Fatal blowback

When the firebox door of a steam locomotive is opened in a tunnel, with the blower on. The action of opening the firebox creates negative pressure in the cab, thus forcing the contents of the firebox into the cab (coal, fire, etc) usually resulting in the deaths of the crew.

Guy 1: did you here how John and Michael died?
Guy 2: no, how?
Guy 1: Fatal Blowback....