where:
R = Maximum allowable thinning ratio for a given batch (L thinner/L coating as supplied);
Vs = Volume fraction of solids in the batch as supplied (L solids/L coating as supplied);
VOHAP limit = Maximum allowable as-applied VOHAP content of the coating (g VOHAP/L solids);
mVOC = VOC content of the batch as supplied [g VOC (including cure volatiles and exempt compounds on the HAP list)/L coating (including water and exempt compounds) as supplied];
Dth = Density of the thinner (g/L).
If Vs is not supplied directly by the coating manufacturer, the owner or operator shall determine Vs as follows:
where:
mvolatiles = Total volatiles in the batch, including VOC, water, and exempt compounds (g/L coating); and
Davg = Average density of volatiles in the batch (g/L).
The procedures specified in § 63.786(d) may be used to determine the values of variables defined in this paragraph. In addition, the owner or operator may choose to construct nomographs, based on Equation 1 of this subpart, similar or identical to the one provided in appendix B of this subpart as a means of easily estimating the maximum allowable thinning ratio.
where:
Vth = Total allowable volume of thinner for the previous month (L thinner);
Vb = Volume of each batch, as supplied and before being thinned, used during non-cold-weather days of the previous month (L coating as supplied);
Rcold = Maximum allowable thinning ratio for each batch used during cold-weather days (L thinner/L coating as supplied);
Vb-cold = Volume of each batch, as supplied and before being thinned, used during cold-weather days of the previous month (L coating as supplied);
i = Each batch of coating; and
n = Total number of batches of the coating.
40 C.F.R. §63.785