Maintain vigilance to prevent silo gas exposure

The mid-range weather forecast shows continued occasional rains through September in Ontario, so the risk of elevated nitrates in harvested corn should remain low.

That doesn’t mean producers of corn silage should let down their guard in protecting themselves and employees against silo gas poisoning.

When filling conventional tower silos, ensure sufficient ventilation and, if it is absolutely necessary to enter the silo, do it immediately after the last load is piled and while the blower is still running.

This is because two gases produced by silage, nitrogen dioxide (NO2) and dinitrogen tetraoxide (N2O4), are both heavier than air and will settle into the lowest connected airspace.

Why it matters: Incidents of silo gas death still occur on Canadian farms and equally troubling are the long-term effects of “silo filler’s disease” that can haunt farmers throughout their lives.

Livestock are also susceptible, and tower silos aren’t the only culprit. A scholarly article on the United States Department of Health website cites a farm where “a cloud of reddish-brown NO2 gas was noticed to escape from underneath the plastic sheet of a horizontal (silage) bunker and to enter a cubicle house for dairy cows one day after ensiling. Eleven cows (developed difficulty breathing), three of which subsequently died.”

NO2 and the less common N2O4 are formed when nitric oxide comes in contact with oxygen. Nitric oxide is present at elevated levels in corn, as well as other plants like lamb’s quarters and pigweed, when crop conditions are less than optimal for conversion of soil nitrates into plant proteins.

“Hence, any practice that adds a significant quantity of nitrates (e.g., high nitrogen fertilization) or reduces the rate at which nitrates are converted to proteins (e.g., adverse growing conditions) will lead to a buildup of nitrates in the plant,” wrote Lactanet nutritionist Jean-Philippe Laroche in a recent article on the dairy service agency’s website.

Silo gas risk increases when there is a prolonged dry period followed by a heavy rain, after which corn is quickly harvested and ensiled. Given this growing season’s weather trends in Ontario and Quebec, that risk seems unlikely in 2023.

However, producers should use best practices to prevent silo gas exposure.

If there is a prolonged dry spell leading into September, the risk of elevated nitrates is higher, according to an OMAFRA factsheet on the topic, “for the 5-7 day period after a rainfall than during the actual period of dry weather.”

Silo gas exposure can have immediate effects, states an article on the Workplace Safety and Prevention Services website, in the form of “severe irritation to the nose and throat and may lead to inflammation of the lungs.

“However, what makes this gas especially dangerous is that low-level exposure to it (can be) accompanied by only a little immediate pain or discomfort,” the article says. “A farmer might breathe the gas without noticing any serious ill effects and then die in his sleep hours later from fluid collecting in his lungs. Many victims can suffer relapses with symptoms similar to pneumonia two to six weeks after the initial exposure.

“For these reasons, it is extremely important for anyone who is exposed to this gas, even for a short time, to seek immediate medical attention,” the WSPS article advises.

Other points in the OMAFRA factsheet:

• Post a “Danger, Deadly Gases” warning sign in a visible location near the silo.
• Do not allow children or visitors near the silo for three weeks after filling.
• During filling, adjust the distributor as needed to level the silage. Do not level the material by hand.
• If it is necessary to enter the silo when filling is complete, do so immediately following the last load, on the same day. Leave the blower running while inside.
• If someone collapses inside a silo, immediately ventilate with the forage blower and contact the local fire department. A fresh air supply is critical for both the victim and rescuers. Never attempt to rescue someone yourself. This has been attempted many times and, without the proper equipment and training, has resulted in many incidents of multiple fatalities.

For livestock, silage with nitrate levels greater than 4,000 parts per million should not be fed.

“Testing at harvest will provide a general idea of the relative levels, but not the concentration in the silage being fed,” says the OMAFRA factsheet.

If elevated levels are suspected, “the best time to test … is after fermentation is complete. Obtain a representative sample. Keep the samples refrigerated and send to the lab as quickly as possible. If high levels are reported, water and other feeds should also be tested.”

When filling silos, be aware of the risk that carbon dioxide, formed when living plant material in the silage converts oxygen to water and CO2, will settle in the silo. Breathing is impossible in high CO2 environments.