Hydrogen Concentration Worksheet

During the recharge process, a lead acid battery releases hydrogen and oxygen through the electrolysis of sulfuric acid. The beginning of gassing is determined by the battery voltage. The amount of gas released depends on the current that is utilized in the electrolysis of the sulfuric acid. As the battery reaches its full state of charge, less current is used in converting lead sulfate from the negative and positive plates and more current is used in the gassing process.

Four percent concentration of hydrogen is dangerous and can potentially explode. The National Fire Protection Association (NFPA) allows up to 1% concentration of hydrogen in a battery charging area. It is important to check with the local fire department for their local code. To keep the hydrogen concentration below 1%, adequate ventilation must be provided.

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Calculate Rate Of Hydrogen Concentration (RHC):

calculations: battery amp hour (Ah) rating * finish rate [in percent] * # of cells * max concentration (ft/Ah/cell)
example:
- Battery: 18-85F-29 (18 cells)
- Amp Hour Capacity: 1190 Amp hours rating
- # Batteries On Charge: 15
  1190 * 0.05 * 18 * 0.016 = 17.14 cu ft/battery
  17.14 * 15 = 257.1 cu ft/hr

Calculate Maximum Hydrogen Concentration (MHC)

formula:
  length * width * height = cubic feet of room
  cubic feet * max concentration = max hydrogen concentration per cubic foot
example:
 - Room: 50 feet long by 30 feet wide by 20 feet high
 - Concentration:  0.01 (maximum allowable concentration)
  50 * 30 * 20 = 30,000 Cubic Feet in room
  30,000 x 0.01 = 300 Cubic Feet (max hydrogen concentration in room

Rate To Maximum Allowable Concentration:

formula:
  max hydrogen conc. / rate of hydrogen conc. = rate to max allowable conc.
example:
  300  / 257.1 = 1.17 hour or 70.01 minutes

Rate Of Air Volume Removal

formula:
  room vol / rate to max allowable concentration = rate of air volume removal
example:
  30,000 cu.ft. / 70.01 minutes = 428.51 cu.ft./minute