An accident at a school construction site in Bedford sent a worker to the hospital Thursday.

Police say the construction worker fell off the scaffolding on the third story of a building addition at Fox Lane High School at around 9:30 a.m. They say they don't know whether he lost his balance or simply took a misstep. He was airlifted to Westchester Medical Center with a serious head injury.

The accident is under investigation by both Bedford police and the Occupational Safety and Health Administration.