Thank you Sheri so much for your reply to this query. Your approach and lessons learned are most helpful.

Yes, hearing and lung function testing annually.

Thank you and all respondents for your helpful advice regarding this matter.

Outside of using a registered safety professional from the HASANZ register to conduct an annual audit against legislative and good practice standards, they could consider the TELARC product 'Q-Safe' certification. From experience this is a well put together standard and I believe is backed by WorkSafe, CHASNZ and the EMA. Not half as expensive as an ISO certification and worth a look.