This was unsustainable even before silver prices went through the roof, says Jack McCall of AMSC (formerly American Superconductor), the world's biggest producer of HTS wires.
Earlier Wednesday, a fifth hole drilled down into the mine found just six inches of open space left between the roof and rubble in an 8-foot-high tunnel, said Jack Kuzar, a district manager with the federal Mine Safety and Health Administration.