Battery Room Hydrogen Ventilation (IEEE 1635)
The cells-not-jars exhaust rate that keeps a battery room under the LEL: charging vented lead-acid/flooded cells liberate hydrogen, and IEEE 1635 sets Q = 0.054 x I x N cfm to hold the room average below 1% (a 75% margin under the 4% explosive limit). The catch that undersizes real rooms is the formula counts individual 2 V CELLS, not jars -- a 12 V jar is six 2 V cells, so twenty-four 12 V jars is 144 cells, not 24. A 24-cell string at 20 A needs 25.9 cfm (1.9 ACH in an 800 ft^3 room); counted as jars (144 cells) it is really 155.5 cfm, six times the airflow. Sealed VRLA in float gasses far less. A design aid; the applicable code and room design govern.
Formula and source
Q_cfm = 0.054 x I x N (N = individual 2 V cells); ACH = Q x 60 / room_volume.
The IEEE 1635 / IEEE-ASHRAE Guide 21 battery-room hydrogen ventilation rate, holding the room-average hydrogen below 1% (NFPA 855 4% LEL), by name; the applicable code and the room design govern.
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