How do two-way fire engines work in tunnel rescue?

In recent years, with the rapid development of the transportation industry, the level of roads has become higher and higher, and the size and length of traffic tunnels have been getting longer and longer. More than 7,000 road tunnels have been built in China , with a total length of more than 5 100 km , of which over 260 are long tunnels and more than 1,140 km . The longest road tunnel is the Qinling Zhongnanshan Highway Tunnel with a total length of 18.02 km and a total length of 36.04 km . The increase in the number and mileage of road tunnels, especially super-long tunnels, has led to an increase in tunnel fires and emergency rescue accidents. Highway tunnel fire accidents have the characteristics of rapid combustion, poisonous smoke accumulation, difficulty in diffusion, low visibility, difficulty in handling, high requirements, and long time. How to effectively do a good job in road tunnel fire extinguishing and emergency rescue work is a major issue that the fire brigade needs to solve urgently in the new situation. The public security firefighting department shall combine the characteristics of tunnel fires and the actual combat needs of firefighting and rescue, and put forward suggestions for strengthening and improving them so as to promote the development, improvement, and improvement of the fire-fighting and rescue performance of tunnel fire engines by fire-fighting vehicle manufacturers.

First, the status quo of the development of fire engines for tunnel accident rescue

Tunnel fire extinguishing and emergency rescue accidents, especially tunnel fire fighting, are recognized problems in the world. In 2011 , the world’s first double-head tunnel evacuation rescue fire truck developed by Croatia’s Ziegler Company has two cabs, three independent rescue cabins with compressed air bottles, computer-controlled real-time monitoring systems, and vehicles. Self-protection system, motor four-wheel drive operation, etc., mainly to save people, detective-based. Other countries such as the German company Schmitz also developed tunnel fire trucks, each with its own advantages. In recent years, China's related fire truck manufacturing enterprises have learned from the advanced experience of similar foreign models, developed and produced a third-generation domestic double-headed tunnel fire truck, with double-headed two-way driving, driving while driving, smoke detection and inspection, and operation interface. And humanized integration and other advantages. Fire-fighting units of a few provincial capital cities or economically developed cities in the country are equipped with tunnel fire engines, but some of them are imported vehicles. This is not only expensive, but also has a long lead time and inconvenience in training and after-sales services. Fire-fighting vehicles made of domestic tunnels are also gaining popularity. Compared with imported vehicles, they have the advantages of cheaper prices, easier training, after-sales and maintenance, but they also need to combine fire-fighting and rescue needs to further improve the performance of fire-fighting operations.

Two, two-way driving fire truck technical characteristics and design requirements

According to the classification of GB 7956-2014 "Fire Truck", the two-way driving fire truck is a dedicated fire engine, and it refers to the pressurized cab, passenger compartment and engine compartment. It has a two-way driving function and is used to extinguish tunnel fires.

1. Use two-way driving function to quickly reach or leave the rescue site

The domestic tunnel fire truck is equipped with a dedicated chassis for two-way driving fire trucks, using hydraulic power steering, dual steering axles, single-axle drive (4 × 2) , two-way driving, ABS systems, etc., in particular, the cab is set at the front and the rear is set to drive The room and crew room effectively solve the difficult problem that the narrow road of the tunnel can not turn the vehicle. It can not only ensure the firefighters arrive at the scene quickly, but also ensure that the rescued personnel can leave the scene quickly or they can quickly withdraw from the site according to the order of the commander. Two-way tunnel fire engine plan, as shown in Figure 1 .

Figure 1 Plan of a two-way tunnel fire truck

2. Install a booster device in the driving room

The large amount of smoke in the tunnel is not easy to spread, causing the pressure in the tunnel to rise rapidly. High temperature and toxic smoke will infiltrate into the cab and passenger compartment along the doors, holes and other places. It is recommended to provide air supply devices such as compressed air cylinders and mobile air supply sources to ensure that the occupant’s room pressure is always greater than the ambient pressure and prevent the smoke from infiltrating into the cabin. Can be equipped with 2 to 3 sets of compressed air cylinder supply ( 1 set = 40 L/ a × 4 × 30 MPa ), through the pressure balance device to monitor the pressure inside and outside the car at any time, automatically adjust the amount of air supply to the cabin , to ensure normal indoor breathing and visual observation, but its disadvantage is the use of vehicle space. According to "Fire Truck" vehicle width ≤ 2.5 m , height ≤ 4 m The regulations require that the length of the vehicle must be increased, which will reduce the mobility and flexibility of the vehicle in a confined area; the use of mobile air supply and the provision of pressure balance and pressure relief devices in the driver's cab have the disadvantage that the rear personnel are not Changes in air pressure inside and outside the occupants are adjusted to adjust the air supply volume, the gas pipelines are laid longer, and excessive replenishment contributes to the spread of fire. In addition, the door joints, holes, and other parts that are connected to the outside of the driving room should be sealed with high-temperature seals to improve the sealing performance of the vehicle.

3, equipped with oxygen concentration sensor

Fire engines generally use internal combustion engines (engines) as their power source. Maintaining the continuous operation of internal combustion engines should ensure that air and fuel reach a certain ratio, ie, air-fuel ratio, in which the oxygen content in the air accounts for approximately 21% . If the minimum oxygen content in gasoline is 14.4% , it cannot be otherwise. combustion. The stoichiometric air-fuel ratio of internal combustion engines (engines) using diesel and gasoline as fuels is 14.3 and 14.8 , respectively . Faced with the toxic and dense smoke and other complex fire conditions in the tunnel, oxygen concentration sensors should be provided inside and outside the vehicle to monitor the oxygen content of the vehicle's environment at any time, prompt the driver to correctly select the vehicle parking location, and accurately determine the evacuation timing. So as not to turn off the vehicle. It can be considered that small and medium-sized vehicles are equipped with electric motors and are assisted by generators . The disadvantages are that the power is relatively small compared to the internal combustion engine. The capacity of the battery pack carried is limited and the power is small. It is difficult to ensure long-term operation of the electric motor and water pump.

4. On-site reconnaissance and environmental testing provide commanders with decision-making basis

The first task of fire suppression in tunnels is to do a good job of on-site reconnaissance and environmental testing, highlighting the guiding ideology of “saving people first”. After the firefighters arrive at the scene, they shall use the detection equipment on the tunnel fire truck at the first time to find out the location and number of the trapped persons, the fire burning status, the fire center point and the spreading direction, the offensive or withdrawal route, and detect and monitor the tunnel at any time. The composition and content of toxic and harmful gases in the interior, changes in the oxygen content in the air, etc. provide decision-making basis for command personnel to determine or adjust rescue plans.

It is recommended that in addition to vehicles equipped with toxic gas, combustible gas, long-range hazardous chemicals monitoring, infrared monitoring of building collapse, temperature measurement, electronic weather, leakage monitoring and other detection equipment and infrared thermal imager firefighting and other detection equipment, but also the radar The life detector incorporates necessary equipment to utilize its non-contact nature, strong penetrating power, and the ability to accurately locate and detect. It is suitable for performing life detection in free space and penetrating non-metallic media, and can be buried in collapsed buildings. Survivors in the rubble, soil, etc., or active exploration of living organisms located in smoke and fog environments can help firefighters search for and rescue trapped people. Compared with fire-fighting infrared imagers and audio/video frequency life detectors , they are not easily affected by factors such as temperature, humidity, noise, and site topography, which overcomes the severe influence of temperature on infrared life detectors and the failure of object-blocking. The problem also overcomes the problems of large spatial attenuation of audio (visual) frequency life detectors, being susceptible to reflection and interference by environmental debris, and being blocked by water, ice, and mud.

5. Implement rescue plan and implement firefighting rescue

After the tunnel fire truck arrives at the scene of a fire accident, the firefighters shall use the on-board fire extinguishing equipment and equipment to carry out firefighting and rescue activities, and at the same time evacuate and guide the transfer of trapped persons or materials.

6, bring equipment to rescue trapped people

On the premise of ensuring the safety of their own protection, firefighters are recommended to use a positive pressure air respirator with his rescue function and an electronic pressure gauge display and pressure head-up display device , carrying a forced-air respirator , a filter-type gas mask , and lifesaving Life-saving equipment such as stretchers and body- mounted airbags are illuminated by work lights and high-intensity light lamps, along which lifesaving lighting lines are laid , self-storage lights or adsorptive light-guiding indicators or lights are placed, and illumination is carried out using vehicle-mounted light illumination lamps. At the same time, it directed the trapped people to evacuate along the correct route and rescue trapped people in time.

7, the use of vehicle equipment smoke exhaust lighting

When the vehicle is on the way or in a fixed position, it can use the front of the vehicle to spray blossom water mist or exhaust smoke, smoke, and cool down, but the direction of the smoke should be clearly defined. Practice tests have proved that according to the direction of smoke flow in the smoke exhaust system of the tunnel, fire fighters can adjust the direction of the smoke from the water cannon or the smoke exhauster in a timely manner, and the consistency of the direction of smoke exhaust must be maintained. Otherwise, the effect of exhaust smoke will be impeded or mitigated. At the same time, the use of vehicle lift lights to the scene lighting. Due to the weak penetration of white light in smoke, it is recommended that some of the lights be changed to yellow light or yellow filter lens covers be installed for the rescue personnel to select the light color according to the site requirements.

8, play equipment performance against fire

Firefighters can use the portable, backpack-style rescue tool kits to perform operations on the obstacles that affect rescue operations. When the fire point is found, the front cannon can be switched to a DC water column or spray foam. It is also possible to use a fire hose to spray fired Class A or B foams for fire extinguishing. It is recommended to use a compressed air foam system ( CAFS system). When the ambient temperature of the tunnel in which the vehicle is located is high, the self-protection system of the fire truck is started, and the water mist is sprayed to protect the temperature of the entire vehicle and the tires of the vehicle.

Third, the conclusion

The development of domestic two-way tunnel fire trucks and related technology research can effectively increase the popularity of the vehicle fire protection department. Once a fire or disaster occurs in the tunnel, the fire department can rush to the scene to carry out fire rescue operations. At the same time, domestic tunnel fire engines have the advantages of obvious price, training and after-sales service compared with similar foreign vehicles. They have good economic and use values, protect people's lives and property, and protect firefighters from carrying out rescue operations. It is of great significance to reduce the degree of damage caused by disasters to public transport facilities. At present, this type of fire truck has been tested and tested in some fire brigade units in Hubei Province, pending further improvement of vehicle functions and technical performance.

Author: Jianjun.