# Flame Barrier for Battery Box Vents



## Nodd (Jun 6, 2008)

Hey folks,

I'm getting my EV ready for inspection & I came across the following entry in the Connecticut Electric Vehicle Requirements:

"Vehicle with battery vents shall have flame barrier provisions to inhibit battery explosions."

Below is a diagram of my current setup. I have a set of 16 flooded batteries in a battery box inside the passenger compartment. I'm venting fresh air into one end of the box & then exhausting it out the other end using a small brushless DC fan.










Anyway, I figured that'd do the trick but I have no clue what a "flame barrier" might be. Any ideas what they're talking about?


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## Manntis (May 22, 2008)

Nodd said:


> Anyway, I figured that'd do the trick but I have no clue what a "flame barrier" might be. Any ideas what they're talking about?


the flame barrier is a flame & spark-retardant barrier that allows gases to pass out of the battery, but stops sparks or flames from entering the cells, reducing explosion hazards from external spark or flame. They're usually built into the caps of the battery.


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## Nodd (Jun 6, 2008)

Duh! Okay now this makes sense. I've not received my batteries yet but I'm guessing they'll have that feature. Okay thanks for clarifying that.


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## MrCrabs (Mar 7, 2008)

Maybe try modifying the intake and exhaust pipes to have an extra 90 degree bend like in the attached pic.

It would prevent flames from going up the pipes to get to any gas (in the event of a fan failure)


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## Nodd (Jun 6, 2008)

My diagram was perhaps a little over simplified but yes, I've considered adding a large forward facing air scoop to the intake pipe. Also I believe that the low pressure zone that forms behind a vehicle while its in motion will actually help suck air out of the rear exhaust vent. So that should help also if the fan fails.


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## e_canuck (May 8, 2008)

Hi. Just a new guy here. But.
I think perhaps the intent is a flame arrester. Like on a carburator to prevent back fires to come out. Or in this case a flame outside the vehicule burning its way in the the battey compartment, where the rest of the hydrogene is.

Take care. DP


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## Nodd (Jun 6, 2008)

Hmmm okay. Yeah that was my first impression when I read that requirement. I guess an example of that would be someone chucking a lit cigarette butt out of the car ahead & me driving over it... spark enters the intake vent & BOOM!

Assuming that's what they mean, anyone know how to make a vent flame arrestor or where I can buy one?


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## ww321q (Mar 28, 2008)

And what are your concerns about venting hydrogen gas from the batteries threw a electric motor (spark!spark!) J.W.


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## e_canuck (May 8, 2008)

Hi. I would have no concern. Computer, server fans are all brushless. No spark. Beside if the fan is actually turning the fuel/air ratio will be to poor to get ignition.

DP

PS If they are not all brushless. Someone please tell me.


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## Nodd (Jun 6, 2008)

*grin*

Yeah that's always worried me some hence the brushless DC motor. Should be less of a hazard but still, yeah the idea is a little nuts. I suppose no worse than an electric fuel pump in a gasoline tank.

As this battery box is in the passenger compartment I can't really consider a pressurized system (fan in the intake vent instead of the exhaust). Any leaks in my box & I end up with fumes in the passenger compartment. Not good.

Anyway, anyone know how to add flame barriers to a battery box' vents?


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## VDubber (Jun 2, 2008)

MrCrabs said:


> Maybe try modifying the intake and exhaust pipes to have an extra 90 degree bend like in the attached pic.
> 
> It would prevent flames from going up the pipes to get to any gas (in the event of a fan failure)


Hydrogen gas (what comes out of batteries) is much lighter then air - it rises rather quickly. Are you sure it would really help that much? Wouldn't the flame happily travel up the corner?

Perhaps locating the exhaust vent so it goes UP out of the box would be better. Then if the fan dies, it will still flow out of the box. Hydrogen will rise out the exhaust vent, which will create a low pressure and pull in fresh air up the intake vent.

And isn't most of the hydrogen produced during charging, not driving?


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## Manntis (May 22, 2008)

Nodd said:


> Hmmm okay. Yeah that was my first impression when I read that requirement. I guess an example of that would be someone chucking a lit cigarette butt out of the car ahead & me driving over it... spark enters the intake vent & BOOM!
> 
> Assuming that's what they mean, anyone know how to make a vent flame arrestor or where I can buy one?


That's not likely what they mean. Intake vents are very rare - normally cabin air is the 'intake' but the hydrogen contaminated air is vented to the outside. 

If, in the interest of bureaucratic silliness, someone interprets Conneticut 14-103b-5 (c) to mean batteries mounted anywhere other than the engine bay (kinda silly when you think about it, since the engine bay is where there's hot air and lots of ignition sources to make the hydrogen go boom compared to trunks or storage bins) this hydrogen venting, if anything, is the explosion hazard - not a cigarette leaping straight up an intake pipe which shouldn't exist in the first place and entering the battery via already existing flame proof barrier vents 

In fact the following line (d) does specify ventilation to maintain hydrogen concentration < 4%, strengthening my suspicion that "battery vents" means the vents on the battery. Otherwise (c) and (d) would be regulating the same thing, in which case they should be one paragraph, not two separate regulations.


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## Nodd (Jun 6, 2008)

Okay thanks everyone for the advice. I think I'm going to interpret this regulation as meaning the battery caps, as Manntis originally suggested. If I fail inspection because that's not the case, I'll update this post.


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## Nodd (Jun 6, 2008)

VDubber said:


> Perhaps locating the exhaust vent so it goes UP out of the box would be better. Then if the fan dies, it will still flow out of the box. Hydrogen will rise out the exhaust vent, which will create a low pressure and pull in fresh air up the intake vent.


Yes ideally I'd have preferred to have my exhaust vent running up & out but my EV is a convertible with a rag top. Other than building a chimney stack sticking through the fabric roof (sure to leak) I'm not sure what could be done. Only other option I can think of would be to exhaust through the side of the car just below where the rag top begins but that'd mean cutting into a side panel (ugly) & wouldn't really net me all that much vertical advantage.


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## adric22 (Jan 17, 2008)

I've never heard of a battery exploding in flames before. When a battery explodes, it is usually just from internal pressure build up. I'd be more worried about getting acid on me than I would be flames.


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