To be safe you should change names, places and identifying characteristics (don't just change a person's name, change their hair colour and height), and also make sure you keep a record of what you've changed and what the new name/place/etc is. Of course, I'm suggesting you do this on the presumption that what you've written is potentially defamatory, or may be construed as such, because that's the main reason to be nervous about using identifying details. But even if you're not defaming anyone else, it's often a good idea in a memoir to be vague about some of this information.
What intrigues me most about your question, though, is that fact that you're writing a 'Bill Bryson memoir' about working in a coal mine. My brain is trying to understand what that would be like!