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O3 Gas and its Sensor

Introduction to Ozone

Ozone is an elemental molecule with the formula O3. It's an explosive, pale blue gas with a pleasant odor. It's produced in the upper atmosphere by the action of solar ultraviolet radiation on atmospheric oxygen or exposing normal oxygen to a high voltage electrical discharge. O3 is an antimicrobial agent used in the production of bottled water, treatment of meat, and handling perishable foods. Ozone is created for commercial and industrial uses by exposing normal oxygen to a high voltage electrical discharge; or exposing oxygen to ultraviolet (UV) radiation.

Welders can experience a number of health related risks from ozone exposure. Short-term symptoms range from irritated throat and chest, metal fume fever, and reduced lung function. Common long-term health effects are asthma, pneumonia, and even cancer.

Gas Characteristics

  • Colorless to bluish gas that condenses to a dark blue liquid, or blue-black crystals
  • Has a pungent odor
  • An oxidizing agent
  • Very high redox potential
  • Nonflammable gas
  • O3 will quickly corrode most metals and will damage most plastics.
  • Rubber exposed to ozone will quickly harden and crack.
  • Manufactured for immediate use because of its instability and tendency to decompose quickly
  • Pure ozone gas is slightly heavier than air
  • OTHER NAMES: Triatomic oxygen, trioxygen
  • CAS Registry 10028-15-6

Industrial O3 hazards and sources

  • Water treatment: Disinfectant since it is an excellent oxidizing agent
  • Welding: Gas metal arc and gas tungsten arc welding produce high ozone concentrations.
  • Treatment of potable water supplies
  • Food storage: Supermarkets use ozonated ice to display and keep perishable foods
  • Cooling tower water treatment
  • Storage water for the fishing industry
  • Disinfection for aquariums and hospitals
  • Ozone is used in combination with chlorine to clean swimming pools.
  • Odor control and smoke elimination
  • Pulp and paper processing - pulp bleaching
  • Perfume manufacturing
  • Cold storage as mold and bacteria inhibitor 
  • Bleaching agent for waxes, textiles, and oils
  • Metal thermal spraying
  • Sewer and wastewater treatment
  • Medical treatments - ozone therapy
  • Air purifiers
  • Textiles

Depending on the concentration, exposure to ozone can result in acute or chronic health problems, or, in high concentrations even death.

(WorkSafe BC)

High Risk Scenarios

  • Ozone has been known to form in welding arcs. The affects can cause short and long term health issues such as respiratory ailments, lung infections, and even types of lung cancer.
  • Arc welding, particularly inert gas shielded welding, can produce
    ozone concentrations up to 10 ppm in the breathing zone of the
  • "According to the US Bureau of Labor Statistics there were over 377,250 welders, solderers, cutters, and brazers employed in the United States in 2017. These workers are exposed to toxic fumes produced because of welding processes."
  • Individuals with asthma or other respiratory concerns, children and older adults are at higher risk from breathing air containing ozone. 
  • Those with a reduction or deficit of vitamins C and E are at a greater risk from ozone exposure.

O3 Sensor Info

Type: Electrochemical Diffusion
Range: 0-1 ppm (0.01 ppm resolution)
How an O3 sensor works: Ozone molecules interact with metal electrodes through a redox reaction, generating a linear voltage output proportional to the ozone concentration.

Default Alarm Levels

Low Alarm: 0.1 ppm
High Alarm: 0.2 ppm
STEL — 15 minute — Short Term Exposure Limit: 0.1 ppm
TWA  — 8 hour time weighted average: 0.05 ppm 

Blackline devices that can detect O3

Questions about the detection of O3?


Special Applications and Considerations

  • Ozone is considered "Good up high - bad nearby" with regards to concentrations in the upper and lower atmospheres.
  • Ventilation whether natural or forced should allow for fresh air to move freely.
  • Enclose operations to reduce exposure risk. Use a respirator or protective equipment when necessary.
  • Ozone is unstable so will decay fairly quickly but it will continue to form where a reaction is taking place.
  • An emergency electrical shut-off switch must be located near an ozone room. This allows for manual shut-off of the generator power during a leak or malfunction. 
  • Welders should be very cautious of O3 levels when working in a confined space.

Health Risks and Handling of O3

0.01 ppm
Odor threshold
0.1 ppm
Minor irritation experienced in the eyes, nose, and throat.
0.10- 0.25 ppm
Headache, dry cough, and some reduction in lung function.
0.30 ppm
Reduction in lung function for most people.
0.6 ppm
Chest pain
1 ppm
Irritation in the lungs often accompanied with coughing and severe fatigue.
1.5 ppm
Brain fog, continued coughing, and extreme fatigue can linger for weeks. Other symptoms such as severe lung irritation and pulmonary edema (fluid build-up) can develop.
9 ppm
Severe pneumonia
11 ppm
Rapid unconsciousness
50 ppm
Immediately fatal
  • The lungs will usually recover within a few days after exposure to elevated concentrations of ozone. However, if ozone exposure is experienced over a longer period of time or on a number of repeated occasions within a year, chronic damage to lung tissue may occur.
  • O3 is highly toxic if inhaled or by contact of liquid to skin, eyes, or mucous membranes. It can cause acute to chronic lung damage, burns, permanent injury, or death.
  • Ozone can be toxic at a concentration of 100 ppm for 1 minute. It's capable of causing death from pulmonary edema.
  • Evaluation of ozone toxicity is similar to the evaluation of any pulmonary irritant. Oxygen saturation monitoring should be implemented and also bedside spirometry.
  • No specific treatment is available for individuals exposed to ozone, though some have suggested that oral intake of Vitamin E is beneficial to the chronic ambient exposure most experience.
  • Take action only if you've been trained. Evacuate the surrounding area. Turn off all possible sources of ignition. Don't inhale gas and ensure the area is well ventilated. Wear a respirator if ventilation isn't adequate. Workers should be wearing personal protective equipment.
  • In case of a spill: Immediately contact emergency personnel. Stop leak if there isn't a risk to yourself. Use spark-proof tools and explosion-proof equipment.


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