I'm not a chemist, but from what I can tell it's created using cesium salt as a precursor or catalyst. This doesn't sound like something punks can safely mix in a bathtub.
I might be a chemist, and I'm not too concerned about the toxicity of the cesium carbonate. I'd be more concerned about the toxicity of the azide and azidirine intermediates. But if some "punks" can pull off a Knovenegal condensation and a Staudinger reaction in a bathtub, I would be quite impressed with their resourcefulness.
It sounds like extremely toxic organic chemistry. I imagine the waste from the reactions has special disposal requirements. Do you think the powder is hazardous as well?