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Classification of buildings and structures by fire resistance.
In assessing the fire safety qualities of buildings and structures great importance has their fire resistance.
Fire resistance is the ability of building structural elements of a building to perform load-bearing and enclosing functions in fire conditions for a certain time. It is characterized by fire resistance.
The fire resistance limits of facility structures must be such that the structures retain their load-bearing and enclosing functions throughout the entire duration of the evacuation of people or their stay in places of collective protection. In this case, fire resistance limits must be assigned without taking into account the impact of extinguishing agents on the development of a fire.
The fire resistance limit of building structures is determined by the time (hours) from the start of the fire until one of the signs occurs: a) the formation of through cracks in the structure; b) an increase in temperature on the unheated surface of the structure by an average of more than 140 ° C or at any point on this surface by more than 180 ° C compared to the temperature of the structure before testing, or by more than 220 ° C regardless of the temperature of the structure before testing; d) loss of load-bearing capacity of the structure.
The fire resistance limit of individual building structures depends on their dimensions (thickness or cross-section) and physical properties materials. For example, the stone walls of a building are 120 mm thick. have a fire resistance limit of 2.5 hours, and with a thickness of 250 mm the fire resistance limit increases to 5.5 hours.
The degree of fire resistance of a building depends on the degree of flammability and the fire resistance limit of its main building structures. All buildings and structures are divided into five degrees according to fire resistance (Table 32).
Table 32 Classification of buildings and structures by fire resistance.
| Fire resistance degree | Basic building structures | |||||
| load-bearing walls, staircase walls, columns | external walls made of curtain panels and external half-timbered walls | slabs, decking and other load-bearing structures of interfloor and attic floors | slabs, decking and other load-bearing structures of coverings | internal load-bearing walls (partitions) | fire walls | |
| I | Fireproof (2.5) | Fireproof (0.5) | Fireproof (1.0) | Fireproof (0.5) | Fireproof (0.5) | Fireproof (2.5) |
| II | Fireproof (2.0) | Fireproof (0.25); fire-resistant (0.5) | Fireproof (0.75) | Fireproof (0.25) | Fire-resistant (0.25) | Fireproof (2.5) |
| III | Fireproof (2.0) | Fireproof (0.25); fire-resistant (0.15) | Fire-resistant (0.75) | Combustible | Fire-resistant (0.25) | Fireproof (2.5) |
| IV | Fire-resistant (0.5) | Fire-resistant (0.25) | Fire-resistant (0.25) | » | Fire-resistant (0.25) | Fireproof (2.5) |
| V | Combustible | Combustible | Combustible | » | Combustible | Fireproof (2.5) |
Note. The fire resistance limits (h) are indicated in parentheses.
This division into degrees was introduced by SNiP II-A. 5-70, which gives nine notes to keep in mind when using the table.
Fire safety is one of the key criteria that is 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 Requirements fire safety”, included in the set of its provisions, specialists use “” SNiP. There is a great demand for the authoritative “RTP Handbook” for managers organizing firefighting.
Concepts and terms
The degree of fire resistance of a building is considered as a classification standard unit that demonstrates 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 established according to a number of physical characteristics indicating that those being tested at the test site material samples Under the influence high temperatures lost theirs quality features. When conducting testing, the time during which destructive changes in states occur is taken into account. The obtained data is recorded. Directories are formed from them, indicating the results with letter markings:
- R– the period of time during which the load-bearing capacity is lost;
- E– the period leading to a violation of integrity;
- I– destruction thermal insulation properties under the influence of increasing temperature;
- W– speed of propagation of the most dense heat flow.
The big picture possible danger structures consists of a combination of functional and design features. Along with them, the standard values of the limit and degree of fire resistance of buildings, presented in the tables of the Technical Regulations, are also taken into account.
What problems do they solve?
Structurally, any structure is complex system, combining many elements made from various materials– metal, brick and others. Each component has unique properties and resists fire in different ways.
An example is the ancient wooden houses. Previously, in emergency situations they flared up like boxes of matches 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 fire. They retain their contours because they have higher fire resistance, the degree of which, in this context, should be considered as a tool that allows comparisons, optimization of design costs, and prediction of the likelihood of ambiguous results.
Reference data on what degrees of fire resistance buildings have is extremely important both for workers in the fire industry and for operational services, builders performing renovation work, technical and forensic experts. It is on them that justice relies when determining guilt or exonerating administrators or subjects economic activity in controversial or criminal cases based on damage resulting from fire.
Assessment methods
In order to establish how much the object being inspected corresponds to the required level of fire safety, inspectors proceed by comparing two basic values:
- The required degree of fire resistance of a building is determined by the minimum acceptable values included in the regulations regarding:
- number of storeys;
- appointments;
- operational category for fire and explosion safety;
- size of areas for fire compartments;
- volume and capacity;
- absence or presence of installations designed to extinguish fire.
- The actual degree of fire resistance of a building is determined by actual values calculated by applying fire resistance limits, summarized information about which is presented in certificates of conformity, technical passports, and 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 test results are considered satisfactory when the values obtained from the actual reports received are greater than or equal to the standards defining the required fire protection.
The procedure for conducting assessment surveys
In practice, employees of the fire inspection service or department, when considering a specific task, receive the information they are interested in on the degree of fire resistance from the technical passport and design documentation.
- applications to Tech. The regulations contain explanations on how to correctly determine the degree of fire resistance of a building using Table 21. You can 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 floors, columns;
- staircases, taking into account flights and landings;
- floorings, thermal insulation and insulation elements.
All information is linked to the lines where the five main degrees of fire resistance provided for buildings are presented 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 who has minimal experience or knows the theory. The symbols, REI 30, indicate that the time resource of objects caught in the fire zone is extremely limited to an interval of 30 minutes, regardless of the exact 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 and unaccounted for moments unexpectedly emerge. Let's look at an example of common mistakes associated with calculating the degree of fire resistance depending on the quality and composition of the floors.
Note! Many business owners pay large fines only because of annoying mistakes made by unprofessional calculations. Business people lose funds that could be invested in business development. Avoiding unnecessary expenses is easy. Contact specialists for. Rely on their competence. They will bring the object and documents into 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 that have reinforced concrete floors belong to at least II degree of fire protection. In its turn wooden floors– these are positions from III and below. This is an example of a misconception that needs to be cleared up.
Let's consider correct order attributions. Let's turn to the table. 21 in the appendix to Techn. regulations. Its rows indicate the categories of fire resistance of buildings, and how to determine these indicators is indicated by the minimum tolerance limits given in the columns. Based on this, only one conclusion can be drawn: those belonging 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?
Obviously, the required value does not depend too much on the floor material. There are others structural elements. They are more meaningful.
The technique is outdated, the stereotype remains
Indeed, earlier attribution methods based on approximate design features, which determines the degree of fire resistance of a building according to SNIP 2.01.02-85, which allowed for an analysis of the condition, as if “by eye”.
This approach was considered dubious. It made it possible to independently set the bar for compliance. Which did not form an objective order of assignment to a certain category.
Absence necessary information introduced the RTP into difficult situations when choosing a fire extinguishing program. The 1985 standard was canceled back in 1997. Today, new clearly defined provisions are in force. However, previously developed stereotypical thinking preserved. Reinforced concrete panels are still recognized as an indisputable factor for classifying a building as II. In turn, they continue to mistakenly enter in line III or IV.
The conditions for the development of fire in buildings and structures are largely determined by the degree of their fire resistance. Fire resistance degree is the ability of a building (structure) as a whole to resist destruction in a fire. Buildings and structures are divided into five degrees according to the degree of fire resistance (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 fire spread through these structures.
Based on flammability, building structures are divided into fireproof, non-combustible and combustible. Fireproof are building structures made of fireproof materials. Non-combustible structures are considered to be those made of non-combustible materials or of combustible materials protected from fire and high temperatures by non-combustible materials (for example, fire door, made of wood and covered with asbestos sheets 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 during a fire:
1. Structural collapse;
2. Formation of through cracks or holes in the structure. (Combustion products penetrate into adjacent rooms);
3. Warming up the structure to temperatures that cause spontaneous combustion 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);
Wood covered with gypsum 2 cm thick (total 25 cm) 1 hour 15 minutes;
Metal structures - 20 min (1100-1200 o C-metal becomes plastic);
Entrance door treated with fire retardant -1 hour.
Porous concrete, hollow brick have great fire resistance.
The lowest fire resistance limit is for unprotected metal constructions, and the largest are reinforced concrete.
According to DBN 1.1.7-2002 “Fire protection. Fire safety of construction projects,” all buildings and structures are divided into eight degrees according to fire resistance (see Table 3).
Table 3
Fire resistance of buildings and structures
| Fire resistance degree | Design characteristics |
| 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 | The same. In building coatings it is allowed to use unprotected steel structures |
| 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 low-flammable sheet and slab materials. Requirements regarding fire resistance limits and fire spread limits are not established for coating elements, while elements of attic coverings made of wood can be treated with fire retardant treatment |
| III a | Buildings predominantly with frame design diagram Frame elements - from unprotected steel structures Enclosing structures - from steel profiled sheets or other non-combustible sheet materials with low-flammable insulation |
| III b | The buildings are predominantly one-story with a frame structural design. Frame elements are made of solid or laminated wood, subjected to fire retardant treatment, which provides the necessary limit for the spread of fire. Enclosing structures are made of panels or element-by-element assembly, made using wood or materials based on it. Wood and other combustible materials. enclosing structures must be subjected to fire retardant treatment or protected from the influence of fire and high temperatures in such a way as to ensure the desired limit of fire spread |
| IV | Buildings with load-bearing and enclosing structures made of solid or laminated wood and other combustible and low-combustible materials, protected from the influence of fire and high temperatures by plaster and other sheet and slab materials. Coating elements are not subject to requirements regarding fire resistance limits and flame propagation limits, while the elements attic floors made of wood can be treated with fire retardant treatment |
| IV a | The buildings are predominantly one-story with a frame structural design. Frame elements are made of unprotected steel structures. Enclosing structures are made of steel profiled sheets or other non-combustible materials with combustible insulation. |
| V | Buildings, the load-bearing and enclosing structures of which are not subject to requirements regarding fire resistance limits and fire spread limits |
Protection of wooden structures from fire:
To protect wooden structures from fire, use:
Impregnation with fire retardants;
Facing;
Plaster.
Fire retardants - chemical substances, intended to impart non-flammability properties to wood (French physicist Gay-Lussac. 1820 Ammonium salts).
Fire retardants - reduce the rate of release of gaseous products, reduce the yield of resin as a result of chemical interaction with cellulose.
For wood impregnation the following is 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 fire retardant solution at a temperature of 90 o C for 24 hours.
Impregnation with fire retardants transforms wood into the category of difficult-to-burn materials. Surface treatment prevents wood from burning within a few minutes.
Cladding and plaster - protect wooden structures from fire (slow heating).
Wet plaster- fire protection 15-20 min.
SNB.2.02.01-98 “Fire-technical classification of buildings, building structures and materials”
Fire resistance- this is the ability of building structures to resist the effects of fire for a certain time while maintaining operational functions.
Fire resistance is characterized by the fire resistance limit.
Fire resistance limit building structures are characterized by limit states normalized according to temporary characteristics:
Load capacity (R)
Integrity (E)
Thermal insulation capacity (I)
(For example: REI120K0 – the object retains its integrity, load-bearing capacity, thermal insulation capacity for 120 minutes, non-fire hazardous)
By fire danger building structures are divided into 4 classes:
K0) Non-flammable
K1) Low fire hazard
K2) Moderately flammable
K3) Fire hazardous
Depending on the fire resistance limit, 8 degrees of fire resistance are established (1st is best, 8th is worst)
1st degree of fire resistance: load-bearing walls R120K0, internal walls RE150K0, flights and landings RE30K0.
Category A) Explosion and fire hazard – Combustible gases (GG), flammable liquids (flammable liquids) with a flash point of no more than 28ºC, flammable liquids in such quantities that they can form explosive vapor-gas-air mixtures, upon ignition of which a calculated overpressure explosion in a room exceeding 5 kPa. Substances and materials capable of exploding and burning when interacting with water or with each other in such quantities that the calculated excess explosion pressure in the room exceeds 5 kPa.
Category B) Explosion and fire hazard – flammable dusts or fibers, flammable liquids (flammable liquids) with a flash point of more than 28ºС, flammable liquids in such quantities that they can form explosive dust or steam-gas-air mixtures, upon ignition of which the calculated excess pressure of explosions in the room develops, exceeding 5 kPa.
Category B) (Divided into B1, B2, B3, B4) Fire hazardous - flammable liquids (flammable liquids), flammable liquids and difficult to combustible liquids, solid flammable and difficult to combustible substances and materials (including dust and fibers), capable of interacting with burn with water, oxygen, air or with each other.
D1) Combustible gases, flammable liquids (flammable liquids), flammable liquids, solid flammable and difficult to combustible substances and materials used as fuel.
D2) Non-combustible substances and materials in a hot, incandescent or molten state, the processing of which is accompanied by the release of radiant heat, sparks and flames.
Fire barriers
The purpose of fire barriers is to stop the spread of fire.
Fire barriers:
Fire wall - crosses perpendicularly the entire building, starting from the zero mark and ending with the roof, and protrudes above the roof (0.3-0.6) m. Fire resistance limit 150 min.
Fire partition - partitions within one room. Fire resistance limit 150 min.
Fireproof ceilings – resist the spread of fire vertically.
Fire belt - protects so that fire does not engulf the building from the outside.
Fire doors can be metal, wood or upholstered with sheet steel.
Fire hatches.
Fire windows (tempered glass, triplex, reinforced glass)
Tambour-gateway.
Water curtains (deluge system).
Fire curtain.
Evacuation routes.
SNB 2-02-01 “Evacuation of people from buildings and structures in case of fire”
Escape routes serve to ensure the evacuation of all people in the building through emergency exits, without taking into account fire extinguishing equipment and smoke protection.
Exits are evacuation if they lead from the premises:
The first floor - directly to the outside or through the corridor and vestibule, corridor and staircase to the outside.
Any above-ground floor - directly into the staircase or into the corridor leading to the staircase, which has access directly to the outside or through a vestibule separated from adjacent corridors by doors.
Basement or ground floor– directly outside or onto the staircase, or into the corridor leading to the staircase. In this case, the staircase must have direct access to the outside, or be isolated from the overlying floors.
To an adjacent room on the same floor, provided with exits, in accordance with points a, b, c.
If a fire occurs, people must leave the building within a time determined by the shortest distance from the fire to the exit outside.
The number of emergency exits from buildings is determined by calculation, but is at least two.
Elevators are not escape routes.
The width of escape routes must be at least 1 meter, doors on escape routes must be at least 0.8 m, and the height must be at least 2 m.
For buildings of 1, 2, 3 degrees of fire resistance, the time for evacuating people from the doors of the most remote premises to exiting outside is accepted:
From premises of buildings of any category with access to a dead-end corridor (0.5 minutes).
External evacuation doors of buildings should not have locks that cannot be opened from the inside in case of fire.
From premises located between two staircases and two external exits:
If it is necessary to install locks on doors, in order to preserve value, it is allowed to install electromagnetic contacts that are activated automatically or manually.
Fire resistance degree
fire resistance limit
Structural collapse;
Fire resistance limits:
— silicate brick — ~5 h
Table 3
| Fire resistance degree | |
| I | |
| II | The same. It is allowed to use unprotected steel structures in building coverings |
| III | |
| III a | |
| III b | |
| IV | |
| IV a | |
| V |
— impregnation with fire retardants;
- cladding;
- plaster.
- borax Na 2 B 4 O 7 * 10H 2 O.
asbestos cement sheets;
Related information:
Search on the site:
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| Topic qualifier: | ||
| last | There are 0 comments in the discussion | |
| We need the help of specialists in determining the degree of fire resistance of a building! The building is 3-storey, wooden attic structures, metal roofing. The walls are brick plastered. The interfloor ceilings are reinforced concrete, including the attic. Wooden structures treated with a fire retardant compound. A controversial question arises: what degree of fire resistance of a building is 2 or 3. In accordance with table. 21 FZ-123 and a guide to determining degrees of fire resistance, it turns out that the building is of the second degree of fire resistance, but the attic is confusing. The inspector claims that 3 is only due to wooden attic. I don't agree (maybe I'm wrong). A reasoned answer would be desirable. |
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| 5.4.5. The fire resistance limits and fire hazard classes of attic covering structures in buildings of all degrees of fire resistance are not standardized, and the roofing, rafters and sheathing, as well as the lining of eaves overhangs, may be made of combustible materials, except in specially specified cases. Gable structures may be designed with non-standardized fire resistance limits, while the gables must have a fire hazard class corresponding to the fire hazard class of external walls with outside. Information on structures related to elements of attic coverings is given design organization V technical documentation on the building. In buildings of I - IV degrees of fire resistance with attic coverings, with rafters and (or) sheathing made of combustible materials, the roof should be made of non-combustible materials, and the rafters and the sheathing in buildings of fire resistance class I should be treated fire retardant compounds I group of fire retardant efficiency, in buildings of II - IV degrees of fire resistance with fire retardant compounds not lower than group II of fire retardant efficiency according to GOST 53292, or carry out their structural fire protection, which does not contribute to the hidden spread of combustion. In buildings of classes C0, C1, the structures of cornices, lining of eaves overhangs of attic coverings should be made from materials NG, G1, or these elements should be sheathed sheet materials flammability group not less than G1. For these structures, the use of flammable insulation is not allowed (with the exception of vapor barriers up to 2 mm thick), and they should not contribute to the hidden spread of combustion. |
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| Yakhont ® why are you considering the attic to determine the fire resistance limit of a building? An 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 down to the attic. And such structures as you described (brick walls, interfloor ceilings reinforced concrete, including attics), as a rule give II degree. | ||
| II CO | ||
| II degree C0. The inspector is wrong. The topic of walls, flights and landings in the staircase, by the way, has not been disclosed. Maybe this is where the reason for the doubts about the third degree lies. |
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| Handsome inspector! The degree of fire resistance of a building can be determined by eye! Actually, the degree of fire resistance is included in the project)) | ||
| Construction norms and rules SNiP 2.01.02-85* "Fire safety standards" Appendix 2, these standards reveal how they are mainly distributed degree of fire resistance, and how can they be identified. They are ancient, but very understandable. The stairs and flights are not indicated in them. According to your description, it is undoubtedly II degree. The inspector is wrong. |
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| Thanks to everyone who responded! | ||
| Discussion closed | ||
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The conditions for the development of fire in buildings and structures are largely determined by the degree of their fire resistance. Fire resistance degree is the ability of a building (structure) as a whole to resist destruction in a fire. Buildings and structures are divided into five degrees according to the degree of fire resistance (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 fire spread through these structures.
Based on flammability, building structures are divided into fireproof, non-combustible and combustible. Fireproof are building structures made of fireproof materials. Non-combustible structures are considered to be structures made of materials that do not burn easily or of combustible materials protected from fire and high temperatures by non-combustible materials (for example, a fire door made of wood and covered with sheet asbestos 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 during a fire:
1. Structural collapse;
2. Formation of through cracks or holes in the structure. (Combustion products penetrate into adjacent rooms);
3. Warming up the structure to temperatures that cause spontaneous combustion 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);
- wood covered with gypsum 2 cm thick (total 25 cm) 1 hour 15 minutes;
- metal structures - 20 minutes (1100-1200 o C-metal becomes plastic);
— Entrance door, treated with fire retardant - 1 hour.
Porous concrete and hollow bricks have greater fire resistance.
Unprotected metal structures have the lowest fire resistance limit, and reinforced concrete ones have the highest.
According to DBN 1.1.7-2002 “Fire protection. Fire safety of construction projects”, all buildings and structures are divided into eight degrees according to fire resistance (see table.
Table 3
Fire resistance of buildings and structures
| Fire resistance degree | Design characteristics |
| 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 | |
| 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 low-flammable sheet and slab materials. Requirements regarding fire resistance limits and fire spread limits are not established for coating elements, while elements of attic coverings made of wood can be treated with fire retardant treatment |
| III a | Buildings predominantly with a frame structural design Frame elements - from unprotected steel structures Enclosing structures - from steel profiled sheets or other non-combustible sheet materials with low-combustible insulation |
| III b | The buildings are predominantly one-story with a frame structural design. Frame elements are made of solid or laminated wood, subjected to fire retardant treatment, which provides the necessary limit for the spread of fire. Enclosing structures are made of panels or element-by-element assembly, made using wood or materials based on it. Wood and other combustible materials. enclosing structures must be subjected to fire retardant treatment or protected from the influence of fire and high temperatures in such a way as to ensure the desired limit of fire spread |
| IV | Buildings with load-bearing and enclosing structures made of solid or laminated wood and other combustible and low-combustible materials, protected from the influence of fire and high temperatures by plaster and other sheet and slab materials. Coating elements are not subject to requirements regarding fire resistance limits and flame propagation limits, while attic elements Wood floors can be treated with fire retardant treatment |
| IV a | The buildings are predominantly one-story with a frame structural design. Frame elements are made of unprotected steel structures. Enclosing structures are made of steel profiled sheets or other non-combustible materials with combustible insulation. |
| V | Buildings, the load-bearing and enclosing structures of which are not subject to requirements regarding fire resistance limits and fire spread limits |
Protection of wooden structures from fire:
To protect wooden structures from fire, use:
— impregnation with fire retardants;
- cladding;
- plaster.
Fire retardants are chemical substances designed to give wood non-flammable properties (French physicist Gay-Lussac. 1820 Ammonium salts).
Fire retardants - reduce the rate of release of gaseous products, reduce the yield of resin as a result of chemical interaction with cellulose.
For wood impregnation the following is 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 fire retardant solution at a temperature of 90 o C for 24 hours.
Impregnation with fire retardants transforms wood into the category of difficult-to-burn materials. Surface treatment prevents wood from burning within a few minutes.
Cladding 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:
Search on the site:
Fire resistance of buildings and structures
The conditions for the development of fire in buildings and structures are largely determined by the degree of their fire resistance.
Fire resistance degree is the ability of a building (structure) as a whole to resist destruction in a fire. Buildings and structures are divided into five degrees according to the degree of fire resistance (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 fire spread through these structures.
Based on flammability, building structures are divided into fireproof, non-combustible and combustible. Fireproof are building structures made of fireproof materials. Non-combustible structures are considered to be structures made of materials that do not burn easily or of combustible materials protected from fire and high temperatures by non-combustible materials (for example, a fire door made of wood and covered with sheet asbestos 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 during a fire:
1. Structural collapse;
2. Formation of through cracks or holes in the structure. (Combustion products penetrate into adjacent rooms);
3. Warming up the structure to temperatures that cause spontaneous combustion 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);
- wood covered with gypsum 2 cm thick (total 25 cm) 1 hour 15 minutes;
- metal structures - 20 minutes (1100-1200 o C-metal becomes plastic);
- entrance door treated with fire retardant - 1 hour.
Porous concrete and hollow bricks have greater fire resistance.
Unprotected metal structures have the lowest fire resistance limit, and reinforced concrete ones have the highest.
According to DBN 1.1.7-2002 “Fire protection. Fire safety of construction projects,” all buildings and structures are divided into eight degrees according to fire resistance (see Table 3).
Table 3
Fire resistance of buildings and structures
| Fire resistance degree | Design characteristics |
| 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 | The 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 floors, it is allowed to use wooden structures protected by plaster or low-flammable sheet and slab materials. Requirements regarding fire resistance limits and fire spread limits are not established for coating elements, while elements of attic coverings made of wood can be treated with fire retardant treatment |
| III a | Buildings predominantly with a frame structural design Frame elements - from unprotected steel structures Enclosing structures - from steel profiled sheets or other non-combustible sheet materials with low-combustible insulation |
| III b | The buildings are predominantly one-story with a frame structural design. Frame elements are made of solid or laminated wood, subjected to fire retardant treatment, which provides the necessary limit for the spread of fire. Enclosing structures are made of panels or element-by-element assembly, made using wood or materials based on it. Wood and other combustible materials. enclosing structures must be subjected to fire retardant treatment or protected from the influence of fire and high temperatures in such a way as to ensure the desired limit of fire spread |
| IV | Buildings with load-bearing and enclosing structures made of solid or laminated wood and other combustible and low-combustible materials, protected from the influence of fire and high temperatures by plaster and other sheet and slab materials. Coating elements are not subject to requirements regarding fire resistance limits and flame propagation limits, while attic elements Wood floors can be treated with fire retardant treatment |
| IV a | The buildings are predominantly one-story with a frame structural design. Frame elements are made of unprotected steel structures. Enclosing structures are made of steel profiled sheets or other non-combustible materials with combustible insulation. |
| V | Buildings, the load-bearing and enclosing structures of which are not subject to requirements regarding fire resistance limits and fire spread limits |
Protection of wooden structures from fire:
To protect wooden structures from fire, use:
— impregnation with fire retardants;
- cladding;
- plaster.
Fire retardants are chemical substances designed to give wood non-flammable properties (French physicist Gay-Lussac. 1820 Ammonium salts).
Fire retardants - reduce the rate of release of gaseous products, reduce the yield of resin as a result of chemical interaction with cellulose.
For wood impregnation the following is 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 fire retardant solution at a temperature of 90 o C for 24 hours.
Impregnation with fire retardants transforms wood into the category of difficult-to-burn materials. Surface treatment prevents wood from burning within a few minutes.
Cladding 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;
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How to determine the actual fire resistance limit and fire hazard class of a building structure?
Question:
Is it possible as load-bearing structures roofs in a school building to use wooden structures? The building has fire resistance degree II, functional fire hazard class F1.1.
Answer:
In accordance with Article 36 Federal Law dated July 22, 2008 N 123-FZ " Technical regulations on fire safety requirements" (as amended on June 23, 2014), building structures based on fire hazard are divided into the following classes:
1) non-fire hazardous (K0);
2) low fire hazard (K1);
3) moderate fire hazard (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 fire resistance limits 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. Load-bearing and enclosing structures."
Based on the results of fire tests, test reports are drawn up (clause 12 GOST 30247.0-94, clause 10 GOST 30247.1-94, clause 11 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, 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 it is made building construction, it is impossible to determine the actual fire resistance limit and fire hazard class of a building structure.
In accordance with Part 10 of Article 87 of the Federal Law of July 22, 2008 N 123-FZ, fire resistance limits and fire hazard classes of building structures similar in shape, materials, design building structures that have passed fire tests can be determined by the calculation and analytical method established 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 is given in the Collections " Technical information(to assist the inspector of the State Fire Service)”, published annually by the Federal State Budgetary Institution “All-Russian Research Institute of Fire Defense” of the Ministry of Emergency Situations of Russia.
Building structures with actual fire hazard classes 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 structural fire hazard of buildings are 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 designed building (for example, functional purpose buildings, height of buildings or structures, number of storeys, floor area within the fire compartment, category of the building for explosion and fire hazard, number of seats, 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 Federal Law N 123-FZ, based on the required class of structural fire hazard, buildings are determined to be minimal required classes fire hazard of building structures.
It is necessary to take 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, based on 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 structural 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 of Federal Law N 123-FZ, based on the required class of structural fire hazard of a 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 a building structure.
Based on information only about the material from which the building structure is made, it is impossible to determine the actual fire resistance limits and fire hazard classes of building structures.
In accordance with clause 5.4.5 of SP 2.13130.2012, fire resistance limits and fire hazard classes of attic covering structures in buildings of all degrees of fire resistance are not standardized, and roofing, rafters and sheathing, as well as lining of eaves overhangs, may be made from combustible materials, with the exception of specially specified cases.
Gable structures may be designed with non-standardized fire resistance limits, while the gables must have a fire hazard class corresponding to the fire hazard class of the external walls on the outside.
Information about structures related to elements of attic coverings is provided 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) sheathing made of combustible materials, the roof should be made of non-combustible materials, and the rafters and sheathing in buildings of I degree of fire resistance should be treated with fire retardant compounds of group I fire retardant effectiveness, in buildings of II-IV degrees of fire resistance with fire retardant compounds not lower than group II of fire retardant efficiency according to GOST 53292*, or perform their structural fire protection that does not contribute to the hidden spread of combustion.
In buildings of classes C0, C1, the structures of cornices, lining of eaves overhangs of attic coverings should be made from 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 flammable insulation is not allowed (with the exception of vapor barriers up to 2 mm thick) and they should not contribute to the hidden spread of combustion.