Battery Room Hydrogen Ventilation (IEEE 1635)

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.

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.

The Q = 0.054 x I x N ventilation relation is a published IEEE 1635 result; the cell count, charge current, and room volume come from the battery installation.

Estimate. AHJ and licensed professional govern.

Field names used by the API: cell_count, charge_current_a, room_volume_ft3, q_cfm, ach

• Cells not jars N counts individual 2 V cells; a 12 V jar is six cells, so counting jars undersizes six-foldIEEE 1635
• 1% target holds the room-average hydrogen below 1%, a 75% margin under the 4% LELIEEE 1635 / NFPA 855
• Bounding case sealed VRLA in normal float gasses far less than this vented-cell bounding ratebattery practice