Fire resistance of wooden houses. The degree of fire resistance of buildings, the required limits of fire resistance of building structures. fire hazard of building materials
When evaluating the fire performance (properties) of various buildings or structures Special attention is given to the degree of fire resistance. Fire resistance refers to the functional ability of structural components of structures to suppress the spread of fire without losing their performance characteristics. These properties include load-bearing and enclosing capacity. Let's consider these concepts in more detail.
Fire resistance limit of a building: definition, factors affecting its values
When the bearing capacity is lost, the integrity of the building is violated, and the loss of the enclosing capacity leads to the appearance of cracks and holes. through type, up to penetration into the buildings of fire, followed by burning.
The fire resistance limit of a building is the time from the start of burning in a fire to the time signs of loss appear, such as:
- the appearance of cracks of a through type;
- increasing the temperature on the unheated part above 140°C or in any place above 180°C in comparison with the temperature of the entire structure before testing;
- loss of load-bearing functional characteristics by the structure.
The value of the fire resistance limit is affected by the dimensions and physical properties materials. The thicker the walls, the longer (in time) the fire resistance will be. The degree of fire resistance of a building is affected by:
- number of storeys of the building;
- square;
- type of building (administrative, residential type, etc.);
- quality and degree of fire resistance of materials.
The degree of fire resistance of a building depends on the fire resistance building structures. They are divided into three main groups:
- fireproof (stone, brick, metal structures);
- slow-burning (combustible materials, the surface of which is protected by a fireproof mixture);
- combustible (wood).
Classification of buildings according to the degree of fire resistance
The fire resistance of a building is determined in strict accordance with building codes and rules (SNiP). So, according to the degree of fire resistance, all buildings are divided into five main groups. First group. Buildings most protected from negative consequences resulting from a fire. The main materials used for these structures are concrete and stone, resistant to impact. elevated temperatures and fire.
Second group also covers buildings with refractory structures, as in the first case, with a slight allowance for the use of unprotected elements in steel structures. To the third grade include buildings in the structural structure of which there are fireproof and slow-burning materials. If the structure includes combustible materials, then they must be treated with a special fire-retardant mixture.
Buildings to which fourth degree of fire resistance, should have in their design fire walls, and for walls of the bearing type, slow-burning materials should be used. For structures included to the fifth group, the use of combustible materials is typical, however, for bearing walls, as for buildings of the fourth degree of fire resistance, fireproof materials are used. The degree of fire resistance of a building (structure) must match the explosion and fire safety of the premises.
Buildings made of bricks have a high degree of fire protection - the first degree of fire resistance. Brick is a material that is resistant to combustion processes - it does not burn or smolder, which is why most developers prefer to build houses from this material.
Factors that affect the degree of fire resistance of a residential building
The degree of fire resistance of any residential building is affected by its number of floors and area - the higher the residential building and the larger in area, the higher the degree of fire resistance. Basically, brick, stone or concrete are used for residential houses, so they are endowed with the first degree of fire resistance. If brick and concrete block elements are used for the construction of such a structure, then this is the second class of fire resistance. For houses built on metal frame, with sheathing made of slow-burning materials, are assigned the third degree of fire resistance.
Houses with a wooden frame base are assigned the fourth degree of fire resistance, and houses classified in the fifth class are those most subject to fire.
In connection with the fires that occur in administrative and residential premises, much attention is paid to such a criterion as the fire resistance of buildings during the construction of buildings. The fire resistance of any building is calculated taking into account the above features and building codes and regulations (SNiP).
The degree of fire resistance of a building is the ability of a building to withstand a fire for some time without collapsing. Based on this indicator, you can evaluate 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.
To determine the degree of fire resistance building materials it is necessary to approach from a position: they are combustible or not. Therefore, the standard classification divides them into “NG” - non-combustible or “G” - combustible. The latter are divided into several classes:
- G1 - low combustible;
- 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 - ignite moderately;
- B3 is easy.
The next characteristic of the degree of fire resistance of building materials is the possibility or impossibility of flame propagation over their surfaces. This parameter is denoted by the abbreviation "RP". So:
- RP1 - do not spread the flame;
- RP2 - weakly spread;
- RP3 - moderately;
- RP4 - strong.
Attention! The indicator "RP" 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 for wooden houses.
The SNiPs do not indicate that smoke and the 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 a role. 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 - a large selection.
By 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 the fact that in SNiPs all 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 the KM1 class are representatives who have all of the above characteristics. minimum value. Accordingly, class KM5 - with maximum values. KM0 is a class of non-combustible.
Having dealt with building materials, we turn 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, not always in all construction projects in each of their parts (floors, rooms, etc.) the same building materials are used. Therefore, the classification according to fire resistance is considered conditional. But in any case, all construction objects are divided into three classes: fireproof, hardly combustible, combustible.
The degree of fire resistance of the 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 what defects load-bearing structures can be taken into account to accurately say that the structure is at the limit of destruction.
- Appear through holes and cracks through which flames of fire and smoke penetrate.
- The heating temperature of structures rises in 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 load-bearing structure is deformed, leading to collapse. This mainly applies to metal components and structures. By the way, unprotected steel profiles are classified as KM4. At a temperature of + 1000C, they simply begin to melt. KM0 includes reinforced concrete products.
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 in 240 minutes, brickwork in 300 minutes, metal structure for 20, wooden door(input, treated with flame retardants) for 60, wooden structure, sheathed with drywall 2 cm thick, burns out in 75 minutes.
Classification according to 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 degree of fire resistance of a building can only be determined by authorized services. It is they who give an 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 building.
| Class | Design features |
| I | Objects built entirely from non-combustible materials: stone, concrete or reinforced concrete. |
| II | Structures in which they are partially used as load-bearing structures metal knots. Brick houses belong to the same class. |
| III |
Buildings belonging to the first category are allowed to be used only in their structures wooden floors, closed plaster mortars or gypsum boards. To cover the wooden floors here, you can use sheet materials belonging to the group of "flammable". As for roofs, wood can also be used here, only with flame retardant treatment. |
| IIIa | Frame houses from metal base(steel profiles), which have a low degree of fire resistance. They are sheathed with non-combustible materials. here you can use a heater made of slow-burning material. |
| IIIb | wooden houses or buildings composite materials, the basis of which is wood. Buildings must be fire treated protective compounds. The main requirement for them is construction away from possible sources of ignition. |
| IV |
Buildings made 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 with the use of fireproof heat-insulating materials. |
| V | Buildings and structures that do not have any requirements regarding fire resistance, ignition rate, etc. |
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 by the results of the fire and technical expertise. The results are based on tabular values, which are 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 normative 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, and so on.
Quote sergey ®What type of substation is this postscript "at KTP outdoor installation"applies? To KTP, STP, MTP?
I think only STP can NOT be referred to KTP, because they are not PS, supplied assembled or fully prepared at the factory for assembly.
Therefore, in PUE-6, clause 4.2.125. applies only to STP.
I believe that the fire distances specified in clause 4.2.131 of PUE-7 apply only to the STP. For all other substations supplied assembled or fully prepared at the factory for assembly, i.e. related to PTS, fire distances should be set according to clause 4.2.68 with an oil amount of 60 kg or more, and with an oil amount of less than 60 kg. according to clause 4.2.131.
Quote sergey ®
There is another opinion
Question:
Paragraph 4.2.131 of the EIC of the 7th ed. determines the minimum, according to fire safety conditions, distances for complete transformer substations outdoor installation, referring at the same time to clause 4.2.68 of the EIC of the section "Open switchgears". Do these clauses apply to the placement of KTPN kiosk version 6-0.4 kV with dry transformers 2 x 400 kVA in the territory with administrative buildings? Glavgosexpertiza claims that the design should be guided by Table. 1 SNiP II-89-80 and clause 7.13, tab. 1 SNiP 2.07.01-89, and not clause 4.2.131 of the PUE, which were agreed with the Gosstroy of Russia and adopted much later than the indicated SNiPs.
Answer:
Viktor Shatrov, Desk Officer of Rostekhnadzor
The instructions of clause 4.2.68 apply to the case of installing oil-filled apparatuses (transformers, oil switches) near the walls of buildings without devices that prevent the spread of fire. They are used if the KTP transformer does not have fire-blocking structures (placed outside the KTP shell). If the transformer is placed inside the KTP shell, then the distances can be taken according to clause 4.2.131. PTS can also be attached, since for certain values of the degree of fire resistance of buildings and structures, the distances between them are not standardized (Table 1 SNiP II-89-80). Limits of distances from the walls of buildings to PTS with dry-type transformers according to fire PUE standards does not install.
SNiP 2.07.01-89, clause 7.13, limits the distance to the windows of residential and public buildings and medical institutions in terms of noise level, and these distances must be observed regardless of the instructions of the EMP.
In addition, we inform you that the standard IEC 61936-1 Electrical installations with voltages above 1 kV alternating current it is allowed to install power transformers at a distance up to .... walls of buildings made of combustible materials:
with a volume of combustible liquid up to 1000 l - 7.6 m;
with a volume of combustible liquid from 2000 l to 20000 l - 10 m;
with a volume of combustible liquid from 20,000 l to 45,000 l - 20 m;
with a volume of combustible liquid more than 45,000 l - 30.5 m3.
The choice of fire distances should be guided by more stringent requirements.
That is, to the package transformer substation, fire distances should be set according to paragraph 4.2.68 of PUE-7 with an amount of oil of 60 kg or more.
In other cases, when establishing fire distances,
i.e. for STP and KTP with an oil mass of less than 60 kg. the requirements of clause 4.2.131 of PUE-7 and clause 7.13 of SNiP 2.07.01-89 * should be applied in the worst case. At the same time, the main "factor of fire prevention distance" should be taken into account the amount of oil and not the power of the transformers. That is, with an oil mass of less than 60 kg. apply the requirement of clause 7.13 of SNiP 2.07.01-89 * (as more stringent), and with an oil mass of 60 kg or more. regardless of the power of the transformer, apply clause 4.2.68 PUE-7.
It is not worth using the degree of fire resistance in choosing a fire distance, since in this case the external substations do not have it.
Karamba® Quote
http://www.norm-load.ru/SNiP/raznoe/...
For pure wood structures without constructive fire protection, you will not find a limit there. With the exception of:
2.37. For the accounting fire regulations at the design stage, the fire resistance limit of wood structures can be roughly determined based on the rate of charring of structural elements. The charring rate is assumed to be 0.7 mm/min for elements with a cross section of 120x120 mm or more, and 1 mm/min for elements with a cross section of less than 120x120 mm.
Fire retardant treatment does not reduce the rate of wood charring.
But I personally don’t understand how to apply this paragraph to determine the limit of a particular design.
The three-story house is located on the plot in such a way that the neighbor's house is very close, only 2 meters from the roof overhang of the first house. Both houses are wooden, covered shingles. Baths and outbuildings are attached to each house.
In the event of a fire, can one house be saved if the other catches fire? Was it possible to build houses so close to each other?
To understand what kind of house you can build according to fire regulations and where you can place the house on the site relative to other buildings and neighboring houses, what the degree of fire resistance of a residential building should be, carefully look at the fire resistance table of buildings.
Fire resistance of a residential building (table):
The degree of fire resistance of a residential building is I. The house must be built of brick, stone, concrete blocks. Insulation must be made with non-combustible materials. Covers must be reinforced concrete slabs. The roof must be made of non-combustible materials - natural tiles, metal tiles, slate, corrugated board.
The degree of fire resistance of a residential building II. The house is built of bricks and blocks. Ceilings can be made of wood with protection by plaster or non-combustible board materials. The truss system when made of wood must be processed flame retardant impregnations. Insulation can be made with non-combustible materials, or materials with a fire resistance limit of G1 and G2.
The degree of fire resistance of a residential building is III. Frame house built on a metal frame. All frame elements are metal, including rafter system. Insulation in a metal frame - non-combustible or group G1 or G2. The cladding of such a house is only made of non-combustible sheet material, for example, metal siding.
The degree of fire resistance of a residential building is IIIb. Single storey frame house on the wooden frame with flame retardant treatment. All wooden elements the frame and cladding of the house are treated with fire retardant impregnations. Insulation - non-combustible or groups with a fire resistance limit of G1 or G2.
The degree of fire resistance of a residential building IV. House on a wooden frame with protection of the frame and walls with plaster coatings. Fire retardant treatment should only be for elements attic floor- lag and crates. Sheathing can be of any material, there are no fire resistance requirements for sheathing in this category.
The degree of fire resistance of a residential building is IVb. The same as grade IV, only the frame is metal and the house is one floor. Enclosing structures must be made of sheet metal or any other non-combustible materials. Insulation can be used groups G3 or G4.
The degree of fire resistance of a residential building is 5. All other buildings that do not fall into the above categories and for which there are no requirements for the limit of the spread of fire and fire resistance.
According to this table, it is possible to determine the fire resistance of a residential building, classify each house according to the materials used to a specific category, and plan the development of the site accordingly. If the houses have already been built, then fire prevention measures can be organized - sheathing with non-combustible materials, insulation with non-combustible heaters, and the like.
This will increase the fire resistance of a residential building, even if it is made of wood or if this house is built high - 3 floors or more.
The degree of fire resistance is an indicator that determines the possible resistance of the room to the direct effects of fire. The indicator is determined according to the rules of SNiP. This is general definition, which allows assessing the established level of safety of any building for its intended purpose, as well as the materials from which it is built.
The rate of fire spread per unit of time in a particular room depends on the fire resistance parameters. All types of buildings and structures, depending on the resistance to fire and the speed of the spread of fire, are divided into five categories and are indicated by Roman numerals.
According to the ability to ignite, structures are classified as follows::
- fireproof;
- Difficult to burn;
- combustible.
Such a classification is conditional, since within the same building, different rooms can be made from different materials. Fireproof are residential or industrial buildings, the construction of which used fireproof materials.
Hardly combustible are those that are made of non-combustible or combustible materials that have additional fire protection. For example, a wooden door covered with a special varnish, asbestos and roofing steel. Combustible are those that ignite easily and the rate of spread of fire is high.
How to determine the fire resistance of a building
The basis for determining the degree of fire resistance of any room is the time taken from the moment of ignition. construction materials, until the appearance of obvious defects in these structures.
- The appearance of cracks or a violation of the integrity of the surface, which can cause the penetration of flames or combustion products;
- Heating of the material by more than 160 C, or more than 190 C, at any point on the surface;
- The deformation of the main nodes, which causes its collapse, is thus lost load bearing capacity support structures.
The safest, in terms of fire, are considered to be reinforced concrete supporting structures, provided that the concrete contains cement with a high level of fire resistance. Unprotected metal materials are considered to be the least flammable.
Classification of materials and their fire resistance
The actual degree of fire resistance depends on the materials that were used in the construction of buildings and structures.
All building materials are classified according to the following characteristics:
- Release of toxic substances;
- Flammability;
- combustibility;
- smoke generation;
- Spread of fire over the surface of the structure.
According to GOST 30244-94, non-combustible materials, fire resistance indicators are not standardized and may not be determined.
According to the deformation time of the structure, the fire resistance standards are determined:
- 300 min. - bricks made of ceramics or silicates;
- 240 min. - concrete, the thickness of which exceeds 250 mm;
- 75 min. - wood with gypsum coating at least 20 mm thick;
- 60 min. – standard Entrance door that is pre-treated with a flame retardant;
- 20 minutes. - metal structures.
Cause of destruction ordinary concrete is the presence of bound water, mass fraction which is about 8%. Metals have a high degree of flammability because at temperatures above 1000 C, they pass from a solid to a liquid state.
Hollow brick and concrete, having a porous structure, are among the most resistant to elevated temperatures and open flames. Buildings made of these materials have I-II degrees of fire resistance and constructive fire safety class.
Rules for determining the fire resistance of buildings
Degree of fire resistance and class fire hazard define authorized services. Any production has a degree of fire resistance and a class of constructive fire safety
According to SNiP 21.01-97, all buildings can be divided into 5 main degrees of fire resistance of structures. The required degree of fire resistance is always indicated in the passport of the boiler room, industrial or residential building. And so the fire resistance is subdivided:
| Degree of fire resistance | Characteristic |
| I | All external walls must be made of synthetic or natural stone, porous concrete or reinforced concrete. Ceilings are made of slabs or other non-combustible materials, which must belong to the protection class: "fireproof". The safest building in terms of the possibility of occurrence and spread of fire. High level security. to them in without fail include boiler rooms. |
| II | This degree of fire resistance is similar to I, the difference lies in the possibility of using open steel structures. (Materials for a brick house). Brick houses have a II degree of fire resistance and a constructive fire safety class |
| III | The third level of security assumes that all the main elements of industrial buildings must be made of synthetic or natural stone. wooden floors are possible if they are covered with plaster or plaster. Can also be installed as a cover sheet materials belonging to the class "flammable". Coating elements are not standardized for the occurrence and spread of fire, but wooden roof slabs are treated with special solutions to prevent fire. |
| III a | Buildings built by type frame structures that are made of bare steel. Enclosing profiles made of steel or other non-combustible materials. Use of slow-burning heaters is possible. |
| III b | Wooden houses on one floor have a III b degree of fire resistance and a constructive fire safety class. All wooden elements are flame retardant treatment to limit the spread of fire. Restrictive structures are made of wood or composite materials containing wood. All protective structures are necessarily subjected to fire retardant treatment in order to prevent possible ignition, overheating of the structure. It is unacceptable to erect such ceilings near a source of heat and high temperatures. |
| IV | 4 degree of fire resistance involves the construction wooden house. Protection against fire is carried out by applying gypsum, plaster or other insulating materials to the wood. Coating elements do not have special requirements for the occurrence and spread of fire, but the wooden roof joists must undergo fire retardant treatment. |
| IV a | One-story buildings that are made of steel that do not have protective insulating coatings. The ceilings are also made of steel, but with insulating fireproof materials. |
| V | This degree of fire resistance of buildings includes all objects (industrial, residential) for which special requirements are not put forward regarding the fire resistance threshold and ignition rate. |
SNiP
People wondering: what is the fire rating of a building and how to determine it, should understand that all the relevant manipulations of determining the fire rating from a container to a large production building fire departments do.
According to the generally accepted rules of SNiP, boiler rooms have a degree of fire resistance and a class of constructive fire safety. All furnaces must be separated from the main boiler room by fireproof partitions of appropriate thickness, which depends on the volume of the fuel chamber.
If the boiler room uses gaseous or liquid fuels, then the room is equipped with materials that can be quickly dismantled. The SNiP rules for a boiler house, depending on the daily heat production, normalize the thickness of both the main and internal walls, as well as the materials from which they are made. According to the degree of fire resistance, such buildings belong to the first group.