(A) Occupations to which articles 20(b)(i) and 24(2)(b)(ii) refer -

1. Any occupation involving -

(a) the mining, quarrying or working of silica rock or the working of dried quartzose sand or any dry deposit or dry residue of silica or any dry admixture containing such materials (including any occupation in which any of the aforesaid operations are carried out incidentally to the mining or quarrying of other minerals or to the manufacture of articles containing crushed or ground silica rock); or

(b) the handling of any of the materials specified in subparagraph (a) in or incidental to any of the operations mentioned therein, or substantial exposure to the dust arising from such operations.

2. Any occupation involving the breaking, crushing or grinding of flint or the working or handling of broken, crushed, or ground flint or materials containing such flint, or substantial exposure to the dust arising from any such operations.

3. Any occupation involving sand blasting by means of compressed air with the use of quartzose sand or crushed silica rock or flint, or substantial exposure to the dust arising from such sand blasting.

4. Any occupation involving work in a foundry or the performance of, or substantial exposure to the dust arising from, any of the following operations -

(a) the freeing of steel castings from adherent siliceous substance;