases and dusts with air.

Combustion is any oxidation reaction in which heat is released and the glow of burning substances or their decomposition products is observed.

For combustion to occur, certain conditions are necessary, namely the combination in one place at one time of three main components:

· flammable substances, in the form of combustible materials (wood, paper, synthetic materials, liquid fuel, etc.);

· an oxidizing agent, which is most often air oxygen during combustion of substances; in addition to oxygen, oxidizing agents can be chemical compounds containing oxygen in their composition (saltpeter, perchlorites, nitric acid, nitrogen oxides) and individual chemical elements: chlorine, fluorine, bromine;

· an ignition source that constantly and in sufficient quantities enters the combustion zone (spark, flame).

ignition source

O 2 flammable substance

The absence of one of the listed elements makes it impossible for a fire to occur or leads to the cessation of combustion and the elimination of the fire.

Most fires involve the combustion of solid materials, although the initial stage of a fire may involve the combustion of liquid and gaseous flammable substances used in modern industrial production.

Ignition and combustion of most flammable substances occurs in the gas or vapor phase. The formation of vapors and gases from solid and liquid flammable substances occurs as a result of heating. In this case, liquids boil with evaporation, and materials volatilize, decompose, or pyrolyze from the surface of solids.

Solid flammable substances behave differently when heated:

· some (sulfur, phosphorus, paraffin) melt;

· others (wood, peat, coal, fibrous materials) decompose with the formation of vapors, gases and solid coal residues;

third (coke, charcoal, some metals) do not melt or decompose when heated. The vapors and gases released from them mix with air and oxidize when heated.

The glow of the flame occurs because light is emitted by hot carbon particles that do not have time to burn.

A mixture of a flammable substance with an oxidizer is called a combustible mixture. Depending on state of aggregation flammable mixture, combustion can be:

Homogeneous (gas-gas);

Heterogeneous (solid-gas, liquid-gas).

In homogeneous combustion, the fuel and oxidizer are mixed; in heterogeneous combustion, they have an interface.

Depending on the ratio of oxidizer and combustible substance in the flammable mixture, two types of combustion are distinguished:

· complete combustion - combustion of lean mixtures, when the oxidizer is much larger than the combustible substance and the resulting products are not capable of further oxidation - carbon dioxide, water, nitrogen oxides and sulfur.

· incomplete combustion - combustion of rich mixtures, when the oxidizer is significantly less than the combustible substance, incomplete oxidation of the decomposition products of substances occurs. Products of incomplete combustion are carbon monoxide, alcohols, ketones, acids.

A sign of incomplete combustion is smoke, which is a mixture of vapor, solid and gaseous particles. In most cases, fires involve incomplete combustion of substances and strong smoke emission.

Combustion can occur in several ways:

· flash – rapid combustion of a combustible mixture, not accompanied by the formation of compressed gases. It does not always lead to fire, since the heat generated is not enough;

· fire – the occurrence of combustion under the influence of an external ignition source;

· ignition – ignition using a flame;

· spontaneous combustion – the occurrence of combustion under the influence of an internal ignition source (thermal-exothermic reactions).

· spontaneous combustion – spontaneous combustion with the appearance of a flame.

Characteristics of flammable substances

Substances that can burn independently after removing the source of ignition are called combustible, in contrast to substances that do not burn in air and are called non-flammable. An intermediate position is occupied by difficultly combustible substances that ignite when exposed to an ignition source, but stop burning after the latter is removed.

All flammable substances are divided into the following main groups.

1. Combustible gases (GG)- substances capable of forming flammable and explosive mixtures with air at temperatures not exceeding 50° C. Combustible gases include individual substances: ammonia, acetylene, butadiene, butane, butyl acetate, hydrogen, vinyl chloride, isobutane, isobutylene, methane, carbon monoxide, propane , propylene, hydrogen sulfide, formaldehyde, as well as vapors of flammable and combustible liquids.

2. Flammable liquids (flammable liquids)- substances capable of burning independently after removal of the ignition source and having a flash point not higher than 61° C (in a closed crucible) or 66° (in an open crucible). These liquids include individual substances: acetone, benzene, hexane, heptane, dimethylforamide, difluorodichloromethane, isopentane, isopropylbenzene, xylene, methyl alcohol, carbon disulfide, styrene, acetic acid, chlorobenzene, cyclohexane, ethyl acetate, ethylbenzene, ethyl alcohol, as well as mixtures and technical products gasoline, diesel fuel, kerosene, white alcohol, solvents.

3. Flammable liquids (FL)- substances capable of burning independently after removal of the ignition source and having a flash point above 61° (in a closed crucible) or 66° C (in an open crucible). Flammable liquids include the following individual substances: aniline, hexadecane, hexyl alcohol, glycerin, ethylene glycol, as well as mixtures and technical products, for example, oils: transformer oil, vaseline, castor oil.

4. Combustible dusts (GP)- solids in a finely dispersed state. Combustible dust in the air (aerosol) can form explosive mixtures with it. Dust (aerogel) settled on walls, ceilings, and equipment surfaces is a fire hazard.

Combustible dusts are divided into four classes according to the degree of explosion and fire hazard.

Class 1 - the most explosive - aerosols with a lower concentration limit of flammability (explosiveness) (LCEL) of up to 15 g/m 3 (sulfur, naphthalene, rosin, mill dust, peat, ebonite).

Class 2 - explosive - aerosols with an LEL value from 15 to 65 g/m 3 (aluminum powder, lignin, flour dust, hay dust, shale dust).

3rd class - the most fire hazardous - aerogels with an LFL value greater than 65 g/m 3 and a self-ignition temperature of up to 250 ° C (tobacco, elevator dust).

4th class - fire hazardous - aerogels with an LFL value greater than 65 g/m 3 and a self-ignition temperature greater than 250 ° C ( sawdust, zinc dust).

Below are some characteristics of flammable substances necessary for predicting emergency situations.

Indicators of explosion and fire hazard of flammable gases and vapors of flammable and combustible liquids

Table 1.

substance	symbols	flash point	concentration limits of explosion (ignition)
		tspr, ° C	lower (NKPV)	upper (VKPV)
			% by volume	g/m 3 at 20° C	by volume	g/m 3 at 20 °C
ETHERS AND ETHERS
Amyl acetate	LVZH		1.08	90.0	10.0	540.0
Butyl acetate	LVZH		1.43	83.0	15.0	721.0
Diethyl alcohol Ethylene oxide	LVZH VV	-4 3 -	1.9 3.66	38.6 54.8	51.0 80.0	1576.0 1462.0
ethyl acetate	LVZH	-3	2.98	80.4	11.4	407.0
ALCOHOLS
Amyl	LVZH		1.48	43.5	-	-
Methyl	LVZH		6.7	46.5	38.5	512.0
Ethyl	LVZH		3.61	50.0	19.0	363.0
LIMIT HYDROCARBONS
Butane	GG	-	1.8	37.4	8.5	204.8
Hexane	LVZH	-23	1.24	39.1	6.0	250.0
Methane	GG	-	5.28	16.66	15.4	102.6
Pentane	LVZH	-44	1.47	32.8	8.0	238.5
Propane	GG	-	2.31	36.6	9.5	173.8
Ethane	GG	-	3.07	31.2	14.95	186.8
UNSATURATE HYDROCARBONS
Acetylene	BB	-	2.5	16.5	82.0	885.6
Butylene	GG	-	1.7	39.5	9.0	209.0
Propylene	GG	-	2.3	34.8	11.1	169.0
Ethylene	BB	-	3.11	35.0	35.0	406.0
AROMATIC HYDROCARBONS
Benzene	LVZH	-12	1.43	42.0	9.5	308.0
Xylene	LVZH		1.0	44.0	7.6	334.0
Naphthalene	GP4	-	0.44	23.5	-	-
Toluene	LVZH		1.25	38.2	7.0	268.0
COMPOUNDS CONTAINING NITROGEN AND SULFUR
Ammonia	GG	-	17.0	112.0	27.0	189.0
Aniline	GJ		1.32	61.0	-	-
Hydrogen sulfide	GG	-	4.0	61.0	44.5	628.0
Carbon disulfide	LVZH	-43	1.33	31.5	50.0	157.0
PETROLEUM PRODUCTS AND OTHER SUBSTANCES
Gasoline (boiling point 105 ° C) Gasoline (same 64...94 ° C) Hydrogen	LVZH LVZH GG	-36 -36 -	2.4 1.9 4.09	137.0 - 3.4	4.9 5.1 880.0	281.0 - 66.4
Kerosene	LVZH	>40	0.64	-	7.0	-
Petroleum gas	GG	-	3.2	-	13.6	-
Carbon monoxide	GG	-	12.5	145.0	80.0	928.0
Turpentine	LVZH		0.73	41.3	-	-
Coke gas	GG	-	5.6	-	30.4	-
Blast gas	GG	-	46.0	-	68.0	-

Flash point- the lowest temperature of a liquid at which a steam-air mixture is formed near its surface, capable of flaring up from a source and burning, without causing a stable combustion of the liquid.

Upper and lower explosive concentration limits(ignition) - respectively, the maximum and minimum concentration of flammable gases, vapors of flammable or combustible liquids, dust or fibers in the air, above and below which an explosion will not occur even if there is a source of initiation of the explosion.

The aerosol is capable of exploding when solid particle sizes are less than 76 microns.

Upper explosive limits dusts are very large and are practically difficult to reach indoors, so they are not of interest. For example, the VCPV of sugar dust is 13.5 kg/m 3 .

BB- explosive substance - a substance capable of explosion or detonation without the participation of oxygen in the air.

Auto-ignition temperature- the lowest temperature of a combustible substance at which a sharp increase in the rate of exothermic reactions occurs, ending in the occurrence of flaming combustion.

General concept of fire. Brief description phenomena occurring during a fire. Hazardous Fire Factors and their secondary manifestations. Classification of fires. Gas exchange in a fire. Conditions conducive to the development of fire, the main routes of fire spread.

Fire – uncontrolled combustion causing material damage, harm to the life and health of citizens, and the interests of society and the state. (No. 69-FZ “On Fire Safety” dated December 21, 1994).

By fire uncontrolled combustion is considered outside a special focus causing material damage (RTP directory, P.P. Klyus, V.P. Ivannikov).

Fire is a complex physical and chemical process, which, in addition to combustion, includes general phenomena that are characteristic of any fire, regardless of its size and place of origin (mass and heat transfer, gas exchange, smoke formation). These phenomena are interconnected and develop in time and space. Only eliminating the fire can lead to their cessation.

General phenomena can lead to the emergence of particular phenomena, i.e. those that may or may not occur in fires. These include: explosions, deformation and collapse of technological devices and installations, building structures, boiling or release of petroleum products from tanks, etc.

A fire is also accompanied by social phenomena that cause not only material but also moral damage to society. These include death, thermal injuries, poisoning by toxic combustion products, and panic. This is a special group of phenomena that causes significant psychological overload and stress in people.

Signs of a fire:

– combustion process;

– gas exchange;

– heat exchange.

They change in time, space and are characterized by fire parameters.

The main factors characterizing the possible development of the combustion process in a fire include: fire load, mass burnout rate, linear speed flame propagation over the surface of burning materials, intensity of heat release, flame temperature, etc.

Under fire load understand the mass of all flammable and slow-burning materials located indoors or in open space, related to the floor area of ​​the room or the area occupied by these materials in open space (kg/m2).

Burnout rate– loss of mass of material (substance) per unit of time or combustion (kg/m 2 s).

Linear speed of combustion propagation– a physical quantity characterized by the translational movement of the flame front in a given direction per unit time (m/s).

Under the temperature of a fire in fences understand the average volumetric temperature of the gas environment in the room.

Under the temperature of fire in open spaces– flame temperature.

During a fire, gaseous, liquid and solid substances are released. They are called combustion products, i.e. substances formed as a result of combustion. They spread in a gaseous environment and create smoke.

Smoke– a dispersed system of combustion products and air, consisting of gases, vapors and hot particles. The volume of smoke released, its density and toxicity depend on the properties of the burning material and on the conditions of the combustion process.

Smoke formation in a fire - the amount of smoke, m 3 /s, emitted from the entire area of ​​the fire.

Smoke concentration– the amount of combustion products contained per unit volume of the room (g/m3, g/l, or in volume fractions).

Fire area(S P)– projection area of ​​surface combustion of solids and liquid substances and materials on the surface of the ground or floor of the room.

Fire area has its own borders: perimeter and front.

Fire perimeter (P P) is the length of the outer boundary of the fire area.

Fire front (F P) – part of the fire perimeter in the direction of which combustion spreads.

Fire area shapes

Depending on the location of the fire, the type of combustible materials, space-planning solutions of the facility, characteristics of structures, meteorological conditions and other factors, the fire area has a circular, angular and rectangular shape (Fig. 2 - 5).

Circular the shape of the fire area (Fig. 2) occurs when a fire occurs in the depths of a large area with a fire load and, in relatively calm weather, spreads in all directions with approximately the same linear speed (timber warehouses, grain tracts, combustible coatings large areas, production and warehouse premises large area etc.).

Corner shape (Fig. 3, 4 ) characteristic of a fire that occurs at the border of a large area with a fire load and spreads inside the corner under any meteorological conditions. This form of fire area can occur on the same objects as the circular one. The maximum angle of the fire area depends on the geometric shape of the area with the fire load and the location of the combustion. Most often, this form is found in areas with an angle of 90° and 180°.

Rectangular the shape of the fire area (Fig. 5) occurs when a fire occurs on the border or in the depths of a long section with a flammable load and spreads in one or several directions: downwind - with a larger one, against the wind - with a smaller one, and in relatively calm weather with approximately the same linear speed (long buildings of small width of any purpose and configuration, rows of residential buildings with outbuildings in rural populated areas etc.).

Fires in buildings with small rooms take on a rectangular shape from the start of combustion. Ultimately, as combustion spreads, the fire can take the shape of a given geometric section (Fig. 6)

The shape of the area of ​​a developing fire is the main one for determining the design scheme, the directions of concentration of forces and extinguishing means, as well as the required quantity of them under the appropriate parameters for carrying out combat operations. To determine the design scheme, the real shape of the fire area is reduced to figures of regular geometric shape (Fig. 7 a, b, c): circle with radius R(with a circular shape), a sector of a circle with a radius R and angle α (with angular shape), rectangle with side width a and length b(with a rectangular shape).

Fig.7. Calculation schemes for fire area shapes

A) circle; b) rectangle; c) sector

Circular shape of the fire area

Fire area – S P = pR 2 S P = 0.785 D 2

Fire perimeter – P P = 2pR

Fire front – Ф П = 2pR

Angular fire shape

Fire area – S P = 0.5 aR 2

Fire perimeter – P P = R(2+a)

Fire front – Ф П = aR

Linear velocity of propagation – V L = R/t

Rectangular fire shape

Fire area – S P = a b.

With development in two directions S P = a (b 1 + b 2)

Fire perimeter – P P = 2 (a+b).

Development in two directions P P = 2)