I have used Nitrogen for years to purge tanks prior to welding on them
As stated Nitrogen makes up the majority of the gases in the air we breath and the only hazard would be if you confined it in an air tight compartment and displaced the Oxygen which could lead to suffocation but if your paint area is airtight you are going to have bigger problems than Oxygen displacement! Actually using Nitrogen would seem to be safer than compressed air because it would significantly reduce the danger of fire but my concern would be having enough volume on hand to do the job and finding a regulator/flow meter that would flow that kind of volume, might be a problem. You can get liquid Nitrogen in large cryo tanks at most welding/gas suppliers and these will contain as much gas as several pressure tanks and may not be a expensive as you might think. I have for years used these cryogenic tanks and the liquid Nitrogen to freeze steel pins and bushings to shrink them when the fit has to be really tight, this is a common procedure around the mines.