It shall be unlawful for any person knowingly to permit the emission from any heating plant or from any apparatus in which fuel is consumed or smoke, vapor, or odor in excess of that which such heating plant or apparatus may reasonably be expected to emit, when the same is properly fired with suitable fuel, or to use automobile tires, rags, or other noxious substances for fuel, at any point in the city within a distance of 500 feet of any habitation located within any business or residential zoning district during a continuous period of more than five minutes or for more than two hours of each day.
('71 Code, § 3-1) Penalty, see § 10.99