Almost forgot about the solvents. The 2-part urethanes have solids content in the 35% range. The rest of the mix is organic solvents, which aren't very good for you either. Still, they are not as hazardous as isocyanates, and routine personal protective measures work against the solvents as well.

There are several upsides to spraying solvent based urethane out of doors. Ventilation is automatic. Using 40-50% reduction with a fast drying solvent like acetone, the stuff will be tack dry within an hour, reducing bugs and crud in the coating. So you can apply 3-5 coats in one day, instead of fussing with it for days. Let the final coat cure out for 2 weeks or so, buff it out with Meguiar's, and it's a done deal.