Coal dust Quartz Time UG (yrs) Approximately cumulative exposure = Intensity x yrs UG = mg/m3-yr   Intensity (mg/m3) Mean (max) Intensity (mg/m3) Mean (max) Mean(max)  Mean (maximum) Coal Dust Quartz Low rank coal(n = 699) 1.68 (6.91) 0.063 (0.88) 14.6 (23) 24.5 (159) 0.92 0.92 (20.2) High rank Coal(n = 670) 2.06 (6.00) 0.038 (0.31) 14.9 (24) 30.7 (144) 0.91 (7.4)

Table 4: Exposure was dissimilar between the two collieries.