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Professional Version

Nitrogen Dioxide as a Veterinary Workplace Hazard

(Silo Filler’s Disease)


Rhian B. Cope

, BVSc, BSc, PhD, DABT, DABVT, FACTRA, Australian Pesticides and Veterinary Medicines Authority, Australian Government

Reviewed/Revised Mar 2021 | Modified Nov 2022

Veterinarians are most likely to encounter nitrogen dioxide in association with grain silos, grain silo chutes in intensive animal production facilities, silage, silage bags, and silage pit vents. When a silo or pit is filled with fresh organic material (grain, grass, etc), nitrogen dioxide is formed by anaerobic fermentation. High levels can develop at the top of grain in silos or at the top of silage pits within hours of their filling. Veterinarians working in or around silo chutes and hatches or silage pits or silage bags during the first 10 days or so after fill will be exposed to nitrogen dioxide. Silo chutes and other nearby structures exposed to significant levels of nitrogen dioxide are often stained yellow to red by the gas.

Nitrogen dioxide is a reddish, water-insoluble, reactive gas with a characteristic pungent odor. Because of its low water solubility, it is not scrubbed by the upper respiratory tract. It penetrates deeply into the lung, where it is reactive with lung surface fluids and acts as a pulmonary irritant. When nitrogen dioxide contacts the lung surface fluids, it slowly hydrolyzes to nitrous and nitric acid, producing chemical pneumonitis and pulmonary edema.

Acute, high-level exposures to nitrogen dioxide result in acute respiratory distress syndrome in people, which is characterized by rapid or delayed onset (up to 72 hours after exposure) progressive pulmonary edema and respiratory failure. Nitrogen dioxide acute respiratory distress syndrome is less common than other toxic injuries, because the pungent odor and other effects of nitrogen dioxide usually trigger an escape from the source of exposure. This type of severe effect is more likely if the affected person cannot escape.

More common acute signs and symptoms include:

  • cough

  • light-headedness

  • dyspnea

  • chest tightness

  • choking

  • sweating

  • chest pain

  • wheezing

Because of nitrogen dioxide’s low water solubility, mucous membrane and eye irritation are relatively uncommon signs.

Usually of greater concern is the capacity of nitrogen dioxide inhalation to induce sometimes severe delayed effects, including bronchiolitis obliterans (fever, cough, and dyspnea), respiratory insufficiency new-onset asthma, COPD, and hypoxia/cyanosis.

There is no specific antidote for nitrogen dioxide poisoning. Treatment requires specialist medical care.

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