(NBC) -- Investigators say a gas worker looking for the source of a leak accidentally triggered the massive explosion in downtown Springfield, Massachusetts Friday night.
"We have determined that human error, not a fault in the gas infrastructure, is the cause of what the explosion was," said Massachusetts State Fire Marshall Stephen Coan.
The blast injured 18 people and destroyed several downtown businesses.
Still, the error was not the worker's.
It was in the markings on the ground incorrectly showing the location of the high-pressured gas line.
"His metal probe inadvertently punctured the high pressure gas line at the foundation of the building," Coan explained.
After puncturing this pipe the worker immediately called the fire department, who along with police, were able to evacuate the surrounding area.
Moments later the explosion leveled one building and damaged dozens more.
Three have already been condemned and engineers are working to inspect the rest to see if they are safe for residents to return.
Officials say most of those injured in the blast were utility workers and firefighters who ducked for cover seconds before the explosion.
All of the 18 injured have been treated and released.