If they cannot use a lathe safely, they should not be operating an airplane,
or possibly even driving a car. Forbid anyone from using the lathe unless
they have verifiable training and use manufacturer recommended safeguards.

There are risks inherent in almost anything. People are hurt using
screwdrivers, electric drills, power saws and shears.

If it still is a concern, limit the use to adults and then have them sign an
appropriate release. In addition, you probably should already have some
liability insurance. The dangers from a lathe are much less than a rotating
propeller. I suspect more injuries occur using a drill press than a lathe.

Colin