1) Fire: You can build your entire machine on metal, that won't prevent the thing you are cutting from catching fire.
Nitrogen canister, regulator, pump to measure gas volume... enclosed container. Fire needs oxygen to burn.
The only deadly thing a Laser lacks is something that can explode and throw shrapnel at you. Now it have it.
2) Smoke: There's a reason most laser cutters have huge ventilation tubes. The laser will produce smoke, if you cut anything but wood it will be toxic smoke. Not good.
Seal the equipment in an air-tight chamber, vent it to atmosphere when safe or pass exhaust through activated-carbon.
Instead of toxic smoke now we have concentrated pressurized toxic smoke.
3) Laser: 40 watts is 100 times the power needed to instantly blind you. Lasers of that power are dangerous even bouncing on non-reflective surfaces. The laser is probable IR so invisible too.
Safety interlocks to prevent chamber from being opened while laser is active; Viewing ports made of laser-safe safety glass to absorb specific wavelength of laser beam (same as the safety goggles you should know to wear...).
Good luck absorbing 40 Watts in 0.1 mm^2 of glass though.
And IMHO the worst: The high-current high-voltage power source (10 KV or more) can instantly kill you.
Isolation transformer, sealed unit, zero-delay ground return fault interrupt from mains, capacitor buffered to smooth initial load during firing (which would otherwise trip the aforementioned). Proper grounding. Oh, and proper grounding. And proper. Fucking. Grounding.
Now you're right, these things are all dangerous and can kill you... but so can climbing into a hot tub if you're drunk. You can't make something perfectly safe, but you can make it reasonably safe. Your microwave also contains a power supply rated for similar voltages... and similar risks for body damage if the safeties are compromised.
Fair enough. When isolating the stuff remember 10 KV can kill you through a 5 cm air gap.
Yes the microwave can kill you that's why there are no DIY microwaves.
