in respect of an employee other than a young person or a woman of reproductive capacity, at least every 6 months, but where the results of the measurements for individuals or for groups of workers have shown on the previous two consecutive occasions on which monitoring was carried out a lead in air exposure greater than 0·075 mg/m³ but less than 0·100 mg/m³ and where the blood-lead concentration of any individual employee is less than 30 μg/dl, the frequency of monitoring may be reduced to once a year;

in respect of any young person or a woman of reproductive capacity, at such intervals as the relevant doctor shall specify, being not greater than 3 months.