We actually use a sort of rail-mounted vacuum cleaner in the Channel Tunnel, to try and reduce the amount of brake-dust etc build-up which can cause false smoke alarms. Experience has taught that it is a Good Thing to use it after the rail-grinder has being through as well- before we did that, it was not uncommon to have twenty or more alarms as the first train of the day passed through the works interval. Anyone passing through Ashford station will see Balfour-Beatty's version of the same thing stabled in the sidings outside their depot there. Brian