Causes of Engine Blowbacks

[greensands]

Recently reading a copy of the Railway Magazine for Feb 1956 I came accross an horrific account of a blowback which occurred on the footplate of a Class 2 2-6-2T which resulted in the death of the fireman and horrendous burns to the driver. From all accounts flames engulfed the footplate and the crew were forced to jump off the engine and it makes you realise just what a dangerous place it was to work. Although the blower was on at the time the error it was said was due to the firedoor not being properly shut and this resulted in the blowback. Given the dangers involved it is not surprising that the authorities were reluctant to allow members of the public onto the footplate but what I wonder would be the chances of something like that occurring again in preservation days?

[ejparrott]

It does, surprising frequently actually, every couple of years. There was one a year or two back but I forget the details now

[Deleted]

It happened not so long ago although I can't remember to which loco. I do recall the loco in question was being headed by a diesel and didn't notice an upcoming tunnel. I'm afraid the rest of the details are deep in my memory somewhere..

Pete

[pault]

The incident referred to was with Oliver Cromwell, which was being piloted by a diesel. The blowback occurred when they entered a tunnel without the blow on, and the fire hole doors open.
www.raib.gov.uk/cms_resources.cfm?file=/120919_B042012_Wood_Green.pdf
There have been others see
www.raib.gov.uk/cms_resources.cfm?file=/070130_R042007_Grosmont.pdf
In extreme cases it has been known for the blowback to be sustained long enough to set the coal on the shovelling plate alight.
Quite a few railways/loco designs have the blower valve directly above the fire hole doors, just where you want it during a blowback situation. The BR std’s moved it to the brake pedestal by the driver which actually makes much more sense.
I have experienced a blowback on a full size loco abroad, luckily the fire hole doors were shut but we had 3 foot long flames coming out of the holes in the Ajax style fire hole door. Once the blower was put on (it was not on when the driver shut off) the blowback was stopped however we then had to deal with back head lagging which was on fire.
They can happen on models as well, I have seen both explosive and sustained blowbacks in 7 ¼ luckily the worst thing that happens is a singed hand.
It’s another one of those ways that a steam loco can bite and usually depends on the crew to prevent it from happening
Que Roger designing automatic blowback arrester

[andyhigham]

About 20 years ago there was a documentary on radio 4. It was about an accident where the inside connecting rod broke and pierced the throat plate, emptying the conents of the firebox into the cab. Needless to say both crew were killed

[Deleted]

Not quite a Blowback as such but with similar results was a Superheater element that failed I THINK on a class 56xx at Didcot about 20 years ago ( PAUL T do you remember this one ??)........To answer GREENSANDS actual question}--- a blowback is caused quite simply by having the air pressure difference acting on the burning fuel but going the "wrong way" ie}-- towards you instead of away from you...The one potential cause most likely to be encountered by a loco's crew is entering a tunnel at speed and linked-up..The sudden transition from open air to totally enclosed space can send a pulse of air pressure down the chimney with dire results for an unprepared crew....IIRC, the routine for entering a tunnel (or deep cutting..) was}---a) make a mental note of the water level then shut down the gauge glass(GWR) or glasses( Rest of the world)....b)Open the blower fully ( to aid the relative weak exhaust)....c) Shut the firehole doors, with maybe just a crack open for lighting....d) Stand close against the cabside and as near to the backhead as possible...If there is a blowback that's as about as far from the flames that you can get !!..........Any naturally draughted chimney can suffer this ( Domestic home fire for instance) if stormy weather puts a down-draught onto your chimney = a sooty SURPRISE !! and Land or Marine based boilers also can suffer this.....Early designs of RN Boiler Stokeholds had a system called a CLOSED STOKEHOLD...Here the whole of the Boiler "Flats" or spaces, containing the boilers was pressurised to about 5 to 10 psi (IIRC that is) so access would be via a Double-Door interlock system with red and green lights to avoid a sudden loss of air, blowback etc.....No good for combat conditions as one breach of the hull and you've lost your boilers !!!...So we now have an OPEN STOKEHOLD with the boiler air being fed direct to the furnace front via dedicated trunking.....Oh, an added bonus is that the Boiler Room crew now have a chance to escape unhindered by those interlocked doors that wouldn't work if the power failedand you were trapped !!------------------ Have a look at this >>>>>>>>>>>>>>>>> www.marineinsight.com/marine/marine-news/headline/10-boiler-operating-mistakes-can-cost-big/ ...............

[marshall5]

I remember the incident with 6697 but thought it was a collapsed superheater flue - could be wrong though, it was a fair while back. Narrow single bore tunnels were the worst causing a sort of 'piston effect'. Wasn't there a blowback incident in a single bore tunnel on the WCML down slow a few years ago. Can't be sure of the location - was it Lechlade? Again, firedoors open and insufficient blower IIRC. Ray.

[RGR 60130]

Alan,

I find that link rather scary, especially when it appears to be dated 2013. I note the writer had a 'brief stint at sea' so can't have much experience. The people posting comments are possibly even worse though. Some of the points mentioned I'd suggest were learnt by heart in a college somewhere and taken as gospel for every ship. They disagree about how long the EGB pump should run, trying to pin it down to a fixed time but it's not like that. In some ports you come screetching in and get tied up in record time. In that case you run the pump a long time. In other ports you trundle in 'on stand-by' for hours and there's no heat left in the EGB so the pumps can be shut down after an hour or two. The picture of an old SACKKE burner betrays the era of learning material and the mention of a scotch boiler is unbelievable. These are the guys that under priced European crews.

The following is a quote from the comments:

Possibly we can collaborate with questions bank for Oral Exams and answers can be verified by us. I have spent 14 years in Marine Department, 10 years in shipping and oil and gas, 2 years in power generation and 5 years in maritime institutions.

These guys collect questions and research the answers between themselves rather than learning their trade so they can make reasoned decisions. To obtain a Certificate of Competency marine engineers need to do written and oral examinations. This seems to refer to learning the answers to oral examination questions parrot fashion.

Back in the present with the computerised combustion control systems we have on marine boilers it is extremely difficult to over-ride any safety systems, just as well when on FPSOs and gas carriers the normal fuel is gas which is essentially free. The systems I have on board my present vessel have 3 operator levels, operator, supervisor and service engineer. Each has their own log-in and password so over-riding of safety systems can't be done willy nilly.
So far I have only been on one ship that experienced a boiler blowback. That occurred in a fruit carrier, tied up in Tilbury. After hours of trying to get the boiler to flash it eventually fired and blew back. 2 guys were kept in hospital and a third came back on board looking like a mummy. No safety systems had been over-ridden but diesel had accumulated in the cracks of the refractory of the furnace floor. When a flame was established the diesel suddenly vaporised and caused the blow-back.

Hopefully that puts us back on topic

Reg

[Shawki Shlemon]

A blow back on the boiler can happen if a fusible plug fails at the time when the fire door is open , I believe it has happened on 7.25" gauge which resulted in sever burns to the driver as I was told a few years ago , I never fit fusible plugs on my boilers as I think they are not necessary on our sizes , my personal opinion .

[marshall5]

A fusible plug blew out of the crown sheet of 'King Haakon' at the G.C.R. in the late 70's/early 80's causing a blowback and severe injury to the crew. IIRC the report concluded that the crown had a 1:20 tapered thread whilst the fitted plug was 1:12 so only a couple of threads were fully engaged and they eventually 'let go'. A mistake easily made but also easily avoided. I always got the plugs from National Vulcan and borrowed the matched tap from their NDT dept in Manchester. Fortunately I never had a fusible plug go but it must have been close on a few occasions! Ray.

[Deleted]

Hello REG, --------- yes, I quite agree with that last posting of yours.....Nowadays it's almost like modern "Fly-by-wire" aircraft ( Aye-aye, is that young Mr.Shawki I hear ??)....... As a "Fruit Carrier" myself I have had several Blowbacks due to an over indulgance of Bananas---but that's just me personal problems come to life, matey, so it is !!!

[greensands]

Going back to the original account given in the RM I find it very surprising that conditions could exist in the firebox which could result in flame engulfing the footplate. Surely there must have been a build up of an explosive mixture of unburnt gases and or fine dust to have this effect. I would have thought that the more common form of blowback would more likely to be a tongue of flame shooting out from an open firedoor and provided that the crew at the time were lucky enough to be out of the line of fire as described by 4930Hagley any exposure to danger although frightening would be minimal.

[Deleted]

Hello Greensands-------- The cab of any tank loco is, by it's very nature a confining space and will tend to magnify the results of a blowback....You only mention a "firedoor not properly shut" from that 1956 Railway Magazine article, but there must have been more than just that ..As you've probably gathered from this thread there are several scenarios which can contribute to a Blowback occuring...One situation that hasn't been mentioned is when first lighting-up a "dead" loco....Apart from the designed rise of the tubes from firebox tubeplate to smokebox tubeplate there is very little in the way of natural draughting and at this stage the blower is not available either...Many running sheds had long, tall ducting and chimneys built-in such to clear smoke AND to help give a draught when lighting-up ( This subject has been covered last year and I posted some photos showing the insides of some depots.)..If your lighting-up coal is high in volatiles these start to be given off as your embryo fire starts to burn and take hold....If they start to accumulate in any volume instead of being cleared away ("Purged") then you do have a potential situation for rapid combustion should a flame catch them and ignite.......You sometimes see this happen at the steaming bays on a model if the person lighting up puts the electric auxillary blower onto the chimney AFTER attempting to light the fire first....It shows as one or more of "POPS" or flashes out of the firedoor and usually makes a smokey mess of your nice paint job on the upper backhead and steam manifold !! ( In this case it might just be accumulated Paraffin fumes or woodsmoke igniting)....Can you find the full details of that RM article for us ??

[greensands]

I have been trying to add a couple of scanned pages of the RM but am coming up with the error message: "The forum has exceeded its space limit. Your file cannot be attached" although the file size of each attachment is <200k Bytes for each copy.
How can I get around this problem?

[Deleted]

That limit is being applied to most of us it would seem...Use a "host" such as PHOTOBUCKET or TINYPICS and follow their instructions.....It may take a bit of practice at first but it does work, I assure you...

[uuu]

This gives me a chance to plug my picture linking guide:

Linking pictures - a three-step guide

Wilf