Oddly enough, I'm not too worried about eye safety, from the normal laser viewpoint at least. At 10.6 microns the beam is an eye hazard more along the lines of a sharp stick rather than a visible laser. By the time it gets to your retina, it's boiled everything else in the way... Organic matter, water, things like that, are completely opaque at CO2 wavelengths.

It won't reflect off anything other than metallic surfaces and if that happens after the lens, the divergence is so large that a metre away you just get a warm face. 100W is a lot focussed to a few microns across but not very significant when it's a few centimetres across instead.

If you managed to get a good reflection without the lens in the way, at close range it could be nasty, but goggles would have no real use, it would go through them instantly, as would be the effect with the normal transparent acrylic lids even the commercial ones have. Those are tinted acrylic more to reduce the light from some materials being cut (glass reinforced plastic is amazing, it's like a tiny carbon arc torch and lights up the whole room) than to prevent the beam getting out and running around the place.

It's nothing to be disrespectful of, very true, but it's dangerous in a way that's quite unlike visible light or near IR lasers. Those are a definite eye hazard at significant ranges with any real power behind them. A CO2 laser is more likely to either electrocute you, or badly burn you along the lines of a gas torch, than cause eye damage in the way you might think when you hear 'laser'.

Some of the little DIY laser engravers I've seen that use high powered bluray violet lasers, a couple of watts at 445nm, on the other hand, terrify me from that aspect It may not sound like much, but that wavelength is a particularly bad one. Not only is it very close to the wavelength that the lens in the eye can focus to the smallest possible spot, it's also one that the human blink reflex doesn't really respond to AND almost the exact right frequency for maximum absorbance by haemoglobin, so it focusses down to a tiny spot, boils the blood, and blows holes in your retina far larger than seems reasonable... Yuck.

I have a couple of laser diodes at that wavelength and power. I ALWAYS wear the relevant safety goggles when using them even at very low power. At 2W just the diffuse reflection off the wall can be be more than enough to cause permanent eye damage. I've seen some pretty dangerous looking applications for them from people who don't seem to quite understand how hazardous they really are.

In the longer term, though, yes, there will be a cover.

A 40W laser is more than enough to be very useful, my little benchtop one is that class, although measuring the actual power shows it's more like 32W at maximum current, and even there the beam quality goes down the toilet if you run more than about 25W or so. You get a much cleaner cut at lower power rather than winding it all the way up to 11. The critical thing for the best results is to keep the tube cool. Ideally it wants to be around 10 degrees C or so, which needs an actual refrigerated chiller rather than the fan cooled heat exchanger that a lot of applications use. By the time it hits 25 degress the beam is getting ropy, certainly on the small ones.

They're damn useful and good fun, laser cutters

pca