A fire that burned a storage structure Friday night in Waipahu was accidentally caused by the burning of green waste, a Honolulu Fire Department spokesman said today.

HFD Capt. Scot Seguirant said the fire at 94-768 Kaaholo St. caused about $60,000 in damage.

Firefighters were sent to the blaze at 6:52 p.m. and found a woman in her 90s outside of the burning structure.

Emergency Medical Services treated the woman, the only person home at the time, and took her to a hospital in stable condition. It was unclear what kind of medical attention she needed.

Twenty-six firefighters with seven units extinguished the fire by 7:24 p.m.