Note:
There is a large body of written material on ozone and the use of ozone
indoors. However, much of this
material makes claims or draws conclusions without substantiation and sound
science. In developing Ozone
Generators that are Sold as Air Cleaners, the EPA reviewed a wide assortment
of this literature, including information provided by a leading manufacturer
of ozone generating devices. In
keeping with EPA's policy of insuring that the information it provides is
based on sound science, only peer reviewed, scientifically supported
findings and conclusions were relied upon in developing this document.
Introduction
and Purpose
Ozone
generators that are sold as air cleaners intentionally produce the gas
ozone. Often the vendors of
ozone generators make statements and distribute material that lead the
public to believe that these devices are always safe and effective in
controlling indoor air pollution. For
almost a century, health professionals have refuted these claims (Sawyer,
et. al 1913; Salls, 1927; Boeniger, 1995; American Lung Association, 1997;
Al-Ahmady, 1997). The purpose of this document is to provide accurate
information regarding the use of ozone-generating devices in indoor occupied
spaces. This information is based on the most credible scientific evidence
currently available.
Some
vendors suggest that these devices have been approved by the federal
government for use in occupied spaces. To the contrary, NO agency of the
federal government has approved these devices for use in occupied spaces. Because
of these claims, and because ozone can cause health problems at high
concentrations, several federal government agencies have worked in
consultation with the U.S. Environmental Protection Agency to produce this
public information document.
WHAT IS
OZONE?
Ozone is a molecule composed of three atoms of oxygen. Two atoms of oxygen form the basic oxygen molecule--the oxygen
we breathe that is essential to life. The
third oxygen atom can detach from the ozone molecule, and re-attach to
molecules of other substances, thereby altering their chemical composition. It
is this ability to react with other substances that forms the basis of
manufacturers’ claims.
IS OZONE HARMFUL?
The same chemical properties that allow high concentrations of ozone to
react with organic material outside the body give it the ability to react
with similar organic material that makes up the body, and potentially cause
harmful health consequences. When
inhaled, ozone can damage the lungs. Relatively
low amounts can cause chest pain, coughing, shortness of breath, and, throat
irritation. Ozone may also
worsen chronic respiratory diseases such as asthma and compromise the
ability of the body to fight respiratory infections. People
vary widely in their susceptibility to ozone. Healthy people, as well as those with respiratory difficulty,
can experience breathing problems when exposed to ozone. Exercise during exposure to ozone causes a greater amount of
ozone to be inhaled, and increases the risk of harmful respiratory effects. Recovery
from the harmful effects can occur following short-term exposure to low
levels of ozone, but health effects may become more damaging and recovery
less certain at higher levels or from longer exposures (US EPA, 1996a,
1996b).
Manufacturers
and vendors of ozone devices often use misleading terms to describe ozone. Terms
such as "energized oxygen" or "pure air" suggest that
ozone is a healthy kind of oxygen. Ozone
is a toxic gas with vastly different chemical and toxicological properties
from oxygen. Several federal agencies have established health standards or
recommendations to limit human exposure to ozone.
The
Food and Drug Administration (FDA) requires ozone output of indoor medical
devices to be no more than 0.05 ppm. The
Occupational Safety and Health Administration (OSHA) requires that workers
not be exposed to an average concentration of more than 0.10 ppm for 8
hours. The National Institute
of Occupational Safety and Health (NIOSH) recommends an upper limit of 0.10
ppm, not to be exceeded at any time. The
Environmental Protection Agency (EPA)’s National Ambient Air Quality
Standard for ozone is a maximum 8 hour average outdoor concentration of 0.08
ppm.
IS THERE
SUCH A THING AS "GOOD OZONE" AND "BAD OZONE"?
The
phrase "good up high - bad nearby" has been used by the U.S.
Environmental Protection Agency (EPA) to make the distinction between ozone
in the upper and lower atmosphere. Ozone
in the upper atmosphere - referred to as "stratospheric ozone" -
helps filter out damaging ultraviolet radiation from the sun. Though
ozone in the stratosphere is protective, ozone in the atmosphere - which is
the air we breathe - can be harmful to the respiratory system. Harmful
levels of ozone can be produced by the interaction of sunlight with certain
chemicals emitted to the environment (e.g., automobile emissions and
chemical emissions of industrial plants). These
harmful concentrations of ozone in the atmosphere are often accompanied by
high concentrations of other pollutants, including nitrogen dioxide, fine
particles, and
hydrocarbons. Whether pure or
mixed with other chemicals, ozone can be harmful to health.
ARE
OZONE GENERATORS EFFECTIVE IN CONTROLLING INDOOR AIR POLLUTION?
Available scientific evidence shows that at concentrations that do not
exceed public health standards, ozone has little potential to remove indoor
air contaminants. Some
manufacturers or vendors suggest that ozone will render almost every
chemical contaminant harmless by producing a chemical reaction whose only
by-products are carbon dioxide, oxygen and water. This
is misleading.
First,
a review of scientific research shows that, for many of the chemicals
commonly found in indoor environments, the reaction process with ozone may
take months or years (Boeniger, 1995). For
all practical purposes, ozone does not react at all with such chemicals. And
contrary to specific claims by some vendors, ozone generators are not
effective in removing carbon monoxide (Salls, 1927; Shaughnessy et al.,
1994) or formaldehyde (Esswein and Boeniger, 1994).
Second,
for many of the chemicals with which ozone does readily react, the reaction
can form a variety of harmful or irritating by-products (Weschler et al.,
1992a, 1992b, 1996; Zhang and Lioy, 1994). For
example, in a laboratory experiment that mixed ozone with chemicals from new
carpet, ozone reduced many of these chemicals, including those which can
produce new carpet odor. However,
in the process, the reaction produced a variety of aldehydes, and the total
concentration of organic chemicals in the air increased rather than
decreased after the introduction of ozone (Weschler, et. al., 1992b). In
addition to aldehydes, ozone may also increase indoor concentrations of
formic acid (Zhang and Lioy, 1994), both of which can irritate the lungs if
produced in sufficient amounts. Some
of the potential by-products produced by ozone’s reactions with other
chemicals are themselves very reactive and capable of producing irritating
and corrosive by-products (Weschler and Shields, 1996, 1997a, 1997b). Given
the complexity of the chemical reactions that occur, additional research is
needed to more completely understand the complex interactions of indoor
chemicals in the presence of ozone.
Third,
ozone does not remove particles (e.g., dust and pollen) from the air,
including the particles that cause most allergies. However, some ozone generators are manufactured with an
"ion generator" or "ionizer" in the same unit. An
ionizer is a device that disperses negatively (and/or positively) charged
ions into the air. These ions attach to particles in the air giving them a
negative (or positive) charge so that the particles may attach to nearby
surfaces such as walls or furniture, or attach to one another and settle out
of the air. In recent experiments, ionizers were found to be less
effective in removing particles of dust, tobacco smoke, pollen or fungal
spores than either high efficiency particle filters or electrostatic
precipitators. (Shaughnessy et al., 1994; Pierce, et al., 1996). However, it is apparent from other experiments that the
effectiveness of particle air cleaners, including electrostatic
precipitators, ion generators, or pleated filters varies widely (U.S. EPA,
1995).
There
is evidence to show that at concentrations that do not exceed public health
standards, ozone is not effective at removing many odor-causing chemicals. In
an experiment designed to produce formaldehyde concentrations representative
of an embalming studio, where formaldehyde is the main odor producer, ozone
showed no effect in reducing formaldehyde concentration (Esswein and
Boeniger, 1994). Other experiments suggest that body odor may be masked by the
smell of ozone but is not removed by ozone (Witheridge and Yaglou, 1939). Ozone
is not considered useful for odor removal in building ventilation systems (ASHRAE,
1989).
While
there are few scientific studies to support the claim that ozone effectively
removes odors, it is plausible that some odorous chemicals will react with
ozone. For example, in some
experiments, ozone appeared to react readily with certain chemicals,
including some chemicals that contribute to the smell of new carpet (Weschler,
1992b; Zhang and Lioy, 1994). Ozone
is also believed to react with acrolein, one of the many odorous and
irritating chemicals found in secondhand tobacco smoke (US EPA, 1995).
If used at concentrations that do not exceed public health standards,
ozone applied to indoor air does not effectively remove viruses, bacteria,
mold, or other biological pollutants.
Some
data suggest that low levels of ozone may reduce airborne concentrations and
inhibit the growth of some biological organisms while ozone is present, but
ozone concentrations would have to be 5 - 10 times higher than public health
standards allow before the ozone could decontaminate the air sufficiently to
prevent survival and regeneration of the organisms once the ozone is removed
(Dyas, et al.,1983; Foarde et al., 1997).
Even
at high concentrations, ozone may have no effect on biological contaminants
embedded in porous material such as duct lining or ceiling tiles (Foarde et
al, 1997). In other words,
ozone produced by ozone generators may inhibit the growth of some biological
agents while it is present, but it is unlikely to fully decontaminate the
air unless concentrations are high enough to be a health concern if people
are present. Even with high
levels of ozone, contaminants embedded in porous material may not be
affected at all.
IF I
FOLLOW MANUFACTURERS’ DIRECTIONS, CAN I BE HARMED?
Results
of some controlled studies show that concentrations of ozone considerably
higher than these standards are possible even when a user follows the
manufacturer’s operating instructions. There
are many brands and models of ozone generators on the market. They vary in the amount of ozone they can produce. In
many circumstances, the use of an ozone generator may not result in ozone
concentrations that exceed public health standards. But
many factors affect the indoor concentration of ozone so that under some
conditions ozone concentrations may exceed public health standards.
In
one study (Shaughnessy and Oatman, 1991), a large ozone generator
recommended by the manufacturer for spaces "up to 3,000 square
feet," was placed in a 350 square foot room and run at a high setting.
The ozone in the room quickly reached concentrations that were exceptionally
high - 0.50 to 0.80 ppm which is 5 -10 times higher than public health
limits.
In
an EPA study, several different devices were placed in a home environment,
in various rooms, with doors alternately opened and closed, and with the
central ventilation system fan alternately turned on and off. The
results showed that some ozone generators, when run at a high setting with
interior doors closed, would frequently produce concentrations of 0.20 -
0.30 ppm. A powerful unit set
on high with the interior doors opened achieved values of 0.12 to 0.20 ppm
in adjacent rooms. When units
were not run on high, and interior doors were open, concentrations generally
did not exceed public health standards (US EPA, 1995).
The
concentrations reported above were adjusted to exclude that portion of the
ozone concentration brought in from the outdoors. Indoor concentrations of ozone brought in from outside are
typically 0.01- 0.02 ppm, but could be as high as 0.03 - 0.05 ppm (Hayes,
1991; U.S. EPA, 1996b; Weschler et al., 1989, 1996; Zhang and Lioy; 1994).
WHY
IS IT DIFFICULT TO CONTROL OZONE EXPOSURE WITH AN OZONE GENERATOR?
The
actual concentration of ozone produced by an ozone generator depends on many
factors. Concentrations will be
higher if a more powerful device or more than one device is used, if a
device is placed in a small space rather than a large space, if interior
doors are closed rather than open and, if the room has fewer rather than
more materials and furnishings that adsorb or react with ozone and, provided
that outdoor concentrations of ozone are low, if there is less rather than
more outdoor air ventilation. The
proximity of a person to the ozone generating device can also affect one’s
exposure. The concentration is
highest at the point where the ozone exits from the device, and generally
decreases as one moves further away.
Manufacturers
and vendors advise users to size the device properly to the space or spaces
in which it is used. Unfortunately,
some manufacturers’ recommendations about appropriate sizes for particular
spaces have not been sufficiently precise to guarantee that ozone
concentrations will not exceed public health limits. Further, some literature distributed by vendors suggests that
users err on the side of operating a more powerful machine than would
normally be appropriate for the intended space, the rationale being that the
user may move in the future, or may want to use the machine in a larger
space later on. Using a more
powerful machine increases the risk of excessive ozone exposure.
Ozone
generators typically provide a control setting by which the ozone output can
be adjusted. The ozone output
of these devices is usually not proportional to the control setting. That is, a setting at medium does not necessarily generate an
ozone level that is halfway between the levels at low and high. The
relationship between the control setting and the output varies considerably
among devices, although most appear to elevate the ozone output much more
than one would expect as the control setting is increased from low to high. In
experiments to date, the high setting in some devices generated 10 times the
level obtained at the medium setting (US EPA, 1995). Manufacturer’s
instructions on some devices link the control setting to room size and thus
indicate what setting is appropriate for different room sizes. However, room size is only one factor affecting ozone levels
in the room.
In
addition to adjusting the control setting to the size of the room, users
have sometimes been advised to lower the ozone setting if they can smell the
ozone. Unfortunately, the ability to detect ozone by smell varies
considerably from person to person, and one’s ability to smell ozone
rapidly deteriorates in the presence of ozone. While the smell of ozone may
indicate that the concentration is too high, lack of odor does not guarantee
that levels are safe.
At
least one manufacturer is offering units with an ozone sensor that turns the
ozone generator on and off with the intent of maintaining ozone
concentrations in the space below health standards. EPA is currently
evaluating the effectiveness and reliability of these sensors, and plans to
conduct further research to improve society’s understanding of ozone
chemistry indoors. EPA will report its findings as the results of this
research become available.
CAN
OZONE BE USED IN UNOCCUPIED SPACES?
Ozone
has been extensively used for water purification, but ozone chemistry in
water is not the same as ozone chemistry in air. High concentrations of ozone in air, when people are not
present, are sometimes used to help decontaminate an unoccupied space from
certain chemical or biological contaminants or odors (e.g., fire
restoration). However, little
is known about the chemical by-products left behind by these processes (Dunston
and Spivak, 1997). While high
concentrations of ozone in air may sometimes be appropriate in these
circumstances, conditions should be sufficiently controlled to insure that
no person or pet becomes exposed. Ozone
can adversely affect indoor plants, and damage materials such as rubber,
electrical wire coatings, and fabrics and art work containing susceptible
dyes and pigments
(U.S.
EPA, 1996a).
WHAT
OTHER METHODS CAN BE USED TO CONTROL INDOOR AIR POLLUTION?
The
three most common approaches to reducing indoor air pollution, in order of
effectiveness, are:
- Source
Control: Eliminate or control the sources of pollution;
- Ventilation:
Dilute and exhaust
pollutants through outdoor air ventilation, and
- Air
Cleaning: Remove pollutants
through proven air cleaning methods.
Of
the three, the first approach - source control - is the most effective. This
involves minimizing the use of products and materials that cause indoor
pollution, employing good hygiene practices to minimize biological
contaminants (including the control of humidity and moisture, and occasional
cleaning and disinfection of wet or moist surfaces), and using good
housekeeping practices to control particles.
The
second approach - outdoor air ventilation - is also effective and commonly
employed. Ventilation methods
include installing an exhaust fan close to the source of contaminants,
increasing outdoor air flows in mechanical ventilation systems, and opening
windows, especially when pollutant sources are in use.
The
third approach - air cleaning - is not generally regarded as sufficient in
itself, but is sometimes used to supplement source control and ventilation. Air
filters, electronic particle air cleaners and ionizers are often used to
remove airborne particles, and gas adsorbing materials are used to remove
gaseous contaminants when source control and ventilation are inadequate.
CONCLUSIONS
Whether in its pure form or mixed with other chemicals, ozone can be harmful
to health. When inhaled, ozone
can damage the lungs. Relatively
low amounts of ozone can cause chest pain, coughing, shortness of breath
and, throat irritation. It may
also worsen chronic respiratory diseases such as asthma as well as
compromise the ability of the body to fight respiratory infections.
Some
studies show that ozone concentrations produced by ozone generators can
exceed health standards even when one follows manufacturer’s instructions.
Many factors affect ozone
concentrations including the amount of ozone produced by the machine(s), the
size of the indoor space, the amount of material in the room with which
ozone reacts, the outdoor ozone concentration, and the amount of
ventilation. These factors make
it difficult to control the ozone concentration in all circumstances.
Available
scientific evidence shows that, at concentrations that do not exceed public
health standards, ozone is generally ineffective in controlling indoor air
pollution. The concentration of
ozone would have to greatly exceed health standards to be effective in
removing most indoor air contaminants. In
the process of reacting with chemicals indoors, ozone can produce other
chemicals that themselves can be irritating and corrosive.
RECOMMENDATION
The public is advised to use proven methods of controlling indoor air
pollution. These methods include eliminating or controlling pollutant
sources, increasing outdoor air ventilation, and using proven methods of air
cleaning.
