Just in time for the spring storm season in North Texas, a high school gym is doing double duty.
The gym at Harmony Science Academy in Carrollton opened in December.
It's providing students with a place to play and peace of mind.
"It's a really smart idea," said sixth grader Pushpita Saha.
The gym is one of the few in North Texas that doubles as a tornado shelter capable of withstanding 250-mile-per-hour winds of an EF-5 tornado.
The walls are 15.5 inches thick, 9.5 inches thicker than typical walls.
The exterior doors are storm-tested and louvers release pressure preventing the roof from lifting in a tornado.
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"It's really just a big giant box of concrete," Linda Leonetti, project administrator for Heights Venture Architects.
Altogether, 3.4 million pounds of concrete were poured, equal to 136 school buses or 11 blue whales, the largest animal on earth.
The roof is made entirely of concrete. It's built like a parking garage and can withstand the weight of about 25 cars parked on top of it.
In 2015, tornadoes damaged schools in Glenn Heights and Van.
The same year, building codes were passed requiring new schools to include a tornado shelter.
"It's kind of nice to know that this building is so sturdy and that there's an element of safety here," said parent Victoria Fick.
Soon, four of Harmony's 17 North Texas campuses will have shelters including schools in Plano, Carrollton and two in Grand Prairie.
The gym can hold up to 1,200 people, enough for the entire Carrollton campus.
"This gym provides much more than just athletics," said eleventh grader Anisa Daou.
School officials said the shelter is about 40-percent more expensive to build than a typical gym.