Improper ventilation can cause the rapid spread of fire and combustion products, death and property damage. Therefore, the calculation and installation of a system such as smoke ventilation is a very serious issue that does not tolerate frivolity. SNiP require the availability of appropriate chimneys at industrial and public facilities. They are calculated at the planning and design stage. This is especially important for facilities through which people are evacuated in emergency situations. The presence of smoke ventilation is mandatory in the elevator shafts, corridors, reception rooms, flights of stairs and walkways. The life of people depends on it.
general characteristics
Supply smoke ventilation is a complex of communications, devices, the combination of which ensures the supply of a sufficient amount of air to the premises at the time of ignition and after it. The ventilation system should provide the ability to evacuate people along the prescribed route.
All their routes should be accessible for movement. This contributes to a significant reduction in mortality due to poisoning by combustion products, eliminates panic during evacuation. The device of forced smoke ventilation assumes the autonomy and incoherence of the system with other air ducts and communications.
The main task of such a system is to ensure visibility on the route of people during evacuation, supply enough air to the stairwells, corridors, elevator shafts, aisles, etc. This can reduce the likelihood of loss of consciousness due to suffocation by carbon monoxide and significantly reduces the number of accidents during emergencies.
The need for a ventilation device
According to the Ministry of Emergency Situations, in the event of fires in residential or industrial premises, 70% of deaths are caused by suffocation by combustion products. Proper smoke ventilation is able to save many lives.
In Russia, as a result of fires in the premises, up to 10 thousand people die. For comparison, in China, with a population of 1.4 billion people, this figure is 1.5 thousand people. In the USA, with a large population as a result of fires, 3 thousand people die annually.
Therefore, the supply and exhaust anti-smoke ventilation is necessary when operating various buildings. In our country, the incidence of fire in 25-story buildings is no more than 20 times a year. Such a low indicator throughout the country clearly illustrates how effective modern, designed according to all the rules and examples, smoke ventilation of the supply type.
But in older buildings with a number of storeys from 17 to 25, 650 cases of fire with a fatal outcome in 20 cases happen annually. In 6-9 storey buildings, this figure reaches 350 people with 8 thousand cases of fires. But in 5-story houses, the number of victims is 9 thousand people annually. This is due to the lack of effective systems for the outflow of combustion products during a fire.
The principle of the system
According to the rules of SP 7.13130.2009, the installation of forced 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 effective evacuation and preservation of property in case of fire. The system also allows rescuers access to the building while containing the spread of fire products along the routes of people.
Supply 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 a control point. Automatic inclusion of the system will allow you to quickly respond to emergency situations. If the smoke ventilation of the supply type determines the situation of the onset of the fire, it opens the air intake valves and its functioning begins.
Work technology
Supply smoke ventilation, the calculation example of which provides for SNiP 2.94.05-91, does not allow the same channels of conventional ventilation systems to be used simultaneously with smoke exhaust. In the room, with the help of fans, an increased pressure is pumped, which pushes the combustion products from 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 the system plan, the installation locations of the smoke receivers, the parameters of the exhaust channels, and also the places in the building where the elements of the system are necessary are taken into account.
The established standards suggest that on one device for the removal of combustion products should be no more than 900 m 2 of the building area. Their location is assumed under the ceiling for convenience. If, for example, the room has a quadrature of 1600 m 2 , then an example of ventilation calculation may look like this:
1600/900 = 1.7
This means that for a given room it will be enough to make two compartments with autonomous communication channels.
Supply smoke ventilation of the staircase and corridors makes it possible to remove carbon monoxide to the roof through the vertical sections of the channels. For basement floors and basements of parking lots, parking, outflow of air through windows and doors of certain dimensions is possible. When calculating the supply of smoke control ventilation through an entrance gate or window openings, it should be noted that they must be geometrically correct, rectangular in shape. Pumps must cope with the load for an hour at a temperature of 600 ° C and 2 hours at 400 ° C. The hood should circulate at least 19 thousand m 3 of air mass.
Lift shafts and stairs
According to fire safety standards, all buildings with a height of 28 m or more must be equipped with a system such as fresh air smoke ventilation of the stairwell and elevator shaft. This is due to the length of equipment for the evacuation of people at the disposal of rescuers. Their stairs can reach a maximum of 28 m.
If the building rises above the ground level by more than 28 m, then the stairwells should be designed before the start of construction due to the non-smoldering type 2 or 3. Smoke protection in such buildings is simply vital.
The calculation of the supply of smoke protection should be carried out by qualified specialists who have certificates for the right to perform such work.
Application area
In addition to buildings with a height of 28 m, smoke ventilation must be used in corridors more than 15 m long without natural light, from common halls with access to non-smoke stairwells. If there is no natural light in the basement or on the basement, the supply smoke ventilation in the corridor must be carried out without fail. Similar systems are also used in structures where the distance from the door farthest 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 that open to these premises, combustion products must be removed without fail. Design of communications in the 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 m 3 , which should be divided into compartments.
Rules for design and installation
When calculating the parameters of the supply-type smoke exhaust system, the norms of maximum permissible pressure are taken into account when the doorways are open and closed, the average air flow from the room, as well as its temperature in the event of a fire. Supply smoke ventilation through the entrance gates, window openings or the roof should take into account the air temperature in summer and the strength of the wind. When calculating the area of openings for the movement of air masses is of importance.
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 standards and requirements.
When calculating the ventilation of the type presented, it is taken as the basis that air is supplied only from the outside using the appropriate air intake points. Therefore, they should be located at a sufficient distance from the smoke exit points.
Air must be supplied at low speed (not more than 1 m / s) and distributed evenly throughout the rooms. 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 boundary of the probable presence of smoke. Supply smoke ventilation, an example of which involves taking into account the flow of air masses, should ensure that the smoke does not reach the upper border of the door during the evacuation of people. Air leakage is calculated by the following formula:
G = F (ΔP / S) 0.5 , where
F is the flow area of the valve, m 2 ;
ΔP is the pressure drop across the closed valve, Pa;
S - specific gas permeability of the valve, m 3 / kg
Minimum S should be 1.6 · 10 3 m 3 / kg.
Recommended air outflow should be 9-11 m / s.
Equipment
Ventilation equipment must be suitable for the conditions in which it is likely to operate.
Ducts must be made of non-combustible materials that can withstand overheating for a long time. Since toxic gases will be transported through them, the vapors generated as a result of combustion should not have leaks at the junctions of the outlet channels.
Fans must withstand high temperatures for a long time. Based on the calculated data, the blades and equipment systems should work 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 not more than 1 m / s, an optimal noise characteristic is created. Forced 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 emergency situations due to the ingress of foreign objects into the system, the channels are protected by special grilles or blinds. They can be made of aluminum or transparent polycarbonate, be single-layer or two-layer.
If the fan is located on the facade of the building, it is possible to paint the grille and make the equipment more invisible. Modern manufacturers of wall-mounted types of fans provide a small recession of equipment in the base of the wall. This allows you to seamlessly integrate them into the surface of the wall of the building. This leaves the impression of a closed appearance. When installing the fan on the roof, its appearance is not so important as its adaptability to environmental conditions. The quality of system elements should not be economized.
Valves
The exhaust system of combustion products necessarily contains such an element as a valve for fresh air ventilation. It happens in such varieties:
- normally open;
- normally closed;
- double action;
- smoke.
The normalized limit state of the valve is indicated by letters, and by the numbers is the limit time in minutes for which this state will be reached.
There are two types of limit states for such system elements. E - loss of density, I - loss of thermal insulation ability. If the designation EI 60 is indicated in the data sheet, then this should be interpreted as reaching the limit of fire resistance up to 60 minutes. Moreover, this condition will be observed on both grounds, regardless of which of them appears earlier.
The test mode for each type of valve is made under its own specific conditions. There are a number of rules and regulations for using each device. Without them, you can not install each instance in the existing conditions of construction.
In the supply ventilation, smoke valves are used, which are normally closed. When a fire occurs, they open, but only in areas of smoke and high temperature. In the remaining compartments, according to calculations, they should remain in the closed position.
The supply of smoke control ventilation, the device of which involves the use of smoke control valves, controls their damper by means of an electric actuator without reacting to a rise in temperature.
They can be used in conjunction with fire extinguishing systems and are used both during and after an emergency. Normally closed valves are most often used on flights of stairs, in the premises of vestibules and corridors. They differ from smoke only in the scope and test modes specified in the certificates.
The use of each type of valve must take into account the conditions in which it will operate.
Control mode
Smoke supply ventilation can be controlled in automatic and remote modes. Automatic mode is triggered when a fire detects a room. The remote system is triggered by pressing buttons in fire cabinets or at emergency exits from floors.
These modes are selected based on the suspected fire situations.
The compatibility of the system with other fire extinguishing means is also determined by the conditions of a particular building. System developers prescribe various possible scenarios for the occurrence of a fire, as well as ways to eliminate it.
Having become acquainted with the device of such a system as smoke ventilation, we can conclude that not only the safety of property, but also the life of people in the room depends on its proper arrangement.