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 a general definition that allows you to assess 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 of different materials. Fireproof are residential or industrial buildings, the construction of which used fireproof materials.

Hard-to-combustible are those that are made of non-combustible or combustible materials with 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 taken from the moment of ignition of structural 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;
• Deformation of the main nodes, which causes its collapse, thus losing the bearing capacity of the supporting structures.

The safest, in terms of fire, is 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;
• The 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. - a standard front door, which is pre-treated with a flame retardant;
• 20 minutes. - metal structures.

The reason for the destruction of ordinary concrete is the presence of bound water, the mass fraction of 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

The degree of fire resistance and the fire hazard class are determined by the 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:

SNiP

People wondering: what is the degree of fire resistance of a building and how to determine it, should understand that all the relevant manipulations of determining the degree of fire resistance from a container to a large industrial building are done by the fire department.

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 room, depending on the daily heat generation, 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.

The degree of resistance to fire is an important parameter, which is determined during construction work and after its completion. It is very important for builders to know that this or that building structure has its own degree of fire resistance. How to determine the fire resistance of a building, you will learn from this article.

The expression fire resistance refers to the ability of certain elements of a building to maintain strength in a fire. Moreover, fire resistance has its own limit, which is determined in hours, i.e. specific figures to the fire hazard of the building. It is generally accepted that the degree of fire resistance is denoted by Roman values: I, II, III, IV, V.

Fire resistance is divided into two types:

1. Actual (SOF). How is it defined? Mainly according to the result of technical and fire examination of building structures. Also, calculations occur based on regulatory documents. The level of resistance to fire is clearly regulated and known. In accordance with official information, the SOF is calculated.
2. Required (SOtr). This concept includes the level of resistance to fire in the 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 values. In this case, the key role is played by the direct purpose of the building, its area, the availability of fire extinguishing equipment, the number of floors, and so on.

To consolidate all this, consider an example. To make the building comply with the requirements of the PB, the SOF must be greater than or equal to SOtr. The limit of fire resistance occurs at the moment when the building completely or partially does not fulfill its functionality in case of fire. This happens when compartments or cracks form in a building. Directly through them, the flame penetrates into neighboring rooms, the surface heats up to 140-180 ° C, and also if the bearing parts of the building are completely eliminated.

Method for determining fire resistance

Appropriate 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 arranged in specially equipped furnaces. The furnace is processed exclusively with refractory bricks. Inside the furnace, kerosene is burned 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, based on the basic rules, then the calculation of the degree of fire resistance has two tasks:

1. Thermotechnical.
2. Statistical.

In order to determine the degree of fire resistance, it is important to first obtain an architectural design. Next, you need to adhere to the standard scheme.

As for the scheme, it looks like this:

• Turning to the fire department, they will conduct an examination on fire resistance. If deficiencies are found, they should be corrected immediately.
• Already at the stage of drawing up sketches, 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, by definition of 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 violated.
• One of five steps is taken for calculation.
• Included in these calculations/calculations is the flammability level of the various materials used in the construction of the building.
• To accurately determine fire resistance, it 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 the SNiP dated January 21, 1997 "Fire Prevention".
• Thus, to determine fire resistance, a wide range of planning and technological aspects are taken into account. But at the same time, one should not forget about the primary fire extinguishing means - fire extinguishers.

As a result, you need to make a list of requirements for the building, which are found out in the process of determining the fire resistance. The documentation and the design of the building are taken as the basis.

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 25. As a result, it is allowed to use unprotected metal structures.

Building codes allow the use of drywall as a facing material. This to some extent increases the fire resistance of the building.

If we talk about building materials and the degree of their combustibility, then they are divided into 3 groups:

1. Non-combustible.
2. Fire resistant.
3. Fireproof.

If you are building a frame, it is better that it be made of non-combustible material. For buildings from 1 to 5, combustible materials can be used, but not in the lobbies. This is important, because plus everything building materials are divided into classifications such as:

• Smoke generating.
• Toxic.

Below we consider an algorithm for calculating the degree of fire resistance of a building and premises of different types. Based on this, you can find out the basic requirements for certain buildings.

residential buildings

The fire resistance index of the house has 5 degrees. According to these degrees, a characteristic is given for each building material from which the house was built. The following are the structural characteristics of residential buildings:

• For residential buildings, preference is given to non-combustible materials.
• Construction is best done from concrete blocks, stone or brick.
• To insulate walls, roofs and other structures, use fire-resistant material.
• Roofing should be made of materials that are resistant to fire, namely: slate, corrugated board, metal tiles or tiles.
• Ceilings are made of reinforced concrete slabs.
• If the floors are wooden, then they should be covered with non-combustible materials, such as non-combustible boards or plaster.
• The wooden truss system must be treated with impregnations that prevent the spread of fire.

For insulation, it is not necessary to use non-combustible materials. You can use items that are resistant to fire categories G1 and G2.

Public buildings

The degree of fire resistance of public buildings is divided into 5 groups: I, II, III, IV, V. So, according to the class of constructive fire hazard of a building, the following are determined:

• I-C0.
• II-C0.
• III-C0.
• IV-C0.
• V is not numbered.

With regard to the permissible height of the room in meters and the area for the fire compartment, the following data are available here:

• I-75m;
• II-C0-50, C1-28;
• III-C0-28, C1-15;
• IV-CO-5-1000 m 2 ;
• C1-3m-1400 m 2;
• C2-5m-800 m 2.

Speaking of clubs, pioneer camps, hospitals, preschools and schools, they often use wooden partitions, ceilings and walls. Their processing must be carried out with fire-resistant materials.

Industrial buildings

• Metallurgical.
• Instrumental.
• Chemical.
• Weaving.
• Repair and others.

And for such establishments, the degree of fire resistance is more important than ever. In addition, some work with toxic and explosive substances that can have a negative impact on humans and the environment.

Production buildings are also divided into 5 stages. Fire resistance is determined based on the building materials used. Hence the conclusion: the degree of fire safety of an 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 are considered the most vulnerable. However, if they are treated with plaster and special impregnations, then their degree of fire resistance increases. Also for this purpose, concrete or ceramic tiles are used.

For warehouses, swollen paints or polymer foam are considered the most effective. Their action prolongs 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. Aluminum doors can also be installed in them, and glass blocks instead of wooden windows.

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.

I
Buildings with load-bearing and enclosing structures made of natural or artificial stone materials, concrete or reinforced concrete using sheet and slab non-combustible materials

II
Same. It is allowed to use unprotected steel structures in the coatings of buildings

III
Buildings with load-bearing and enclosing structures made of natural or artificial stone materials, concrete or reinforced concrete. For floors, it is allowed to use wooden structures protected by plaster or slow-burning sheet, as well as slab materials. There are no requirements for fire resistance limits and fire propagation limits for roofing elements, while attic wood roofing elements are subjected to fire retardant treatment.

IIIa
Buildings are predominantly with a frame structural scheme. Frame elements - from steel unprotected structures. Enclosing structures - from profiled steel sheets or other non-combustible sheet materials with slow-burning insulation

IIIb
The buildings are predominantly one-storey with a frame structural scheme. Frame elements - from solid or glued wood, subjected to fire retardant treatment, providing the required fire spread limit. Enclosing structures - from panels or element-by-element assembly, made using wood or materials based on it. Wood and other combustible materials of building envelopes must be subjected to fire retardant treatment or protected from fire and high temperatures in such a way as to ensure the required fire spread limit.

IV
Buildings with load-bearing and enclosing structures made of solid or glued wood and other combustible or slow-burning materials, protected from fire and high temperatures by plaster or other sheet or plate materials. There are no requirements for fire resistance limits and fire propagation limits for roofing elements, while attic wood roofing elements are subjected to fire retardant treatment.

IVa
The buildings are predominantly one-storey with a frame structural scheme. Frame elements - from steel unprotected structures. Enclosing structures - from profiled steel sheets or other non-combustible materials with combustible insulation

V
Buildings, for the bearing and enclosing structures of which there are no requirements for fire resistance limits and limits for the spread of fire

Note. The building structures of buildings given in this appendix must meet the requirements of Table. 1 and other norms of this SNiP.

The highest degree of fire resistance I (mausoleum).

During the construction of any building, it is necessary to consider the organization of emergency exits in the construction, escape routes in emergency cases, and the location of funds even at the design stage. But these points can be considered only if you know the degree of fire resistance of the building. Difficulties at present with this may arise, since most often the same type of structures are being built in cities. But then we will try to figure out how fire resistance is determined, on what it depends.

What is fire resistance?

This is the ability of structures and individual structures to withstand the onslaught of a fire without destruction and deformation. It is the degree of fire resistance of the building that will show how quickly the fire can spread through the structure if a fire occurs.

All indicators are determined taking into account SNiP. These standards allow you to determine the level of not only the building, but also all the materials that were used in the construction.

Flammability classification

1. Fireproof.
2. Difficult to be affected by fire. They can be made of combustible materials, but which have a special treatment or coating on top. An example is a wooden door lined with steel or covered with asbestos.
3. combustible. They have a low ignition temperature and quickly burn out under the influence of fire.

Basis for determining fire resistance

As a determining basis for determining the degree of fire resistance of a building, the time that has passed from the moment the fire began to the appearance of the first noticeable defects is taken. These include:

• Cracks and damage to the integrity of the surface, which can facilitate the penetration of flames or products of its combustion.
• Increasing the temperature of materials by more than 160 degrees.
• Deformation of load-bearing structures and main units, which causes the collapse of the entire structure.

Buildings built of wooden structures have a low degree of fire resistance; reinforced concrete buildings are considered the safest in terms of fire, especially if they contain cement with a high level of fire resistance.

Dependence of fire resistance on materials

The ability of a building to withstand fire largely depends on the materials from which it is built. They can be classified based on the following characteristics:

The degree of fire resistance of building structures depends on the time required for the deformation of the material:

• Ceramic bricks or silicate bricks begin to deform 300 minutes after the start of the fire.
• Concrete floors, more than 25 cm thick, after two hours.
• 75 minutes are required to start the deformation of plaster-coated wooden structures.
• An hour will pass before the door treated with fire retardant begins to deform.
• 20 minutes exposure to fire is enough.

The degree of fire resistance of brick buildings is quite high, which cannot be said about metal buildings, which already at 1000 degrees pass into a liquid state.

Assignment of a fire safety category

According to regulatory requirements, only after the structure has been assigned a certain fire safety category, it is possible to determine the degree of fire resistance of the building. And this is done on the basis of the following signs:

• By changing the indicators of thermal insulation, when compared with the state before the fire.
• By blocking effect, which eliminates the formation of cracks in structures.
• By reducing the ability to perform load-bearing functions.

When determining the degree of fire resistance of a building, the area of ​​\u200b\u200bthe structure and the quality of all materials used must be taken into account.

Characteristics of the degrees of fire resistance

Their determination is made on the basis of SNiP, the fire resistance of the main functional structures is always taken as the basis. Consider how many degrees of fire resistance of buildings and structures exist and what are their main characteristics:

Types of fire resistance

Special requirements for the ability to withstand fire are imposed on all building structures. For them, the following indicators are important:

• The ability to perform a load-bearing function.
• Thermal insulation.
• Integrity.

The safety of the building also plays an important role. Experts today divide the fire resistance of structures into two types:

1. Actual.
2. Required.

The actual degree of fire resistance of a building is the ability to withstand fire, which was determined during the examination. The available regulatory documents are taken as criteria for evaluation. Fire resistance limits have already been developed for structures of various types. This data is very easy to find and use for work.

The required fire resistance is the indicators that a building must have in order to comply with all fire safety standards. They are determined by regulatory documents and depend on many characteristics of the structure:

• The total area of ​​the building.
• Number of floors.
• Purpose.
• Availability of means and installations for extinguishing fires.

If during the inspection it turned out that the actual degree of fire resistance of buildings and structures is equal to or exceeds the required one, then the structure complies with all standards.

Fire Hazard Classes

To determine the fire resistance of the entire building, structures are divided into several categories, and buildings into several classes.

1. KO is non-flammable. There are no materials in the premises that ignite quickly, and the main structures do not ignite spontaneously and ignite at temperatures close to 500 degrees.
2. K1 - low fire hazard. Minor damage may be allowed, but not more than 40 cm. No burning, no thermal effect.
3. K2 - moderate fire hazard. Damage can reach 80 cm, but there is no thermal effect.
4. K3 - fire hazard. Integrity violations of more than 80 cm, there is a thermal effect and fire is possible.

1. CO. All utility rooms, main structures and staircases with openings comply with the KO class.
2. C1. There may be slight damage to the leading structures up to K1, and the outer ones up to K2. Stairs and openings must be in excellent condition.
3. C2. Damage to the main structures can reach K2, external K3, and staircases up to K1.
4. C3. Stairs with openings are damaged up to K1, and everything else is not taken into account.

Rules for determining the resistance of a building to fire

It is not enough to know about the importance of fire resistance of buildings and structures, it is also important to be able to determine it. And there are some rules for this:

1. Testing a building involves having its plan at hand, and you will also need:

• Code of Practice for Ensuring Fire Resistance of Reinforced Concrete Structures.
• Guide to determining the limits of fire resistance.
• Manual for SNiP "Prevention of the spread of fire."

2. The fire resistance limit is determined by the time of exposure to the structure of fire. When the structures reach one of the limits, the fire is stopped.

3. Before starting testing, it is necessary to study the documentation for the building, where there is information about the materials and their approximate fire resistance.

4. It is necessary to pay attention in the documents to the existing conclusion on the use of special technologies to improve fire safety.

5. A preliminary study of the building also involves the consideration of all utility rooms, stairs and stairwells, attic compartments. They may be constructed from other materials or show visible damage at the time of testing.

6. Modern architecture very often uses the latest technologies in construction, which can affect the strength and resistance to fire. These points must also be taken into account.

7. Before carrying out the determination of fire resistance, it is necessary to prepare extinguishing agents, check the serviceability of the hoses, call the fire brigade.

When all the preliminary measures have been taken, then you can proceed directly to the practical determination of fire resistance.

Practical definition of resistance to fire

When starting the practical part, it is important to take the architectural plan with you, even if it has been carefully studied. The next steps are:

An indicator of the fire resistance of the material will be the time of exposure to fire and the speed of its spread. For different buildings, this figure can vary from 20 minutes to 2.5 hours. The ignition rate is even less - from instantaneous to 40 cm per minute.

This is how the fire resistance of a building is calculated in practice.

Ways to improve fire resistance

It is not always possible to use only non-combustible or low-combustible materials during construction, so ways to increase their resistance to fire come to the rescue.

The most commonly used are:

If multicomponent chemicals are used to improve fire resistance, then it must be borne in mind that some of them contain organic substances that decompose at temperatures above 300 degrees with the release of toxic substances. Therefore, it is better to give preference to mineral-based coatings with liquid glass.

It is not difficult to determine the fire resistance of buildings and structures. It is important to carry out all preliminary preparations and it can be considered that most of the work has been completed. The calculation can be attributed more to costly than complex. The most important thing is special care during testing and temperature control in the oven.

The approach to the construction of any buildings and structures should be based on safety from different points of view. And last but not least is fire safety. In emergency situations, human lives depend on the resistance of the structure to fire.

Classification of buildings and structures by fire resistance.

In assessing the fire-prevention qualities of buildings and structures, their fire resistance is of great importance.

Fire resistance is the ability of building structural elements of a building to perform load-bearing and enclosing functions in a fire for a certain time. It is characterized by a fire resistance limit.

The fire resistance limits of the structures of the facility must be such that the structures retain their load-bearing and enclosing functions during the entire duration of the evacuation of people or their stay in places of collective protection. At the same time, fire resistance limits should be assigned without taking into account the effect of extinguishing agents on the development of a fire.

The fire resistance limit of building structures is determined by the time (h) from the start of a fire to the occurrence of one of the signs: a) the formation of through cracks in the structure; b) an increase in temperature on the unheated surface of the structure by an average of more than 140 ° C or at any point on this surface by more than 180 ° C compared to the temperature of the structure before the test, or more than 220 ° C regardless of the temperature of the structure before the test; d) loss of bearing capacity by the structure.

The fire resistance limit of individual building structures depends on their dimensions (thickness or section) and the physical properties of the materials. For example, the stone walls of a building with a thickness of 120 mm. have a fire resistance limit of 2.5 hours, and with a thickness of 250 mm, the fire resistance increases to 5.5 hours.

The degree of fire resistance of a building depends on the degree of flammability and the fire resistance limit of its main building structures. All buildings and structures in terms of fire resistance are divided into five degrees (Table 32).

Table 32 Classification of buildings and structures by fire resistance.

Note. The limits of fire resistance (h) are indicated in brackets.

This division into degrees was introduced by SNiP II-A. 5-70, which gives nine notes on what to keep in mind when using the table.