Hi,
As mentioned it can depend on the individual and their past experience.
If a person is brand new to renal but has general engineering skills I would still leave it around 2 years to be able to carry the weight of an entire technical service on your shoulders. This is only my personal opinion though.
With us having a large home dialysis service the majority of our on-call enquiries come from home patients at all times of the night. You need to know the machine and its menus like the back of your hand to be able to explain to an individual who is usually flustered and panicking what to do when you can't see what's going on and you might be half asleep yourself! To apply that kind of pressure to a "newbie" can make them or break them plus unknowingly it can also have a lasting affect on a home patient and their relationship with both home dialysis and the techs.
Water plant failure is also another one that fills everyone with dread when you have a consultant and an entire nursing team breathing down your neck asking when is the water going to be back on because there's another shift of 30 patients waiting for dialysis and another 30 after that with nowhere to go. You need to be able to problem solve (sometimes for other staff disciplines too!) make a decision (the correct and safest one), give reason for it and stand your ground with the medical staff if required.
I suppose it depends on what kind of responsibility your on-call tech has and over how many different sites. If it is just moving machines about or similar then i suppose you could place someone on-call sooner. You will know by working with them day to day if they're ready to be able to handle anything that can be thrown at them.
For me your technical knowledge of machines, water plants, clinical knowledge and also knowledge of standard operating procedures within your trust needs to be at an optimum when on-call and I think it takes time to develop all that.
Ian Wilde