During the construction of any building, the organization’s issues in the construction of emergency exits, emergency escape routes, and the location of fire safety equipment are considered at the project stage . But you can consider these points only if you know the degree of fire resistance of the building. Difficulties at the present time may arise with this, since most often the same structures are being built in cities. But then we will try to figure out how fire resistance is determined, on which 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 building if a fire occurs.
All indicators are determined taking into account SNiP. These standards make it possible to determine the fire safety level of not only the building, but also of all the materials used in the construction.
Fire classification
It can be considered conditional, given that in the same building separate rooms can be built using various materials. The following classification of buildings according to the degree of fire resistance can be distinguished:
- Fireproof.
- Difficult to fire. They can be made of combustible materials, but which on top have a special treatment or coating. An example is a wooden door lined with steel or covered with asbestos.
- Combustible. They have a low flash point and quickly burn out under the influence of fire.
The basis for determining fire resistance
As a determining basis, to determine the degree of fire resistance of a building, the time taken from the moment of the fire to the first noticeable defects is taken. These include:
- Cracks and violation of the integrity of the surface, which can contribute to the penetration of the flame or its combustion products.
- Increase in temperature of materials by more than 160 degrees.
- The deformation of the supporting structures and the main components, which becomes the cause of the collapse of the entire structure.
Buildings made of wooden structures have a low degree of fire resistance, reinforced concrete are considered the most safe for fire, especially if the composition of the cement is with a high level of fire resistance.
The dependence of fire resistance on materials
The ability of a building to withstand fire largely depends on the materials of which it is built. They can be classified based on the following characteristics:
- Release of toxic substances.
- Flammability.
- Combustibility
- Smoke formation.
- Spread of fire.
The degree of fire resistance of building structures depends on the time required for the deformation of the material:
- Ceramic or silicate bricks begin to deform 300 minutes after the start of the fire.
- Concrete floors, more than 25 cm thick, in two hours.
- 75 minutes is required to begin the deformation of gypsum-plated wooden structures.
- An hour will pass before the door treated with flame retardant begins to deform.
- Metal construction is enough for a 20-minute exposure to fire.
The degree of fire resistance of brick buildings is quite high, which can not be said about metal, which already at 1000 degrees turn into a liquid state.
Fire Rating
According to regulatory requirements, only after a certain fire safety category has been assigned to a building can the degree of fire resistance of a building be determined. And this is done on the basis of the following features:
- By the change in thermal insulation, when compared with the state before the fire.
- By the barrier effect, which eliminates the formation of cracks in the structures.
- To reduce the ability to perform bearing functions.
When determining the degree of fire resistance of a building, the area of the structure and the quality of all materials used must be taken into account.
Characterization of degrees of fire resistance
Their determination is made on the basis of SNiP, the basis is always taken as the fire resistance of the main functional structures. Consider how many degrees of fire resistance of buildings and structures exist and what are their main characteristics:
- First degree. It is assigned to structures that are built from non-combustible materials, the supporting structures in such structures are made of concrete or reinforced concrete.
- Grade 2 has similar characteristics. The materials from which the structure is built may have an external coating of steel.
- 3 degree of fire resistance of the building. The basic structures of the bearing nature and the enclosing elements are made of natural or artificial materials, such as stone. In the presence of wooden floors, they are protected from above by highly inflammable materials, for example, plaster or slabs. Necessarily in such constructions attics have fireproof treatment.
- 3A degree. Buildings are frame, the main structures are steel. Non- combustible materials or profiled sheets may be used.
- 3B degree of fire resistance is assigned to wooden buildings. But all the main and additional structures are processed without fail with flame retardants. Structures are built of wood or materials with its contents. Guards must also be machined to prevent the spread of fire and overheating of the entire structure.
- Grade 4 is assigned to wooden houses with fire protection in the form of gypsum, plaster or other non-combustible materials. There are no special requirements for the coatings of such buildings, but they must have fire-retardant impregnation on a wooden roof.
- 4A degree. This includes one-story buildings of a frame structure. The building frame is most often made of steel without coatings, and the enclosing elements are constructed from materials that are not susceptible to fire or have a special insulation made of iron.
- The maximum degree of fire resistance of a building is 5. It has all buildings with structures of bearing and enclosing nature with any indicator of resistance to fire. There are no special requirements for the degree of fire resistance of the building in such cases. This may include both some residential premises and industrial facilities.
Types of fire resistance
Special requirements for the ability to resist fire are imposed on all building structures. The following indicators are important for them:
- The ability to perform a bearing function.
- Thermal insulation.
- Integrity.
The safety of the building also plays a large role. Specialists today divide the fire resistance of structures into two types:
- Actual.
- Required.
The actual degree of fire resistance of a building is the ability to withstand fire, which was determined during the examination. The available regulatory documents are taken as criteria for the assessment. For structures of various types, fire resistance limits have already been developed. 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.
- Destination
- Availability of facilities and facilities 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, then the structure meets 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.
There is a category K, it distinguishes:
- KO - fireproof. There are no materials in the rooms that quickly ignite, and the main structures do not differ in spontaneous combustion and ignition at temperatures close to 500 degrees.
- K1 - low fire hazard. Small damage may be allowed, but not more than 40 cm. No burning, no thermal effect.
- K2 - moderate fire hazard. Damage can reach 80 cm, but there is no thermal effect.
- K3 - fire hazard. Violations of the integrity of more than 80 cm, there is a thermal effect and possibly a fire.
Category C characterizes the entire structure as a whole:
- With. All utility rooms, main structures and staircases with openings correspond to the class KO.
- C1. Minor damage to the leading structures to K1, and external to K2, may be present. Stairs and openings must be in excellent condition.
- C2. Damage to the main structures can reach K2, external K3, and stairs to K1.
- C3. Stairs with openings damaged to K1, and everything else is not taken into account.
Both categories are inextricably linked and necessary to finally determine the degree of fire resistance of residential buildings.
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 for this there are some rules:
1. Testing the building requires the availability of its plan at hand, and you will also need:
- Code of practice for ensuring fire resistance of reinforced concrete structures.
- Guidelines for determining fire resistance limits.
- Guide to SNiP "Prevention of the spread of fire."
2. The fire resistance limit is determined by the exposure time to the fire structure. When the structures reach one of the limits, the fire is stopped.
3. Before starting testing, you need 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 involves the consideration of all the utility rooms, stairs and stairways, attic compartments. They can be constructed from other materials or have visible damage at the time of testing.
6. Modern architecture very often during construction uses the latest technology, which can affect the strength and resistance to fire. These points also need to be considered.
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 are carried out, then you can proceed directly to the practical definition of fire resistance.
Practical definition of fire resistance
Getting to the practical part, it is important to take the architectural plan with you, even if it has been carefully studied. Further actions are as follows:
- For testing, it is necessary to install the furnace at a distance of 10 cm from the tested part of the structure.
- Kerosene is sprayed into the oven and set on fire.
- The temperature can be adjusted using a thermocouple.
- During testing, it is necessary to use ready-made tables with data on the melting and burning temperatures of various materials in order to exclude the occurrence of a real fire.
- Fire must be applied to the material under investigation until visible disturbances and deformations appear. It can be his fire, softening.
An indicator of the fire resistance of a material will be the exposure time of the fire and the speed of its spread. For different buildings, this figure can vary from 20 minutes to 2.5 hours. The ignition speed is even lower - from instant to 40 cm per minute.
So, in practice, the fire resistance of a building is calculated.
Ways to increase fire resistance
It is not always possible to use only non-combustible or non-combustible materials during construction, so ways to increase their resistance to fire come to the aid.
The following are most commonly used:
- Plaster. An affordable way to protect wooden structures, concrete blocks, metals and polymers. It is used not only on supporting structures, but also on building envelopes. The protective layer should be at least 2.5 cm. Lime-cement plaster, vermiculite have proven their effectiveness.
- Facing. For these purposes gypsum boards, ceramic bricks can be used. Efficiency is directly proportional to the thickness of the protective layer and the selected material. A clay slab up to 8 cm thick increases fire resistance up to 4.8 hours, and a brick only up to 2.
- Protective screen. They are most often used in the form of suspended ceilings from fireproof plates to protect floors. Screens differ in their effect, some are heat-absorbing, and others are heat-removing.
- Chemical protection. For these purposes, flame retardants are used, which are used to process wooden structures. But the method compared to others is more expensive and requires a lot of labor. And the efficiency is not always at its best, as the structure and density of wood affects.
- Protection by paints and varnishes. They can be used on any building material. Under the influence of fire, the paint swells and a layer of thermal insulation is formed. Such tools are available, easy to use.
- Pressing wood. The method is new, but expensive. It consists in introducing special substances into the wood, which will soften cellulose and make it subject to pressing under high pressure. After this process, the tree gains maximum strength and becomes resistant to fire.
If multicomponent chemicals are used to increase fire resistance, it should 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 the preliminary preparations and it can be considered that most of the work has been completed. Calculation can be attributed more to costly than complex. The most important thing is special care during testing and temperature control in the furnace.
The approach to the construction of any buildings and structures should be based on safety from different points of view. And fire safety is not the last place here. Human life depends on the stability of the structure in relation to fire in emergency situations.