The Science of Propane Safety

[capngeo]

Originally Posted by Delancy

According to the leak test gauge on my propane system I've got a leak somewhere. Could be in the propane locker but let's say it's at the connection to the stove or possibly the stove itself and assume it ends up in the bilge.

We have been livingaboard for about six months now and haven't blown ourselves up yet. What happens to the bit of propane that leaks out whenever I valve on and off to use the stove?

Does the propane degrade naturally into it's base elements over time? Does it move from a greater to lesser concentration as a matter of course? Have I not met with disaster because it simply hasn't reached the necessary ratio of fuel to air?

Also, for the extra educated among us, how persistent are the odorants which are added to the propane so we can smell it? Are they also heavier than air and do they remain with the propane once it has settled in the bottom of the bilge? or do they have a shorter life and I could have a bilge full of propane and not know it? Do sniffers sense the propane itself or the odorant?

***SIGH***
A lot of answers, but none to the question asked.

All burnable vapors have an upper and lower explosive limit (as a percentage in air); outside that range and nothing happens... well except acetylene, which will pretty much burn anywhere between 1-99%.

The odorant ethyl mercaptan (which is a lot of fun to put a drop of under the car seat of someone you hate) is the primary additive to give most cooking gasses a detectable odor (propane, butane, natural gas have no odor naturally). BTW, detectors sense the hydrocarbons in gas, not the odorant.

As to the question of why you haven't exploded.... the concentration never reached the lower explosive limit, and your bilge obviously has good ventilation (the solution to pollution is dilution).

The panicked suggestions of imminent doom are not all together off base, as common sense would dictate a gas leak is not a good thing..... BUT if your system leaks down over a period of days (as opposed to hours or minutes) when the solenoid is shut off, I would be more concerned about when my zincs were last changed!

[Jim Cate]

Originally Posted by capngeo

***SIGH***
A lot of answers, but none to the question asked.

All burnable vapors have an upper and lower explosive limit (as a percentage in air); outside that range and nothing happens... well except acetylene, which will pretty much burn anywhere between 1-99%.

The odorant ethyl mercaptan (which is a lot of fun to put a drop of under the car seat of someone you hate) is the primary additive to give most cooking gasses a detectable odor (propane, butane, natural gas have no odor naturally). BTW, detectors sense the hydrocarbons in gas, not the odorant.

As to the question of why you haven't exploded.... the concentration never reached the lower explosive limit, and your bilge obviously has good ventilation (the solution to pollution is dilution).

The panicked suggestions of imminent doom are not all together off base, as common sense would dictate a gas leak is not a good thing..... BUT if your system leaks down over a period of days (as opposed to hours or minutes) when the solenoid is shut off, I would be more concerned about when my zincs were last changed!

Capn geo, thanks for adding some non-panicked thoughts to this thread.

I'll agree that the leak should be addressed, but seems pretty obvious that his situation isn't likely to degenerate too rapidly without an easily detected faster leakdown.

And FWIW, the stench from the odorant becomes unbearable LONG before the lower explosive limit is reached... like really reeking

Cheers,

Jim

[HopCar]

"All burnable vapors have an upper and lower explosive limit (as a percentage in air); outside that range and nothing happens.."
For propane I beleive this is between 2% and 10%. Less than 2% propane and the mixture is too lean to burn. Above 10% and it's too rich.

[Delancey]

Originally Posted by Jim Cate

Capn geo, thanks for adding some non-panicked thoughts to this thread.

I'll agree that the leak should be addressed, but seems pretty obvious that his situation isn't likely to degenerate too rapidly without an easily detected faster leakdown.

And FWIW, the stench from the odorant becomes unbearable LONG before the lower explosive limit is reached... like really reeking

Cheers,

Jim

Thank you. Thank you both. I love you cruiser's forum. Happy holidays!

[daddle]

The odorant is less volatile than the LPG. So it tend to accumulate in the tank and lines.But your nose is not in the bilge where the LPG accumulates.

If the LPG will explode in your situation cannot be causally predicted. If the gasses in your bilge are very calm the LPG will accumulate without dissipation but at the same time be too dense to burn. If there is a little mixing in the bilge of air and LPG you have a good situation for an explosion. If somehow your bilge is well ventilated the mixture will be too lean to explode. So who knows? Throw a match into the bulge each morning and report back. When the thread suddenly stops we'll have our answer.

Seriously. Only a fool would smell the leak and not immediately take corrective action.

[GordMay]

Under certain circumstances, the odourant (ethyl mercaptan) in propane gas may oxidize and lose it's distinctive odour. This odour fade can occur in new steel containers when first placed into service and in older steel containers that have been left open to the atmosphere.
Not all people are able to detect the presence of the propane's odourant.
Physical conditions such as competing odorus, colds, flus, allergies, or smoking etc. may diminish a person's ability to detect the odourant.

Odourant Fade ➥ http://www.cpsc.gov/library/foia/foi...propanept1.PDF

And ➥ http://www.bp.com/liveassets/bp_inte...o_bulletin.pdf

[Richard5]

Originally Posted by RabidRabbit

We could better advise you on this propane issue if you told use what kind of anchor you use. To be really safe in heavy weather I use 50' 1/4" clothes line, 10' of plastic chain (hanging lamp style) and a frying pan as kellet.

With that comment I think you owe a key board to a lot of people. Me, it was a near miss.

[Maine Sail]

Considering my wife and I watched a Bristol 32 BLOW UP in Boothbay Harbor Maine some years ago, during some early spring cruising, I know it can happen.

At the time my wife and I had no idea what had happened. We heard a huge boom then some screaming and a high pitched yelping. When I poked above deck we could not tell where it was coming from but the harbor was not very full and I soon realized it was coming from the Bristol.... It literally split the hull deck joint on the boat.... Scary $hit..

Bolded below is an excerpt from their story that was later published in Points East Magazine (posted with permission).. It was good to get teh "whole story" from the magazine article cause otherwise we would have never know the details..


"By mid-afternoon, it was raining. Back on board for dinner, they prepared something new on the little galley stove: stir-fry Thai chicken.

As a precaution, propane tanks are usually contained inside a box that vents outside the boat. That was the case with Chanticleer: the tank was contained in a box under a seat cushion in the cockpit. A hole in the bottom of the locker allowed leaking gas to flow overboard above the waterline. But a previous owner of Chanticleer had modified the design, leaving the regulator outside the box. From this point, leaking gas could only drop into the bilge.


And on that rainy April evening in Boothbay Harbor that’s exactly what the leaking propane began to do. At first, the fuel collected in a pocket just above the keel. When that filled, the propane spread under the floorboards, the cloud expanding forward and aft. Gradually, the propane level rose, like invisible water in a bathtub. When the bilge was filled, propane seeped into the lower cabinets, mingling with tools, engine parts and emergency supplies. “I had emergency electrical kits, filters, nuts, bolts, lots of hardware,” Baker said. There were dishes, silverware, glassware,” he said. Had Baker or Plamondon gotten down on all fours, they might have smelled the propane, since an unpleasant scent is added to the otherwise colorless and odorless gas. They would have known something was wrong. Instead, as the propane rose around their feet, they busied themselves with preparing supper, oblivious to the danger that had invaded their quiet evening. All the gas needed was a spark or flame to set it off.

By suppertime, a cold rain drummed overhead. Below deck, it was cozy. By the tiny coal stove, it was warm enough for bare feet and a T-shirt. Plamondon was at the two-burner cookstove, tossing veggies and chicken into the heavy-duty wok. Baker put on a favorite Willy Nelson CD, “The Healing Hands of Time,” then opened the hatches to let out the smoke that the wind kept blowing back down the stack into the cabin from the coal stove. “Finally, I got it regulated,” he said. “We were just vegging out. I had just mixed a Sundowner – rum and orange juice.” In the next moment, Plamondon was slammed violently backward.


“I remember flying backward through the air and landing on my back and butt,” she said. “I remember Kira’s blood-curdling yelping.”


Somewhere on the boat, the swelling cloud of propane had found its spark, exploding in an instant of extreme violence. The flash shocked their pupils closed. Suddenly, all was dark. “I just felt the tremendous devastation of the blast,” Baker said. “Stuff was flying everywhere. I couldn’t find Kira. I thought it was the middle of the night. I was scrambling around, feeling for her.” Plamondon was thrown against a bulkhead door.


“Everything was dark,” she said. “(Phil) screamed at me to get out of the boat, but there were no more stairs.”


She turned to exit forward, but the door was jammed closed from debris piled up from the blast. She turned again to exit toward the cockpit and saw a ball of fire on top of the engine, where the stairs would have been. “No way could I jump that,” she said. “But I did. I don’t know how, but I did it.” Baker reached for a fire extinguisher, but the bulkhead where it had been mounted was gone. “I thought if I got the fire out, we’d have an easier time getting off the boat,” he said. Somehow, he managed to get out of the cabin with Kira.

About a hundred yards away, dockmaster Peter Chase was aboard his boat at the Tugboat Inn Marina. “I heard an explosion. It shuddered my boat. It almost reminded me of someone touching off a cannon,” he said. “I went up on deck and looked around.”

By then, they had managed to climb off the boat into the dinghy, carrying the lifeless body of Kira. “It was pouring rain, freezing rain, and we were barefoot,” said Baker. In the boat, he got a better look at Plamondon, who had taken the worst of the blast. Her face was blackened and her hair singed short. Her eyebrows were burned off. Her eyelashes were singed together. Her jeans were torn. Her hand was bleeding. She thought she had a broken leg. In his lap, Baker felt Kira’s crispy fur and saw her staring eyes. “Kira’s dead,” he said. “I had lost the boat, Kira was dead, Debi was crying,” said Baker. “It was awful.” Then, he felt Kira’s tiny chest move. Miraculously, Chanticleer’s trio of passengers, now huddled in the rain in the tiny dinghy, had all survived.

Chanticleer was not so fortunate. Having absorbed most of the force of the blast, her hull was declared a total loss. The blast cracked apart the fiberglass deck in several spots. Stuck in the jagged fissures were the remains of the meal that never got eaten: pieces of broccoli and red pepper. The deck was separated from the hull along the starboard rail. The wood around the cockpit was splintered. Below deck, it looked like someone had ransacked the place. Drawers and contents were scattered about. Baker said he would receive a $35,000 insurance settlement, most of which will go to the bank. Safety experts say he is lucky to be around to collect any of it.

“They were very fortunate to have survived,” said Jeff Ciampa, a marine safety inspector for the Coast Guard. Baker and Plomondon are convinced that opening the hatch shortly before the explosion to let the smoke out gave the force of the explosion somewhere to go.

There was very little fire damage to the boat, probably because the propane mixture was rich enough to detonate, but too lean to ignite, said Steve Dixon, an investigator from the Maine State Fire Marshal’s office. Dixon said the source of ignition appears to have been the open flame on the galley stove. Initially, it was thought to be a spark belowdeck somewhere in the boat’s 12-volt electrical system. “We are 100 percent sure it wasn’t that,” said Dixon. “Both the bilge pump and the water pump are protected.”

Plamondon’s first- and -second-degree burns have healed. What she thought had been a broken leg was a bruise that turned her lower leg black and blue for several weeks. A penny-sized puncture wound in the back of her hand –possibly from the handle of the wok – eventually healed. She later had surgery to remove a piece of glass from her hand. The shard had come from a lead crystal glass that Baker had given her earlier as a gift.

Once, he awoke convinced that the boat he had worked so hard on was salvageable. “I went up to see it. I thought I could rescue it if I had two years. I drove up to Boothbay. It was very discouraging. I’d forgotten how bad it was. I had to abandon the idea.”

But neither Baker nor Plamondon has abandoned cruising. And neither thinks twice about using propane again, though Baker said next time he’ll install a propane sensor in the bilge. Since the accident, they have spent their weekends boat hunting."

After that event we changed the "rules" on our boat in regards to propane systems. Rule #1 I am the only one who changes bottles or touches anything in the propane locker. Rule #2 is that only my wife or myself touch the oven & solenoid switch..

Having watched a couple get BLOWN UP, we make no exceptions to this rule. If my wife finds something amiss, such as a burner not lighting immediately, the solenoid goes OFF instantly then she calls me to help. She knows proper procedure and I trust her but not anyone else.

No matter how experienced the guests they do not operate the stove/oven/LPG system other than looking at items already baking or cooking..NO ONE TOUCHES THE KNOBS OR EVEN ADJUSTS A FLAME EXCEPT MY WIFE OR I. When you see a boat blow up it changes your approach to LPG safety.. Call me cautious or a safety nut if you will...

We also have two LPG switches per ABYC standards and both have bright red LED's... No mistaking those circuits for any other as all the rest are amber colored. You see a red LED and the stove / oven better damn well be running.....

One other protocol we use is the two handed turn off. One hand on the knob turning it off and the other on the solenoid, which is flipped off a split second after the knob.. Using the two handed method makes it very tough to forget the solenoid.

Our LPG leak detector also breaks the solenoid if there is a leak and we use a high pressure solenoid that goes BEFORE the regulator not after the regulator. I do this because I have seen failed & corroded regulators and don't like the solenoid on the low pressure side.

I will only use & install solenoids made by Advanced Fuel Components (AFC), specifically the model 151, and have never had or seen one fail, not one. I have probably installed 45 -50 of these most to them replace the crappy & rather unreliable low pressure side solenoids marketed by companies such as Trident. While some were installed for CNG conversions they still work perfectly and I have yet to see one fail. In my experience they are far more reliable than the low pressure versions.

I also test my propane sniffer using a butane lighter on a fairly regular basis. These are not as reliable as solenoids but at least when they fail they fail in a "fail safe" manner. I carry a spare...

[denverd0n]

Originally Posted by capngeo

***SIGH***
A lot of answers, but none to the question asked.

Isn't that how it usually goes? You beat me to it, and said almost exactly what I was going to. I'm glad that someone did finally answer the actual question.

The only real issue that I see with ignoring a tiny, harmless leak is that it could very easily become a dangerous leak at the most inopportune time. Small holes have a way of becoming larger, bad seals have a way of becoming worse. You might safely ignore a tiny propane leak for years, and then one day, as you hear a loud boom and see a flash of flame, the very last thought that passes through your brain is "DAMN! I was gonna fix that leak tomorrow!"

[Delancey]

So, for the sake of discussion, let's say that after a day ashore in a distant harbor we return to the boat to the strong smell of gas. A quick check of the propane locker reveals that the leak test gauge is at zero and we believe the little leak became a big leak and the entire contents of the cylinder have discharged the boat. The result of some freakishly impossible event. Now what?

Get off the boat and row away as fast as possible. Great. Now what? We're in a distant harbor and I can't call the fire department because there is no fire department. Abandon our house? Beg for food and shelter? What if you we're offshore and something fails horribly and rowing the dink to the beach is simply not an option?

What then? Grab a bucket, start bailing gas out of the boat and pray?

[HopCar]

Good Grief Delancy, fix the damn leak and don't get in that situation!
If you do get a boat full of propane, get away from it. If you can't get away from it, open everything up and hope it disapates before you die.

[evm1024]

I have similar rules as to Maine Sails. Instead of the 2 hand rule we have the burn down rule. When shutting off the stove we turn off the solenoid first and watch the burner flame go out with our hand on the burner knob. Once the flame is out we then turn off the burner only then letting go of the knob.

IF we are not going to use the stove in the next few minutes I shut the gas off at the bottle.


And to answer your question: We don't come back to the boat with the bottle having emptied its'self into the boat because we never leave the bottle valve open when not using the stove. This is a hard and fast rule.

As for a boat filled with gas... DO nothing drastic (like flipping light switches) Have one of you on board with the other standing off and open the hatches. Do nothing to cause a spark. THen get off the boat and let the gas vet for a while. As long as you can. Then one of you boards and sniffs around while opening everything and then let it dissipate for a long while again. More sniffing and finely both reboarding.

The key is a balance between safety and getting the ventilation that you need to dissipate the gas. Your partner is in the dingy a ways off so as to pick up your body as it goes flying through space.


Bit don't let it happen, turn off the gas at the bottle.

regards

[MarkSF]

I retro-fitted one of these recently and I do believe they are well worth the money.

Xintex S-1A 2" Square Bezel Propane Detector w/ Plug-In Sensor and Solenoid Valve (S-1A) - ManVenture Outpost, LLC.

[mikereed100]

In regards to Delancy's original question, this is something that I have wondered as well; "where does the propane that leaked into my bilge go?". I googled "propane degradation" and found some interesting stuff. Apparantly it can be degraded by Cloride and Hydroxyl in the atmosphere. Not sure if there's anything in the bilge that might degrade it, but looking at my bilges would not be surprised.
Atmospheric oxidation pathways of propane and its by-products: Acetone, acetaldehyde, and propionaldehyde

Concerning proper installation, I came across this interesting article:
Safe Boat Propane System Installation

He mentions that ABYC says it's OK to put a solenoid on either side of the regulator, but I think MaineSail's recommendation to put it on the high pressure side makes more sense.

[Thumbs Up]

explosion - YouTube

,

http://www.youtube.com/watch?v=pZnjAYG3XM0