Lead-Acid Storage Batteries
a. Rate of gas Formation is from Linden, 1984 (Handbook of Batteries and Fuel Cells).
thoroughly with clean water if acid gets into the eyes, skin, or clothing and obtain medical
attention when eyes are affected. A bicarbonate of soda solution is commonly used to
neutralize any acid accidentally spilled. After neutralization the area should be rinsed with
Precautions must be routinely practiced to prevent explosions from ignition of the flammable
gas mixture of hydrogen and oxygen formed during overcharge of lead-acid cells. The
maximum rate of formation is 0.42 L of hydrogen and 0.21 L of oxygen per ampere-hour
overcharge at standard temperature and pressure. The gas mixture is explosive when
hydrogen in air exceeds 4% by volume. A standard practice is to set warning devices to ring
alarms at 20 to 25% of this lower explosive limit (LEL). Hydrogen detectors are available
commercially for this purpose.
With good air circulation around a battery, hydrogen accumulation is normally not a
problem. However, if relatively large batteries are confined in small rooms, exhaust fans
should be installed to vent the room constantly or to be turned on automatically when
hydrogen accumulation exceeds 20% of the lower explosive limit. Battery boxes should also
be vented to the atmosphere. Sparks or flame can ignite these hydrogen mixtures above the
LEL. To prevent ignition, electrical sources of arcs, sparks, or flame should be mounted in
explosion-proof metal boxes. Flooded batteries can similarly be equipped with flame
arrestors in the vents to prevent outside sparks from igniting explosive gases inside the cell
cases. It is mandatory to refrain from smoking, using open flames, or creating sparks in the
vicinity of the battery. A considerable number of the reported explosions of batteries come
from uncontrolled charging in non-automotive applications. Often batteries will be charged,
off the vehicle, for long periods of time with an unregulated charger. In spite of the fact that
the charge currents can be low, considerable volumes of gas can accumulate. When the
battery is then moved, this gas vents, and if a spark is present, explosions have been known
to occur. The introduction of calcium alloy grids has minimized this problem, but the
possibility of explosion is still present.
Some types of batteries can release small quantities of the toxic gases, stibine and arsine.
These batteries have positive or negative plates that contain small quantities of the metals
antimony and arsenic in the grid alloy to harden the grid and to reduce the rate of corrosion
of the grid during cycling. Arsine (AsH ) and stibine (SbH ) are formed when the arsenic or
antimony alloy material comes into contact with hydrogen, generated during overcharge of
the battery. They are extremely dangerous and can cause serious illness and death.
Ventilation of the battery area is very important. Indications are that ventilation designed to
maintain hydrogen below 20% LEL (approximately 1% hydrogen) will also maintain stibine
and arsine below their toxic limits.
The following summary of safety precautions as found in DOE-STD-3003-94, Backup Power
Sources for DOE Facilities, will aid in preventing personal injury and damage to facilities: