Liquid Sky with 150mw

Ok, so somewhat related to my first post about my eye anxiety, I got ordered this 150mw 405nm line lens laser to use as a liquid sky effect over dance floors. I realize I probably should have gotten a lower powered laser and made a scanner, but I figured this looked like a relatively easy way to produce a similar effect.

My question is with that power of laser, what type of surface should I have the beam terminating on so that if people on the dance decide to look up at the line, they will be 100% safe. Should I get some blackout curtains/material and apply that to where the line will be projecting? I plan on keeping it on for like 10-15 minutes at a time in a fixed position well above everyone's heads.

Should I just cut my losses and make a scanner with a lower powered laser? Would love any advice you could provide, very new here but want to make sure I do everything as safe as possible!

:beer: