Blowbacks & dropped fusible plugs etc.

I had a similar (in terms of physics) incident a couple of years ago with the stove in the sitting room. I was burning coal on it, had put new on, closed door, air vents shut down so it was just ticking over. After a while opened door to throw something on, and BANG - WHOOSH. singed eyebrows and face, and soot all over the room. Now, this was from a 1ft square firebox, one can only imagine how much more terrible it must have been with a fire and firebox many many times that size - as evidenced by the poor crew going to hospital. Hope they get fully better, and a wake up call for other crews. We all need them from time to time - whatever our profession.

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

Hmmmm, what you describe with your stove sounds like a carbon monoxide explosion - you put fresh coal on with the air vents shut so you ended up with a producer gas retort (as in manufacture of coal gas - also known as town gas and producer gas) so when you opened the door you added oxygen which allowed the CO to explode. This also sounds like the A3 explosion described above.

I understood blowback to be the effects of the exhaust being throttled by an obstruction close to the chimney - a bridge or tunnel roof for instance - which pressurises the smokebox and forces the fire gas back through the tubes, into the firebox, and blows the flames through the firebox door. There would not be an explosion - just a rush of gas and flame.

The problem with 70013 could have been either, but they would be due to completely different physical effects.

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

A couple of clarifications required here.

First of all, producer gas and coal gas are definitely not the same. Producer gas is produced by blowing air through red hot coke. It's basically a mixture of carbon monoxide and nitrogen. It's an exothermic reaction, and sometimes it was produced in conjunction with water gas, which is produced by blowing steam through red hot coke and is endothermic. The processes were alternated, or sometimes steam was introduced to maintain a steady temperature, and so a mixture of producer gas and water gas resulted. Water gas is basically a mixture of hydrogen, carbon monoxide and nitrogen.

Coal gas on the other hand is made by baking coal until it becomes coke, and the volatile matter becomes the coal gas. It is basically a mixture of hydrogen, methane, ethane and carbon monoxide plus a few other gases such as hydrogen sulphide produced by the impurities in the coal.

Concerning blowbacks on locomotives, the term originated to describe what happened when combustion in the firebox was interrupted for any reason, and an explosive mixture built up which then ignited and flames erupted into the cab with explosive force. Reasons for this are many and varied. For example a large quantity of fresh coal can reduce the gas temperature so much that the flames go out and then re-ignite. Or there could be a shock wave down the chimney caused by a passing bridge or tunnel which interrupted the continuous flow. Combustion in the firebox can be quite erratic. Many people who work on steam locomotives will be familiar with the sound produced when a hole develops in the fire and an oscillating flame results. Flames can erupt into the cab for other reasons, such as a broken steam pipe, or a boiler or tube failure of some kind, and this is usually also referred to as a blowback, although it is not the same thing. The last serious boiler failure on BR occurred on a southbound passenger train at Bletchley in Jan 1962. The crown of the firebox failed and the crew were lucky not to be seriously injured and this was referred to at the time as a blowback incident.

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

Thank you for the information. It does seem that the term blowback is a bit loose considering all the various reasons that problems can occur.

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

Surely the collapse of the crown is due to low water in the boiler? And, before that, don't the fusible plugs melt and blow steam into the 'box to damp the fire, cutting off the oxygen, thus stopping further combustion?

Blowbacks, as I understand them, usually occur through pressure downdraughts down the chimney, i.e, when diving into tunnels, etc. The blower, which is the driver's responsibilty, is put on when entering tunnels, to stop the positve pressure wave blasting flames back through the fire-hole doors and into the cab.

Kilsby tunnel on the WCML was notorious back in steam days, especially with a 'Duchess'. The usual thing was to put the flap up, close the doors, put the blower on full and wedge youself in the far coners of the cab, by the forward cab windows and cross your fingers. So I've heard....

A tube collapsing or a superheater element bursting is different, this, obviously, didn't happen to Ollie.

My memory is going, but didn't a superheater element burst on Taw Valley ( or some other southern engine) a few years ago and the fireman was badly burned?

Alan.

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

In a word 'no'.

The fusible plug in a large locomotive boiler provides some warning and may dampen the fire a little. With a large fire, however, the effect can be missed. In fact 6224 "Princess Alexandra" TWICE had the firebox collapse after the plugs were dropped.

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

Thanks for that. My knowledge is not that extensive regarding steam. However, what is the point is having fusible plugs if the effect is so negligible? Just a question you understand, not to be classed as dismissive in anyway.

****Disregard the above - just Googled the fact about P'Alexander' and it appears that it's only a warning and not a fail-safe device and can be overlooked. ****

Cheers,

Alan.

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

Well... perhaps I was a little dismissive of the effect. It should be noticeable, and in the case of the second incident with 6224 it was noticed, the loco was checked for the sound, and due to a gauge glass issue the reason couldn't be discerned. They continued and the crown collapsed.

This is a statement from a report on a low water incident - "Witness evidence mentioned a ‘high pitched whistling sound’ from the locomotive after it had stopped. This is likely to have been the sound of the fusible plug operating. The fusible plug is provided to indicate to the crew the need to drop the fire".

Again in this case, the driver of the locomotive didn't immediately recognise what was happening. It's a signal, but the signal has to be understood to be able to act upon it.

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

That's the theory. But in practice -'fraid not. It's something of an illusion to imagine that the fusible plugs give any protection at all.

Fusilble plugs tend to be a warning device. And usually a very poor one. They do NOT put the fire out. Unless the fire is almost out already. Worse than that, if the engine is working hard, or the crew is otherwise distracted, the chances are they won't even notice dropped plugs. There are numerous examples of that being the case, many of them ending with fatalities.

Crown failure is usually due to low water, but it could also happen if the support to the crown fails. Which is one reason why the inspection regime is rather hot on crown stays these days. Some would say excessively so.

That is one of many situations that can cause a blowback. And it has to be said that in such a case it is the relative small reduction in gas flow which creates the conditions for a blowback, rather than any reverse flow occurring. A real blowback is an explosive event, not only flames entering the cab.

Sorry to differ, but Kilsby was not a tunnel that had any such particular reputation. The clearance is larger than in most tunnels. It was more renown for rough riding within the tunnel. Linslade was the tunnel with the worst reputation. The down fast and up slow are single line with tight clearances and it was in one of those that the crew on 34027 experienced a problem. Also the Duchesses were not as prone to blowbacks than some other classes. The larger fireboxes could cause a more fierce effect when they did occur though, and with the habit some of them had of filling the box up, when it did happen it could be bad. From what I've been told by Enginemen on that particular line, it was the Royal Scots that were the engines to be really wary of. Working out of Euston, Kensal Green tunnel was where it used to happen often, and that is a twin track tunnel, so it didn't take much to trigger a blowback on a relatively cold engine.

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

The incident I think you're referring to involved 35005 Canadian Pacific but at this present moment in time I cannot remember much about it nor can I find any information on it. I believe it involved a steam pipe fracture but don't quote me on that one and I'm sure that someone on here will have more information on it.

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

IIRC it was at Paddock Wood and there was a high-up from NR on the footplate at the time who was quite badly burned? Surprisingly little to be found on Google however.

Found this - incident was Oct 2002 (must have been a lot less t'inernet chat back then) ...... https://groups.google.com/group/uk.railway/browse_thread/thread/5a8ebeb957cf6e6/b3c9ad071666fd9a%3Fq%3D%2522Andrew%2BNaish%2522%23b3c9ad071666fd9a&ei=iGwTS6eaOpW8Qpmqic0O&sa=t&ct=res&cd=1&source=groups&usg=AFQjCNGdl5NhtVvwcrxYgcDoVCxfhCjcYA

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

That's the one! Told you my memory was going....also thanks for the extra info.

Alan. ;-)

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

A lot of people, including some regular posters on here, are of the misguided opniion that a dropped fusible plug will put out or sgnificantly dampen the fire. This is far from being the case. In the relatively recent incident with 35028 the dropped plugs had no effect (and I think they have four), causing at least one poster (who was present) to change his mind on the subject. In the most recent incident on the Kirklees Light Railway, the driver didn't realise that the plug had dropped and it certainly had no effect on the fire, which is relatively small by any standards. The firebox came very close to imploding before the fire was dropped.

see http://www.raib.gov.uk/cms_resources.cfm?file=/120313_R042012_Kirklees.pdf

The Black Book and all the other good books say that, if a fusible plug is dropped due to overheating, you should take immediate steps to deaden or drop the fire. What would you do if you had the knowledge that the firebox crown had become overheated and was in imminent danger of collapsing?

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

Panic?

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

Six beats in both directions then leg it?

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

Put both injectors on, drop the fire and take very long steps as quick as possible.

Roger

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

Post removed by houghtonga:

referenced report into King Haakon VII incident at Loughbrough 1976 from Railway Archive website mentions names of persons who might be known to persons on this forum.

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

Not necessarily the easiest thing to do, though... Not so bad on an engine with some kind of rocking grate, but lots of old engines have no such thing, so getting the fire out means through the firehole door. Add in that the engine might be a tank engine with a fairly small cab and the simple statement "drop the fire" takes on a vastly different complexion.

(I'm not disagreeing with the advice, by the way; simply pointing out that dropping the fire on, say, a Bulleid, and doing so on, say, a Terrier, are two entirely different matters).

This is getting rather a long way away from 70013, though, where AFAIK we don't really know what happened, and certainly not the cause. IMHO.

Tom

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

One of the most common causes of dropped plugs is injector failure.

 

Re: Reported Incident with 70013 Sun 27th May on the Peak Forrester.

What is the correct procedure? or does it vary according to circumstances?

May sound a stupid question, but as some have posted, in incidents of plugs dropping, it can go un-noticed, I am curious as to then why have them? Or was it conceived to serve as a basic warning device? ie something better than nothing?

Why also, is there such a myth, that the dropping of the plug will extinguish / reduce the fire?