Have you shouted to them and shone a light in to look for movement/cheeping? (Won't affect the temp. or humidity).
If absolutely intent on opening the 'bator again have a basin of slightly warm water and drop an egg in it gently....if it wobbles there's a live chick in there.
If absolutely intent on opening the 'bator again have a basin of slightly warm water and drop an egg in it gently....if it wobbles there's a live chick in there.