Quote:do you have any reference for what 400 ppm is qualitatively like?
400ppm for naphtha would be 1.6g/m3. So if the volume of your room is, say, 30m3 then, if you evaporate 48g of the solvent and let it spread around the room, you will reach the exposure limit. When you are working close to the fumes, your exposure is higher though.
Quote:it's hard to know if there are long term effects to worry about
The "VM&P" naphtha (petroleum benzine) is a mix of pentane, hexane, heptane, octane, nonane in unknown proportions, as well as cyclical hydrocarbons (cyclohexane, etc.) possibly with trace amounts of aromatic hydrocarbons (benzene, etc.). Out of the above, the least desirable are benzene (proven human carcinogen) and hexane (metabolizes into neurotoxic 2-hexanone and 2,5-hexanedione). The peripheral nerve damage is permanent and irreversible, but it takes several weeks of daily exposure to develop the symptoms.