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Silo gas, also known as Nitrogen dioxide, NO2, is a dangerous chemical asphyxiant and is produced almost immediately after plant material is placed into a silo. The greatest risk is the first 12 to 60 hours after filling the silo, and then risk declines for approximately 4 - 6 weeks when silage fermentation is complete. Silo gas has a characteristic bleach-like odour and may be visible as a reddish-brown haze. However, it is not always visible.
Even short-term human exposure can result in severely injured lung tissue and sudden death.
When inhaled, nitrogen dioxide mixes with body moisture to form nitric acid which causes severe burning of the lungs and the rest of the respiratory system. Pulmonary edema results. Victims often collapse. Other people attempting a rescue can also be overcome. Farmers exposed to silo gas should get immediate medical attention.
Do not enter the Silo for 4 to 6 weeks after filling stops. If a silo must be entered, do it immediately after blowing the last load into the structure ensuring the blower is running for 15 to 45 minutes prior to entry. Leave the blower running for ventilation while anyone is inside. Running the Silo blower for 15 to 45 minutes before entering the silo and while you are in the silo will help remove silo gas, but this is not a substitute for a self-contained breathing apparatus. Never enter a silo if you are alone, without a self-contain breathing apparatus and a lifeline, especially during the danger period when gases may still be forming. Also ventilate the silo room and chute. Post appropriate warning signs, and keep people and animals away.
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