Thanks so much for the thoughtful note. It’s something I worry about too, as I’ve had a giant industrial laser in my garage for a year or more.
I’ll start at the end: Don’t leave Glowforge unattended during prints. It’s unlikely anything will need your attention, but if it does, you should be nearby.
That said, the design was created from plastic that softens rather than ignites, and as you probably saw, the lid is a very solid piece of glass. It’s designed to fail in a way that does not spread any fire.
We’ve also added a number of safety systems to avoid all the major causes of fires we’ve seen in laser postmortems. For example, we won’t leave the head blowing air on the ember left from a cut - we shut off the air when the cut is done, unlike most systems. As another example, we can detect the collisions that are usually the start of a problem with our onboard accelerometers.
This isn’t something I’d let a child use unattended, but I worry about it less than, say, my blender when they’re around.
–dan