Fire resistance is determined. How to determine the fire resistance of a building? Classification of building materials and their fire resistance. How to determine the actual fire resistance limit and fire hazard class of a building structure
The degree of fire resistance is an important parameter that is determined when construction work and after their completion. It is very important for builders to know that a particular building structure has its own degree of fire resistance. You will learn how to determine the fire resistance of a building in this article.
The expression fire resistance refers to the ability of certain elements of a building to maintain strength in the event of a fire. Moreover, fire resistance has its own limit, which is determined in hours, i.e. specific numbers to the fire danger of the building. It is generally accepted to denote the degree of fire resistance using Roman values: I, II, III, IV, V.
Fire resistance is divided into two types:
- Actual (SOF). How is it determined? Mainly based on the result of technical and fire expertise construction structures. Also, calculations take place based on regulatory documents. The level of fire resistance is clearly regulated and known. In accordance with official information, the SOF is calculated.
- Required (SOtr). This concept includes the level of fire resistance at a minimum value. In order for a building to meet all safety requirements, the structure must comply with them. This degree of fire resistance is determined on the basis of regulatory documents that have industry and specialized meanings. In this case, the direct purpose of the building, its area, the availability of fire extinguishing equipment, the number of floors, etc. play a key role.
To solidify all this, let's look at an example. To make a building comply with the fire safety requirements, the SOF must be greater than or equal to SOtr. The limit of fire resistance occurs at the moment when a building completely or partially fails to perform its functionality in a fire. This happens when compartments or cracks develop in a building. The flame penetrates directly through them into adjacent rooms, the surface heats up to 140–180°C, and also if the load-bearing parts of the building are completely eliminated.
Method for determining fire resistance
Proper tests are carried out to determine the limits of fire coverage as well as the damage caused by burning. This is implemented in practice as follows: a fire is started in specially equipped furnaces. The stove is processed exclusively with refractory bricks. Kerosene is burned inside the stove using special nozzles. Using thermal vapors, the temperature inside the furnace is controlled. With all this, the operation of the nozzles must be carried out so that they do not come into contact with thermal vapors and do not come into contact with the surface of the structure. So, if we are based on basic rules, then calculating the degree of fire resistance has two tasks:
- Heat engineering.
- Statistical.
To determine the degree of fire resistance, it is important to first obtain an architect's design. Next, you need to adhere to the standard scheme.
As for the diagram, it looks like this:
- By contacting the firefighters, they will conduct a fire resistance examination. If any deficiencies are found, they should be corrected immediately.
- Already at the sketching stage, the degree of fire resistance will be indicated. And for this you should contact only competent architects who will take into account all these nuances.
In practice, this whole process, to determine fire resistance, looks like this:
- The fire resistance limit is calculated in hours or minutes. The countdown should begin from the moment of a critical situation, when the structure does not withstand the test, namely, it collapses or its integrity is compromised.
- For the calculation, one of five steps is taken.
- Flammability level is included in these calculations/calculations different materials, which were used in the construction of the building.
- For precise definition fire resistance is not enough to have superficial information. Here it is important to have a complete picture even for such structures as: additional staircases, flights of stairs, partitions and all other structures. Even the material from which these structures are made is taken into account.
- It would also be useful to study additional and mandatory materials that relate to the rules for ensuring the fire resistance of reinforced concrete structures. As a basis, for example, you can take the manual to SNiP dated January 21, 1997 “Prevention of Fire”.
- Thus, a wide range of planning and technological aspects are taken into account to determine fire resistance. But at the same time, we should not forget about the primary fire extinguishing means - fire extinguishers.
As a result, you need to create a list of requirements for the building, which are clarified during the fire resistance determination process. The basis is taken from the documentation and design of the building.
SNiP
In most cases, structures and buildings have type 1 walls, i.e. fire compartment. As for the minimum fire resistance threshold of a building, it is equal to 25. As a result, it is allowed to use unprotected metal constructions.
Building codes allow the use of drywall as facing material. This to some extent increases the fire resistance of the building.
If we talk about building materials and their degree of combustibility, they are divided into 3 groups:
- Non-flammable.
- Difficult to burn.
- Fireproof.
If you are building a frame, it is better that it be made of non-combustible material. For buildings from grade 1 to 5, combustible materials can be used, but not in the lobbies. This is important, because in addition to everything, building materials are divided into classifications such as:
- Producing smoke.
- Toxic.
Below we will consider an algorithm for calculating the degree of fire resistance of a building and premises different types. Based on this, you can find out the basic requirements for certain buildings.
Residential buildings
The fire resistance of a house has 5 levels. According to these degrees, characteristics are given for each building material from which the house was built. The following are the design characteristics of residential buildings:
- For residential buildings, preference is given to non-combustible materials.
- Construction is best done from concrete blocks, stone or brick.
- Use fire-resistant material to insulate walls, roofs and other structures.
- The roofing must be made from materials that are resistant to fire, namely: slate, corrugated sheets, metal tiles or tiles.
- Floors are made of reinforced concrete slabs.
- If the floors are wooden, then they should be covered with non-combustible materials, for example, non-combustible slabs or plaster.
- Wooden rafter system must be treated with impregnations that prevent the spread of fire.
It is not necessary to use non-combustible materials for insulation. You can use items that are resistant to fire categories G1 and G2.
Public buildings
Fire resistance degree public buildings is divided into 5 groups: I, II, III, IV, V. Thus, according to the class of structural fire hazard of a building, the following are determined:
- I-C0.
- II-C0.
- III-C0.
- IV-C0.
- V- is not numbered.
As for the permissible room height in meters and area for the fire compartment, the following data is available:
- I-75m;
- II-С0-50, С1-28;
- III-C0-28, C1-15;
- IV-CO-5-1000 m 2 ;
- S1-3m-1400 m 2;
- S2-5m-800 m2.
If we speak for clubs, pioneer camps, hospitals, preschools and schools, then they often use wooden partitions, ceilings and walls. Their processing must be carried out with fire-resistant materials.
Industrial buildings
- Metallurgical.
- Instrumental.
- Chemical.
- Tkatskoye.
- Repair and others.
And for such establishments, the degree of fire resistance is more important than ever. Plus, some work with poisonous and explosive substances, which can have Negative influence human and environment.
Industrial buildings are also divided into 5 levels. Fire resistance is determined based on the used building materials. Hence the conclusion: degree fire safety industrial building directly depends on the fire resistance of the building materials used.
Warehouses
As a rule, those warehouses that are made of wooden materials. However, if they are treated with plaster and special impregnations, their degree of fire resistance increases. Concrete or ceramic tiles are also used for this purpose.
For storage facilities Intumescent paints or polymer foam are considered the most effective. Their action extends the period of raising the critical temperature.
In general, a number of measures are being taken to increase the degree of fire resistance of premises built of wood. They can also install aluminum doors, and instead wooden windows glass blocks.
So, it is worth noting that before determining the fire resistance of a building, it is important to take into account the characteristics and purpose of each building, as well as methods and materials that have different specifics.
The degree of fire resistance of a building is the ability of a building to withstand fire for some time without collapsing. Based on this indicator, any structure can be assessed in terms of fire safety. It is the degree of fire resistance of the building that determines how quickly the fire will spread throughout its premises and structures. For obvious reasons, this indicator will largely depend on the materials from which the structure is built.
Determining the degree of fire resistance of building materials must be approached from the standpoint of whether they are flammable or not. Therefore, the standard classification divides them into “NG” - non-flammable or “G” - flammable. The latter are divided into several classes:
- G1 – low-flammable;
- G2 – moderate;
- G3 – normal;
- G4 – strong.
There is another parameter that determines the fire resistance of building materials - this is their flammability, denoted by the letter “B”. There are three classes here:
- B1 – materials that ignite with great difficulty;
- B2 – moderately flammable;
- B3 – easy.
The next characteristic of the degree of fire resistance of building materials is the possibility or impossibility of flame spreading over its surfaces. This parameter is designated by the abbreviation “RP”. So:
- RP1 – do not spread the flame;
- RP2 – weakly spread;
- RP3 – moderate;
- RP4 – strong.
Attention! The “RP” indicator is determined only for floor bases and their coverings, as well as for roofs. To the rest structural elements it has nothing to do with it, except perhaps for wooden houses.
SNiPs do not indicate that smoke and the toxicity of emitted combustion products affect the degree of fire resistance of a building. And it is right. But when a fire occurs, where the main task is not only to extinguish it, but also to evacuate people in time, these two factors play important role. Therefore, they must be indicated in the building’s passport.
Smoke content or the coefficient of smoke emission from building materials is indicated by the letter “D”. According to this characteristic, all buildings are divided into three groups:
- D1 – with low smoke emission;
- D2 – moderate;
- D3 – large discharge.
According to toxicity during combustion, all building materials are divided into four groups:
- T1 – low danger;
- T2 – moderate;
- T3 – high;
- T4 is extremely dangerous for people.
Summarizing all of the above, we can conclude about the degree of fire resistance of building materials by saying that in SNiPs all of the above indicators (and there are five of them) are combined into one common one, which is denoted by the abbreviation “KM”.
According to the “KM” indicator, building materials are divided into five classes, where class KM1 are representatives for which all the above-described characteristics have a minimum value. Accordingly, class KM5 – with maximum values. KM0 is a non-flammable class.
Having dealt with building materials, we move on to the fire resistance of buildings and structures. It is necessary to indicate that not all buildings have identical materials throughout the structure. That is, the same building materials are not always used in all construction projects in each part (floors, rooms, etc.). Therefore, the classification by fire resistance is considered conditional. But in any case, all construction projects are divided into three classes: fireproof, difficult to burn, combustible.
The degree of fire resistance of a building - how to determine. The calculation is based on the time from the start of the fire to the moment of destruction or the appearance of defects. Therefore, it is important to understand what defects load-bearing structures can be taken into account in order to accurately say that the structure is at the limit of destruction.
- Through holes and cracks appear through which fire flames and smoke penetrate.
- The heating temperature of structures increases from +160C to +190C. This refers to the non-burning side. For example, if a room is on fire, and the wall on the other side heats up to the above levels, then this is a critical moment.
- The supporting structure becomes deformed, leading to collapse. This mainly concerns metal components and structures. By the way, unprotected steel profiles belong to the KM4 category. At a temperature of +1000C they simply begin to melt. “KM0” includes reinforced concrete products.
As for the speed and time of combustion, as mentioned above, everything depends on the materials from which they are built. Eg, concrete structure 25 cm thick burns in 240 minutes, brickwork in 300 minutes, metal structure in 20, wooden door(entrance, treated with fire retardants) for 60, a wooden structure covered with plasterboard 2 cm thick burns out in 75 minutes.
Classification according to the degree of fire resistance of buildings, structures and fire compartments
All construction projects are divided into five degrees. And this indicator must be indicated in the building’s passport.
Attention! The degree of fire resistance of a building can only be determined by authorized services. They are the ones who give the assessment and determine the class that is entered in the passport.
So, the degree of fire resistance of buildings and structures is a table of five fire resistance classes (I-V), which determine the fire hazard of the structure.
| Class | Design Features |
| I | Objects built entirely from non-combustible materials: stone, concrete or reinforced concrete. |
| II | Structures in which metal components are partially used as load-bearing structures. Brick houses also belong to this class. |
| III |
Buildings belonging to the first category are only allowed to use wooden floors in their structures, covered with plaster mortars or gypsum boards. To cover wooden floors here you can use sheet materials belonging to the group of “hard-to-burn” materials. As for roofs, wood can be used here too, only with treatment with fire-retardant compounds. |
| IIIa | Frame houses made of a metal base (steel profiles), which have a low degree of fire resistance. They are sheathed with non-flammable materials. here you can use insulation made of fire-resistant material. |
| IIIb | Wooden houses or buildings made of composite materials, the basis of which is wood. Buildings must be subjected to fire treatment protective compounds. The main requirement for them is to build away from possible sources of fire. |
| IV |
Buildings constructed of wood, the structures of which are covered on all sides with plaster mortars, gypsum boards or other insulating materials, capable of containing the effects of fire for some time. The roof must be fire protected. |
| IVa | Building structures assembled from steel profiles untreated with protective compounds. The only thing is the floors, which are also assembled from steel structures, but using fireproof heat-insulating materials. |
| V | Buildings and structures that are not subject to any requirements regarding fire resistance, ignition rate, etc. |
Having understood the classes of fire resistance of buildings, it is necessary to identify the types of this characteristic. There are only two positions here: the actual fire resistance, denoted SO f, and the required resistance, denoted SO tr.
The first is the actual indicator of the constructed building or structure, which was determined based on the results of a fire-technical examination. The results are based on the table values shown in the photo below.
The second is the implied (planned) minimum value of the building’s fire resistance rating. It is formed on the basis of regulatory documents (industry or specialized). This takes into account the purpose of the building, its area, number of floors, whether explosive technologies are used inside, whether there is a fire extinguishing system, etc.
Attention! When comparing two types of fire resistance, you must always take as a basis the ratio that CO f should not be less than CO tr.
Conclusion
The classification of buildings and structures according to their degree of fire resistance must be taken seriously. Taking into account this indicator, it is necessary to determine the requirements for the fire safety system. And the lower the fire resistance limit of a building, the more investment will have to be done by organizing a fire protection system.
Fire resistance degree
fire resistance limit
Structural collapse;
Fire resistance limits:
— silicate brick — ~5 h
Table 3
| Fire resistance degree | |
| I | |
| II | The same. In building coatings it is allowed to use unprotected steel structures |
| 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;
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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. Fire resistance limits and fire hazard classes of attic covering structures in buildings of all degrees of fire resistance are not standardized, but roofing, rafters and sheathing, as well as sheathing eaves overhangs may be made from flammable materials, except in special cases. Gable structures can 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 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 the I degree of fire resistance should be treated with fire retardant compounds of the I group of fire retardant efficiency, in buildings of II - IV degrees of fire resistance with fire retardant compounds not lower than the II group of fire retardant efficiency according to GOST 53292, or they should be structurally fire protected, which does not contribute to the latent 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. |
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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, reinforced concrete floors, including attics), as a rule, give grade II. | ||
| II CO | ||
| II degree C0. The inspector is wrong. The theme of walls, flights and landings of stairs in 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. Refractory structures are considered to be those made of materials that are difficult to burn or of combustible materials protected from fire and high temperatures fireproof materials (for example, a 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 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, the use of wooden structures, protected by plaster or highly flammable sheets, as well as slab materials Requirements regarding fire resistance limits and fire spread limits are not established for roofing elements, while attic roofing elements made of wood can be 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-flammability 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 wood-based materials Wood and other combustible materials of 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 required 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;
- cladding;
- 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.
Facing materials: gypsum plaster(fire protection 10 min);
asbestos cement sheets;
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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 to use wooden structures as load-bearing roof structures in a school building? 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), fire hazard building structures 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 only on information about the material from which the building structure is made, it is impossible to determine the actual fire resistance limit and fire hazard class 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 to building structures that have passed fire tests can be determined by the calculation and analytical method , installed 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 protection objects" (as amended on October 23, 2013) 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, category of the building for explosion and fire hazard, 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 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 building structures are determined.
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 can 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.
How to determine the degree of fire resistance of a building, on what factors does the fire resistance limit depend? Any architect or owner should know the answers to these questions. Thanks to this knowledge, it is possible to easily develop a fire escape route, the position of emergency exits, etc. But nowadays there are many architectural solutions for the construction of buildings of the same type, so determining the fire resistance of each can cause some difficulties.
What is the fire resistance of a building and why is it determined?
Buildings with a capacity of more than 100 seats and a height of 3 m must have C1 fire safety and III degree of fire resistance of the building. How to determine the number of seats? This indicator depends on the population of the area. According to SNiP, the number of places in nurseries is allowed to increase to 120 per 1000 residents of the region, on average 60-90.
Gardens with a capacity of more than 150 seats must have fire resistance class II and fire safety class C1. At a height of at least 6 m.
Children's institutions with more than 350 children's places and a height of 9 m have level II or I of resistance and C0 or C1 safety.
Determining the resilience of a community hospital
It is already known how to determine the degree of fire resistance of a building, if it is a school or kindergarten, and what to do with hospitals? They have their own rules and regulations.
Near public buildings similar type the maximum permissible height is 18 m, and the degree of fire resistance must be I or II, and safety C0.
At a height of up to 10 m, fire resistance is reduced to II, and structural safety to C1.
If the height of the building is 5 meters or less, then the degree of fire resistance can be III, IV or V, and the level of structural safety, respectively, is C1, C1-C2, C1-C3.
There is nothing more difficult in studying the topic “The degree of fire resistance of a building”, how to determine the RB (district hospital) safety level.
Conclusion
It is actually not that difficult to determine the fire resistance rating of a building. Difficulties only arise when practical stage, however, this is less than half and even less than a third general work. After studying architectural plan, the condition of the building as a whole and the condition of the supporting structures, the tester has already done most of work!
IIIa from SNiP 2.01.02-85* APPENDIX 2 ReferenceSAMPLE CONSTRUCTION CHARACTERISTICS OF BUILDINGS
DEPENDING ON THEIR DEGREE OF FIRE RESISTANCE
1. Fire resistance rating
2. 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
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-flammability sheet and slab materials. There are no requirements for fire resistance limits and fire spread limits for coating elements, while attic wood roofing elements are subject to fire retardant treatment
IIIa
Buildings predominantly have a frame structural design. The frame elements are made of unprotected steel structures. Enclosing structures - made of profiled steel sheets or other non-combustible sheet materials with low-flammable insulation
IIIb
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, ensuring the required limit of fire spread. Enclosing structures - made of panels or element-by-element assembly, made using wood or wood-based materials. Wood and other combustible materials of enclosing structures must be subjected to fire retardant treatment or protected from exposure to fire and high temperatures in such a way as to ensure the required limit of fire spread.
IV
Buildings with load-bearing and enclosing structures made of solid or laminated wood and other combustible or low-combustible materials, protected from fire and high temperatures by plaster or other sheet or slab materials. There are no requirements for fire resistance limits and fire spread limits for coating elements, while attic wood roofing elements are subject to fire retardant treatment
IVа
The buildings are predominantly one-story with a frame structural design. The frame elements are made of unprotected steel structures. Enclosing structures - made of profiled steel sheets or other non-combustible materials with combustible insulation
V
Buildings, the load-bearing and enclosing structures of which are not subject to requirements for fire resistance limits and fire spread limits
Note. The building structures given in this appendix must meet the requirements of Table. 1 and other standards of this SNiP.
The highest degree of fire resistance is I (mausoleum).
