Incorrect ventilation can cause the rapid spread of fire and combustion products, lead to death of people, damage to property. Therefore, the calculation and installation of such a system as smoke ventilation is a very serious issue that does not tolerate frivolity. SNiP require the mandatory availability of appropriate chimneys at industrial and public facilities. Their calculation is made at the stage of planning and designing premises. This is especially important for facilities through which people are evacuated in emergency situations. The presence of smoke ventilation is mandatory in elevator shafts, corridors, reception rooms, flights of stairs and walk-through rooms. People's lives depend on it.
General characteristics
Supply smoke ventilation is a complex of communications, devices, the totality of which ensures the supply of a sufficient amount of air to the premises at the time of fire and after it. The ventilation system must providethe possibility of evacuating people along the provided route.
All their routes must be accessible for movement. This contributes to a significant reduction in mortality due to poisoning by combustion products, eliminates panic during evacuation. The supply smoke ventilation device assumes the autonomy and disconnection of the system from other air ducts and communications.
The main task of such a system is to provide visibility along the route of people during evacuation, to supply enough air to stairwells, corridors, elevator shafts, passage rooms, etc. This reduces the likelihood of loss of consciousness due to carbon monoxide asphyxiation and greatly reduces the number of accidents during emergencies.
Need for ventilation device
According to the Ministry of Emergency Situations, when fires occur in residential or industrial premises, 70% of deaths are caused by suffocation by combustion products. Smoke ventilation, properly installed, can save many lives.
In Russia up to 10,000 people die as a result of indoor fires. For comparison, in China, with a population of 1.4 billion people, this figure is 1.5 thousand people. In the United States, with a large population, 3,000 people die each year as a result of fires.
Therefore, supply and exhaust smoke ventilation is necessary in the operation of various buildings. In our countrythe frequency of fire incidents in 25-storey buildings is no more than 20 times a year. Such a low figure throughout the country clearly illustrates how effective modern, designed according to all the rules and examples, smoke-fighting supply type ventilation is.
But in older buildings with a number of storeys from 17 to 25, 650 fires occur annually with a fatal outcome in 20 cases. In 6-9-storey buildings, this figure reaches 350 people with 8 thousand cases of fires. But in 5-storey buildings, the number of victims is 9 thousand people annually. This is due to the lack of effective systems for the outflow of combustion products in a fire.
How the system works
According to the rules of SP 7.13130.2009, the installation of supply smoke ventilation is mandatory for high-rise buildings, office buildings, underground garages, parking lots, office complexes.
The principle of operation of any smoke ventilation is to ensure efficient evacuation and preservation of property in case of fire. The system also makes it possible to provide rescuers with access to the inside of the building while containing the spread of ignition products along the paths of people.
Inlet smoke ventilation will be even more effective if there are automation elements in the system. Sensors will quickly respond to the occurrence of fires and smoke, transmit a signal to the control point. Automatic activation of the system will allow you to quickly respond to emergencies. If smoke controlsupply type ventilation determines the situation of the start of a fire, it opens the air intake valves, and its operation begins.
Technology of work
Supply smoke ventilation, an example of the calculation of which is provided by SNiP 2.94.05-91, does not allow the simultaneous use of the same channels of conventional ventilation systems along with smoke extraction. In the room, with the help of fans, increased pressure is pumped, which pushes the products of combustion out of the room.
Calculations are made to determine the parameters, noise characteristics, power of any smoke-free flow ventilation system (for example, VKOP-1, ESSMANN, etc.). When developing a system plan, the installation locations of smoke detectors, the parameters of the exhaust channels, as well as the places in the building where the elements of the system are necessary are taken into account.
The established norms assume that no more than 900 m22 of the building area should fall on one device for removing combustion products. Their location is supposed to be under the ceiling for convenience. If, for example, a room has a square of 1600 m2, then an example of calculating ventilation might look like this:
1600/900=1, 7
So, for a given room, it will be enough to make two compartments with autonomous communication channels.
Inlet smoke ventilation of the staircase, corridors makes it possible to remove carbon monoxide to the roof through the vertical sections of the channels. For the basement floors and basements of parking lots, parking, air outflow through windows and doors of certain dimensions is possible. When calculating the intake smoke ventilation through the entrance gates or window openings, it should be noted that they must be geometrically correct, rectangular in shape. The pumps must be able to handle the load for one hour at 600°C and 2 hours at 400°C. The hood must circulate at least 19 thousand m33 air masses.
Elevator shafts and stairs
According to fire regulations, all buildings with a height of 28 m must be equipped with a system such as forced smoke ventilation of the staircase and elevator shaft. This is due to the length of the equipment for the evacuation of people at the disposal of the rescuers. Their stairs can reach a maximum height of 28 m.
If the building rises above ground level by more than 28 m, then the stairwells must be designed before the start of construction for smoke-free type 2 or 3. Smoke protection in such buildings is simply vital.
Calculation of supply smoke ventilation should be carried out by qualified specialists with certificates for the right to carry out such work.
Scope of application
In addition to buildings 28 m high, forced ventilation to eliminate smoke must be used in corridors over 15 m long without natural light, from common halls with access to smoke-free stairwells. If there is no natural light in the basement or on the basement floor, supply smoke ventilation into the corridor must be carried out without fail. Also similar systemsused in facilities where the distance from the door furthest to the landing is more than 12 m.
From atriums and passages with a height of more than 15 m, as well as on balconies or doorways facing these premises, combustion products must be removed without fail. The design of communications in corridors should be carried out separately from systems in residential or industrial premises.
Smoke removal is carried out from hazardous areas with an area of not more than 1600 m23, which must be divided into compartments.
Design and installation rules
When calculating the parameters of a supply-type smoke exhaust system, the norms for the maximum allowable pressure with closed and open doorways, the average outflow of air from the room, and its temperature in the event of a fire are taken into account. Supply smoke ventilation through entrance gates, window openings or the roof should take into account the air temperature in the summer and the strength of the wind. The area of openings for the movement of air masses is important in calculations.
Experts, based on the existing conditions in the room, decide on the choice of fans, ducts and valves. Air shafts must be designed in accordance with fire safety regulations and requirements.
When calculating the ventilation of the presented type, it is taken as a basis that the air is supplied only from the outside usingcorresponding air intake points. Therefore, they should be located at a sufficient distance from smoke outlets.
The air must be supplied at low speed (no more than 1 m/s) and distributed evenly throughout the premises. Also, when designing, it should be taken into account that the air should not come from above, but from below and not reach the lower limit of the probable presence of smoke. Supply smoke ventilation, the calculation example of which takes into account the flow of air masses, should ensure that smoke does not reach the upper border of the door during the evacuation of people. Air intake is calculated using the following formula:
G=F(ΔP/S)0, 5 where
F – valve flow area, m2;
ΔP – pressure drop across the closed valve, Pa;
S – valve gas permeability specific resistance, m3/kg.
Minimum S should be 1.6 103 m3/kg.
Recommended air outflow should be 9-11 m/s.
Equipment
Ventilation equipment should be suitable for the environment it is likely to be exposed to.
Ducts should be made of non-flammable materials that can withstand overheating for a long time. Since poisonous gases will be transported through them, the vapors generated as a result of combustion, there should be no loose connections at the junctions of the outlet channels.
Fans must withstand high temperatures for a long time. Based on the calculated data, the blades and systemsequipment must operate for at least half an hour at an air temperature of 300 to 600°C. They remove heat and create the necessary draft for the flow of oxygen inside the building. Placement of fans is permissible on the roof or walls of the house separately from other similar structures. When air is supplied at a speed of no more than 1 m/s, an optimal noise characteristic is created. Supply smoke ventilation VKOP1 is most often used in our country when designing such systems. Fans are most often equipped with anti-explosion technology. In order to avoid emergencies due to the ingress of foreign objects into the system, the channels are protected by special gratings or blinds. They can be made of aluminum or transparent polycarbonate, be single-layer or double-layer.
If the fan is located on the facade of the building, it is possible to paint the grille and make the equipment more inconspicuous. Modern manufacturers of wall-mounted types of fans provide for a small recession of the equipment into the base of the wall. This allows them to be integrated into the wall surface of the building as discreetly as possible. This maintains the impression of a closed appearance. When mounting a fan on a roof, its appearance is not as important as its adaptability to environmental conditions. You should not save on the quality of the system elements.
Valves
The combustion products removal system necessarily contains such an element as a supply smoke ventilation valve. It comes in the following varieties:
- normally open;
- normally closed;
- double action;
- smoke.
The normalized limit state of the valve is indicated by letters, and the numbers indicate the time limit in minutes for which this state will be reached.
There are two types of limit states for similar elements of the system. E - loss of density, I - loss of thermal insulation ability. If the data sheet contains the designation EI 60, then this should be interpreted as reaching the maximum fire resistance limit of up to 60 minutes. Moreover, such a state will be observed according to both signs, regardless of which of them manifests itself first.
Test mode for each type of valve is made under its own specific conditions. For the use of each device, there are a number of rules and regulations. Without them, it is impossible to install each instance in the existing conditions of the structure.
In supply ventilation, smoke valves are used, which are normally closed. In the event of a fire, they open, but only in areas of smoke and high temperature. In the remaining compartments, according to the calculations, they should remain in the closed position.
Inlet smoke ventilation, the device of which involves the use of smoke dampers, controls their damper with an electric drive without responding to temperature rise.
They can be used in conjunction with fire extinguishing systems and are used both during an emergency and after it. On flights of stairs, indoorsvestibules and corridors more often use normally closed valves. They differ from smoke only in the scope and test modes specified in the certificates.
The application of each type of valve must take into account the conditions in which it will operate.
Control Mode
Anti-smoke supply ventilation can be controlled in automatic and remote modes. The automatic mode is triggered when a fire detector detects a fire in the room. The remote system is activated by pressing the buttons in the fire cabinets or at the emergency exits from the floors.
These modes are selected based on presumed fire situations.
Compatibility of the system with other fire fighting equipment is also determined by the conditions of a particular building. System developers prescribe various possible fire scenarios, as well as ways to eliminate it.
