Coating VOC Content and Compliance Rate

ScopeVOC as supplied is pounds of VOC per gallon of the coating as it comes, and it is the number on the can. VOC LESS WATER divides the same VOC by the coating volume minus its water and minus any exempt solvents, and it is the regulatory basis in most coating rules. The less-water basis exists to prevent compliance by dilution: if VOC were measured per gallon as supplied, adding water to a solvent coating would lower the number without reducing the solvent applied per square foot of surface. So the rule subtracts the water and the exempt compounds and measures the VOC against what remains, which is roughly the material that forms the film plus the solvent in it. The consequence is that waterborne coatings can fail limits they appear to pass. A coating that is mostly water with a modest amount of coalescing solvent has a low VOC per gallon as supplied and can have a high VOC less water, because the denominator is small -- and the smaller the denominator, the larger the gap between the two numbers. That is a genuine and frequent surprise, and it is why a technical data sheet reports both and why the regulatory one governs. Thinning moves it further. A solvent thinner adds VOC to the numerator and its volume to the denominator, and a coating with comfortable margin as supplied can exceed its limit as applied; a water or exempt thinner comes back out of the denominator with the coating's own water, so thinning a waterborne coating with water does not change its less-water figure (Ohio EPA). That is the number a rule is enforced against, so it is the one this reports as governing whenever a thinner is entered. Exempt solvents are compounds EPA has determined are negligibly photochemically reactive, and the list is specific and changes; treating a solvent as exempt because it seems similar to one that is will produce a wrong answer. This computes content from ENTERED volumes and masses off a technical data sheet. It does not determine which compounds are exempt, apply transfer efficiency credits that some rules allow for high-efficiency application equipment, address VOC limits expressed per gallon of SOLIDS, compute emissions from usage, or determine which rule applies. The technical data sheet, the applicable coating rule, and the permit govern.

Formula or tableVOC as supplied = lb of VOC / gallons of coating; VOC less water = the same VOC / (gallons of coating minus water minus exempt solvent); as applied adds the thinner's VOC to the numerator and its non-water, non-exempt volume to the denominator (a water or exempt thinner leaves the less-water figure unchanged).

Source and editionThe VOC content bases as coating rules define them, with less water the regulatory basis in most rules. Volumes and masses are ENTERED from the technical data sheet. It does not determine which compounds are exempt (the list is specific and changes), apply transfer-efficiency credits some rules allow, address limits expressed per gallon of SOLIDS, compute emissions from usage, or determine which rule applies.

Free accessTwo divisions on numbers from a data sheet.

What governsEstimate. AHJ and licensed professional govern.

API field namescoating_gal, voc_lb, water_gal, exempt_gal, thinner_gal, thinner_voc_lb_per_gal, limit_lb_per_gal, voc_as_supplied, voc_less_water, applied_voc_less_water, governing_voc, margin_lb_per_gal

• Exempt compounds are entered the list is specific and changes, and similarity is not exemptionthe applicable rule
• No transfer efficiency credit some rules credit high-efficiency application equipment separatelythe coating rule
• Not a usage-based emission estimate this is content, not tonsthe permit