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  #11  
Old 04-03-2013
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Re: Propane leak into the bilge. What to do?

Any computer fan, all of which are non-brush type fans, will do the job of evacuating the gas. These have permanent magnet motors that cannot generate sparks. Just make sure the fan is connected to a battery and turned on prior to entering the boat.

A safer method would be to merely open the boat's front hatch, insert an air-scoop, open the back hatch, bilge hatches, motor access hatches, and if there's any breeze at all the entire air contents of the cabin and bilge will quickly be exchanged.

For the future, get a sniffer with a selonoid valve that automatically shuts off the gas if the slightest concentration of propane, and other explosive gasses, is detected. They can be found for under $200 at most marine stores, and in some RV stores, under $100.

Good luck,

Gary
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  #12  
Old 04-03-2013
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Re: Propane leak into the bilge. What to do?

Quote:
Originally Posted by BubbleheadMd View Post
I served on submarines where evacuating toxic/explosive gases and replacing them with clean air is a daily part of life. There is a factor called the "half-life". The half-life is the time that it takes to replace HALF of the atmosphere on the entire vessel.

A recreational sailboat (even a serious cruiser) is much smaller than a submarine, so the half-life is considerably shorter.

In your scenario of a catastrophic hose or seal failure, yes, an ignition proof blower like the one for gasoline marine engines is a good idea. Obviously, open all hatches and ports if weather conditions are calm enough. The diaphram bilge pump will not move a significant amount of gas.

If you disperse CO2 into the bilge, you could displace the propane from the bilge, into the main cabin.

To calculate your half-life, estimate the volume of your cabin (or bilge if you prefer), and the CFM rating of your ignition-proof blower, then calculate how long it will take the blower to move HALF of the volume of the bilge.

This will help you determine how long you need to run the blower, in order to clear the bilge of propane.

Hope this helps.
That's good info. BubbleheadMd. The questions that need to be answered are whether or not "spark protected" devices that were designed for gasoline vapor are good for propane as well. I also wonder whether CO2 or Halon would be displaced, diluted, or mixed with a bilge full of concentrated propane. Propane and CO2 molecules are very close in molecular weight, so who would displace whom? Most of the info. on fire suppression substances is based on after-the-fire-starts scenarios. The issue of intervening to eliminate an explosion before it can occur is not usually discussed and is a good topic to explore. I once popped a large CO2 cylinder with a "Cutter Valve" mechanism in an old wood boat because it was showing signs of rust. The resultant gas lingering in the bilge took HOURS to dissipate and would be quite dangerous if you couldn't get off the boat.
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  #13  
Old 04-03-2013
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Re: Propane leak into the bilge. What to do?

Propane along with other explosive gases have a window or opportunity for an explosions. There has to be the right mix of oxygen to propane to allow an explosion. If it were me an I found the boat filled with propane I would shut off all electrical before opening and hatches. If you have a blower to remove air from the bilge I would run that and not open any hatches. Once you open hatches you allow air and oxygen in and may make it worse. If you have no other option just shut everything down before opening. I would open hatches aft and move forward lifting them open. If you cannot get off the boat or into a dinghy then I would sit on the bow pulpit and sweat till I thought it all clear. The real solution is to have a proper system that will not allow this in the first place. I heard a story once of a boat at sea running the engine. The engine sputtered and died when they opened the hatch to find out why they found the bilges filled with propane so dense the engine could not run in it. They aired out and got going again but my guess it it tightened them up a bit lol

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Old 04-03-2013
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Re: Propane leak into the bilge. What to do?

Propane is more dense than air. However, I think is would be close enough in density that any circulation will basically 'splash' the propane in the bilge around enough to mix with the air in the cabin. Then is can be ventilated with open hatches. I would second using bilge fans. The motor for the fan (and the switch if you want) is usually located somewhere remote (like in a cockpit locker).

Boats with gas engines also, sometimes, have dual cowls. One pointed forward and one pointed aft. The hoses feed to the bilge to have a constant (small) flow of fresh air.

Quote:
I heard a story once of a boat at sea running the engine. The engine sputtered and died when they opened the hatch to find out why they found the bilges filled with propane so dense the engine could not run in it.
That is impressive and eye opening. I suppose a running engine would tend to keep any gasses at bay in the area of the engine b/c it is always drawing in fresh air.
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  #15  
Old 04-03-2013
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Re: Propane leak into the bilge. What to do?

smurph, if you knew what a Halon bottle costs to fill these days, you'd never suggest using one, even for a fire, unless your life was at stake. OTOH I'd agree that a CO2 bottle might be a good idea although over ten years ago that was a $40? $50? refill as well. I'm afraid to ask what it would cost today. Weighed one of my CO2 bottles last week and it was well OVER the gross weight, so I just dusted it off and backed away respectfully.

Med, you just need to ventilate without sparking. A plastic bucket would work, you can haul the stuff out with a bucket. A sheet of cardboard fanning it will work. Open hatches and a good breeze might work even if you have one of those 6' deep bilge sumps.

I'd worry more about putting the boat in "absolutely can't spark" mode than in how to get the propane out. Once you are sure it won't be set off, there's no urgency about the rest. An "explosion resistant" main battery disconnect might be in order, with nothing hooked up bypassing it.
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Old 04-03-2013
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Re: Propane leak into the bilge. What to do?

Air (roughly 78% Nitrogen, 21% Oxygen), propane, CO2, and Halon (or the ozone-safe replacement gas) are all miscible at atmospheric pressure. So, while adding CO2 or Halon would reduce the LEC (lower explosion level) fastest, simply adding air will do the same thing. Using an ignition protected blower is simple and safe, and many boats already have them in place. That's what I would do.
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Old 04-04-2013
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Re: Propane leak into the bilge. What to do?

Quote:
Originally Posted by smurphny View Post
That's good info. BubbleheadMd. The questions that need to be answered are whether or not "spark protected" devices that were designed for gasoline vapor are good for propane as well. I also wonder whether CO2 or Halon would be displaced, diluted, or mixed with a bilge full of concentrated propane. Propane and CO2 molecules are very close in molecular weight, so who would displace whom? Most of the info. on fire suppression substances is based on after-the-fire-starts scenarios. The issue of intervening to eliminate an explosion before it can occur is not usually discussed and is a good topic to explore.
Smurphny, to answer your questions:

1. Yes, a "spark protected" device good for gasoline vapour will also be fine for propane.

2. Commercial Propane is mix of gases (mostly Propane, Propene, Butane and a bit of Ethyl Mercaptan) and, being not all that much heavier than air, will mix with pretty much everything around including lots of oxygen inside a small, rocking, boat and then go off nicely with a little spark.

3. You REALLY don't want to let off either CO2 or Halon extingushers on a small boat and I actually thought it was illegal in many countries to have them on board. Reason being, you might put out a potential fire - but you'll asphxiate yourself first.

Quote:
Originally Posted by Barquito View Post
That is impressive and eye opening. I suppose a running engine would tend to keep any gasses at bay in the area of the engine b/c it is always drawing in fresh air.
It's already been pointed out that a diesel engine will run happily on propane up the air intake - often to destruction, since there is no (safe) way to shut down the engine. I guess that would make using the engine a BAD way to keep any gases at bay..


The best, most practical, most normal, most-used-everywhere option is, as mentioned earlier, is to turn off all electrical devices and ventilate the boat.
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  #18  
Old 04-06-2013
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Re: Propane leak into the bilge. What to do?

Quote:
Originally Posted by Hartley18 View Post
Smurphny, to answer your questions:

1. Yes, a "spark protected" device good for gasoline vapour will also be fine for propane.

2. Commercial Propane is mix of gases (mostly Propane, Propene, Butane and a bit of Ethyl Mercaptan) and, being not all that much heavier than air, will mix with pretty much everything around including lots of oxygen inside a small, rocking, boat and then go off nicely with a little spark.

3. You REALLY don't want to let off either CO2 or Halon extingushers on a small boat and I actually thought it was illegal in many countries to have them on board. Reason being, you might put out a potential fire - but you'll asphxiate yourself first.



It's already been pointed out that a diesel engine will run happily on propane up the air intake - often to destruction, since there is no (safe) way to shut down the engine. I guess that would make using the engine a BAD way to keep any gases at bay..


The best, most practical, most normal, most-used-everywhere option is, as mentioned earlier, is to turn off all electrical devices and ventilate the boat.
The main concern is certainly getting the gas out of the bilge and dissipated into the air. The dilemma is that in this situation it is difficult to know what sequence of events would be safest. If there is wind blowing and you can open up, it seems it should be possible in a reasonable amount of time to blow it out. I have never had the contents of a 20# bottle of propane settled in the bilge so can't really say how difficult dissipating it might be. My thought was that in this situation, immediately prohibiting combustion would be a better way than to screw around with a certain bomb-in-the-bilge. We all have seen the results of propane ignition. Quickly eliminating any possibility of this happening would make sense to me, rather than hoping to avoid generating a spark while fiddling around trying to turn off switches. Refrigeration, bilge pumps, computers, radios, etc, could all supply ignition. Many laminate workers have discovered the hard way how refrigerators can ignite contact cement fumes.

CO2 IS dangerous as far as asphyxiation but if used with that knowledge might stop any potential explosion. Not being a chemist, I don't know if it would possibly just sit on top of the propane (which would not solve the problem), settle under the propane (forcing it up and out), or mix with it chemically. We need a chemist or someone in the industry to chime in on that. Same for Halon. Hand-held CO2 extinguishers are still available and, yes Hello, those Halon units are wicked expensive.
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  #19  
Old 04-06-2013
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Re: Propane leak into the bilge. What to do?

Quote:
Originally Posted by travlineasy View Post
For the future, get a sniffer with a solenoid valve that automatically shuts off the gas if the slightest concentration of propane, and other explosive gasses, is detected. They can be found for under $200 at most marine stores, and in some RV stores, under $100.

Gary
And test the system each spring. Simply wave a propane torch or similar (butane lighter works) near the detector an confirm it cuts the gas and alarms. Takes only moments. Depending on dampness, the element has a finite life. One more reason to keep a dry boat.

It is also the season to change those CO and smoke alarm batteries!

--------

Being in the industry and having done gas explosion accident investigations, I know what I would do; close the gas bottle (should be accessible in a locker on deck, open a few hatches I could reach from on deck, and immediately leave, if only to sit in the dingy for 30 minutes (much longer if at dock and I can go get lunch!). Bad weather at sea? I would hope you noticed sooner, but a broken line is possible. Turn off the bottle, open every hatch, and not touch any switches. If the gas is not yet strong in the cabin I might turn off the main. I would wait some time and then ventilate the bilge by gently removing covers. Even in a marine environment some boat cabins build static, so I would ground my hands before reaching for the boards; I've seen some nasty static triggered explosions.

--------

Any actions (other than closing the bottle and opening a few hatches) carry some ignition or exposure risk. Better do little and wait for dispersion.
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Old 04-06-2013
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Re: Propane leak into the bilge. What to do?

Er - dumb question - my propane tanks are in their own compartments, with a hinged lid for access, and a drain hold on the bottom leading to the outside of the boat. The solenoid and tubing is at the top, and the caulked in so it can't leak gas. Isn't that the best way to set them up?

I wouldn't want a loose propane tank inside my boat. I've seen tanks in various locations. but they are always in their own boxes and "drain" externally to the cabin.
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