UNIVERSITY PARK, Pa. — The hot, dry summer experienced by Pennsylvania likely will lead to an increased potential for the creation of silo gas, creating a hazard for both animals and farmers and their families, warns a farm safety expert in Penn State's College of Agricultural Sciences.
During the fermentation process of silage, a number of gases are given off. Of particular concern is a family of gases called "oxides of nitrogen." The formation of these gases peaks a day or two after filling a silo and can last for 10 days to two weeks after the fresh, green forage is chopped and blown into the farm structure. 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.
The presence and concentration of silo gas is dependent on the storage structure and the quality of the forage material that is chopped, according to Dave Hill, senior extension associate in agricultural and biological engineering. "Corn crops that have received nitrogen fertilizer 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," he explained.
"This is due to the high levels of inorganic nitrates within the plant that occurs during these conditions. It appears that this year's long droughty period across much of the state, which stunted the corn crop, means there will be more corn harvested for silage, and that will be done fairly early. The high levels of nitrates in this crop will lead to higher than normal concentrations of silo gas produced during the ensiling process."
Operators need to be aware of this danger and take precautions, warned Hill, a farm safety specialist. These precautions include assuring that all spaces at the base of silos are well ventilated and silo doors are closed well above the level of the silage surface. He advises farmers to stay out of a silo for three weeks after it is filled, and to always use the silo blower to ventilate a filled silo for at least 20 minutes prior to entry.
Sometimes, silo gas production is so great that it is mistaken for smoke from a silo fire. Hill noted that farmers and passersby might witness "smoke" coming from the silo chute and believe the silo is on fire.
"Farmers and fire personnel need to realize that it would be nearly impossible for a silo fire to start so soon after filling. This is why we always suggest attempting to locate the actual fire location within a silo before making any attempts to extinguish it."
If the fire company is called, Hill recommends making sure they don't just start pumping water into the silo. "Ask them to use a thermal imaging camera to try to identify any excessive heating of the silo," he said. "A burning silo will give off temperatures of more than 190 degrees at the general location of the fire as viewed with a thermal imaging camera."
Silo gas sometimes has a bleach-like odor and under certain conditions can be visible as a fog from a distance. 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 parts of the silo may be stained yellow, orange or 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 and exiting out through the fill door. The highest concentration of gas will be at the surface of the silage, which is where a person would enter the silo.
"If a silo door is open near the surface of the silage, the high concentration of gas could exit the silo through this door, flow down the chute and settle at the base of the silo in the feed room or into the barn area," Hill said. "If there is little ventilation in the barn area, a dangerous buildup of silo gas can occur, which could easily affect livestock or people in that area."
Individual reactions to silo gas depend on the concentration of gas that is inhaled and the length of exposure, Hill pointed out. Very high concentrations of gas will cause immediate distress, which will result in collapse and death within minutes. When gas levels are extremely high, normally an individual will not be able to withstand the symptoms and will vacate the area quickly. More mild concentrations could cause upper respiratory congestion, watering eyes, cough, difficulty breathing, fatigue and nausea.
If symptoms are mild, individuals may think they can stay in the area to finish the job at hand, he said. This can make the effects of silo gas worse, as these effects can last for many hours in the body, causing symptoms to become progressively worse over the next day or two.
Anyone experiencing symptoms when inside or near a freshly filled silo should immediately exit to fresh air and leave the task for another day, Hill added. Affected people also should go to their doctor or a hospital emergency room immediately and report they have had a serious "silo gas poisoning" exposure.
"One aftereffect of silo gas poisoning is fluid in the lungs leading to chemical pneumonia and perhaps death if not treated promptly," Hill said. "The effects of fluid filling the lungs may not be felt until several hours after the exposure — then it may be too late."
Several technical experts are available throughout Pennsylvania to help farmers and firefighters think through the many management strategies when dealing with silo fires. This emergency information can be found by calling 814-865-2808 during work hours or 814-404-5441 after hours. The Penn State Agricultural Safety and Health "Farm Emergencies" website offers resources for fire companies to use in managing silo fires.