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THE
SAFETY ZONE
- ARE
EXPLODING
BATTERIES
A THREAT
TO MINERS?
BY HAROLD
HOUGH
A recent spate of battery explosions in
notebook computers has highlighted the potential dangers of rechargeable
batteries. The question is if this danger extends to miners lamps? Let’s take
a look at the chemistry of rechargeable batteries and what dangers they actually
pose. The first serious rechargeable battery was the lead acid battery, the same
one you have in your car. The advantage is that they are reliable. That’s one
reason why they are still used in some miner’s lamps. The problem is that they
are heavy and don’t have the same energy density as other batteries. And, they
do pose a potential explosion problem because they produce hydrogen while they
recharge.
The
first step in dry rechargeable batteries was the Nickel-Cadmium battery. They
didn’t release any gasses although they did get warm when they were recharged.
There weren’t any explosion risks. However, they did have a down side. First
was the “memory effect’ which caused them to quickly lose their charge if
improperly used or charged. Second, cadmium is toxic and they posed a serious
environmental problem. In the end, they weren’t the right battery for the high
power needs of today’s electronics.
Today’s
rechargeable battery of choice is the lithium battery – usually the LiCoO2
Lithium Ion battery. It isn’t as toxic, it has a higher energy density, and it
has a better recharging profile than nickel cadmium. That’s one reason why it
is used in miners’ cap lamps. But it’s also the same battery that has been
involved in these well-publicized computer battery explosions. So, why do
lithium batteries explode? It comes down to chemistry. Lithium is a light metal
that reacts poorly to water, air, and fire. Note that lithium ion batteries also
contain oxygen, the active element in air. A little heat is all that is needed
to start decomposing LiCoO2 into oxygen, cobalt, and lithium. And, anyone who
has rechargeable batteries at home knows that recharging or discharging
batteries produces a lot of heat.
Chemistry
is only part of the problem. As engineers have tried to increase the power
density of the batteries, they have tightened tolerances, made cell walls
thinner, and put more materials inside. That means more dangerous stuff in
smaller spaces. So what happens if
there is too much heat? The lithium compound decomposes and releases oxygen and
lithium. If they start to react with each other, they produce more heat, which
decomposes more LiCoO2, which produces more fuel for the reaction. All this
occurs in an enclosed container, which increases pressure, which pushes the
reaction that much faster. It becomes a runaway reaction that occurs in a
fraction of a second.
So,
how dangerous are lithium ion batteries? In reality, they are very safe.
However, they can cause problems if they are mistreated or are defective. If you
looked inside a lithium battery, they look like the cross section of a jelly
roll. Each roll is a cell and they are wired together to provide the necessary
power. However, if the different layers come together, the cell short circuits,
heat is created, and it goes boom. That can occur if they are defective. But, it
also happens if they are mishandled. Rechargeable lithium ion batteries can
explode if they are damaged or punctured (that’s why you don’t find them in
electric or hybrid cars). Although that isn’t as big a problem with notebook
computers, it is more likely in a mining environment. Consequently, even though
many lithium ion batteries have short circuit protection, mining companies and
miners have to be careful about how they are handled during use.
With
that in mind, here are some suggestions to lower any threat of batteries
exploding:
DO
NOT DROP, PUNCTURE, OR CRUSH THE BATTERIES.
This could cause a short circuit inside the battery. Any battery that is damaged
should be checked out before being used.
DON’T
KEEP THE BATTERIES IN HOT PLACES.
Heat causes decomposition of the lithium compound, which can lead to problems.
KEEP
THE BATTERIES DRY. Water
can cause corrosion, which could lead to short circuits.
DON’T
USE INCOMPATABLE BATTERIES OR CHARGERS.
A second hand dealer may try to sell batteries or chargers that “are just as
good.” A mismatch between the light, the battery, or the charger could cause
excessive heat and a possible explosion.
That
said, the lamps used in the mining industry are very safe and better than what
we had in the past. However, a little common sense will considerably lessen any
potential problem.
NOTE:
Since this article was written, the MSHA has published recommendations to lessen
the threat posed by lithium batteries. They can be found on the MSHA website WWW.MSHA.GOV
. The document is PIB
P07-26.
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