FARMINGTON — Low water pressure triggered the alarm on a sprinkler system at Mt. Blue High School early Wednesday morning.

Students had just started the first class of the day when the fire alarm sent them out of the building at 8:21 a.m. They waited for nearly a half hour while Farmington Fire and Rescue checked the building.

The cause of the low water pressure was unknown, Fire Chief Terry Bell said. When the pressure drops, it triggers the alarm, he said.

The alarm went off in the portable classroom units and the nearly completed gym, Superintendent Michael Cormier said. All students, about 730, and all teachers left the building, he said.

abryant@sunjournal.com