Lower limits of concentration
18.—(1) Subject to sub-paragraph (2), in relation to preparations to which this Schedule applies no account shall be taken of substances, whether or not listed in the approved supply list, whether existing as impurities or as additives, if their concentration by weight is less than—
(a)0.1% for substances classified as very toxic or toxic; or
(b)1% for substances classified as harmful, corrosive or irritant,
unless in either case lower limits are referred to in Part V of the approved supply list, or in the case of gases in Part II.
(2) Where any substance has more than one health effect each of these effects shall be characterised by its appropriate specific concentration limit.