Farm Safety - Silo Gas Hazards!


Silo gases formed during and after silo filling pose a serious threat to human health.  Silo gases are composed of oxides of nitrogen.  They form from nitrates (NO3) ions accumulated from soil by corn plants.  Lower stalks contain most nitrate at harvest.  The gases form during chemical and biological activity, soon after filling begins.  The nitrate is reduced to nitrite (NO2) ions and nitric acid and then to nitric oxide (NO), a colorless gas. When it contacts air above the silage, this gas is converted to reddish-brown nitrogen dioxide gas, which further changes to nitrogen tetroxide a yellow gas.  All gases can be present at the same time.  All are extremely toxic to humans and animals.


These silo gases are heavier than air and will collect inside the silo.  When the silo becomes full, they will spill over the top, flow down the chute into the unloading room.  Turbulence could cause them to move anywhere, including into the barn and injure or kill your animals.  The following safety rules were offered by Win Way, a retired Vermont Extension Agronomist.


1.  Stay out of silos during and after filling, unless necessary to enter.  Be on the alert for pungent odors and brightly yellowed or orange discoloration of any silage lying around the chute, or silo room.  Watch for yellow, orange or brown gases.  However, nitric oxide is colorlessBe sure help is around before entering a silo.


2.  Ventilate by leaving all doors, windows and roofs open for 3 weeks after final filling.  Keep barn doors closed.  Chute doors should be level with the silage.  Run blowers for 20-30 minutes before entering a silo.  Keep telephone numbers of your fire department and rescue squad handy by both barn and house phones.  Be sure to mention silo gas if making an emergency call.


3.  Keep all children, pets and livestock away from silos for 3-4 weeks.  Post caution signs on silos.


4.  Ventilate before opening a silo for feeding. Be careful in removing plastic silo covers from bunkers or silos as they too may collect gas.  Leave the area immediately if any adverse effects are experienced.


5. Test forage for nitrate before feeding. Nitrates, not converted to gas, can persist to cause abortions and lowered milk production.  They are converted to toxic nitrite in ruminant animals.  Lowered blood oxygen could cause death.


6.  Raise harvesting equipment to leave a foot or more of stubble if excess nitrates are suspected.


Medical histories are not good for severely exposed persons.  Care and fore thought is the best way to prevent suffering and death.


Stephen J. Herbert

Dept. of Plant and Soil Sciences

University of Massachusetts Amherst

Crops, Dairy, Livestock News. Vol. 2:2, Summer 1997

 Copyright or other proprietary statement goes here.
For problems or questions regarding this web contact [ProjectEmail].
Last updated: 11/11/02.