Coating VOC Content and Compliance Rate

VOC 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. Thinner adds VOC to the numerator and adds volume to the denominator, but the added volume is not water, so it does not come back out -- and a coating with comfortable margin as supplied can exceed its limit as applied. 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.

VOC 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 volume to the denominator, with the water unchanged.

The 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.

Two divisions on numbers from a data sheet.

Estimate. AHJ and licensed professional govern.

Field names used by the API: coating_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