Design of a smoke protection system for a closed car park

. Today, this topic is relevant due to the fact that smoke and toxic combustion products that are released during fires are the main cause of death. According to statistics, about 42% of victims of smoke exposure get severe poisoning, eventually leading to death. At the same time, 70% of all those killed in a fire die precisely from the effects of smoke. The article discusses two types of smoke removal systems for closed car parks (traditional and impulse), analyzes the design features of these systems, performs calculations and evaluates the profitability of these systems in terms of energy consumption and economic costs.


Introduction
Currently, closed-type parking lots have become an integral part of the infrastructure of various cities of the world [1][2][3][4][5][6], due to the rapid growth in motorization, while the number of parking spaces is lagging behind.In closed car parks, there are risks that are associated with the release of harmful substances from the exhaust gases of cars into the surrounding air, thereby creating high fire loads in emergency situations.
Today, this topic is relevant due to the fact that smoke and toxic combustion products that are released during fires are the main cause of death.According to statistics, about 42% of victims of smoke exposure get severe poisoning, eventually leading to death.At the same time, 70% of all those killed in a fire die precisely from the effects of smoke.
Of particular importance in the modern world is given to energy and economic assessments of various engineering systems of buildings, but on the basis of which profitable options are selected [7][8][9][10][11].

Methods
The parking lot is intended for temporary storage of passenger cars of visitors to the multifunctional center.Passenger cars with a size of not more than 1900x5000 mm, equipped with gasoline engines with a fuel injection system.The total capacity of the car park is 22 cars, including two parking spaces for MNG.Storage of cars of the arena type -1 parking space.The parking lot is located in a single hall, conditionally divided into 2 storage areas.The height of the parking lot is H= 3.3 m.The power of the fire Qp= 4.5 MW.Outside air temperature TP 26 ℃.The height of the smoke-free zone Z= 2 m.
The area of the smoke exhaust opening is close to the projection area on the plane of the floor of a car, and therefore the design of a smoke exhaust system with natural draft induction is not an appropriate solution.Thus, a design decision was made to use a smoke exhaust system with mechanical draft induction.
When installing elevator shafts that communicate with the underground and aboveground parts, it is necessary to provide for separate air supply, respectively, to the upper and lower parts of the protected elevator shafts.
It is necessary to provide a separate air supply to the upper and lower parts of the elevator shafts associated with the underground and aboveground parts.However, in some cases where a single tambour lock is used on the parking floor, air supply to the lower part of the elevator shaft can be omitted if the unit is located on the main floor of the elevator hall and is equipped with an independent smoke ventilation system.Since the hydraulic resistance of the elevator shaft is not large, we can neglect the pressure loss along the height of the elevator shaft and assume that the pressure along the height of the elevator shaft does not change.
The outdoor air flow rate for supply smoke ventilation should be calculated provided that an overpressure of at least 20 Pa is provided.
The advantage of channelless smoke ventilation systems is that the upper part of the volume is freed from long and rather large channels.There are more cons.Firstly, the operation of such a system is effective only if the ceiling of the room is smooth, free from various engineering systems, in particular from pipelines, signs of emergency exits and other signs that are located in any underground parking lot.Secondly, it is not clear how the system will work in the presence of building jumpers.Thirdly, this system may work well only for open car parks, i.e. without external enclosing structures.In this case, it will be necessary to additionally provide climate systems that will take into account the direction of the wind and reverse the draft of the fans.And for closed parking lots, including underground ones, in any case, combustion products will have to be brought to the smoke intake device.Fourthly, this system, due to the fact that it is no longer concentrated smoke that is removed, but a certain gas-air mixture, should have an enormous productivityaccording to various estimates, from 100,000 to 300,000-400,000 m 3 /h.

Results
For a traditional smoke exhaust system, as a result of calculations, the consumption of combustion products was 53,000 m 3 /h.
For a pulsed smoke exhaust system, as a result of calculations, the performance of jet fans was 439,058 m 3 /h.
Taking into account the maximum performance of the selected fan model 9440 m 3 /h, installation of 47 fans is required.The estimated number of fans cannot be located in the car park.
It can be seen from these calculations that the use of a jet smoke exhaust system for small car parks is not advisable.
To determine the cost of construction and installation works, a local estimate is drawn up.The estimate is compiled by the basis-index method.The cost of the object, determined by local estimates, includes direct costs, overhead costs and estimated profit.
Direct costs take into account the cost of wages for workers, materials, products, structures for the operation of construction machines.Overhead costs take into account the costs of construction and installation organizations associated with the creation of general conditions for construction, its maintenance, organization and management.
The estimated profit is the amount of funds necessary to cover the individual costs of construction and installation organizations for the development of production, the social sphere and material incentives.
The cost of building materials, parts and structures required for a traditional smoke exhaust system are presented in Table 1.The cost of building materials, parts and structures required for a pulsed smoke exhaust system are presented in table 2.

Discussion
The rate of fire propagation depends on the ability of the material to quickly heat up and ignite, which is determined by its thermal conductivity.There are three types of heat transfer during a fire: conduction, convection and radiation.Convective heat transfer occurs due to the movement of heated gases, which rise up due to their lower density compared to air.In open space, the movement of gases does not affect the spread of flames on the ground, and the nature of their movement (laminar or turbulent) determines how combustible gases mix with the oxidizer and how combustion occurs.Radiation is the determining type of heat transfer in a fire, since its action can manifest itself over long distances.When a heat flux passes through a gaseous medium, it is weakened as a result of the absorption and scattering of radiant energy.
In order to maintain combustion in a fire, it is necessary to constantly supply fresh air to the area where chemical reactions take place, as well as to remove the resulting gases from there, that is, to ensure gas exchange.If a fire occurs in an open area, then gas exchange occurs between the zone of chemical reactions and the environment and is limited mainly by the diffusion of the oxidizer.In case of fires in premises, gas exchange is actually the ventilation of premises through openings in building envelopes, caused and regulated by combustion and heat exchange processes.However, the more fresh air is supplied, the faster combustion occurs, more heat is released and the fire spreads faster.
Thus, a complex of interrelated processes that determine such a complex phenomenon as a fire can be represented as a conditional "fire triangle": combustion -gas exchangeheat exchange.
During a fire, the movement of smoke in a room is the same as the movement of air under normal conditions.The smoke that accumulates under the ceiling gradually descends and passes through the openings in the building envelope, spreading to neighboring rooms and emergency exits.This can pose a danger to people who are inside the building.Smoke spreads through various openings and channels in technological, engineering and electrical equipment.The movement of smoke is determined by pressure drops, temperature, the effect of wind on building envelopes and the operation of ventilation systems.
When a fire occurs, the fire does not immediately cover the entire building, but spreads through it at a certain speed, gradually increasing the area of the fire.The evacuation of people should take place in the initial stage of the fire, while the fire has not yet flared up and covered a significant area.The evacuation of people occurs along the evacuation routes, which include doors, corridors, stairs and elevators, along which the evacuating human flow moves.
From a burning room, smoke can penetrate along the escape routes, to prevent this, special measures must be taken, since the escape routes can be filled with smoke, and people will not be able to move along the corridors.Therefore, measures to ensure smokefree escape routes are extremely important.The smoke exhaust system is divided into two types: passive and active.Passive, based on the architectural solutions of the building itself.That is, planning and design solutions are created in which smoke cannot quickly spread throughout the building.Active is the technical smoke removal system itself, based on fans, air ducts, valves and other elements.
For smoke protection systems and fresh air supply to the building, it is necessary to install fans in separate rooms separated by fire barriers that will not be used for other purposes.In addition, fans can be installed on the roof and outside of the building, protected from unauthorized access.To ensure excess pressure in the system, it is necessary to calculate the air flow rate for the inflow of at least 20 Pa, but only in those areas where the outdoor air temperature does not fall below minus 40 °C (parameters B).
The use of pulsed (jet) smoke ventilation: pulsed smoke ventilation differs from the classic smoke exhaust system in that it does not have air ducts.Instead, the additional impulse transmitted to the subceiling layer of flue gases moves the combustion products from the fire to the smoke inlets of the exhaust shafts.The subceiling layer of flue gases is moved by means of jet fans.In this case, both axial and radial fans are used.
The location of the jet fans in the smoke ventilation system must be installed in such a way as to prevent the spread of smoke to a distance of more than 10 meters from possible sources of ignition, in the opposite direction to the air flow.When designing, it is necessary to take into account the presence of beams that can affect the movement of flue gases.In addition, the system must continue to function even if the pulse fan fails due to a fire, and the air inlets must be large enough to prevent the formation of closed air flows in the car park.The supply velocity must not exceed 2 meters per second.
When using a jet ventilation system for the purpose of smoke protection of closed car parks, partial smoke removal from the premises is possible by limiting the spread of flue gases over the width of the car park at certain speeds of air jets coming out of the fans.
When a fire source is detected, fire detectors turn on jet fans, and it is possible to turn on not all fans in the room, but only those whose operation will prevent the spread of flue gases from the combustion source and move them to the smoke inlets of the exhaust shafts.The speed of air jets should be higher than the speed of flue gases at the boundaries of the ventilated area to prevent the spread of smoke to the rest of the room.
Another advantage of jet ventilation in closed car parks is the ability of this system to work in reverse mode.Depending on which part of the room the fire broke out in, with the help of impulse fans, the combustion products move in the appropriate direction to the smoke inlets of the exhaust shafts, leaving the other part of the room smoke-free.In this case, all fans must be of the reversible type, including supply and exhaust.
The efficiency of pulsed smoke ventilation can be affected by a significant number of factors: the diameter and speed of the jet at the outlet of the jet fan, the number, draft and performance of fans, the geometric parameters of the room, the heat output during a fire, the smoke generating capacity of the fire load, the size of the exhaust openings and the performance of the exhaust fans and etc.

Conclusion
Two types of smoke removal systems for closed car parks (traditional and impulse) were considered, an analysis was made of the design features of these systems, calculations were made and estimates were made of the benefits of these systems in terms of energy consumption and economic costs, in accordance with which a traditional smoke removal system was selected and designed for a multifunctional center.

Table 1 .
The cost of building materials, parts and structures required for a traditional smoke exhaust system

Table 2 .
The cost of building materials, parts and structures required for a pulsed smoke exhaust system