the tunnel ventilation system involves the use of a suspended ceiling with 2 partitions ( 2 ) above it , or 3 ducts with built - in fire - resistant flaps ( 4 ) and ( 5 ), the dimensions of which ensure a sufficient air intake velocity during aspiration and extend from one to the other lateral side of the duct , virtually from one to the other lateral wall of the tunnel . the flaps ( 4 ) in the lateral ducts open up along the longitudinal axis , and the flaps ( 5 ) in the middle duct along the axis perpendicular to the longitudinal axis of the duct . all flap drives are placed and can be maintained with the ventilation ducts also while traffic is in progress . the tunnel ventilation system in normal and in fire conditions , where at a given height the tunnel is divided by a horizontal partition ( 1 ) into traffic and ventilation parts , where the system contains a lateral escape passage ( 16 ) accessed from the traffic part through a pressure door ( 15 ) with springs , where the ventilation part is placed above the horizontal partition ( 1 ) and divided by vertical partitions ( 2 ) into three separate ventilation ducts , where the ventilation ducts , spaced 50 - 100 metres along the length of the tunnel , contain built - in rows of flaps ( 4 ) and ( 5 ), where the system in question further contains a system for the detection of tunnel conditions , a control system with a computer program for monitoring and control of the system in normal and in fire conditions , and at least three fans ( 3 , 3 a ) at the entry to the ventilation ducts on at least one portal . in the lateral escape passage ( 16 ) overpressure is provided by one or more fans ( 14 ) mounted in the engine rooms on at least one portal of the tunnel ; where the system further incorporates a tube - shaped tank ( 9 ) placed longitudinally underneath the carriageway , containing air with reduced oxygen content , of capacity sufficient for extinguishing 2 sections , where one section represents the space between 2 adjacent rows of the flaps ( 4 ) and ( 5 ), where in the event of fire air with reduced oxygen content is brought into the fire - affected section of the tunnel through a latticed duct ( 12 ) via explosive valves ( 10 ) and a distribution pipe ( 11 ); on at least one side of the tunnel the system contains fans ( 6 ) generating air screens ( 6 a ) that prevent the influx of fresh air from the environment into the tunnel in excess of the designed quantity , and sustain the stationary air motion in the tunnel in the event of fire . the fans ( 3 ) installed in the lateral ducts are axial / diagonal fitted with a system for separation of solid particles , whereas the fans ( 3 a ) installed in the middle duct are reversible / axial . the flaps ( 4 ) and ( 5 ) are fire - fighting electromotor or hydraulic flaps installed in the horizontal partition ( 1 ) in all three ventilation ducts by way of covering the whole width of the ceiling from one side of the tunnel to the other and , when closed , providing perfect sealing , where the flaps ( 4 ) in the lateral ducts open up along the longitudinal axis , and the flaps ( 5 ) in the middle duct along the axis perpendicular to the longitudinal axis of the duct . the system for the detection of conditions in the tunnel consists of probes ( 13 ) for measurement of o 2 , co concentrations , chambers and / or sensors for visibility measurement , probes ( 7 ) for temperature and smoke measurement , and probes ( 8 ) for measurement of air velocity , where through the measured parameters of the probes ( 13 ) and the visibility sensors the operation of the fans ( 3 , 3 a ) in the ventilation ducts is controlled , and through the measured parameters of the probes ( 8 ) at least one fan ( 6 ) is switched on / off to control the air screen ( 6 a ). furthermore , the lateral ducts have a larger profile , where all the mentioned ventilation ducts serve to ensure continuous aspiration of contaminated air out of the tunnel and smoke in the event of fire , where the middle duct in normal conditions at a heightened co concentration and diminished air visibility in the tunnel serves to bring added fresh air into the tunnel . in fire conditions the middle duct serves to remove contaminated air and smoke from the tunnel , where in the event of fire in the section located closer to one of the portals it serves for bringing fresh air . fig1 shows a tunnel cross - section where it can be seen that at a given traffic height the tunnel is divided by the horizontal partition ( 1 ) into traffic and ventilation parts . the ventilation part above the horizontal partition is divided by the vertical partitions ( 2 ) into three separate ventilation ducts , of which the lateral ducts have a larger and the middle duct a smaller profile . at the entry to the ventilation ducts on each portal at least three fans ( 3 , 3 a ) are installed , where the fans ( 3 ), installed in the lateral ducts are axial / diagonal fans , and the fans ( 3 a ), installed in the middle duct are reversible / axial fans . the fans ( 3 , 3 a ) are mounted in the engine rooms above each portal , where they can be maintained without interrupting traffic in the tunnel . fig3 shows the cross - section of the tunnel and air flow in normal conditions , where the lateral ducts serve for continuous aspiration of polluted air out of the tunnel at minimum level , and fresh air comes as a rule through the portals . in an emergency and in normal conditions , fresh air can be brought through the middle duct . if the o 2 , co values or visibility exceed the permissible limits in a certain section of the tunnel , fresh air is injected to that place via the middle duct . should the co concentration continue to rise or the visibility continues to diminish , the operation of the lateral fans will be automatically regulated , whereby the lowest possible electricity consumption , combined with highly efficacious tunnel ventilation , is ensured . the middle and lateral ducts contain the installed flaps ( 4 ) and ( 5 ) which in the event of fire provide perfect sealing , unlike the conventional shutters , a difference that greatly matters in relation to known solutions . looking at the cross - section , the flaps ( 4 ) and ( 5 ) are mounted on all three ducts , spaced 50 - 100 metres along the length of the tunnel . the flaps ( 4 ) and ( 5 ) are installed in the horizontal partition ( 1 ) by way of covering the whole width of the ceiling from one side of the tunnel to the other ( see fig1 ). fig2 and 3 show the tunnel cross - section with the escape passage ( 16 ) and the longitudinal section of the escape passage ( 16 ). in the partitioned lateral escape passage ( 16 ) overpressure is some 50 pa , and entries are provided from the tunnel &# 39 ; s traffic part through the pressure door ( 15 ) with springs at every 250 m . overpressure is produced by means of the fans ( 14 ) mounted in the engine rooms on the tunnel portals . the escape passage ( 16 ) replaces an additional service tunnel that for longer two - way tunnels must be built parallel to the road traffic tunnel . overpressure in the escape passage ( 16 ) prevents a possible penetration of contaminated air from the tunnel &# 39 ; s road section into the said escape passage ( 16 ). at each of the entries to the tunnel , air screens ( 6 a ) are created by special fans ( 6 ) to prevent air from entering the tunnel in excess of designed quantities . this is very important in areas characterized by strong winds , a great difference in elevations between the portals or diverse weather conditions at the location of the constructed tunnel . depending on the above mentioned conditions , the air screen ( 6 a ) may be provided at only one side of the tunnel . in fire conditions a very important role is played by the ventilation system and rapid detection of the place of fire . after detection of the exact place of fire , all flaps ( 4 ) and ( 5 ) automatically and hermetically close on all three ducts at both portals , except for the flaps ( 4 ) and ( 5 ) at the place of fire . the operation of the fans on the portals is controlled by measuring the air velocity ( 8 ) before the flaps ( 4 ) and ( 5 ), thus making sure that there is no longitudinal flow of fresh air ( its supply to the place of fire ) through the place of fire . the middle duct with the reversible fans takes care of it regardless of which part of the tunnel is affected by a fire incident . the flaps ( 5 ) in the middle duct also function as a partition , enabling the middle duct to operate at one side as an aspiratory , at the other side as a feeding system . along the tunnel and beneath the suspended ceiling a system is installed for accurate and rapid detection of conditions in the tunnel , including the location of fire . the detection system consists of a probe ( 13 ) for measurement of o 2 , co concentrations , chambers and / or sensors for visibility measurement , probes ( 7 ) for temperature and smoke measurement , and probes ( 8 ) for measurement of air velocity . the fans in the lateral ducts are controlled by the o 2 , co probe ( 13 ) and the visibility sensor , so that the supply of minimum required fresh air quantity coming through the portals is continuously provided and is carried away uniformly . should the values of measured parameters exceed the permissible limits , as the first step additional fresh air is injected via the middle duct to the respective places . should the values continue to raise , in the next step the operation of the lateral aspiration fans and thereby the supply of extra fresh air through the portals is intensified . if the values of harmful gases continue to rise , the middle duct will be used for aspiration or feeding . all three ducts will then provide maximum designed air carried away . what we have during any regime is the effect of continuous fresh air motion from the portal into the tunnel . the air velocity probes ( 8 ) are installed at every 300 to 500 m to control the fans mounted in the engine rooms on the tunnel portals in order to ensure equal fresh air velocity in normal conditions and in fire conditions . underneath the carriageway is a tube - shaped tank ( 9 ). the tank ( 9 ) contains air with reduced oxygen content , of capacity sufficient for extinguishing 2 sections , where one section represents the space between 2 adjacent rows of the flaps ( 4 ) and ( 5 ). in the event of fire , air with reduced oxygen content is blown via the explosive valves ( 10 ) and is brought into the tunnel space through latticed ducts ( 12 ), which at the same time send out a sound alarm signalling the moment when a vehicle crosses from one traffic lane to the other . once the stationary state is reached at the place of fire ( where there is no longitudinal air motion ), pressurized air with reduced oxygen content is blown , whereby oxygen concentration in the fire zone is reduced to 9 - 15 %, which makes any burning impossible and poses no threat to human lives . the pressurized air with reduced oxygen content is stored in the tank ( 9 ) placed longitudinally underneath the tunnel carriageway , of a volume sufficient to put out at least one fire . the pressurized air with reduced oxygen content in the tank ( 9 ) is let out via electromagnetic explosive valves ( 10 ), a distribution pipe ( 11 ) and lattice ducts ( 12 ) along the carriageway . the same also serve as a warning to drivers not to cross from one traffic lane to the other . mixing of air with reduced oxygen content and the existing air in the fire section occurs instantaneously and fills the whole fire section with the mixture in which the oxygen content ranges from 9 to 15 %. fire may also be extinguished with any other fire - fighting system , however , due to the air motion status in the fire section it is also possible to apply air with reduced oxygen content . the tunnel ventilation process in normal and in fire conditions requires a definition of air quantity needed for tunnel ventilation in normal and in fire conditions . the process involves the use of a suspended ceiling with 2 partitions above it , or 3 ventilation ducts with built - in fire - resistant flaps , the dimensions of which ensure a sufficient air intake velocity during aspiration and extend from one to the other lateral side of the duct , virtually from one to the other lateral wall of the tunnel . the lateral flaps ( 4 ) open up along the longitudinal axis , and the middle flap ( 5 ) along the axis perpendicular to the longitudinal axis of the duct . all flap drives are placed and can be maintained with the ventilation ducts also while traffic is in progress . the fans are mounted in the engine rooms above each portal , where they can be maintained without interrupting traffic in the tunnel . at 50 m distance from the entry to the tunnel the velocity v 2 , 3 of air entering through the portal is measured and , depending on the designed velocity v 1 , the air screen fans ( 6 ) are controlled ; the air screens allow entry of fresh air through the portals into the tunnel only up to the designed maximum permissible air quantity q max that the installed fans can remove . along the tunnel and under the suspended ceiling a system is installed for accurate and rapid detection of conditions in the tunnel , including the location of fire . the system comprises video surveillance , smoke analysis , thermosensitive cable , etc . the operation of the fan ( 3 ) in the lateral ducts is controlled in dependence on the parameters of the probes ( 13 ) for o 2 , co and visibility measurement . the fans ( 3 ) in the lateral ventilation ducts generate underpressure by which continuous supply of minimum required air quantity coming through the portals is provided . if the value of measured o 2 and co concentrations and measured visibility rises / falls beyond permissible levels , as the first step additional fresh air is injected via the middle duct to the respective places . should the values continue to rise , in the next step the operation of the lateral aspiration fans ( 3 ) and thereby the supply of extra fresh air through the portals is intensified . if the values of harmful gases continue to rise , the middle duct will be used for aspiration or feeding . all three ducts will then provide maximum designed aspirated air . what we have during any regime is the effect of continuous fresh air motion from the portal into the tunnel . in the conditions of minimum traffic the aspiratory ventilation in the lateral ducts must operate at minimum level and thereby ensure the effect of continuous fresh air motion from the portal into the tunnel at a velocity approximating 0 . 3 m / s . this is a requirement for the ventilation system , after the location of fire is determined , to fulfil its function very quickly , all due to the underpressure in the lateral ventilation ducts . the normal and fire ventilation system also prevents a change in microclimate at both sides of the tunnel , because the air flowing into the tunnel returns to the side where it was drawn in . due to uniform and continuous aspiration of polluted air through the lateral ducts , the internal walls of the tunnel will remain clean for a prolonged time , which means less cleaning work inside the traffic part of the tunnel . the ventilation ducts can be cleaned during the operation of the ventilation system . high energy efficiency of the system operating in accordance with traffic conditions in the tunnel . the fans are controlled by rpm regulators and they use only the amount of energy needed for effective operation . as soon as the location of fire is determined , on all three ventilation ducts all the flaps ( 4 ) and ( 5 ) will close from the portal to the flaps ( 4 ) and ( 5 ) which are in close proximity to the fire zone and are fully open . in addition to the system for the detection of tunnel conditions , at every 300 to 500 m the air velocity probes ( 8 ) are installed which control the fans ( 3 , 3 a ) mounted in the engine rooms on the tunnel portals in a way ensuring equal velocity v 1 and v 2 of fresh air coming from the portals to the open flaps close to the fire zone . the aspiration capacity of the fans in the engine rooms are changing with the measuring of air velocity in the tunnel . if , looking at the tunnel &# 39 ; s longitudinal section , the fire zone is situated asymmetrically , the middle duct will provide sufficient aspiration at the shorter side and at the side farther out will by fresh air facilitate the equalization of the above mentioned air velocities . this is achieved by the design of the flap ( 5 ) which during opening causes the partitioning of the middle duct . the flap ( 5 ), which is used for that purpose , should be at least so much away from the fire zone that the position of the velocity measurement probe ( 8 ) is between the flap and the fire zone . the system as a whole operates so that the air motion alongside the fire looks like a reverse air screen which does not allow entry of fresh air to the fire zone and the spread of smoke from it . what is achieved is that there is no longitudinal air motion in the fire zone , the fire smoke instead moves towards the open flaps ( 4 ) and ( 5 ) from both sides . smoke and fresh air get mixed and are carried away through the ducts via the open flaps ( 4 ) and ( 5 ) to the fan , whereby it is additionally routed by the closed flaps ( 4 ) and ( 5 ) which are 100 % airtight . while travelling through the ducts , the mixture cools off and is discharged into the atmosphere by the fans ( 3 , 3 a ). it is possible to install filters for purification of the polluted air in both normal and fire conditions . the fans ( 3 , 3 a ), owing to the 100 % airtight flaps ( 4 ) and ( 5 ), need not be dimensioned for an additional air quantity that should otherwise be provided because of the permeability of the usually applied shutters . upon closing the flaps ( 4 ) and ( 5 ) from the portals to those in immediate proximity the fire zone , fire is isolated and extinguishing can go ahead . due to the stationary state in the fire zone between two adjacent rows of flaps , it is possible to apply extinguishing by means of air with reduced oxygen content . air with reduced oxygen content in the tube - shaped tank ( 9 ) is positioned underneath the carriageway in the whole length of the tunnel . the capacity of the tank ( 9 ) suffices for fire fighting in 2 sections . one section is a space between 2 adjacent rows of the flaps ( 4 ) and ( 5 ). air with reduced oxygen content is brought through the latticed ducts ( 12 ), which at the same time send out a sound alarm signalling the moment when a vehicle crosses from one traffic lane to the other . mixing of air with reduced oxygen content with the existing air in the fire section occurs instantaneously and fills the whole fire section with the mixture , the oxygen content of which ranges from 9 to 15 %. fire may also be fought with any other fire - fighting system . the ventilation and fire - fighting process in normal and in fire conditions defines through the system the maximum permissible designed air quantity q max for tunnel ventilation in normal conditions and in fire conditions , where the process involves : measurement of air velocity v at maximum distance of 50 m from the entry to the tunnel , and switching of the air screens ( 6 a ) on and off by means of the fan ( 6 ) allowing entry of fresh air through the portals into the tunnel only up to the designed maximum permissible air quantity q max that the installed fans ( 3 , 3 a ) can remove , and simultaneous measurement of air velocity v in the tunnel at every 300 to 500 metres , where , depending on the air velocity v , the probes ( 8 ) control the operation capacity of the fans ( 3 ) and ( 3 a ) mounted in the engine rooms on the tunnel portals , and simultaneous measurement of o 2 , co values and air visibility in the tunnel by means of the probes ( 13 ), where the probes ( 13 ) control the fans ( 3 ) and ( 3 a ), and , depending on the values of the measured parameters , uniform aspiration of air out of the tunnel by means of the lateral ventilation ducts , whereby the supply of minimum required fresh air quantity is continuously provided through the portals , temperature and smoke measurement by means of the probes and detection of the location of fire conditions , and control of the opening of the flaps ( 4 ) and ( 5 ) in the ventilation ducts in dependence on the measured temperature and smoke parameters where all the mentioned previous steps are functionally interconnected in a way that in the tunnel the designed air velocity v 2 is established whether in normal or in fire conditions ; where the lateral ventilation ducts serve for continuous removal of contaminated air from the tunnel or of smoke in the event of fire ; where the middle ventilation duct , in the conditions of higher / lower o 2 , co concentration and diminished air visibility in the tunnel , serves to bring into the tunnel additional fresh air , whereas in fire conditions serves to remove polluted air and smoke from the tunnel , where in the event of fire in a section closer to one of the portals serves to supply air ; where in both normal and fire conditions continuous fresh air supply is provided from the portals to the tunnel , where in fire conditions air is brought from the portals to the flaps ( 4 ) and ( 5 ) placed close to the fire - affected section of the tunnel . if at a certain place in the tunnel the values of measured parameters are outside the permissible limits , as the first step additional fresh air is injected via the middle duct to the respective place ; should the values continue to depart from the permissible limits , in the second step the operation of the lateral aspiration fans ( 3 ) and thereby the supply of extra fresh air through the portals is intensified ; should the values continue to depart from the permissible limits , in the third step the middle duct will perform the aspiratory function . the measured parameters are oxygen concentration , co , air visibility , air velocity v , temperature , smoke and exhaust gas concentration , as well as any combinations of two or more parameters . after detection of the exact place of fire , all flaps ( 4 ) and ( 5 ) automatically and hermetically close on all three ducts at both portals , except for the flaps ( 4 ) and ( 5 ) at the fire . after detection of fire conditions in a section nearer to one of the portals , the flap ( 5 ) in the middle ventilation duct will hermetically close the duct profile , where the said flap ( 5 ) is at least so much away from the fire zone that the air velocity measurement probe ( 8 ) is placed between the flap ( 5 ) and the fire , whereas the other flaps ( 5 ) in the middle duct are down and the fans ( 3 a ), which are farther away from the fire zone , operate in such a way that they bring fresh air , whereas the fans ( 3 a ) nearer to the fire zone operate in such a way that they carry air and smoke away from the fire zone , where the fans ( 6 ) of the air screens ( 6 a ) start operating if air velocity v on at least one of the portals rises beyond the designed velocity v 2 . after detection of fire conditions in a section nearer to the middle of the tunnel , the adjacent flaps ( 5 ) bounding the fire zone will close the duct profile in such a way that they will direct the air and smoke flow through the middle ventilation duct towards the tunnel exit , whereas the other flaps ( 5 ) in the middle duct are down , and the fans ( 3 a ) on both portals operate by way of carrying air and smoke away from the fire zone , where the air screen ( 6 a ) starts operating if air velocity v on at least one of the portals rises above the designed velocity v 2 . in the lateral ducts , after detecting fire conditions in any area of the tunnel , the adjacent flaps ( 4 ) bounding the fire zone will restrict the profile of the lateral ducts by way of directing the air and smoke flow through the middle ventilation duct towards the tunnel exit , whereas the other flaps ( 5 ) in the middle duct are down , and the fans ( 3 a ) on both portals operate by way of carrying air and smoke away from the fire zone , where the air screen ( 6 a ) starts operating if air velocity v on at least one of the portals rises above the designed velocity v 2 . once fire has been isolated , between two adjacent rows of the flaps ( 4 ) and ( 5 ) pressurized air with reduced oxygen content is simultaneously brought from the tank ( 9 ) into the fire zone through the latticed duct ( 12 ) via the explosive valves ( 10 ) and the distribution pipe ( 11 ), where the mixing of air with reduced oxygen content and thereby fire extinguishing occurs instantaneously . fire fighting can be performed with any other agent suitable for the purpose . the operation capacity and direction of the fans ( 3 , 3 a ) is controlled by measuring the air velocity v and the o 2 , co concentrations and air visibility in the tunnel in dependence on the designed air velocity v 2 and at least one air screen ( 6 a ) is switched on / off , whereby the influx of the designed air quantity from the environment into the tunnel is regulated and the designed air motion is achieved in normal conditions , in the conditions corresponding to the values of the measured parameters outside the permissible limits and in fire conditions prevailing in the fire zone . in the fire zone , after attaining the positions of the adjacent flaps ( 5 ) in a way that they close the middle duct or direct the air flow in all three ventilation ducts and by regulating the operation capacity and direction of the fans ( 3 , 3 a ) and switching on / off at least one air screen ( 6 a ), a state without longitudinal air motion in the fire zone will be achieved . the above described fire ventilation process ensures efficacious fire fighting for persons found in the fire zone and unimpeded and safe escape for passengers in the tunnel to an area of fresh air , no matter in which direction they move . firemen and rescuers can thus reach the fire zone together with fresh air .
a tunnel ventilation system located in an upper section of a tunnel has a ventilation section divided into two or three ventilation ducts . one or more of the ducts are connected to reversible fan units so the ducts can serve as either an air infeed or an air exhaust system . the ducts contain a series of remotely controlled flaps which can be opened to ventilate different tunnel zones or closed to isolate other parts of the tunnel . air blowers at tunnel entrances create an air screen that prevents unintended air circulation into the tunnel . heat , smoke and other sensors and a software control system enable the system to detect smoke and fire , then to isolate and control ventilation in the fire zone . a fire suppression system using low oxygen air or other fire suppression fluids to blanket and smother the fire operates in conjunction with the ventilation system .