Page 38 www.enersys.com Publication No. US-RE-IOM-002 January 2012
APPENDIX
HYDROGEN EVOLUTION CALCULATION OF RE CELLS
Every battery gives of hydrogen and oxygen during recharge. Most of the gassing occurs after
the 80% point has been reached. The concentration of the gasses is proportional to the current
being delivered to the battery.
To calculate the hydrogen produced, use the following formula, and ventilate the area as
required. Hydrogen must be ventilated in order to avoid an explosion. Hydrogen concentrations
of 4% or greater will cause an explosion.
Cubic Feet per Minute (cfm) of Hydrogen = 0.000013 x (nominal Ah capacity) x (number of
cells)
For example, an installation with 24 cells of 1RE85-21 would be:
0.000013 x (960 Ah) x (24 cells) = 0.30 cfm of Hydrogen
The National Fire Protection Association (NFPA) allows up to 1% concentration. Make sure the
ventilation system can remove the hydrogen before it reaches concentrations of 1% within the
battery area.
NOTE: The above values apply when the electrolyte temperature is 77
o
F (25
o
C). The cfm
values will double for every 15
o
F (8
o
C) of temperature rise. If the temperature drops, the cfm
values will be halved for every 15
o
F (8
o
C) decrease.
