Gilbert Fire Department investigators are trying to determine what caused two large hay piles to catch on fire within the last two weeks, destroying at least one metal barn and causing heavy amounts of smoke in the area.
The most recent fire was reported about 4:05 a.m. Sunday at 3597 S. Greenfield Road between Pecos and Germann roads that involved 1,500 tons of hay, according to Mike Connor, a Gilbert fire spokesman. Some of the contents in the open metal barn, including a semi-tractor trailer and a hay loader, were destroyed, Connor said.
About 2:30 a.m. on July 11, 100 tons of hay burned in a field between Val Vista Drive and Ocotillo Road.
No injuries were reported from either fire.
Connor said that the investigation was not leaning toward arson as the cause of the fires, but possibly spontaneous combustion caused by a mixture of the hot temperatures and the hay being in a closed in area.
Wet hay is more likely to lead to a spontaneous combustion fire than dry hay, according to information from Washington State University’s Department of Agriculture. If hay is put into a barn or stack when it has more than about 22 percent moisture, not only does the hay lose forage quality, but also it has an increased risk of spontaneous combustion.
High moisture hay stacks can have chemical reactions that build heat. Hay insulates, so the larger the haystack, the less cooling there is to offset the heat.
When the internal temperature of hay rises above 130 degrees Fahrenheit (55 degrees Celsius), a chemical reaction begins to produce flammable gas that can ignite if the temperature goes high enough. Hay fires generally occur within six weeks of baling, according to Washington State University’s Agricultural Department and the United States Department of Agriculture.
Early Monday, investigators still were not able to get close to the building from Sunday’s fire because the smoke was smoldering and the building was too hot and smoky to attempt to determine a cause, Connor said.
Air quality monitors in Maricopa County did not register an increase in levels in the past few days due to the hay fires, according to Holly Ward, a spokeswoman for Maricopa County’s Air Quality Department.
“With current wind patterns, we are not seeing any effect,” Ward said.
A dollar amount on the damage from Sunday’s hay fire has not been determined.