(CNN) -- Human error is to blame in last week's gas-fueled explosion that ripped through a strip club in the western Massachusetts city of Springfield, officials said Sunday.
The blast injured at least 21 people, including firefighters.
A utility worker, responding to a report of a gas odor inside a building, inadvertently punctured a hole in a high-pressure gas line at the foundation of that building, according to a statement from the Office of the State Fire Marshal.
Markings on the sidewalk incorrectly indicated where the line was.
Once the pipe was punctured, the worker called the gas company and the fire department to shut off the gas, and the area around the building was evacuated. Investigators believe gas from the leak entered the building and later ignited.
"They (investigators) have determined that human error as opposed to a fault of the gas infrastructure provided the fuel for the explosion. Exactly whose human error will be the subject of the Department of Public Utilities' ongoing investigation," the statement read.
The blast occurred at 5:25 p.m.Friday.
Twelve of the 14 firefighters on scene were injured, according to Springfield Fire Commissioner Joseph Conant.
"All have been treated and released but several will face a long recovery road," he said.
Four gas company employees, two police officers, a municipal water and sewer department employee and two civilians were also injured, according to the city's mayor.
People as far away as South Hadley, 10 miles north, felt the blast.
Video showed that the facade of one building was shredded by the blast, while glass from blown-out windows littered streets blocks away.
Besides the leveled multistory structure that housed Club Scores, 12 buildings suffered significant damage, and at least a dozen others had collateral damage, Conant said.