I am about to run a test sheet on a non-PG material- just to have a settings chart for it. Before doing so I’ve done some research on the boards to see what others have done.; and I have a question-- What do I do if it catches fire?
Should I just never test cut/engrave at low speed/max power? If it does catch fire (some of the sheets I’ve seen on here look like they did) do I just stop the process?
So yeah. What do you do if materials start burning? 
Thank you!
Crack the lid to stop the machine. Having a damp rag handy will work. In case of flair up just lifting the lid cancels the job and the head retreats to the upper left corner. Just drop the rag on the flame. Having a squirt bottle handy would be a good idea too.
Paper like corrugated cardboard is one thing to monitor closely, but wood generally doesn’t pose much risk.
Lift the lid immediately which will stop the unit from firing instantly. Keep a damp cloth nearby if you’d like.
That said, you may sometimes see some flame that quickly gets put out by the air-assist. But “a fire” would be something to worry about.
Awesome! Thank you! I never thought about a damp cloth or a spray bottle. Obvious choices. (I did buy an extra fire extinguisher just for my glowforge area just in case haha) I just didn’t want to ever have to actually use it.
Thank you!!!
“Put it out” is good advice. 
Also…Support has some good info at https://glowforge.com/support/topic/safety/safety-overview
The safety sheet I read before and during setup just made me worried that if a fire started at all (even one I could put out with a wet cloth) that I needed to use an extinguisher or something. Or, I know this is going to sound silly, but if one started and I opened it to toss a wet cloth on top it would get bigger from the increase in air.
I figured better to ask then to whip out an extinguisher for no good cause.
Absolutely!
I thought about that too, but there is already a flow of air into the machine, from the intake and through the cracks around the door. The material wouldn’t burn at all if there wasn’t. So opening the lid doesn’t increase the air, it just kills the beam.
Thanks for writing and thanks @dwardio! Since your question deals with materials from other suppliers, I’m going to move it to Beyond the Manual so the community can continue to offer advice.