Terms used in this subpart are defined in the Clean Air Act, §63.2, and in this section as follows:

Area source means any stationary source of hazardous air pollutants that is not a major source as defined in this part.

Compliance ratio means the ratio of the actual HAP loss from the previous 12 months to the allowable HAP loss from the previous 12 months. Equation 1 in §63.5330 is used to calculate this value. If the value is less than or equal to 1.00, the source is in compliance. If the value is greater than 1.00, the source is deviating from compliance.

Deviation means any instance in which an affected source subject to this subpart, or an owner or operator of such a source fails to meet any requirement or obligation established by this subpart, including, but not limited to, any emission limits or work practice standards.

Drying means the process of removing all but equilibrium moisture from the leather. Drying methods currently in use include: toggling, hanging, pasting, and vacuum drying.

Finish add-on means the amount of solid material deposited on the leather substrate due to finishing operations. Typically, the solid deposition is a dye or other chemical used to enhance the color and performance of the leather. Finish add-on is quantified as mass per surface area of substrate, such as grams of finish add-on per square foot of leather substrate.

Hazardous air pollutants (HAP) means any substance or mixture of substances listed as a hazardous air pollutant under section 112(b) of the Clean Air Act.

Leather means the pelt or hide of an animal which has been transformed by a tanning process into a nonputrescible and useful material.

Leather finishing means a single process or group of processes used to adjust and improve the physical and aesthetic characteristics of the leather surface through the multistage application of a coating comprised of dyes, pigments, film-forming materials, and performance modifiers dissolved or suspended in liquid carriers.

Leather substrate means a nonputrescible leather surface intended for the application of finishing chemicals and materials. The leather substrate may be a continuous piece of material such as side leather or may be a combination of smaller leather pieces and leather fibers, which when joined together, form an integral composite leather material.

Leather tanning means the processes, commonly referred to as wet operations, used to purify and stabilize the collagen content of the hide. Wet operations are divided into three phases, the beamhouse (includes soaking and unhairing); the tanyard (includes bating, pickling, tanning, trimming/siding, and splitting); and the coloring department (includes retanning, coloring, and atliquoring operations).

Month means that all references to a month in this subpart refer to a calendar month.

Nonwater-resistant leather means nonupholstery leather that is not treated with any type of waterproof finish and, thus, cannot withstand 5,000 Maeser Flexes with a Maeser Flex Testing Machine or a method approved by the Administrator prior to initial water penetration. This leather is typically used for dress shoes, handbags, and garments.

Product process operation means any one of the four leather production classifications developed for ease of compliance with this subpart. The four leather product process operations are as follows: upholstery leather with greater than or equal to 4 grams finish add-on per square foot, upholstery leather with less than 4 grams finish add-on per square foot, water-resistant/specialty leather, and nonwater-resistant leather.

Specialty leather means a select grade of chrome tanned, bark retanned, or fat liquored leather that is retanned through the application of grease, waxes, and oil in quantities greater than 12 percent of the dry leather weight or high-quality dress or performance shoe leather that can withstand one or more of the following visual tests: moisture injection into the leather using vacuum mulling without signs of blistering, or prolonged ironing at 200 °F for smoothing out surface roughness without finish lift off. Specialty leather is also finished with higher solvent-based finishes that provide rich color, luster, or an oily/tacky feel. Specialty leather products are generally low volume, high-quality leather, such as specialty shoe leather and top grade football leathers.

Upholstery leather (greater than or equal to 4 grams finish add-on per square foot) means an upholstery leather with a final finish add-on to leather ratio of 4 or more grams of finish per square foot of leather. These types of finishes are used primarily for automobile seating covers. These finishes tend to be aqueous-based.

Upholstery leather (less than 4 grams finish add-on per square foot) means an upholstery leather with a final finish add-on to leather ratio of less than 4 grams of finish per square foot of leather. These types of finishes are typically used for furniture seating covers. The finishes tend to be solvent-based and leave a thinner, softer, and more natural leather texture.

Vacuum mulling means the injection of water into the leather substrate using a vacuum process to increase the moisture content of the leather.

Water-resistant leather means nonupholstery leather that has been treated with one or more waterproof finishes such that the leather can withstand 5,000 or more Maeser Flexes with a Maeser Flex Testing Machine or a method approved by the Administrator prior to initial water penetration. This leather is used for outerwear, boots and outdoor applications.

[67 FR 9162, Feb. 27, 2002, as amended at 70 FR 6360, Feb. 7, 2005; 84 FR 3322, Feb. 12, 2019]