I've seen the advice that musicians should never go barefoot at concert venues/clubs, given nontrivial risk of incorrectly grounded amps and PA's, but i can't f

I've seen the advice that musicians should never go barefoot at concert venues/clubs, given nontrivial risk of incorrectly grounded amps and PA's, but i can't find a source on googles 1st 10 results ("musician barefoot, electrocution, incorrectly grounded PA"). Below link is similar advice: don't plug in amp while kneeling on wet ground, essentially, don't complete a circuit through your heart http://www.noshockzone.org/stopping-hums-buzzes-and-shocks-on-stage-%E2%80%94-part-1-volts/ http://www.noshockzone.org/stopping-hums-buzzes-and-shocks-o...