(a)Manufacturing ceramic products (including roofing tiles, bricks, refractory bricks, tiles, stoneware or porcelain) by firing in kilns, where—
(i)the kiln production capacity is more than 75 tonnes per day; or
(ii)the kiln capacity is more than 4m3 and the setting density is more than 300 kg/m3,
and a reducing atmosphere is used other than for the purposes of colouration.