0--1.0)0.2 (0.1--1.3)0.2 (0.1--0.5)Silica dust in sections mg/m^3^, Median (Range) Crusher Attend0.6 (0.1--1.0)0.3 (0.1--0.9)0.3 (0.1--0.5) Blasting Tech/Foreman0.5 (0.2--0.9)0.4 (0.1--1.1)0.3 (0.1--0.4) Lasher0.4 (0.0--1.0)0.2 (0.1--1.0)0.2 (0.1--0.4) Driller0.4 (0.2--0.9)0.2 (0.1--0.9)0.2 (0.1--0.5) Trammer0.4 (0.2--0.8)0.3 (0.1--1.3)0.2 (0.1--0.4) W/shop foreman/Attend0.4 (0.1--0.7)0.2 (0.1--0.6)0.2 (0.1--0.4) Others-workman0.4 (0.1--0.9)0.2 (0.1--1.0)0.2 (0.1--0.4)Cumulative respirable silica dust mg.y/m^3^, Mean (SD) (Range)1.3 (0.7) (0.3--3.2)1.1 (0.5) (0.3--2.2)2.3 (1.0) (0.7--4.7)*SD* Standard deviation, *tech* Technician, *Attend* attendant, *W/shop* workshop

Medium and high CDE categories, age at certification, smoking status, and length of service were significantly associated with PTB (Table [3](#Tab3){ref-type="table"}). There was a statistically significant increasing trend (p~trend~ \< 0.01) of disease prevalence with increasing categories of dust exposure (low CDE = 2.5 % (3); medium CDE = 8.7 % (10) and high CDE = 17.1 % (21)).Table 3PTB status across the variables of interestCharacteristicsPTB cases\
(*n* = 34)No PTB\
(*n* = 323)Age at certification, years, Mean, (SD) ^a\*^34 (6.0)31.0 (6.2)Smoking status^b^ Non-smokers, n, (%)22 (64.7)273 (84.5) Current smokers, n, (%)^\*\*^12 (35.3)39 (12.1)Length of service, Mean, (SD) ^a\*^6.1 (2.0)5.1 (2.5)Sex Male, n, (%)34 (9.5)323 (90.5)Cumulative respirable silica Dust Exposure, Mean, (SD) ^a\*\*^2.2 (1.0)1.5 (0.9)Cumulative respirable silica dust categories^b^ Low, n, (%)3 (8.8)116 (35.9) Medium, n, (%)^\*^10 (29.4)105 (32.5) High, n, (%)^\*\*^21 (61.8)102 (31.6)\**p*-value \< 0.05; \*\* *p*-value \< 0.01^a^t-test^b^Chi-square test

The high CDE category, compared with the lowest category, was statistically significantly associated with PTB (OR = 6.4 (95 % CI 1.8--23.0)), after adjusting for age, gender and smoking status. Medium CDE showed a non-statistically significant elevated risk