Hydrogen Concentration Worksheet

Compliments of: Industrial Battery and Charger, Inc.
Charlotte, North Carolina

During the recharging process, a lead battery releases hydrogen and oxygen through the electrolysis of sulfuric acid. The beginning of gassing is determined by the battery voltage, but the amount of gas depends on the current that isn't absorbed by the battery and is used in the electrolysis. As the battery reaches its full state of charge, the acceptance of current becomes less and the liberation of hydrogen is more.

Four percent (4%) concentration of hydrogen is dangerous and has a potential for an explosion. Generally, the maximum allowable concentration of hydrogen is 1.50% of the room's cubic footage. To keep the hydrogen concentration below 4%, adequate ventilation must be provided.

Rate of Hydrogen Release

1 Ampere x 1 Hour x 1 Cell = 0.016 cubic feet / Ampere Hour / Cell

Battery Hydrogen Calculation

Ampere Hour x Finish Rate (percent) x Number of Cells x 0.016 Cubic Feet / Ampere Hour / Cell


Quantity = 10 Batteries
Type = 18-85-21
Ampere Hour = Ampere Hour per Positive x Number of Positive Plates
Ampere Hour = 85 Ampere Hour Plate x 10 Positive Plates
Ampere Hour = 850 Ampere Hour

Battery Hydrogen Calculation

850 AH x 0.05 x 18 Cells x 0.016 Cubic Feet / Ampere Hour / Cell =
12.24 Cubic Feet / Hour / Battery x 10 Batteries = 122.40 Cubic Feet / Hour

Room Calculation

40' Long x 30' Wide x 15' High = 18,000 Cubic Feet
18,000 Cubic Feet x 0.015 (Maximum Allowable Concentration) = 270 Cubic Feet (Maximum)

Rate of Concentration Calculation

270 Cubic Feet (Maximum Allowable) 122.40 Cubic Feet / Hour = 2.2 Hours or 132 Minutes

Rate of Air Volume Removal

18,000 Cubic Feet 132 Minutes = 136.40 Cubic Feet / Minute