A fire that closed the Channel Tunnel railway in January was almost certainly caused by an electrical arc between the overhead wiring and a lorry's over-height radio aerial, investigators have found.
The fire on a freight shuttle completely destroyed two lorries and damaged the train, railway infrastructure and the tunnel lining. Everyone on board was safely evacuated. Services through the tunnel were severely disrupted for several days after the incident on 17 January.
Britain's Railway Accident Investigation Branch (RAIB) has been working with its French counterpart, the Bureau d’Enque^tes sur les Accidents de Transport Terrestre (BEA-TT), which is leading the enquiry because the train stopped in the French section of the tunnel. RAIB's role has primarily been to determine the cause of the fire.
RAIB investigators found the incident began as Eurotunnel freight shuttle 7340 was entering the UK portal of the Channel Tunnel, when an arc occurred between the overhead power line and the train, above a lorry on the 15th of 32 carrier wagons. The power supply tripped automatically and the train came to a halt. Control centre staff didn't know the reason for the trip, but restored power and gave the driver permission to restart.
About 23 minutes later, control centre staff received a fire alarm from a detector in the tunnel, and at the same time an alarm system on the train detected a fire, which the driver reported to the control centre. Shortly afterwards, the power tripped again. The driver brought the train to a controlled stop with the 'amenity coach' (for passengers and crew) alongside an emergency escape passage.
CCTV footage taken as the train was loaded at Folkestone shows that the lorry on the 15th carrier wagon had a whip aerial standing higher than the leading edge of the trailer. With the help of the lorry and trailer manufacturers, RAIB found that this aerial was above Eurotunnel's height limit. The loading ramps are equipped with sensors, but tests organised after the incident indicate that the system was not sensitive enough to reliably detect thin aerials passing in front of it at typical lorry speeds.
One of the loading agents responsible for observing the train on departure did see a metal aerial but was unsure whether it was over-height and asked a more experienced member of staff, who reminded him that the lorry had passed the aerial detection system. No further action was taken. RAIB reviewed the working instructions for loading agents and "witnessed the difficulties associated with identifying thin aerials on a departing train", while noting that in this instance an opportunity to stop the train was missed.
The investigation into the cause of the fire is now complete. The investigation into Eurotunnel's response to the second power trip and the fire is still going on. BEA-TT and RAIB will jointly publish all their findings, including any recommendations, when the work is concluded.