To a certain degree there are quite a few things that all the systems have in common, Doc & Records control, Competence, Awareness & Training, and even the internal audit itself.
The challenge of competence I speak of is directly related to the differences between Environmental management, Safety Management and Quality Management. Do you have training in all of them? Do you have experience with all of them? Do you have a working knowledge of Environmental technology and science? Do you have an understanding of Risk management? What experience do you have in product realization? The list goes on.
Unless you can talk-the-talk and walk-the-talk when it comes to safety, environment and quality how can you effectively and honestly audit them?