An 8 by 9 foot area enclose the area immediately inside the shop garage door. 3 inexpense house box fans provide positive pressure to the room. When in use I open the garage door a few inches for exhaust. The fan push clean air for greater fire safety.
You can see the 6 inch metal duct across the cieling and down the wall of the paint booth. I pull fresh air from outside my shop to feed my pressurized painting mask. A 6 inch duct booster fan pushes enough air to my mask to create a positive mask pressure and plenty of fresh outside air for breathing. It is a full face mask that includes eye protection.