1 . Overview
With the development of engineering construction and transportation as well as the continuous demand for human production and living, the mileage of traffic tunnels built in various countries around the world has been rapidly extended. According to statistics, in 2000 the whole of Europe regional transport network of tunnels stretching over 10000km; our country in the Second National Highway census, the construction above the county level highway tunnel length of nearly 550km. In the past 10 years, due to the increasing traffic flow and road conditions as well as the complexity of transported goods, the fire risk of traffic tunnels has increased, causing many serious fire accidents. For example, 1999 March 24 occurred between France and Italy MontBlanc tunnel fire, the death of 41 people, 36 cars were destroyed; tunnel fire in Austria TauemMotorway May 29, 1999 occurred, the death of 12 people and injuring 50 people; November 11, 2000 Austrian Kabu Lun mountains over mountain cable car fire, 155 people died, 18 were injured.
Tunnel fires not only seriously threaten human life and property safety, but also cause huge damage to transportation facilities and human activities. Therefore, in the past 20 years , various countries have invested considerable effort in the tunnel fire behavior and fire protection research. They have achieved certain results and formulated some technical requirements and standards.
Traffic tunnels generally include road tunnels, railway tunnels and subway tunnels, and other urban traffic tunnels. Different types of tunnels have no essential difference in fire protection. In principle, they should consider the possible fire scenes according to the vehicles and goods allowed by the tunnel, so as to determine reasonable and effective fire safety measures. According to relevant studies, the fire risk of highway tunnels is 20-25 times that of railway tunnels . Therefore, on the basis of analyzing and summarizing related research at home and abroad, this paper presents some views on the design, research and development of fire safety in China's highway tunnels and urban traffic tunnels.
2 . Research Status of Fire Prevention in Tunnels at Home and Abroad
Since the 1980s , research has been carried out abroad in the following aspects: the combustion characteristics of vehicles, the effect of simulated ventilation on vehicle combustion, the increase in smoke, the comparison of normal fire loads with wood fires and heptane fires, and smoke Analyze the generation of toxic components, fire growth in tunnels, numerical simulation of smoke movements, performance of tunnel lining in fires, psychological and behavioral factors of drivers in tunnels, and relevant influencing factors, fire rescue methods and strategies, and self-help principles, etc. . According to the study, the scale of tunnel fires mainly depends on the type of vehicles. The temperature and fire loads that can be reached inside the tunnel can be seen in Table 1 .
Vehicle Type Maximum Temperature °C Maximum Heat Release Rate ( MW )
Car 400-500 3-5
Bus 700-800 15-20
Trucks (excluding oil tankers) 1000-1200 50-100
China has also done a lot of research on numerical simulation of flue gas in tunnels, evaluation of lining bearing capacity, and distribution of temperature field in tunnels.
2 . 1 Technical requirements and standards in tunnel design at home and abroad
In China, there are currently national standards published in 1992 , “Code for the Design of Underground Railways†(as amended ) , “Standards for the Design of Railway Tunnels†issued by the Ministry of Railways in 1985 , and “ Standards for the Design of Highway Tunnels†issued by the Ministry of Transport in 1989. "(under revision). These standards partially stipulated the fire prevention and evacuation of subways, railway tunnels and mountain highway tunnels, but they were not perfect. They did not provide for the fire protection design of traffic and sightseeing tunnels in urban areas. At present, the national standard "Code for Fire Protection in Architectural Design" is supplementing the fire protection design requirements for urban traffic tunnels ( except subways ) .
In foreign countries, the Netherlands has compiled the “ TNO Report 98-CVB-R1161 Tunnel Fire Prevention†and the TNO Test Standard “Tunnel Fire Test Methodsâ€, which stipulates the tunnel fire scene determination method and relevant fire safety engineering design methods and the fire resistance test method of the tunnel structure. . Germany in 1994 developed a "RABT highway tunnel facilities and operational criteria", in which the scale tunnel fire have made provisions; in 1995 developed a "ZTV- tunnel, tunnel construction on highway supplementary technical provisions and guidelines" where the first 10 The chapter “Building Fire Protection†stipulates the temperature rise curve inside the tunnel and the fire protection measures that should be taken for the building structure and its internal systems. The United Kingdom developed the “ BD78/99 , Road and Bridge Design Manual†to guide the use of fire safety engineering methods to design fire protection tunnels. The American Fire Protection Association has developed the " NFPA502 Highway Tunnels, Bridges, and Other Limiting Highway Standards," which specifies fire protection requirements for different types of tunnels, and requires that tunnels over 240m in length should be based on specific tunnel design parameters ( such as length, cross-section, grading). , dominant wind, traffic flow direction, cargo type, design fire parameters, etc. ) The ventilation facilities are designed using engineering analysis methods. Japan has established the “Standard for the Establishment of Emergency Facilities for Road Tunnels in Japan’s Construction Provinceâ€, which classifies the tunnels according to the length of the highway tunnel and the amount of vehicle traffic, and stipulates fire protection requirements for highway tunnels according to different levels.
2 . Several foreign tunnel structure 2 of the test temperature curve
Although countries have used the temperature - time curve specified in IS0834 international standards for testing the fire resistance of building components , studies have shown that such as hydrocarbon fuels or other chemical substances such as automotive petrol and vehicle-carried petrochemical products, liquefied petroleum gas, etc. The combustion release rate, firefield temperature gradient, and possible maximum ambient temperature are very different from those described by this warming curve. Therefore, the structural design and fire protection in the tunnel need to adapt to this situation. For this reason, European countries have developed a series of time / temperature curves for different tunnel fire types .
The RWS curve was developed on the basis of the research results of the TNO laboratory in the Netherlands in 1979 . It assumes that under the most unfavorable fire conditions, the latent heat value is continuously burning for 120 minutes for a 300 MW fuel tanker or tanker , and assuming 120 minutes later the firefighters have already controlled the fire, approaching the fire source and starting to extinguish the fire source. This curve mainly simulates the combustion of the tanker in the tunnel. The initial temperature rises rapidly, and then gradually decreases as the fuel decreases.
In Switzerland, due to the longer length of the tunnel and away from the fire brigade , the design time was extended to 180 minutes when the RWS curve was used . In addition, the tunnel heating curve adopted by France is similar to RWS , except that the highest point temperature is 1300 °C.
The hydrocarbon combustion curve mainly simulates fires that occur in more open areas where heat can be emitted.
The RABT curve was developed in Germany through the results of a series of experiments, such as the EUREKA project. This curve assumes that the temperature of the fire field rapidly rises to 1200 °C within 5 min and cools for 110 min after continuing for a short time .
This curve simulates the warming up of a simple truck fire, but for some special types of fires, the duration of the maximum temperature can be extended to 60 minutes or more, and then cooled for 110 minutes .
3 . Tunnel Fire Scene and Fire Development
In the past 20 years, a large number of studies have been conducted internationally to determine the types of fires and fires that may occur in tunnels and other underground buildings, some of which are conducted in real, abandoned tunnels and laboratory conditions. Studies have shown that the heat release rate of highway tunnel fires increases rapidly within 10-15 min after a fire , and the temperature rises rapidly. Most fires can reach temperatures above 1000 °C in 5-10 minutes . The tunnel fire scenario mainly depends on the type of vehicle.
The heat output of a fire is dominated by thermal radiation and determines the temperature; while the heat loss of a smoke layer is dominated by convection, and has little effect on temperature, so the heat obtained at high temperatures always exceeds the amount of heat lost. As the tunnel is a relatively closed underground structure, most of the heat is absorbed by the tunnel roof and walls. At the same time, the hot smoke layer and the top wall transmit heat to the flame through radiation and aggravate the fire development rate. Therefore, if a tunnel fire cannot be extinguished during the ignition phase, it will quickly develop into a fully developed fire, accompanied by rapid temperature rise.
Typical fire scenarios can be assumed to be: multiple car fires, bus fires, cargo truck fires, and flammable liquids or oil / gas tanker fires. The fire duration, heat release rate, etc., vary greatly from subject to subject. For multiple small and car fires ( taking four cars as an example), the maximum value of 12 MW can be reached after 30 seconds and lasts for about 60 minutes . The bus fire reached a maximum of 25 MW after 10 minutes and lasted for about 90 minutes . Fire trucks around 5min can reach a maximum of 180MW for about 60min, flame propagation up to 40-60m.
The main influence of fire on the ambient temperature is thermal radiation, whereas the smoke layer is dominated by convection. As the tunnel is a relatively closed underground structure, most of the heat released during the fire will be absorbed by the tunnel roof and wall. The hot smoke layer and the hot top wall will also transmit heat back to the flame through radiation, exacerbating the fire. Therefore, if the tunnel fire cannot be extinguished during the ignition phase, it will rapidly develop into a fully developed fire and cause the temperature in the nearby area to rise rapidly.
In the Sydney Harbour Tunnel study, researchers defined the car fire as 3MW (a = 0.0115) , the truck fire as 10MW (a = 0.18) , the dangerous goods truck as (a = 0.18) , and the road tanker as 50MW (a =0.18) . Different fire growth parameters have a greater impact on the dangerous temperature field and the smoke diffusion zone. For example, ordinary cars (0.1kW/s2) and small trucks (0.3kW/s2) have little effect on the temperature field in the hazardous area and the change of the smoke diffusion zone, but petroleum tankers, liquefied petroleum gas tankers (1.54kW/s2) - 10.5 kW/s2), etc. can quickly increase the temperature field in the hazardous area and spread the smoke very quickly.
4 . Tunnel fire safety engineering design
A tunnel is a relatively closed space with limited direct communication with the outside world. The limited escape conditions in the tunnel and the removal of smoke from the hot smoke make the tunnel fire have features such as rapid increase in ambient temperature after combustion, long duration, large fire range, difficulty in fighting fires, and difficulty in entering, which increases the lives of evacuees and rescue workers. Danger, tunnel linings and structures are also damaged, and their direct and indirect losses are huge. Therefore, fire protection measures must be considered in tunnel design.
Fire hazards in tunnels mainly include passengers’ luggage, dangerous goods, and vehicles and tunnels themselves.
The fire safety control targets of the tunnel mainly include: providing possible evacuation facilities, reducing casualties; facilitating rescue and extinguishing operations; avoiding cracks in the concrete lining of the tunnel and protecting the tunnel structure and equipment, reducing the tunnel repair and the interruption of tunnels. The damage caused.
In the design of fire protection for highway tunnels, the fire resistance and collapse prevention of the structure should be taken into consideration. The combustion performance of the materials in the tunnel should be reduced. Fire detection and alarm and monitoring signal systems should be set up. Planning and setting up emergency systems for separation, rescue, evacuation and shelter, and flue gas control System and so on.
4 . 1 Structural protection of the tunnel
Fire in the tunnel is often longer duration, such as MontBlanc tunnel fire continued 55h, 36 vehicles were involved in the fire. Studies have shown that when the surface of a concrete structure is heated, it will burst, and deep cracks will occur after the concrete is cooled. The higher the load pressure of the structure and the moisture content of the concrete ( including the physical water content and the molecularly bound water ) , the greater the probability of cracking, and even if polypropylene fiber is added to the concrete mix, there will be no significant improvement. Unprotected concrete, if its mass moisture content exceeds 3% , will burst within 5-30 minutes after encountering high temperature or flame , and the depth may even reach 40-50mm . This is the main cause of tunnel collapse. Generally at 150-200 °C, the concrete surface begins to burst.
Tunnel construction has a round, rectangular or arched shape. The failure of the rectangular structure is usually caused by the temperature of the concrete or its reinforcing steel leading to premature sagging plastic bending moment, the rectangular tunnel than the circular tunnel by the pressure load is smaller, resulting in a lighter burst. Reinforced steel bars in circular tunnels do not undergo tension under sagging bending moments and are only subjected to pressure loads. Shield-type circular tunnels usually use high-grade concrete with a grade of C50 , and are highly likely to burst in fire.
After the concrete bursts, it will not only directly threaten rescue and escape, but also make the reinforcing steel directly exposed to the fire and reduce the cross-sectional area of ​​the bearing structure. Therefore, the fire resistance design of the tunnel structure should take into account the maximum temperature, temperature rise characteristics, and fire behavior of the structure that can be achieved within the tunnel structure. Determine the appropriate fire scale and time - temperature curve, and ensure that the tunnel structure is under the specified type of fire conditions. The integrity and stability.
The fire protection of the tunnel structure can be generally implemented by adding polypropylene fiber to the concrete or by installing a fireproof thermal insulation protection layer under the concrete lining, or installing an automatic sprinkler system in the tunnel.
4 . 2 Ventilation and smoke prevention
According to the analysis of tunnel fire accidents, the death caused by carbon monoxide accounts for about 50% of the total , and about 50% of deaths are caused by direct burns, explosive forces, and other toxic gases . In general, the use of ventilation and smoke control measures to control the product and movement of smoke can improve the fire environment, and reduce the temperature of the fire field and the concentration of hot smoke and fire thermal decomposition products, improve sight. However, mechanical ventilation will affect different types and scales of fire through different ways. In some cases, it will aggravate the development and spread of fire. Experiments show that: in low-velocity ventilation, the impact on small car fires is not significant; the heat release rate of small oil pool fires ( ~ 10m2) can be reduced , and the large-scale oil pool fires ( ~ 100m2) for ventilation control are enhanced ; The fire growth rate of trucks can reach ten times that of natural ventilation.
Tunnel ventilation mainly includes natural, horizontal, semi-lateral and vertical ventilation. Short tunnels can use the "piston wind" inside the tunnel to take vertical ventilation, while long tunnels require horizontal and semi-lateral ventilation. The ventilation system in the tunnel must play the role of smoke exhaust in the fire, and its ventilation duct and smoke exhaust equipment must have certain fire resistance.
Gasoline-powered PPV turbine exhauster
For tunnel ventilation design, the characteristics of specific tunnels ( such as length, cross-section, grading, dominant wind, traffic flow and flow, cargo type, fire parameters, etc. ) generally need to be designed through engineering analysis methods. The field model or regional model simulates the smoke movement in the tunnel, such as FASIT and JASMIN .
At present, most researches on tunnel ventilation and smoke exhaust are focused on its influence on the flow of smoke, and there is a lack of research on the effect of ventilation on the fire itself.
4 . 3 Safe Evacuation and Refuge Facilities
The normal evacuation rate for personnel within the tunnel is 1.5 m/s but may be only 1 m/s in the presence of smoke . The average person's limit radiant heat tolerance value is 2 to 2.5 kW/m2 , and the firefighter's tolerance limit with air breathing apparatus is 30 min , 5 kW/m2 . In general, the radiant heat of the smoke layer at 160 °C is 2 kW/m2 , and the radiant heat of the smoke layer at 270 °C is 5 kW/m2 . The maximum air temperature during evacuation should not exceed 80 °C, and the tolerance time at this temperature is approximately 15 min .
Refuge facilities not only provide protection for evacuees, but also can be used by firefighters to temporarily escape smoke and heat. In the design of medium and long tunnels, the installation of personnel safety shelters must be considered, and the layout of the passages, the distribution of compartments and spaces, and the need for supporting facilities must be considered. Some fires indicate that some people have entered safe havens at the time of the fire but they eventually died as a result of heat and smoke leaks. Therefore, the minimum fire-resistance limit of a safety shelter should be consistent with the fire-resistance limit of the tunnel structure. It should also be able to isolate high heat and prevent the entry of flue gas. Usually an independent air supply system should be considered in these areas.
In addition, the location of evacuation openings in the tunnel and the form of evacuation doors are very important. Although a side-open, swing-open or split door can provide a suitably sized opening for the passage of a person or motor vehicle, a normally closed fire door that automatically closes should be used for access to the evacuation channel or shelter. Fire resistance of fire doors should be consistent with the fire resistance of the corresponding structure, and have good smoke, heat insulation performance.
4 . 4 automatic sprinkler system
Automatic sprinkler systems are the most widely used fire extinguishing facilities in buildings. However, from the perspective of existing tests and usage, there are still great controversies about the application of automatic sprinkler systems and their effectiveness in highway traffic tunnels. In general, automatic sprinkler systems installed in traffic tunnels should fully consider the following:
(1) Fires in tunnels usually occur in the lower part of the vehicle, in the carriage, or in the engine part of the vehicle. The sprinklers mounted on the upper part of the tunnel often fail to achieve the fire extinguishing effect.
(2) There is a delay between the igniting of the fire and the action of the sprinkler. Rapidly increasing fire in the tunnel vaporizes the small droplets of spray and generates large amounts of high-temperature steam. This will not only extinguish the fire but will increase the hazard to the escapee.
(3) The interior of the tunnel is long and narrow, and the piston wind generated by the vehicle's operation causes heat and combustion products to spread rapidly along the tunnel. Only activating the sprinkler above the fire point often does not work.
(4) The cooling effect resulting from the action of the fire suppression system tends to lower the hot smoke layer along the tunnel roof and destroy the smoke stratification.
(5) The water sprayed from the system will make the road surface slippery and dangerous, and it may lead to further expansion of the flammable liquid fire.
(6) Water sources and corresponding drainage systems, pump stations, system maintenance, power security, etc.
According to the report of the World Association of Roads (PIARC) , most countries believe that the vast majority of tunnel fires occur in fuel tanks and cars. Automatic sprinkler systems have little effect. Therefore, in Europe, sprinkler systems are used only for special purposes. For example, Norway has two sprinkler systems installed in tunnels to protect tunnel linings with polyurethane. Tunnels in Belgium, Denmark, France, Italy, the Netherlands, and the United Kingdom never installed automatic sprinkler systems. In Japan, only a long tunnel of more than 10km and a short tunnel of more than 3km with heavy trucks require the installation of an automatic sprinkler system. In the United States, only a few tunnels that allow vehicles carrying dangerous goods have automatic sprinkler systems installed.
NFPA 502 also recommends the use of a water-forming film-foam rain system only when the vehicle is transporting dangerous goods.
4 . 5 Other firefighting facilities
Other fire safety facilities in the tunnel include: emergency lighting and signal systems, monitoring and fire alarm systems, communications facilities, fire hydrants, fire pumps, and fire extinguishers.
Whether or not a system is adopted in the design and what type of system is adopted depends on the specific conditions of the particular tunnel. For example, when selecting the automatic alarm system, it should be considered that although the smoke-detecting probe reacts faster than the temperature-sensitive probe, the possibility of false alarms is greater due to the influence of vehicle exhaust emissions in the tunnel. In Austria, fire detectors have been installed in motor tunnels and high-flow tunnels over 1500m in length . Switzerland, Sweden and Japan also set fire detectors according to the requirements of the tunnel. Other countries are generally only installed in some special tunnels.
When designing the signal and communication facilities, the closed environment in the tunnel, the physiological and psychological impact of the noise on the personnel should be taken into consideration, and how to effectively convey information to the traffic personnel and reduce the panic mentality of the escapee.
When a fire breaks out, the normal operation of the power system is crucial to the escape of people in the tunnel. Therefore, these systems must be protected from fire in a certain period of time, including fire pump rooms, fire alarm systems, evacuation emergency lighting systems, and exhaust pipe systems.
5 . Fire Prevention Design of China Highway Tunnel and Related Suggestions on Fire Safety Research
5 . 1 Suggestions for Fire Protection Design of China Highway Tunnels
According to the relevant tunnel studies and fire conditions, we suggest that the tunnel design should be based on the number and type of combustibles in the tunnel, the use of the tunnel, physical conditions, length, and ventilation and exhaust smoke and other factors taken into consideration, and the single hole and Double-hole tunnels are
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