Naptha VS Mineral Spirits
I am a US finisher, Naptha is listed as Neil stated as a carcinegen as is no longer used or sold to walk in customers. it was replaced with Mineral Spirits over here, and White Spirits over there.
Naptha, is consided a fast evaporating solvent (4 - minutes) Whereas, the Mineral Spirits is much slower it takes 50 minutes to evaporate.
Over here, not every state has the same exact laws, some are very strick, while others are laxed, and are slow to comply with the goverment regulations.
Mineral Spirits, over here it is used in both Varnish and Polyurethane as the reducer.
MacS