UPDATE (9 p.m.)—Bates Middle School was evacuated after an explosion was reported in its boiler room that injured two employees on Wednesday morning.

“Maintenance workers were attempting to refire a boiler at the school shortly before 9 a.m. this morning when a small ‘puffback,’ or release of built-up pressure, occurred,” said Bob Mosier, a spokesman for Anne Arundel County Public Schools, in a press release. "There was no fire, but lots of smoke and soot in the boiler room.”

Mosier said Wednesday night that air tests and other safety inspections were  completed and the school has heat and running water, so it will open on time for students and staff on Thursday.

Two men were in the boiler room at the time of the incident, and Mosier said they were taken to the hospital as a precautionary measure and are still under observation as of 4 p.m. on Wednesday.

“Neither suffered any burns, but both were impacted by the smoke and soot,” Mosier said.

Sixth-grade student Sydney McEwan was in her first period math class when the incident occurred.

"It made a really loud noise, and my teacher Miss Kerley almost fell over," McEwan said. "I looked out the window and saw it fuming and it had smoke coming out of it. It was kind of scary."

Marje Sovinski, who lives about a quarter-mile away from the school, posted on Patch’s Facebook page that she heard the blast from her home.

“I heard the explosion this morning and was wondering what had happened,” Sovinski wrote.

Officials evacuated the school’s 750 students to an auditorium at Maryland Hall, which sits a few hundred feet from the middle school.

McEwan said the parking lot was filled with police, firefighters and emergency responders when her class walked outside.

"I was kind of scared because I knew it was something serious," McEwan said.

The kids returned to the school at 11:30 a.m. Wednesday to collect their belongings and be dismissed.

The building uses alternating boilers to heat its water and classrooms. Mosier said employees ran a safety test on the second boiler in anticipation of using it on Thursday.

He also noted that the evacuation and re-entry of students proceeded without incident.

“Our schools, as you know, practice emergency drills five times a year and that practice paid off,” Mosier said.

Patch will update this story as it develops. For up to the minute updates, follow Annapolis Patch on Facebook and Twitter.

Editor's Note: The headline on this story was revised to avoid confusion and clarify that the incident occurred at Bates Middle School in Annapolis.

Broadneck Patch editor D. Frank Smith contributed to this article.