An employer or self-employed person shall ensure that the exposure of a person to lead is either prevented or, where this is not reasonably practicable, adequately controlled: Provided that the control of the exposure shall be regarded as adequate if-
(a) the level of airborne lead is- (i) at or below the OEL; or
(ii) above the OEL but the reason has been identified and action has been taken, as soon is reasonably practicable to lower the airborne level by means other than respiratory protective equipment, so that it does not exceed the OEL for lead; or
(b) in the case of exposure to- (i) ingestible lead, the blood lead level is less than 20 μg/100 mℓ; or
(ii) lead alkyls, the urinary lead level is less than 120 μg /ℓ.