Janesville police are involved in the investigation of circumstances surrounding a fire on Janesville’s south side.  Fire officials say they were called to the blaze at a single story family home in the 3600 block of Birdsong Lane about 3:00 p.m. Thursday.  Officials say the police department is involved because of a disturbance associated with the fire.  The fire is believed to have started in a bedroom.  One firefighter was injured.  Damage is estimated around $75 thousand.