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The estimated number of significant
size lead-acid batteries installed in non-vehicular applications in the United States is
in the tens of millions of cells. Installations of batteries range from heavy industry
applications all the way into the home where the battery may be found in a computer
peripheral underneath or next to a desk. A battery is more than chemistry. The battery has
far reaching implications due to its electrical and electrochemical characteristics. This
document will address what we believe to be issues not generally known, including the
effects of a self propagating battery fire.
A significant amount of lead-acid
batteries may be found in just about all industrial and commercial business applications.
These are applications that generally rely on electric energy without connection to
commercial electric power sources or require continued electric power backup even when
commercial power is interrupted. The size of the battery installation varies from
completely filling a 10,000 square foot room to a battery inside a Uninterruptible Power
Supply (UPS) "protecting" a personal computer either in business or in the home.
The electric power from lead-acid batteries used to be confined to industrial and large
business applications. Now, batteries are used in just about every area of occupancy
classification. Until recently not many people were even aware of hazardous materials
present in lead-acid batteries. Morning Star Industries estimates there is well over
20,000,000 gallons of battery acid in non industrial classified business use facilities in
the United States. A large data center or telephone central office may easily contain over
10,000 gallons of sulfuric acid. If this same sulfuric acid were stored in 55 gallon
drums, the presence of approximately 200 drums would, in all likelihood, cause no small
concern. Drum storage of sulfuric acid in comparison to sulfuric acid in batteries, is
substantially safer since there are additional serious failure mechanisms and consequences
to be found in batteries and their applications.
Lead-acid
batteries are, in a way, a chemical miracle. The active materials are simply lead and
sulfuric acid and lead compounds formed through the charging and discharging of the
battery. When a battery is charged, additional energy is "stored" in chemistry
changes. When a battery is discharged, energy is "removed" through the reversal
of these chemistry changes. When the battery is fully charged, the positive plate is lead
and the negative plate is lead dioxide. The sulfuric acid is the strongest when the
battery is fully charged and may be as high as 40% pure sulfuric acid mixed with 60%
water. When the battery is substantially discharged, both the positive and negative plates
are converted to lead sulfate and the sulfuric acid is less than 10% sulfuric acid mixed
with more than 90% pure water. Sulfuric acid is classified as an Extremely Hazardous
Substance (EHS) and lead, lead dioxide, and lead sulfate are classified as Hazardous
Materials.
While
battery manufacturers have many names for their lead-acid batteries, there are basically
only two types. The first, and also the one Thomas Edison made popular, is the
"Flooded" or "Wet" cell battery. The second, and more recently
introduced is the Valve Regulated Lead Acid (VRLA) battery. The flooded battery has
"free" electrolyte sulfuric acid while the VRLA battery has "starved"
electrolyte sulfuric acid. The primary difference between these two basic cells lies in
the recombination of hydrogen with oxygen within the battery during the overcharging of
the battery. Generally, once the battery has been charged, continued charging separates
the hydrogen from the oxygen in the water mixed with the sulfuric acid. In the case of the
Wet cell, the hydrogen gas floats to the top of the electrolyte before it finds the oxygen
in the liquid solution. This hydrogen gas is vented to the outside of the battery. In the
VRLA cell, the electrolyte is deliberately "starved" by having a porous mat or a
gel separating the positive and negative plates. Since the hydrogen gas is freer to
migrate toward the negative plate, the hydrogen recombines with the oxygen within the
battery. Recombination of oxygen and hydrogen efficiency is typically over 95%. This means
there is less hydrogen given off from the VRLA battery in comparison with the Wet cell
under the same overcharging conditions. This means there is less water loss in the VRLA.
While there are advantages with VRLA batteries, there is also additional problems. Wet
cells are relatively abuse forgiving, while VRLA cells are relatively abuse unforgiving.
We will be addressing some of these aspects later.
Both
lead-acid battery types have the same chemical reactions during charge and discharge. In
general, the amount that a battery may be discharged is determined by the amount of the
electrolyte (sulfuric acid) present (electrolyte limited). A rule of thumb for both
batteries is the sulfuric acid is one third of the weight and the lead and lead compounds
comprise the rest or two thirds of the reactive elements. For a thousand gallons of
electrolyte, there will be over 20,000 pounds of lead and lead compounds. A car battery
that weighs 30 pounds will contain about one gallon of electrolyte. The electrochemical
energy of a fully charged battery is substantial enough to vaporize or evaporate over half
of the battery materials. This one fact alone should sensitize us that the dangers of a
battery are much more than sulfuric acid being stored in a container.
The
typical lead-acid battery has a jar, top cover with vents (both Wet and VRLA), watering
opening with cover, and battery posts. Due to chemical compatibility considerations, the
battery posts and terminals are made out of lead or a lead alloy. The exposed posts and
terminals contain a hazardous material, lead, and may contain Extremely Hazardous
Substances or hazardous materials including antimony, arsenic, and calcium metal. Also
associated with the battery posts is the wicking of sulfuric acid past the post seal and
onto the post terminal and battery cover. It is believed battery acid wicking past the
post seal is considered a normal event by the battery manufacturer in that it is not
covered in the battery warranty. Sampling of automobile battery posts further confirms
sulfuric acid and lead sulfates on the top of the battery cover is the "norm."
Vent "slobbering" in both Wet and VRLA is also common as well as filler cap acid
"creepage" in the Wet cell. All of these sources of contamination may be
considered normal operation based on the number of units exhibiting these characteristics.
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Battery
jars do craze and crack. Root causes of jar failures may include:
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Manufacturing
defect(s)Aging
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"Foreign"
chemical incompatibility with cleaners used
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Chemical
degradation between jar material, sulfuric acid, and other chemicals
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Abuse,
accidents, earthquakes, fires, improper installation
What
happens if a fully charged lead-acid battery cell is shorted? Hopefully the device
shorting the battery becomes hot and melts or vaporizes and clears the short. In large
installations, there is enough energy available to vaporize copper buss bars and other
circuitry. Vaporizing copper has the same expansion rate as exploding dynamite.
If a
shorted battery cell does not clear the external short, the electrical connection between
the battery terminals allows for a very rapid chemical reaction as the sulfuric acid
converts the lead and lead dioxide to lead sulfate. Now the electrical energy is not
dissipated externally, but internally in the form of heat. The resulting temperature rise
inside the battery cell literally destroys the cell and actually may vaporize the battery
materials including the electrolyte and lead.
Actual
battery applications are comprised of multiple battery cells. A typical car battery has
six cells in series. Telecommunications typically have battery strings of 12 and 24 cells
each. Industrial Supervisory Control and Data Acquisition (SCADA) systems typically have
60 cells in series. When a short is placed across a string of batteries, the resulting
fault current will begin discharging all of the cells until one or more cells fail. Now,
instead of each cell destroying itself, the cells that have not failed dissipate their
energy into the failed cells. Not only do the failed cells typically melt and give off
vapors, but these failed cells often become arc furnaces due to the energy contribution
from the rest of the battery string. The amount of energy dissipated in the failed cell(s)
is usually enough to totally vaporize the whole battery unless the battery fails in such a
way as to disconnect the circuit. When the battery cell is on a grounded rack or mounting
surface, the circuit continuity is continued through the battery cell’s melted parts
and the conductive mounting surface. This type of destruction of the battery cell(s) is
typically what is called a battery fire. Substantial clouds of acid mist and vapor will be
present during this type of fire and will typically overwhelm a typical ventilation
system.
Normal
operation during the useful life of the battery under normal conditions includes exposure
to extremely hazardous substances and hazardous materials. Hydrogen gas from either type
of battery may be released and accumulate to explosive levels. Sulfuric acid and lead
sulfate accumulations are also typical and considered a normal condition by those in the
battery industry and is not generally covered under warranty or workmanship standards.
Lead and other materials, under normal use, may be easily transferred from the battery
posts to other areas including the hands. Because of potential exposure to EHS and
hazardous materials under normal conditions of use, we do not believe either Wet or VRLA
batteries should arbitrarily be exempted as an "article" under 29 CFR 1910.1200
(2)(b). We are pleased that EPCRA has ruled that battery materials are to be counted
toward the reporting quantity threshold requirements. In addition, while EPCRA does permit
the household product exemption for car and truck batteries, it does not exempt larger
commercial type batteries for facilities such as telephone offices or for batteries of the
type for electric forklift vehicles. We have grave concern regarding a facility that has
substantial amount of batteries outside of motor vehicles that have not reported the
presence of these batteries to the Local Emergency Planning Committee or the local fire
department. |
