The good, bad and deadly of silo gases
As producers fill silos, bunkers or bags, I often get calls about gases coming off the silage. During fermentation, many different gases are formed. For the most past, this is very normal. I expect gas formation to occur for roughly a week after a silo is sealed, although some silos can produce gas longer.
Carbon dioxide (CO2) is typically the most abundant gas produced and is harmless to inhale in small doses. Different fermentations produce different quantities of CO2, which is why some fermentations are more efficient in dry matter (DM) recovery than others. For example, a true homolactic fermentation does not produce any CO2, whereas a clostridial fermentation produces a lot, resulting in a great deal of DM loss.
CO2 formation is not necessarily a bad thing as it does help preserve the silage. Once aerobic bacteria respire all the oxygen into CO2, they are no longer able to thrive and fermentation begins.
Volatile organic compounds (VOC) are produced during a normal fermentation. Examples include ethanol, methanol and aldehydes. Acetic acid, a common antifungal, is one of many common gases. When combined with oxides of nitrogen, they form ozone gases. VOCs can also have serious implications on human health, including allergies, respiratory diseases, irritation, immune system depression and nausea.
Nitrogen dioxide – DANGER!
We typically think of the poisonous nitrogen dioxide when we hear “silo gas.”
Nitrates may accumulate in a plant, especially (but not exclusively) in stressed conditions, including drought, hail, frost, cloudy weather, and heavy nitrogen fertilization. If your crop has experienced any of these stressors, it is more prone to silo gas formation.
In the silo, nitrates combine with organic compounds and turn into nitrous acid, which decomposes to nitrous oxides as the temperature increases during a normal fermentation. Bacteria also convert plant nitrates into nitrogen oxides.
Nitrogen dioxide is the most dangerous silo gas and peaks about three days post-harvest. Brownish-colored gases and yellow silages are traditionally associated with silo gas.
If you see the brownish gas or smell a bleach aroma, leave the area immediately and alert anyone else who may work with the silage. Keep kids, adults and animals away from the silo.
Nitrogen dioxide can also be colorless and odorless. Even in a silo that appears normal, silo gas may be present and deadly. Silo gas is heavier than oxygen, so it can displace oxygen, giving a person little warning before he or she is overcome.
Inhalation can lead to severe irritation, inflammation and burns to the nose, throat, and lungs. A person can collapse and die within minutes of inhaling silo gas.
Low levels of silo gas can result in delayed symptoms. Therefore, a person may continue working and inhaling silo gas, ignoring mild irritation. Later in the day, more severe symptoms (fluid in the lungs, chemical pneumonia) can set in and, by then, it may be too late.
Most important harvest job – BE SAFE!
The most important thing you can do this fall is be safe. Here are a few safety steps:
- Never enter a silo within the first three weeks after ensiling.
- Use of a self-contained breathing apparatus would be beneficial if you need to enter the silo before it properly cures. Dust masks or chemical respirators do not offer sufficient protection.
- Vent the silo by running the blower at least 15 to 20 minutes before entering.
- Never enter a silo alone; make sure someone is located outside the silo to act as a spotter and contact rescue services if needed.
- Never enter to perform a rescue without the proper equipment and assistance. Approximately 60 percent of fatalities reported are rescue attempts.
Steps to avoid silo gas formation
- In drought-stressed situations, do not harvest for at least three days after a soaking rain. (Nitrates typically accumulate in the bottoms of drought-stressed plants and, when it rains, they travel up the plant.)
- Raise the cutter bar for stressed crops.
- Typical fermentations will destroy 30 to 60 percent of silo gases, so allow the silage to undergo a good fermentation before opening it.
- If you think you may have nitrates in your feed, after it is ensiled, send it out for testing. Nitrate-nitrogen levels:
- Less than 1,000 ppm are safe
- Between 1,000 and 1,700 ppm need to be gradually introduced into ration
- Above 1,700 can cause toxicity
About the author: Dr. Michelle Der Bedrosian is a Vita Plus forage products and dairy technical service specialist. Der Bedrosian earned her bachelor’s and master’s degrees in animal science at the University of Delaware. She continued there to earn her Ph.D. in animal and food science, specializing in forage research with Dr. Limin Kung. Her thesis research centered on the use of a protease to improve starch digestibility earlier in the ensiling process. A New Jersey native, Der Bedrosian gained much of her farm experience during her collegiate years, milking cows, working in a forage laboratory, and performing dairy research. Based in Madison, Wisconsin, Windle’s responsibilities at Vita Plus include forage product research and development, dairy research, and dairy technical services.
Feed quality and nutrition
Forage storage and management