Silo Unloader Syndrome

Silo Unloader Syndrome is an occupational lung disease that occurs in farm workers who go into a silo and breath in the nitrogen dioxide which is toxic to the body. Some sources erroneously claim that the causing agent is dust from food or feed that is present in a silo, but that syndrome is better described by the Organic Dust Toxicity Syndrome.

When a silo 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.

Nitrogen dioxide penetrates deeply into the lungs, 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.

Signs and symptoms of Silo Unloader Syndrome include cough, light-headedness, shortness of breath (dyspnea), chest tightness, choking, sweating, chest pain, and wheezing.

When afflicted, the farmer may die immediately of asphyxia or succumb to pulmonary edema within 24 hours. Survivors often develop progressive bronchitis within a few weeks.