For the purposes of this chapter, the following terms are defined as follows:
(a) "Combustion for indirect heating" means the burning of fuel in equipment, such as steam boilers, water or air heaters, stills or brew kettles, where there is no contact between the products of combustion and the materials being heated.
(b) "Dust" means solid particulate matter capable of being air- or gas-borne.
(c) "Particulate matter" means any finely divided liquid or solid matter capable of being air- or gas-borne.
(d) "Process weight" means the total weight of all materials used in any process which discharges dust into the atmosphere. Such materials shall include solid fuels, but not liquid or gaseous fuels or combustion air
(e) "Smoke" means any visible emission into the open air from any source except emissions of an uncontaminated water vapor.
(f) "Smoke unit" means a measure of the quantity of smoke being discharged, which is the number obtained by multiplying the smoke density in a Standard Smoke Chart by the time of emission in minutes. For example, the emission of Standard Smoke Chart Number 1 for one minute equals one smoke unit.
(g) "Standard Smoke Chart numbers" means the numbers on the Standard Smoke Chart that coincide most nearly with the grids on the Standard Smoke Chart indicating graduations of the light obscuring capacity of smoke.