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 disinfectants).

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 to ozone.  

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 furniture.
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.