What is ozone?
Ozone, (O3), sometimes called "activated oxygen", contains three atoms of oxygen rather than the two atoms we normally breathe. Ozone is the second most powerful sterilizer in the world and can be used to destroy bacteria, viruses and odours. Interestingly ozone occurs quite readily in nature, most often as a result of lightning strikes that occur during thunderstorms. In fact the "fresh, clean, spring rain" smell that we notice after a storm most often results from nature's creation of ozone.
However, we are probably most familiar with ozone from reading about the "ozone layer" that circles the planet above the earth's atmosphere. Here ozone is created by the sun's ultra-violet rays. This serves to protect us from the ultra-violet radiation.
The history of ozone
- Ozone was discovered by Schonbein in 1840.
- In 1893 it was used as a disinfectant in drinking water.
- In 1909 it was used as a food preservative for cold storage of meat.
- In 1939 it was found to prevent the growth of yeast and mould during the storage of fruit.
How does ozone work?
The third oxygen atom of ozone makes it extremely reactive. This atom readily attaches itself to other odour molecules. When contaminants such as odours, bacteria or viruses make contact with ozone, their chemical structure is changed to less odorous compounds. As more ozone attacks the remaining compounds, the odour is eventually destroyed. This process is called oxidation. Ozone essentially reverts back to oxygen after it is used. This makes it a very environmentally friendly oxidant.
How is ozone produced?
There are basically two methods of producing ozone...ultra-violet and corona discharge. Corona discharge creates ozone by applying high voltage to a metallic grid sandwiched between two dielectrics. The high voltage passes through the dielectric to a grounded screen/plate and in the process, creates ozone from oxygen present in the chamber. Ultra-violet (UV) light creates ozone when a wavelength at 254 nm (Nano-meters) hits an oxygen atom. Both processes split oxygen molecules into single oxygen atoms (O). These atoms combine with another oxygen molecule (O2) to form ozone (O3).
How long does the ozone last?
As soon as ozone is formed in the generator and dispersed in a room, it will start to revert back to oxygen. This step occurs by several processes including the following: Oxidation reactions with an organic material such as odours or smoke and oxidation reaction with bacteria etc., which again consumes ozone. Additionally ozone breaks down thermally. Higher temperatures destroy ozone quicker than lower temperatures. The ozone that remains is referred to as Residual ozone.
"Residual" ozone created will return to oxygen usually within 30 minutes, in amounts equal to half its level. What this means is that after each subsequent 30 minute period there would be half as much residual ozone left at the end of the period as was present at the beginning of the period.
This is similar to a geometric progression of 16; 8; 4; 2; 1. In practice the half-life is usually less than 30 minutes due to temperature, dust, and other contaminants in the air. Therefore, ozone, while very powerful, doesn't last long. It does its job and then disappears back into safe oxygen.
Will the odour come back?
No. If ozone is applied properly it destroys the source of the odour. Treatment times may vary depending on the strength of the odour but 98% of ozone treatments are successful. In the case of mildew the odour will return if you are unable to get rid of the moisture that is the source of the mildew.
What is the right level of ozone?
The right level is when all the generated ozone is being consumed. This only applies to continuous ozone use in occupied environments not for shock treating. However, this is difficult to attain because it becomes a balancing act. Initially the machine's output is set high to get rid of the problem odour as quickly as possible. As this is being accomplished less ozone is required for the diminishing odour etc., thereby leaving some residual ozone in the air.
If the machine output is not turned down, then more residual ozone will remain. If a strong smell of ozone is noticed, then there is more ozone present than is required. Simply decrease the rheostat (output level control). With ozone, MORE IS NOT CONSIDERED BETTER! One must be careful when using ozone in an occupied environment. NOTE: It is not necessary that ozone be detected by humans for it to be effective. Ozone can work even when humans are not able to smell it.
Is ozone harmful and what, if any, are the long term effects?
Ozone was discovered almost two centuries ago, so a great deal is known about it. Several regulatory agencies, including the Occupational Safety and Health Administration, USA (OSHA), have stipulated that the safe allowable level of residual is 0.1 ppm (parts per million). Note that this permissible level is for continuous exposure throughout an entire 8 hour day. The temporary effects of such a low exposure would range from headaches, to sore throats, irritation in the eyes, and nose. No long term effects have ever been documented from ozone exposure.
Is ozone safe?
Ozone is safe if used correctly. However, high concentrations of ozone can cause health problems if proper safety measures are not taken.
How does ozone kill bacteria?
Ozone kills bacteria by destroying the cell wall of the bacteria. Once the cell wall is destroyed, the bacteria will be unable to survive.