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. With this knowledge, it is easy to design a fire escape route, emergency exit position, 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 the nursery is allowed to increase to 120 per 1000 residents of the district, on average 60-90.
Gardens with a capacity of more than 150 places must have II degree of fire resistance and C1 fire safety. With a height of at least 6 m.
Kindergartens with more than 350 child seats and a height of 9 m have a level II or I level of resistance and C0 or C1 safety.
Determining the resilience of the district 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.
For public buildings of this type, the maximum permissible height is 18 m, while the degree of fire resistance should be I or II, and safety C0.
At a height of up to 10 m, fire resistance decreases 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, 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) level of security.
Output
It is not so difficult to actually determine the degree of fire resistance of a building. Difficulties arise only at the practical stage, but this is less than half or even less than a third of the total work. After studying the architectural plan, the state of the building as a whole and the state of the supporting structures, the tester has already done most of the work!
Among the main causes of fires occurring are human activities and non-compliance with construction technologies. Therefore, when erecting a residential building, one of the most important criteria must be taken into account - its fire resistance.
Fire resistance
Definition
Fire resistance is understood as the ability of the main structures of a building to prevent the spread of fire.
It depends on the following factors:
- Number of floors.
- The nature of the activities carried out indoors.
- The total area of the building.
- The quality and main characteristics of the materials used in the construction process.
Fire resistance values are determined as a result of fire tests occurring over specified periods of time.
Views
There is a classification of all buildings depending on their constructive fire hazard, it includes 5 categories of buildings:
- Class F1 includes hospitals, kindergartens, nursing homes, hotels and hostels. This also includes all types of private houses and urban apartment buildings.
- Class F2 includes any building with seating for visitors and spectators, museums, libraries, exhibition centers.
- Class F3 includes healthcare facilities, trade enterprises, sports facilities without stands and any other buildings where public services are provided.
- Class F4 includes all educational and scientific institutions.
- Class F5 includes production facilities, laboratories, warehouses, logistics centers, archives, parking and service areas for road transport, agricultural buildings.
How to determine the degree of fire resistance?
table
residential building can be defined according to the table below:
| Fire resistance index | Design features | Overlapping | Coating |
| I and II degree | Stone, concrete, reinforced concrete. | Any kind of non-combustible plate or sheet materials. | |
| III degree | Load-bearing and enclosing structures made of stone, concrete and reinforced concrete. | Wood, which is additionally protected with plaster or various sheet materials of a non-combustible type or with a reduced degree of combustibility. | The only material requirement is to be treated with fire retardants. |
| IIIa degree | Frame structures or enclosing structures made of metal profiles. | Similar to the previous point. | |
| IIIb degree | Frame structures, no more than 1 floor, fences can be wooden. | Pretreated wood. | There are no requirements. |
| IV degree | Frame and enclosing structures made of wood or materials based on it, protected by non-combustible sheet materials. | There are no requirements. | Requirements apply only to materials for attic spaces: they must be pre-treated to increase fire resistance. |
| IVa degree | Frame structures, no more than 1 floor. | Metal structures and insulation materials related to flammability groups G3 or G4. | Similar to the previous point. |
| Vdegree | There are no requirements. | There are no requirements. | There are no requirements. |
Normative acts
The main normative act, which contains information on the rules for determining the fire resistance of buildings, is SNiP 21-01-97.
When assessing the fire characteristics (properties) of various buildings or structures, special attention is paid to taking into account the degree of fire resistance. Fire resistance means the functional ability of structural components of structures to suppress the spread of fire without losing their operational characteristics. These properties include bearing and enclosing capacity. Let's consider these concepts in more detail.
Fire resistance limit of a building: definition, factors affecting its values
With the loss of the bearing capacity, the integrity of the building is violated, and the loss of the enclosing capacity entails the appearance of cracks and through-type holes, up to the penetration of fire into the buildings, followed by combustion.
The fire resistance limit of a building is the time from the onset of combustion in a fire until the appearance of signs of loss, namely, such as:
- the appearance of through-type cracks;
- an increase in temperature indicators on the unheated part above 140 ° C or anywhere above 180 ° C in comparison with the temperature of the entire structure before testing;
- loss of bearing functional characteristics by the structure.
The fire resistance value is influenced by the size and physical properties of the materials. The thicker the walls, the longer (in time) the fire resistance will be. The degree of fire resistance of a building is influenced by:
- number of storeys of the structure;
- square;
- type of building (administrative, residential, etc.);
- quality and degree of refractoriness of materials.
The fire resistance of a building depends on the fire resistance of the building structures. They are divided into three main groups:
- fireproof (stone, brick, metal structures);
- hardly combustible (combustible materials, the surface of which is protected by a non-combustible mixture);
- easily combustible (wood).
Classification of buildings according to the degree of fire resistance
The fire resistance of a building is determined in strict accordance with building codes and regulations (SNiP). So, according to the degree of fire resistance, all buildings are divided into five main groups. First group. Buildings that are most protected from the negative consequences of a fire. The main materials used for these structures are concrete and stone, which are resistant to high temperatures and fire.
Second group also covers buildings with refractory structures, as in the first case, with a slight allowance for the use of unprotected elements in steel structures. By the third grade include buildings in the structural structure of which there are non-combustible and non-combustible materials. If the structure includes combustible materials, then they must be treated with a special fire-retardant mixture.
Buildings that are assigned fourth degree of fire resistance, must have fireproof walls in their construction, and non-combustible materials must be used for load-bearing walls. For structures included to the fifth group, the use of combustible materials is characteristic, however, for load-bearing walls, as well as for buildings of the fourth degree of fire resistance, materials of a non-combustible nature are used. The degree of fire resistance of the building (structure) must coincide with the explosion and fire safety of the premises.
Buildings made of bricks have a high degree of protection against fire - the first degree of fire resistance. Brick is a material that is resistant to combustion processes - it does not burn or smolder, and therefore most developer companies prefer to build houses from this material.
Factors that affect the degree of fire resistance of a residential building
The degree of fire resistance of any residential building is influenced by its number of storeys and area - the higher the residential building and the wider in area, the higher the degree of fire resistance. Mostly brick, stone or concrete is used for residential houses, therefore they are endowed with the first degree of fire resistance. If brick and concrete block elements are used for the construction of such a structure, then this is the second class of fire resistance. For houses built on a metal frame, with cladding made of non-combustible materials, a third degree of fire resistance is assigned.
Houses with a wooden frame base are assigned the fourth degree of fire resistance, and the fifth class includes houses that are most susceptible to fire.
In connection with the fires occurring in administrative and residential premises, great attention is paid to such a criterion as the fire resistance of buildings during the construction of buildings. The fire resistance of any building is calculated taking into account the above features and building codes and regulations (SNiP).
The degree of fire resistance of a building is the ability of a structure to withstand a fire for some time without collapsing. Based on this indicator, it is possible to assess any structure in terms of fire safety. It depends on the degree of fire resistance of the building how quickly the fire will spread through its premises and structures. For obvious reasons, this indicator will largely depend on the materials from which the structure is being built.
The definition of the degree of fire resistance of building materials must be approached from the position: are they combustible or not. Therefore, the standard classification divides them into "NG" - non-combustible or "G" - combustible. The latter are divided into several classes:
- G1 - slightly 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 are flammable with great difficulty;
- B2 - moderately flammable;
- B3 is easy.
The next characteristic of the degree of fire resistance of building materials is the possibility or impossibility of flame spread over their surfaces. This parameter is designated by the abbreviation "RP". So:
- RP1 - do not spread the flame;
- RP2 - poorly distributed;
- RP3 - moderately;
- RP4 - strong.
Attention! The "RP" indicator is determined only for floor bases and their coatings, as well as for roofs. It has nothing to do with the rest of the structural elements, except perhaps for wooden houses.
SNiPs do not indicate that the smoke and toxicity of the emitted combustion products affect the degree of fire resistance of the building. And it is right. But in the event of a fire, where the main task is not only to extinguish it, but also to evacuate people in time, these two factors play an important role. Therefore, they must be indicated in the building passport.
Smoke or smoke emission coefficient of 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 - with moderate;
- D3 is a big selection.
In terms of toxicity during combustion, all building materials are divided into four groups:
- T1 - low hazard;
- T2 - moderate;
- T3 - high;
- T4 is extremely dangerous for humans.
Summarizing all of the above, we can finish about the degree of fire resistance of building materials by the fact that in SNiPs all the above indicators (and there are five of them) are combined into one common one, which is designated by the abbreviation "KM".
According to the "KM" indicator, building materials are divided into five classes, where the KM1 class are representatives in whom all the above characteristics have a minimum value. Accordingly, the KM5 class - with the maximum values. KM0 is a class of non-flammable.
Having dealt with the building materials, we turn to the fire resistance of buildings and structures. It should be noted that not all buildings have identical materials throughout the structure... That is, not always in all construction projects in each of their parts (floors, premises, etc.), the same building materials are used. Therefore, the classification made according to fire resistance is considered conditional. But in any case, all construction objects are divided into three classes: non-combustible, hard to burn, combustible.
The degree of fire resistance of a building - how to determine. The calculation is based on the time from the onset of ignition to the moment of destruction or the appearance of defects. Therefore, it is important to understand which defects in the supporting 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 the structures rises within the range 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 indicators, then this is a critical moment.
- The supporting structure is deformed, leading to collapse. This mainly applies to metal assemblies and structures. By the way, unprotected steel profiles belong to the KM4 category. At a temperature of + 1000C, they simply begin to melt. Reinforced concrete products belong to "KM0".
As for the speed and time of combustion, then, as mentioned above, it all depends on the materials from which they are built. For example, concrete structure 25 cm thick burns out in 240 minutes, brickwork in 300 minutes, metal structure for 20, wooden door (entrance, treated with fire retardants) for 60, wooden structure sheathed with plasterboard 2 cm thick, burns out in 75 minutes.
Classification by the degree of fire resistance of buildings, structures and fire compartments
All construction objects are divided into five degrees. And this indicator must be indicated in the passport of the building.
Attention! The fire resistance of a building can only be determined by an authorized service. It is they who give the assessment, 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 a structure.
| Class | Design features |
| I | Objects erected entirely from non-combustible materials: stone, concrete or reinforced concrete. |
| II | Structures in which metal assemblies are partially used as load-bearing structures. Brick houses belong to this class. |
| III |
Buildings belonging to the first category, only in their structures it is allowed to use wooden floors, covered with plaster solutions or gypsum boards. For covering wooden floors, here you can use sheet materials belonging to the group of "hard-to-burn". As for roofs, wood can also be used here, only with treatment with flame 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-combustible materials. here you can also use a fireproofing material. |
| IIIb | Wooden houses or buildings made of composite materials, the basis of which is wood. Buildings must be treated with fire retardants. The main requirement for them is construction away from possible sources of fire. |
| IV |
Buildings erected of wood, the structures of which are covered on all sides with plaster mortars, gypsum boards or other insulating materials capable of holding back the effects of fire for some time. The roof is necessarily exposed to fire protection. |
| 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 non-combustible heat-insulating materials. |
| V | Buildings and structures that are not subject to any requirements regarding fire resistance, speed of combustion and others. |
Having dealt with the classes of the degree of fire resistance of buildings, it is necessary to designate the types of this characteristic. There are only two positions here: the actual fire resistance, denoted by CO f and required - CO tr.
The first is the actual indicator of the erected building or structure, which was determined based on the results of a fire-technical examination. The results are based on the tabular values shown in the photo below.
The second is the implied (planned) minimum value of the fire resistance of the building. 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 storeys, whether explosive technologies are used inside, whether there is a fire extinguishing system, etc.
Attention! Comparing the two types of fire resistance, it is always necessary to 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 the degree of fire resistance must be taken seriously. Given this indicator, it is necessary to determine the requirements for the fire safety system. And the lower the limit of fire resistance of the building, the more investments will have to be made when organizing a fire protection system.
Similar questions have been raised many times. I keep an extract from the Soviet still norms
IIIa from SNiP 2.01.02-85 * APPENDIX 2 Reference
EXAMPLE DESIGN CHARACTERISTICS OF BUILDINGS
DEPENDING ON THEIR DEGREE OF FIRE RESISTANCE
1. Degree of fire resistance
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
Also. It is allowed to use unprotected steel structures in the coatings of buildings.
III
Buildings with load-bearing and enclosing structures made of natural or artificial stone materials, concrete or reinforced concrete. For floors, it is allowed to use wooden structures protected by plaster or low-combustible sheet, as well as plate materials. The elements of the coatings are not subject to requirements for the limits of fire resistance and the limits of the spread of fire, while the elements of the attic covering made of wood are subjected to fire retardant treatment
IIIa
Buildings are predominantly framed. The frame elements are made of unprotected steel structures. Fencing structures - made of profiled steel sheets or other non-combustible sheet materials with low-combustible insulation
IIIb
Buildings are mainly one-story with a frame structural scheme. The frame elements are made of solid or glued wood, subjected to a fire retardant treatment, which ensures the required limit of fire propagation. Fencing structures - from panels or element-by-element assemblies, made with the use of wood or materials based on it. Wood and other combustible materials of building envelopes must be subjected to fire retardant treatment or protected from the effects of fire and high temperatures in such a way as to ensure the required limit of fire propagation.
IV
Buildings with load-bearing and enclosing structures made of solid or glued wood and other combustible or hardly combustible materials, protected from fire and high temperatures by plaster or other sheet or plate materials. The elements of the coatings are not subject to requirements for the limits of fire resistance and the limits of the spread of fire, while the elements of the attic covering made of wood are subjected to fire retardant treatment
IVa
Buildings are mainly one-story with a frame structural scheme. The frame elements are made of unprotected steel structures. Fencing structures - from 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 for fire resistance and fire propagation limits
Note. The building structures of buildings given in this annex must meet the requirements of table. 1 and other norms of this SNiP.
Highest degree of fire resistance I (mausoleum).
