Abstract:Taking the underground integrated pipe gallery of an airport terminal as an example, this paper systematically analyzes the fire occurrence and spread characteristics of the airport integrated pipe gallery, and discusses the fire protection design points and safety management measures of the airport integrated pipe gallery from the aspects of pipe gallery structure, fire separation, fire fighting, ventilation and smoke extraction, safe evacuation, decoration and materials.

    Key words:integrated pipe gallery; fire protection; design; operation management

The utility tunnel is an important lifeline project to ensure the various functions of the airport. Its main purpose is to avoid interference with the aviation airspace. It integrates various pipelines such as power, telecommunications, monitoring, water supply, drainage, heat and even gas. The way of the corridor is arranged. This arrangement method is also the trend and trend of urban infrastructure modernization and construction, but its disadvantage is that the fire protection and fire prevention problems of pipe corridors are more concentrated. Once a fire occurs, it will affect the normal take-off and landing of the aircraft and cause large-scale aircraft delays. Therefore, ensuring the safety of the utility tunnel has become an important part of the airport construction.

 First, the fire risk analysis of the integrated pipe gallery.

1.1 fire cause

The utility tunnel is an important lifeline project to ensure the various functions of the airport. Its main purpose is to avoid interference with the aviation airspace. It integrates various pipelines such as power, telecommunications, monitoring, water supply, drainage, heat and even gas. The way of the corridor is arranged. The main point of the layout of the integrated pipe gallery is that it can effectively shield the interference of the power optical cable and the communication optical cable to the external signal. At the same time, due to the integration of water supply pipelines, drainage pipelines and thermal pipelines, it also saves a lot of pipe gallery slotting and construction costs. However, in the integrated pipe gallery, the gas pipeline is generally not included in it. The main reason is to prevent the integrated pipe gallery from exploding due to fire, but there are still a large number of power and cables in the integrated pipe gallery, and the existence of this type of line is easy to cause a short-term flow of a large current in the power line due to a short circuit, which makes the temperature of the line rise rapidly, prompting the fire.

Analysis of 1.2 Fire Characteristics

(1) The pipe gallery is closed and has backburning characteristics. For the integrated pipe gallery, due to the large number of pipelines buried inside, there are a large number of communication lines in addition to power cables, and the closure of the pipe gallery is relatively strict. In the case of a fire, it will lead to the incomplete combustion of a large number of insulating materials and produce a large amount of smoke and dust, which will make the fire fighting more difficult and the risk of fire is greater. In addition, due to insufficient combustion in the closed pipe gallery, it is in a smoldering state. Once the ventilation environment in the pipe gallery changes, the phenomenon of re-ignition will trigger the fire again or affect the fire fighting of other fire points.

(2) Difficulty in finding and saving. As the utility tunnel is a closed space and has no personnel on duty, it is usually not easy to be found in case of fire accident. When it is found that the temperature in the utility tunnel rises very high, a large amount of smoke and heat are difficult to release, and it is not easy for personnel to enter the utility tunnel to carry out fire fighting. It is difficult to put out fire, which is not conducive to fire control and fire fighting.

(3) The indirect loss of fire is large. There are mainly two kinds of pipelines affected by fire in the utility tunnel. The first is power cable. The second is the communication cable. These two kinds of cable fraud itself is more expensive, power cable fraud can reach 100 yuan/meter, and communication cable fraud is generally more than 50 yuan/meter. Once a fire occurs in the utility tunnel, the first is the economic loss caused by the re-laying of optical cables and power cables. The second is the indirect loss caused by the interruption of communication and power supply, such as the loss caused by the normal takeoff of the aircraft.

  Second, the airport integrated pipe gallery fire protection design.

Design of Fire Protection Partition and Combustion Performance of Structural Materials for 2.1 Pipe Gallery

Large airport utility tunnel usually has a large section and a long distance due to multiple pipelines. In order to avoid the spread of fire along the inside of the tunnel, fire prevention separation is usually required. At present, there is no regulation on the spacing of fire separation. If the spacing is too large, the fire area is too large to achieve the function of separation protection. If it is too small, it is not convenient for ventilation and internal passage. At the same time, the equipment will also increase. The author thinks that it can be considered according to structures, referring to the requirements of "Code for Fire Protection Design of Buildings" and "Code for Design of Fire Extinguisher Configuration of Buildings" and drawing lessons from the construction experience of common ditches in other cities, the area of fire prevention zones can be controlled to about 2000~2500m2, so that for the general utility tunnel with a width of about 7m, a firewall can be set up and equipped with fire doors for separation at about 300m, in this way, the fire can be controlled in a limited range, which is also beneficial to fire extinguishing.

The combustion performance of the load-bearing structure of the integrated pipe gallery shall be non-combustible, and the fire resistance limit shall not be less than 3.0 hours. Interior decoration materials shall be non-combustible materials except caulking materials. Firewall combustion performance should be non-combustible body, fire resistance limit should not be less than 3.0 hours, the inspection hole and its related cover plate should also consider the corresponding fire resistance rating, the cable used should also try to use flame retardant halogen-free cable.

2.2 automatic fire alarm system

The indirect loss of the airport utility tunnel fire is large, and the use function needs to be restored quickly after the fire. Because the airport utility tunnel is generally unattended, the installation of automatic alarm system plays a very important role in ensuring the safe operation of the airport. The automatic alarm system in the general pipe rack includes gas leak detection and fire detection. The gas will be laid separately in the airport utility tunnel, so it is mainly for fire detection in the pipeline corridor. The automatic alarm system generally has a fire sensor to detect the fire signal, and then transmits the situation to the controller through the signal transmission line arranged in the pipe gallery, which is analyzed and processed by the controller. The controller isFire alarmThe key part of the system, which includes signal processing, signal recognition, signal memory, intelligent judgment and its linkage functions, is used to control ventilation,automatic fire extinguishingSuch as linkage equipment. According to the size of the utility tunnel, the automatic alarm system can be divided into regional alarm system, centralized alarm system and fire control center alarm system.

    2.3Fire extinguishing system

Usually, the utility tunnel should be set upFire hydrantSystem, according to the tunnel fire code, generally every 45 meters or so set up a group of fire hydrant system, hose length of 25m, in addition according to this distance set fire extinguisher, each configuration point should not be less than 2 sets of 8kg portableDry powder fire extinguishingA wheeled dry powder fire extinguisher can also be configured in the pipe gallery.

Regarding the automatic fire extinguishing system, according to the construction experience at home and abroad, it can generally be divided into water extinguishing andgas fire extinguishingTwo kinds. Water agent fire extinguishing common water spray, high-pressure water mist 2 kinds, gas fire extinguishing includesheptafluoropropaneType SAerosoland the latest development of fire detection tube fire extinguishing systems.

   Analysis of fire protection engineering example of integrated pipe gallery in a terminal building in 3.

In the expansion project of a large airport, the underground pipe gallery of the terminal building and the municipal comprehensive pipe gallery project are constructed. The project is divided into a north-south line and two east-west lines. The north-south line runs through the whole airport area from south to north, and the east-west line is in the north-south working area respectively, with a "U" shape as a whole. The total length of the pipe gallery is 5Km, and the cross section of the pipe gallery is in the form of single cabin, two cabins and three cabins. The reason for setting up the warehouse is to separate the strong current from the weak current. The width is between 3.2~11.9m, the section height is between 4~6m, and the soil covering height on the top of the pipe gallery is between 3~8.5m. According to the characteristics of the project, combined with the current development of fire technology at home and abroad, mainly from the perspective of passive fire prevention and active fire prevention to carry out related research, put forward the corresponding design scheme.

Design of Fire Protection Partition and Combustion Performance of Structural Materials for 3.1 Pipe Gallery

The utility tunnel is divided into 14 fire prevention zones according to the requirements of flight area, work area and terminal area, as well as security and safety. The spacing between fire prevention zones ranges from 300m to 900m, and the area of fire prevention zones is controlled at about 2500m2. For pipe corridors with small sections and large fire prevention spacing, fire prevention separation is mainly carried out by considering comprehensive factors such as the setting of fans, the arrangement of air outlets, operation and maintenance, etc. Firewalls, Class A fire doors, fire retardant bags, etc. are set up between fire prevention zones for fire prevention separation.

Selection of 3.2 Automatic Fire Extinguishing Mode

Layout of Fire Probe Tube at Cable Joint

Since strong current and weak current are separated in this project, all cables in the strong current warehouse are flame retardant, and there are no combustibles in the water and heating warehouse. From the perspective of fire extinguishing mode, the design only considers that the cable joints in the strong current warehouse may have fire hazards due to heat generation. Therefore, only gas fire extinguishing is provided at the cable joints for local protection, and the fire extinguishing method of fire detection pipe is selected in the project.

In the design, a circle of thin-walled stainless steel pipe is wrapped at the cable joint, and the part is relatively sealed, and the fire probe is set in the confined space. When a fire occurs at the cable joint, blasting occurs at the weakest part of the pressurized fire probe above the fire source, which causes the fire probe device to start and release carbon dioxide, thus achieving the purpose of automatic fire control and fire extinguishing. When the equipment is started, due to the loss of pressure in the fire detection pipe, the terminal pressure check valve automatically converts the gas pressure signal into a dry contact signal, which is linked with the fire alarm system. Figure 2 is a schematic diagram of a fire probe arrangement.

3.3 fire alarm system

The utility tunnel is usually unattended. Once a fire occurs, it can only be detected in time by monitoring facilities. Therefore, an automatic fire alarm system is installed in the utility tunnel. For the strong electric warehouse, a cable-type linear temperature-sensitive fire detection system is set up, which can monitor the operation of the cable in time and avoid the loss caused by the cable fire. For other storehouses, moistureproof point smoke detectors shall be provided.

In addition, portable fire extinguishers MF/ABC4 are set up in the utility tunnel according to the medium danger level, 2 fire extinguishers are placed at the evacuation exit through the ground, 2 fire extinguishers are set up every 40m in other areas, and the minimum fire extinguishing level for a single fire extinguisher is 2A.

  4 Conclusion

With the continuous development of airport upgrading and urban construction in China, the utility tunnel has become an important engineering facility for arranging various pipelines, and it is very worthy of attention to ensure the safety of the utility tunnel. Taking the airport integrated pipe gallery as an example, this paper comprehensively analyzes the fire characteristics and causes of the integrated pipe gallery, and puts forward the corresponding solutions from the perspectives of passive fire prevention and active fire extinguishing in fire prevention, management and fire protection design. Finally, combined with the construction of a large airport utility tunnel in central China, the corresponding fire protection design scheme is put forward.