Electric current and humidity?

The christmas type lights do not use enough voltage to cause an arc through humid air to a person.

They would have to be a lot stronger than what they are to generate an electric arc. However, if he is that cavalier about placing lights in a potentially unsafe environment, I would be inclined to have an electrician look at his handiwork before climbing in the hot tub to celebrate his accomplishment. Yikes!

Who is your friend,,,,Kramer from Seinfeld !

sauna != hot tub

I wouldn’t be that worried about getting electrocuted from it. The voltage is so low that it wouldn’t matter.

I would be concerned about condensation forming on the wire for the lights and dripping into the outlet the lights are plugged into. But that is a simple fix. Just make sure there is a U shape bend in the cord that is lower then the outlet. That is assuming they actually plug in inside the sauna.

These lights won’t last very long in an extremely humid environment (corrosion and short-cicuits). I would be extremely concerned about proper grounding and GFCI protection in any “home built” like this; that is what could get someone killed (accidentally touching something not properly grounded). If the builder is not a licensed electrician, have it thoroughly inspected by someone who is. This could be a life or death matter.

Welcome to Fluther!

I second @stranger_in_a_strange_land ‘s recommendation for a GFCI—that’s one of the best options for very simple protection.

That, and test the GFCI after you install it with a GFCI tester.