Dangerous silo gas can result from drought-stressed corn

From the University of Minnesota Extension

Farm workers always need to be aware of dangerous silo gas at silo filling time, but this year presents an especially dangerous threat.

Silo gas, also known as nitrogen dioxide, is apt to be at higher levels in plants that have been drought-stressed, says John Shutske, professor and safety and health specialist with University of Minnesota Extension.

“Stay out of a newly filled silo and surrounding areas for two to three weeks after it’s been filled,” Shutske said. “When it’s safe to enter, run the blower for at least an hour to assure that the gas has been removed and there’s a supply of fresh air.”

Farm workers who must enter the silo need to do it immediately after filling, according to Shutske.
“But even then, there could be significant levels of gas, so maximum ventilation is essential,” he said. “The silo must be treated as a dangerous confined space.”

Silo gas is the common term for nitrogen dioxide. Most farmers who make silage are somewhat familiar with the gas, but don’t always understand the true risks, says Shutske. Silo gas is formed as a natural by-product of silage production when chopped-up plant material ferments.

Silo gas dangers aren’t limited to upright silos, says Shutske.

“We typically associate silo gas with upright, concrete silos,” he points out. “But silage in bag systems and bunker silos also produce silo gas. The risks with these other storage systems are lower, however, since they are more easily ventilated with ambient outside airflow.”

Shutske says silo gas has a bleach-like odor and a yellow-brown, hazy color, but it can be hard to see in dim lighting. It’s heavier than air, causing it to settle into low-lying areas. These may include the bottom of silo chutes, between silage bags or in low spots within a bunker silo.

“Silo gas is highly toxic, even at low levels,” said Shutske.