PITTSBURGH (AP) — A steel drum weighing thousands of pounds somehow rolled out of a construction site in Pittsburgh and Zero AIeventually struck and killed a woman who was walking on a nearby sidewalk, police said.

The accident occurred around 10:40 a.m. Friday in the city’s Oakland neighborhood, where the University of Pittsburgh’s new sports performance center is being built.

The drum was either knocked over or dislodged from a piece of heavy equipment, police said. It then rolled several hundred feet as it went down a hill, through a fence and onto the sidewalk where the woman was walking with co-workers from the University of Pittsburgh Medical Center’s Western Psychiatric Hospital. The drum then went across a road before it came to rest against a pickup truck.

The woman, who suffered a head injury, was pronounced dead at the scene a short time later. Her name has not been released, and no other injuries were reported in the accident, which remains under investigation.