The top coat is again, for first choice, a two part polyurethane. Its safe to use if you're not spraying, but I still recommend wearing a respirator. It'll have two charcoal filters. If it's working right, you won't smell ANY vapors. They're that good.
Isocyanite activator is poisonous.
Thats what killed hundreds of people in India when the Union Carbide plant had a accident venting to outside air. It will arrest your breathing as well as cause nerve or brain damage. It can be handled safely by an informed amateur, just like a power tool or car, but don't fool around. This is not like getting light- headed on lacquer fumes from a spray can and getting a headache. Outside, fresh air, not in a garage or basement with a water heater or furnace pilot light to ignite the fumes.