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Boat fire. What caused it?

Old 01-13-2021, 05:50 PM
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Default Boat fire. What caused it?

Not my boat but this is what I know. Trying to figure out why.

Older center console with new (200hrs) outboard engine. Internal tank. Inspection hatch for tank on floor inside console (I think). 2 trolling motor batteries inside console. Unsure of age or type of batteries. No report of any smell of gas and boat is used very regularly. Friend first turns his battery switch inside console to normal "ON" position, then a few seconds later goes to crank the boat (on the lift) and there is an explosion heard a mile away followed by a fire that caused a lot of damage. The fire dept ripped up the floor during extinguishing I guess to make sure it was all out, internal tank still full, never ignited (luckily) and friend walks away somehow relatively unscathed. Cranking batteries were in rear boxes, only trolling motor batteries in console. Friend feels like it was a battery that blew and of course he was ground zero.

My question is how would this happen? Trolling motor batteries degassing, hydrogen gas couped up in console, somehow ignited by ignition key? (cranking batteries in stern...)

Fuel vapors coming from inspection hatch? Again, how would that be ignited by turning the key if starting batteries are in the rear?

What are your thoughts? May be more details forthcoming, it just happened and thats all the info I have. But would like to know how the hell it's even possible so I can do some system checks on my own vessels.
Old 01-13-2021, 06:12 PM
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Have you ever seen the movie Casino?
Old 01-13-2021, 06:29 PM
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How much damage did it do? Did it blow him off the boat? Most likely gas fumes. I don't think a batt will blow a boat apart if that's what happened.
Old 01-13-2021, 06:40 PM
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Boat didnít sink, no damage to hull itself and stringers still possibly salvageable.Fire destroyed console and spread topside and melted cowling and some plastic inside engine (totaled Iím sure). Fire dept response was relatively quick. If it was vapors from fuel itís amazing it didnít track back to tank but I did some looking into battery explosion and didnít really see where they are necessarily fiery type explosions. However hydrogen gas explosions I found out are really loud and that is in line with witnesses about a mile away that heard it in their house

he didnít get blown off the boat. For whatever reason he was sitting in the gunnel beside the console when he hit the switch. That was probably the single thing that saved him. It was close call

Last edited by bluejack; 01-13-2021 at 06:46 PM.
Old 01-13-2021, 06:46 PM
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If tops are on the batteries then can rule them out. Usually not fire when they blow as it is wet.

From what you describe my guess if fuel sender leaking allowing fuel vapors to escape and collect in bilge, or fuel got into bilge by some other means.
Old 01-13-2021, 07:00 PM
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Batteries were toasted and at least one I saw had no top left at all. He had no fuel smell that he was aware of. If fuel in bilge causing vapors then I would think explosion would have tracked down below decks which it didnít seem to do. But I suppose itís a plausible explanation
Old 01-13-2021, 07:10 PM
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Whatís left of a battery. Not sure how much damage is from explosion vs fire dept pulling up damaged decking but mostly topside damage

Last edited by bluejack; 01-13-2021 at 07:16 PM.
Old 01-13-2021, 07:25 PM
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When a wet cell battery is left on a charger all the time it can get low on electrolyte which creates an empty space between the top of the battery and the plates. The space will be a gas. When you turn the key to start, the high current of the starter can create a spark in the plates and the gas explodes the top of the battery. As mentioned, it's usually a wet explosion. However, if the charger was still plugged in, the cables could have shorted and melted together and caused a fire after the explosion. I have seen this happen multiple times. This is a very simplified explanation. I'm sure someone will chime in with the scientific terms
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Old 01-13-2021, 07:31 PM
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Starting batteries were in stern boxes, not where explosion started (which was under console) and no charger connected. Only 2 TM batteries in console where fire started. Can the key assembly in the dash for an outboard generate a spark?
Old 01-13-2021, 07:52 PM
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Keep in mind that hydrogen gas (as in from a charging battery) is lighter than air and rises, so it may have filled the underside of the instrument panel where the key switch was (?)

also, if it was fuel vapors, a fuel tank really wonít explode. Liquid gasoline doesnít explode, the vapors do when mixed with oxygen and there is no oxygen in the tank, only fuel vapors. Also, fuel vents have screens over them to prevent tank explosions if something goes wrong.
Old 01-13-2021, 08:37 PM
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Wow! He’s lucky to be alive.
Old 01-13-2021, 09:18 PM
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When a wet cell battery is left on a charger all the time it can get low on electrolyte which creates an empty space between the top of the battery and the plates. The space will be a gas. When you turn the key to start, the high current of the starter can create a spark in the plates and the gas explodes the top of the battery. As mentioned, it's usually a wet explosion. However, if the charger was still plugged in, the cables could have shorted and melted together and caused a fire after the explosion. I have seen this happen multiple times. This is a very simplified explanation. I'm sure someone will chime in with the scientific terms
Most likely answer I have looked at hundreds of boat fire investigations, and done close to 100 investigations myself. Contrary to popular belief, even AGMs and Gel batteries will outgas hydrogen if overcharge and over heated. If that gas is contained in a space (in this case, probably in the battery itself) the slightest spark will set it off. When he tried to start, something under the console sparked, probably the switch itself or the plates in the battery were warped and sparked. The clearest evidence is the battery that was blown apart. And yes hydrogen gas when contained can cause that kind of explosion. I once saw a 25 foot cabin cruiser that was missing the entire cabin because the explosion blew it off the boat, but at the same time did not even singe the hair on the operators head.
Old 01-14-2021, 06:45 AM
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Originally Posted by PeterDE View Post
Most likely answer I have looked at hundreds of boat fire investigations, and done close to 100 investigations myself. Contrary to popular belief, even AGMs and Gel batteries will outgas hydrogen if overcharge and over heated. If that gas is contained in a space (in this case, probably in the battery itself) the slightest spark will set it off. When he tried to start, something under the console sparked, probably the switch itself or the plates in the battery were warped and sparked. The clearest evidence is the battery that was blown apart. And yes hydrogen gas when contained can cause that kind of explosion. I once saw a 25 foot cabin cruiser that was missing the entire cabin because the explosion blew it off the boat, but at the same time did not even singe the hair on the operators head.
This^^^^^^

We used to make hydrogen bombs out of a big gulp cup full of Hydrogen gas. Fill the cup with the gas and duct tape it shut. Put a fuse on it and run like hell.
The blast would lay the grass down for yards and never catch fire. The concussion blast was impressive. I also had a battery blow in the shop. What a mess and it blew the windows out. No fire.
Old 01-14-2021, 08:23 AM
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Interesting and scary. Might be a good reason not to locate a battery in a console with wiring that may arc or cause a spark. One thing I have never liked is the crappy battery boxes that are available, they are not made to really fit the various standard size battery boxes, and putting them in a box, allows the fumes to build up in an enclosed space, another concern. I have mine in trays now (used to use boxes) and since I have an inboard I have the blower fan on all the time anyway. This brings up the issue, how careful you have to be with wiring in a marine application. While bilge pumps, and bilge switches are ignition protected, how many know this: Modern style fuses come in two styles, ATC and ATO. The part of the fuse in an ATO fuse between the blades is open, that means if it blows, the spark that may result can be exposed to a flammable gas. You should always use an ATC fuse in an engine compartment or in any fuse box where vapors can be present (like in a console with batteries mounted there) because the part between the blades is closed on an ATC fuse and therefore can't ignite a combustible mixture.
I'd like so see better quality battery boxes that are made to fit the battery snugly, and equipped with vents with screens just like marine distributors and alternators. Yes I'd be willing to pay a lot more for a good one instead of the normal junk that's sold.
Old 01-14-2021, 08:47 AM
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It does point to a battery explosion.
A good reminder just how they can ruin your day.
Glad your buddy is ok, sorry for the boat.
Old 01-14-2021, 09:11 AM
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Crazy, quite a few variables, but my guess is battery or fuel vapors

If wet cell/serviceable batteries, were water levels being checked regularly?

Proper battery charger, on the proper setting, for the battery type?

Any batteries mixed and matched?

Any recent electrical / battery issues?

Any recent smells of fuel odor?

Some chargers have heat sensors to stop charging a battery when it gets hot. Issue is what if your bank is like a dozen batteries.

I make sure all of my batteries can vent, nothing in a 100% sealed environment. Winter storage worries me a bit because I do try to limit air exchange in the engine room, where there are some batteries, but at least I dont spend much time on the boat during winter.

My boat neighbor recently had a battery issue. Battery was super super hot, boiling, even hours after being disconnected. He removed it and left it on the deck of his boat. I called him when I could smell the acid in the air 100 feet away and used a heat gun to see it was still super hot, recommending he remove it from his boat deck, and the dock. He dumped it in the middle of the parking lot. If that happened to me, I may call the fire department as they wear safety gear, in case a battery explodes.
Old 01-14-2021, 09:26 AM
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My guess would be something in the console arced when he hit the switch and ignited the hydrogen gas coming off those deep-cycle trolling motor batteries in there. Would not have to be the switch. Just anything that comes on when the ignition switch is turned. Console lights, gauge lights, etc..
Always keep water levels up above the plates in batteries. Even maintenance free. We had a battery blow the hood off our family car back when the kids were small. Wife gets kids in car, turns key, BOOOOM! Hood flies up and everybody screaming. I run outside to see the damage and thank God it was confined to engine compartment. Sure enough, top of battery blown to the next house over. I check levels routinely now. Kids still talk about that day, some 20 years ago now.
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