Boiler Overheat Accident

[gondolier88]

Re the use of dry powder type fire extinguishers- probably telling you hows to suck eggs, but the way the powder works is to stick to any hot surface it comes into contact with- thus assuming that the fire is going to be hot (they usually are) and that the powder will stick to whatever fuel is burning and smother it.

However, in a typical steam launch there is pipework, the engine, boiler fittings etc that would all get covered in it. As has already been said, it isn't very nice stuff to cover a steam plant with. However it doesn't end there- any electrical components that happen to be on won't get away scot free either- mobile phone, GPS, nav lights- if they get it inside them say goodbye! The powder was after all designed specifically to suit electrical fires.

I don't know if any of you have ever let one of them off, but they make a massive amount of mess everywhere- a typical 1kg extinguisher would cover an 18ft boat no problem.

The best thing to do if you did suddenly lose water is to go to the source of the problem- the fire, in the case of oil or LPG it is a quick thing to do, but with solid fuel a little more difficult, but still easy to do before any damage has been done;

1.Open the fire door and shut bottom draft control- already you are introducing massive amounts of cold air above the bed of the fire and taking the furnace temperature down by 3-400deg.

2. Drop the fire- if you can get to the grate with a fire iron lift a fire bars and drop the fire through the gaps, if this is difficult to do even in a non-emergency situation the carry a small bucket of sand and a small enough shovel to deploy the sand accurately over the fire.

3. Damage limitation- assess, if you can the temperature of the firebox crown- a combination of things, mostly experience with your own plant, will tell you if you have damaged the boiler already or not. The first one of course is the fusible plug- if you can get down to have a look through the firedoor up at the crown- is the fusible plug dripping- if not and it looks sound then you should in all likelihood not have caused any damage- if you have dropped the plug you will tell without looking!!! If all looks ok then if you have a hand feed pump introduce a small amount of water into the boiler- watch the pressure gauge- if it ramps up in pressure then your boiler is still overheated and is acting as a flash boiler- the combined shock loading of cold water and sudden pressure increase will do a typical shell boiler no good at all- wait for what you think is a safe amount of time and introduce water again until you see it in the glass, then keep filling if all seems ok until you have full gauge glasses. This will have cooled the boiler down enough to have a good inspection for where potential leaks may have caused a sudden loss of water.

Having operated SY Gondola's engine room for 10 years I know how quickly things can go from perfect to potential disaster. The worst one I had was only last year- we had been having problems with the blowdown pipework and couldn't isolate the valve on the boiler, nor the one on the hull properly. I came in one morning- having given prior verbal instructions and a written notice in the engineer's daily checklist folder so anyone operating the engineroom would know that BOTH valves MUST be shut as far as possible overnight- however the one on the hull had only been placed in the shut position and hadn't had the glands tightened- a standard procedure for any sort of positive isolation as the valves had become that bad.

The result- as I lit up and increased pressure, everything appeared fine- but as I got to around 20psi and in the middle of polishing etc I looked at the glasses and saw nothing!!!!! Oh dear!! I had a roaring fire as I was getting pressure up for the day and no water to make steam for the injectors- we have no manual feed pump provision. An added dimension is that being a passenger boat if I caused damage to the boiler she would not sail for the rest of the year and would make no money, but even if I just dropped the plug we would still be 3-4 days off the water- in summer around £5000 worth of lost income.

I shut the bottom draft, opened the firedoor and raked the fire through the grate, what was left I banked up at the back of the firebox, we also have a flue damper as we burn wood so I half shut this- this kept a flow of cool air running through the boiler with the firebox door open. This done I checked the fusible plug and the firebox crown- all was fine. I removed one of the blanking plates off the backhead and inserted a hosepipe- pushing it as far past the crown as possible and started filling slowly- after around 10mins of slowly filling I had water in the glasses- the crown was definitely covered again so the hose went on full, 15mins later I had a roaring fire, 30psi and a full boiler, we only missed the first sailing of the day and the boiler was fine- I'm in no doubt that had I not seen the situation as early as I did things could have been a lot worse.

Goes without saying the blowdown pipework is now all new with new valves!!

Greg

[87gn@tahoe]

I would be a bit leery sticking my head down there to check the fusible plug for fear of it letting loose whilst checking. Id it did let loose wilst your face was down there, it is very likely that you would suffer excruciating paint that would be drawn out for days until your untimely death. Nothing like getting your face boiled.

May I suggest a mirror with a handle?

Another thing one must remember is that fusible plugs should be replaced every few years, as the material that is supposed to melt out can oxidize which takes MUCH higher temperatures to melt.

[gondolier88]

You could get a lovely clean shave after a steaming like that though! I would be wary doing anything near a possibly overheating boiler, but having an idea of the state of the plug is paramount- and yes, an inspection mirror would be very handy- but I bet you can't find yours in your toolbox quicker than you can have a quick look in the firebox...

Over here plugs are usually replaced on the 5 yearly hydro test, or sooner at the boiler inspector's discretion.

Just out of interest, does anyone know the ratios of metals in the alloy in fusible plugs?

Greg

[Mike Rometer]

It is one thing having a fusible plug, but quite another where it is positioned. Ideally somewhere where it can be fairly easily seen, but not where it will eject the contents of the grate out the firedoor, and therefore no need to "stick your head through to door" to see.

[Lopez Mike]

I had no idea that the plugs might increase their melting points with age. On my boiler, the lower tube sheet is so far below the bottom of the glass that I'm pretty sure there is no plug. One more thing on the list. The one on the Shay locomotive was probably older than the hills.

On my sailboat I have a freon bottle in the engine compartment that is supposed to let go all on its own in a fire emergency.

I would hesitate to make my own plug. Too important and not that expensive.

[DetroiTug]

Mike, I see you mentioning Shay loco's, thought you might like to see the one I have, here are a few pics. In G scale.







Sorry for the sorta off-topic. Carry on with boiler overheating

-Ron

[gondolier88]

"stick your head through to door".

or, as I wrote; "look through the firedoor"! Quite different!

[RogerV]

Pardon my ignorance, but I'm still very much in the learing stages... anyway, do VFT boilers as typically used in many steam launches have fusible plugs in them. And is it possible to "drop the fire" in a boiler like that, or does it depend on what model you have?

And regarding fire extinguisers, I am on the Safety Committee at my place of employment, which is a public television and radio station. When the building was built, it was equipped with halon fire extinguishers, which you can no longer get, though you are allowed to keep the ones you have.

The committee was discussing buying additional fire extinguishers, and the chief engineer was adamant about not wanting the dry chemical type, saying "that's really nasty stuff in them."

I countered with "FIRES are nasty!" After some wrangling, I made the suggestion that we move the halon extinguishers into the areas with the most expensive and sensitive equipment in them, and put the dry chemical types in more general areas like offices.

And by the way, halon is totally ineffective outside. We had an engineer attempt to help put out a grass fire with a halon extinguisher, and it did nothing but cost $300 to have it recharged. I THINK there is now an acceptable substitute for halon on the market now, but I don't know its name.

[Lopez Mike]

Ron, your Shay is in much better condition that ours was in spite of ours being over twenty times larger. Better looking crew too.

[Dhutch]

Just read the report, seriously scary stuff. Im very aware of the importance of keeping water in the boiler and have always been taught that it the most important thing to check but am equally aware how rapidly it is used should something out of normal operation occur.



Daniel