1. A person shall not discharge into the atmosphere from any source whatsoever any air contaminant for a period or periods aggregating more than three (3) minutes in any one hour which is as dark or darker in shade as that designated as No. 2 on the Ringlemann Chart, as published by the United States Bureau of Mines; or of such opacity as to obscure an observer's view to a degree equal to or greater than Ringlemann 2 or forty (40) percent opacity. (H&S 41701)

  2. The provisions of Rule 410(a) do not apply to excessive visible emissions caused by:
  1. Failure of the emission to meet the requirements solely because of the presence of uncombined water.

  2. Smoke from fires set pursuant to Regulation 2 of the North Coast Air Basin.

  3. Smoke from fires set or permitted by any public officer in the performance of his official duty for the improvement of watershed, range or pasture. (H&S 41704c)

  4. Use of any aircraft to distribute seed, fertilizer, insecticides, or other agricultural aids over lands devoted to the growing of crops or raising of fowl or animals. (H&S 41704d)

  5. Open outdoor fires used only for cooking of food for human beings or for recreational purposes. (H&S 41704e)

  6. The use of orchard, vineyard, or citrus grove heaters which do not produce more than one gram per minute of unconsumed solid carbonaceous material. (H&S 41704f and 41860)