OKLAHOMA CITY - Oklahoma City firefighters quickly extinguished a fire on the city's southwest side, Thursday morning. 

Crews responded to the house near Southwest 23rd and Pennsylvania Avenue.Officials said a passerby discovered the flame, opened the front door, and alerted the occupant who was sleeping on a mattress inside the front room. 

Officials said the fire was contained mostly to the rear of the home. 

Crews said the passerby refused treatment.

Officials determined the fire was accidental with the specific cause being electrical in nature. Damage estimates were set at $10,000.