Uh-oh. Self charbroiled battery box.

[russ]

Sunking,

Huge batteries gassing inside without contained ventilation? That doesn't sound like a good idea to me! I know my installer would balk at the idea and he's been doing this for 30 years. Curious why you think it would be OK?

Green,

That's the leading theory on this end. I would explain all the facts, including the lack of visible damage to terminals. Hmmm... and it is also concentrated near the far (longest) vent tube in the corner of the box. Poorest venting would definitely be in that area.

I'm going to have to take another look at the venting. It's probable there is some variable that's not playing happily with its buddies.

Steve

Of course there is ventilation - that is not what Sunking said.

H2 goes up and away immediately unless somehow it is trapped. I spent a lifetime working with the stuff - really quite a safe gas to work with providing the rules are followed.

If the H2 lit off there would have been an instantaneous poof and gone.

It's probable there is some variable that's not playing happily with its buddies - What is that supposed to mean?

[russ]

A lot depends on just how the box is vented. Ideally, if you insist on using a closed box, there should be a low vent which is open all the way to the bottom of the box and a high vent which is open to the highest point of the enclosure, since hydrogen will rise and potentially collect in any pockets in the cover structure. (For example, if the top has a grid of 2x4s, each of the separate areas of the grid should be vented or there should be an air passage hole between them at the top. Although this is a minor factor if there is any bulk air movement.)

A relatively small volume of hydrogen is produced, even during heavy gassing (although it sounds like you have a lot of batteries), so just leaving the top of the batteries open to the inside room and then venting that room should be fine. What you want to avoid is anything which will capture and hold the hydrogen (and oxygen).

WTF is the low vent for? Heavy H2 maybe? It wouldn't hurt anything but won't do anything good either.

Any place where H2 can be trapped as it tries to rise is problematic - but due to explosion concerns - not fire.

The plants I designed, built and managed recirculated millions of NCMH (normal cubic meters per hour) of H2 - No way make anything perfectly leak proof - you just prevent concentrations when leaks occur.

[green]

No it wasn't and that wasn't really a thought you came up with - more like a lack of knowing how H2 behaves - a H2 fire would have been over in an instant.

I have quite the extensive scientific knowledge of how things work. I'm here to share as well as learn.

[inetdog]

WTF is the low vent for? Heavy H2 maybe? It wouldn't hurt anything but won't do anything good either.

I was thinking primarily of getting good convection in case the batteries heat up and also dealing with any acid vapor from really vigorous gassing. No relation to H2 management.

[Sunking]

Sunking,

Huge batteries gassing inside without contained ventilation? That doesn't sound like a good idea to me! I know my installer would balk at the idea and he's been doing this for 30 years. Curious why you think it would be OK?

Because I have been designing and building battery plants for Telephone company for 33 years as a licensed engineer. What you call large, is a watch battery to my applications. A typical -48 VDC plant in a level 5 Telephone office is 30,000 AH in a dark basement without windows under a high rise building weighing around 90,000 pounds of lead and acid, powered by 18,000 amps of rectifiers.

As long as the room has a draft there is no real threat .Hydrogen needs to reach 4% saturation before it becomes explosive.

[Sunking]

Could it have been a hydrogen fire?

No. Hydrogen ignition is a POOF or bang at low temperature and it is over. The box would be shattered or shown signs of stress damage from high pressure with almost no burning damage. Charring indicates long heat and hot heat exposure from flame.

[green]

Ok I had another thought. Was this wood Pressure Treated Wood by any chance? Lumber mills use different chemicals in treating thier pressure treated products. I'm not an expert in these pressure treated products flamabilty but I was just thinking it was a possibility. Maybe even a chemical reaction with the hydrogen.

Just a thought,
Green

[SolarSteve]

More good stuff! Various responses...

1. As for venting, I'm living in the same space as these batteries. They give off more than just Hydrogen. I personally would rather direct those gasses outside of my living space than inhale them. It might be safe from an explosion standpoint, as long as my house has proper ventilation in the winter when it is shut tight (it does), but I'm still not crazy about the idea of breathing in byproducts from chemical reactions. Each to his own, I suppose.

2. OK, so it sounds like a Hydrogen flash explosion isn't practical. As I understand the physics now, if there was enough to combust then it wouldn't have been limited to a very small area and it wouldn't have produced burn. It would have been catastrophic explosion with an emphasis on force, not flame. That sound about right?

3. Slow heat will definitely cause charcoaling. But I can find no source for that heat. The terminal connectors are rubber coated and there is no signs of melting. I've cooked battery cables before on a vehicle from over cranking. The damage is as one would expect from rubber/plastic on top of something very hot. Yet I had these cables off and in my hands... nothing wrong with them.

4. My "variable not playing nice with its buddy" comment was just another way of saying that something is out of balance. There's lots of variables at play here and that's why there's no solid answer yet as to what might have happened.

5. My "huge batteries" comment should be taken into context of the space which contains it. Especially if we're talking about gas density. On an absolute scale, sure it's a watch battery. If we're talking about watches it makes sense to talk about watch batteries, not car batteries.

6. My installer guy said he has never seen anything like this in his 30 years. He did have a customer's battery setup experience a catastrophic explosion. He didn't do the original system (he only sold the guy panels or something) so he has no idea what might have caused it. By catastrophic I mean nothing left of the batteries and acid cleanup through the entire basement.

7. Convection improvement, by adding a low vent, would be a very bad thing in the event of a fire. Best way to contain it is to denny it a supply of fresh oxygen. For all I know that's why I still have a house right now.

8. All wood in the battery box is building grade kiln dried lumber, not pressure treated. PT when new gasses quite a bit. No sense adding that to the list of variables.

Thanks again!

Steve

[inetdog]

More good stuff! Various responses...

8. All wood in the battery box is building grade kiln dried lumber, not pressure treated. PT when new gasses quite a bit. No sense adding that to the list of variables.

Thanks again!

Steve

Although wood is non-conductive, it is not particularly good in acid resistance (nor are most metals, of course.) I would factor that into my search for a possible explanation, although I do not see a simple explanation down that road either. Perhaps there is a suitable non-reactive protective coating you could use on the bare wood?
I would not want pressure treated wood exposed in the interior of my house either!

[Sunking]

Steve lets say for a minute it was hydrogen OK? In order for a gas to ignite, it has to have an ignition source like a spark from a poor connection.

You electrician is right, when a hydrogen explosion occurs from charging batteries, the battery itself explodes spewing acid and debris everywhere.

So with that said I think it is safe to conclude it was not a hydrogen source heat.

[RussN9ZP]

Loose or bad connection sounds more like the culprit.

[inetdog]

Loose or bad connection sounds more like the culprit.

That is certainly where sustained energy sufficient to ignite or char wood would most likely come from.

Temperature/differential-expansion related or some other reason that it looks and feels good when inspected? Or just not a thorough enough inspection?
Bad crimp of wire inside connector where you don't see it?
Why no signs of heat on the wires or connectors?

[mapmaker]

I think a sulfuric acid mist has done the damage. Organic materials (wood) are carbonized by sulfuric acid. The reaction is exothermic, but a slow exposure to a mist would not heat up enough to burst into flames.

[SolarSteve]

I'm extremely grateful for the attention you guys are giving my problem here. Especially because this one appears to be more than a little odd.

OK, the usual suspect is a loose connection or defective wire. My installer (a Master Electrician) immediately thought of this possibility as well. However, observations of the crime scene don't easily support that possibility. Enough energy released to char would should have melted the wire insulation and/or left some sort of mark on the terminals. That plus the very tight connections (I purposefully tugged on each wire to see if I could move them. Not a bit of movement) means the chances are there was no reason for an arc as well as no evidence of one.

NOTE: The furthest exhaust point (i.e. has the longest to travel) is the rear left corner and the charcoaling happened right there. There was a bit of white in the area closest to the corner. Not sure if that tips anybody off as to what might have happened.

The idea of sulfuric acid is the one I'm really interested in right now. It does explain the charing (high school chemistry... it's in the brain somewhere!) as a quick double check on the web shows (YouTube is so versatile). It explains why the terminals and/or wires were seemingly not involved. No ignition is necessary to produce the effect. It probably isn't a coincidence it's in the furtherest vented area and a corner. Also rules out fire which is sensible since there was no shortage of fuel but the affected area is relatively small. We have had nothing but bright sun for nearly two months, which means the batteries have been heavily charged every day. Lastly, by not opening the box for 6 weeks meant that there was more than usual amount of time for the fumes to build up. Another reason to open the cover every week or two is to give the box a complete venting.

With this theory in mind, anybody see any flaws in this premise?

Steve

P.S. A few years ago I found an interesting university study about PT wood and it's nasty properties on the environment. They concluded gassing and leaching (to soil) were highest in the first 2 years of manufacture. After that only trace evidence of passive transfer, even when outside in the elements. I found this interesting since we inherited a lot of PT outside and I'm trying to repurpose it "smartly".

[Sunking]

The idea of sulfuric acid is the one I'm really interested in right now.

The only way for that to happen other than a spill is a damaged battery plate or low electrolyte levels while charging. A normal healthy battery only emits hydrogen and oxygen while charging. A damaged battery or low electrolyte will emit hydrogen sulfide.