In the midst of a scorching heat wave that has been record breaking in some areas, a farm-safety expert in Penn State's College of Agricultural Sciences is warning about the danger of silo fires.

Many crop fields are drought-stressed, meaning that the crop is low in moisture to begin with and will dry down very quickly once it is harvested, according to Davis Hill Sr., extension associate in agricultural and biological engineering.

"This year's silage might be too dry and be more prone to silo fires," he said. "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, Hill explained. This occurs naturally and happens with any material being stored. 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 said. "The drier the material, the more air that is trapped; conversely, the wetter the material, the less air that is trapped."

The fuel is the forage material itself. Generally, it is not a good source of fuel from a burning standpoint, because even material that is too dry for good silage is too wet to burn quickly.

That's a good thing to keep in mind when discovering a silo fire, Hill noted, because when a silo burns, a farm operator 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 said. "Good hay-crop silage would be considerably more.