It's safe for anyone with a fairly decent tolerance to do a whole one, but people who are opiate inexperienced absolutely have to be careful. We're talking literally for someone not new to opiates but with a small tolerance, 5mg or 10mg will make them vomit and nod like hell.
My rl friend snorted a half a 20 of mine and he was fucked up and threw up a couple times, hes taken about everything around but hadn't had any opiates in quite a long time so his tolerance was low. It completely kicked his ass, he said it was the best drug hes EVER had.
Just watch out for tolerance / addiction, I got to the point after snorting Opana that I ran through all mine within a week or so every month. We were talking me doing 6-10 20mg opana er everyday until I ran out.