The day was organized by the University of Girona, according to local media, with the aim of getting children interested in science.
Images of the accident are circulating on social media. The video shows a smoking steel barrel, surrounded by a large audience. A man is on his knees by the barrel, after which the whole thing explodes.
According to the authorities of Catalonia, nine children are among the injured. The person conducting the experiment would have been most seriously injured. Five people had to go to hospital.
How the accident could have happened is under investigation.