I’ve lived through a few demo accidents. In high school we cracked a few windows doing the “blow out a jack-o-lanterns face” trick. My freshman year at university saw a lecture auditorium’s smoke alarm set off by the screaming gummy bear demo. But this… How dense do you have to be to see a methane bubble sitting next to a sprinkler head and light it not once, but twice.
I do not envy those kids. Fire system water tends to just sit in a cistern getting fouler and fouler till it finally gets used. The shower is not a pleasant one.