Dangerous Gases and Fires Can Make Silos Death Traps

John M. Smith 
Auglaize Co., Ext. Agt.

This is the time of year when farmers begin storing their silage feeds for the coming winter. And their silos can become towers of death if safety practices are not followed carefully.

Silos can be dangerous in two serious ways. They can become cylinders of highly toxic gases as well as the site of fires and explosions.

Toxic gases are a side effect of the necessary process that turns green plant materials into silage. Silage is formed by natural chemical fermentation that takes place in the chopped materials. Fermentation begins shortly after the plant material is placed into the silo.

During the ensiling process, several gases -- including carbon dioxide, methane and nitric oxide are released. All of these can seriously threaten human and animal life. Normally, they are present in low enough concentrations in silos such that they are not of great concern. The real danger, however, occurs when nitric oxide combines with oxygen. The resulting gas, nitrogen dioxide, is highly toxic and can cause death or permanent lung damage.

Nitrogen gases have a disagreeable odor and range in color from red to orange and dark brown. Also, because these gases are heavier than air, they will naturally settle to the lowest possible level, near the silage surface level. Therefore, great caution should be taken when working near the base of a tower silo during the first few weeks after filling.

Caution should also be exercised when working in barns and stables located near a recently filled silo. These can become death traps for man and animal when nitrogen gases are present. The greatest danger occurs one to three days after harvest, but can continue for up to three weeks in some situations. A potential toxic gas hazard also exists when silos are being opened the first time for feeding. 
Unfortunately, it is possible to work in the presence of toxic silo gases for some time without ever feeling major discomfort. The resulting lung damage, however, may cause death just a few hours later. No one should assume that they are safe just because they have not been affected by silo gases in the past.


1) Run the silage blower for 15 or 20 minutes before entering a partially filled tower silo. Keep the blower running while anyone is within the structure.

2) It's best to stay out of the silo for two weeks after filling. Never enter a silo under any circumstances without a safety harness and unless someone else is nearby.

3) Leave the blower pipe close to the silage level to draw off gas.

4) At the slightest indication of coughing or throat irritation, get out of the silo and into the fresh air at once. Immediate medical attention will reduce lung damage and stop pneumonia from developing.

5) Keep children and animals away from the silo during the filling period and for at least one week afterward.

6) Keep the door between the silo room and the barn closed during the danger period to protect livestock.

7) Ventilate the silo room for at least two weeks after filling the silo by opening any available outside doors and windows to carry away any toxic gases. Removing chute doors to the level of the settled silage will permit natural ventilation at the point where gas tends to concentrate.

8) If gases are present, an air line or an air backpack is a must for entering the silo. The best rule is to stay outside, but if there is a necessary reason for entering the silo use supplied air.

Besides holding deadly gases, silos can also become the sites of fires and explosions. Silo fires often result from ensiling feeds too low in moisture, usually below 45% moisture. The heating of the materials in combination with air leaks in the silo structure can permit a fire to start anywhere within the structure and to continue burning for long periods of time. Once a fire starts, it is very difficult to control or stop.

Ensiled materials should contain 50% or more moisture for safe storage in conventional tower structures and 45-48% for haylage in oxygen limiting structures. In addition, cracks and leaks at the base of the silo and silo doors should be sealed before filling. After filling, keep the silo sealed until the silage is needed.

Contact your local OSU County Extension Service offices for additional information on silo hazards and safety procedures for proper and safe handling of silo emergencies.