There is no difference, as far as I know, either in the letter of electrical regulation, or in the biology of what happens during a shock, between an unskilled adult of any age, and an unskilled trainee doing an exercise at college or working alongside experienced hands as part of their apprenticeship or whatever.

As such the same health and safety regime should apply and the risk assessment of what folk are able to do at various levels in training needs to be performed by someone with practical as well as theoretical experience.

There is guidance out there that colleges and so on work to, but  I don't have up to date copy- probably others here do - Lyle may well for example.

Ideally no one would ever touch live metal with bare skin, inexperienced or otherwise, though how hard we should make that to happen accidentally does, of course vary with experience. In practice, some kit has to be configured with the lid open, so one or more of the layers of safety that would protect unskilled persons is then compromised, and folk like DNO jointing teams routinely work on live cables, relying heavily on procedure and the right tools to make the job safe - but of course they also avoid live metal to bare skin contact, just in a different way.

Equally consider the normal lamp holder - clearly not finger proof, but apart from in Tom and Jerry cartoons and The Addams family, it is very rare that anyone actually sticks their fingers in one, and they are used by unskilled persons.

As per above, there should always be defence in depth, i.e. multiple things must go wrong to reach a truly dangerous situation. For example training benches are also fed by RCD, and be on a dry non-conductive floor,  even though the users will have been taught the principles of isolation, and should only be touching terminals that are dead, and verifying they are before they do.

In terms of the biology, its not the voltage per-se that kills but also how long it is present for, and how much current is flows or is available during that time, and references to voltages should be tempered by an understanding of the type of contact - a large area of sweaty or damged skin is a much better contact than a finger tip so more dangerous, while a gloved hand is better than a bare one.
It is for this reason that there is gravel on the ground at substations - water drains, so there will be no puddles, and the contact between stones and foot is small pointy areas ,and the discomfort of feet on gravel means that even the most gung-ho folk are most unlikely to be wearing anything less than boots with a proper sole.

A shock hand to hand or hand to opposite foot crosses the bit with heart and lungs in and so is  the most  serious, and currents that are short duration compared to half a heartbeat period can be higher with reducing duration for the same risk of fatality - so  an electric fence is 10,000V but for a few  hundred microseconds, but an RCD must remove the mains from a person within 0.4 seconds at 230V, and rather longer at 110V.
So non conductive footwear, and ADS speeds are set this way ;-)

Its a bit of a ramble, but let's see what others say.

Mike.

of course when the trainees come to test RCD breaking times, an RCD protected bench may need something else to allow the test to not cut everything.
Mike.

Mike:

The best piece of safety advice I ever got was---  don't wear any metal on your body- like rings or tie clips !

Peter Brooks

Palm Bay 

Is there any specific guidance, code of practice or legislation which determines a safe working voltage for apprentices in a training facility (school)?

I'd add it might depend on the nature of the activity ... e.g. wiring a plug that is then inspected/tested by a tutor before being plugged by the student to complete the demonstration isn't quite the same as live working on bare live conductors (e.g. proving dead) - even though the same voltage is nominally involved in both. So maybe it's more a case of choosing the activity rather than the voltage.

   - Andy.

Is there any specific guidance, code of practice or legislation which determines a safe working voltage for apprentices in a training facility (school)?

I'd add it might depend on the nature of the activity ... e.g. wiring a plug that is then inspected/tested by a tutor before being plugged by the student to complete the demonstration isn't quite the same as live working on bare live conductors (e.g. proving dead) - even though the same voltage is nominally involved in both. So maybe it's more a case of choosing the activity rather than the voltage.

   - Andy.