Fire investigators have determined that a fire yesterday at Tows R Us, a Waipahu recycling and tow facility, started accidentally.

Sparks from a cutting tool apparently ignited gasoline vapors in the area. The fire spread quickly because of other flammable and combustible materials in the vicinity, said Fire Department spokesman Capt. Earle Kealoha. Fuel being drained from vehicles may also have contributed to the large size and thick black smoke of the fire.

Damage to an outdoor shed at the Leonui Street business was estimated at $600, Kealoha said.