(a) Product process operations that finish leather for use in automobile and furniture seat coverings are categorized as an upholstery product process operation. There are two upholstery product process operations subject to the requirements of this subpart - operations with less than 4 grams of finish add-on per square foot, and operations with 4 grams or more of finish add-on per square foot. You must distinguish between the two upholstery product process operations so that you can determine which HAP emission limit in Table 1 of this subpart applies to your affected source.

(b) You must determine finish add-on by calculating the difference in mass before and after the finishing process. You may use an empirical method to determine the amount of finish add-on applied during the finishing process, as described in paragraphs (b)(1) through (4) of this section:

(4) After the finishing and drying process, weigh the representative section of substrate to determine the final mass. Divide the net mass in grams gained on the representative section by its surface area in square feet to determine grams per square foot of finish add-on. Equation 1 of this section illustrates this calculation, as follows:

Where:

Finish Add-On = Grams per square foot of finish add-on applied to a representative section of polyester film or equivalent material substrate.

Final Mass = Final mass in grams of representative section of polyester film or equivalent material substrate, after finishing and drying.

Initial Mass = Initial mass in grams of representative section of polyester film or equivalent material substrate, prior to finishing.

Surface Area = Surface area in square feet of a representative section of polyester film or equivalent material substrate.

(c) Any appropriate engineering units may be used for determining the finish add-on. However, finish add-on results must be converted to the units of grams of finish add-on per square foot of leather processed. If multiple representative leather sections are analyzed, then use the average of these measurements for selecting the appropriate product process operation.

(d) For each leather product with a unique finish application, you must maintain records to support how the leather product was categorized to a product process operations type. You must repeat the leather product categorization to a product process operation type no less frequently than once every 5 years if the applied finish chemical characteristics of the leather product have not changed, or when the applied finish chemical characteristics of the leather product change, whichever is sooner.