A gas leak at Tracy High School forced temporary evacuation of classrooms on Tuesday morning, but students were back at work a half-hour later after the leak was isolated and the gas shut off.

“They got it shut off pretty rapidly,” said Tracy Fire Department Division Chief Andy Kellogg.

He said a blade from a grader tore open a low-pressure three-inch line on the construction site of the new 40-classroom building at the high school. A crew from PG&E helped shut off the line.

The smell of gas was reported in classrooms at the west end of the campus, right next to the construction site, after the mishap. A school-wide alarm sounded at about 9:20 a.m. and students and staff all went to the practice fields at the north end of the campus.

Principal Pat Anastasio said it was an orderly evacuation, just like fire drills the school has practiced in the past.

“That’s the safety precaution when you have a gas leak,” he said.

Anastasio and school security guards directed students away from the classrooms closest to the leak, and students returned to class about a half hour later.