Hah, I've been to plenty of Transmission raves in Prague as I'm from CZ and I remember quite a few times various close-encounters with their firework displays 
They used to have a wire going from the front of stage to the very back and launch rocket that was attached to the wire, so it was fully guided, however the sparkles of the burning aluminium powder that's used as propellant did reach couple of people at the end, but it wasn't this serious.
The most serious injury I've had from this production was Sensation White in O2 Arena in Prague during the "waterfall" of stars effect, when the fireworks were "dripping" down as fire fountains onto audience. Let's just say that some pieces of aluminium did not completely burn out when reaching the audience and I was hit on my shoulder, it did string but nothing serious, like a mosquito bite. But safe? No. Effective? Very much!
My mate got serious shoulder and back burns from Kavos party though, but yeah.. Kavos. Safety is a word that's forbidden in that town of vice
My kit: Mamba Elements V3 & DAC, ILD SOS & LaserCam, LaserDock DAC, Kvant Clubmax 1800 (2017)