It is a unique area in itself. Your experience in any aspect of nursing is always valuable and does account. The OHN role is usually has quite the responsibility from initiating and implementation of E/ee health programs, surveillance programs (lead levels, etc), and providing first aid and counsel'g (pysch/soc).
I used to work in OH and then returned to active (hospital) nursing. It was a challenge with respect to all the changes in medications, protocals, etc...but with a great orientation and determination, it all worked out.
Hope this helps.