VRLA Battery in Explosion Proof Enclosure

[NewMechanicalEngr]

Hi folks,

Would like some comments on installing a VRLA (valve regulated lead acid) battery in an explosion proof enclosure that will be installed outdoors. The area is Class I Div 2 Group D.

Originally planned to install in a louvered battery box.
Client questioned classification of battery, specifically whether the battery would emit an arc and possibly ignite a flammable atmosphere if the battery exploded or malfunctioned due to perhaps a runaway charger (which has protection). No battery manufacturer would say "yes" or "no", so the explosion proof enclosure came into the plan. If there is an arc emitted during a battery explosion, it should not ignite the atmosphere around the enclosure.

BTW: We are including signage to open a disconnect prior to connecting and/or disconnecting wires to battery to prevent arcing.

What about hydrogen inside the enclosure?
Max allowable hydrogen in enclosure is 1% by volume (25% of LEL which is 4% for Hydrogen)
The specified battery has an almost negligible hydrogen evolution since it has a recombination process for the hydrogen and oxygen.

The enclosure will have a breather and drain (suited for C1D2) which is capable of venting air at 0.05 ft^3/min.
The hydrogen evolution from the battery is much lower at 0.0000351 ft^3/min.

Enclosure volume is 1 ft^3
Free space in enclosure (after subtracting battery volume) is 0.67 ft^3

Some of the questions in my head:
1) Can I assume there will always be a constant natural convection flow to vent the hydrogen?
2) Will the hydrogen concentration in the enclosure be below 1%?
3) Does venting the hydrogen affect the classification outside the enclosure (is it now C1D1, Group B?


I'd like to get your comments on this and see if you folks have been down this road already.

Sincere thanks!!!

 

[waross]

I've cleaned up the damage resulting from a number of battery explosions. You have to see the damage to an automobile hood to realize the violent force resulting from the explosion of hydrogen fumes INSIDE THE BATTERY.
If your enclosure will not withstand an internal hydrogen explosion, it may be futile.
Another question: Even though the hydrogen in the enclosure surrounding the battery may be below the LEL, is there a possibility that when subject to the pressure of an exploding battery it may become explosive?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

1) No, where would it convect to?
2) For a while, but not guaranteed to stay that way
3) Probably not, but I don't work with North American codes so not sure.


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If we learn from our mistakes I'm getting a great education!

 

[NewMechanicalEngr]

Thanks for your responses.

The enclosure has a vent on the top and drain on the bottom to facilitate airflow.

 

[DRWeig]

Hi NewMechanicalEngineer,

Since hydrogen is the potential internal culprit, even though the outside of the box is Group D, I'd have to go to an enclosure rated Class I Div 1 Group B (with equal rating for breather and drain). It might not be possible to find anything large enough, but you could query Crouse-Hinds or Akron Electric or Appleton. A Class I Div 1 Group B enclosure will contain a worst-case hydrogen explosion within.

Failing a hydrogen-rated enclosure, I'd have to say it'll be safest anyway to put your battery somewhere in the non-hazardous area and run cable to the box, even if it's a long ways...

Good on ya,

Goober Dave

 

[VEBill]

My car's battery is installed under the carpet in the trunk. The battery is marked "VRLA". The trunk is essentially part of the passenger compartment, separated only by split-folding rear seats.

The only precautionary equipment I can see is a little clear plastic ventilation hose running from the battery (top, an intentional vent port on the battery) to vent hydrogen gas outside (through the car's floor).

 

[DRWeig]

Good points, VE1BLL.

I most often do not even classify battery rooms that include some proper ventilation. I can't find the study, but somebody (APC?) calculated that if the batteries are ventilated enough to keep them from melting on rapid charge, then the hydrogen level will be really small.

It's the location with a single vent that is attractive to nesting birds that will get you. Or, the vent is not at the actual high point in the room, so you get some pooling of H2 up at the peak.

Difference here, in my opinion, is that it'll be enclosed in a small space. Breather/drain will help, but those are not generally rated for hydrogen. Might generate enough hydrogen after a few charging cycles to pool in the enclosure as well.

As waross mentioned, the bad action can happen inside the battery too. I have also cleaned up after one of those.

I'd just be inclined to err on the safe side, do everything Div 1, Group B. This is especially true when giving opinions about a system I haven't seen. I might say different stuff if I were standing there looking at it!

Good on ya,

Goober Dave

 

[raithrovers1]

Try these guys:

http://www.orga.nl/index.php?page=149&l=en&pid=66&from=28&allpr=297&pl=

UPS engineer

http://www.calibrepower.co.uk