In recent years, the mileage of highways and urban traffic tunnels in China has increased rapidly, bringing challenges to tunnel fire safety. The hazards caused by traffic tunnel accidents at home and abroad have aroused great attention to tunnel fire safety. Most fires in tunnels are open fires with thick smoke, with a heat release rate of several megawatts, and a fire can form within minutes. According to extensive tests (including road vehicles and metro trains), a fire usually fully forms in 8-10 minutes; for large freight trucks, about 20-30 minutes; when fuel leaks and forms a pit/pool, a fire fully forms within 1-3 minutes. Tests of "tunnel fire" cases show that after about 5 minutes, the temperature of a vehicle fire rises to about 200℃. Research results indicate that when a serious fire occurs in a tunnel, in the first 4 minutes, a temperature rise of more than 50℃ per minute can be detected in the hot air layer above the fire point. In addition, tunnel ventilation will produce specific effects. Tests generally show that with a longitudinal wind greater than 2m/s, the flame of a car or train drifts upward and the temperature at the top only reaches 60 degrees Celsius; and at a location 20 meters away from the fire, the top temperature will drop below 50 degrees Celsius.
Because the tunnel is long and narrow with usually low visibility, plus the "black hole" effect when entering, tunnels are accident-prone sections where various fires occur. Due to the "tubular" spatial structure of tunnels, even a very small fire can induce a big fire. Therefore, the policy of "prevention first, combining prevention with firefighting" should be implemented in tunnels, and effective fire prevention measures should be taken to prevent and reduce fire hazards. For temperature-measuring fire detectors, differential temperature alarm based on temperature rise gradient is the preferred alarm method for tunnel fire protection, followed by fixed-temperature warning and alarm. Among the existing fire detection schemes, due to safety, long-distance transmission, reliability and other reasons, none can well solve the fire detection problem of this industry. The fiber Bragg grating fire detector is a new generation of fiber optic fire detector in the world, with intrinsic safety and explosion proofing, strong anti-electromagnetic interference, good electrical insulation, lightning protection, high accuracy, light weight and small size, and the ability to conveniently use wavelength division multiplexing to connect multiple FBGs in one fiber for distributed measurement. Therefore, the FBG fire detector has received worldwide attention and is being widely applied. At present, there is no unified industry standard for traffic tunnel fire protection, and traditional temperature measurement technologies all have certain limitations. But no matter what technology is adopted, only timely and accurate fire detection and early warning can minimize fire losses — such technology is the fire alarm technology we really pursue.
Ningbo Light of the East Safety Technology Co., Ltd. is a high-tech enterprise located in the Ningbo Science Park of the China Academy of Engineering Physics. The company's technology originates from the "Two Bombs" development base — the China Academy of Engineering Physics (CAEP). Founded in 1958, CAEP is the state-planned and sole nuclear weapons development unit of China — a comprehensive research institute integrating theory, experiment, design and production, dedicated to advanced national defense science and technology. Outstanding scientists such as Yu Min, Wang Ganchang, Deng Jiaxian and Zhu Guangya, winners of the "Two Bombs and One Satellite Merit Medal", have all held important leadership positions in CAEP, which now has 22 academicians. The Institute of Optoelectronics of CAEP is an applied technology research institution jointly established by the China Academy of Engineering Physics and the Ningbo Municipal Government. Ningbo Light of the East Safety Technology Co., Ltd. was jointly funded and established by the Institute of Optoelectronics of CAEP and doctors returning from overseas. Relying on the strong technical support of CAEP, the company is provided with a strong guarantee for product technology upgrading. The company's core technology is a Ningbo "3315" key introduction project and has received strong support from the Ningbo Municipal Government since its establishment. Based on photon counting detection and photoelectric imaging technology, the company focuses on the R&D and promotion of flame and temperature test systems for high-risk environments. The company has a strong technical team, has independently developed a series of distributed fiber optic temperature measurement systems, fiber Bragg grating temperature measurement systems and red/ultraviolet flame detectors, and has self-developed software systems, providing a strong guarantee for product upgrading. The products are widely used in aviation, shipping, transportation, electric power, petroleum and petrochemical, banking and other fields.
