In May 1994, the National Institute for Occupational Safety and Health (NIOSH) considered crystalline silica to be a potential occupational carcinogen as defined by the Occupational Safety and Health Administration’s (OSHA) carcinogen policy [29 CFR 1990], and this information was used in establishing the NIOSH Recommended Exposure Limit (REL) at 50 µg/m3 . NIOSH has long realized that occupational overexposure to respirable crystalline silica (RCS) dust can lead to the development of silicosis, an incurable and often fatal lung disease, but it can also result in health problems that include chronic obstructive pulmonary disease, tuberculosis, chronic bronchitis, emphysema and chronic renal disease. Probably the most significant occupational travesty that brought focus to the effects of silicosis was the Hawk’s Nest Tunnel Disaster in southern West Virginia where a 4.83-km (3-mile) tunnel was driven through the Gauley Mountain. The material being removed during the mining of this tunnel for the development of a hydroelectric power plant was a sandstone and limestone ore containing very high levels of crystalline silica. Within months of the completion of this work, 476 of the workers died from acute silicosis [2,3]. This acute silicosis was caused by extremely high respirable dust concentrations while driving this tunnel and was attributed to inconsistent dust-control methods, including poor ventilation and minimal use of water, not allowing the dust to settle after blasting occurred before workers returned back inside the tunnel and no use of respiratory protection.