It's just some random all-purpose spray varnish (the spray-outdoors-don't-breathe-in-whilst-doing-it-type)
It's normally fine to handle once it's fully dry and stops smelling so since I have it, I'll be using that. It's likely no worse than whatever is used to finish the covers in the first place anyway. You can probably find some less lethal stuff if you go looking on the net though