Hi Poppet,
For your discussion you could say that in order to make judgements on skills and knowledge of anything an assessor should have the skills and knowledge themselves.
However, it could be argued that an assessor who has undertaken specific training such as skin care (including pressure care), risk assessment, infection control and handling and moving etc. and who has worked with the group at risk, is able to assess a candidate in the same way that a first aid trainer is able to assess a trainee on a course without having the experience of dealing with every incident they teach.
If in doubt the lead IV can request clarity from the EV.
Hope that helps
Aunty Sue | 
