If you're at ≈30', then you're probably fine. Blanks are used on movie sets where the crews are safely situated sometimes at shorter than those distances. You'll definitely be fine at 30'. I'm no expert, but I might say that even 12' is fairly safe. I wouldn't recommend aiming for the eyes or face, though.
If you have multiple alleged blanks, and you want to feel safe, try firing them at the ground or at soft targets from a distance or no one is around.
I am not sure if this is relevant or not, but you might want to search the internet for any possible licensure are permits that you need in order to fire blanks off in your state or province, even for filmmaking purposes.