What causes blowback in steam locomotive fireboxes?

[PaxmanValenta]

(Admin Please relocate to another forum if this is in wrong place.)

I was reading about how in 1965 driver Wallace Oakes was killed when the fire blew back in a BR standard class 7 locomotive filling the cab with flames.

What can cause blowback in a steam loco to happen? Could it be blocked fire tubes?

 

[The Lad]

Typically it is caused when the chimney is obstructed by a close bridge or when a tube bursts preventing the normal flow of the products of combustion or if the draught is disrupted by movement or failure of the blastpipe or of the screens fitted to reduce sparks being thrown out. There have been RAIB reports over the last few years about such incidents. Don't wear synthetics on the footplate.

 

[Martin66]

https://assets.publishing.service.g...0f0b6024400015f/120919_B042012_Wood_Green.pdf

Blowback of a locomotive fire at Wood Green tunnel, London, on 27 May 2012
Description of the accident: At 11:04 hrs on Sunday 27 May 2012, train 1Z54, the 09:38 hrs special service from Finsbury Park to Rowsley operated by West Coast Railways (WCR), suffered a blowback of the locomotive fire as the train entered Wood Green tunnel in north London. There were three staff on the footplate at the time and all of them were injured by the flames. Two of them, the fireman and a member of the support crew, were taken to hospital for treatment to their burns. Both were released later the same day.

 

[John Webb]

The Wallace Oakes incident was due to a superheater tube that failed, causing steam to pressurise the firebox and forcing flames out into the cab. The Wood Green incident was in a single bore tunnel (so little clearance) and the 'blower' valve had not been turned fully on to keep a draught going from firebox to chimney to overcome the extra 'back pressure' from the confining tunnel - the driver was able to turn on the blower valve to full and stop the blowback. The other form of blowback is the operation of the 'fusible plug' in the top of the firebox when the water level gets too low - although this is a little more controlled and the crew are rather more likely to be aware that that it is about to happen.

 

[theageofthetra]

Wasn't there one on an East German loco in the 70's which was so violent it blew the boiler clear off the frames?- sure I saw a pic of it on here?

 

[randyrippley]

RAIB report of the Wood Green incident
https://www.gov.uk/government/uploa...ata/file/410862/120919_B042012_Wood_Green.pdf

 

[PaxmanValenta]

The Wallace Oakes incident was due to a superheater tube that failed, causing steam to pressurise the firebox and forcing flames out into the cab. The Wood Green incident was in a single bore tunnel (so little clearance) and the 'blower' valve had not been turned fully on to keep a draught going from firebox to chimney to overcome the extra 'back pressure' from the confining tunnel - the driver was able to turn on the blower valve to full and stop the blowback. The other form of blowback is the operation of the 'fusible plug' in the top of the firebox when the water level gets too low - although this is a little more controlled and the crew are rather more likely to be aware that that it is about to happen.

Thanks for that a failed superheater tube makes sense, was it a design fault, and did other BR Standard class 7s have this fault?

I guess some tunnels such as Dainton tunnel when going up hill requires the fireman to be coaling the fire to provide power for the hill so the fire box door would be open when going through the tunnel. Is the blower fully open sufficient to prevent blow back with the firebox door open in this scenario?

In normal operating conditions if the blower is not fully open is having the firebox door closed sufficient to prevent blowback into the cab?

 

[The Lad]

At Dainton by and large the firing has been done a little earlier but the firehole door will be open to provide secondary air and reduce smoke emissions

 

[blackfive460]

Wasn't there one on an East German loco in the 70's which was so violent it blew the boiler clear off the frames?- sure I saw a pic of it on here?

You may be thinking of the boiler explosion at Bitterfeld in November 1977.
01 1516 was the loco and the explosion was due to insufficient water in the boiler coupled with the failure of the fusible plugs which did not melt due to a build up of scale. 9 people including the crew died and over 40 were injured.

 

[John Webb]

Thanks for that a failed superheater tube makes sense, was it a design fault, and did other BR Standard class 7s have this fault?

I guess some tunnels such as Dainton tunnel when going up hill requires the fireman to be coaling the fire to provide power for the hill so the fire box door would be open when going through the tunnel. Is the blower fully open sufficient to prevent blow back with the firebox door open in this scenario?

In normal operating conditions if the blower is not fully open is having the firebox door closed sufficient to prevent blowback into the cab?

I don't know about the life of superheater tubes, neither can I answer your other questions. The BR "Handbook for Railway Steam Locomotive Enginemen" (reprinted by Ian Allan at various times) does not go into great detail about these matters.

 

[AndrewE]

The BR "Handbook for Railway Steam Locomotive Enginemen" (reprinted by Ian Allan at various times) does not go into great detail about these matters.

My BR original says about "Blower and valve"

...Its function is to create a smokebox vacuum for the following purposes:-
(a) to increase the draught on the fire when the locomotive is stationary in order to raise steam pressure,
(b) to clear smoke,
(c) to counteract back draught
(d) To supplement the blast, if necessary.
In the case of (c), whilst working a train or light engine, the blower must always be opened prior to closing the regulator, also before entering a tunnel, and when passing over water troughs should also be used as a further precaution to closing the ashpan dampers and firehole door.

I thought it was to be opened at low bridges too...
p.s. there is over a page (31) on Blowbacks, including

...to avoid incidents of this nature:-...
(2) Always open the blower before closing the regulator, and also when approaching low tunnels, deep cuttings or bridges, especially when using hard coal or briquettes.

 

[Bevan Price]

Thanks for that a failed superheater tube makes sense, was it a design fault, and did other BR Standard class 7s have this fault?

?

Any metal tube in contact with steam or water, and subject to wide changes in temperature, can be subject to corrosion and/or stress fractures.

 

[theageofthetra]

You may be thinking of the boiler explosion at Bitterfeld in November 1977.
01 1516 was the loco and the explosion was due to insufficient water in the boiler coupled with the failure of the fusible plugs which did not melt due to a build up of scale. 9 people including the crew died and over 40 were injured.

Thats the one. The pictures of the aftermath are a sombre reminder of the sheer energy stored in a high pressure boiler & why maintenance is so important.