Written By:
Henry P. Shotwell, Ph.D., CIH
Senior Vice-President
Recently, a client of ours called because of some very
unusual carbon dioxide (CO2) readings they
were getting in their refrigerated warehouse. This client
stored perishable food that was packed with chips of
dry ice. All of a sudden their typical CO2
meter readings went from about 3,000 ppm to 26,000 ppm.
The OSHA Permissible Exposure Limit is 5,000 ppm (averaged
over an 8-hour work shift), so this represented a potentially
serious condition.
Our CO2 meter scale went up to 50,000 ppm
and we were seeing levels of 30,000 to 35,000 ppm in
the warehouse and in the adjoining packing plant. This
was a head scratcher. Where was the excess CO2
coming from? After a careful review of the packing procedures
and CO2 use patterns, we could find no change
in the amount of CO2 used or the way in which
it had been used for years. The answer had to lie somewhere
else.
Next, we drove along the nearby roads, about a mile
out in every direction. The CO2 levels rapidly
dropped off to an average of 400 ppm and stayed there.
Obviously, the source of the excessive CO2
was somewhere on the property. We made a contour map
of the dual plant facility with the CO2 meter
readings and were able to pinpoint the source of the
CO2. The map led us straight to a large (50
foot tall) CO2 storage tank located in the
middle of the plant complex.
Subsequent investigation showed that the tank had just
been refilled with CO2 and may have been
over-pressurized in the process. The plant was located
in a Deep South state and the incident occurred in mid-July
of the year. The pressure relief valve at the top of
the tank was open but the audible alarm had malfunctioned.
Since carbon dioxide is colorless and odorless, the
escaping gas went undetected until routine monitoring
discovered it. The compressed gas supplier was notified
and immediately began repairs, resulting in a savings
in CO2 costs and eliminating the likelihood
of a significant occupational exposure.
Carbon dioxide is a natural component of our atmosphere.
Actually, it’s the fourth most abundant gas in the earth’s
atmosphere. On average, the earth’s atmosphere contains
between 385 and 390 parts per million (0.0385 to 0.0390%).
It is also referred to as the “Greenhouse Gas.”
Carbon dioxide has some interesting properties. It
stimulates plant growth (plants use CO2 for
food, transforming it to sugar in the presence of ultraviolet
light (sunlight). Carbon dioxide is one of the three
end products of mammalian metabolism: heat energy and
water vapor being the other two. Interestingly, while
carbon dioxide is a simple asphyxiant in concentrations
high enough to reduce the oxygen concentration in air
to hazardous levels, it’s also essential for any creature
that has lungs. Receptors in the aorta, carotid arteries
and the brainstem are sensitive to carbon dioxide in
the bloodstream. If the CO2 levels in blood
rise above a certain point, the breathing reflex kicks
in and we begin breathing deeper and more rapidly. Breathing
air supplied to divers and to patients on respirators
contain up to 1,000 ppm (0.1%) of CO2 to
ensure that the breathing reflex is stimulated. So,
while breathing excessive amounts of carbon dioxide
can be hazardous, so can not breathing enough!
Carbon dioxide is used as “Dry Ice” in food storage,
in medical preservatives, in carbonated beverages, as
an inerting gas in vessels where an explosion of volatiles
may occur, and in some fire extinguishers. It is also
a byproduct of combustion, and involved in some chemical
processes. Carbon dioxide levels can rise in confined
spaces, as well as in poorly ventilated offices. Where
these activities occur, the potential exists for overexposure
to workers and others.
Thus, there are both sides to this story—it is essential
to us humans—as air breathers—but also hazardous at
high concentrations (above 5,000 parts per million).
Environmental and Industrial Hygiene consultants such
as Atlantic Environmental, Inc. have the ability to
test for hazardous levels of CO2 whenever
it exists.
