Boiler explosions, but particularly during accidents?

[Cowley]

Hi everyone.

I was wondering if there were many occasions where a rail accident lead to a boiler explosion?
Thinking about the huge forces involved in some of the railway disasters in the steam era, I don’t recall there being much more than large leaks of steam rather than full scale explosions (which I assume would have been fairly devastating)?
But the boilers of the locos must have still been working at high pressures?
Any help with knowledge would be much appreciated.

 

[Richard Scott]

Not heard of that happening, have a recollection that an A4 took a hit from a bomb causing the boiler to explode? Anyone confirm correct or if I just made that up?!

 

[Elecman]

I can’t think of any where the boiler exploded after an accident, but there were a large number of steam engine boiler explosions As well as firebox splittings

 

[Ash Bridge]

Not heard of that happening, have a recollection that an A4 took a hit from a bomb causing the boiler to explode? Anyone confirm correct or if I just made that up?!

Off the top of my head, I recall seeing a photograph of an A4 I think it may have been at York shed which was more or less hit directly, can't confirm if a boiler explosion occurred on this occasion though.

 

[DerekC]

There is a horrific picture in LTC Rolt's Red for Danger of a "Precedent" class 2-4-0 which had hit a bridge at Ditton Junction in 1912, with the boiler barrel sheared from the firebox. There couldn't have been much steam left in that after the accident.

 

[edwin_m]

I don't recall boiler explosion being mentioned as a consequence of an accident, and I've read all the reports on Railways Archive back to the Grouping.

The mechanism of a boiler explosion starts with a leak resulting in loss of pressure. Boiling point is greater at high pressure, so the liquid water in the boiler is at more than 100degC and if the pressure loss is great enough then some of the water will boil off very rapidly. The force of this expansion causes more damage and throws bits of boiler and water outwards at great speed.

I do wonder if this depends on the initial leak being within a certain size range. Clearly a small leak such as from a fusible plug doesn't trigger an explosion, and nor does taking steam from the boiler in normal use. A small leak due to over-pressure or structural weakness would weaken the material around it, so could grow to the size where explosion became possible. But a very large instantaneous rupture caused by serious damage in an accident might allow the excess pressure to dissipate more quickly and lead to a relatively gradual depressurization rather than a sudden explosion. However this is only conjecture on my part (and Wikipedia mentions that in America's worst maritime accident, the Sultana in 1865, explosion of one boiler precipitated the same in two others).

 

[Cowley]

I don't recall boiler explosion being mentioned as a consequence of an accident, and I've read all the reports on Railways Archive back to the Grouping.

The mechanism of a boiler explosion starts with a leak resulting in loss of pressure. Boiling point is greater at high pressure, so the liquid water in the boiler is at more than 100degC and if the pressure loss is great enough then some of the water will boil off very rapidly. The force of this expansion causes more damage and throws bits of boiler and water outwards at great speed.

I do wonder if this depends on the initial leak being within a certain size range. Clearly a small leak such as from a fusible plug doesn't trigger an explosion, and nor does taking steam from the boiler in normal use. A small leak due to over-pressure or structural weakness would weaken the material around it, so could grow to the size where explosion became possible. But a very large instantaneous rupture caused by serious damage in an accident might allow the excess pressure to dissipate more quickly and lead to a relatively gradual depressurization rather than a sudden explosion. However this is only conjecture on my part (and Wikipedia mentions that in America's worst maritime accident, the Sultana in 1865, explosion of one boiler precipitated the same in two others).

That’s a very informative answer @edwin_m thanks very much.

 

[hexagon789]

Off the top of my head, I recall seeing a photograph of an A4 I think it may have been at York shed which was more or less hit directly, can't confirm if a boiler explosion occurred on this occasion though.

A4 No. 4469 Sir Ralph Wedgwood and a B16 were both damaged by a bomb explosion at York North Road in one of the so-called "Baedeker Raids" in April 1942. The bomb fell between the locomotives and while 4469 was towed to Doncaster with a view to repairing her, she was ultimately written off as beyond economic repair.

No boiler explosion though.

 

[Ash Bridge]

A4 No. 4469 Sir Ralph Wedgwood and a B16 were both damaged by a bomb explosion at York North Road in one of the so-called "Baedeker Raids" in April 1942. The bomb fell between the locomotives and while 4469 was towed to Doncaster with a view to repairing her, she was ultimately written off as beyond economic repair.

No boiler explosion though.

Thanks for confirming that for me @hexagon789

 

[Merle Haggard]

There was a planned head-on collision in the USA in the 19th century. It was, I think, a publicity stunt in front of spectators but unexpectedly (??) the collision triggered a boiler explosion

 

[randyrippley]

from https://en.wikipedia.org/wiki/Boiler_explosion#Locomotive_boiler_explosions_in_the_UK

Throughout the 20th century, two boiler barrel failures and thirteen firebox collapses occurred in the UK. The boiler barrel failures occurred at Cardiff in 1909 and Buxton in 1921; both were caused by misassembly of the safety valves causing the boilers to exceed their design pressures. Of the 13 firebox collapses, four were due to broken stays, one to scale buildup on the firebox, and the rest were due to low water level

 

[Cowley]

There was a planned head-on collision in the USA in the 19th century. It was, I think, a publicity stunt in front of spectators but unexpectedly (??) the collision triggered a boiler explosion

Yes of course. I’d forgotten about that one.
There’s a wiki page about it here, and I found a YouTube clip with a couple of photos and an explanation:

 

[Bevan Price]

I don't recall boiler explosion being mentioned as a consequence of an accident, and I've read all the reports on Railways Archive back to the Grouping.

The mechanism of a boiler explosion starts with a leak resulting in loss of pressure. Boiling point is greater at high pressure, so the liquid water in the boiler is at more than 100degC and if the pressure loss is great enough then some of the water will boil off very rapidly. The force of this expansion causes more damage and throws bits of boiler and water outwards at great speed.

I do wonder if this depends on the initial leak being within a certain size range. Clearly a small leak such as from a fusible plug doesn't trigger an explosion, and nor does taking steam from the boiler in normal use. A small leak due to over-pressure or structural weakness would weaken the material around it, so could grow to the size where explosion became possible. But a very large instantaneous rupture caused by serious damage in an accident might allow the excess pressure to dissipate more quickly and lead to a relatively gradual depressurization rather than a sudden explosion. However this is only conjecture on my part (and Wikipedia mentions that in America's worst maritime accident, the Sultana in 1865, explosion of one boiler precipitated the same in two others).

Sometimes, explosions occurred because train crews deliberately mis-set the safety valves to try and improve loco performance by getting more steam (at higher pressure) -- but the new setting permitted higher steam pressures than the safe pressure limit of the boiler.

Also, in early years of steam power, the knowledge about materials technology & performance was poorly understood, so component failures (including boilers, fireboxes, etc.) were fairly common.

 

[Cowley]

Thanks for the replies so far everyone.

In the photo below, where the loco has spewed its boiler tubes everywhere (sort of a classic boiler explosion view), what’s actually given way there to cause that? Going on the explanation by @edwin_m and trying to understand it from a layman’s point of view, has there basically been a split in the boiler somewhere (due to a fault like a failed weld, or an excessive pressure buildup) causing a huge and sudden mismatch in pressure leading to the explosion then?
(I know I started this talking about rail crashes, but it’s good to understand what happens when a boiler explodes.
I’ll change the title of the thread slightly so that I don’t have to report myself. )

C&O T-1 steam locomotive, number 3020, after a boiler explosion in 1943. Located near Chillicothe, Ross County… | Locomotive, Railroad photography, Steam locomotive

Oct 18, 2019 - C&O T-1 steam locomotive, number 3020, after a boiler explosion in 1943. Located near Chillicothe, Ross County, Ohio. Image No. cohs-6198

www.pinterest.com

 

[Taunton]

Sometimes, explosions occurred because train crews deliberately mis-set the safety valves to try and improve loco performance by getting more steam (at higher pressure) -- but the new setting permitted higher steam pressures than the safe pressure limit of the boiler.

Although that did indeed happen, some 19th Century safety valves being adjustable, or even had a weight tied to their balance lever (David L Smith's classic books about the G&SW of the era refer), the increased pressure would only be a proportion of what the boiler had even been tested to in its overpressure test at the factory. No recorded explosion though.

One would have thought that, before a major failure of the structure, if the safety valves didn't operate various components like the gauge glasses might fail first.

 

[randyrippley]

Thanks for the replies so far everyone.

In the photo below, where the loco has spewed its boiler tubes everywhere (sort of a classic boiler explosion view), what’s actually given way there to cause that? Going on the explanation by @edwin_m and trying to understand it from a layman’s point of view, has there basically been a split in the boiler somewhere (due to a fault like a failed weld, or an excessive pressure buildup) causing a huge and sudden mismatch in pressure leading to the explosion then?
(I know I started this talking about rail crashes, but it’s good to understand what happens when a boiler explodes.
I’ll change the title of the thread slightly so that I don’t have to report myself. )

C&O T-1 steam locomotive, number 3020, after a boiler explosion in 1943. Located near Chillicothe, Ross County… | Locomotive, Railroad photography, Steam locomotive

Oct 18, 2019 - C&O T-1 steam locomotive, number 3020, after a boiler explosion in 1943. Located near Chillicothe, Ross County, Ohio. Image No. cohs-6198

www.pinterest.com

All the crew died in that incident so the truth is uncertain, but the general speculation on the internet seems to be that the crew allowed the water level to run too low, the firebox crownsheet got red hot so more water was added - and flashed to steam, explosively. The smokebox blew off the front of the boiler - presumably the weakest part, allowing the superheater tubes to come loose. Other photos of the incident show the smokebox lying alongside the loco, blown clear. The fact that all three footplate staff were scalded to death suggests the firebox crown also failed catastrophically

 

[edwin_m]

Sometimes, explosions occurred because train crews deliberately mis-set the safety valves to try and improve loco performance by getting more steam (at higher pressure) -- but the new setting permitted higher steam pressures than the safe pressure limit of the boiler.

A faulty safety valve is another possible cause, as is letting the water level get too low so it no longer covers the firebox crown. If the crew don't notice or don't act on the steam from the fusible plug the resulting rupture can blow the fire back into the cab. Something similar happened with one of the American designs brought in during WW2, mainly because the crew weren't familiar with the different arrangement for working the water gauges.

In the photo below, where the loco has spewed its boiler tubes everywhere (sort of a classic boiler explosion view), what’s actually given way there to cause that? Going on the explanation by @edwin_m and trying to understand it from a layman’s point of view, has there basically been a split in the boiler somewhere (due to a fault like a failed weld, or an excessive pressure buildup) causing a huge and sudden mismatch in pressure leading to the explosion then?

All the crew died in that incident so the truth is uncertain, but the general speculation on the internet seems to be that the crew allowed the water level to run too low, the firebox crownsheet got red hot so more water was added - and flashed to steam, explosively. The smokebox blew off the front of the boiler - presumably the weakest part, allowing the superheater tubes to come loose. Other photos of the incident show the smokebox lying alongside the loco, blown clear. The fact that all three footplate staff were scalded to death suggests the firebox crown also failed catastrophically

I agree the source of failure would be somewhere in the firebox area, crown being the most likely, and the expansion of water into steam starting in that area would push outwards in all directions. The tubes must have been mostly forward of the failure so most of the force on them would be pushing them towards the smokebox.

Another possibility is an explosion in the firebox itself.

 

[pdeaves]

A4 No. 4469 Sir Ralph Wedgwood and a B16 were both damaged by a bomb explosion at York North Road in one of the so-called "Baedeker Raids" in April 1942. The bomb fell between the locomotives and while 4469 was towed to Doncaster with a view to repairing her, she was ultimately written off as beyond economic repair.

Was it one of those that was reputed to have 'shot down' an enemy aircraft by the debris thrown up by the bomb? Or is the story I remember a GWR one?

 

[Gloster]

Was it one of those that was reputed to have 'shot down' an enemy aircraft by the debris thrown up by the bomb? Or is the story I remember a GWR one?

You may be thinking of when two Fw190 attacked a train on the New Romney branch in November 1942. The second aircraft was brought down by an explosion of steam caused by the steam dome of ex-LBSCR D3 2365 being ripped off; the aircraft’s wing may also have clipped the loco.

 

[pdeaves]

You may be thinking of when two Fw190 attacked a train on the New Romney branch in November 1942. The second aircraft was brought down by an explosion of steam caused by the steam dome of ex-LBSCR D3 2365 being ripped off; the aircraft’s wing may also have clipped the loco.

That's probably it than, thanks.

 

[Taunton]

A4 No. 4469 Sir Ralph Wedgwood and a B16 were both damaged by a bomb explosion at York North Road in one of the so-called "Baedeker Raids" in April 1942. The bomb fell between the locomotives and while 4469 was towed to Doncaster with a view to repairing her, she was ultimately written off as beyond economic repair.

No boiler explosion though.

Photo of the damaged A4 here. https://blog.railwaymuseum.org.uk/scribbling-on-a4/

It does look somewhat repairable. I've seen worse recovered. Boiler looks intact. Very few locomotives were actually written off in WW2, in distinct contrast to the situation in France/Germany. GWR Hall 4911 was scrapped after a blast at Devonport in 1941 https://www.steampicturelibrary.com...-hall-locomotive-keyham-station-19929931.html , sometimes described as a direct hit although it wasn't, again the boiler has survived where the cab sheet metal is gone and the wheels, and likely frame, distorted. The firebox cladding is gone, but not the boiler cladding. Notice how the houses behind have their roofs tarpaulined over, presumably roof tiles all gone.

 

[hexagon789]

Photo of the damaged A4 here. https://blog.railwaymuseum.org.uk/scribbling-on-a4/

It does look somewhat repairable. I've seen worse recovered. Boiler looks intact. Very few locomotives were actually written off in WW2, in distinct contrast to the situation in France/Germany. GWR Hall 4911 was scrapped after a blast at Devonport in 1941 https://www.steampicturelibrary.com...-hall-locomotive-keyham-station-19929931.html , sometimes described as a direct hit although it wasn't, again the boiler has survived where the cab sheet metal is gone and the wheels, and likely frame, distorted. The firebox cladding is gone, but not the boiler cladding. Notice how the houses behind have their roofs tarpaulined over, presumably roof tiles all gone.

There was a particular reason they decided not to repair her, I imagine it can't have been too trivial given it was wartime and they would I assume have been more inclined to repair than in peacetime if you know what I mean

Was it one of those that was reputed to have 'shot down' an enemy aircraft by the debris thrown up by the bomb? Or is the story I remember a GWR one?

Was what reputed to have shot down an enemy aircraft, sorry?

 

[trebor79]

I don't recall boiler explosion being mentioned as a consequence of an accident, and I've read all the reports on Railways Archive back to the Grouping.

The mechanism of a boiler explosion starts with a leak resulting in loss of pressure. Boiling point is greater at high pressure, so the liquid water in the boiler is at more than 100degC and if the pressure loss is great enough then some of the water will boil off very rapidly. The force of this expansion causes more damage and throws bits of boiler and water outwards at great speed.

A leak of any size will not cause water to flash off at a rate greater than the flow of steam out of the leak. So you can't have a leak which then somehow causes a massive volume of water to flash off and burst the boiler due to overpressure in the way you describe. It's thermodynamically impossible.
What it might cause is swell and priming, carrying water over into the superheaters and cylinders, causing cylinder and and motion damage.

Sudden evolution of steam beyond the ultimate strength of the boiler and at a rate greater than the safety valves can deal has caused boiler explosions in the past. These are never due to an initial leak. They have always been due to the water level being allowed to drop below the crown of the firebox for a significant period of time. If the water level suddenly covers the crown again, a very large amount of steam will be generated very quickly, and this can ind ed cause an explosion. For example, low water level descending a gradient, the gradient changes to an uphill and water sloshes over the firebox crown. The water is already at booking point so all of the energy contained in the red hot metal goes into booking rather than heating the water.
A bit like pouring boiling water from a kettle into a very hot pan (do not try this at home!).
Alternatively, if the water doesn't eventually cover the crown again, it will deform and cause an explosion that way.

 

[edwin_m]

A leak of any size will not cause water to flash off at a rate greater than the flow of steam out of the leak. So you can't have a leak which then somehow causes a massive volume of water to flash off and burst the boiler due to overpressure in the way you describe. It's thermodynamically impossible.
What it might cause is swell and priming, carrying water over into the superheaters and cylinders, causing cylinder and and motion damage.

Even if the initial flashing off rapidly increases the size of the leak, where the surrounding material was probably nearly as weak as where the leak was, and is now subject to higher stresses due to the leak itself?

 

[randyrippley]

Photo of the damaged A4 here. https://blog.railwaymuseum.org.uk/scribbling-on-a4/

It does look somewhat repairable. I've seen worse recovered. Boiler looks intact. Very few locomotives were actually written off in WW2, in distinct contrast to the situation in France/Germany. GWR Hall 4911 was scrapped after a blast at Devonport in 1941 https://www.steampicturelibrary.com...-hall-locomotive-keyham-station-19929931.html , sometimes described as a direct hit although it wasn't, again the boiler has survived where the cab sheet metal is gone and the wheels, and likely frame, distorted. The firebox cladding is gone, but not the boiler cladding. Notice how the houses behind have their roofs tarpaulined over, presumably roof tiles all gone.

Under wartime supply problems it may have been more use as a source of parts than as a working loco

 

[Elecman]

There is an excellent book on Locomotive Boiler Explosions by CW Hewison

 

[trebor79]

Even if the initial flashing off rapidly increases the size of the leak, where the surrounding material was probably nearly as weak as where the leak was, and is now subject to higher stresses due to the leak itself?

Just a hole in itself isn't going to cause structural failure. Consider for example a mudhole door or washout plug coming adrift. You'll need a change of underwear and want to rake the fire out pronto, but there's no chance of a catastrophic failure, unless the firebox crown gets exposed and melts before the fire is extinguished.

What actually happens in boiler barrel explosions is that there's a catastrophic failure, and the water flashing off blows it apart. But it's not the expansion of water into steam, or a sudden increase in pressure that causes that failure as a result of a little leak.
Once the boiler has failed substantially, the water will flash off almost instantaneously, and it's the steam accelerating through the rupture that then causes further damage like throwing the boiler off the frames etc.

This is why boilers are hydraulically tested. If there's a failure, there's no explosion as water is incompressible. As soon as the vessel ruptures the pressure is released and there's no energy left in the system to start blasting metal all over the place.
You only steam test once the hydraulic test has proven there is no structural issue.
Every year there are examples of poor safety management in industry where vessels are pneumatically tested. If they fail the pneumatic test, death and destruction occurs instead of there just being a small puddle on the floor.

 

[pdeaves]

Was what reputed to have shot down an enemy aircraft, sorry?

One of the bomb damaged LNER locos mentioned. However, as Gloster said, it was probably a Southern one I was thinking of. The incident being that a bomb damaged a loco and the explosion caused bits of loco to fly up and damage the offending aircraft, bringing it down.

 

[randyrippley]

This page describes how the loco "shot down" the german aircraft

The Engine that Brought Down a German Bomber – Rye's Own Magazine

this photo shows the exploded loco, I'm amazed that they managed to repair it

 

[Cowley]

This page describes how the loco "shot down" the german aircraft

The Engine that Brought Down a German Bomber – Rye's Own Magazine

this photo shows the exploded loco, I'm amazed that they managed to repair it
View attachment 84088

Wow. I mean there is literally nothing on it that isn’t bent apart from the smokebox door!