The Dark Smoke (Permitted Periods) (Vessels) Regulations 1958

3.—(1) Emissions of dark smoke from a chimney of a vessel for not longer than the period specified in column (2) of the schedule to these regulations in respect of the class of case specified in column (1) shall be left out of account for the purposes of section 1 of the Clean Air Act, 1956:

Provided that—

(a) continuous emissions of dark smoke caused otherwise than by the soot blowing of a water tube boiler shall not exceed

(i) in the case of classes 1 and 2, 4 minutes;

(ii) in the case of natural draught oil-fired boiler furnaces in class 4, 10 minutes; and

(b) in no case shall black smoke be emitted for more than 3 minutes in the aggregate in any period of 30 minutes.

In this paragraph “black smoke” means smoke which, if compared in the appropriate manner with a chart of the type known at the date of the passing of the Clean Air Act, 1956, as the Ringelmann Chart, would appear to be as dark as or darker than shade 4 on the chart.

(2) For the purposes of the said schedule a vessel is not under way when it is at anchor or made fast to the shore or bottom, and a vessel which is aground shall be deemed to be under way.