The Danger of Fires in Cable Tunnels Cable tunnels are critical parts of infrastructure, and fires inside them pose a serious threat. In a closed tunnel, fire quickly produces thick, toxic smoke and can destroy supporting structures. A clear example is the cable fire on the Chaobai Bridge (Beijing) in April 2025: the cables had no fire suppression system, and the fire caused structural failure and partial bridge collapse (Cable fire caused bridge’s partial collapse in Beijing — Chinadaily.com.cn ). This incident clearly showed that the lack of a dedicated fire suppression system in cable tunnels can lead to disasters for infrastructure and the economy.
Weaknesses of Current Fire Suppression Technologies Current fire protection systems in tunnels do not provide a safe or reliable solution:

• Gas-based systems (inert gases, CO₂): These systems need airtight spaces and are extremely dangerous for people. They work by removing oxygen, which can be deadly if leaked or activated by mistake. Between 1975 and 2000, there were 72 recorded deaths caused by CO₂ fire suppression systems (Carbon Dioxide Major Accident Hazards Awareness | AIChE). These systems are also very expensive to install and maintain due to the high-pressure cylinders, pipes, and ventilation systems.
• High-pressure water mist systems: These systems are effective for cooling, but they are complex, unreliable underground, and expensive. They require strong pumps, pipes, and nozzles throughout the tunnel. Installing them in existing tunnels is especially difficult. They need tons of water or agent, making installation and refilling costly. Any damage to the pipes can render the entire system useless.
• Aerosol generators (condensed aerosol, UL 2775 standard): These systems are easier to install and do not require pipes. But they have a major problem: high temperatures and toxic byproducts. According to standards, they can only be used in spaces where people have already been evacuated. But the standard does not account for people being present during installation. A real incident on the ship Resurgam showed how deadly they can be: when the aerosol was released, the area filled with fine particles, and an engineer who inhaled it died from poisoning. Aside from the danger to people, the aerosol salts can damage electrical equipment and require long clean-up times. Important: According to a UK MAIB investigation, even UL 2775-certified aerosol systems are unsafe for tunnels due to risk to people and poor ventilation. If an aerosol unit is triggered in a tunnel, anyone inside without ventilation will likely die or suffer severe poisoning. The high temperature of the aerosol cloud in a closed space may also fuel the fire instead of stopping it.
  The Solution: RADEX Technology RADEX-W is a unique patented fire suppression system designed specifically for cable tunnels. It uses a pressure generator (RDX-generator) that activates during a fire and instantly releases high pressure to spray a water tank into a fine mist — all without pumps or pipes. This creates a cloud of ultra-fine water droplets that quickly fills the tunnel section. The mist contains free radicals and neutral gas that:
• Cools the flames and hot structures, rapidly reducing temperature;
• Pushes out oxygen in the fire zone, acting like gas suppression (forms an inert “blanket” around the fire);
• Delivers free radicals to the flames, breaking the fire’s chemical chain reaction;
• Stops the fire from spreading along the cables and prevents reignition.
  Thanks to this combination of effects, RADEX can instantly extinguish a fire at its source. Unlike traditional gas, mist, or aerosol systems, RADEX is:
• Safe for people and electronics;
• Free of toxic byproducts;
• Simple to install and needs no complex infrastructure.
  Advantages of RADEX
• Safety: Uses water and air displacement without toxic gases – safe for people, the environment, and equipment.
• Cost-effectiveness: 10–12 times cheaper than gas or mist systems, with no need for pumps, pipes, or gas cylinders.
• Easy installation: RADEX-W modules are placed directly next to the cables inside the tunnel. No pipe installation or major reconstruction needed – ideal for existing tunnels.
• Zero maintenance: The system has no moving parts or pressure storage. It works independently and needs no servicing for 3 years, cutting operating costs to nearly zero.
  Conclusion RADEX is the first and only real solution for protecting cable tunnels from fire. It combines the benefits of gas, mist, and aerosol systems — without their downsides. Thanks to RADEX, cable tunnels and infrastructure can finally be protected from fires with minimal cost and maximum safety.
  Video of live prototype tests