Calculations: VOC, HAP, Exempt Compounds

CALCULATING VOC FOR WATER THINNED COATINGS

Q. When considering the VOC content of thinned coating (minus water and exempt VOC), I have found that the addition of water or exempt VOC leaves the VOC content (minus water and exempt VOC) of the thinned coating the same as the original coating prior to thinning. The amount of water or exempt VOC added is irrelevant to the calculation. All well and good, but I am not 100% comfortable. So my question: are the following statements true:

1. The VOC content (minus water and exempt VOC) of a coating thinned with water or exempt VOC is identical to the VOC amount (minus water and exempt VOC) of the unthinned coating.

2. A coating can not be "thinned into compliance" by adding water or exempt VOC.

A. Your observations and assumptions are correct. The VOC content (lbs VOC/gal, less water and exempt compounds) is the same no matter how much water or exempt solvents you add. The compliance status (lbs/gal, less water or exempt compounds) does not change regardless of the amount of thinning that takes place. Thinning does not help you get into compliance.

However, the number of gallons of thinned coating used to do the job DOES change. The more you thin the coating, the greater the number of gallons will be needed to get the job done. Therefore, when you calculate your total emissions from a spray booth you need to know how many gallons of actual thinned paint were used, and then multiply this by the actual amount of VOC in a thinned gallon. 

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