(a) No person shall cause, suffer or allow to be emitted into the open air from any fuel burning equipment, internal combustion engine, premises or open fire any smoke, the shade or appearance of which is equal to or darker than No. 2 of the Ringelmann Chart, except the following:
(1) Smoke, the shade or appearance of which is equal to but not darker than No. 2 of the Ringelmann Chart for a period aggregating four minutes in any thirty minutes; or
(2) When building a new fire or blowing down or clearing flues, or when breakdown of equipment occurs such as to make it evident that the emission was not reasonably preventable, smoke, the shade or appearance of which is equal to but not darker than No. 3 of the Ringelmann Chart for a period aggregating three minutes in any fifteen minutes, provided that, wherever possible, flues shall be blown down or cleaned during the nighttime.
(b) For the purpose of grading the shade or appearance of smoke, the Ringelmann Chart as now published and used by the United States Bureau of Mines, which Chart is made a part of this chapter by reference, shall be the standard.
(c) No person shall cause, suffer or allow to be emitted into the open air from any fuel burning equipment or premises, or to pass a convenient measuring point nearest to the stack outlet, dust in the gases to exceed 0.85 pound per 1,000 pounds of gases, adjusted to fifty percent excess air for products of combustion. However, for fuel burning equipment constructed or installed subsequent to the effective date of this chapter, special dust separating equipment with up to eighty-five percent efficiency may be required, and for fuel burning equipment constructed or installed prior to the effective date of this chapter, special dust separating equipment with up to seventy-five percent efficiency may be required. The limitations given shall be waived during periods when the breakdown of equipment occurs such as to make it evident that the emission was not reasonably preventable. The amount of solids in the gases shall be determined according to the Test Code for Dust Separating Apparatus of the American Society of Mechanical Engineers, revised and amended to the date of the adoption in this chapter by reference.
(1979 Code Sec. 15.20.040)