Chlorine Dioxide (ClO₂)

CAS Number: 10049-04-4
Chlorine dioxide (ClO₂) is a yellow-to-red, highly reactive oxidizing gas with a pungent odor similar to chlorine and nitric acid. Unlike chlorine gas, chlorine dioxide is generated on-site and is too unstable to store or ship in bulk, meaning exposure risk is concentrated near generation equipment. It is widely used as a disinfectant in municipal water and wastewater treatment, as a bleaching agent in pulp and paper manufacturing, as a sanitizer in food and beverage processing, and as a fumigant for mold remediation and pest control. ClO₂ is heavier than air (vapor density 2.33) and tends to accumulate in low-lying areas and confined spaces near generation points. It is also a methemoglobin-forming agent, meaning elevated exposures interfere with the blood's ability to carry oxygen. Because its odor threshold is close to or above occupational exposure limits, olfactory warning is unreliable and real-time monitoring is essential in any environment where ClO₂ is generated or used.

Chlorine dioxide (ClO₂) is a powerful oxidizing gas used as a disinfectant and bleaching agent in water treatment, pulp and paper processing, food sanitation, and mold remediation. Even at low concentrations, ClO₂ is highly toxic, the OSHA PEL and NIOSH REL are both set at 0.1 ppm TWA, with an IDLH of just 5 ppm. Because ClO₂ is heavier than air and is generated on-site rather than stored in bulk, exposure risks are highest in confined areas where the gas can accumulate near the generation point.

Rent ClO₂-capable gas monitors from RAECO Rents for water and wastewater treatment facilities, pulp and paper mills, food processing plants, pharmaceutical manufacturing, and fumigation or mold remediation projects. All instruments are bump tested or span calibrated on the day of shipment. Our team can confirm the right monitor, sensor range, and alarm settings for your specific application — with fast turnaround and phone support so you can get reliable field readings quickly.

Regulatory Exposure Limits

Updated on April 29, 2026

OSHA PEL
TWA: 0.1 ppm (0.3 mg/m³)
STEL: N/A
C: N/A
NIOSH REL
TWA: 0.1 ppm (0.3 mg/m³)
STEL: 0.3 ppm (0.9 mg/m³)
C: N/A
ACGIH TLV
TWA: 0.1 ppm (0.28 mg/m³)
STEL: 0.3 ppm (0.84 mg/m³)
C: N/A
Frequently Asked Questions
Common questions about
Where should I place chlorine dioxide (ClO₂) monitors to catch leaks early?
Place monitors near likely release points and within the work zone, using airflow patterns and 'dead zone' awareness — not only at entry points. Larger areas typically need multiple monitor locations to avoid missing pockets of accumulation, especially since ClO₂ is heavier than air.
When do I need continuous chlorine dioxide (ClO₂) monitoring?
Use continuous monitoring during gas generation, transfers, maintenance, and any task where releases can change throughout the shift. Continuous alarming is especially critical in enclosed or low-ventilation areas where concentrations can rise quickly and reach dangerous levels before a spot check would catch them.
Can a standard chlorine sensor detect chlorine dioxide (ClO₂)?
No — chlorine gas (Cl₂) and chlorine dioxide (ClO₂) require different sensors. Don't assume a chlorine sensor covers ClO₂. Use ClO₂-capable detection and confirm the right sensor type and range before the job starts.
What kind of monitor detects chlorine dioxide (ClO₂)?
Use a ClO₂-capable monitor — standard 4-gas monitors do not detect chlorine dioxide. Choose sensor-based monitoring for personal and general area alarming, and tape-based (ChemCassette) monitoring when you need higher specificity or fixed-location area coverage at lower concentration levels.
What should I know before renting chlorine dioxide (ClO₂) monitors?
Confirm the expected concentration range, whether work is in an enclosed space, and whether you need simple alarming or time-stamped datalogging for documentation. Also clarify whether you need personal monitoring, fixed area points, or both — this determines whether sensor-based or tape-based instruments are the right fit.
Do I need a sensor monitor or a ChemCassette/tape-based monitor for ClO₂?
For most site work, an electrochemical sensor monitor is sufficient. ChemCassette or tape-based monitors are better for lower detection limits or validation scenarios where sensor cross-sensitivity is a concern.
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