Silica from Handheld Rock Drilling in Artisanal Mining: The Wet-Drilling Retrofit, Budgeted

Computed respirable crystalline silica exposure for dry handheld drilling in hard rock versus a gravity-fed water-feed retrofit, for surface and underground cases. SIMULATED, NOT MEASURED; nothing was built or field-tested. Dry drilling gives a driller 8-hour TWA of 4.29 mg/m3 at the surface and 4.59 mg/m3 underground; wet drilling at 92 percent suppression reduces these to 0.296 and 0.312 mg/m3, still 5.9 and 6.2 times the 0.050 mg/m3 limit. The retrofit kit costs $87, uses 1.47 litres of water per metre, and carries a 15 percent drilling-rate penalty. Because wet drilling alone does not reach the limit, a fit-tested P100 half-mask respirator is a forced additional layer.