Can you deliberately rig a hydrogen flask from a plasma weapon to explode like an emergency weapon? Can you shoot a hydrogen flask to detonate it? Cod you attach a grenade to one to detonate it?

What ever suits your story.

You should keep in mind tho that a Flask on its own is not really dangerous. It still requires energy to turn it into plasma and just a grenade wont do much.

A flask on its own is not something I would consider beneficial to an explosive in a meaningful way.

hmmm, I'd noticed a quote in the rules somewhere about improper handling of a photonic hydrogen flask had probably lead to the invention of the plasma grenade.

I always viewed them as being in need of some kind of high and concentrated initial energy spike to get really nasty tho the hydrogen being compressed on its own might also have some kind of an effect.

Strapping a Grenade on them imho would not realy be enough to my imagination to make them go "mini sun" but in the end you can do what ever suits your campaign.

Interesting, as a pressurised hydrogen container is would go boom nicely, and readily around any ignition source (or even a hot enough object). But the temperature of the explosion and the fact that it burns off very quickly means it isn't as dangerous as promethium. Maybe if you fired at it one with a plasma or melta gun you might end up with a plasma grenade.

Not sure how misshandling would lead to that.

Well, I could see it as adding some oomph to a plasma grenade if it we're attached to one, but not to the residual effect. I imagine one night go boom if hit by a plasma or high power Las shot. It would not have that residual effect.