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ClO2 Gas and its Sensor

Intro to Chlorine Dioxide

Chlorine dioxide is a chemical compound with the formula CIO2, meaning its molecule has one atom of chlorine and two atoms of oxygen. In an industrial setting, its typically handled as an aqueous solution and appears a rusty red liquid when below 11°C (52°F). Its most common uses are antimicrobial and oxidizing agents in drinking water, poultry process water, swimming pools, and mouthwash preparations. Other uses include bleaching wood pulp, food processing - fats, oil, and flour, and sterilizing medical equipment. When comparing to chlorine gas, chlorine dioxide has a higher oxidation capacity and a lower oxidation strength—making it over 2.5 times more potent per ppm and significantly less corrosive.

While CIO2 is a hazardous gas, the risk to industrial workers isn't typically in this form since it rapidly breaks down into chlorine gas and oxygen. In the case of  an exposure, short-term symptoms are typically irritation of the eyes, nose, throat, and lungs. Coughing, wheezing, and severe breathing difficulties can develop at any exposure limit. Longer-term exposure can often result in chronic bronchitis. 

Gas Characteristics

  • Penetrating and irritating odor (similar to chlorine and nitric acid).
  • Gas: yellowish- green gas at room temperature.
  • Liquid: reddish-brown between 11  and -59°C.
  • Solid: orange in color like a block of ice, with a faint chlorine odor.
  • As an oxidizer, may cause or intensify a fire.
  • Gas is heavier than air.
  • Signal word: Danger.
  • Toxic if inhaled.
  • Other names: Chlorine oxide, Chlorine peroxide.
  • CAS 10049-04-4
ClO2 GHS WHMIS Toxic Hazard
ClO2 GHS WHMIS Oxidizing Hazard
ClO2 GHS WHMIS Corrosive Hazard
ClO2 GHS Environmental Hazard
icon GHS symbol Chlorine Dioxide compressed gas

Industrial ClO2 hazards and sources

  • Pulp and paper industry: commonly used as a bleach to manufacture paper.
  • Water and wastewater industry: CIO2 is an oxidizing agent for sanitizing industrial waste and sewage and removing taste and odor from water supplies. Also as an additive in swimming pools.
  • Food processing industry: microbicide and algicide in processing systems and flour maturing operations.
  • Oil and Gas: used in fracking and other applications
  • Medical: therapeutic uses are in the trial stage using chlorine dioxide for various purposes —a mouth rinse, disinfectant for E-coli and staph, and suppressing scar formation on infected wounds.
  • Bleaching agent- fats, oils, and flour for baking 
  • Leather manufacturing
  • Odor control
  • Disinfectant
  • Biocide

Global demand for chlorine dioxide is forecasted to increase 6.5% by 2027 to $1.38B, largely due to demand for safe drinking water.

Global Market Insights

High Risk Scenarios

  • As chlorine dioxide gas is heavier than air, it can collect in dangerous amounts near ground level and in low areas of confined spaces. 
  • High concentrations can occur in the vicinity of its release. This can result in asphyxia with respiratory failure, pulmonary edema, likely acute pulmonary hypertension, cardiomegaly, pulmonary vascular congestion, acute burns of the lower airways and death.
  • Keep chlorine dioxide out of a confined space, such as a sewer, because of the possibility of an explosion.
  • Patients with a history of smoking, wheezing, or asthma are at a greater risk for airway obstructions following chlorine dioxide inhalation.
  • CIO2 is an oxidizer and can cause or intensify fires.
  • Chlorine dioxide is on the Hazardous Substance List because it is regulated by OSHA and cited by ACGIH, DOT, NIOSH, DEP, IRIS and EPA.




ClO2 Sensor Info

Type: Electrochemical
Range: 0-2 ppm (0.1 ppm resolution)

Default Alarm Levels

Low Alarm: 0.1 ppm
High Alarm: 0.3 ppm
STEL — 15 minute — Short Term Exposure Limit: 0.3 ppm 
TWA  — 8 hour time weighted average: 0.1 ppm 

Blackline devices that can detect ClO2

Questions about the detection of ClO2?


Special Applications and Considerations

  • The gas and liquid are rapidly decomposed by organic materials.
  • As a gas, it will decompose explosively at temperatures below the boiling point of water.
  • CIO2 is a chlorine compound and oxidizing agent with disinfectant, antiviral and antibacterial activities.
  • Repeated exposure to chlorine dioxide may cause chronic bronchitis.
  • Chlorine dioxide solutions have been marketed under various names (eg. Miracle Mineral Solution, 28% sodium chlorite) and touted as a cure for autism, malaria, cancer, and recently Covid-19. There is no evidence to support these claims and concentrated levels of CIO2 aren't intended for human consumption.
  • Chlorine dioxide doesn't require air for it to burn.
  • When added to water it forms chlorite ion, a highly reactive chemical.
  • Can cause severe skin burns and eye damage.
  • Chlorine gas can easily corrode and cause significant damage to metals, plastics, rubbers, and other materials if it is not properly accounted for.
  • Contact with dust and combustible materials may cause fire and explosions.
  • In and industrial setting, install a safety shower and eyewash station close to the chemical handling area.
  • Very toxic to aquatic life.

Health Risks and Handling of ClO2

0.1 ppm
Likely to experience mild mucous membrane irritation.
0.3 ppm
Many people will suffer immediate coughing, vomiting, difficulty breathing, and chest pain.
0.5 ppm
Moderate irritation of both mucus membrane and the respiratory tract. Symptoms such as bronchitis and pronounced emphysema. A toxic pneumonitis and/or acute pulmonary edema can develop.
5 ppm
IDLH - Immediately Dangerous to Life or Health
Chlorine Dioxide First Aid Icon
  • Ensure anyone conducting first aid is adequately protected (safety goggles & chemical protective clothing).
  • If INHALED move the person to fresh air right away. If breathing has stopped begin artificial respiration. Keep the victim still and upright if possible. Trained personnel can administer additional oxygen if necessary. Get medical attention as soon as possible.
  • If SKIN CONTACT is made rinse the impacted area with soap and water immediately. See a doctor if the pain/irritation does not subside.
  • If the EYES are contacted, immediately wash the eyes with large amounts of water. Next cover both eyes with sterile gauze to minimize light. Get medical attention immediately.
Chlorine dioxide gas dangers
  • Evacuate the area ASAP, and keep out any personnel who are not wearing protective equipment. 
  • Isolate the area that is concentrated with chlorine dioxide.
  • If you have the necessary protection to do so, attempt to remove any incompatible/hazardous materials that could escalate the situation. 
  • If the gas is leaked, stop the flow if it can be done safely. If the source is in a cylinder remove it to open air. To stop the leak in place, bubble chlorine dioxide through a solution made from a reducing agent like sodium bisulfite and sodium bicarbonate with a trap in the line. Try to ventilate the area. 
  • If the leak is larger, follow the same steps as for a small leak. However, you can also consider knocking down the gas with fine water spray or fog. If the leak cannot be contained, contact local emergency services. 
  • Potential contamination in water systems should be communicated to downstream users.


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