# 63.11412 What definitions apply to this subpart?
Terms used in this subpart are defined in the CAA, in 40 CFR 63.2, and in this section as follows:
*Bag leak detection system* means a system that is capable of continuously monitoring relative particulate matter (dust loadings) in the exhaust of a baghouse to detect bag leaks and other upset conditions. A bag leak detection system includes, but is not limited to, an instrument that operates on triboelectric, light scattering, light transmittance, or other effect to continuously monitor relative particulate matter loadings.
*Chromic acid* means chromium trioxide (CrO<sub>3</sub>). It is produced by the electrolytic reaction or acidification of sodium dichromate.
*Chromium compounds manufacturing* means any process that uses chromite ore as the basic feedstock to manufacture chromium compounds, primarily sodium dichromate, chromic acid, and chromic oxide.
*Chromium compounds manufacturing facility* means the collection of processes and equipment at a plant engaged in chromium compounds manufacturing.
*Chromite ore* means an oxide of chromium and iron (FeCr<sub>2</sub>O<sub>4</sub>) that is the primary feedstock for chromium compounds manufacturing.
*Chromic oxide* means Cr<sub>2</sub>O<sub>3</sub>. In the production of chromic oxide, ammonium sulfate and sodium dichromate that have been concentrated by evaporation are mixed and fed to a rotary roasting kiln to produce chromic oxide, sodium sulfate and nitrogen gas.
*Roasting* means a heating (oxidizing) process where ground chromite ore is mixed with alkaline material (such as soda ash, sodium bicarbonate, and sodium hydroxide) and fed to a rotary kiln where it is heated to about 2,000 F, converting the majority of the chromium in the ore from trivalent to hexavalent chromium.
*Sodium chromate* means Na<sub>2</sub>CrO<sub>4</sub>. It is produced by roasting chromite ore in a rotary kiln.
*Sodium dichromate* means sodium bichromate or sodium bichromate dihydrate and is known technically as sodium dichromate dihydrate (Na<sub>2</sub>Cr<sub>2</sub>O<sub>7</sub> • 2H<sub>2</sub>O). It is produced by the electrolytic reaction or acidification of sodium chromate.