NO2 Exposure: Which Industries Are Most at Risk?

• Nitrogen dioxide (NO2) is released mainly through high-temperature combustion and as a byproduct of industrial reactions.
• Industries that must monitor NO2 include agricultural silos, ice arenas, mining, metal production, welding and metalwork, power generation, chemical, glass, and cement manufacturing, and automotive hubs.
• Fixed and portable NO2 detection devices are necessary to monitor the gas.

Nitrogen dioxide is a common, highly toxic gas generated by industrial processes and working conditions. Because it is released in industries that do not use it as a raw material, its risk can be overlooked. However, nitrogen dioxide is an occupational hazard that must be monitored to protect workers’ safety and health.  This article discusses the work conditions and industries where nitrogen dioxide is produced and where it must be monitored.

Occupational Hazards of Exposure to Nitrogen Dioxide

Nitrogen dioxide (NO2) is a reddish-brown gas with an acrid odor at ambient temperatures and an oxidizing, nitrating agent used in industry.

Nitrogen dioxide is an occupational hazard because it is toxic and can cause both acute and chronic health effects. Inhalation is the main route of entry, but it can also irritate the eyes and skin.

Acute exposure causes cough, shortness of breath, and acute respiratory distress syndrome (ARDS). Health effects can take time to manifest, so workers exposed to NO2 must be monitored after exposure. In severe short-term exposure, mortality due to cardiovascular and respiratory causes can occur.

Chronic exposure can cause respiratory problems and aggravate existing conditions like asthma and chronic obstructive pulmonary disease (COPD). Repeated, long-duration exposure allows the gas to reach the lower respiratory tract, increasing its impact.

Since NO2 has low water solubility, it does not react with moisture in the upper tract and settle there. As a result, people may not react or be warned immediately, leaving them in high-risk areas, increasing their exposure duration, and allowing the gas to reach distal bronchioles and alveoli. Eventually, NO2 reacts with moisture to produce nitric acid that damages pulmonary tissue. Nitrogen dioxide’s low water solubility also delays the onset of symptoms during acute exposures.

Higher exposure to 25 to 100 ppm (parts per million) of NO2 increases the risk of pulmonary edema. Exposure to levels over 100 ppm can cause chronic bronchiolitis obliterans organizing pneumonia (BOOP).

Given its toxicity, various agencies in the USA have set strict standards limiting workplace exposure to the gas; see Table 1.

Nitrogen dioxide also escapes through stacks and pollutes the environment. It is a major air pollutant that must be monitored to protect the environment and local communities. NO2 leads to nitrogen deposition, a major global challenge affecting forests and agriculture.

Table 1: Exposure Limits for Nitrogen Dioxide, OSHA (2025). (Credits: https://www.osha.gov/chemicaldata/21) 

Sources of Nitrogen Dioxide in Industries

The main sources of NO2 in industries are its thermal formation during combustion and byproduct formation, though other industry-specific sources also exist. Moreover, NO2 accumulates in confined spaces or poorly ventilated areas in industrial workplaces, increasing exposure risks for workers.

NO2 from High-Temperature Combustion

Industries that use high processing temperatures produce NO2. Air has 78% nitrogen and 21% oxygen. Nitrogen dioxide forms during combustion when nitrogen and oxygen in air combine at high temperatures in industrial processes. Nitrogen reacts with oxygen to form a mixture of nitric oxide (NO) and nitrogen dioxide (NO2). Only 5-10% of nitrogen oxides are nitrogen dioxide, and 90-95% are nitric oxide. This nitric oxide is further converted to NO2 through oxidation by oxygen, ozone, and VOCs in the air.

Several factors can influence the amount of NO2 that is produced thermally. These are temperature and fuel.

• Temperature: The higher the temperature used in industrial processes, the more nitric oxide is produced, which is eventually converted to NO2.
• Type of fuel engine: Petrol engines produce only 30% as much NO2 as diesel engines. Heating air produces NO2 in both diesel and petrol engines. However, petrol engines have a three-way catalytic converter that uses noble elements like platinum, palladium, and rhodium as catalysts to reduce NO2 to nitrogen by removing the oxygen.

Any industrial process using high temperatures will produce NO2 in the air, such as glass and cement making, or combustion in vehicles and power plants.

NO2 as a Byproduct

NO2 is also produced as a byproduct from several reactions involving nitrogen-based chemicals:

• Reactions between nitric acid and organic materials
• Burning of nitrocellulose
• Decomposition and detonations of rocket fuel

Accidental leaks and releases from equipment can increase gas concentrations in air, so NO2 levels should be monitored.

Industries that must monitor NO2 include agriculture, chemical production, glass and cement, mining, metal processing, ice arenas, welding, power generation, and transportation hubs.

1. Silos in Agriculture

Nitrogen dioxide toxicity is also called “silo filler’s disease.” NO2 gas is formed when chopped forage is stored in silos or bags. The gas formation depends on crop quality. When rains follow a dry period during the crop-growing season, it encourages large uptake of nitrates from the soil. If the silage crop, for example corn, is harvested before the plants can convert these nitrates into proteins, fermentation in silos produces nitrogen oxides: nitric oxide, nitrogen tetroxide, and NO2. The silo gas formation starts immediately, with the highest risk being 12-60 hours after filling the silo, and decreases after 4-6 weeks, once the fermentation process is complete.

NO2 is heavier than air, so it settles to the bottom of silos and flows into chutes and feed rooms. Tower silos where workers enter at ground level to unload and handle silage, or open the hatch without respiratory protection, are at high risk of exposure. The gas can also escape from the silos into the surrounding air, so children or visitors should not be allowed near silos for three weeks after a silo is filled.

Silo filler’s disease refers to the health effects of inhaling nitrogen oxides and is entirely preventable with workplace gas controls and personal protective equipment (PPE).

2. Ice Arenas

Ice resurfacing machines in ice arenas that use propane or diesel generate NO2 due to high-temperature combustion. Since many indoor ice arenas, such as ice rinks and ice hockey grounds, have poor ventilation, NO2 can accumulate. This can pose an NO2 exposure risk not only for workers using the machines but also for players and visitors using the facility. Fixed and portable gas monitors are useful in this case.

3. Metals Processing

NO2 is produced thermally during high-temperature metallurgical processes. These include smelting copper and lead and processing during the production of iron, steel, aluminum, and mineral wool. Smelting and processing of various metals rely on high-temperature furnaces and pickling operations, where NO2 forms thermally from nitrogen and oxygen in the air.

Moreover, in the USA, natural gas used as fuel in these processes also contains small amounts of nitrogen, adding to the NO2 levels formed and released. These industries consume large amounts of fuel, producing large amounts of NO2.

In the steel production industry, another source of NO2 is dissolved nitrogen used to make steel corrosion-resistant.

Metal-producing industries should install fixed gas analyzers to monitor NO2 production in workplaces with high-temperature processes and equipment.

4. Mining

Mining for natural gas, coal, and metals, especially underground, has NO2 exposure risks. These can come from NO2 production during detonations of explosive materials, blasting agents, natural gases from rocks, and diesel-powered heavy and self-propelled machinery. NO2 accumulates in confined mine spaces due to inadequate ventilation. No research has identified specific NO2 production points. However, monitor gas levels at processes and equipment that use diesel and at detonation sites.

Fixed gas analyzers for continuous monitoring and portable devices for NO2 detection before entry into confined spaces are advisable.

5. Chemical Manufacturing

Chemical facilities use high-temperature processes, which should be treated as NO2 production sites and monitored accordingly.

NO2 is also produced as a byproduct in some chemical industries due to chemical processing and handling, such as producing nitric acid for explosives and fertilizer manufacturing. Polymer production that uses nitrogen-based raw materials will also produce NO2 as a byproduct. Workplaces that process nitric acid or other nitrogen-based chemicals should be monitored for NO2 releases and accumulation.

6. Power Generation & Utilities

Thermal power generation plants and utilities must reckon with NO2 production during high-temperature combustion of fossil fuels like coal, oil, natural gas, or biomass. Moreover, fuels such as natural gas and oil that contain nitrogen provide another source of nitrogen that can convert to NO2.

These facilities release enormous quantities of NO2 from boilers and furnaces, which must be monitored.

7. Cement & Glass Manufacturing

Glass and cement production require high processing temperatures.  These facilities can involve melting furnaces and kilns that produce NO2 from high-temperature combustion using nitrogen in the air. Monitor equipment and sites for NO2 levels.

8. Welding & Metal Work

Metal work such as welding and cutting operations uses high temperatures that produce NO2 from nitrogen in ambient air. Because these workers perform close-range tasks, their risk of exposure to NO2 is high. Fixed and portable sensors that detect NO2 levels can help in these cases.

9. Automotive & Transportation Hubs

Logistics centers such as depots, underground parking garages, large maintenance bays, indoor testing areas, and warehouses using heavy machinery like forklifts can have many vehicles running in a small space. These produce NO2 from burning fossil fuels like diesel and petrol. NO2 is released in vehicle exhaust and can accumulate in underground or indoor areas without adequate ventilation.

Fixed gas detectors distributed at lower levels are ideal for detecting NO2 spikes.

Nitrogen Dioxide Gas Monitors

Industries can use two types of gas detectors to monitor NO2 gas emissions: fixed and portable.

Fixed gas detectors are used for continuous air monitoring, with several sensors installed in high-risk areas and connected online to a central unit that triggers audio and visual alarms when NO2 levels exceed permitted limits. These devices can also log NO2 levels for record-keeping, which is essential for identifying NO2 health effects. Workers can use portable gas detectors before entering confined spaces or areas with no ventilation to estimate NO2 levels.

Interscan provides both types of gas sensors for real-time NO2 detection: the portable GASD 8000 for spot checks and the fixed AccuSafe for continuous gas monitoring.

Contact us to schedule a demo of these two devices for NO2 detection and to help keep workers safe.

Sources

Amaducci, A., & Downs, J. W. (2023). Nitrogen dioxide toxicity. In StatPearls [Internet]. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK554539/

Banasiewicz, A. (2021, March). Analysis of historical changes in the limit value of nitrogen oxides concentrations for underground mining. In IOP Conference Series: Earth and Environmental Science (Vol. 684, No. 1, p. 012018). IOP Publishing.

Cowbrough, M. (2025, Sept 5). Silo Gas. Retrieved from https://fieldcropnews.com/2025/09/silo-gas/

Jarvis, D.J., Adamkiewicz, G., Heroux, M.E., et al. (2010). Nitrogen dioxide. In: WHO Guidelines for Indoor Air Quality: Selected Pollutants. Geneva: World Health Organization. Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK138707/

Johnson, K. & Shelton, B. (2022, Sept 22). An Eerie Poisonous Fog. Retrieved from https://extension.entm.purdue.edu/newsletters/pestandcrop/article/an-eerie-poisonous-fog/

New Jersey Department of Health and Senior Services. (2000, April). Hazardous Substance Fact Sheet- Nitrogen Dioxide. Retrieved from https://www.nj.gov/health/eoh/rtkweb/documents/fs/1376.pdf

Nitrogen Oxides. (n.d.). Retrieved from https://scied.ucar.edu/learning-zone/air-quality/nitrogen-oxides

Occupational Safety and Health Administration. (2025, April 14). Nitrogen Dioxide. Retrieved from https://www.osha.gov/chemicaldata/21

Royal Belgian Institute for Space Aeronomy. (n.d.). Nitrogen dioxide NO2, a pollutant gas, released during combustion processes. Retrieved from https://www.aeronomie.be/en/encyclopedia/nitrogen-dioxide-no2-pollutant-gas-released-during-combustion-processes

Schoonover, T., Conroy, L., Lacey, S., & Plavka, J. (2011). Personal exposure to metal fume, NO2, and O3 among production welders and non-welders. Industrial health, 49(1), 63-72.

Yudha Irianto, R., Kusumayati, A., & Suyud, S. (2020). Health Risk Assessment on Human Exposed of Nitrogen Dioxide in Adults Around Steel Industry. Indian Journal of Public Health Research & Development, 11(3), 2465-2470.