Ozone Generators – Are
They Right For You?
By Robin and Audrey Barrett
AEHA National Update – Summer 96
Recently we have been fielding a lot
of questions about ozone generators and their effectiveness and safety
when used as air purifiers. To deal with this recent round of questions,
we have updated our Summer ’94 article with some of the recent research.
Ozone is a naturally occurring (lightning
and natural smog from terpenes) or manmade (electric motors, electronic
air filters, photocopiers, chemical smog and Ozone generators) very reactive,
heavier than air, colourless gas. It is made up of three oxygen atoms,
unlike the oxygen in air which consists of two oxygen atoms. Recently
I have seen air purifiers advertising it as “Electrified Oxygen, Tri-atomic
Oxygen, Activated Oxygen and Concentrated Oxygen.” While there may
be many benefits to these units there are also hazards.
Ozone at varying levels can be used
for: purifying water, bleaching, sterilization, to accelerate aging in
some materials, to remove smoke and to help purify air by killing some
bacteria and moulds. ozone generators have been commonly used as
air cleaners in motel and hotel rooms between occupancies to clear tobacco
smoke and other odours. They have been used to increase the rate
of aging in some products. They have been used to reduce or remove
the smell of smoke in fire restoration jobs, to get rid of the odours produced
by bacteria and mould in garbage rooms and to reduce bacteriological levels
in food processing plants (allowing a reduction in the use of chemical
Ozone has a very short life span in
air and will either react with other chemicals it encounters or decompose
on its own into normal oxygen.
At concentrations of 1,000 ppb (parts
per billion) ozone may cause headaches, irritation of the eyes and respiratory
tract, and increased frequency of lung disease. Lower levels have
been linked to skin, eye, upper respiratory system and mucous membrane
irritation, and increased responsiveness to allergens, adverse effects
on lung elasticity and the lung’s ability to resist disease. There
is still a great deal of uncertainty about safe levels. Environment
Canada states “The maximum acceptable annual mean levels (National Ambient
Air Quality Objective (1981 to 1990)) for ozone is 15 ppb.” The odour
threshold varies from 2 ppb to 100 ppb, but continuous exposure will often
deaden your sense of smell to significant levels of ozone within 5 to 20
minutes. This means your sense of smell is only a good indicator
of the presence of ozone upon your initial exposure when first entering
a building, not after a continuous exposure. The fact that ozone
works by reacting with most surfaces it comes in contact with means that
it does not discriminate between surfaces, whether it is attacking a bacteria,
a VOC (Volatile Organic Compound), or one of your lung cells.
Ozone has been used to age products
and accelerate the decay of smoke or other chemicals, but it must be used
with care. While ozone will react with chemicals such as 4-phenyl
cyclohexane (4-PC) (emitted from most carpets) or styrene, the break down
products from these reactions may be just as hazardous as the initial chemical,
and less likely to break down further. Ideally, the end product of
ozone reacting with chemicals will be carbon dioxide and water vapour,
but this will not necessarily happen quickly. For example, at an
ozone level of 100 ppb (above Environment Canada’s recommended levels)
the half life of formaldehyde is 4,400 years.
The major concern we have with the use
of low level ozone generating units in occupied spaces is that while there
are some controls to adjust the output of the machines there is no way
to monitor the actual level to which you are being exposed. The rate
at which these machines produce ozone and the rate of ozone decay vary
with the weather and with the type, construction and use of the room in
which they are placed. When dealing with sensitive individuals, we
find it is better to avoid any unnecessary exposures, including exposure
So just where is the use of an ozone
generator appropriate? From personal experience we have found that they
are effective under the following conditions:
1. The most effective usage
is at high levels with the room or building sealed off (i.e., no people,
plants or animals in the area) during treatment.
2. Ozone will provide only temporary
relief of some problems if the source of contamination has not been removed.
For example, it may kill surface mould but if the moisture problem is not
solved, the mould will return.
3. It will not help with chlorinated
hydrocarbons (vinyl, plastics etc.).
4. When dealing with mould, the ozone
will kill many spores but will not eliminate the toxins they contain.
It is also limited to dealing with only those spores found on the surface
of a material so it is not useful in dealing with things such as musty
5. Since composition of all the products
in a building is not always known, it is impossible to predict how much
benefit can be expected from an ozone treatment. A limited trial
is always recommended.
6. If you know that the material you
are trying to treat reacts with the oxygen in the air, to cure (e.g., some
paints and finishes) the use of ozone will usually accelerate this process.
7. While ozone is supposed to decay
rapidly, people have noted the odour coming out of furniture cushions up
to two weeks after a treatment.
8. Because unknown VOC’s may have been
created in the process of ozonating, it is important that the treated area
be well ventilated prior to occupying the space again.
9. Most importantly, if you are sensitive…
DON’T TAKE RISKS.
Robin Barrett is a
past president of the AEHA NS Branch. He has been involved in helping
people create healthier housing since 1980. In 1991 he started his
own business, Healthy Homes Consulting.
Audrey Barrett is a
registered nurse with a special interest in Environmental Health.