4.—(1) Subject to the following paragraph, no person shall use a dangerous substance or preparation in the treatment of wood.
(2) A dangerous substance or preparation may be so used—
(a)in industrial installations; or
(b)by professionals covered by European Community legislation on the protection of workers for in situ retreatment,
provided that the dangerous substance or preparation is applied only for an industrial or professional use and contains—
(i)benzo-a-pyrene at a concentration of less than 0.005 per cent by mass; and
(ii)water extractable phenols at a concentration of less than 3 per cent by mass.