What causes Blowback in a steam locomotive firebox?

[Simon Robinson 4Participant @simonrobinson4]

I read about an incident in a BR standard class 7 in the 1960s where a driver was killed when the firebox blew back filling the cab with flames. What causes blowback to happen?

[Simon Robinson 4Participant @simonrobinson4]

[Paul KempParticipant @paulkemp46892]

Any interruption to the normal flow of gasses through the boiler! Passing through a tunnel or under a bridge are the common ones where the normal draughting of the blast pipe / chimney is disturbed. The fix is to have the bower on to augment the draught to keep things flowing in the right direction.

There are other circumstances where the same thing happens, notable the driver shutting off (closing the regulator) to coast down a grade or when stopping, the draw from the blast pipe is lost so there is no good draught through the boiler from firebox to smokebox so the flames will come out of the fire door if opened as they are given a nice ready supply of top air!

One of the first things drummed into you as a fireman is the proper use of the blower (blower is a shared control – ie used by driver and fireman) and the risk of blow backs. It's not an uncommon thing! In the last couple of years there was an incident on a mainline steam special where the footplate crew were quite badly burned and was the subject of an RAIB enquiry.

It's easilly done if the driver / fireman are not on the ball!

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