An Oklahoma town reportedly installed bulletproof shelters in its school classrooms to protect students in the event of a mass shooting on campus.

The Healdton school district has installed seven bulletproof storm shelters in its elementary school and two inside the middle school, with plans to add shelters to the high school, KOCO 5 reported on Wednesday.

"When tornadoes strike, and Lord help us, when you have an intruder on campus, to know that you have somewhere to go quickly for the safety of your students, it's very relaxing," Terry Shaw, the superintendent, told the station.

Shaw tested one of the Shelter-In-Place models. He sat inside one while bullets were fired. The ballistics test used “every gun that has ever been used in a school shooting,” according to the company’s website.

The 8-by-8-foot classroom shelters cost about $30,000, Newsweek reported. A company spokesman told the outlet that the price depended on the shelter’s size, but averaged to cost about $1,000 for every child that can fit inside.

The Healdton shelters can hold up to 35 students and two teachers, KOCO 5 reported. The school superintendent told the station that in an emergency, students would run into the shelters while teachers followed behind them and locked it down.

The town of 3,000 people was the first district in the U.S. to use the bulletproof shelters in schools.