The fire in the rail tunnel, which since 1994 has connected the UK and France running under the English Channel, was apparently caused by a truck/lorry overturning on one of the vehicle transport trains. Some injuries have been reported and hundreds of passengers have been left stranded. By some miracle, there were no passenger trains in the tunnel at the time of the blaze, amazing considering that 100 trains pass through the tunnel each day. The injured people were evacuated through the central service tunnel (the BBC has a cool diagram of how the chunnel works here).
Even more worrying, the overturned truck/lorry reportedly contained phenol, a deadly chemical that isn't allowed to be transported through the tunnel. The people who are reportedly in the hospital for smoke inhalation could have inhaled this chemical as it burned.
According to Wikipedia, the toxic chemical was used in the Second World War at
As someone who was planning to take the Eurostar train many times over the next several months, this is quite worrying. But for the economies of England and France in general, a shutdown of the tunnel for several months could be devastating. The majority of freight traffic between the UK and continental Europe now goes through the chunnel. In addition, the Eurotunnel just recently turned a profit for the first time, and there were big plans for expansion of the passenger services through it.
Just hours before the fire broke out yesterday, Air France announced it was launching its own high-speed train company through the tunnel which would take less than 2 hours, breaking the Eurostar monopoly. The journey currently takes a minimum of 2h 15m. Clearly there's a lot riding on the tunnel and its activity is only increasing. If anything were to go wrong with the tunnel at this crucial time it would have huge reverberations through France and Britain's economy.