The blog Bicultural Mom has a great post with instructions on how to add adminsitrators to your Facebook Page:
I always recommend to my students that they set up at least one backup admin to their pages. If you lose access to the only admin account, or get hacked or whatever, and you are the only admin, then you’ve just lost all access to your page. Pick someone you trust and set them up with admin access.
Also, if you have an employee as an admin, remember to remove their access before they leave your employment.