DETAILED INFO ON OZONE
What is ozone?
Ozone (O3) is a form of oxygen (O2) generated using one of two methods: exposing normal oxygen
to a high voltage electrical discharge; or exposing oxygen to ultraviolet (UV) radiation. Stratospheric
ozone is formed naturally by chemical reactions involving solar ultraviolet radiation (sunlight) and
oxygen molecules. Industrially, ozone is derived from oxygen by electrical discharges and/or
ultraviolet light. Ozone is manufactured on-site for immediate use because it is unstable and
decomposes quickly.
Pure ozone has a bluish colour, but ozone/air mixtures are invisible even at the normal concentration
produced in any ozone generator. Ozone has a distinctive, pungent odour and is soluble in water,
sulphuric acid and carbon tetrachloride.
Although pure ozone gas is slightly heavier than air, at “ppm” concentrations it mixes completely
with air and does not necessarily settle to the floor. Although the gas is only slightly soluble in water,
concentrations up to 10 mg/L are possible.
Ozone is naturally produced by lightning and its clean fresh scent is evident after a thunderstorm.
Ozone’s half-life
Ozone is an unstable molecule that quickly changes back to normal oxygen. The time for half of the
ozone in air to decompose (its half-life) is four to 12 hours, depending on the temperature and
humidity of the surrounding air. Ozone’s half-life in water is between three and 20 minutes,
depending on the temperature and quality of the water. In high-quality water, such as water that has
undergone double ozonation and filtration, ozone’s half-life may be as long as 2.5 hours. Ozone
decomposes faster in alkaline water.
The most important factors influencing the rate at which ozone will dissipate are temperature, pH
and the quality of the water.
Temperature is a significant influencing factor of the decomposition of ozone
Air
Temp (°C)
Dissolved in Water (pH 7)
Half Life
Temp (°C)
Half Life
-25
8 days
15
30 min
20
3 days
20
20 min
120
1.5hrs
25
15 min
Dependent on the pH and quality of the water, the half-life of ozone is in the range of hours to
minutes.
pH
pH
Time
Residual Ozone
7.6
18 min
78%
8.85
18 min
14%
9.9
9 min
4.4%
Water at 20°C commencing with 10 pM/l
Water Quality
Time
Ozone Concentration
Double Distilled
80 min
9.5 pM/l
Distilled Water
65 min
3 pM/l
Tap Water
65 min
2 pM/l
Reactivity
Ozone is a strong, naturally occurring oxidizing agent. The structure of an organic molecule is
changed by oxidization, causing the whole molecule to come apart. Bacteria, virus and naturally
occurring cells are therefore literally split apart by ozone.
Ozone’s impact on Materials
Ozone's impact on materials has been studied directly for the last thirty years. It has been shown to
deteriorate the useful life of natural materials such as rubber and participates in the chemistry of
corrosion.
As a guide, herewith a table of materials tested at ozone levels exceeding 1000ppm.
If in doubt about the effect on your equipment, kindly contact ArcAqua for further information.
Excellent
Good
Fair
Poor
Butyl
ABS Plastic
Acetal
Buna-N (Nitrile)
Chemraz
Acrylic (Perspex)
Aluminim
Magnesium
CPVC
Brass
Cast Iron
Natural Rubber (V
Durachlor-51
Bronze
Galvanized Steel (in
Poor)
Durion 9000
Copper
water)
Nylon
EPDM
LDPE
Hypalon ®
Polyamide (V Poor)
EPR
Polyacrylate
Hytrel ®
Mild Steel (HSLA)
Ethelene-Propylene
Polyethylene (in
Monel
Zinc
Flexelene
water)
Neoprene
Flurosilicone
Polysulfide
Polyethylene (in Air)
Galvanized Steel (in
PVC
Polypropolene
air)
Tygon®
Glass
HDPE
Inconel
Kalrez
Kel-F®(PCTFE)
Peek
Polycarbonate
Polyurethane
PTFE (Teflon®)
PVDF (Kynatr®)
Santoprene
Silicone
Stainless Steel
(304/316)
Teflon
Titanium
Vacmac
Viton®
Permissible Exposure Limits (PEL)
Occupational Health and Safety Standards (OSHA) guidelines for ozone exposure in the workplace
are based on time-weighted averages. Ozone levels should never exceed the following average:
0.10 ppm (parts per million) for 8 hours per day exposure.
Additional guidelines on safe ozone levels, see the bullet points below.
The OSHA website cites several ACGIH (American Conference of Governmental Industrial
Hygienists) guidelines for ozone in the workplace:
-
0.2 ppm for no more than 2 hours exposure
-
0.1 ppm for 8 hours per day exposure doing light work
-
0.08 ppm for 8 hours per day exposure doing moderate work
-
0.05 ppm for 8 hours per day exposure doing heavy work