I've spoken against people on here sensationalising smoke bombs been set off, describing them as flares. Most aren't flares, they are pretty harmless smoke generators, don't get hot don't have any flame.
The thing set off on the South stand side of the kop was a real flare. They burn very hot, designed not to go out when wet etc.
Very dangerous, would cause a really bad burn, probably to somebody not involved.
Setting that off in the ground is way OTT. They need to have a good think about the chance of something going badly wrong, especially to other people.