Drought-scorched corn will dry down very quickly, warns Davis Hill, Penn State Extension ag engineer. That may make this year's silage too dry and more prone to silo fires," he cautions.
"Internal combustion of silage material can occur if the silage is put in when it's too dry for the silo. For anything to burn, you need three ingredients -- a heat source, air and fuel."
With silage, the heat source is the heat generated as the material goes through the fermentation process, he explains. Proper moisture levels help keep the material from getting too hot.
"Air is trapped in the chopped forage during harvest and when blowing the material into the silo," he adds. "The drier the material, the more air is trapped; and conversely, the wetter the material, the less air that is trapped."
The fuel is the forage material itself. Generally it isn't a good fuel source because even material that's too dry for good silage is too wet to burn quickly.
But once a silo starts smoldering, you can lose a tremendous investment and be faced with an unmanageable cost to replace ruined feed. "If you have a 20-foot diameter by 60-foot high silo that contains 400 tons of corn silage, and you had to purchase that 400 tons of feed, it would cost you nearly $20,000 -- $50 per ton," he calculates. "Good hay-crop silage would be worth considerably more."
Another common cause of spontaneous combustion in silos is putting new silage on top of old silage. Old silage can be quite dry, Hill notes.
Remember, the dryer the material, the more air that can be trapped in that material. When fresh material is put on this older material, the natural heating that the new material will go through could be too hot at this location. It also won't pack down as tightly, leaving more air. This would be the first place to look if a fire does occur.
Limit the damage
Limiting the fire while protecting unaffected silage is difficult, but not impossible. "The earlier you detect a fire, the easier it is to control. So regularly monitor your silos for a good three weeks after harvest. This is a critical time when natural fermentation and heating are taking place inside the silo."
A silo fire usually is discovered when smoke comes from the top of the silo, when charred silage or burnt silo doors drop down the chute, or when a burning smell is evident. The initial decisions made can mean the difference between salvaging a viable crop or ruining it.
"Remember, a fire inside a stack of silage in a silo doesn't have adequate air to burn aggressively," he says. "So you don't need to panic. The fire isn't going anywhere in a hurry. You have time to evaluate what you have, to report it to your local fire company and seek out additional expertise if needed."
"Several technical experts are available throughout Pennsylvania to help farmers and firefighters think through the many management strategies when dealing with silo fires," he said. "This emergency information can be found by calling 814-865-2808 during working hours or 814-404-5441 after hours."
Information about managing silo fires also is available at the following website: http://www.farmemergencies.psu.edu.