Parts of buildings and structures and their fire resistance. How to determine the fire resistance of a building. What tasks are solved

When evaluating the fire performance (properties) of various buildings or structures, special attention is paid to taking into account the degree of fire resistance. Fire resistance refers to the functional ability of structural components of structures to suppress the spread of fire without losing their operational characteristics. These properties include load-bearing and enclosing capacity. Let's consider these concepts in more detail.

Fire resistance limit of a building: definition, factors affecting its values

With the loss of the bearing capacity, the integrity of the building is violated, and the loss of the enclosing capacity entails the appearance of cracks and holes of the through type, up to the penetration of fire into the buildings, followed by burning.

The fire resistance limit of a building is the time from the start of burning in a fire to the time signs of loss appear, such as:

the appearance of cracks of a through type;
increasing the temperature on the unheated part above 140°C or in any place above 180°C in comparison with the temperature of the entire structure before testing;
loss of load-bearing functional characteristics by the structure.

The value of the fire resistance limit is influenced by the dimensions and physical properties of the materials. The thicker the walls, the longer (in time) the fire resistance will be. The degree of fire resistance of a building is affected by:

number of storeys of the building;
square;
type of building (administrative, residential type, etc.);
quality and degree of fire resistance of materials.

The degree of fire resistance of a building depends on the fire resistance of building structures. They are divided into three main groups:

fireproof (stone, brick, metal structures);
slow-burning (combustible materials, the surface of which is protected by a fireproof mixture);
combustible (wood).

Classification of buildings according to the degree of fire resistance

The fire resistance of a building is determined in strict accordance with building codes and regulations (SNiP). So, according to the degree of fire resistance, all buildings are divided into five main groups. First group. Buildings that are most protected from the negative effects of fire. The main materials used for these structures are concrete and stone, resistant to high temperatures and fire.

Second group also covers buildings with refractory structures, as in the first case, with a slight allowance for the use of unprotected elements in steel structures. To the third grade include buildings in the structural structure of which there are fireproof and slow-burning materials. If the structure includes combustible materials, then they must be treated with a special fire-retardant mixture.

Buildings to which fourth degree of fire resistance, must have fire walls in their construction, and for walls of the bearing type, slow-burning materials must be used. For structures included to the fifth group, the use of combustible materials is typical, however, for load-bearing walls, as well as for buildings of the fourth degree of fire resistance, materials of a fireproof nature are used. The degree of fire resistance of a building (structure) must match the explosion and fire safety of the premises.

Buildings made of bricks have a high degree of fire protection - the first degree of fire resistance. Brick is a material that is resistant to combustion processes - it does not burn or smolder, which is why most developers prefer to build houses from this material.

Factors that affect the degree of fire resistance of a residential building

The degree of fire resistance of any residential building is affected by its number of floors and area - the higher the residential building and the larger in area, the higher the degree of fire resistance. Basically, brick, stone or concrete are used for residential houses, so they are endowed with the first degree of fire resistance. If brick and concrete block elements are used for the construction of such a structure, then this is the second class of fire resistance. For houses built on a metal frame, with sheathing made of slow-burning materials, a third degree of fire resistance is assigned.

Houses with a wooden frame base are assigned the fourth degree of fire resistance, and the fifth class includes houses that are most susceptible to fire.

In connection with the fires that occur in administrative and residential premises, much attention is paid to such a criterion as the fire resistance of buildings during the construction of buildings. The fire resistance of any building is calculated taking into account the above features and building codes and regulations (SNiP).

BENEFITS

TO DETERMINE THE FIRE RESISTANCE LIMITS OF STRUCTURES,

FIRE PROPAGATION LIMITS BY STRUCTURES AND GROUPS OF FIREABILITY OF MATERIALS

ATTENTION!!!

Developed for SNiP II-2-80 "Fire safety standards for the design of buildings and structures". Reference data are given on the limits of fire resistance and the spread of fire on building structures made of reinforced concrete, metal, wood, asbestos cement, plastics and other building materials, as well as data on the flammability groups of building materials.

For engineering and technical workers of design, construction organizations and state fire supervision authorities. Tab. 15, fig. 3.

FOREWORD

This Handbook has been developed for SNiP II-2-80 "Fire safety standards for the design of buildings and structures". It contains data on the standardized indicators of fire resistance and fire hazard of building structures and materials.

Section 1 of the manual was developed by TsNIISK them. Kucherenko (Doctor of Engineering Sciences Prof. I.G. Romanenkov, Candidate of Engineering Sciences V.N. Siegern-Korn). Section 2 was developed by TsNIISK im. Kucherenko (Doctor of Engineering Sciences I.G. Romanenkov, Candidates of Engineering Sciences V.N. Siegern-Korn, L.N. Bruskova, G.M. Kirpichenkov, V.A. Orlov, V.V. Sorokin, engineers A. V. Pestritsky, V. I. Yashin); NIIZhB (Doctor of Engineering Sciences V.V. Zhukov; Doctor of Engineering Sciences, Professor A.F. Milovanov; Candidate of Physical and Mathematical Sciences A.E. Segalov, Candidates of Engineering Sciences A.A. Gusev, VV Solomonov, VM Samoilenko, engineers VF Gulyaeva, TN Malkina); TsNIIEP them. Mezentsev (Ph.D. in Engineering Sciences L.M. Schmidt, engineer P.E. Zhavoronkov); TsNIIPromzdaniy (Candidate of Technical Sciences V.V. Fedorov, engineers E.S. Giller, V.V. Sipin) and VNIIPO (Doctor of Technical Sciences, Prof. A.I. Yakovlev; Candidates of Technical Sciences V.V. P. Bushev, S. V. Davydov, V. G. Olimpiyev, N. F. Gavrikov, engineers V. Z. Volokhatykh, Yu. A. Grinchik, N. P. Savkin, A. N. Sorokin, V. S. Kharitonov, L.V. Sheinina, V.I. Shchelkunov). Section 3 was developed by TsNIISK im. Kucherenko (Doctor of Technical Sciences, Prof. I.G. Romanenkov, Candidate of Chemical Sciences N.V. Kovyrshina, engineer V.G. Gonchar) and the Institute of Mining Mechanics of the Academy of Sciences of Georgia. SSR (Candidate of Technical Sciences G.S. Abashidze, engineers L.I. Mirashvili, L.V. Gurchumelia).

When developing the Manual, materials from the TsNIIEP of housing and the TsNIIEP of educational buildings of Gosgrazhdanstroy, MIIT of the Ministry of Railways of the USSR, VNIISTROM and NIPIsilicatobeton of the USSR Ministry of Industry and Construction Materials were used.

The text of SNiP II-2-80 used in the Guidelines is in bold type. Its paragraphs are double numbered, numbering according to SNiP is given in brackets.

In cases where the information given in the Handbook is not sufficient to establish the relevant indicators of structures and materials, for advice and applications for fire tests, you should contact TsNIISK them. Kucherenko or NIIZhB Gosstroy of the USSR. The basis for establishing these indicators can also serve as the results of tests performed in accordance with the standards and methods approved or agreed by the USSR State Construction Committee.

Please send comments and suggestions on the Manual to the address: Moscow, 109389, 2nd Institutskaya st., 6, TsNIISK im. V.A. Kucherenko.

1. GENERAL PROVISIONS

1.1. The manual was compiled to help design, construction organizations and fire protection authorities in order to reduce the time, labor and materials spent on establishing the fire resistance limits of building structures, the limits of fire spread over them and the flammability groups of materials standardized by SNiP II-2-80.

1.2.(2.1). Buildings and structures for fire resistance are divided into five degrees. The degree of fire resistance of buildings and structures is determined by the fire resistance limits of the main building structures and the limits of the spread of fire over these structures.

1.3.(2.4). Building materials according to flammability are divided into three groups: fireproof, slow-burning and combustible.

1.4. The fire resistance limits of structures, the limits of the spread of fire along them, as well as the flammability groups of materials given in this Guide, should be included in the designs of structures, provided that their execution fully complies with the description given in the Guide. The materials of the Handbook should also be used in the development of new designs.

2. BUILDING STRUCTURES. FIRE RESISTANCE AND FIRE PROPAGATION LIMITS

2.1(2.3). The fire resistance limits of building structures are determined according to the SEV 1000-78 standard "Fire safety standards for building design. Method for testing building structures for fire resistance."

The limit of the spread of fire on building structures is determined by the method given in Appendix 2.

FIRE RESISTANCE LIMIT

2.2. The fire resistance limit of building structures is taken as the time (in hours or minutes) from the beginning of their standard fire test to the occurrence of one of the fire resistance limit states.

2.3. The SEV 1000-78 standard distinguishes the following four types of limit states for fire resistance: by loss of bearing capacity of structures and assemblies (collapse or deflection, depending on the type of structures); to thermal insulation. capacity - temperature increase on an unheated surface by more than 160 °C on average or at any point on this surface by more than 190 °C compared to the temperature of the structure before the test, or more than 220 °C regardless of the temperature of the structure before the test; by density - the formation of through cracks or through holes in structures through which combustion products or flames penetrate; for structures protected by fire-retardant coatings and tested without loads, the limit state will be the achievement of the critical temperature of the material of the structure.

For external walls, coverings, beams, trusses, columns and pillars, the limit state is only the loss of the bearing capacity of structures and nodes.

2.4. The limit states of structures in terms of fire resistance, specified in clause 2.3, in the future, for brevity, we will call, respectively, I, II, III and IV limit states of the structure in terms of fire resistance.

In cases of determining the fire resistance limit under loads determined on the basis of a detailed analysis of the conditions that occur during a fire and differ from the normative ones, the limit state of the structure will be denoted as 1A.

2.5. The fire resistance limits of structures can also be determined by calculation. In these cases, the test may not be carried out.

The determination of the fire resistance limits by calculation should be carried out according to the methods approved by the Glavtekhnormirovanie Gosstroy of the USSR.

2.6. For an approximate assessment of the fire resistance limit of structures during their development and design, one can be guided by the following provisions:

a) the fire resistance limit of layered enclosing structures in terms of heat-insulating ability is equal to, and, as a rule, higher than the sum of the fire resistance limits of individual layers. It follows that an increase in the number of layers of the building envelope (plastering, cladding) does not reduce its fire resistance limit in terms of heat-insulating ability. In some cases, the introduction of an additional layer may not have an effect, for example, when facing with sheet metal from the unheated side;

b) the fire resistance limits of enclosing structures with an air gap are on average 10% higher than the fire resistance limits of the same structures, but without an air gap; the efficiency of the air layer is the higher, the more it is removed from the heated plane; with closed air gaps, their thickness does not affect the fire resistance limit;

c) the fire resistance limits of enclosing structures with an asymmetric arrangement of layers depend on the direction of the heat flow. On the side where the likelihood of a fire is higher, it is recommended to place fireproof materials with low thermal conductivity;

d) an increase in the humidity of structures helps to reduce the heating rate and increase fire resistance, except in cases where an increase in humidity increases the likelihood of sudden brittle fracture of the material or the appearance of local punctures, this phenomenon is especially dangerous for concrete and asbestos-cement structures;

e) the fire resistance of loaded structures decreases with increasing load. The most intense section of structures exposed to fire and high temperatures, as a rule, determines the value of the fire resistance limit;

f) the fire resistance limit of the structure is the higher, the smaller the ratio of the heated perimeter of the section of its elements to their area;

g) the fire resistance limit of statically indeterminate structures, as a rule, is higher than the fire resistance limit of similar statically determinate structures due to the redistribution of efforts to less stressed and heated elements at a slower rate; in this case, it is necessary to take into account the influence of additional forces arising due to temperature deformations;

h) the flammability of the materials from which the structure is made does not determine its fire resistance limit. For example, structures made of thin-walled metal profiles have a minimum fire resistance limit, and structures made of wood have a higher fire resistance limit than steel structures with the same ratios of the heated perimeter of the section to its area and the magnitude of the acting stresses to the tensile strength or yield strength. At the same time, it should be borne in mind that the use of combustible materials instead of slow-burning or non-combustible ones can lower the fire resistance limit of the structure if its burnout rate is higher than the heating rate.

To assess the fire resistance limit of structures on the basis of the above provisions, it is necessary to have sufficient information about the fire resistance limits of structures similar to those considered in form, materials used and design, as well as information about the main patterns of their behavior in case of fire or fire tests.

2.7. In cases where in tables 2-15 the fire resistance limits are indicated for the same type of structures of various sizes, the fire resistance limit of a structure having an intermediate size can be determined by linear interpolation. For reinforced concrete structures, interpolation should also be carried out according to the distance to the axis of the reinforcement.

FIRE LIMIT

2.8. (Appendix 2, Clause 1). The test of building structures for the spread of fire consists in determining the extent of damage to the structure due to its burning outside the heating zone - in the control zone.

2.9. Damage is considered to be charring or burnout of materials that can be visually detected, as well as melting of thermoplastic materials.

The maximum damage size (cm) is taken as the limit for the spread of fire, determined according to the test method set forth in Appendix 2 to SNiP II-2-80.

2.10. For the spread of fire, structures are tested that are made using combustible and slow-burning materials, as a rule, without finishing and cladding.

Structures made only of non-combustible materials should be considered non-spreading fire (the limit of fire spread over them should be taken equal to zero).

If, during the fire propagation test, damage to structures in the control zone is no more than 5 cm, it should also be considered not to spread fire.

2.11. For a preliminary assessment of the limit of the spread of fire, the following provisions can be used:

a) structures made of combustible materials have a horizontal fire spread limit (for horizontal structures - ceilings, coatings, beams, etc.) of more than 25 cm, and vertically (for vertical structures - walls, partitions, columns, etc. .p.) - more than 40 cm;

b) structures made of combustible or slow-burning materials, protected from fire and high temperatures by non-combustible materials, may have a horizontal fire spread limit of less than 25 cm, and vertically less than 40 cm, provided that the protective layer during the entire test period (until the structure has completely cooled down) will not warm up in the control zone to the ignition temperature or the beginning of intensive thermal decomposition of the protected material. The structure may not spread fire, provided that the outer layer, made of non-combustible materials, during the entire test period (until the structure has completely cooled down) does not warm up in the heating zone to the ignition temperature or the beginning of intensive thermal decomposition of the protected material;

c) in cases where the structure may have a different fire spread limit when heated from different sides (for example, with an asymmetric arrangement of layers in the building envelope), this limit is set at its maximum value.

CONCRETE AND REINFORCED CONCRETE STRUCTURES

2.12. The main parameters that affect the fire resistance of concrete and reinforced concrete structures are: type of concrete, binder and aggregate; reinforcement class; construction type; cross section shape; element sizes; conditions for their heating; load and moisture content of concrete.

2.13. The increase in temperature in the concrete section of the element during a fire depends on the type of concrete, binder and aggregates, on the ratio of the surface on which the flame acts to the cross-sectional area. Heavy concretes with silicate aggregates warm up faster than those with carbonate aggregates. Lightweight and lightweight concretes warm up more slowly, the lower their density. The polymer binder, like the carbonate filler, reduces the heating rate of the concrete due to the decomposition reactions occurring in them, which consume heat.

Massive structural elements better resist the effects of fire; the fire resistance limit of columns heated from four sides is less than the fire resistance limit of columns with one-sided heating; the fire resistance limit of beams when exposed to fire from three sides is less than the fire resistance limit of beams heated from one side.

2.14. The minimum dimensions of the elements and the distances from the axis of the reinforcement to the surfaces of the element are taken according to the tables of this section, but not less than those required by chapter SNiP II-21-75 "Concrete and reinforced concrete structures".

2.15. The distance to the axis of the reinforcement and the minimum dimensions of the elements to ensure the required fire resistance of structures depend on the type of concrete. Lightweight concretes have a thermal conductivity of 10-20%, and concretes with large carbonate aggregates are 5-10% less than heavy concretes with silicate aggregates. In this regard, the distance to the reinforcement axis for a structure made of lightweight concrete or heavy concrete with carbonate filler can be taken less than for structures made of heavy concrete with silicate filler with the same fire resistance of structures made of these concretes.

The fire resistance values given in Tables 2-6, 8 refer to concrete with coarse aggregate of silicate rocks, as well as to dense silicate concrete. When using filler from carbonate rocks, the minimum dimensions of both the cross section and the distance from the axes of the reinforcement to the surface of the bent element can be reduced by 10%. For lightweight concrete, the reduction can be 20% with a concrete density of 1.2 t / m 3 and 30% for bending elements (see tables 3, 5, 6, 8) with a concrete density of 0.8 t / m 3 and expanded clay perlite concrete with a density of 1.2 t / m 3.

2.16. During a fire, the protective layer of concrete protects the reinforcement from rapid heating and reaching its critical temperature, at which the fire resistance limit of the structure occurs.

If the distance to the axis of the reinforcement adopted in the project is less than required to ensure the required fire resistance of structures, it should be increased or additional heat-insulating coatings should be applied on the surfaces of the element exposed to fire *. A thermal insulation coating of lime-cement plaster (15 mm thick), gypsum plaster (10 mm) and vermiculite plaster or mineral fiber thermal insulation (5 mm) is equivalent to a 10 mm increase in the thickness of a layer of heavy concrete. If the thickness of the protective layer of concrete is more than 40 mm for heavy concrete and 60 mm for light concrete, the protective layer of concrete must have additional reinforcement from the fire side in the form of a reinforcement mesh with a diameter of 2.5-3 mm (cells 150x150 mm). Protective heat-insulating coatings with a thickness of more than 40 mm must also have additional reinforcement.

* Additional heat-insulating coatings can be performed in accordance with the "Recommendations for the use of fire-retardant coatings for metal structures" - M.; Stroyizdat, 1984.

Tables 2, 4-8 show the distances from the heated surface to the reinforcement axis (Fig. 1 and 2).

Fig.1. Distances to the reinforcement axis

Fig.2. Average distance to the reinforcement axis

In cases where the reinforcement is located at different levels, the average distance to the axis of the reinforcement a must be determined taking into account the areas of reinforcement ( A 1 , A 2 , …, A n) and their corresponding distances to the axes ( a 1 , a 2 , …, a n), measured from the nearest of the heated (bottom or side) surfaces of the element, according to the formula

2.17. All steels reduce tensile or compressive strength when heated. The degree of resistance reduction is greater for hardened high-strength reinforcing wire steel than for bar reinforcement made of low carbon steel.

The fire resistance limit of bending and eccentrically compressed elements with a large eccentricity in terms of loss of bearing capacity depends on the critical heating temperature of the reinforcement. The critical heating temperature of the reinforcement is the temperature at which the tensile or compression resistance decreases to the value of the stress that occurs in the reinforcement from the standard load.

2.18. Tables 5-8 are compiled for reinforced concrete elements with non-stressed and prestressed reinforcement, assuming that the critical heating temperature of the reinforcement is 500 °C. This corresponds to reinforcing steels of classes A-I, A-II, A-Iv, A-IIIv, A-IV, At-IV, A-V, At-V. The difference in critical temperatures for other classes of reinforcement should be taken into account by multiplying the fire resistance limits given in Tables 5-8 by the coefficient j or dividing the distances to the reinforcement axes given in Tables 5-8 by this factor. Values j should be taken:

1. For floors and roofs made of prefabricated reinforced concrete flat slabs, solid and multi-hollow, reinforced:

a) steel class A-III, equal to 1.2;

b) steels of classes A-VI, AT-VI, AT-VII, B-I, BP-I, equal to 0.9;

c) high-strength reinforcing wire of classes B-II, Vr-II or reinforcing ropes of class K-7, equal to 0.8.

2. For floors and roofs made of prefabricated reinforced concrete slabs with longitudinal bearing ribs "down" and box section, as well as beams, crossbars and purlins in accordance with the specified classes of reinforcement: a) j= 1.1; b) j= 0.95; in) j = 0,9.

2.19. For structures made of any type of concrete, the minimum requirements for structures made of heavy concrete with a fire resistance of 0.25 or 0.5 hours must be met.

2.20. The fire resistance limits of load-bearing structures in tables 2, 4-8 and in the text are given for full standard loads with the ratio of the long-term part of the load Gser to full load Vser equal to 1. If this ratio is 0.3, then the fire resistance increases by 2 times. For intermediate values Gser / Vser the fire resistance limit is taken by linear interpolation.

2.21. The fire resistance limit of reinforced concrete structures depends on their static scheme of work. The fire resistance limit of statically indeterminate structures is greater than the fire resistance limit of statically determinable structures, if there is the necessary reinforcement in the places of action of negative moments. The increase in the fire resistance limit of statically indeterminate bent reinforced concrete elements depends on the ratio of the cross-sectional areas of the reinforcement above the support and in the span according to Table 1.

Table 1

The ratio of the area of reinforcement above the support to the area of reinforcement in the span	Increase in the fire resistance limit of a bent statically indeterminate element, %, in comparison with the fire resistance limit of a statically determinable element

Note. For intermediate area ratios, the increase in fire resistance is taken by interpolation.

The influence of the static indeterminacy of structures on the fire resistance limit is taken into account if the following requirements are met:

a) at least 20% of the top reinforcement required on the support should pass over the middle of the span;

b) the upper reinforcement above the extreme supports of the continuous system must be installed at a distance of at least 0.4 l in the direction of the span from the support and then gradually break off ( l- span length);

c) all the upper reinforcement above the intermediate supports should continue to the span by at least 0.15 l and then gradually break off.

Bending elements embedded on supports can be considered as continuous systems.

2.22. Table 2 shows the requirements for reinforced concrete columns made of heavy and light concrete. They include requirements for the dimensions of columns exposed to fire from all sides, as well as those located in walls and heated from one side. At the same time, the size b applies only to columns whose heated surface is flush with the wall, or to the part of the column that protrudes from the wall and carries the load. It is assumed that there are no openings in the wall near the column in the direction of the minimum dimension. b.

For solid round columns as dimension b take their diameter.

Columns with the parameters given in Table 2 have an eccentrically applied load or a load with random eccentricity when reinforcing the columns is not more than 3% of the concrete cross section, with the exception of joints.

The fire resistance limit of reinforced concrete columns with additional reinforcement in the form of welded transverse meshes installed in increments of not more than 250 mm should be taken from Table 2, multiplying them by a factor of 1.5.

1.1. Buildings, structures, as well as parts of buildings and structures, allocated with fire walls of the 1st type (fire compartments), are subdivided according to the degrees of fire resistance. The degree of fire resistance of buildings is determined by the minimum fire resistance limits of building structures and the maximum limits for the spread of fire through these structures.

The fire resistance limits of self-supporting walls, which are taken into account when calculating the rigidity and stability of buildings, must be taken according to gr. 2 tab. 10.1.

In cases where in the table. 10.1. the minimum fire resistance limit of structures is 0.25 h, it is allowed to use unprotected steel structures, and in hard-to-reach construction sites, in addition, in addition, external enclosing structures made of aluminum sheets, regardless of their fire resistance limit.

In buildings of the 2nd degree of fire resistance for industrial and warehouse purposes, it is allowed to use columns with a fire resistance limit of 0.75 hours.

It is allowed in buildings of all degrees of fire resistance to use gypsum boards in accordance with GOST 6266 - 89 for facing metal structures in order to increase their fire resistance limit.

In buildings of all degrees of fire resistance, to allocate workplaces within the premises, it is allowed to use partitions (glazed or with a mesh with a height of the deaf part of not more than 1.2 m, collapsible and sliding) with non-standard fire resistance limits and fire spread limits.

1.2. The degree of fire resistance of buildings is adopted in the project depending on their purpose, category for explosion and fire hazard, number of storeys, floor area within the fire compartment, except for cases established in regulatory documents.

Approximate structural characteristics of buildings, depending on their degree of fire resistance, are given in Table. 10.1.

Table 10.1. Fire resistance limits of building structures

The degree of fire resistance of buildings	The minimum limits of fire resistance of building structures, h (above the line), and the maximum limits for the spread of fire under it, cm (below the line)
					Landings, stringers, steps, beams and flights of staircases	Flooring slabs (including those with insulation) and other supporting structures	Coating elements
	Bearing stairwells	self-supporting	External non-bearing (including hinged panels)	Internal non-load-bearing partitions	Landings, stringers, steps, beams and flights of staircases		Slabs, floorings (including those with insulation) and girders	Beams, trusses, arches, frames





							0,25/0;0,5/25(40)


	Not standardized

Table 10.2. Approximate structural characteristics of buildings depending on their degree of fire resistance.

Fire-Bone Degree	Structural features
	Buildings with load-bearing and enclosing structures made of natural or artificial stone materials, concrete or reinforced concrete using sheet and slab non-combustible materials
	Same. It is allowed to use unprotected steel structures in the coverings of buildings.

	Buildings with a predominantly frame structural scheme. The frame elements are made of unprotected steel structures. Enclosing structures - from profiled steel sheets or other non-combustible sheet materials with slow-burning insulation.
	The buildings are predominantly one-storey with a frame structural scheme. The frame elements are made of solid or glued wood, subjected to fire retardant treatment, providing the required fire propagation limit. Enclosing structures - from panels or element-by-element assembly, made using wood or materials based on it. Wood and other combustible materials of building envelopes must be subjected to fire retardant treatment or protected from fire and high temperatures in such a way as to ensure the required fire spread limit.
	Buildings with load-bearing and enclosing structures made of solid or glued wood and other combustible or hardly combustible materials, protected from fire and high temperatures by plaster or other sheet or plate materials. There are no requirements for fire resistance limits and fire propagation limits for the elements of the roofing, while the elements of the attic flooring made of wood are subjected to fire retardant treatment.
	The buildings are predominantly one-storey with a frame structural scheme. The frame elements are made of unprotected steel structures. Enclosing structures - from profiled steel sheets or other non-combustible materials with combustible insulation.
	Buildings, for the load-bearing and enclosing structures of which there are no requirements for fire resistance limits and limits for the spread of fire.

IIIa from SNiP 2.01.02-85* APPENDIX 2 Reference
EXAMPLE STRUCTURAL CHARACTERISTICS OF BUILDINGS
DEPENDING ON THEIR DEGREE OF FIRE RESISTANCE
1. Degree of fire resistance
2. Structural features

I
Buildings with load-bearing and enclosing structures made of natural or artificial stone materials, concrete or reinforced concrete using sheet and slab non-combustible materials

II
Same. It is allowed to use unprotected steel structures in the coatings of buildings

III
Buildings with load-bearing and enclosing structures made of natural or artificial stone materials, concrete or reinforced concrete. For floors, it is allowed to use wooden structures protected by plaster or slow-burning sheet, as well as slab materials. There are no requirements for fire resistance limits and fire propagation limits for roofing elements, while attic wood roofing elements are subjected to fire retardant treatment.

IIIa
Buildings are predominantly with a frame structural scheme. Frame elements - from steel unprotected structures. Enclosing structures - from profiled steel sheets or other non-combustible sheet materials with slow-burning insulation

IIIb
The buildings are predominantly one-storey with a frame structural scheme. Frame elements - from solid or glued wood, subjected to fire retardant treatment, providing the required fire spread limit. Enclosing structures - from panels or element-by-element assembly, made using wood or materials based on it. Wood and other combustible materials of building envelopes must be subjected to fire retardant treatment or protected from fire and high temperatures in such a way as to ensure the required fire spread limit.

IV
Buildings with load-bearing and enclosing structures made of solid or glued wood and other combustible or slow-burning materials, protected from fire and high temperatures by plaster or other sheet or plate materials. There are no requirements for fire resistance limits and fire propagation limits for roofing elements, while attic wood roofing elements are subjected to fire retardant treatment.

IVa
The buildings are predominantly one-storey with a frame structural scheme. Frame elements - from steel unprotected structures. Enclosing structures - from profiled steel sheets or other non-combustible materials with combustible insulation

V
Buildings, for the bearing and enclosing structures of which there are no requirements for fire resistance limits and limits for the spread of fire

Note. The building structures of buildings given in this appendix must meet the requirements of Table. 1 and other norms of this SNiP.

The highest degree of fire resistance I (mausoleum).

When constructing important facilities, it is necessary to approach the choice of materials and technologies with great responsibility. One of the important parameters is the ability of all building components to resist fire. How to determine the degree of fire resistance of a building, what factors affect the limit of this property? Only a specialist can answer these questions. It is thanks to the knowledge gained during training at a higher educational institution that one can think over evacuation routes in advance, correctly position fire exits and do everything possible so that the building and all its inhabitants do not suffer during a fire.

Currently, there are many new solutions used in architecture. That is why the determination of the fire resistance of buildings and structures causes some difficulties.

Safety in case of fire, the conditions for the spread of flame in them directly depend on the flammability and ability to resist fire of the materials that were used during construction and decoration. These qualities for building components are established during the design of the facility. Much depends on the category of fire and explosion hazard of the premises located in a particular building. But first things first, so that it is possible to determine with high accuracy the degree of resistance to fire of any structures.

What is meant by the degree of fire resistance?

Before answering the question of how to determine the degree of fire resistance, you need to understand what it is in general. This is an indicator that allows you to determine the possible resistance of a particular room to the effects of fire. It can be calculated according to the rules of SNiP. This is a general provision that makes it possible to give an accurate assessment and establish the level of safety of a building for any purpose, as well as the materials from which it was built.

The fire resistance value determines how quickly a fire can spread in a particular room. And this directly affects the safety of people. All types of buildings, depending on the resistance to fire and the speed of the spread of fire, are divided into 5 categories.

Rules for determining the fire resistance of buildings

To correctly determine the resistance to fire of a particular structure (whether it is a residential building or an industrial building), you need to have:

architectural plan;
rules for ensuring the stability and fire safety of reinforced concrete structures;
a manual that allows you to determine the limits for these parameters of structures to SNiP;
allowance for SNiP - helping to prevent the spread of a fire.

The resistance limit of any building object is determined by the time of fire exposure to the tested structure. When the state reaches one of the limits, the fire is artificially stopped. Before proceeding with testing, it is necessary to carefully study the documents for the structure. This includes what building materials were used, the characteristics of the building, possible estimates of fire resistance and other points.

It is necessary to carefully study the presence or absence in the documentation for the structure of information on the use of modern technologies that could help increase the level of fire resistance. During the preliminary review of the construction of the structure, all rooms should be examined, including utility rooms, stairwells and others. It is possible that completely different materials were used during their construction. Indeed, often builders, in order to reduce the amount of the estimate, save on the arrangement of utility rooms and stairwells, which leads to a sharp decrease in their strength and resistance to fire. In extreme situations, these areas of the building are the cause of the spread of fire.

When constructing modern buildings, architects often use innovations. But in most cases, certain areas are not as strong as the rest of the structure. Therefore, this point is important to consider. It is worthwhile to carry out all the necessary measures in advance in order to quickly cope with the fire in case of fire:

hire a fire brigade;
check the serviceability of hoses and fire extinguishers.
equip a fire shield.

Only after all safety standards are fully observed, you can start working. After the preparatory activities, you can proceed to the practical.

What is SNiP?

Often answering the question of how to determine the degree of fire resistance of a building, one has to deal with such a definition as SNIP. But what is it?

"Building Norms and Rules" is a collection of legislative documents that were previously approved by the authorities of the Russian Federation and regulate the rules for the construction of urban and rural buildings. In addition, projects developed by architects and engineering searches are included in such a document.

After a thorough study of such paper, any owner will be able to independently understand all the drawings and determine the state of the structures. In any situation, you need to use special reference books. This is the only way to easily determine the 2nd degree of fire resistance of buildings or any other. This is what special documentation is required for.

But how to determine the SNiP for a particular building with the help of reference manuals and a passport for the building? In this case, experienced specialists carefully read the code of SNiP (21.01.97) "On the safety of structures and buildings during a fire." And in order to properly prepare for the tests, it is necessary to carefully study another SNiP (03/31/2001), which details all the laws relating to the construction and operation of buildings in the Russian Federation.

What are the fire resistance levels of buildings?

As we said earlier, there are 5 degrees of resistance to fire, and they depend on the degree of ignition and the resistance limit of the main structures. Below is a table of fire resistance of buildings and structures.

Degrees of resistance to fire	Structural characteristics
1 degree of fire resistance of the building	Buildings with load-bearing and enclosing structures erected using artificial and natural stones, concrete or reinforced concrete using non-combustible types of materials in the form of sheets or slabs.
	Identical to grade 1, but only steel structures are allowed to be used in building coatings.
	Structures with load-bearing structures and fences made of stone materials, reinforced concrete and concrete. Overlappings can be wooden, protected from above with a layer of plaster, slow-burning sheet materials, as well as slabs. There are no special requirements for coatings in terms of fire resistance, but in the attic all wooden structures must be treated with a special protective composition from fire.
	The buildings are mostly frame type. All structures are made of unprotected steel. Fences made of steel profiled sheets and other sheet materials that are not afraid of fire.
	Mostly buildings on one floor with a frame structure. The frame is made of wood, which has previously undergone a special treatment to protect against fire. Piece-by-piece panel fences made of wood or materials. All wood structures must be reliably protected from high temperatures.
	Buildings with load-bearing structures and fences made of wood and other flammable materials, which are protected from the effects of fire by a layer of plaster or materials in the form of plates. There are no special requirements for overlapping. But the elements of the attic made of wood must be carefully processed with flame retardants or materials.
	The buildings are mostly one-storey with a frame scheme. The frame is made of steel, and the fence is made of profiled sheets or other elements with combustible insulation.
	Buildings to which there are no special requirements for the qualities of fire resistance and the spread of fire.

Types of fire hazard of building structures

All construction sites must meet fire safety requirements. Determines the degree of fire resistance of the building fz 123, which stipulates all the requirements and criteria. Today, 4 classes of fire hazard of construction objects are distinguished:

K0 - not flammable.
K1 - little fire hazard.
K2 - moderately flammable.
K3 - fire hazard.

When determining the fire resistance of buildings, it is necessary to take into account:

number of floors;
functional fire hazard;
the area of the building and the fire compartment;
fire hazard of processes taking place inside the building;
building category;
distance to nearby buildings.

When all these factors are taken into account, it will not be difficult to determine the fire resistance.

Purposes and scope of the technical regulation

As mentioned earlier, it is impossible to determine the stability of any building in relation to fire without Federal Law 123, but besides this, it is necessary to take into account SP 2 13130 2012. The degree of fire resistance of buildings should be determined when:

design, construction, overhaul, during the reconstruction, changes in functional purpose;
development, adoption and implementation of the Federal Law on technical regulations, which include fire safety requirements;
at the stage of developing documentation for protected objects.

If all these requirements are met, it will not be necessary in the event of a fire to find out where the mistake was made.

Instructions for determining the fire resistance limit

Those who are going to start construction ask themselves one of the most important questions: "How to determine the degree of fire resistance of buildings?". Using our instructions, anyone can cope with this task. Even during the execution of project documentation, a calculated indicator for each parameter is indicated. But it’s better to check and compare all the data yourself, guided by SNiP. The limit for this property can be considered the time that elapses from the beginning of the action of fire on the structure and until the moment of the appearance of critical changes. The overall indicator is determined by the maximum resistance values. At the same time, this must be taken into account for all elements: partitions, vertical structures that are load-bearing, doors, windows and others.

Information on the level of ignition of building materials should be included in the calculation.

Analyze the entire building project in detail. Information about the main elements used in construction may not be enough to get more real data. Therefore, it is better to review and check everything personally, examining each site, including utility rooms and stairwells. In order to study this entire mechanism in detail and make the calculations correctly, you need to use the manuals for SNiP.

How can the fire resistance of a building be improved?

In order for the load-bearing supports to withstand the fire, and for everyone who is in the building at that time to be able to escape, there are several methods for increasing fire resistance. First of all, it is worth choosing the right materials that have been certified and fully comply with fire safety standards. Fortunately, there are plenty of such raw materials on the construction market at present. But the lives of people depend on skillfully and, one might say, professionally carried out measures to protect buildings from fire.

Today, a huge variety of high-quality materials from European and domestic manufacturers is presented, with the help of which it is possible to carry out fire protection.

How to carry out fire protection?

The best protection against fire is concreting and brick finishing. Another important function is the strengthening of the structure. Brick is mainly used for vertically arranged structures; reinforcement of the concrete layer is also used. Its thickness is selected individually for each object. Facing of sheets, slabs and screens is used to protect columns, beams, racks. It is also good to use plaster.

Finishing is good in that it provides reliable protection from fire, but it is also inexpensive. But there are also disadvantages. Cladding requires special skills and the thickness of the layer must be chosen correctly.

Finally

It is not difficult to determine the degree of fire resistance of buildings 3 or 5. Difficulties, of course, may arise. But if you have at hand all the necessary documents, a set of rules, then the difficulties will be quickly resolved. After studying the plan, the condition of all building structures, determining the fire resistance can be expensive, but not so difficult. The main thing is to follow safety precautions during testing, be careful and be careful, control the temperature in the furnace.

In modern times, with such a huge scale of construction, it is important that the fire resistance of buildings and materials from which residential buildings, offices and important institutions are built meet the standards. The lives of citizens depend on it. It is no secret that many accidents occur as a result of the use of unsuitable materials and violations of construction techniques.