A 5-year-old boy was killed and his mother was injured Friday after a hyperbaric chamber exploded at a medical facility in Troy, Michigan.

The chamber contained 100% oxygen, making it extremely flammable, according to Lt. Keith Young of the Detroit Fire Department.

Officers and firefighters responded to the explosion shortly before 8 a.m.

"Upon arrival, the first responding units unfortunately discovered a 5-year-old boy deceased on the scene," Lt. Ben Hancock of the Troy Police Department said at a press conference.

The boy’s mother was standing next to the chamber when it exploded and suffered injuries to her arms, officials said. A few medical staff members were also present but were not seriously hurt.

It’s not clear what kind of treatment the boy was receiving at the time.

The explosion was contained to the chamber and firefighters quickly brought the fire under control, they said.

"I've been with the department for 10 years, and we've never responded to anything like this," Young said.

The cause of the explosion is still under investigation, and multiple state agencies are involved in examining safety regulations at the facility. In the meantime, the medical center remains closed.