refresher training for what?

Unless there's an external standard that requires 'refresher training', why would you do it at all? I'm referring of course to skills that are regularly exercised at work after the initial training and competence assessment, not to things like emergency response where the skills may not be exercised regularly. If the crane is being used regualrly, your normal supervision systems should pick up any evidence that the operator's skills are not what they should be. If there's no such evidence and you want reassurance, don't bother redoing any training, just carry out whatever competence assessment was used originally. If the person passes, you've just demonstrated no need to waste resources on 'refresher training'. If they have any areas of weakness, just 'refresh' these and retest. Initially you could do the competence reassessment at the same interval as the previous refresher training. If every operator passes easily, you could extend the interval - just as you would with inspection/maintainence intervals for equipment.

I'm with imwaldra.

I would agree with the above. But: Would you only apply this to safety critical roles? Would you want a welder tested every 3 years if he is doing the job every day? compared to: A Loading shovel driver who does the job every day being refreshed every 3 years? Who and what would be required to be refresher trained and on what equipment?