H2scan BSS Catalog 2025 - Flipbook - Page 28
Introduction
Following industry best practices outlined in IEEE documents and fire codes, managing hydrogen is crucial and
can be achieved in two ways:
1. Demonstrating hydrogen evolution of the battery using IEEE 1635/ASHRAE 21 standards.
2. Ensuring continuous ventilation of 1 CFM per ft2 in the room.
Vented Lead Acid Batteries (VLA) release hydrogen through the flame arrester, particularly during charge and
discharge cycles. VRLA batteries are predominantly recombinant but may occasionally release small amounts
of hydrogen and oxygen during normal operations. Both types of batteries can release more hydrogen during
equalize charging or unusual charge scenarios. While Lithium-Ion (Li-Ion) batteries typically do not emit gas
during regular use, this document also covers abnormal situations that could lead to gas release in Li-Ion
Battery Technology and Hydrogen Evolution
Valve Regulated Lead Acid (VRLA)
The VRLA battery is a spill-proof, recombinant type. It features a
one-way pop-up valve in each cell within the container to prevent
gas buildup. Under normal conditions, the valve stays shut,
trapping hydrogen gas to aid in the recombination process and
minimize water loss. As long as the pressure remains below the
manufacturer’s specified level, usually around 5 psi, the valve
will stay closed. However, it may open during recharging, charge
equalization or any irregular charging situation, releasing hydrogen
into the surrounding area. This can happen due to increased
current, leading to more recombination and heat generation,
potentially causing thermal runaway and increased hydrogen
Figure 1 Absorbed Glass
Mat (AGM) VRLA Battery
Vented Lead Acid (VLA) and Ni-Cad Batteries (Ni-Cad)
Vented Lead Acid and Ni-Cad batteries fall into two categories: fully
vented or partially recombinant. These battery types have a liquid
electrolyte that allows any gases produced during charging to be
released into the atmosphere, as shown in Figure 2. For partially
recombinant batteries, a catalyst device is used instead of a flame
arrestor, leading to half of the hydrogen being released. The area below
the cover and above the electrolyte contains 67% hydrogen and 33%
oxygen by volume. Hydrogen production peaks during charging and
after reaching 90% state of charge, resulting in water electrolysis.
Thermal runaway (see Fig. 1) can occur in cases of overcharging
or abnormal conditions, leading to increased current, voltage or
temperature and releasing more hydrogen into the atmosphere.
90000266
Figure 2 Vented Lead Acid (VLA)
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