How many groups are combustible building materials. Fire hazard indicators of building materials

Penoleks is a type of heat-insulating materials, which is an extruded polystyrene foam.
Most people, choosing the right insulation for the home, are guided by various characteristics of the material. Many are interested in low price, some prefer ease of installation, and only a small part thinks about environmental safety and resistance to fire. What are the characteristics of penoplex, is it combustible or completely non-combustible? Strange, but there are a lot of opinions about this indicator, so it’s worth understanding the fire safety of foam plastic in more detail.

What class of flammability does penoplex belong to?

When studying the combustible properties of extruded polystyrene foam, it is necessary to take into account the fact that manufacturers produce different grades of this material. All of them have different characteristics, and therefore there are various opinions about their flammability.

All building materials are divided into several groups according to flammability:

G1 - materials are slightly combustible.
G2 - moderately combustible materials.
G3 - materials with normal combustibility.
G4 - materials with highly combustible properties.
NG - absolutely non-combustible materials.

Most sellers prefer to remain silent about the vapor barrier properties of the foam, since their main task is to implement it in any way. Some even claim that only they can buy non-flammable extruded polystyrene foam. As soon as you hear such statements, immediately leave. To date, there is simply no non-combustible foam plastic, but it can be classified as a class of low-combustible building materials.

Is penoplex dangerous in case of fire?

You need to figure out whether extruded polystyrene foam is dangerous in a fire. Previously, all types of foam plastic belonged to the group of materials with normal flammability or with highly combustible properties. Such materials, in addition to their flammability, emitted dangerous gases, which made the penoplex especially dangerous in case of fire. But recently, manufacturers have switched to the technology for the production of class G1 foam, that is, slightly combustible. The insulation received such properties due to the addition of a flame retardant, a substance that can increase the resistance of building materials to open fire. According to the statement of experts, the new penoplex does not emit harmful substances, it, like wood, emits only carbon dioxide and carbon gases.
But even with such statements by manufacturers, buyers are not inclined to believe them. All due to the fact that, according to state standards, extruded polystyrene foam cannot be slightly combustible. And all its species belong to the G3 or G4 group.

Penoplex is combustible or not?

Official manufacturers do not give any information about absolute incombustibility. There are only references to an independent study, according to which penoplex began to be classified as class G1. But there are no such records in official state documents. This is what causes controversy, some consumers are sure that an independent examination was interested in the result, so the statement that penoplex does not emit harmful substances is simply absurd.
But based on the statements of both sides, it can be concluded that opponents of the incombustibility of polystyrene are simply unfamiliar with the properties of the fire retardant. Of course, such substances will not be able to prevent ignition, but they will not allow the material to burn out. How to explain it? Everything is simple. Under the direct influence of the flame, the penoplex will ignite, but as soon as the fire ceases to affect it, it immediately goes out. It is based on these characteristics that polystyrene is called non-combustible, since by itself it can cause a fire.
If we evaluate the statements that penoplex emits no more harmful substances than wood, it looks debatable. Since extruded polystyrene foam is a synthetic material, in addition to carbon monoxide, it releases other chemical compounds that can cause pulmonary edema, severe poisoning and even suffocation in humans.

Can penoplex be called non-combustible?

To sum up the above information, is penoplex non-combustible and is it safe in case of fire?

Classic extruded polystyrene foam belongs to the groups of highly and normally combustible materials.
Only by adding flame retardants, foam plastic is made slightly combustible.
It cannot be called non-combustible, because even despite its high fire resistance, it is still flammable under the direct influence of fire.
Substances that are released during the combustion of penoplex are dangerous to humans.

Given all the characteristics, experts advise buying low-flammable foam. From significantly different in price, but its performance is worth it. The main difference is in the density of the insulation blocks, treated with anti-foam, the foam is denser. On the building materials market, heaters from various manufacturers are presented, which makes it possible to choose the best option.

How to choose the right penoplex?

Proper insulation should be aimed at maximizing the preservation of heat inside the room, at the same time not exposing it to the risk of fire. In order to purchase the quality product you need, you need to contact only experienced manufacturers who have a good reputation in the building materials market.
After choosing a manufacturer, you need to familiarize yourself with all related documents, which will indicate all state standards and compliance with them. You can also rely on the conclusions of independent expert institutions, which are often available from manufacturers. Nowadays, you can meet construction companies that are able to conduct a small experiment, after which you will be convinced of the fire resistance of the material.

Output

The main thing to remember is that the purchase of insulation treated with anti-foam does not guarantee complete fire safety. To maintain all its fire-fighting properties, the necessary installation and processing instructions must be observed. Most often, extruded polystyrene foam is used to insulate the floor, basement and foundation. It is strictly forbidden to use it for insulation of walls and facades. It is because of the fire hazard that this insulation cannot be used in all areas of construction. Fortunately, manufacturers are constantly working to improve it, using various production technologies and processing insulation with protective substances. Soon, penoplex will acquire all the necessary qualities for widespread use in the field of insulation of residential and industrial premises.

In order to protect the life, health, property of citizens and legal entities, state and municipal property, the legislation of the Russian Federation provides for requirements for various types of products.

Such requirements are contained in the technical regulations.

Federal Law No. 123-FZ of July 22, 2008 "Technical Regulations on Fire Safety Requirements" (hereinafter referred to as the Technical Regulations) establishes requirements for building materials.

Article 13 of the Technical Regulations establishes the classification of building materials according to fire hazard.

This classification is based on the properties of materials to form fire hazards.

The fire hazard of building materials is characterized by the following properties:

1) combustibility;

2) flammability;

3) the ability to spread the flame over the surface;

4) smoke generating capacity;

5) toxicity of combustion products.

By combustibility, building materials are divided into combustible (G) and non-combustible (NG).

Building materials are classified as non-combustible with the following values of combustibility parameters determined experimentally: temperature increase - no more than 50ºС, sample weight loss - no more than 50%, duration of stable flame burning - no more than 10 seconds. Building materials that do not satisfy at least one of the specified parameter values are classified as combustible.

Combustible building materials are divided into the following groups:

Slightly combustible (G1), having a flue gas temperature of not more than 135 ºС, the degree of damage along the length of the test sample is not more than 65%, the degree of damage by weight of the test sample is not more than 20%, the duration of self-burning is 0 seconds;

Moderately combustible (G2), having a flue gas temperature of not more than 235 ºС, the degree of damage along the length of the test sample is not more than 85%, the degree of damage by weight of the test sample is not more than 50%, the duration of independent combustion is not more than 30 seconds;

Normally combustible (G3), having a flue gas temperature of not more than 450 C, the degree of damage along the length of the test sample is more than 85%, the degree of damage by weight of the test sample is not more than 50%, the duration of independent combustion is not more than 300 seconds;

Highly combustible (G4), having a flue gas temperature of more than 450 ºС, the degree of damage along the length of the test sample is more than 85%, the degree of damage by weight of the test sample is more than 50%, the duration of self-burning is more than 300 seconds.

At the same time, for materials belonging to the flammability groups G1 - G3, the formation of burning melt drops during testing is not allowed (for materials belonging to the flammability groups G1 and G2, the formation of melt drops is not allowed). For non-combustible building materials, other fire hazard indicators are not determined and not standardized.

7. In terms of flammability, combustible building materials (including floor carpets), depending on the value of the critical surface heat flux density, are divided into the following groups:

Flame-retardant (B1), having a critical surface heat flux density of more than 35 kW / m 2;

Moderately flammable (B2), having a critical surface heat flux density of at least 20, but not more than 35 kW / m 2;

Highly flammable (B3), having a critical surface heat flux density of less than 20 kW / m 2.

8. According to the speed of flame propagation over the surface, combustible building materials (including floor carpets), depending on the value of the critical surface heat flux density, are divided into the following groups:

Non-propagating (RP1), having a value of critical surface heat flux density of more than 11 kW / m 2;

Weakly propagating (RP2), having a value of critical surface heat flux density of at least 8, but not more than 11 kW / m 2;

Moderately spreading (RP3), having a value of critical surface heat flux density of at least 5, but not more than 8 kW / m 2;

Strongly spreading (RP4), having a critical surface heat flux density of less than 5 kW / m 2.

9. According to the smoke-generating ability, combustible building materials, depending on the value of the smoke generation coefficient, are divided into the following groups:

With a low smoke generating capacity (D1), having a smoke generating coefficient of less than 50 m 2 /kg;

With moderate smoke-generating ability (D2), having a smoke-generating coefficient of at least 50, but not more than 500 m 2 /kg;

With a high smoke generating capacity (D3), having a smoke generating coefficient of more than 500 m 2 /kg.

10. According to the toxicity of combustion products, combustible building materials are divided into the following groups:

Low-dangerous (T1);

Moderately hazardous (T2);

Highly dangerous (T3);

Extremely dangerous (T4).

The purpose of determining the fire hazard groups of materials is to assess the possibility of their use in specific buildings and structures.

Based on the fire hazard groups of materials, fire hazard classes are determined in accordance with Part 11 of Article 3 and Appendix 3 of the Technical Regulations.

Fire hazard classes of building materials

Fire hazard properties of building materials	Fire hazard class of building materials depending on groups
Fire hazard properties of building materials	KM0	KM1	KM2	KM3	KM4	KM5
combustibility	NG	G1	G1	G2	G3	G4
Flammability		IN 1	IN 2	IN 2	IN 2	IN 3
Smoke generating capacity		D 2	D 2	D3	D3	D3
Toxicity		T2	T2	T2	T3	T4
Flame spread		RP1	RP1	RP2	RP2	WP4

And, in turn, on the basis of hazard classes, the scope of application of decorative and finishing, facing materials and floor coverings on escape routes and in halls in buildings of various functional purposes, number of storeys and capacity is determined, in accordance with Part 6 of Article 134 and Annexes 28, 29 of the Technical Regulations.

Scope of decorative and finishing, facing

materials and floor coverings on escape routes

	Floors and building height	Fire hazard class of material, not more than specified
		for walls and ceilings		for flooring
			Common corridors, halls, foyers	Vestibules, stairwells, lift lobbies	Common corridors, halls, foyers
F1.2; F1.3; F2.3; F2.4; F3.1; F3.2; F3.6; F4.2; F4.3; F4.4; F5.1; F5.2; F5.3	no more than 9 floors or no more than 28 meters	KM2	KM3	KM3	KM4
	more than 9 but not more than 17 floors or more than 28 but not more than 50 meters	KM1	KM2	KM2	KM3
	more than 17 floors or more than 50 meters	KM0	KM1	KM1	KM2
	regardless of number of storeys and height	KM0	KM1	KM1	KM2

Scope of decorative and finishing, facing materials and floor coverings in halls, with the exception of floor coverings of sports arenas of sports facilities and floors of dance halls

Class (subclass) of the functional fire hazard of the building	Hall capacity, people	Material class, not more than specified
	Hall capacity, people	for walls and ceilings	for floor coverings
F1.2; F2.3; F2.4; F3.1; F3.2; F3.6; F4.2; F4.3; F4.4; F5.1	over 800	KM0	KM2
	more than 300 but not more than 800	KM1	KM2
	more than 50 but not more than 300	KM2	KM3
	no more than 50	KM3	KM4
F1.1; F2.1; F2.2; F3.3; F3.4; F3.5; F4.1	over 300	KM0	KM2
	more than 15 but not more than 300	KM1	KM2
	no more than 15	KM3	KM4

To determine the fire hazard groups of building materials, tests are carried out according to the methods contained in the national standards included in the List approved by Order of the Government of the Russian Federation dated March 10, 2009 No. 304-r:

Tests for incombustibility are carried out according to GOST 30244-94. Construction materials. Flammability test methods (MethodI);

Tests to determine the flammability groups are carried out according to GOST 30244-94. Construction materials. Flammability test methods (MethodII);

Tests to determine flammability groups are carried out in accordance with GOST 30402-96 Building materials. Flammability test method;

Tests to determine the flame propagation groups over the surface are carried out in accordance with GOST R 51032-97 Building materials. Flame propagation test method;

Tests to determine the smoke-generating ability groups are carried out in accordance with GOST 12.1.044-89 (ISO 4589-84) Interstate standard. System of labor safety standards. Fire and explosion hazard of substances and materials. Nomenclature of indicators and methods for their determination (clause 4.18);

Tests to determine the toxicity groups of combustion products are carried out in accordance with GOST 12.1.044-89 (ISO 4589-84) Interstate standard. System of labor safety standards. Fire and explosion hazard of substances and materials. Nomenclature of indicators and methods for their determination (clause 4.20).

As part of the Center for Expertise, Research and Testing in Construction, the Fire Testing Laboratory and the Fire Control Department operate. At the same time, the Fire Control Department is entrusted with the functions of an inspection body for sampling and evaluating test results. The fire test laboratory performs the functions of testing product samples, while the test results are sent by means of sample encryption to the Fire Control Department for assessment and assignment of specific fire hazard groups.

The fire test laboratory of the State Budgetary Institution "Center for Expertise, Research and Testing in Construction" conducts daily tests of building materials.

For 9 months of 2017, 285 tests were carried out, according to the results of which protocols were drawn up containing indicators of materials used directly at new construction sites in Moscow.

The main types of products tested are: facing boards for facade systems (121 tests), paints (28 tests), insulation (74 tests), linoleums (15 tests), other types of products (59 tests) [lacquer, floor coverings, vapor barrier, wallpaper].

It should be noted that a significant number of tests reveal the discrepancy between the materials used and the requirements imposed on them.

So 73% of the tested fiber cement boards for facades are not non-combustible (NG). At the same time, 100% of fiber cement boards tested for flammability correspond to the flammability group G1.

Also, many linoleum samples do not pass tests for the declared flammability groups (B). 83% of linoleum samples correspond to the B3 flammability group, while products with higher rates (B1 or B2) should be used.

The paints used at construction sites also often do not correspond to the declared indicators. 100% of the tested paints do not meet the incombustibility index (NG). In terms of combustibility (G) - 85% of the tested paint samples correspond to the combustibility group G1 and 15% - to the group G2. In terms of flammability (B), 22% of the tested paint samples do not meet the declared values. 78% of them correspond to the B1 group, the rest to the B2 and B3 groups.

100% of the tested samples of mineral wool insulation correspond to the incombustibility index (NG).

Based on the laboratory protocols, the inspection body of the State Budgetary Institution "CEIIS" issues conclusions containing the fire hazard groups of materials, as well as conclusions on the compliance or non-compliance of the materials used with the requirements of design and regulatory documentation.

Tests to determine the fire hazard indicators of building materials used directly at construction sites is a necessary input control aimed at preventing fires and reducing damage from fires at new construction sites.

Literature:

1. Federal Law No. 184-FZ of December 27, 2002 "On Technical Regulation".

2. Federal Law of July 22, 2008 No. 123-FZ "Technical Regulations on Fire Safety Requirements".

3. GOST 30244-94. Construction materials. Test methods for combustibility.

4. GOST 30402-96 Construction materials. Flammability test method.

5. GOST R 51032-97 Construction materials. Flame propagation test method.

6. GOST 12.1.044-89 (ISO 4589-84) Interstate standard. System of labor safety standards. Fire and explosion hazard of substances and materials. Nomenclature of indicators and methods for their determination.

The text of the article was:

Leading engineer of the LOI GBU "CEIIS" S.V. Rusyaev

Checked:

Head of the LOI GBU "CEIIS" N.V. Afanasiev

Fire safety of construction objects directly depends on the type of materials used. During the construction of structures, the latter are tested for flammability and behavior in emergency situations, in particular, fire. The intensity, nature of the flow and the immediate outcome of the incident is determined by the combination of the properties of the raw materials that were used in the construction of the building. According to DBN B 1.1-7.2016 of Ukraine, materials are conditionally divided into combustible and non-combustible substances, this and a more detailed classification will be discussed later.

The main test method: how is the combustibility of the material determined?

To understand the process of testing substances, it is necessary to understand the terminology. There are the following classes of combustibility of materials:

non-combustible;
difficult to burn;
combustible.

To determine which of them the substance belongs to, testing is carried out by a single method in the laboratory. All types of materials fall under the test: facing, finishing and others (including liquids, paint and varnish coatings). The process looks like this: samples in the amount of 12 pieces for each unit of the test substance are kept for three days in a room, the air temperature is room temperature. During this period, potentially combustible and non-combustible materials are weighed until they reach constant mass. Under the "room" should be understood as a structure consisting of three parts: a chamber, air supply and exhaust systems.

Combustibility classes of building materials: explanation of terminology

So, we figured out how the combustibility of building materials is checked, it remains only to give a clear definition of the classification. Let's consider in more detail:

combustible. It is obvious that such substances actively burn on their own under certain environmental conditions and continue to blaze with and/or without a source of flame. It is this class that is divided into 4 groups of combustibility of building materials, which we will consider in more detail below.
Difficult to burn. This category includes compounds that can actively burn only if there is a supply of oxygen and ignition takes place in the open air. That is, in the absence of a source of fire, the material will stop burning.
Non-combustible building materials. They do not ignite in air, however, they can enter into chemical reactions with each other, oxidizing agents, and water. On this basis, individual materials present a potential fire hazard. According to state rules and regulations, the combustibility group of NG substances is determined by two types of studies, according to the results of which a number is assigned (1 or 2).

Let us consider in more detail the last type of substances - non-combustible, as well as directly the tests that are carried out on them. In 1 case, we are talking about studies in which the temperature in a special furnace increases by no more than 50 degrees, while the mass of the sample is reduced to a maximum of 50%, heat is released - up to 2.0 MJ / kg. There is no combustion process. The second group includes materials with similar indicators, with the exception of the heat released (here it is no more than 3 MJ / kg), but there is still a flame, and it burns up to 20 seconds.

Combustibility groups of materials according to DBN V.1.1-7-2016: main criteria

To classify the raw materials used in the construction of buildings and various structures, the following characteristics are analyzed:

the temperature of the gases that are released along with the smoke;
reduction in the mass of the material;
degree of volume reduction;
the duration of the flame without a source of combustion.

The combustibility groups of materials and substances are obviously designated by the letter G. They are in turn divided into four classes. Let's consider each of them in more detail:

Combustibility G1 is characteristic of substances and materials that cannot burn without a source of flame. However, under appropriate conditions, they are capable of emitting smoke-forming gases. The temperature of the latter is no more than 135 degrees. At the same time, damage along the length caused by the flame does not exceed 65%, and complete destruction - a maximum of 20% of the total.
Group G2 includes building materials that, after the elimination of the flame source, continue to burn for no more than 30 seconds. The maximum flue gas temperature in this case is 235 degrees, damage along the length is up to 85%, and weight loss is up to half of the total.
The flammability group G3 is assigned to those materials that are capable of maintaining the combustion process for another five minutes after the flame source has been removed. The temperature of the gases that are released in this case can reach 450 degrees Celsius. Length and weight are reduced in the same way as in the case of raw materials from class G2.
Highly combustible materials are classified as group G4. In all respects, they are identical to substances from the previous group, but with one caveat: flue gases are released at a temperature of 450 degrees, or even more.

We confirm the flammability class: the specifics of the process

Non-combustible and combustible materials are examined separately in laboratory conditions and in open space. Since samples can consist of several layers, each of them is subjected to verification.

Previously, researchers/laboratory technicians check and calibrate the equipment, warm it up, and then fix the test objects in special holders. The latter are located inside the furnace, which, in turn, is equipped with recorders. The exposure of the sample in the heating chamber continues until it reaches a balanced temperature. That is, when the range of fluctuations stabilizes at around 2 degrees Celsius.

To obtain a correct result and assign the material a flammability class G1/2/3/4, it is necessary to cool the sample in a desiccator and then measure its mass and length. According to the data obtained, the test substance is assigned to the current group.

Raw materials of various aggregate states in the context of combustibility should be considered separately:

Liquids. They are considered combustible if they can ignite at a certain temperature. If there is no external source of fire, and the liquid is not capable of supporting the process, then it is considered to be difficult to combust. Non-flammable substances under normal conditions with a full supply of oxygen do not ignite at all. Those that flare up already with a slight increase in air temperature are considered especially dangerous. For example, ether and acetone ignite already at 28 degrees Celsius.
Solid. In the construction industry, materials cannot be used on site without testing. The safest are those that belong to the non-combustible or group G1.
gaseous. The limiting concentration of a gas contained in a mixture with air is estimated, at which a flame can spread from the point of ignition to an arbitrarily large distance. If such a value cannot be derived, the gaseous material is classified as non-combustible.

Why is it necessary to determine the flammability group of a material?

When assessing the fire hazard, not only the combustibility group G1 / G2 / G3 / G4 is taken into account, but also a number of other properties of materials. Namely:

Flammability (difficult, moderately and flammable).
Speed of spread of fire (non-propagating, weakly, moderately and strongly spreading).
The intensity of smoke generation (small, moderate and high).
The degree of toxicity of gases released during combustion (slightly, moderately and highly dangerous, extremely dangerous).

Based on the analysis of the totality of all five properties, the fire hazard class of the building is formed. The scope of use of a particular material is determined by its combustibility, its group. Properly selected raw materials and compliance with technological processes not only make the finished structure safe for operation, but also minimize the risk of emergencies at the construction site.

Summing up: when is the combustibility testing of building materials carried out?

For most buildings, construction by definition includes obtaining various permits, as well as restoration, expansion, technical re-equipment of the building, repairs and other activities. Also, sometimes a fire examination is required for a certain type of building, this issue is regulated by law. The latter includes an assessment of building materials for flammability, combustibility, etc. That is, a change in the functional purpose of a structure is also a sufficient reason for examining raw materials, and, if necessary, assigning a structure to a different fire hazard class.

Please note that the KP for the structure is determined initially, and only after that building materials are selected for it. But there are pitfalls here too: the same, for example, composite cassettes, cannot be used for cladding different buildings - a shopping center (it is possible), a school or a medical institution - it is impossible. In addition, it is forbidden to finish evacuation passages and many other public areas with materials of combustibility groups 3 and 4, while in private low-rise construction they are used everywhere (MDF panels, etc., created on the basis of organic raw materials). These and other subtleties are spelled out in Ukrainian legislation, you just need to study them or entrust this matter to specialists.

Classification of building materials

By origin and destination

By origin, building materials can be divided into two groups: natural and artificial.

natural called such materials that are found in nature in finished form and can be used in construction without significant processing.

artificial called building materials that are not found in nature, but are manufactured using various technological processes.

According to their purpose, building materials are divided into the following groups:

Materials intended for the construction of walls (brick, wood, metals, concrete, reinforced concrete);

Binders (cement, lime, gypsum) used to produce non-fired products, masonry and plaster;

Thermal insulation materials (foam and aerated concrete, felt, mineral wool, foam plastics, etc.);

Finishing and facing materials (rocks, ceramic tiles, various types of plastics, linoleum, etc.);

Roofing and waterproofing materials (roofing steel, tiles, asbestos-cement sheets, slate, roofing felt, roofing felt, isol, brizol, poroizol, etc.)

NON-COMBUSTABLE BUILDING MATERIALS

natural stone materials. Natural stone materials are called building materials obtained from rocks through the use of only mechanical processing (crushing, sawing, splitting, grinding, etc.). They are used for the construction of walls, floors, stairs and building foundations, cladding of various structures. In addition, rocks are used in the production of artificial stone materials (glass, ceramics, heat-insulating materials), as well as raw materials for the production of binders: gypsum, lime, cement.

The effect of high temperatures on natural stone materials. All natural stone materials used in construction are non-combustible, however, under the influence of high temperatures, various processes occur in stone materials, leading to a decrease in strength and destruction.

The minerals included in stone materials have different coefficients of thermal expansion, which can lead to internal stresses in the stone during heating and the appearance of defects in its internal structure.

The material undergoes a modification transformation of the structure of the crystal lattice associated with an abrupt increase in volume. This process leads to cracking of the monolith and a drop in the strength of the stone due to large thermal deformations resulting from sudden cooling.

It should be emphasized that all stone materials under the influence of high temperatures lose their properties irreversibly.

Ceramic products. Since all ceramic materials and products are fired at high temperatures during their production, repeated exposure to high temperatures under fire conditions does not significantly affect their physical and mechanical properties if these temperatures do not reach the softening (melting) temperatures of the materials. Porous ceramic materials (ordinary clay brick, etc.), obtained by firing without being brought to sintering, can be exposed to moderately high temperatures, as a result of which some shrinkage of structures made from them is possible. The impact of high temperatures during a fire on dense ceramic products, which are fired at temperatures of about 1300 ° C, practically does not have any harmful effect, since the temperature in the fire does not exceed the firing temperature.

Red clay brick is the best material for building fire walls.

Metals. In construction, metals are widely used for the construction of frames for industrial and civil buildings in the form of rolled steel profiles. A large amount of steel is used to make reinforcement for reinforced concrete. Steel and cast-iron pipes, roofing steel are used. In recent years, light building structures made of aluminum alloys have been increasingly used.

Behavior of steels in a fire. One of the most characteristic features of all metals is the ability to soften when heated and restore their physical and mechanical properties after cooling. During a fire, metal structures heat up very quickly, lose strength, deform and collapse.

Reinforcing steels (see the Reference Materials section), which are obtained by additional hardening by heat treatment or cold drawing (work hardening), will behave worse in fire conditions. The reason for this phenomenon is that these steels receive additional strength due to crystal lattice distortion, and under the influence of heating, the crystal lattice returns to an equilibrium state and the increase in strength is lost.

aluminum alloys. The disadvantage of aluminum alloys is a high coefficient of thermal expansion (2-3 times higher than that of steel). When heated, there is also a sharp decrease in their physical and mechanical properties. The tensile strength and yield strength of aluminum alloys used in construction are reduced by about half at a temperature of 235-325 °C. Under fire conditions, the temperature in the room volume can reach these values in less than one minute.

Materials and products based on mineral melts and products from glass melts. This group includes: glass materials, products made of slag and stone casting, glass-ceramics and slag glass-ceramics, sheet window and display glass, patterned, reinforced, sun and heat protection, facing glass, glass profiles, double-glazed windows, glass mosaic tiles, glass blocks, etc. .

Behavior of materials and products from mineral melts at high temperatures. Materials and products made from mineral melts are non-combustible and cannot contribute to the development of a fire. Exceptions are materials based on mineral fibers containing some organic binder, such as thermal insulation mineral boards, silica boards, basalt fiber boards and rolled mats. The combustibility of such materials depends on the amount of binder introduced. In this case, its fire hazard will be determined mainly by the properties and amount of the polymer present in the composition.

Window glass does not withstand prolonged heat loads during a fire, but with slow heating it may not break down for quite a long time. The destruction of glass in light openings begins almost immediately after the flame begins to touch its surface.

Structures made of tiles, stones, blocks, obtained on the basis of mineral melts, have a significantly higher fire resistance than sheet glass, since, even after cracking, they continue to bear the load and remain sufficiently impervious to combustion products. Porous materials from mineral melts retain their structure almost to the melting point (for foam glass, for example, this temperature is about 850 ° C) and perform heat-shielding functions for a long time. Since porous materials have a very low coefficient of thermal conductivity, even at the moment when the side facing the fire melts, deeper layers can perform heat-shielding functions.

COMBUSTIBLE BUILDING MATERIALS

Wood. When wood is heated to 110 ° C, moisture is removed from it, and gaseous products of thermal destruction (decomposition) begin to be released. When heated to 150 ° C, the heated surface of the wood turns yellow, the amount of volatile substances released increases. At 150-250 °C, the wood becomes brown due to charring, and at 250-300 °C, the products of wood decomposition ignite. The self-ignition temperature of wood is in the range of 350-450 °C.

Thus, the process of thermal decomposition of wood proceeds in two phases: the first phase - decomposition - is observed when heated to 250 ° C (to the ignition temperature) and proceeds with the absorption of heat, the second, the combustion process itself, proceeds with the release of heat. The second phase, in turn, is divided into two periods: the combustion of gases formed during the thermal decomposition of wood (the fiery phase of combustion), and the combustion of the formed charcoal (the smoldering phase).

Bituminous and tar materials. Building materials, which include bitumen or tar, are called bituminous or tar.

Ruberoid and roofing felt roofs can catch fire even from low-power sources of fire, such as sparks, and continue to burn on their own, emitting a large amount of thick black smoke. When burning, bitumen and tar soften and spread, which significantly complicates the situation in a fire.

The most common and effective way to reduce the flammability of roofs made of bituminous and tar materials is to sprinkle them with sand, fill them with a continuous layer of gravel or slag, and cover them with some non-combustible tiles. A certain fire-retardant effect is obtained by coating rolled materials with foil - such coatings do not ignite under the influence of sparks.

It should be borne in mind that rolled materials made using bitumen and tar are prone to spontaneous combustion when rolled up. This circumstance must be taken into account when storing such materials.

polymer building materials. Polymer building materials (PSM) are classified according to various criteria: the type of polymer (polyvinyl chloride, polyethylene, phenol-formaldehyde, etc.), production technology (extrusion, molding, roller-calender, etc.), purpose in construction (structural, finishing, flooring materials , heat and sound insulating materials, pipes, sanitary and molded products, mastics and adhesives). All polymeric building materials are highly combustible, smoke generating and toxic.

Flammability group materials is determined according to GOST 30244-94 "Building materials. Test methods for combustibility", which corresponds to the International Standard ISO 1182-80 "Fire tests - Building materials - Non-combastibility test". Materials, depending on the values of the combustibility parameters determined according to this GOST, are divided into non-combustible (NG) and combustible (G).

Materials refer to non-combustible with the following values of combustibility parameters:

temperature increase in the furnace is not more than 50°С;
weight loss of the sample is not more than 50%;
the duration of stable flame burning is not more than 10 sec.

Materials that do not satisfy at least one of the indicated parameter values are classified as combustible.

Combustible materials, depending on the values of the combustibility parameters, are divided into four combustibility groups in accordance with table 1.

Table 1. Combustibility groups of materials.

Flammability group of materials is determined according to GOST 30402-96 "Construction materials. Flammability test method", which complies with the international standard ISO 5657-86.

In this test, the sample surface is subjected to radiant heat flux and flame from an ignition source. In this case, the surface heat flux density (SPTP) is measured, that is, the magnitude of the radiant heat flux acting on the unit surface area of the sample. Ultimately, the Critical Surface Heat Flux Density (CCTP) is determined - the minimum value of the surface heat flux density (CCTP) at which stable flaming combustion of the sample occurs after exposure to a flame.

Materials are divided into three flammability groups, depending on the values of the CATI, shown in Table 2.

Table 2. Flammability groups of materials.

To classify materials according to smoke abilities use the value of the smoke generation coefficient, which is determined according to GOST 12.1.044.

Smoke generation coefficient - an indicator characterizing the optical density of smoke generated during flame combustion or thermal-oxidative destruction (smoldering) of a certain amount of a solid substance (material) under special test conditions.

Depending on the relative density of smoke, materials are divided into three groups:
D1- with low smoke generating capacity - smoke generation coefficient up to 50 m²/kg inclusive;
D 2- with moderate smoke generating capacity - smoke generation coefficient from 50 to 500 m²/kg inclusive;
D3- with high smoke generating capacity - smoke generating coefficient over 500 m²/kg.

Toxicity group combustion products of building materials is determined according to GOST 12.1.044. The combustion products of the material sample are sent to a special chamber where experimental animals (mice) are located. Depending on the state of the experimental animals after exposure to combustion products (including a lethal case), the materials are divided into four groups:
T1- little dangerous;
T2- moderately dangerous;
T3- highly dangerous;
T4- extremely dangerous.