Author Topic: MID-EAST OHIO MODEL ENGINEERING EXPO Propane Accident  (Read 2789 times)

Offline Bobsmodels

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MID-EAST OHIO MODEL ENGINEERING EXPO Propane Accident
« on: October 23, 2017, 07:12:56 PM »
At the North East Ohio Model Engineering Show I had an accident with my Rider Hot Engine when shutting down.  It caused a bit of excitement for about a minute or so.  I was removing the propane tube from the engine when it caught fire.  I dropped the tube and attempted to put out the fire with a display board I had and it would not extinguish immediately. There were some napkins, a piece of paper, and heavy oil cloth I use for the table covering which kept things burning. While I checked the regulator to insure it was off, a fellow modeler stepped in and he slapped the remaining fire out.  I think the whole incident lasted no more than a minute or so, but it seemed like a lot longer. 

We were packing up to leave so I just made sure everything was out, cleaned up the mess, and we were on our way.  Today I wanted to figure out what happened to insure it would not occur again.

My normal shutting down procedure for the engine is too turn off the propane regulator.  I next empty the water tank which takes about five minutes to disassemble the pipes, remove the tank and dump the water.  I then pull the tube off the burner barb, remove the regulator and store everything away.

For whatever reason this time I turned off the regulator and immediately pulled the tube off the burner.  Clearly there was gas in the tube and the flame had not gone out so it ignited the end of the tube which I dropped so as not to burn myself and then the paper and table cover caught fire. This was a new regulator I had not used before so I wanted to try and repeat the process outside my shop today to insure it was not something with the regulator.

I tried to make it happen about six times with no fire result.  What I was doing was turning the regulator off with my right hand and then with my right hand removing the tube.  However, when I turned the regulator off with my left hand and virtually simultaneously pulled the tube off with my right hand a flame occurred on 4 out of 5 times I tried it.   That is what I must have done.  Using my right hand for both operations must have allowed enough time for the flame to extinguish, whereas using both hands did not allow time for the flame to go out.  I am not sure why I changed my sequence of shut down but clearly it was that change that caused the fire.  The regulator was just fine, just my process change that caused the accident.

What have I learned from this incident is simple; make sure the flame is out before taking apart equipment even if the regulator is off for five minutes while I am emptying out the water tank. I should have been doing that check all the time.

I hope sharing this information may be of some value for others and to let those who were at the show know I have figured out what happened –I screwed up!

Bob

Offline Admiral_dk

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Re: MID-EAST OHIO MODEL ENGINEERING EXPO Propane Accident
« Reply #1 on: October 23, 2017, 09:14:06 PM »
I'm glad to hear that you only got a scare + a lesson  :o

It's always nice when the hard lesson isn't too hard  :)

Best wishes

Per

Offline b.lindsey

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Re: MID-EAST OHIO MODEL ENGINEERING EXPO Propane Accident
« Reply #2 on: October 24, 2017, 12:24:28 AM »
A good reminder for all of us running RE engines or others on propane. Glad it wasn't worse. Thanks for sharing Bob.

Bill.

Offline Rustkolector

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Re: MID-EAST OHIO MODEL ENGINEERING EXPO Propane Accident
« Reply #3 on: October 24, 2017, 05:36:17 PM »
Bob's accident has reminded me that while many model engine builders are quite used to handling flammable fuels at home and at shows, I suspect few of us carry with us any means of effectively extinguishing a small fire at a show. While fire safety should always be on our minds when handling fuel, none of us are above a mistake or an accident. I would hate to see one of my models sprayed with a huge dry chemical extinguisher in an emergency, but it's better than the alternative. Are there any VFD members out there that could suggest a small extinguisher that would be effective without the mess? I have witnessed two fires (both small) at shows in past years and I would like to have one handy. Bob's accident now makes me think we all should.

Jeff

Offline b.lindsey

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Re: MID-EAST OHIO MODEL ENGINEERING EXPO Propane Accident
« Reply #4 on: October 25, 2017, 12:33:37 AM »
Not a VFD member, but is there such a thing as a compressed nitrogen extinguisher. That would rob the flames of oxygen in theory, and leave no mess behind.

Bill

Offline Walsheng

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Re: MID-EAST OHIO MODEL ENGINEERING EXPO Propane Accident
« Reply #5 on: October 25, 2017, 01:22:41 AM »
I just googled compressed nitrogen extinguisher and the only one that came up was $4,000+ and was on wheels?

John

Offline Dave Otto

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Re: MID-EAST OHIO MODEL ENGINEERING EXPO Propane Accident
« Reply #6 on: October 25, 2017, 01:36:29 AM »
I have a small Halon fire extinguisher that I purchased from the Snap-On tool truck years ago; it is approximately 2" in diameter and approximately 7" tall. it is an amazing fire putter outer, I wish that they hadn't banned the use of it. I used it one day at an outdoor engine show when my 1:1 Lake Breeze model B hot air fan caught on fire. It only took one quick burst and the fire was out, there is still close to 90% of the liquid Halon still left. That little fire extinguisher is always in my engine show tool box. Had I known way back when I bought this one, I would have stocked up. CO2 is most likely the next best (clean) choice but they do come at a price and I'm not sure how small they make them.


Dave

Offline Stuart

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Re: MID-EAST OHIO MODEL ENGINEERING EXPO Propane Accident
« Reply #7 on: November 01, 2017, 08:26:27 AM »
Dave

Not to be OTT. But be very careful with halon it’s very dangerous , years ago at the bank computer center we had to remove the halon system on the fire brigades recommendation .  From what I remember it breaks down when in use like CTC .

now the funny thing is they did not object to the 40tons of CO2 for the main floor .

It’s messy in use but I have a dry powder in the workshop by the door and one in the house .


Now a nasty one if you have any magnesium metal you must keep some dry cement powder (if it’s a powder it’s dry ) if it gets alight , it will melt down the machine you are cutting it on , the same applies to titanium. DO NOT UNDER ANY CIRCUMSTANCES USE WATER it will decompose to hydrogen and oxygen ,and go bang

Be careful around any flammable gas,liquid,solid and metals 
My aim is for a accurate part with a good finish

Offline MJM460

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Re: MID-EAST OHIO MODEL ENGINEERING EXPO Propane Accident
« Reply #8 on: November 05, 2017, 07:07:47 AM »
Hi Bob, thanks for posting that, it is only by making sure we know what happened that such accidents can be prevented from happening again, perhaps with a less happy ending.

When you isolate gas at the bottle, there is still gas in the connection to the regulator and in the hose to the burner, enough to keep the burner going for a considerable time.  The regulator opens as the pressure falls and the burner continues until nearly all the gas is burned.  I know from experience with a very small burner I use for silver soldering small components, that after I turn the gas off at the bottle, the burner continues for a very long time on the gas remaining in the hose and ends with a tiny flame that eventually contracts into the burner shroud before it finally goes out.  This would be very hard to see if the burner was installed in the furnace box of a boiler.  So I agree with your conclusion that it was probably your change of procedure that was the root cause of the problem. 

With propane as fuel for an ic engine, a further factor is the demand valve which shuts when the engine stops, thus trapping gas between the demand valve and the regulator and gas bottle valve, so requiring a slightly different procedure.

The question is what procedures or facilities should be recommended to help others avoid learning the hard way.  Without knowing your arrangement better, it is hard to know what might be practical.  But pulling the hose off a barb on the burner does not seem ideal.  The hose will eventually stretch and leak gas when the flame is burning for real.

The principal with control of gas fires is that the fuel should be isolated then the fire allowed to extinguish itself when it has no more fuel.  This principal is based on the fact that once the fire is out, we cannot see where the gas is, and if there is any significant quantity it is highly likely to find an ignition source, often a glowing spark or hot metal remaining from the fire and reignite, possibly with an explosion.  In the mean time, you use water to cool things that might catch a light or be damaged by heat and to extinguish any sparks.  It is hard to know just how much of this carries down to our small scale, and I would be reluctant to advocate heavy handedness.  In a self contained model, the connecting tubes are very small, and the burner quickly exhausts the remaining gas.  At home barbecue scale, hoses are longer but burners are big and again the burner quickly exhausts the remaining gas.  Our silver soldering with small burners generally includes suitable isolation and screwed fittings, but even then, things should be allowed to cool down before disassembling the equipment as closing the valve at the handle traps gas under pressure in the hose which is best burned out if we are taking it all apart to store.

It is when we run our model boilers from a larger bottle on a long hose at home or at a show that things conspire against us.  It is always best to shut off at the bottle first, then wait until the flame is extinguished, but it is difficult to observe inside a small firebox, and we should wait until everything is really cool before pulling hoses off.  An isolation valve close to the burner is perhaps best when it is time for a lunch break, however when everything is to be taken apart and packed for storage or for transport home that it is preferred to empty the hoses of all gas, as there are plenty of ignition sources in a vehicle.

Perhaps a little more discussion would uncover some simple sensible precautions we could all incorporate in our setups for the benefit of all.

When it comes to extinguishers, the best and most available is usually water, it is not a problem on gas fires as it is with liquid fuels, but still ok for alcohol.  Perhaps having beaters and a fire blanket or two available would be the best precaution, obviously your fire was easily put out and lack of a suitable implement seems to have been the main problem. There is no need for an industrial scale extinguisher, for a small situation as you have described. 

Nitrogen is usually a large scale installation, too hard to store enough in a small bottle.  Foam ones for small wood fires is very messy, and the foam is more about smothering glowing embers from paper and wood.  Various halogens, while effective, are now discouraged for various adverse health and environmental effects as others have mentioned. 

CO2 is an asphyxiant in a closed space, but not poisonous, and is usually recommended for electrical fires where conductive compounds are not desirable.  It is available in small extinguishers for car, marine and household use and would be suitable to have on hand.  Dry powder in small extinguishers is also suitable, a bit of a pain, but relatively easy to clean up.  Also readily available in small extinguishers.  But use  water, unless you have liquid hydrocarbon fuels.  Less well known is that water is also perfectly suitable and effective for alcohol fires, or methylated spirits.  It absorbs the alcohol, cools it below vaporisation point which snuffs the fire and cools everything down.  I have even seen beer used, some might feel it was a waste, but it worked perfectly, but do not use spirit drinks with high alcohol content!  The table cloth in the restaurant where it happened was not even singed.

I hope this can help you encourage a little more constructive discussion for the benefit of all.

MJM460
The more I learn, the more I find that I still have to learn!

 

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