Riddle Me This? Propane Safety?

[mbianka]

I've recently disabled my boats 23 year old propane system in favor of using the small one pound canisters of propane and a butane stove as a backup/second burner. spent several months last year to see if it would work for me and it did. I could still have a propane leak but, it will be less than a pound not a full 10+ gallon tank to worry about.

[Delancey]

I could have it wrong but I believe Yachting Monthly's crash test boat gets blown up with a one pound tank worth of gas.


Not sure how I feel about using small bottles, they have no valve that can be turned off, doesn't that bother you a little bit? Or do you just disconnect the bottle after every use?

http://m.youtube.com/watch?v=Yxm3uMy6MPI&feature=kp

[mbianka]

Originally Posted by cheoah

Assuming this is all hypothetical? Essentially whaddya do when your boat fills up with LP....

If someone left their solenoid on, and mono turned the knob of the old force 10, that would do it, no?

You also have to look under that nice polished stainless steel cook top. I recently did and discovered a possible future cause of a leak namely corrosion of the gas header pipe:
THE BIANKA LOG BLOG: RETHINKING PROPANE ON BOARD

[jtsailjt]

Originally Posted by BandB

Apologize for repeating myself but still waiting to hear the OP's answer to this question. Seems to me the monkey isn't the only part of the scene that's absurd. Would any of you store propane below deck? I sure hope not. We don't carry it period but if we did it wouldn't be there.

Hopefully nobody is stupid enough to store propane below deck, but if the solenoid valve in your propane locker somehow stuck open or was accidentally left open, then it's possible that all that propane could flow into your boat through the properly connected hose if there was also a malfunction in the heat activated valve in your stove or heater. Unlikely, but it could happen.

Some older stoves didn't have a safety device to prevent propane from flowing when the stove wasn't lit. I was cooking dinner on/in my 60's vintage Luke propane stove and went out into cockpit to access the battery switch in the lazarette. When I turned off the battery switch it closed the solenoid valve, causing the flame to extinguish, but when I turned the battery switch back on, the solenoid re-opened, but with no flame to ignite it, it just flowed into the oven and filled it with propane. Shortly after I relit the burner on top of the stove, that oven full of propane exploded. Fortunately, I was back out in the cockpit when it happened but I can still remember the BOOM and seeing the fiberglass cabin top deflect upwards about an inch or so. Since then, I've been VERY careful around propane!

[mbianka]

Originally Posted by Delancey

I could have it wrong but I believe Yachting Monthly's crash test boat gets blown up with a one pound tank worth of gas.


Not sure how I feel about using small bottles, they have no valve that can be turned off, doesn't that bother you a little bit? Or do you just disconnect the bottle after every use?

I think it was a lot more than one pound that they used and they also had to try several times to blow up the boat including putting the tank in the main cabin and then opening valve. Not the usual set up I would imagine.

[a64pilot]

There is risk in everything, trick is of course to reduce the associated risks, it's why most check weather for instance.
A very good way to reduce propane use risks is to ensure everything is in proper order. It's such a simple system you should be able to inspect every part of it in ten min. or less, might want to replace any flexible hoses and the regulator if over 5 yrs old.
5 yrs comes from the recommended service life of flexible hoses used in aviation, number has to come from somewhere.

[mrohr]

I have a compartment , former ice chest ,in my galley that measures 1 sq. ft . opening by 2ft deep, therefore 2 cubic feet volume. I store pots and a propane stove ( 1 lb. tank ) there.One day I smelled propane as I removed my little stove I smelled gas in that little compartment.Drain was closed off ,so time for ann experiment after sniffing the bilges.
I held a battery fan above and in this space for minute or so and with the heavy locker lid at the ready ,I feeling smug with my chemistry degree and experience causing minor mayhem with this knowledge for my own entrainment ,I expecting nothing……………………
lit a match.
WOW!!
I had created a 1 foot square candle flame in my galley!
Buy quick application or the heavy lid all was made whole again. Thinking about it, my guess is that the pots jumbled in the compartment prevented adequate ventilation and even with direct application with a frisky fan, and did not (luckily) even reduce the gas/oxygen ratio to create a proper explosion. The gas bottle had been 1/2 empty so I have little doubt that a full bottle could easily dismantle a stout boat and its occupants.
To those, who in the interest of science wish to repeat this experiment, remember to stand under a open hatch as the match is lit so as to blown straight up out of the boat when the match is lighted.
Give the monkey the finger as you go by.
………………..luv you all …………………………………………………….mike…………………...

[Cavalier]

Originally Posted by mbianka

You also have to look under that nice polished stainless steel cook top. I recently did and discovered a possible future cause of a leak namely corrosion of the gas header pipe:


THE BIANKA LOG BLOG: RETHINKING PROPANE ON BOARD

Good point. I've just finished stripping down and restoring my Force10. I was surprised to discover the poor condition of the supply fittings and tubing to the burners (unlike metals).

[Cavalier]

Originally Posted by Delancey

I could have it wrong but I believe Yachting Monthly's crash test boat gets blown up with a one pound tank worth of gas.


Not sure how I feel about using small bottles, they have no valve that can be turned off, doesn't that bother you a little bit? Or do you just disconnect the bottle after every use?

Wasn't that boat one of the surprisingly unpopular 2004 Beneteau Semtex 40s?

[Cavalier]

Originally Posted by Delancey

This is great. RMS took me to Maxwell-Boltzmann Distribution which is what I was really looking for, to understand the mechanism by which gases dissipate. Any idea how long it would take a given quantity of propane to clear from a boat?

Also, for your heavier-than-air viewing pleasure-

Yes. It's part of the Kinetic Theory of Gases. Maxwell-Boltzmann distributions are more of a statistical distribution method which works well with idealized gases.

To answer your question regarding how long would it take for the propane to clear from the boat, then we could consider the RMS Velocity of Propane.

If Propane (C3H8) was in a container by itself, at 1 atmosphere (absolute) pressure at 25C (298K), then the Root-Mean-Square (average, rectified for directionality) velocity of the gas molecules would be:

Firstly, we need the molar mass (kg/mol) for C3H8, which is
(44.0962/mol) * (1kg/1000g) = 0.0440962 Kg/mol

Then the RMS velocity of the propane would be

Vrms = Root(3RT/M) = Root((3*8.31*298)/(0.0440962)) = 410 m/sec

Remember this is a vector corrected mean, such that you'll get a standard distribution (bell curve) of molecular velocities, some slower, some faster.

Note that this appears like a high speed, but bear in mind that we have a more complex mix in the cabin of and actual boat, and only a small percentage of the inner surface area of the cabin is a hole through which the gas can diffuse (and escape). The rate at which the gas diffuses is dependent upon, the volume of the cabin, the geometry of the cabin, the size of the companion-way as a percentage of the overall cabin surface area, the initial volume of the gas (at 1atm), the temperature of the gas, and the rate of throughput (ventilation) of other gases through the volume of the cabin... As you can imagine, there are many, many variables which could give you too many answers. I could have worked through an example calculation using my own boat, but I'm already finding the typing equations into this text-box in 'excel' format a real pain, and the webpage already crashes once while I was halfway through typing.. (Sorry for that)

On that last note regarding molar mass of the gas, you may recall Graham's Law:
"The rate of effusion and diffusion is inversely proportional to the square root of the molar mass of the molecules."

So, for two gases..
(RateX/RateY)=(Root(MassY)/Root(MassX)

If we say that Gas X is Methane (CH4), and Gas Y is Propane (C3H8), you'll note that Propane's molar mass is much greater than Methane:

Gas X = CH4 = 16.04g/mol
Gas Y = C3H8 = 44.09g/mol

Calculate through and you'll see that Methane diffuses 1.65 times faster than Propane. Indeed, the heavier the molar mass of a gas, the slower the diffusion, due to the lower V(rms).. If you look up at the original RMS calculation, you'll see that the molar mass of the gas is the denominator (at the bottom) of the fraction inside the Root.. the bigger this number, the lower the Velocity..

Back to the diffusion issue - when you consider all of the parameters required to calculate the time to 100% escape for the gas from the cabin, you'll note that statistically, it'd take a very long time for that last (un-trapped) molecule of propane to leave the cabin... the better question to ask is, when will the concentration of gas (compared to air) fall below the Lower Explosive Limit for propane.. and at what point can you reenter the cabin without inhaling pure propane (thereby displacing air from your lungs)... lots of things to think about.

For these reasons, that's why my recommendation was to open what vents you can and then hit the bar for a few hours so you can discuss more interesting stuff!

..hope this went part the way to answer your question.