Is it safe/effective to use butane for supercritical fluid extraction of cannabis oils?

My friend wants to make some blender hash but I've been wanting to try and make some blond hash for a while and I read a tutorial online that uses butane. My friend is a little wary about two things, he doesn't want to smoke butane, and he doesn't think it will extract the thc. I am asking A. will butane evaporate like alcohol if we let it sit out for a while, and will the leftover oil be safe to smoke, and B. will it even work? Is it efficient? Are we going to waste thc? are we even going to get any?