An Oklahoma town became the first in the U.S. to install bulletproof shelters in its school classrooms in February to protect students in case a mass shooting takes place.

The Healdton School District installed two bulletproof storm shelters inside its middle school, seven inside its elementary school, and plans to add a few to the high school, KOCO reported.

“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 KOCO.

Shaw tested one of the “Shelter in Place” models to show how they would protect people in a mass shooting. In a video posted on January 30, Shaw sat inside one of the bulletproof shelters while someone fired bullets as part of a ballistics test.

During the test, someone fired bullets from “every gun that has ever been used in a school shooting,” according to the “Shelter in Place” website.

Newsweek reported that the classroom shelters, which are eight feet by eight feet in length, cost about $30,000 each.

A company spokesperson said that prices for the shelter vary depending on its size, but the average price for a shelter is about $1,000 for every child it can hold.

The shelters in the Healdton schools can fit 35 students and two teachers. Shaw said that students would run to the shelters in the event of an attack while teachers would follow behind them and lock the shelter in place.

Healdton, a town with about 3,000 residents, was the first school system in the U.S. to use the bulletproof shelters in schools.