The Clean Air (Emission of Grit and Dust from Furnaces) Regulations 1971
Section 2 of the Clean Air Act 1968 contains provisions with respect to the emission of grit and dust from the chimneys of certain furnaces, and in particular empowers the making of regulations which prescribe specific limits on the quantities which may be emitted in particular cases. These Regulations prescribe limits applicable to certain furnaces, namely—furnaces of steam boilers and of appliances for the indirect heating of gas or liquid with a Maximum Continuous Rating of between—825 and 475,000 pounds of steam per hour (from and at 100°C. (212°F.)) or (the alternative being an equivalent)825,000 and 475 million British thermal units per hour andother furnaces of indirect heating appliances or in which the material being heated does not contribute to the emission, with a designated heat input of between 1·25 million and 575 million British thermal units per hour.