Fuel tank explosion (see picture). Why??

[mochosla]

Hi guys,

I bought a 26' aluminum boat that I'm planning to fix. Yesterday, I was moving a ladder around in my yard and it touched the boat. Immediately after, one of the 70 gallon aluminum tanks exploded. Thanks God the thing stayed in one piece and nothing came out flying. Nevertheless, it scared the %&^ out of me. It was so loud that even my neighbor came out see what happened. Luckily, the second tank did not explode and aside from the cross members that held the tank in place, everything else seems to be fine. So my questions are, why did this happen? My only assumption is that since the day was dry and windy, there was static and me holding the ladder and touching the boat created a spark in the tank and that was the reason for it to explode. My other question is, how do I prevent it from happening again? I now need to cut the cross members to remove them and replace the tank and do not want the second tank to explode too. Any advice will be greatly appreciated.

BTW, let me know what you think of the boat.

Thanks.

 

[marauder11]

Re: Fuel tank explosion (see picture). Why??

Would these tanks have a ground wire? That is really scary stuff to happen.

 

[mochosla]

Re: Fuel tank explosion (see picture). Why??

I do not see a ground wire anywhere. And yes, it is scary. So much that I do not want to touch the boat until I figure out what happened and how to prevent it from happening again.

 

[74bayliner]

Re: Fuel tank explosion (see picture). Why??

I think that might your problem as it not having a ground wire... Thank goodness your safe!
I know for sure on my boat I had one before i took it all apart, I know when i put it back together, everything will be grounded accordingly. but i would wait for one of the smarter people who know more than me get home from work and chime in.

 

[oops!]

Re: Fuel tank explosion (see picture). Why??

OMG..........

DAMM you are lucky !!!!

The only thing it could be is a un grounded tank.

there is a wire running form the reciver screws to the hull.

this could have happened at any time. if this is a manufacturers flaw.....they could be sued.

how is the bottom of the hull?.....look for warpage.....that might be a full insurance claim.

 

[mochosla]

Re: Fuel tank explosion (see picture). Why??

The hull looks fine. I just checked both tanks and they both have the ground wire going to the receiver but that's it.

 

[herefishy]

Re: Fuel tank explosion (see picture). Why??

http://www.uscgboating.org/assets/pdf/recalls/BSC83.pdf

The phenomenon must be a grounding issue. Page 7 of above dictates USCG requirements for fuel tanks. Of particular interest (to me) is the specifications relating to metal fuel tanks, and the bonding of different metal components of a fuel tank (fuel gauge sending unit, etc.), that they all be grounded to each other. Also, that the grounding be done at a ground (negative) bus, NOT to the metal hull.

I might think that referencing the linked document, then inspecting your craft - you might find the cause of the accident.

Thank goodness no one nor anything was hurt.

~Fishy

 

[CR CRUISER]

Re: Fuel tank explosion (see picture). Why??

Any chance that the ladder touch and resulting static spark were near the fuel tank vent?

 

[rfdfirecaptain]

Re: Fuel tank explosion (see picture). Why??

Stranger things have happened. I don?t know that I buy the static charge from the ladder, but the timing of the explosion is coincidentally suspect. Regardless of the source of ignition I think the most important question is if this was an actual explosion, how did any ignition source reach the vapors in your fuel tank, or vice versa? Remember you still have another tank sitting there.

Ok I have a few more detailed questions and comments about this 70 gallon tank. What time of day did this occur? I can see a shadow mark across the helm, but I have no way to know if the sun is ascending or descending. Had the tank been sitting in direct sunlight, if so how long? What was the ambient temperature at the time of the incident? Was it windy, if so how windy? How full was the gas tank? Less gasoline means more available vapors in reserve. Were any of the attached fuel, or vapor lines breeched, thus allowing ?significant? vapors to escape and find an ignition source? Think about the upper and lower explosive limits of gasoline (aka rich and lean). It?s doubtful that due to static electricity an explosion occurred ?inside? a tank so small (again how full was the tank), and it?s doubtful that it could have occurred far away from the tank. But, somewhere in between (the flammable range), if there is a vapor leak I?m sure an explosion is possible. But, the lack of significant tank damage just puzzles me.

You said it ?exploded?, but I see no evidence of an ?explosion? as a result of flash fire, however there is obvious evidence that the metal structure of the tank expanded. How hard did you ?touch? the boat? Was it enough to rock the boat a little causing gasoline to slosh around inside the tank? While static electricity is a possibility I have never seen a fuel tank suffer so little damage due to an external flashback inside the tank. Have you checked to see if your vapor escape line is clogged? Without more information and in consideration of the lack of more significant fuel tank and surrounding boat damage this really presents more like a build up of internal pressure, IMO. Here is an example of what negative pressure caused by offloading a railcar caused. http://www.youtube.com/watch?v=Zz95_VvTxZM Think of this in reverse. Expansion would be caused by a significant expansion of vapors inside the tank. Not necessarily a likely possibility, but under the right conditions, plausible?

Of course, I?m not trying to discount any possibility that there could have been an actual explosion. Maybe with more information I would lean more that way. I?m just looking at alternative possibilities. If in fact this was vapor ignition, as one other member posted, ?DAMM you are lucky !!!!?

Good luck finding a cause that let?s you sleep at night.

 

[Grandad]

Re: Fuel tank explosion (see picture). Why??

Yesterday, I was moving a ladder around in my yard and it touched the boat. Immediately after, one of the 70 gallon aluminum tanks exploded.

Hi mochosia,
If we are to assume that contact with your (statically charged aluminum?) ladder contributed, where was the contact point between the ladder and the boat? If it happened to be near the fuel tank vent, you could get an explosion at that point. I don't think that an explosion outside the vent normally propagates to the tank itself, since the oxygen to fumes ratio within the tank won't normally support combustion. However, if the tank was empty for some time, the fume ratio might change to a combustible range. As important as grounding the tank is, that may not have anything to do with this incident. - Grandad

 

[herefishy]

Re: Fuel tank explosion (see picture). Why??

hmmmmm re-reading the first post "I bought a boat that I'm planning on repairing", makes me wonder in what state the craft was relative to any progress (dis-assembly) of any repairs. perhaps the electrical/grounding system was disabled and left the tanks subject to malfunction.

I hear you, firecaptain - all the same questions in my head. If there was only a limited amount of air (oxidizer) in the tank, combustion would only occur up to the point that (oxygen) is depleted, if combustion was involved.

Maybe due to repairs the tank vents were somehow disabled (plugged or capped) in some manner.

This event may bring some concern to those with their craft in certain conditions of repair, and the disabling of electrical (grounding) systems or venting systems.

~Fishy

 

[rfdfirecaptain]

Re: Fuel tank explosion (see picture). Why??

The hull looks fine. I just checked both tanks and they both have the ground wire going to the receiver but that's it.

You said "ground". Technically that is not a "ground". The wire you?re talking about actually refers to "bonding". "Grounding" would be when you have bonded all tanks etc. through an electrical conductor (wire) to an actual "ground". So let?s define ?ground?. When speaking of static electricity, the word ?ground? could actually be used interchangeably with the word Earth.

Have you tested the bonding on the very wire to which you refer? You can do this with a simple ohm meter and a secondary bonding wire. What you want to do is add the secondary wire to some other point of contact and completed the loop using your ohm meter. If there is little or no resistance then you have successfully verified your boat?s bonding wire.

Let?s assume that your boat is properly bonded. The fact that your boat is all aluminum makes any question of the conductivity of current more possible than in that of a fiberglass hull. Here is the question: Is there any way possible your boat?s fuel tank could find an electrical pathway down to the ground = earth? For example: This could include the use of bonding wire that leads to an aluminum hull, which leads to a metal trailer, with leads a jack stand with a metal shoe.

Also, were you standing in the grass or on a pavement when you touched the boat with the ladder? I?m just trying to assess how you could have been so well ?grounded? while holding the ladder or if there is any possibility that your boat could have already been grounded to the Earth.

 

[herefishy]

Re: Fuel tank explosion (see picture). Why??

There doesn't seem to be any grass around the boat on the trailer in the pcitures - just concrete.

I do see an electrostatically charged plastic tarp lying by the trailer tires.

 

[rfdfirecaptain]

Re: Fuel tank explosion (see picture). Why??

Hi mochosia,
If we are to assume that contact with your (statically charged aluminum?) ladder contributed, where was the contact point between the ladder and the boat? If it happened to be near the fuel tank vent, you could get an explosion at that point. I don't think that an explosion outside the vent normally propagates to the tank itself, since the oxygen to fumes ratio within the tank won't normally support combustion. However, if the tank was empty for some time, the fume ratio might change to a combustible range. As important as grounding the tank is, that may not have anything to do with this incident. - Grandad

I had the same thought about the vent as you, but he said it was windy. I was hoping he would quantify what he described as windy. I don't want to guess what he means, but I would think that any chance that vapors from the vent being involved would be slim since it would only take a steady ?breeze? of maybe 5mph to disperse the vapors rapidly.

Also I agree with you on the question of flashback down the vent tube. Flashback from the point of ignition toward the fuel source gets tricky since the fuel becomes more rich as the fireball travels in that direction. There are a lot of unknowns in this case to really put a lot of weight on that possibility.

 

[mochosla]

Re: Fuel tank explosion (see picture). Why??

So many good points and questions. Let me start by clarifying and few things as well as sharing some information that I have remembered or figured out by now.

Yes, the boat is a project boat and I have been working on the wiring for the past couple of weeks but nothing in relation to the fuel tanks yet. That was the last thing I was going to work on. If you notice on the picture, you can see that the positive wire was cut (not by me) and I was going to repair it and test the gauges. Now, I also now remembered that as I was working on the boat over the past few weeks, I would smell gas from time to time so I now assume that the tank was leaking. The gas was very old and had sat under the sun ever since I bought the boat. The vent was not blocked. In fact, there are 2 black burnt marks coming out of the vent holes. These showed up after the explosion so this confirms that there was no blockage. Talking about the explosion, it was a loud boom! followed by the sound of air escaping. I now realize the air escaped through the gauge sending unit in the tank and the vent holes. When I bought the boat the guy told me that he had removed the unit to check the fuel. I now assume he left them loose.

The incident took place at around 7 PM and it was windy. There was a lot of static on the air. I was standing behind the boat and the ladder touched the top of the transom. I actually slid the ladder on the transom but it was soft. I tend to be careful with my things so I would not throw the ladder or hit the boat hard. The ladder was a lot further away from the tank that exploded than the rear one and the vent is nowhere near the transom. I was standing on concrete and the boat/trailer was not in direct contact with the ground. Only tires and the the jack which was sitting on 4x4 pieces of wood were touching the ground.

By the way, this morning, I noticed a very strong smell of gas coming from the boat. By lifting the bow, I retrieved about 4 gallons of gas that came from the bottom of the hull. I also verified that the tank is completely empty.

On a different note, I just came back from my local boat mechanic. I went to see if he had a used tank for sale. He confirmed some of your comments. He feels very strongly that there was a leak and the fumes are what caused the explosion. Obviously, the fumes directed the spark to the leaky tank and not the other one.

keep your comments and questions coming. More than anything, I'm glad I'm okay and the damage is nothing money can't fix.

Thank you!

 

[mochosla]

Re: Fuel tank explosion (see picture). Why??

Stranger things have happened. I don?t know that I buy the static charge from the ladder, but the timing of the explosion is coincidentally suspect. Regardless of the source of ignition I think the most important question is if this was an actual explosion, how did any ignition source reach the vapors in your fuel tank, or vice versa? Remember you still have another tank sitting there.

Ok I have a few more detailed questions and comments about this 70 gallon tank. What time of day did this occur? I can see a shadow mark across the helm, but I have no way to know if the sun is ascending or descending. Had the tank been sitting in direct sunlight, if so how long? What was the ambient temperature at the time of the incident? Was it windy, if so how windy? How full was the gas tank? Less gasoline means more available vapors in reserve. Were any of the attached fuel, or vapor lines breeched, thus allowing ?significant? vapors to escape and find an ignition source? Think about the upper and lower explosive limits of gasoline (aka rich and lean). It?s doubtful that due to static electricity an explosion occurred ?inside? a tank so small (again how full was the tank), and it?s doubtful that it could have occurred far away from the tank. But, somewhere in between (the flammable range), if there is a vapor leak I?m sure an explosion is possible. But, the lack of significant tank damage just puzzles me.

You said it ?exploded?, but I see no evidence of an ?explosion? as a result of flash fire, however there is obvious evidence that the metal structure of the tank expanded. How hard did you ?touch? the boat? Was it enough to rock the boat a little causing gasoline to slosh around inside the tank? While static electricity is a possibility I have never seen a fuel tank suffer so little damage due to an external flashback inside the tank. Have you checked to see if your vapor escape line is clogged? Without more information and in consideration of the lack of more significant fuel tank and surrounding boat damage this really presents more like a build up of internal pressure, IMO. Here is an example of what negative pressure caused by offloading a railcar caused. http://www.youtube.com/watch?v=Zz95_VvTxZM Think of this in reverse. Expansion would be caused by a significant expansion of vapors inside the tank. Not necessarily a likely possibility, but under the right conditions, plausible?

Of course, I?m not trying to discount any possibility that there could have been an actual explosion. Maybe with more information I would lean more that way. I?m just looking at alternative possibilities. If in fact this was vapor ignition, as one other member posted, ?DAMM you are lucky !!!!?

BTW, my tank exploded it did not implode.

 

[herefishy]

Re: Fuel tank explosion (see picture). Why??

The tank being empty - that gives credibility to an explosion have occurred (technically).

The sending unit being loose - not secured to the tank - I think points to the culprit. The sending unit possibly not being "electrically bonded" to the tank - and according to what I see as one wire going to the sending unit (no ground), I would suspect a static-induced spark could have occurred at the location of the unsecured sending unit. Plus, the unsecured sending unit was allowing the tank that is mostly empty of liquid, but full of vapors to breath.

Do you read the warnings about filling a gas can at a fuel pump in the bed of a truck - you're supposed to put it on the ground to prevent static spark. Your boat is sitting on a trailer (on tires), the jack is on wood - not directly in contact with earth.

I am intrigued by what happened here.

~Fishy

 

[rfdfirecaptain]

Re: Fuel tank explosion (see picture). Why??

I understand there was "expansion" and not "compression" to your tank. It's the "pressure" I was focusing on and I couldn't find a youtube video on expanding metal tanks. That's why I say to think in "reverse". Anyway based on your updated information I think you can now rule out all non-fire related over-pressurizations.

You said there ?2 black burnt marks coming out of the vent holes?. Actually what that confirms to me is the presence of fire. The fact that you said the burn pattern indicates the burnt marks are coming out of the vent holes indicates to me the likelihood that any flashback to the tank, that would have come from the vent and down the vent pipe, is very unlikely. Obviously there were escaping vapors, but the question is where did they leak out of the tank? You mentioned the sending unit was loose and I think that?s a good place to start looking unless you have a suspicion that the tank itself may have had a leak. Accidental puncture, cracked weld seam maybe?

Knowing what I know now I think you had a flashback to the tank, which caused a rapid over-pressurization, that tried to escape through the vent pipe and caused the 2 black burnt marks you described as the heat was venting. When the vent pipe couldn?t handle the pressure the tank expanded. Of course all this happened in milliseconds. Those tanks are pressure tested. You are lucky that it held. Had the tank breeched and spewed raw gas into the atmosphere I am certain you would not be talking to us today and at best you would be a patient in a burn center.

I still think you should look into where the spark came from. I would need to do a little research, but off the cuff I?m not certain that aluminum striking aluminum will cause a spark. Also, you standing on pavement, holding a ladder, that just touches a boat has a lot of points of contact. I?m not saying I don?t think you could have provided the charge through the described pathway. I just don?t think it?s very likely. Although static electricity doesn?t have to have completed circuitry to Earth, to arc, I would be more likely to believe that you caused the spark yourself if you had touched the boat directly with your hand than that if the charge followed the aforementioned pathway.

Was there a battery onboard? Any chance there was something onboard that could be suspect as a power source? Maybe this was a one in a million occurrence and you just got lucky.

 

[rfdfirecaptain]

Re: Fuel tank explosion (see picture). Why??

Just an FYI about ?grounding?. If you ever need a really fast ground, or can?t find one make your own. Remember that it?s not about the depth of the grounding device. It?s all about square area. Here?s a trick that I can give personal testament to.

Use a shovel to dig out a grove about 2 shovel widths, by 6 feet long, by about 4 inches deep. Fill the groove with water, or about 10 gallons of water. Sprinkle about a cup of salt in the groove and let the water settle out. Place a sheet of Aluminum foil about 6.5 feet long in the groove, leaving the extra 6 inches sticking out. Sprinkle about a cup of salt on top of the foil. Pour about a half gallon of water on the foil. Cover the foil with dirt from your pile. Walk it down to pack the dirt. If very dry you can pour more water on top of the packed dirt. Use the protruding foil as your point of contact. You now have a ground that is comparable to, or in some cases even better that one of those 8 foot galvanized rods that are driven into the ground.

 

[FastFission]

Re: Fuel tank explosion (see picture). Why??

It's kind of hard to tell from the photos, but it looks like there is a pretty significant scortch mark on the fore-aft aluminum frame just above the gap between the tanks, and a smaller one at the fuel gage sender (which appears to have two of five screws removed).

I wonder the front tank was corroded through and you had a small flash that started in the bilge just between the tanks. Either that or perhaps the flash blew a hole in the tank in that area. That might explain why the tank didn't expand more that it did.

Carl