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Locomotive boiler explosions (and how to avoid them)

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Firebox _on _a _steam _train -sml

As anyone who’s seen the classic 1953 British comedy The Titfield Thunderbolt will know, letting a steam locomotive’s boiler run dry can be a disastrous situation!

As he mentioned in our previous interview with Bressingham Locomotive Driver John Riley, Driving a steam locomotive involves constant monitoring of the steam pressure - failure to do so could result in a boiler explosion!

What is a boiler explosion?

There are actually two types of ways a steam locomotives’ boiler can explode - the first is when is parts of the train connected with steam and water fail under pressure (this is a boiler explosion)

The second type is when the explosion is to do with the fuel and air parts of the locomotive - this is more accurately called a Firebox explosion.

Either way, they’re both bad and can result in disaster!

Steam -Train -boiler -explosion -2

This is a photo of a locomotive after a boiler explosion - the things that look like tentacles are the remains of the tubes that are normally filled with pressurised, super-heated water.

In the comments someone has noted that it looks like something out of one of H.P. Lovecraft’s Call of Cthulhu stories!

What Causes boiler explosions

There can be numerous causes of a boiler explosion such as failure of the safety valvecorrosion of critical parts of the boiler, or low water level. Corrosion along the edges of lap joints was a common cause of early boiler explosions apparently.

As with any industrial accident, a boiler explosion would need to be thoroughly investigated and reported on to help avoid any future incidents. Whilst researching this post we came upon such a boiler explosion safety report - Intriguingly compiled by NASA! (Possibly as an exercise or illustration of methods?)

The report investigates a Steam Locomotive Firebox Explosion on the Gettysburg Railroad in Pennsylvania in 1995 in which a Steam locomotive with six passenger cars during slow climb up moderate grade, the boiler exploded, unfortunately seriously burning the engineer and two firemen.

The report’s findings present a list of contributing factors such as:

  • Operators began climb with too little water in boiler

  • Water-level continued to drop and by the time the locomotive had crested the grade the crownsheet of boiler was not covered by water and failed due to thermal overstress.

  • Failure of crownsheet opened boiler to the firebox (atmosphere) and the water in boiler flashed into high pressure steam.

  • Prior to operation the feed pump gauge had been removed.

  • Preparing to ascend grade first fireman shut off the feed pump to the boiler because a leaking check valve between the feed-pump and the boiler could potentially cause slippage on driving wheels.

  • On climbing grade at approximately 15 mph the boiler pressure dropped from 230 psi to 175 psi. Firemen did not add water but did monitor water glass to make sure water level didn’t become dangerously low.

These and other factors resulted in Steam exploding through firebox door into the locomotive cab, seriously burning the engineer (third degree burns over 65% of body) and two firemen.

Fortunately such incidents are very rare!

Avoiding Boiler explosions

The same report presented methods of preventing the same thing happening again - many of which involve greater attention to detail and improved maintenance (all of which Bressingham spare no expense in carrying out!):

  • Boiler water-level indicators (water-glass and gage cocks) must be blown out and tested before each trip. (49 CFR 230.40)

  • Boiler water-level indicators must be removed and thoroughly cleaned of scale and sediment at least once a month.

  • Boiler must be washed at least once a month to minimize scale build-up.

  • Records indicate that boiler wash and boiler waterlevel indicators had been cleaned. (NTSB Investigation later revealed that cleaning had not occurred as recorded and that testing and blow-out of water-level indicators had not been performed properly).

  • Feed-pump gage that indicates if pump is effectively pumping water into the boiler was removed.

  • The check-valve between the feed-water pump and the boiler had been leaking on earlier trips.

  • Water-glass light inoperative.

Is there anything we should’ve mentioned?

Do you have any thoughts, comments or views on Steam Locomotive safety?

Is there anything you think we should have mentioned?

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By Alastair Baker at 18 Oct 2017, 00:00 AM