One type of blowback is caused when atmospheric air blows down the locomotive's chimney, causing the flow of hot gases through the boiler tubes to be reversed, with the fire itself being blown through the firehole onto the footplate, with potentially serious consequences for the crew.
[1] In the days when steam-hauled trains were common in the United Kingdom, blowbacks occurred fairly frequently.
In 1954, the number of occurrences and of injuries were the same and there was also one fatal casualty.He also recommended that the British Transport Commission carry out an investigation into the causes of blowbacks.
[1] Other potential causes are unused mining explosives in the coal used to fuel the engine, and unburnt gases collecting in the firebox and then igniting.
[1] Driver Wallace Oakes died as a result, and his fireman Gwilym Roberts was severely injured.