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CARMEL, Ind. – The Indiana Department of Homeland Security has determined that a natural gas leak was the cause of an explosion at Carmel High School on Wednesday.

IDHS said Thursday that it appears the gas was ignited when a maintenance worker and contractor were doing routine services on two boilers on the school’s second floor. Officials don’t believe there was any boiler malfunction.

The city’s fire department says the workers were both injured in the blast and one suffered severe burns. Both were transported to Eskenazi Hospital for treatment.

Carmel Clay Schools says there were about 100 students at the school at the time of the explosion, but none were hurt during the incident. They were evacuated to the stadium locker rooms, where they reunited with their parents.

All activities at the high school are canceled until further notice.

Thursday, the fire department released photos that showed the extent of the damage: