WORCESTER, Mass. - A fire at the new Doherty Memorial High School building Monday afternoon was caused by a welding incident that ignited a pile of roofing material, according to the Worcester Fire Department. 

At the time of the incident, construction crews were welding with a lapsed hot work permit, which is required by the Worcester Fire Department. 

"The Worcester Fire Department will not issue another hot work permit until an acceptable construction safety plan is presented and approved," the fire department said in a news release Tuesday evening. 

The city's Department of Inspectional Services is currently working to assess damage and determine whether the building's structural integrity has been compromised. 

Hundreds of concerned Worcester residents stared at the thick cloud of billowing smoke on Monday. While the investigation is still ongoing, Worcester School Committee member Laura Clancey is relieved the damage wasn't worse. 

"The quick response of the fire department really decreased the damages we could've had here, and thankfully there were no students on campus," Clancey said.

At a Monday press conference, Mayor Joseph Petty sounded optimistic about continuing with the project's original scope and timeline.

"We'll figure this out, assess the building, how long it will delay the project if it delays it at all," Petty said. "I'm sure we can make it up somewhere if we have to. This is going to be one of the best facilities built, and that will continue to be the case."

City and school district leaders will be meeting with the project manager to review, update and implement the site's new safety plan.