A false fire alarm at the beginning of second block resulted in a mass exodus of students and staff, as well as confusion about proper evacuation procedures.

The first alarm sounded in the big gym, which set off several other alarms nearby. Students and staff promptly exited the building. Some classes followed the previous year’s fire drill procedures and gathered around the building by second-block class. Others, however, followed the new evacuation procedure, implemented this year, in which students gathered by homeroom on the practice field, leading to incomplete classes and missing students.

After the fire department confirmed that there was no actual fire, students and staff were allowed to re-enter the building, though nearly a half an hour of class time had passed.

Principal Larry Wooldridge said that the incident would prompt a review of evacuation procedures, including where students should go and whether there would be a difference between planned fire drills and other evacuation procedures.

“We’re going to reevaluate and see what we can do better,” Mr. Wooldridge said.

The cause of the false alarm was unknown, though Mr. Wooldridge said it could have been anything from dust accumulation on the alarm to water pressure in the sprinkler system.

Zoe Schaver contributed to this article.