A Thai senior high school student died when an extinguisher blew up during a fire drill on his campus.

The event on Friday at Bangkok’s Rajavinit Mathayom School hurt 21 people, the city’s governor said. Seven were taken to hospital.

The blast sent the fire extinguisher flying toward the victim, who was about 10 meters away.

Rescuers said the fire extinguisher might not have worked because it had been in the sun or heat for a long time.

He was in his last year of school when he died. No one knows for sure how old he is.

Police have been trying to figure out what happened by putting up a fence around the scene, which was still full of broken things.

The fire extinguishers that were used in the drill have all been sent to the forensics section of the police.

The Ruamkatanyu Foundation, a relief group on the scene, said that the cannister that exploded had carbon dioxide in it.

When the extinguishers are empty, they are usually replaced with chemicals. However, the city’s police chief said, “How and where they were refilled must be looked into, and the safety valves must be checked.”

The school is in the Dusit area, which has a lot of government buildings.

Permanent secretary Atthaphon Sangkhawasee said that people from the Ministry of Education have also been sent to the school to find out what happened.

He told the family of the student who had died that he was sorry and that the ministry would help and pay them, according to The Nation.