Authorities say DUI and hit-and-run charges may be filed against a San Francisco firefighter after a ladder truck he was driving plowed into a motorcyclist and left the scene.The San Francisco Chronicle says (http://bit.ly/12BYbv8) 43-year-old Michael Quinn was arrested about two hours after the crash late Saturday.The newspaper says Quinn was driving a truck with lights flashing and the siren blaring, responding to what turned out to be a false alarm.Sources tell the Chronicle Quinn’s blood-alcohol level was measured at 0.13 percent, well above the legal driving limit.