Tim Daneliuk wrote:

So ... what - if anything - can I use to heat a garage safely
that is: a) Not electrically powered, b) Won't kill me of CO
poisoning, and c) Won't ignite sawdust as it flies around in the air?

Natural gas or propane devices, vented to the outside. You can get a
unit heater (with a fan) or else a radiant heat device.

If the area isn't insulated you're going to waste a lot of energy.

Chris