A worker emerges from the deadly tunnel.

As the men drilled and blasted a tunnel through the mountain, they drilled through rock that contained high levels of silica. The dry drilling technique that was used released large amounts of silica dust into the air. Black diggers emerged from the hole in the mountain covered with layers of white dust. The interior of the tunnel was a white cloud of silica, impairing vision and clogging the lungs of workers.