Great question I was asked just recently. Now usually I would say when a new employee starts working with you.
However, I have recently had a client that has moved work premises, so we have decided that an induction session is required.
I have suggested the following topics are covered for them:
Fire Procedures
First Aid Procedures
H&S Policy
Health & Safety Procedures
Policies
Emergency Procedures
Open/Close Checks
Maintenance Procedures
A different business will have a different set of induction topics that will need to be covered.
All of this information will be explained and shown to the staff and then they will be able to ask any questions they may have and finally sign off understanding and acceptance.