Fire authorities in McHenry County, Ill., have ruled out arson as the cause of a deadly barn fire last week.

The fire broke out around 5:00 p.m. on April 11 in a barn at the Black Tie Stable in McHenry, said stable owner Richard Wright. Forty horses were contained in the barn at the time of the blaze. Of those, 18 were killed in fire, Wright said. The McHenry County Animal Control personnel and volunteers rescued the remaining 22, said Debra Quackenbush, spokeswoman for the McHenry County Health Department.

On April 16 McHenry County Director of Fire Prevention Tony Oliver said fire investigators do not believe the fire was set deliberately.

"At this point the investigation has been concluded, and we do not believe arson is involved," Oliver said. "Basically, it was an accidental fire of undetermined origin