I know primers use perchlorates and some other oxidizers and sensitizers that I won’t mention on here. The exact explosive compound I’m not sure but they seem to be rendered safe when wet to handle, but then when they dry it can go back to being explosive.
Just my 2 cents but I’m really just sub’d out of curiosity if anyone else knows of a tool.
I've been loading for 55+ years, so....don't know how many live primers I have removed, however I have always used my press and a decapping die. I've never had an issue. Also as dfanonymous wrote put it back into the gun, if you have it, and fire the primer off.
I usually just either load the case with primer or fire it. Yes I have deprimed cases using standard dies and a press and haven't had an issue. But I've also seen people set off whole primer tubes while loading too. So now I just either fire them or load them. Some distributers sell primed cases that have had the bullets pulled. I just remove the decapping pin, neck size to clean up the case mouths and then load.
I don't know of a tool designated SAFE for this, I've decapped my share of live primers in a press. Just don't ram and jam, feel the pin contact the primer, nice easy push out. Remember one thing, if the primer detonates, it is coming out of that piece of brass, so if your primer retention system is a slot in the ram of the press, you do not want to be standing in front of it, get off to the side. Or if it is a coax type, remove the container that catches them and put a garbage can underneath to collect them.
do not bother the only way to DEACTIVATE a primer is to fire it. THEY ARE PUT TOGETER WET AND ALLOWED TO DRY. LOTS OF TESTS, but bottom line when they dry they are active again, So' use a press and PUSH them out. they are an IMPACT EXPLOSIVE. do not bang on them with the press oh and yes you can reuse them.
I use a standard "decapping die" made for 22-45 cal from RCBS. Never had a detonation. For all my rifle brass, there is no capture of gas by what a full length die might provide. Safety glasses are a must. I consider the primers as non usable after removal. They are cheap by my standards and don't want a problem trying to re-use.
Salvaged hundreds over the years. Never had one go off while depriming and they have all fired when reused. They go in a separate flat marked "used"....use them for foulers, load development and practice (hunting loads get "new ones"). I use a press, safety glasses, ear protection and go slow. Remember when primers were less than .50 cents a flat at $4 to more than $5 now they are not "cheap".