Video of crews working on the fire shows smoke moving in a very specific direction out of the Downtown Tunnel in Portsmouth. For some, it was a good indication that the fans in the tunnel worked.

However, the second purpose is less obvious. The fans also get rid of fossil fuels that build up in the tunnel, acting as a ventilation system of sorts. Watch: Crews extinguishing car fire in ...

The Amersham vent shaft headhouse in Buckinghamshire will provide ventilation and emergency access to the 10 mile-long (16km) Chiltern tunnel Images ... with fans and other equipment designed ...