VRLA in Class 1 Zone 2 w/ Type Z Purge 1

[MECE23]

Hello All:

I have a control cabin in a NEC 505 Class 1 Zone 2 Area.
The cabin is Type Z purged per NFPA 496
Upon loss of purge i can still run equipment, i just have to monitor the environment.
If i lose purge i am likely now on UPS battery power.
The question is, if the VRLA's are inside the cabin, and i have no airexhanges to keep below LEL from the VRLA hydrogen off gassing, is this going to be a concern and will it harm the personnel inside? How do you mitigate this? Stick the batteries outside the cabin?

The batteries say they are classified for the hazardous area, but i dont see how that can be so if they themselves emit gas.
Maybe they are only classified if they are also in a purged environment?

What happens when i lose purge AND gas alarms trigger? Everything shuts down except my Zone 1 F&G panel and alarms and my batteries that are contributing to the cause?

-Sorry, I'm a Mech eng in an electrical world at the moment

 

[cherryg]

Hello MEC23, first of all, you need to get in touch with the battery vendor and get the hydrogen evolution data from him. To the best of my knowledge, there is very limited evolution of Hydrogen, that too during boost charging only, and not during discharging. This needs to be confirmed with the vendor. Secondly, the battery with UPS will mostly be rated for half an hour (please confirm), and unless somebody opens the door of the cabin (again assumed to be unmanned), there will be enough positive pressure left after the first half an hour. Possibly, an isolation procedure can be written, to prevent anybody from opening the door for the first half an hour when the UPS is under operation.

 

[MECE23]

Yes, the hydrogen emission seemed to be very small for the size of the Cabin (8x20x9.5). But we have a 9Kva UPS and about 15 backup batteries (60min backup required). So with that many batteries it became more of a concern than having just 1 or 2. The cabin IS a manned space, at all times. Thus the HSE concern. I found a blurb in API 14F Section 10.3.4.2 " rechargable type batteries release hydrogen to the atmosphere in varying degrees; even battery types commonly referred to as sealed batteries; or VRLA batteries, normally contain pressure relief devices and thus may vent hydrogen under overcharge conditions. large rechargable batteries can produce enough hydrogen to create a flammable mixture under certain conditions. All rechargable battery systems should be installed such that hydrogen cannot collect in sufficient quantity to create a hazard. This may require that batteries inside buildings be installed in enclosures VENTED TO THE OUTSIDE. It is recommended that a minimum ventiliation levels specified by API 500 be maintained to ensure that the interiors of battery enclosures remain unclassified"

thanks for the (long awaited) reply cherryg.