Degree of fire resistance, constructive fire hazard class. SNiP

Engineering systems 26.06.2020
Engineering systems

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. ability - temperature rise 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 from this 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 contributes to a decrease in the heating rate and an increase in 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 an 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 reinforcement axes 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 resistance to tension or compression 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 coefficient. 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 bending 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.

Degree of fire resistance

fire resistance limit

Structural collapse;

Fire resistance limits:

– silicate brick – ~5 h

Table 3

Degree of fire resistance
I
II Same.

It is allowed to use unprotected steel structures in building coverings.
III
III a
III b
IV
IV a
V

- impregnation with flame retardants;

- facing;

- plaster.

- borax Na 2 B 4 O 7 * 10H 2 O.

asbestos cement sheets;

Related information:

Site search:

All about fire safety 0-1.ru

DIRECTORY DISCUSSIONS ARTICLES LAWS SCORE PRICES SEARCH
Topic classifier:
last 0 replies in discussion
Need help from experts in determining the degree of fire resistance of the building!
The building is 3-storey, wooden attic structures, metal roofing. The walls are brick plastered. Interfloor floors are reinforced concrete, including the attic. Wooden structures treated with fire retardant. There is a controversial question what degree of fire resistance of the building 2 or 3. In accordance with the table. 21 FZ-123 and a manual for determining the degrees of fire resistance, it turns out that the building is of the second degree of fire resistance, but the attic is embarrassing. The inspector claims that 3 is only because of the wooden attic. I disagree (maybe I'm wrong). Reasonable answer required
5.4.5. Fire resistance limits and fire hazard classes of attic roofing structures in buildings of all fire resistance degrees are not standardized, and roofing, rafters and lathing, as well as filing of eaves overhangs, are allowed to be made of combustible materials, except for specially stipulated cases. It is allowed to design gable structures with non-standardized fire resistance limits, while the gables must have a fire hazard class corresponding to the fire hazard class of the outer walls from the outside. Information about the structures related to the elements of attic coverings is given by the design organization in the technical documentation for the building. In buildings of I - IV degrees of fire resistance with attic coverings, with rafters and (or) lathing made of combustible materials, the roof should be made of non-combustible materials, and rafters and
the crate in buildings of the I degree of fire resistance should be treated with fire retardants of the I group of fire retardant efficiency, in buildings of the II - IV degrees of fire resistance with fire retardants not lower than the II group of fire retardant efficiency in accordance with GOST 53292, or to carry out their constructive fire protection that does not contribute to the latent spread of combustion. In buildings of classes C0, C1, the structures of cornices, filing of cornice overhangs of attic coverings should be made of materials NG, G1, or these elements should be sheathed with sheet materials of a flammability group of at least G1. For these structures, the use of combustible heaters is not allowed (with the exception of a vapor barrier up to 2 mm thick), and they should not contribute to the latent spread of combustion.
yahont ® why are you considering an attic to determine the fire resistance limit of a building? The attic is not a floor (see the term building and the term attic), and rooms can only be placed on a floor. You need to consider the building to the attic. And such constructions, as you described (brick walls, reinforced concrete floors, including the attic), as a rule, give the II degree.
II CO
II degree C0. The inspector is wrong.
The theme of walls, marches and landings of stairs in the stairwell, by the way, is not disclosed. Maybe it is there that there is a reason for doubts about the III degree.
Handsome Inspector! The degree of fire resistance of the building by eye determines! In fact, the degree of fire resistance is laid down in the project))
Building codes and rules SNiP 2.01.02-85*
"Fire standards" Appendix 2, these standards reveal how the degrees of fire resistance are mainly distributed, and how they can be determined. They are ancient, but very understandable.
Stairs and marches are not indicated in them. According to your description, no doubt, II degree. The inspector is wrong.
Thanks to everyone who responded!
Discussion closed

^ Back to list ^

The conditions for the development of a fire in buildings and structures are largely determined by the degree of their fire resistance. Degree of fire resistance called the ability of a building (structure) as a whole to resist destruction in a fire. Buildings and structures according to the degree of fire resistance are divided into five degrees (I, II, III, IV, V). The degree of fire resistance of a building (structure) depends on the flammability and fire resistance of the main building structures and on the limits of the spread of fire through these structures.

By flammability, building structures are divided into fireproof, slow-burning and combustible. Fireproof are building structures made of fireproof materials. Fire-retardant structures are those made of fire-retardant materials or combustible materials protected from fire and high temperatures by fireproof materials (for example, a fire door made of wood and covered with asbestos sheet and roofing steel).

The fire resistance of building structures is characterized by their fire resistance limit, which is understood as the time in hours, after which 1 of 3 signs occurs in case of fire:

1. Structure collapse;

2. Formation of through cracks or holes in the structure. (Combustion products penetrate into neighboring rooms);

3. Warming up the structure to temperatures that cause spontaneous ignition of substances in adjacent rooms (140-220 o).

Fire resistance limits:

- ceramic brick - 5 hours (25 cm-5.5; 38-11 hours)

– silicate brick – ~5 h

- concrete 25 cm thick - 4 hours (the cause of destruction is the presence of up to 8% water);

- a tree covered with plaster 2 cm thick (total 25 cm) 1 hour 15 minutes;

- metal structures - 20 min (1100-1200 o C-metal becomes plastic);

- front door treated with flame retardant -1 hour.

Porous concrete, hollow bricks have great fire resistance.

Unprotected metal structures have the lowest fire resistance limit, and reinforced concrete structures have the highest.

According to DBN 1.1.7-2002 “Fire protection. Fire safety of construction objects", all buildings and structures are divided into eight degrees according to fire resistance (see table.

Table 3

Fire resistance of buildings and structures

Degree of fire resistance Design characteristic
I Buildings with load-bearing and protective structures made of natural or artificial stone materials, concrete or reinforced concrete using sheet and slab non-combustible materials
II
III Buildings with load-bearing and enclosing structures made of natural or artificial stone materials, concrete or reinforced concrete For ceilings, it is allowed to use wooden structures protected by plaster or hardly combustible sheet materials, as well as slab materials. Requirements regarding the fire resistance limit and the limits of fire spread are not established for the elements of the coating, while elements of attic coverings made of wood are amenable to fire retardant treatment
III a Buildings predominantly with a frame structural scheme Frame elements - from steel unprotected structures Enclosing structures - from steel profiled sheets or other non-combustible sheet materials with slow-burning insulation
III b Buildings are predominantly one-story with a frame structural scheme Frame elements - made of solid or glued wood, subjected to fire retardant treatment, which provides the desired boundary for the spread of fire Enclosing structures - made of panels or element-by-element assembly, made using wood or materials based on it Wood and other combustible materials protective structures must be subjected to fire retardant treatment or protected from the effects of fire and high temperatures in such a way as to ensure the desired border of the spread of fire
IV Buildings with load-bearing and protective structures made of solid or glued wood and other combustible and slow-burning materials protected from the effects of fire and high temperatures by plaster and other sheet and slab materials timber floors are fire-retardant
IV a Buildings are predominantly one-story with a frame structural scheme Frame elements - from steel unprotected structures Enclosing structures - from steel profiled sheets or other non-combustible materials with combustible insulation
V Buildings, the load-bearing and protective structures of which are not subject to requirements regarding the limits of fire resistance and the limits of the spread of fire

Protection of wooden structures from fire:

To protect wooden structures from fire, apply:

- impregnation with flame retardants;

- facing;

- plaster.

Flame retardants are chemicals designed to impart fireproof properties to wood (French physicist Gay-Lussac. 1820 Ammonium salts).

Flame retardants - reduce the rate of release of gaseous products, reduce the yield of resin as a result of chemical interaction with cellulose.

For the impregnation of wood used:

- ammonium phosphate (NH 4) 2 HPO 4

- ammonium sulfate (NH 4) 2 SO4

- borax Na 2 B 4 O 7 * 10H 2 O.

Deep impregnation is carried out in autoclaves at a pressure of 10-15 atm for 2-20 hours.

Soaking is carried out in a flame retardant solution at a temperature of 90 ° C for 24 hours.

Impregnation with flame retardants transforms wood into the category of hardly combustible materials. Surface treatment - prevents fire wood within a few minutes.

Facing and plaster - protect wooden structures from fire (slow heating).

Wet plaster - fire protection 15-20 min.

Facing materials: gypsum plaster (fire protection 10 min);

asbestos cement sheets;

Related information:

Site search:

Fire resistance of buildings and structures

The conditions for the development of a fire in buildings and structures are largely determined by the degree of their fire resistance.

Degree of fire resistance called the ability of a building (structure) as a whole to resist destruction in a fire. Buildings and structures according to the degree of fire resistance are divided into five degrees (I, II, III, IV, V). The degree of fire resistance of a building (structure) depends on the flammability and fire resistance of the main building structures and on the limits of the spread of fire through these structures.

By flammability, building structures are divided into fireproof, slow-burning and combustible. Fireproof are building structures made of fireproof materials. Fire-retardant structures are those made of fire-retardant materials or combustible materials protected from fire and high temperatures by fireproof materials (for example, a fire door made of wood and covered with asbestos sheet and roofing steel).

The fire resistance of building structures is characterized by their fire resistance limit, which is understood as the time in hours, after which 1 of 3 signs occurs in case of fire:

1. Structure collapse;

2. Formation of through cracks or holes in the structure. (Combustion products penetrate into neighboring rooms);

3. Warming up the structure to temperatures that cause spontaneous ignition of substances in adjacent rooms (140-220 o).

Fire resistance limits:

- ceramic brick - 5 hours (25 cm-5.5; 38-11 hours)

– silicate brick – ~5 h

- concrete 25 cm thick - 4 hours (the cause of destruction is the presence of up to 8% water);

- a tree covered with plaster 2 cm thick (total 25 cm) 1 hour 15 minutes;

- metal structures - 20 min (1100-1200 o C-metal becomes plastic);

- front door treated with flame retardant -1 hour.

Porous concrete, hollow bricks have great fire resistance.

Unprotected metal structures have the lowest fire resistance limit, and reinforced concrete structures have the highest.

According to DBN 1.1.7-2002 “Fire protection. Fire safety of construction objects”, all buildings and structures are divided into eight degrees according to fire resistance (see Table 3).

Table 3

Fire resistance of buildings and structures

Degree of fire resistance Design characteristic
I Buildings with load-bearing and protective 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 building coverings.
III Buildings with load-bearing and enclosing structures made of natural or artificial stone materials, concrete or reinforced concrete For ceilings, it is allowed to use wooden structures protected by plaster or hardly combustible sheet materials, as well as slab materials. Requirements regarding the fire resistance limit and the limits of fire spread are not established for the elements of the coating, while elements of attic coverings made of wood are amenable to fire retardant treatment
III a Buildings predominantly with a frame structural scheme Frame elements - from steel unprotected structures Enclosing structures - from steel profiled sheets or other non-combustible sheet materials with slow-burning insulation
III b Buildings are predominantly one-story with a frame structural scheme Frame elements - made of solid or glued wood, subjected to fire retardant treatment, which provides the desired boundary for the spread of fire Enclosing structures - made of panels or element-by-element assembly, made using wood or materials based on it Wood and other combustible materials protective structures must be subjected to fire retardant treatment or protected from the effects of fire and high temperatures in such a way as to ensure the desired border of the spread of fire
IV Buildings with load-bearing and protective structures made of solid or glued wood and other combustible and slow-burning materials protected from the effects of fire and high temperatures by plaster and other sheet and slab materials timber floors are fire-retardant
IV a Buildings are predominantly one-story with a frame structural scheme Frame elements - from steel unprotected structures Enclosing structures - from steel profiled sheets or other non-combustible materials with combustible insulation
V Buildings, the load-bearing and protective structures of which are not subject to requirements regarding the limits of fire resistance and the limits of the spread of fire

Protection of wooden structures from fire:

To protect wooden structures from fire, apply:

- impregnation with flame retardants;

- facing;

- plaster.

Flame retardants are chemicals designed to impart fireproof properties to wood (French physicist Gay-Lussac. 1820 Ammonium salts).

Flame retardants - reduce the rate of release of gaseous products, reduce the yield of resin as a result of chemical interaction with cellulose.

For the impregnation of wood used:

- ammonium phosphate (NH 4) 2 HPO 4

- ammonium sulfate (NH 4) 2 SO4

- borax Na 2 B 4 O 7 * 10H 2 O.

Deep impregnation is carried out in autoclaves at a pressure of 10-15 atm for 2-20 hours.

Soaking is carried out in a flame retardant solution at a temperature of 90 ° C for 24 hours.

Impregnation with flame retardants transforms wood into the category of hardly combustible materials. Surface treatment - prevents fire wood within a few minutes.

Facing and plaster - protect wooden structures from fire (slow heating).

Wet plaster - fire protection 15-20 min.

Facing materials: gypsum plaster (fire protection 10 min);

asbestos cement sheets;

Related information:

Site search:

How to determine the indicators of the actual fire resistance limit and fire hazard class of a building structure?

Question:

Is it possible to use wooden structures as load-bearing roof structures in a school building? The building has II degree of fire resistance, functional fire hazard class F1.1.

Answer:

In accordance with Article 36 of the Federal Law of July 22, 2008 N 123-FZ "Technical Regulations on Fire Safety Requirements" (as amended on June 23, 2014), building structures for fire hazard are divided into the following classes:

1) non-flammable (K0);

2) low fire risk (K1);

3) moderately flammable (K2);

4) fire hazardous (K3).

Currently, when determining the actual fire hazard classes of building structures, the following is used:

— GOST 30403-2012 “Building structures.

Test Method for Fire Hazard".

Currently, when determining the actual limits of fire resistance of structures, the following are used:

— GOST 30247.0-94 “Building structures. Test methods for fire resistance. General requirements";

— GOST 30247.1-94 “Building structures. Test methods for fire resistance. Bearing and enclosing structures.

According to the results of fire tests, test reports are drawn up (clause 12 of GOST 30247.0-94, clause 10 of GOST 30247.1-94, clause 11 of GOST 30403-2012), which indicate the relevant data, including the actual fire resistance limits of building structures and actual fire hazard classes of building structures.

Accordingly, in order to determine the actual fire resistance limits and fire hazard classes of building structures, it is necessary to conduct fire tests in an accredited testing laboratory.

Based on information only about the material from which the building structure is made, it is impossible to determine the indicators of the actual fire resistance limit and the fire hazard class of the building structure.

In accordance with part 10 of article 87 of the Federal Law of July 22, 2008 N 123-FZ, the fire resistance limits and fire hazard classes of building structures similar in shape, materials, design to building structures that have passed fire tests can be determined by the calculation and analytical method established by regulatory documents on fire safety.

At the moment, information on the actual fire resistance limits and fire hazard classes of various building structures that have previously passed fire tests are given in the Collections "Technical Information (to help the inspector of the State Fire Service)", annually published by the Federal State Budgetary Institution "All-Russian Research Institute of Fire Defense" of the Ministry of Emergency Situations Russia.

Building structures with an actual fire hazard class K1 (low fire hazard), K2 (moderate fire hazard), K3 (fire hazard) can only be used if the required structural fire hazard class of the building is allowed C1, C2, C3, respectively (Table 22 of the Federal Law of July 22 2008 N 123-FZ).

The required degree of fire resistance and the required class of constructive fire hazard of buildings is determined in accordance with SP 2.13130.2012 “Fire protection systems. Ensuring the fire resistance of protected objects ”(as amended on October 23, 2013) based on certain parameters of the building being designed (for example, the functional purpose of the building, the height of buildings or structures, the number of storeys, the floor area within the fire compartment, the category of the building for explosion and fire hazard, the number places, etc.).

Further, in accordance with Table N 21 of the Federal Law of July 22, 2008 N 123-FZ, based on the required degree of fire resistance of the building, the minimum required fire resistance limits of building structures are determined.

In accordance with Table N 22 FZ N 123-FZ, based on the required structural fire hazard class of the building, the minimum required fire hazard classes of building structures are determined.

At the same time, it should be taken into account that fire safety requirements will be met only if the building structure meets both the required fire resistance limit and the required fire hazard class at the same time.

Accordingly, it is initially necessary, on the basis of SP 2.13130.2012, based on certain parameters of the designed building (for example, the functional purpose of the building, the height of buildings or structures, number of storeys, floor area within the fire compartment, number of seats, etc.) to determine the required degree of fire resistance and the required class of constructive fire hazard of buildings.

Further, in accordance with Table N 21 of the Federal Law of July 22, 2008 N 123-FZ, based on the required degree of fire resistance of the building, the minimum required fire resistance limits of specific building structures are determined.

In accordance with Table N 22 FZ N 123-FZ, based on the required structural fire hazard class of the building, the minimum required fire hazard classes of specific building structures are determined.

Further, based on certain minimum required fire hazard classes and minimum required fire resistance limits of specific building structures based on fire test reports or information on actual fire resistance limits and fire hazard classes given in the Collections "Technical Information (to assist the inspector of the State Fire Service)", select building structure.

Based on information only about the material from which the building structure is made, it is impossible to determine the indicators of the actual fire resistance limits and fire hazard classes of building structures.

In accordance with paragraph 5.4.5 of SP 2.13130.2012, the fire resistance limits and fire hazard classes of attic structures in buildings of all degrees of fire resistance are not standardized, and the roof, rafters and lathing, as well as filing of eaves overhangs, are allowed to be made of combustible materials, with the exception of specially stipulated cases.

It is allowed to design gable structures with non-standardized fire resistance limits, while the gables must have a fire hazard class corresponding to the fire hazard class of the outer walls from the outside.

Information about the structures related to the elements of attic coverings is given by the design organization in the technical documentation for the building.

In buildings of I-IV degrees of fire resistance with attic coverings, with rafters and (or) lathing made of combustible materials, the roof should be made of non-combustible materials, and the rafters and lathing in buildings of I degree of fire resistance should be treated with fire retardants of group I of fire retardant efficiency, in buildings of II-IV degrees of fire resistance with fire retardants not lower than group II of fire retardant efficiency in accordance with GOST 53292 *, or perform their constructive fire protection that does not contribute to the latent spread of combustion.

In buildings of classes C0, C1, the structures of cornices, filing of cornice overhangs of attic coverings should be made of materials NG, G1, or these elements should be sheathed with sheet materials of a combustibility group of at least G1. For these structures, the use of combustible heaters is not allowed (with the exception of a vapor barrier up to 2 mm thick) and they should not contribute to the latent spread of combustion.

The degree of fire resistance of buildings and structures, a table of indicators of these values ​​\u200b\u200bis needed in order to know at what temperature the structure is destroyed by fire. Now the number of fires caused by careless handling of fire has increased, so you need to know the level of fire resistance of various objects.

What is the fire resistance of a building, what does it depend on and what does this indicator affect?

The intensity of the spread of fire depends on the fire resistance of the object and its structures. All building materials according to the change in characteristics in a fire are divided into:

  • non-combustible;
  • slow-burning;
  • combustible.

Fire resistance is the ability of a building to withstand the action of an open flame for a certain period of time, during which its performance characteristics, such as thermal conductivity, bearing capacity of supports, resistance to fire, are maintained. To determine this indicator, you need to know the periods during which the structure is destroyed to a state where it cannot be restored.

Fire resistance of buildings is an important parameter that must be taken into account in the design and construction of buildings and structures. The fire resistance of a house depends on the level of fire resistance of its structures.

To determine the fire resistance limit, calculations or practical methods are used that make it possible to obtain these indicators from the test results. After comparing the values, a conclusion is made about the state of the building and a classification is assigned to it. When assessing the fire protection of an object, it must be taken into account that its calculation is based on the classification according to category C (support structures, flights of stairs). After that, it is determined whether the building complies with building codes in terms of the degree of resistance to combustion.

A fire is an uncontrolled process of burning and flame growth, which is accompanied by the destruction of property and creates a danger to the health and life of people in this area. Combustion is a chemical process of converting combustible substances into combustion products, it is accompanied by the release of fire, toxic gases, heat, which is carried out as a result of the oxygen oxidation reaction.

Fires are divided according to their intensity into the following types:

  1. Separate, arising in one structure. The movement of people and equipment across the area between such fires can be carried out without means of fire protection.
  2. Continuous, which is a simultaneous strong burning of several structures in one area. The movement of people and equipment across the area of ​​a continuous fire cannot occur without fire protection equipment.

Determination of fire resistance limit

The fire resistance limit of a material is the time during which it retains its characteristics during combustion. The incombustibility limit of materials depends on the protective coating layer, profile cross-section, the level of fire resistance of building materials, and the ability to maintain their parameters during combustion. The degree of fire resistance is characterized by such factors:

  • fire resistance;
  • fire resistance level;
  • level of fire spread.

There are limiting fire resistance standards:

  1. Loss of technological characteristics due to collapse or the appearance of limiting deformations is marked with the Latin letter R.
  2. Loss of integrity due to damage or holes through which combustion products and fire enter the outside. Designated with the letter E.
  3. Loss of insulating function as a result of an increase in surface temperature. Designate I.

The following limiting indicators are regulated for load-bearing structures according to the degree of resistance to fire:

  • beams, racks, arches, trusses loss of bearing capacity - R;
  • load-bearing walls and ceilings - loss of bearing capacity R and integrity E;
  • exterior walls of a building that are not considered load-bearing - loss of integrity E;
  • internal walls and partitions - loss of integrity E and the ability to thermal insulation I;
  • internal walls and fences - loss of bearing capacity R, integrity E and insulating characteristic I.

How to determine the degree of fire resistance?

The classification of buildings according to the degree of fire resistance depends on:

  • the number of floors in this building;
  • the area of ​​its territory;
  • production processes or other activities that are carried out at the facility;
  • characteristics and degree of flammability of materials used in the construction of the facility.

The fire resistance of a structure characterizes the duration of the period during which these structures were tested by flame. The resistance of objects to fire is regulated by SNiP, where there are 5 degrees of resistance of buildings to fire.

All buildings are divided into 5 categories:

  1. Explosive and fire hazardous, they carry out technical processes associated with the appearance of fire, combustible gases, flammable liquids with a flash limit of up to + 28ºC.
  2. Structures where work is carried out using flammable liquids with a flash limit greater than +28ºC, which can create explosive substances and, when burned, an explosion pressure of more than 5 kPa occurs.
  3. Objects where production processes take place using flammable liquids and solid materials that, when combined with oxygen, can burn. This is a fire category.
  4. Structures where technological actions are carried out using non-flammable materials in a hot form.
  5. Objects where production processes with the use of solid non-combustible substances take place.

Types of fire resistance degrees

The larger the number of storeys and the area of ​​the structure, the higher the required degree of fire resistance of the building should be. Residential facilities are built of brick, concrete, stone, they are classified as 1st degree.

Residential buildings made of bricks and concrete panels belong to the 2nd degree. Residential buildings with a metal frame are classified as grade 3. The lining of these structures is made of non-combustible materials. The 4th degree includes objects that have a wooden frame, i.e. it is assigned to a wooden house. Class 5 includes all other houses that are prone to fire. Given this classification of buildings, the design and construction of buildings is carried out.

It happens that the house has a low classification in terms of fire resistance. Then its partitions, floors, load-bearing structures are treated with a non-combustible coating that protects them from fire. You can also cover the house with non-combustible materials. With the help of these comprehensive measures, the fire resistance of residential buildings is increased. In residential buildings of 1st, 2nd and 3rd degrees, partitions are installed that can contain a fire for at least 45 minutes, and in houses of 4th degree - 15 minutes.

If the structure is built of sandwich panels, then a heater is installed between them. This material can withstand frost, so they are used in construction in regions with a cold climate. The material is used for the construction of rapidly erected houses, it is easy to install.

Sandwich panels are safe for human health, have excellent sound insulation and high fire resistance. The fire resistance limit of this substance depends on its thickness: the thicker the material, the longer it will be able to withstand the effects of fire. It is impossible to build houses of the 1st degree of fire resistance from sandwich panels.

Consider the resistance of a brick building to fire. Brick houses have the highest rate of fire safety, so they are classified as 1st degree. The indicator depends on the building material from which the structure is made. Brick is a non-combustible material, it does not smolder, does not deform from a fire, so it is often chosen for the construction of residential buildings. Such material will ensure the safety of people and property in the event of a fire.

Thus, any building material has its own fire resistance index, therefore, when choosing them for the construction of a building, one should take into account the characteristics of materials and structural elements that will make up the object under construction.

Degrees of fire resistance: table

Table of indicators of fire resistance of structures:

This table shows the dependence of the indicator on the fire characteristics of walls, columns, beams, runs of landings and other structures of the house. Knowing this indicator, designers carry out the project, create schemes, conduct calculations, develop the design of a residential building, taking into account fire safety requirements.

Fire safety is one of the key criteria that are primarily taken into account when assessing the condition of real estate. In Russia, the main standards that determine the degree of fire resistance of a building are dated July 22, 2008. In addition to the "Technical Regulations on Fire Safety Requirements", included in the set of its provisions, specialists use "" SNiP. There is a great demand for an authoritative "RTP Handbook" for managers organizing fire extinguishing.

Concepts and terms

The degree of fire resistance of a building is considered as a classification standardized unit, demonstrating its ability to withstand the effects of flame in the event of a fire.

To determine the power exponent of any structure or its individual compartment, they use the totality of building materials used in its construction.

They are installed according to a number of physical signs, indicating that the material samples tested at the test site have lost their qualitative features under the influence of high temperatures. When testing, the time during which destructive state changes occur is taken into account. The received data is recorded. Of these, directories are formed, denoting the results with letter marking:

  • R- the period of time during which the bearing capacity is lost;
  • E- the period leading to a violation of integrity;
  • I- destruction of heat-insulating properties under the influence of increasing temperature;
  • W is the propagation velocity of the maximum dense heat flux.

The overall picture of the possible danger of structures is made up of a combination of functional and design features. Along with them, the normative values ​​\u200b\u200bof the limit and degree of fire resistance of buildings, presented in the tables of the "Technical Regulations", are also taken into account.

What tasks are solved

Structurally, any building is a complex system that combines many elements made of various materials - metal, brick and others. Each constituent component has unique properties and resists fire in different ways.

An example is the old wooden houses. Previously, in emergency situations, they flared up like matchboxes and burned to the ground in almost minutes, because they were not treated with special impregnations. In contrast, the walls of a stone house are more resistant to fires. They retain their contours, as they have a higher fire resistance, the degree of which, in this context, should be considered as a tool for making comparisons, optimizing design costs, and predicting the likelihood of ambiguous results.

Reference data on what degrees of fire resistance buildings have is extremely important for both fire industry workers and for operational services, builders performing repairs, technical and forensic experts. It is on them that justice relies when determining the guilt or exculpation of administrators or business entities in contentious or criminal cases based on damages resulting from a fire.

Assessment Methods

In order to establish how the object being checked corresponds to the required level of fire safety, inspectors go by comparing two basic values:

  1. The required degree of fire resistance of a building is determined by the minimum allowable values ​​included in the regulations regarding:
  • number of storeys;
  • appointments;
  • operational category for explosion and fire safety;
  • sizes of areas for fire compartments;
  • volume and capacity;
  • the absence or presence of installations designed to extinguish fire.
  1. The actual degree of fire resistance of the building is determined by the actual values ​​calculated by applying the fire resistance limits, generalized information about which is presented in certificates of conformity, data sheets, manuals. Refined indicators are obtained by conducting fire tests and performing professional calculations. When examining typical buildings, they are limited to experimental testing.

Important! The results of the check are considered satisfactory when the values ​​obtained according to the actually received reports are greater than or equal to the standards that determine the required fire protection.

The procedure for conducting evaluation surveys

In practice, employees of the fire and supervision service or department, considering a specific task, receive the information they are interested in on the degrees of fire resistance from the technical passport and project documentation.

  • applications to Tech. the regulations have explanations on how to correctly determine the degree of fire resistance of a building using table 21. You see it in the figure.

The vertical structure of the table shows the fire resistance limits for all positions:

  • building structures, including internal and external load-bearing walls, interfloor, attic, non-attic and basement ceilings, columns;
  • staircases, taking into account marches, platforms;
  • flooring, heat-insulating and warming elements.

All information is related to the lines, which represent the five main degrees of fire resistance provided for buildings of various types. The main factor determining one or another of them is the magnitude of the fire load.

Using the table is not difficult for a person with minimal experience or knowledge of theory. The symbols, REI 30, indicate that the time resource of items that have fallen into the fire zone is extremely limited by an interval of 30 minutes, regardless of the sequence in which destruction occurs:

  • loss of bearing capacity;
  • integrity violations;
  • loss of thermal insulation protection, etc., or vice versa.

However, not all so simple. In any case, hidden nuances, unaccounted moments unexpectedly pop up. Consider an example of common errors associated with the calculation of the degree of fire resistance, depending on the quality and composition of the floors.

Note! Many business executives pay large fines, only because of annoying flaws made by unprofessional calculations. Business people lose funds that could be invested in business development. It's easy to avoid overspending. Contact the experts for Rely on their competence. They will bring the object and documents in full order, and you will forget about the unpleasant moments associated with supervision and inspections.

Floor materials

In the business environment, there has historically been an opinion that all construction projects with reinforced concrete floors belong to at least the II degree of fire protection. In turn, wooden floors are positions from III and below. This is an example of a misconception that needs to be cleared up.

Consider the correct order of assignment. Let's turn to tab. 21 in the appendix to Techn. regulations. Its rows indicate the categories of the degree of fire resistance of buildings, and how to determine these indicators indicate the minimum tolerances of the limits given in the columns. On the basis of which, only one conclusion can be drawn that those related to rows II and III do not have differences in the values ​​of the overlap limits. It is equal to REI 45 - in both positions. Why?

It is obvious that the desired value does not depend too much on the floor material. There are other constructive elements. They are more significant.

The technique is outdated, the stereotype remains

Indeed, earlier methods of attribution were applied according to approximate design features that determine the degree of fire resistance of a building according to SNIP 2.01.02-85, which made it possible to analyze the state, as it were, “by eye”.

Such an approach was considered dubious. He made it possible to independently set the bar of compliance. What did not form an objective order of assignment to a certain category.

The lack of necessary information led RTP into difficult situations when choosing a fire extinguishing program. The 1985 regulation was canceled back in 1997. Today, new clearly defined provisions are in force. However, the previously developed stereotypical thinking has been preserved. Reinforced concrete panels are still recognized as an indisputable factor for classifying a building as II. In turn, they continue to erroneously enter in the III or IV line.

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 the 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;
  • increase in 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 buildings, 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).

We recommend reading