Beware of Silo Gas; It Could Be Common Again This Summer

By CnAgri2012-07-26 19:28:39 Print

A unique set of circumstances that could lead to a heightened threat of deadly gas again is being created in silos across the Northeast, according to a farm-safety expert in Penn State's College of Agricultural Sciences.

The phenomenon may have started with the scorching heat wave the region experienced in early July -- which has some areas on the edge of drought conditions -- according to Davis Hill, senior extension associate in agricultural and biological engineering. It could develop if the region receives normal amounts of rainfall through the rest of the summer.

"There is now a lot of drought-stressed corn, particularly on manured fields," he said. "If this crop receives sufficient rainfall later in the season, there will be a potential for higher-than-average nitrates to build up in the corn plants just prior to harvest. This condition can lead to high gas levels in silos."

During the fermentation process of silage, a number of gases are given off, Hill explained. Of particular concern is a family of gases called oxides of nitrogen -- often referred to as "silo gas."

"The formation of these gases peaks in one to two days after filling and can last for 10 days to two weeks after the fresh, green forage is chopped and blown into the silo," he said. "This is a naturally occurring process and is necessary to ferment the forage so it is usable feed for livestock and for long-term storage."

Hill said that sometimes gas production is so great that it is mistaken for a silo fire.

"Farmers and passersby may witness 'smoke' coming from the silo chute and believe the silo is on fire," he said. "There has been at least one instance where a fire company was called to a farm for a 'silo fire' just two days after the farmer finished filling the silo.

"Firemen proceeded to pump water into the top of the silo, only to learn later that the silo was just gassing off."

Farmers and fire personnel need to realize that it would be nearly impossible for a silo fire to start so soon after filling, Hill noted. "This is why we always talk of attempting to locate the actual fire location within the silo before any attempts of extinguishment proceed," he said.

Silo gas sometimes has a bleach-like odor and under certain conditions can be visible as a fog from a distance (thus the mistake for smoke). If the gas is high enough in concentration, this fog will appear to be yellow to reddish brown in color, and the silage surface, silo wall, base of the chute and other structures of the silo may be stained (yellow, orange, reddish) from the gas.

This gas is heavier than air, which means it will settle at the surface of the silage instead of rising to the top of the silo, exiting through the fill door. This is an important factor, Hill pointed out.

"The highest concentration of gas will be at the surface of the silage, which is where a person will be going if he or she needs to enter the silo for any reason," he said. "Also, if a silo door is open near the surface of the silage, the high concentration of gas -- being heavier than air -- could exit the silo through this door, flow down the chute and settle at the base of the silo in the feed room or in the barn area.

"If there is little ventilation in the barn, a dangerous buildup of silo gas can occur, which can affect livestock or people who enter the area."

The presence and concentration of silo gas is dependent on the storage structure and the quality of the forage material that is chopped. Those crops that have received nitrogen fertilizer (corn) and those crops that have suffered prolonged drought or especially prolonged drought conditions followed by rain just prior to harvest often lead to high gas production.