Carbon Dioxide
Fact Book
INTRODUCTION
Carbon dioxide (CO2) is a colorless, odorless gas that occurs
naturally in our environment. It is normally present in the atmosphere
at a concentration of approximately 0.036%. Although it comprises
a very small percentage of our atmosphere, it is vital for nearly
all forms of life. Without CO2 we would probably not exist because
carbon dioxide is the principle inorganic compound that plants
use to construct their tissues. Consequently, we derive our energy
resources by either consuming plants directly, or indirectly when
we eat the animals that consume the plants. Therefore, it is clear
that carbon dioxide enhances and makes possible the very existence
of life on earth. As a vital atmospheric ingredient, CO2 makes
our planet a place where all forms of life may flourish.
Carbon dioxide is formed as a
by-product of combustion. For example, whenever an organic carbon
compound (e.g., wood) is broken down in the presence of oxygen,
energy in the form of heat and light is released, and carbon dioxide
(CO2) and water (H2O) are produced.
Carbon dioxide is generated within
our bodies continually. This happens as a result of the life-sustaining
chemical reactions that are occurring within the cells of our
bodies. The CO2 is subsequently transported by the blood to our
lungs. When we breathe, we exhale air laden with carbon dioxide
and we inhale oxygen-rich air.
Because we breathe out carbon dioxide,
the highest concentrations of this gas within our homes would
be found in those rooms where most people spend their time. In
addition, animals, cooking appliances and cigarette smoking can
also increase the carbon dioxide content within our homes and
can also add various odors.
If we work in a building with
poor ventilation, the buildup of CO2 may cause us to experience
adverse health effects. If we travel by air and the plane recycles
a significant portion of the ventilated air, the air may become
stale. This could also have negative consequences upon our health.
Carbon dioxide in our atmosphere
is known as a "greenhouse" gas. This gas, along with
other gases, prevents heat from escaping the earth's atmosphere.
Because of these greenhouse gases, our planet is warm enough for
us to live on it. However, scientists predict that, with the burning
of fossil fuels and subsequent release of CO2, our planet is getting
warmer.
Carbon dioxide is also generated
artificially and has many commercial applications. The use of
CO2 for carbonation of beverages is perhaps one of its most widely
recognized applications. Because CO2 will not support combustion,
it is used frequently for fire suppression.
WHERE DOES CARBON DIOXIDE COME
FROM?
Carbon dioxide is a natural component
of the atmosphere. It is normally present in the atmosphere at
a concentration of approximately 0.036%. Although it represents
a relatively small percentage of our atmosphere, it is the principle
inorganic compound that plants and animals use to live and grow.
Photosynthesis
Plants absorb CO2 through the process of photosynthesis, which
means "putting together with light." In this process,
plants use the light energy from the sun to turn carbon dioxide
and water into carbohydrates (e.g., sugars). In this process oxygen
is produced as a byproduct.
Respiration
Respiration is a process which generates carbon dioxide. In the
normal usage of this term, it describes the process of inhaling
oxygen-rich air and exhaling air laden with carbon dioxide. However,
respiration is also used to describe a process occurring within
living cells by which the chemical energy of organic molecules
is released in a series of steps where oxygen is consumed and
carbon dioxide and water are produced. For example, the carbohydrates
that are produced by plants (described above) are subsequently
"burned" in the presence of oxygen so that the plant
can live and grow. Also, in order for us to live and function
properly, we are constantly producing carbon dioxide within the
cells of our bodies as oxygen is consumed in the "burning"
of organic compounds such as carbohydrates.
The burning of any fuel produces
carbon dioxide. This means cars, trains, electric generating power
plants, etc. also produce carbon dioxide. Anytime that an organic
compound which contains hydrogen and carbon atoms (e.g., gasoline,
diesel fuel) is burned in the presence of oxygen, the hydrogen
in the fuel converts to water and the carbon in the fuel converts
to carbon dioxide.
FUEL (hydrocarbons) + AIR (oxygen)
= CARBON DIOXIDE + water.
CHEMISTRY & PHYSIOLOGY
Chemistry
Carbon Dioxide is a chemical compound formed by combining one
atom of carbon with two atoms of oxygen and is expressed by the
chemical symbol CO2. It can exist in three states: a gas, a liquid
or a solid. At room temperature and normal pressure, carbon dioxide
is a colorless gas. When compressed and cooled to the proper temperature,
the gas turns into a liquid. The liquid, upon further cooling,
can be converted into solid dry ice. The dry ice, on absorbing
heat, returns to its natural gaseous state.
Most forms of life on our planet
consume oxygen as they burn energy to live. These chemical reactions
subsequently produce carbon dioxide as a by-product. In plants,
the carbon (C) in the carbon dioxide (CO2) molecule is "bound
up" during the chemical reactions to form carbohydrates (sugars),
and the oxygen (O2) molecule is released by the plant. The chemical
energy of carbohydrates is subsequently used by the plant to live,
and in the process, oxygen is consumed and carbon dioxide is produced
as a by-product. This cycle of binding up and releasing of carbon
and oxygen has been constant over millions of years.
Physiology
Whenever an organic carbon compound is broken down in the presence
of oxygen, energy is released, and carbon dioxide (CO2) and water
(H2O) are produced. This process occurs continually within our
own bodies and is called respiration, which means "breathe
again."
Within our living cells, energy is stored in the form of organic
carbon compounds (e.g., sugars). The chemical energy of these
organic compounds is released as oxygen is consumed. The energy
is subsequently used by our bodies to function properly. As these
chemical reactions are occurring, carbon dioxide is generated.
When the pressure of carbon dioxide in the cells exceeds that
of the blood, carbon dioxide moves from the cell into the blood
and is transported to the lungs. As we breath, we release CO2
and we take in oxygen (O2). The oxygen is subsequently transported
by our blood to those sites in our bodies where these life-generating
chemical reactions can continue to occur. Once the oxygen enriched
blood encounters cells with a lower oxygen pressure, oxygen moves
from the blood into that cell.
Respiration is very critical for
life because it is necessary to supply all parts of the body with
oxygen and to get rid of the carbon dioxide that is produced.
If the oxygen supply to the cells of our body is too low, then
they will not be able to produce enough energy to function normally.
Similarly, if the carbon dioxide is not carried away efficiently,
it can accumulate within the cells thereby inhibiting their ability
to function properly. Respiration refers not only to the chemical
reactions that are occurring within the cells of our bodies, (cellular
respiration), but also applies to the gas exchange that occurs
between the cells and the blood, the blood and the air in our
lungs, as well as the gas exchange between our lungs and the outside
environment.
CARBON DIOXIDE POISONING
Ordinary outside air normally
contains CO2 at a concentration of about 300 ppm (300 parts of
CO2 gas per million parts of air.) Indoors, however, whether we're
at home, office, or traveling in a confined space like a plane,
the CO2 content can vary considerably.
Adults take more than 20,000 breaths
a day, and when we breath, we exhale carbon dioxide. When we're
at home, the highest concentrations of CO2 gas would normally
be found in those rooms where most people spend their time. In
addition, animals, cooking with unvented gas burning appliances
(e.g., space heaters, stoves and clothes dryers), as well as cigarette
smoking can also increase the carbon dioxide content within our
homes and can also add various odors.
The CO2 levels and odors could increase unless fresh air is introduced
to dilute these concentrations.
It has been observed that CO2
concentrations between 300-600 ppm are adequate, i.e., people
don't usually notice whether or not the air is "stale".
However, as CO2 concentrations increase beyond these levels, one
will notice ill effects. This is especially true if room temperatures
rise and/or CO2 levels increase above 800 ppm. As these conditions
persist, fresh air will need to be introduced.
Carbon Dioxide acts upon our vital
bodily functions in a number of ways, including stimulating respiration,
regulation of blood circulation, and the acidity of body fluids.
Common complaints from increases in CO2 levels include difficulty
in breathing, increase in the breathing rate and/or pulse rate,
headaches, sweating, shortness of breath, abnormal fatigue and
a feeling of "stuffiness". Introduction of fresh air
can assist in eliminating these problems.
Usually in a home, the CO2 levels
can vary as much as 300 - 2000 ppm. Several studies have indicated
that CO2 does not seriously impact human health until levels reach
approximately 15,000 ppm. This level is more than 40 times greater
than the normal concentration of atmospheric CO2. At extremely
high levels, i.e., 30,000 ppm, (these concentrations are usually
never reached in a standard home) the symptoms can include
nausea, dizziness, mental depression, shaking, visual disturbances
and vomiting. At extremely high levels, loss of consciousness
may occur. The seriousness of the symptoms is dependent on the
concentration of carbon dioxide and the length of time the individual
is exposed.
Finally, CO2 is an asphyxiate,
a condition in which an extreme decrease in the amount of oxygen
in the body, accompanied by an increase of carbon dioxide, leads
to loss of consciousness or death. Concentrations of 100,000 ppm
or more of CO2 can produce unconsciousness or death.
Many of the symptoms mentioned
above are related to the fact that as carbon dioxide levels increase,
oxygen levels decrease, thereby reducing the flow of oxygen to
the brain. When the oxygen level in the blood falls too low, or
the carbon dioxide goes too high (as happens when a person stops
breathing or holds his breath), the breathing center automatically
clicks on to stimulate breathing. This protective mechanism normally
functions even when one is in a deep sleep.
However, in some infants, for
some unknown reason, breathing does not automatically restart
when the infant is asleep. In Sudden Infant Death Syndrome ("SIDS")
babies have a disorder of arousal from sleep.
Hyperventilation
When we are under a stressful situation, one of our unconscious
responses is rapid, shallow breathing, otherwise known as hyperventilation.
This kind of breathing reduces the carbon dioxide level in the
blood causing blood vessels to constrict. This creates an adverse
reaction and bring about feelings of anxiety. Another effect of
hyperventilation is loss of oxygen to the brain. Hyperventilation
can cause muscle tension, headache, tingling in extremities, nervousness,
lightheaded feelings, drowsiness or dizziness.
Smoking
Cigarettes not only pose a health risk for those who smoke, but
scientific studies cited by the U.S. Environmental Protection
Agency ("EPA") reveal that when non-smokers are regularly
exposed to cigarette smoke, they run increased risk for lung,
cervical, and breast cancer, and also for heart disease, emphysema,
bronchitis, and stroke. Smoke from another's cigarette is called
"side-stream" smoke. This smoke has 2.5 times more carbon
dioxide than "mainstream" smoke (smoke filtered and
exhaled by a smoker), and is more dangerous to others in the room.
While the Surgeon General suggests that smoking be banned in the
workplace, and over 40 states have already regulated smoking in
public places, no one can legislate smoking in the home.
Children who live with smokers
have more middle ear and respiratory infections, more severe symptoms
of asthma, and more hospitalizations for bronchitis and pneumonia
than children from non-smoking homes. The susceptibility to most
respiratory diseases is greatly increased by cigarette smoking
and the most striking consequences of smoking are lung cancer.
Exercise
When we exercise, the heart pumps blood containing oxygen, fluids
and nutrients to the active muscles of our body. When more blood
is pumped, more oxygen is made available to the exercising muscles.
During exercise, the flow of blood is redistributed - less blood
goes to the major organs of our body (except the heart and brain),
and more blood flows to the exercising muscles and the skin. This
increased blood flow not only allows for more oxygen to reach
the muscles, but also allows for the efficient removal of wastes
(i.e., lactic acid and carbon dioxide) from the exercising muscles.
The increased blood flow also removes the heat that is generated
by all of these chemical reactions. The blood subsequently transports
this heat to the skin where it is released to the atmosphere.
It is therefore very important to drink plenty of fluids while
exercising. This will prevent dehydration which can cause blood
volume to decrease. If dehydration occurs, this means that your
circulatory system will be able to carry less oxygen and fewer
nutrients to your exercising muscles, and also will be able to
remove less carbon dioxide and heat.
Sick-building Syndrome
The recycled air that we breath in office buildings and condominiums
may be making us sick. Common complaints can include nose and
throat irritations, headaches, coughing, sneezing, fatigue, difficulty
concentrating, nausea, and bleary eyes. These symptoms have come
to be known as sick building syndrome. The cause of these ailments
has been related to elevated levels of carbon dioxide, as well
as many harmful air contaminants. Chemicals, bacteria and especially
poor ventilation have been linked to the causes of these ailments.
The use of a well-designed, properly
operated, mechanical ventilation system is the most effective
way to reduce indoor carbon dioxide levels. A 4-year study at
the Walter Reed Army Institute of Research made a clear connection
between disease symptoms and poor ventilation. Elevated levels
of CO2, volatile organic compounds (e.g., paints, adhesives) and
biological agents (e.g., bacteria, spores, pollen and algae) have
been suspected as being the cause of these symptoms. The Occupational
Health and Safety Administration says employees have the right
to work in a hazard-free environment, and they should document
any adverse symptoms that may be occurring among employees. Further,
employees should learn about the ventilation from the building
engineer.
Air Travel
It has been reported that sharply higher fuel prices have prompted
airline companies to search for ways to conserve energy and save
money. One of the ways was to look at the ventilation system.
Recycling part of the ventilated air has led to cost savings for
many airlines. Most of the filters currently in use by the airlines
are capable of removing 90-95 percent of dust, bacteria, and viruses.
However, the filters do not remove CO2, and may not be able to
remove odors.
Consequently, the newer models
of planes recycle as much as half of the ventilated air instead
of providing 100 percent fresh air, as older models of planes
did. This has prompted air-quality related complaints of headaches,
dizziness, nausea, burning eyes, breathlessness, noxious fumes,
and persistent respiratory illnesses. In addition, a general lack
of fresh air can lead to negative consequences for passengers
with chronic bronchitis, asthma, emphysema, allergies, or an impaired
immune system.
A study conducted found that about
one in four flights had at least one CO2 reading in excess of
1000 ppm. This level was used as a benchmark above which occupants
perceive a stuffy atmosphere and are more likely to notice odors.
It is not surprising that fully-occupied flights had relatively
high concentrations of CO2, and the flights with the highest CO2
readings had higher-than-average temperature and humidity.
The Federal Aviation Administration
(FAA) has yet to adopt minimum ventilation standards for airline
cabins. According to Dr. James E. Cone, medical consultant for
the Association of Flight Attendants, current FAA requirements
are inadequate to protect the health of passengers, as they permit
air in cabins with "nearly 100 times the level of carbon
dioxide in outdoor air, and 30 times the recommended standard
for carbon dioxide concentration in buildings" set by the
American Society for Heating, Refrigerating, and Air-Conditioning
Engineers. A recent Consumer Reports study, testing air quality
on 158 flights, confirmed that "passenger cabin air in almost
one in four commercial airline flights flunks a ventilation industry
guideline for freshness."
Sick Plane Syndrome
Poor air quality, like that of the sick building syndrome suffered
by some office workers, has been noted by airline flight attendants
and frequent flyers. Symptoms include headaches, dizziness, and
nausea. These symptoms have been called sick plane syndrome. However,
these symptoms are not the only drawbacks of inadequate ventilation.
Flight attendants and frequent travelers have also complained
that they often catch severe colds after long flights.
A recent article posted on the
Internet by CNN on March 17, 1999 stated that "The Federal
Aviation Administration toughened air quality guidelines in 1996,
requiring more fresh air in the cabin. Numerous studies indicate
cabin air is actually lower in bacterial content and other contaminates
than the air in an average office." However, the report also
stated that "There's a lower amount of oxygen available."
In order to avoid the onset of
many of these ailments, airline passengers should make every effort
to get off their plane if it makes a stop en route in order to
breathe fresh air. It has been reported that when a plane is parked,
ventilation is usually worse than during a flight.
When you book a flight, you may want to check with the airline
and ask them if your plane has all-fresh or partly recycled air.
Just as complaints were effective in eliminating in-flight smoking,
so too will complaints make the airline companies aware of concerns
about air quality. Also, if you begin to feel stuffy during a
flight, make your concerns known to the flight attendants. They
may be able to increase ventilation in the plane.
CO2 - Denser Than Air
Gaseous carbon dioxide is 1.5 times denser than air. Therefore,
it will be found in greater concentrations at low levels. In the
bulletin, the Occupational Safety and Health Administration (OSHA)
warns that high concentrations of CO2 can displace oxygen, and
can subsequently cause death especially if allowed to accumulate
in open pits and other areas below grade.
This warning was prompted by the
delivery driver who succumbed to carbon dioxide asphyxiation while
dispensing CO2 from his tractor-trailer. The CO2 fill station
was located in a below-ground stairwell. The accident apparently
resulted from a fault in CO2 of the delivery mechanism. The condition
was aggravated by the fact that the below grade location allowed
the CO2 to accumulate.
FIRST AID FOR EXPOSURE TO CARBON
DIOXIDE
Carbon dioxide is a colorless,
odorless gas and should be treated as a material with poor warning
properties. To prevent the concentration of carbon dioxide from
accumulation to undesirable levels, measures should be taken to
improve ventilation by:
o adding fresh air to a room periodically by opening doors and
windows;
o ensuring that all gas burning appliances are properly vented
o turning on exhaust fans over cooking equipment and in bathrooms.
STANDARDS AND RECOMMENDATIONS
FOR CO2 EXPOSURE
The Occupational Safety and Health
Administration (OSHA) has set a standard for the maximum allowable
concentration of carbon dioxide in the air of 0.5% (5000 ppm)
for eight continuous hours of exposure. The maximum time weighted
average exposure to carbon dioxide in the air is set at 1.0% (10,000
PPM) for a ten hour shift in a 40 hour week.
ENVIRONMENTAL EFFECTS OF CARBON
DIOXIDE
Carbon dioxide in our atmosphere
is known as a "greenhouse" gas. This naturally occurring
gas, along with hydrogen vapor, methane, nitrous oxide, and ozone
act something like the glass walls and ceiling of a greenhouse.
It lets sunlight in to keep things warm, but it doesn't let the
heat escape. That's why scientists began to call gases "greenhouse"
gases because of their warming effect on the earth. If it were
not for these greenhouse gases, scientists predict that our planet
would be unhabitable with an average temperature of about -23°C.
However, the higher the concentration
of these gases in the atmosphere, the warmer the atmosphere. Every
time we burn a fossil fuel (e.g., oil, natural gas, coal), or
wood and wood products, carbon dioxide is released into the air.
With the burning of these fuels and subsequent release of CO2,
many scientists predict that our planet is getting warmer. Therefore,
CO2 is probably the most important of the greenhouse gases because
human activities generate so much of it.
Many kinds of scientific measurements
have shown that the concentration of CO2 in the atmosphere has
been increasing over the past several centuries. During this time
the human population increased geometrically, the steam engine
was put to industrial use, and the gasoline-powered automobile
came into use across the globe. In addition, less CO2 became "tied
up" by plants because farmer-settlers cleared native vegetation
from vast expanses of the Americas, Australia, and parts of Asia.
During this same period, the atmospheric concentration of carbon
dioxide has increased from a pre-industrial (1750) level of about
280 ppm to about 353 ppm, an increase of about 25 percent. That's
enough to make a potentially significant difference, if climate
is as sensitive to greenhouse gases as many scientists suspect
it is.
BENEFICIAL USES OF CARBON DIOXIDE
Carbon dioxide generated artificially
and has many applications. The use of CO2 for carbonation of beverages
is perhaps one of its most widely recognized applications. It
is also used in the shipping and processing of fresh meat. Because
CO2 is denser than air and will not support combustion, it has
become one of the most significant methods of suppressing and
fighting electrical and grease fires. In addition, the application
of CO2 in firefighting is clean, non-toxic and leaves no residue.
If you've ever wondered why your
soufflé puffs up so high, or why your bread rises, it's
because of leavening agents, the most common of which are baking
soda, baking powder, and yeast. When mixed with a liquid, the
leavening agents produce carbon dioxide gas, which causes batter
or dough to rise when heated. When water is added to these mixtures,
chemical reactions occur, producing carbon dioxide which becomes
trapped in tiny air pockets in the dough or batter. Heat releases
additional CO2 and expands the trapped gas and air to create steam.
For more information, e-mail us
at wek@airspill.com
Copyright 1999 W.
E. Kuriger Associates
All Rights Reserved
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