Fire on Board: UIC Leaflet 625-7 Protection Standards

Introduction to UIC Leaflet 625-7

A diesel locomotive carries thousands of liters of fuel and high-voltage electrical equipment, often heating up to hundreds of degrees. If a fuel line ruptures near a hot turbocharger, the result can be catastrophic, especially in a tunnel. UIC Leaflet 625-7, titled “Fire fighting equipment in driver’s cabs and engine compartments of tractive units with internal combustion engines,” is the safety manual for preventing such disasters.

This leaflet mandates that every diesel train must have the means to detect a fire instantly and suppress it—either manually by the driver or automatically—before it consumes the vehicle.

Snippet Definition: What is UIC 625-7?

UIC Leaflet 625-7 is a technical regulation specifying the requirements for fire protection on railway vehicles powered by internal combustion engines. It defines the number and type of portable fire extinguishers required in driver’s cabs and mandates the installation of fixed fire detection and extinguishing systems in high-risk zones like the engine compartment.

The Three Lines of Defense

UIC 625-7 structures fire safety into detection, containment, and suppression.

1. Portable Extinguishers (Driver’s Cab)

The first line of defense is the driver. The standard specifies:

• Location: At least one portable extinguisher must be easily accessible in each driver’s cab.
• Capacity: Typically 6 kg powder or CO2 extinguishers (Class A, B, C fires).
• Inspection: Must be checked regularly to ensure pressure is maintained.

2. Fixed Detection Systems (Engine Room)

Since the driver cannot see inside the engine room while driving, sensors are mandatory.

• Detectors: Usually heat detectors (thermal fuses that melt at a specific temp, e.g., 180°C) or smoke detectors.
• Alarm: Detection must trigger an immediate acoustic and visual alarm on the driver’s desk.

3. Fixed Extinguishing Installations

For the engine compartment, relying on a handheld extinguisher is dangerous and ineffective. UIC 625-7 requires (especially for larger engines) a piped suppression system.

• Agent: High-pressure gas (e.g., Nitrogen, FM-200, or formerly Halon) or water mist nozzles.
• Activation: Can be automatic or manually triggered by the driver after confirming the alarm.

Operational Logic: The “Fuel Cut-Off”

UIC 625-7 dictates that fighting a fire is useless if the pump keeps feeding it diesel. Therefore, the fire protection system must be interlocked with the vehicle control logic:

1. Detection occurs.
2. Engine Shutdown: The system immediately cuts the power supply to the engine control.
3. Fuel Isolation: A solenoid valve on the fuel supply line snaps shut to starve the fire.
4. Ventilation Stop: Cooling fans are turned off to prevent fanning the flames or spreading the extinguishing gas.

Comparison: UIC 625-7 vs. EN 45545-6

The industry has transitioned from the prescriptive UIC leaflet to the comprehensive EN standard.

Tunnel Safety Context

The requirements of UIC 625-7 are heavily influenced by tunnel safety. In a tunnel, a train on fire should ideally keep moving to reach the exit (“Running Capability”). However, for an engine fire, the risk of explosion often necessitates immediate shutdown. Modern interpretations balance these needs by isolating the burning engine while allowing the train to coast or use other engines to escape.