A worker was injured Monday morning when a roof collapsed and knocked him over the side of a new house under construction in Brunswick.

The injured man was one of three working on the house at 52 Carriage Lane about 10:45 a.m. when trusses of the partially finished roof collapsed, with one truss falling against another in a domino effect, Brunswick Fire Capt. Matthew Barnes said.

The worker – later identified as Arvo Krosman, 53 – had been standing on top of the first-floor wall at the time of the collapse, and first was pinned and then fell about 20 feet to the ground, Barnes said.

Krosman suffered possible neck and back injuries and was transported to Maine Medical Center in Portland, police said. His hometown and condition were unavailable Monday night.

The three men had been working on a 32-by-36-foot house and had used a crane to install 18 40-foot trusses. They had four more trusses to install when the collapse occurred, Barnes said.

A second worker escaped from the collapse through a window. A third worker escaped through the front door.

Barnes said the two men who escaped the collapse declined medical treatment.

“The construction site was shut down, taped off,” Barnes said.

Investigators from the U.S. Occupational Safety and Health Administration are expected at the construction site Tuesday and Wednesday to try to determine the cause of the collapse and what went wrong.

“They are all very lucky,” Barnes said of the workers.