F Gas Regs and understanding them?

Hi Guys!
One for the trainers I suspect?
If a piece of kit fails and releases an amount of refrigerant.
At what point is the release notifiable?
Meaning bad practices etc. are reportable, is it necessary to report a loss of refrigerant from a system? If so at what amount does it become necessary.
I have several customers with exceptional questioning attitudes, particularly where environmental issues are concerned.
I was asked is a leak reportable and if so what size?
I did not know, hence the question!
Thanks Grizzly