Gas and Engineering
Linde Gas Division
Safety Instructions
Safe Handling of OZONE − O3
1. Introduction
Ozone is an unstable molecule and an allotropic form
of Oxygen. It is formed in the atmosphere by shortwave ultraviolet radiation, which reacts with diatomic
oxygen molecules (O2) to form ozone. Ozone
absorbs radiation in the ultraviolet and infrared
wavelength. The ultraviolet absorption is vital for the
maintenance of life on the earth. Without it,
decomposition of organic molecules in living
organisms would occur. The infrared absorption
reduces heat radiation from the earth. Its
concentration at the surface of the earth is very low,
about 24-35 ppb.
At ordinary temperatures, concentrated ozone is a
blue gas heavier than air. At the concentrations and
temperatures prevailing in the manufacturing
process, the gas is nearly colorless. Liquid ozone is
dark blue. Ozone has a characteristic pungent odor.
2. Chemical and physical properties
Ozone is non-flammable but reacts (oxidize)
spontaneously with many substances, which ignites
easily, and flames can spread even when ozone is
diluted with an inert gas. Flames will spread in O2/O3
– mixtures at room temperature if the ozone
concentration is 17% or higher.
When ozone decomposes, the heat liberated is
sufficient to reach an adiabatic flame temperature of
2400 °C. When fuel is added, this temperature rises
still further. The flame propagation velocity varies
linearly with the ozone concentration in O2/O3 –
mixtures. At 17% ozone, it is 9.2 cm/s, rising to 475
cm/s in pure ozone.
Liquid ozone and concentrated O2/O3 – gas
mixtures explodes readily. Explosions can be initiated
by small quantities of organic matter, shocks, electric
sparks, or sudden changes in temperature and
pressure.
Liquid ozone has limited miscibility with liquid
oxygen. Thus, in storage, the heavier ozone-rich
mixture sinks to the bottom, where it becomes an
explosion hazard. Moreover, the mutual solubility of
the two liquids decreases with decreasing
temperature. Ozone is soluble in water 13 times
better than oxygen and ozone dissolves completely
at concentrations of up to 50% in chlorofluorinated
methane and in ethane derivates.
Refer to attached Table: “Physical properties” for
some common physical data.
3. Manufacture
25
08.2002
Commercially ozone is produced photo chemically or
by means of so-called dark electrical discharges.
Other methods include the electrolysis of water at
high anode potential and low temperature, and
radiochemical and thermal production.
By far the most important production method is
the use of electrical discharges between glasscovered, cooled electrodes. Oxygen forms a
conductor between the electrodes and is partially
atomized, forming ozone.
In the most common versions of the ozone
generator, the ozonator, the electrodes are
concentric metal tubes between which is sandwiched
a concentric tube of insulating material. Without
insulation, sparks and electric arcs would occur
between the electrodes. The insulation requires
alternating current (AC) to transport the electrical
charge. Voltages of up to 20 kV and frequencies
between 50-500 Hz are used commercially.
Provisions for the cooling limit the amount of
electrical energy that can be applied to the ozonator,
since up to 90% of the electrical energy applied is
converted to heat. Cooling is usually done by water,
but air is also used. A high gas flow through the
ozonator helps to keep the gas temperature down,
but this results in low ozone level in the gas efflux.
Before passing through the ozonator, the gas is dried
to a dew point corresponding to -60°C. With air,
ozone concentrations of about 1-2% can be
achieved; with pure oxygen, about 2-7% can be
obtained.
Ozonized air contains small quantities of nitrogen
pentoxide as well as inert nitrous oxide. Nitrogen
pentoxide reacts with moister in the air and form nitric
acid, which causes corrosion inside the ozonator.
This is the most important reason why the air is
dehumidified before the ozonization.
Pure ozone can be obtained by condensation and
fractionated distillation of gas mixtures containing
ozone.
4. Applications
• Chemical industry:
Ozone is used in the chemical processing industry to
manufacture fatty acids, which are used after
estrification as plasticizers in PVC.
The special properties of ozone make it
particularly suitable for structural studies in organic
Linde AG; Linde Gas Division, Seitnerstrasse 70, D-820 49 Höllriegelskreuth. Tel. + 49 89 7446-0
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chemistry. Small portable ozone generators are used
for this purpose.
•
Water treatment:
Ozone has twice the oxidation effect of chlorine,
providing an effective means of killing viruses and
bacteria. Ozone reactions are considerably faster
than chlorine reactions. Ozone is being used
increasingly to purify and disinfect drinking water,
water in swimming pools and spas.
• Waste water treatment:
The phenol content of industrial wastewater
containing cyanides and phenols can be reduced to
1ppb after oxidation with ozone. Cyanides react
completely and very rapidly with ozone to form
th
cyanates, whose toxicity is only 1/1000 that of the
cyanides.
When ozone is used in conventional sewage
treatment plants, there is a reduction of the BOD
(Biological Oxygen Demand), the COD (Chemical
Oxygen Demand), and the amount of organic carbon,
along with sterilization of the wastewater.
Ozone is also more effective than oxygen as an
oxidant in sludge water treatment, where it also
improves the conditions for dewatering.
• Other fields:
Ozone is also used to bleach textile fibers, paper
pulp, and sugar. Ozone improves the strength of
paper pulp.
5. Health hazards
• Inhalation hazards:
The odor of ozone is perceptible at levels (0.05 ppm)
far below what is considered harmful to the human
organism, see figure below. However after being
exposed for some time the perception will decrease
as the mucous membrane in the nose become
damaged. The 8 hours exposure limit (TLV) is in
many countries 0.1 ppm.
Figure: Effects of Ozone on man
After prolonged (long-term or continued) exposure
the lungs may become critical affected and there is
ultimately a risk of death. Work strain and room
temperature will increase the toxicity of ozone, e.g.
increasing the room temperature 8 °C will double the
toxicity of ozone. The symptoms of lung oedema may
often not appear until a few hours after exposure.
• Contact hazards:
Ozone as a liquid or cold gas can cause serious cold
burns on contact with skin.
6. Important safety reminders
Protective gloves, goggles, and other protective
clothing must be worn, especially when working with
liquid ozone. The gas should be handled only in wellventilated areas. Wherever there is a risk of
inhalation, a fresh air mask shall be used.
If ozone poisoning is suspected, the victim should
be moved to an ozone-fee place and kept warm and
still. If the victim’s breathing is impaired, artificial
respiration should be administered. Medical attention
shall be obtained immediately.
7. Storage and transports
Ozone is manufactured primarily at atmospheric
pressure, and at a maximum of 1 bar gauge.
Leakage seldom leads to serious injury.
Since ozone decomposes relatively rapidly, it is
almost always produced at the user’s location. For
laboratory use, ozone can be transported in cylinders.
It
is
then
completely
dissolved
in
chlorotrifluormethane, and is relatively safe to
handle.
The handling and storage instructions for oxygen
applies also to gaseous ozone produced from oxygen
or mixtures whose primary content is oxygen.
•
Fire and explosion hazards:
Ozone acts as a combustion-supporting oxidant
similar to oxygen. See discussion of fire and
explosion hazards in section 2.
•
Solid and liquid Ozone:
Solid and liquid ozone should be handled only in wellventilated areas, and preferably not in the vicinity of
other personnel. At least two persons familiar with the
safety hazards of ozone and first-aid measures
should supervise the handling of solid or liquid ozone.
• Health risks:
At higher exposures levels there will be more severe
effects: (ppm)
0.5 Nausea and headache
1-2 Respiration and coughing
5-25 Pulmonary oedema
Linde AG; Linde Gas Division, Seitnerstrasse 70, D-820 49 Höllriegelskreuth. Tel. + 49 89 7446-0
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8. Choice of materials
Heat, shock and the presence of catalysts such as
copper, chromium and iron should be avoided when
handling ozone. If ozone comes in contact with
unsaturated organic substances, it will lead to the
formation of ozonides, which decompose explosively.
9. Risk Assessments
Projects involving Ozone production should undergo
a risk assessment to ensure that the production sites
and equipment don’t lead to people being exposed to
toxic concentrations or other hazards involving
Ozone, e.g. fire and/or explosive decompositions.
Basic safety precautions will lead to separation of
production sites, e.g. to have the ozonators in a
separate room where people don’t normally stay. The
room should have adequate ventilation and
preferably a lower ventilation pressure than the
neighboring rooms. Systems for automatic start and
shut down from remote “safe” areas shall be
considered. The following safety systems shall be
used as appropriate:
1.
2.
Production in separate, non-manned room.
Closed production and destruction of residual
Ozone.
3. Ozone leak detectors shall be used.
4. Ventilation and exhausts from rooms into a
controlled zone outdoors.
5. Automatic alarms& trips, emergency shut off
system.
6. Construction materials shall be compatible with
Ozone (risk of severe corrosion, fire etc.).
7. Rooms where there is a risk for Ozone enrichment
shall be built in non-combustible materials.
8. Warning signs, non-smoking signs etc. shall be
posted at entrances to rooms where there is a risk
for Ozone enrichment.
9. Emergency showers, eye emergency showers
shall be appropriate to the recognized need.
Number and marking of emergency exits shall be
sufficient.
10. Emergency plans, training of the personnel, first
aid etc.
Figure 2: Ozone destroyers from Ozono
Three different principles for ozone destructions are
offered:
• Direct temperature (DOT)
• Heat recovery (DTR)
• With catalyst (DOCAT)
10. Table of physical properties for Ozone:
Boiling point at 101.3 kPa
Critical compressibility factor
Critical pressure
Critical temperature
Critical volume
Density of gas at 101.3 kPa at 0 °C
Freezing point at 101.3 kPa at 0 °C
Latent heat of vaporization
at 101.3 kPa at 0 °C
Molecular weight
Relative density of the gas (air=1)
at 101.3 kPa at 0 °C
-3
Triple point at 1.14x10 kPa
-111.9 °C
0.228
5573 kPa, abs
-12.1 °C
3
0.089 m /kmol
3
2.154 kg/ m
-192.5 °C
233.0 kJ/kg
47.998
1.66
-192.5 °C
Figure 3: Ozonator type TPF from Ozono
Electronica Internazionale (OEI) for production of
Ozone
Fig.3
12. References:
1. Ozon – BG Chemie Merkbladt M 052-12/88.
2. CGA P-34- 2001 “Safe Handling of OzoneContaining mixtures including the installation and
operation of ozone-generating equipment”.
Linde AG; Linde Gas Division, Seitnerstrasse 70, D-820 49 Höllriegelskreuth. Tel. + 49 89 7446-0
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