Characterization of gas propagation and ventilation in battery rooms

There has been a proliferation of application-sensitive, normally gas efficient recombining VRLA batteries. In many applications this product is housed in relatively small rooms with minimal control of ambient temperature or battery charge current. At less than extreme excesses of these variables the recombination of the hydrogen and oxygen evolving from the battery becomes inefficient. Under these conditions potentially explosive mixtures of hydrogen in air develop and the battery room is no longer a safe environment. A thorough understanding of the properties of hydrogen transport and its ventilation is essential to prevent a dangerous buildup of hydrogen. We have tested the parameters necessary to provide efficient hydrogen ventilation and have found the following: a H₂ diffusion coefficient that is approximately a fifth of the literature value; the vent path length association to the hydrogen concentration in the battery room is not one to one, as indicated by the classical diffusion equations; hydrogen ventilation calculations and methods are presented for simple diffusion and forced air convection (fans); and it is experimentally demonstrated that the friction and turbulence of air flow when using fans needs to be determined by direct measurement