The blank itself is decently safe, but if there is any obstruction or object in the chamber then that basically becomes a bullet.
That’s what happened to Brandon Lee. The blank didn’t kill him, at least the real ones didn’t. They used improvised “blanks” in an earlier scene that looked like real bullets and even had a “bullet” in them. One of said bullet separated from its casing and became lodged in the barrel. When a real blank was fired, the explosion propelled the bullet stuck in the barrel and struck him.
The expanding hot gases of a blank, while dangerous, likely wouldn’t kill you on it’s own. Even pressed against the temple. It’d likely give you a concussion, hearing damage, and a pretty bad burn.