The degree of fire resistance of buildings, the required fire resistance limits Ptr of building structures. Fire hazard of building materials
DEGREE OF FIRE RESISTANCE OF BUILDINGS, REQUIRED LIMITS OF FIRE RESISTANCE OF THE PTR OF BUILDING STRUCTURES.
FIRE HAZARD OF BUILDING MATERIALS.
For residential buildings, the degree of fire resistance of the building is determined according to SNiP 31-01-03, depending on the height of the building (Table 5). For example, for buildings up to 50 m high with a floor area up to 2500 m2, the degree of fire resistance should be I.
Knowing the degree of fire resistance of the building according to the table. 6 of SNiP 21-01-97 * "Fire safety of buildings and structures" defines the required fire resistance limits Ptr of all building structures.
The fire resistance limit of building structures is set in time (in minutes) until the onset of one or several successively normalized signs for a given structure: for load-bearing structures on the basis of loss of bearing capacity R, in minutes; for external non-bearing walls, floor slabs along E - loss of structural integrity, i.e. until the moment of formation of through cracks, in min.; for ceilings, floorings, internal walls along J - loss of heat-insulating ability, when on the side of the ceiling opposite from the effect of fire, the temperature rises by an average of 160 ° C. The required fire resistance limits of building structures Ptr are set according to R; RE; REJ, they are given in Table. 6 (SNiP 21-01-97).
To ensure fire safety, the following condition is required: the actual fire resistance limit of structures (Pf) (see Table 2) must be equal to or exceed the required fire resistance limit (Pf) according to the standards: (Pf>Ptr).
Comparison of fire resistance limits Ptr and Pf is made in the form presented in Table. 1. For load-bearing elements of a building, the fire resistance limit is determined according to R, according to RE - for elements of non-attic floors, according to REJ - for floors, including basement and attic floors, according to E - for external non-bearing walls.
The fire resistance limit when filling openings in fire barriers (doors, gates, glazed doors, valves, curtains, screens) sets in when integrity is lost E; heat-insulating ability J; reaching the limit value of the heat flux density W and (or) smoke and gas tightness S. For example, smoke and gas tight doors with more than 25% glazing must have a fire resistance limit of EJWS60 for the first type of filling; EJSW30 - for the second type of aperture filling and EJSW15 - for the third type of aperture filling in fire limits.
The fire resistance limit for W is characterized by the achievement of the limiting value of the heat flux density at a normalized distance from the unheated surface of the building structure (see Technical Regulations on Fire Safety Requirements No. 123-FZ).
The fire hazard of building materials is assessed by a number of fire-technical characteristics: combustibility, flammability, flame spread over the surface, smoke-generating ability and toxicity. For example, according to combustibility, building materials are divided into:
G1-slightly combustible;
G2-moderately combustible;
G3-normally combustible;
G4 - highly flammable.
Similarly, they are divided into building materials according to other fire hazard characteristics (see SNiP 21-01-97 * "Fire hazard of buildings and structures").
Table 3
| Room categories | Characteristics of substances and materials in the room |
| A. Explosive | Combustible gases, flammable liquids with a flash point of not more than 28 ° C in such an amount that they can form vapor-gas-air mixtures, upon ignition of which an excess explosion pressure in the room develops in excess of 5 kPa. Substances and materials capable of exploding and burning when interacting with water, oxygen in the air or with each other in such an amount that the excess design explosion pressure in the room exceeds 5 kPa (0.05 kgf / cm2) |
| B. Explosive | Combustible dusts and fibres, flammable liquids with a flash point over 28°C. Flammable liquids in such quantities that they can form explosive dust-air or vapor-air mixtures, when ignited, an excess explosion pressure in the room develops in excess of 5 kPa (0.05 kgf / cm2) |
| B1-B4. flammable | Combustible and slow-burning liquids, solid combustible and slow-burning substances and materials (including dust and fibers), substances and materials that can only burn when interacting with water, atmospheric oxygen or with each other, provided that the premises in which they are in stock or in circulation, do not belong to categories A and B |
| G. | Non-combustible substances and materials in a hot state, the processing of which is accompanied by the release of radiant heat, sparks and flames. Combustible gases, liquids and solids that are burned or disposed of as fuel. |
| D. | Non-flammable substances and materials in a cold state. |
Table 4
Table 5
| The degree of fire resistance of the building | Building constructive fire hazard class | The highest allowable height of the building, m | Permissible floor area, fire compartment, m2 |
| I | SO SO Cl | 75 50 28 | 2500 2500 2200 |
| II | CO CO Cl | 28 28 15 | 1800 1800 1800 |
| III | CO Cl C2 | 5 5 2 | 100 800 1200 |
| IV | Not standardized | 5 | 500 |
| V | Not standardized | 5;3 | 500;800 |
Table6
Any building or structure is a collection of individual structural elements. At the same time, each such element has a certain degree of fire resistance, sometimes greater, sometimes less compared to the rest of the structures that make up the building.
The general concept of the degree of fire resistance
So what is it - the degree of fire resistance of the building? This is the ability of the building as a whole to avoid destruction and maintain stability under the influence of open fire - fire. Each building has its own quality characteristics in terms of fire resistance.
This classification of the object is determined taking into account the difference in the fire resistance of the individual components of its structures. When determining the overall degree of fire resistance of a structure, its level is indicated by Roman numerals: I, II, III, and so on. In total, according to SP 2.13130.2012 (Code of Rules), there are five degrees - I, II, III, IV, V (see table), which are assigned depending on the fire resistance limits of all the main elements of the building, taking into account their functional load.
Requirements for individual elements of buildings
In SP 2.13130.2012 and other regulations, additional or increased requirements for fire resistance are imposed on some elements of structures. For example, this applies to load-bearing walls and similar enclosing structures. To determine the degree of fire resistance of such building elements, the following parameters are taken into account:
Loss of bearing capacity (R);
Violation of integrity (E);
Loss of heat-insulating ability (I).
Determination of the actual and required fire resistance of buildings and structures
There is an actual as well as a required degree of fire resistance.
Actual. It is determined on the basis of an act of fire and technical expertise using the regulatory framework (the same joint venture - the Code of Rules). Moreover, experts are quite capable of giving an unambiguous conclusion not only on buildings and structures that have already been built, but also on those that are at the design stage. In the table above, you can find out the fire resistance limits of the structural elements of the building, which are used to determine the actual degree of fire resistance of the building as a whole.
Required. This is the minimum acceptable degree of fire resistance of a building to meet all fire safety standards. It is determined on the basis of specialized regulations and industry documents (norms, orders, etc.), depending on the total area of the building, its purpose, number of floors, explosion hazard category, availability of equipment for primary fire extinguishing systems, etc.
1.22.* Degree of fire resistance, constructive fire hazard class, allowable height (according to SNiP 21-01-97) and floor area within the fire compartment of detached buildings, extensions 1) and inserts should be taken according to Table. four .
1 Annex - a part of the building designed to accommodate administrative and amenity premises, separated from industrial buildings and premises by fire barriers. It is allowed to place (partially) engineering equipment in extensions.
In buildings of the IV degree of fire resistance, two floors or more high, the elements of the supporting structures must have a fire resistance rating of at least R 45.
In buildings of III and IV degrees of fire resistance, only structural fire protection should be used to ensure the required fire resistance of load-bearing structures.
In buildings of I, II, III degrees of fire resistance for the attic floor, it is allowed to accept the fire resistance limit of load-bearing building structures R 45 with the provision of their fire hazard class K0, when separating it from the lower floors with a type 2 fire ceiling. In this case, the attic floor should be divided by fire partitions of the 1st type into compartments with an area: for buildings of I and II degrees of fire resistance no more than 2000 sq. m, for buildings of the III degree of fire resistance - no more than 1400 sq. m. In this case, the fire partition should rise above the roof in the same way as a fire wall.
In the attics of buildings up to 10 floors inclusive, it is allowed to use wooden structures with fire protection that provides fire hazard class K0.
Table 4
The degree of fire resistance of buildings |
Constructive fire hazard class |
Permissible height, m |
Floor area within the fire compartment, sq. m., with the number of floors |
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1.23.* When designing buildings with a height of 10-16 floors (more than 28 m according to SNiP 21-01-97), additional requirements for these buildings should be taken into account in accordance with SNiP 2.08.02-89 * and SNiP 21-01-97.
1.24.* Annexes of I and II degrees of fire resistance should be separated from industrial buildings of I and II degrees of fire resistance by fire partitions of the 1st type.
Extensions below the II degree of fire resistance, as well as extensions to industrial buildings below the II degree of fire resistance and extensions to rooms and buildings of categories A and B should be separated by fire walls of the 1st type. Annexes of IV degree of fire resistance of class C0 are allowed to be separated from industrial buildings of IV degree of fire resistance of classes C0 and C1 by fire walls of the 2nd type.
1.25.* Inserts should be separated from the production premises by fire walls of the 1st type.
Inserts in buildings I, II degrees of fire resistance of classes C0 and C1, III degrees of fire resistance of class C0 can be separated from industrial premises of categories C, D and D by fire partitions of the 1st type, in buildings of III degrees of fire resistance of class C1 and IV degrees of fire resistance of classes C0 and C1 - fire walls of the 2nd type.
Buildings should be taken with no more than two floors and separated from industrial premises of categories C, D, D by fire partitions with a fire resistance limit of EJ 90 and fire ceilings of the 3rd type.
The total area of inserts allocated by fire partitions of the 1st and fire walls of the 2nd type, as well as built-ins and industrial premises, should not exceed the area of the fire compartment established by SNiP 31-03-01.
1.26. Corridors should be divided by fire partitions of the 2nd type into compartments with a length of not more than 60 m.
1.27. From the corridors located in the above-ground and basement floors and not having natural light, with any area and dressing rooms with an area of more than 200 m 2, exhaust ventilation must be provided to remove smoke in accordance with SNiP 2.04.05-91 *.
1.28. * In buildings, extensions, inserts and extensions, ordinary staircases of the 1st type should be provided, with the exception of cases specified in clause 1.23.
In buildings, I and II degrees of fire resistance with the number of floors of no more than three 50% of the staircases, it is allowed to provide type 2 with overhead natural lighting; at the same time, the distance between flights of stairs must be at least 1.5 m. In these buildings, the main stairs can be designed open to the entire height of the building, provided that the remaining (at least two) stairs are placed in ordinary stairwells of the 1st type. At the same time, lobbies and floor halls, in which open staircases are located, must be separated from adjacent rooms and corridors by fireproof partitions of the 1st type.
1.29. Glazed doors and transoms above them in the inner walls of staircases can be used in buildings of all degrees of fire resistance; at the same time, in buildings with a height of more than four floors, glazing should be made of reinforced glass.
1.30.* Facing and surface finishing of walls, partitions and ceilings of halls for more than 75 seats (except for halls in buildings of the V degree of fire resistance) should be provided from materials of combustibility groups of at least G2.
1.31. Automatic fire alarms should be in separate buildings and extensions with more than four floors, in inserts and extensions - regardless of the number of floors in all rooms, except for rooms with wet processes.
During the construction of any building, the organization of emergency exits, escape routes in emergency cases, and the location of funds are always considered at the design stage. But these points can be considered only if you know the degree of fire resistance of the building. Difficulties at present with this may arise, since most often the same type of structures are being built in cities. But then we will try to figure out how fire resistance is determined, on what it depends.
What is fire resistance?
This is the ability of structures and individual structures to withstand the onslaught of a fire without destruction and deformation. It is the degree of fire resistance of the building that will show how quickly the fire can spread through the structure if a fire occurs.
All indicators are determined taking into account SNiP. These standards allow you to determine the level of not only the building, but also all the materials that were used in the construction.
Flammability classification
- Fireproof.
- Difficult to be affected by fire. They can be made of combustible materials, but which have a special treatment or coating on top. An example is a wooden door lined with steel or covered with asbestos.
- combustible. They have a low ignition temperature and quickly burn out under the influence of fire.
Basis for determining fire resistance
As a determining basis for determining the degree of fire resistance of a building, the time that has passed from the moment the fire began to the appearance of the first noticeable defects is taken. These include:
- Cracks and damage to the integrity of the surface, which can facilitate the penetration of flames or products of its combustion.
- Increasing the temperature of materials by more than 160 degrees.
- Deformation of load-bearing structures and main units, which causes the collapse of the entire structure.
Buildings built of wooden structures have a low degree of fire resistance; reinforced concrete buildings are considered the safest in terms of fire, especially if they contain cement with a high level of fire resistance.
Dependence of fire resistance on materials
The ability of a building to withstand fire largely depends on the materials from which it is built. They can be classified based on the following characteristics:
The degree of fire resistance of building structures depends on the time required for the deformation of the material:
- Ceramic bricks or silicate bricks begin to deform 300 minutes after the start of the fire.
- Concrete floors, more than 25 cm thick, after two hours.
- 75 minutes are required to start the deformation of plaster-coated wooden structures.
- An hour will pass before the door treated with fire retardant begins to deform.
- 20 minutes exposure to fire is enough.
The degree of fire resistance of brick buildings is quite high, which cannot be said about metal buildings, which already at 1000 degrees pass into a liquid state.
Assignment of a fire safety category
According to regulatory requirements, only after the structure has been assigned a certain fire safety category, it is possible to determine the degree of fire resistance of the building. And this is done on the basis of the following signs:
- By changing the indicators of thermal insulation, when compared with the state before the fire.
- By blocking effect, which eliminates the formation of cracks in structures.
- By reducing the ability to perform load-bearing functions.
When determining the degree of fire resistance of a building, the area of \u200b\u200bthe structure and the quality of all materials used must be taken into account.
Characteristics of the degrees of fire resistance
Their determination is made on the basis of SNiP, the fire resistance of the main functional structures is always taken as the basis. Consider how many degrees of fire resistance of buildings and structures exist and what are their main characteristics:
Types of fire resistance
Special requirements for the ability to withstand fire are imposed on all building structures. For them, the following indicators are important:
- The ability to perform a load-bearing function.
- Thermal insulation.
- Integrity.
The safety of the building also plays an important role. Experts today divide the fire resistance of structures into two types:
- Actual.
- Required.
The actual degree of fire resistance of a building is the ability to withstand fire, which was determined during the examination. The available regulatory documents are taken as criteria for evaluation. Fire resistance limits have already been developed for structures of various types. This data is very easy to find and use for work.
The required fire resistance is the indicators that a building must have in order to comply with all fire safety standards. They are determined by regulatory documents and depend on many characteristics of the structure:
- The total area of the building.
- Number of floors.
- Purpose.
- Availability of means and installations for extinguishing fires.
If during the inspection it turned out that the actual degree of fire resistance of buildings and structures is equal to or exceeds the required one, then the structure complies with all standards.
Fire Hazard Classes
To determine the fire resistance of the entire building, structures are divided into several categories, and buildings into several classes.
- KO is non-flammable. There are no materials in the premises that ignite quickly, and the main structures do not ignite spontaneously and ignite at temperatures close to 500 degrees.
- K1 - low fire hazard. Minor damage may be allowed, but not more than 40 cm. No burning, no thermal effect.
- K2 - moderate fire hazard. Damage can reach 80 cm, but there is no thermal effect.
- K3 - fire hazard. Integrity violations of more than 80 cm, there is a thermal effect and fire is possible.
- CO. All utility rooms, main structures and staircases with openings comply with the KO class.
- C1. There may be slight damage to the leading structures up to K1, and the outer ones up to K2. Stairs and openings must be in excellent condition.
- C2. Damage to the main structures can reach K2, external K3, and stairs up to K1.
- C3. Stairs with openings are damaged up to K1, and everything else is not taken into account.
Rules for determining the resistance of a building to fire
It is not enough to know about the importance of fire resistance of buildings and structures, it is also important to be able to determine it. And there are some rules for this:
1. Testing a building involves having its plan at hand, and you will also need:
- Code of Practice for Ensuring Fire Resistance of Reinforced Concrete Structures.
- Guide to determining the limits of fire resistance.
- Manual for SNiP "Prevention of the spread of fire."
2. The fire resistance limit is determined by the time of exposure to the structure of fire. When the structures reach one of the limits, the fire is stopped.
3. Before starting testing, it is necessary to study the documentation for the building, where there is information about the materials and their approximate fire resistance.
4. It is necessary to pay attention in the documents to the existing conclusion on the use of special technologies to improve fire safety.
5. A preliminary study of the building also involves the consideration of all utility rooms, stairs and stairwells, attic compartments. They may be constructed from other materials or show visible damage at the time of testing.
6. Modern architecture very often uses the latest technologies in construction, which can affect the strength and resistance to fire. These points must also be taken into account.
7. Before carrying out the determination of fire resistance, it is necessary to prepare extinguishing agents, check the serviceability of the hoses, and call the fire brigade.
When all the preliminary measures have been taken, then you can proceed directly to the practical determination of fire resistance.
Practical definition of resistance to fire
Coming to the practical part, it is important to take the architectural plan with you, even if it has been carefully studied. The next steps are:
An indicator of the fire resistance of the material will be the time of exposure to fire and the speed of its spread. For different buildings, this figure can vary from 20 minutes to 2.5 hours. The ignition rate is even less - from instantaneous to 40 cm per minute.
This is how the fire resistance of a building is calculated in practice.
Ways to improve fire resistance
It is not always possible to use only non-combustible or low-combustible materials during construction, so ways to increase their resistance to fire come to the rescue.
The most commonly used are:
If multicomponent chemicals are used to increase fire resistance, then it must be taken into account that some of them contain organic substances that decompose at temperatures above 300 degrees with the release of toxic substances. Therefore, it is better to give preference to mineral-based coatings with liquid glass.
It is not difficult to determine the fire resistance of buildings and structures. It is important to carry out all preliminary preparations and it can be considered that most of the work has been completed. The calculation can be attributed more to costly than complex. The most important thing is special care during testing and temperature control in the furnace.
The approach to the construction of any buildings and structures should be based on safety from different points of view. And last but not least is fire safety. In emergency situations, human lives depend on the resistance of the structure to fire.
IIIa from SNiP 2.01.02-85* APPENDIX 2 ReferenceEXAMPLE STRUCTURAL CHARACTERISTICS OF BUILDINGS
DEPENDING ON THEIR DEGREE OF FIRE RESISTANCE
1. Degree of fire resistance
2. Structural features
I
Buildings with load-bearing and enclosing structures made of natural or artificial stone materials, concrete or reinforced concrete using sheet and slab non-combustible materials
II
Same. It is allowed to use unprotected steel structures in the coatings of buildings
III
Buildings with load-bearing and enclosing structures made of natural or artificial stone materials, concrete or reinforced concrete. For ceilings, it is allowed to use wooden structures protected by plaster or slow-burning sheet, as well as slab materials. There are no requirements for fire resistance limits and fire propagation limits for roofing elements, while attic wood roofing elements are subjected to fire retardant treatment.
IIIa
Buildings are predominantly with a frame structural scheme. Frame elements - from steel unprotected structures. Enclosing structures - from profiled steel sheets or other non-combustible sheet materials with slow-burning insulation
IIIb
The buildings are predominantly one-storey with a frame structural scheme. Frame elements - from solid or glued wood, subjected to fire-retardant treatment, providing the required fire spread limit. Enclosing structures - from panels or element-by-element assembly, made using wood or materials based on it. Wood and other combustible materials of building envelopes must be subjected to fire retardant treatment or protected from fire and high temperatures in such a way as to ensure the required fire spread limit.
IV
Buildings with load-bearing and enclosing structures made of solid or glued wood and other combustible or slow-burning materials, protected from fire and high temperatures by plaster or other sheet or plate materials. There are no requirements for fire resistance limits and fire propagation limits for roofing elements, while attic wood roofing elements are subjected to fire retardant treatment.
IVa
The buildings are predominantly one-storey with a frame structural scheme. Frame elements - from steel unprotected structures. Enclosing structures - from profiled steel sheets or other non-combustible materials with combustible insulation
V
Buildings, for the bearing and enclosing structures of which there are no requirements for fire resistance limits and limits for the spread of fire
Note. The building structures of buildings given in this appendix must meet the requirements of Table. 1 and other norms of this SNiP.
The highest degree of fire resistance I (mausoleum).
