Apolgies for the necro post, but i think i may have something relevant to add.
I use these a lot..admittedly I am based in the UK. perfectly safe when used properly, the biggest mistake people seem to make is that they don't prime the grenade..then wait...then wait a little longer...then screw the blank into the top. people do it in a rush, prime it put the cap on then BOOM. because a they have primed it they have missed the mark and set off the timer.
what terrifies me is the impact version, not the grenades themselves, but peoples propensity to prime them..then just stick them in a pocket without a pin in them. i havent seen it yet, but i have heard of people doing this, then falling over and setting off 5 impact grenades in their pockets. fortunately little damage occurred beyond some minor burns to his "mr squishy"
All in all these are a really well made and thoroughly useful bit of kit for cqb, but for the love of god..read the manual. Also. dont use them so much for woodland..they dissapear and when using them in cqb, make sure you are in the room pretty swiftly..in certain places they tend to "magically" disappear into peoples pockets