Pottsgrove Middle School was evacuated this morning because several students were hospitalized after passing out, but investigators found no environmental hazard in the building.

A call about medical emergencies at the school, located at 1351 N. Hanover St., came in shortly after 10:15 a.m., according to Montgomery County dispatchers. The Pottsgrove School District said three students fainted during a choral practice. As medical responders were treating those students, others reported that they felt light-headed or dizzy.

In total, 22 students were taken to Pottstown and Phoenixville hospitals for evaluation. But the school district said emergency crews found no apparent environmental hazard in the building and no cause for most of the students' symptoms.

"It was panic that ensued, seeing the other kids who were sick," Superintendent Shellie A. Feola said.

She said the students had been treated and released from the hospitals and were doing "fine."

The choral rehearsal room may have been warm, Feola said, but it was not dangerously so. She denied reports that the stage lights were excessively hot.

Fire department investigators found no chemcial or environmental hazards at the school that would have caused the students' symptoms.

The middle school - which enrolls about 800 students - was evacuated while investigators probed the cause of the illness. Students were outside for about an hour; buses then took them to Pottsgrove High School, about a mile and a half away.

School officials say it's safe to return to the middle school, but those students are being kept at the high school today to accomodate the afternoon bus schedule. Parents are urged not to pick up their children until the end of the school day.

The middle school choral concert slated for tonight will be rescheduled.

The district was posting regular updates to its website, Twitter feed and Facebook page, and answering parents in real-time on social media. Still, many parents were unsatisfied with the notification system.

"Why are we getting more updates from the media than from the school district?" Amy Marazas asked on Facebook. "And WHY did I first have to hear it from a friend who was on FB getting a FB message from the Pottstown Mercury and NOT from the SD?"

A district spokeswoman answered: "Amy, the district was trying to craft a message with all the appropriate information and attempting to send it out over all media (Facebook, Twitter, Web Page, automated phone dialer, etc...). The Mercury and other major media follow the police scanners and were notified when the 911 call went out."

Another parent, Shannon Mullins Gruninger, wrote: "The phone call that went out WAS alarming. You can't say there is a medical emergency and the kids were evacuated but don't worry ... your kids are safe ... as a parent that makes me MORE alarmed and the fact that NOTHING has been sent since except they are at the high school but don't worry ... don't pick up your kid is ridiculous."

The district responded: "Shannon, we apologize but attendance needs to be taken so that we may verify that every child is present for the evacuation. Please continue to check for updates."

This story has been updated.

Contact Emily Babay at 215-854-2153 or ebabay@philly.com. Follow her on Twitter @emilybabay.