Case Study

Abstract

Occupational exposure to silica in the construction industry has been well documented,(1–7) and respirable crystalline silica (quartz and cristobalite) has been associated with silicosis,(8,9) lung cancer,(10,11) pulmonary tuberculosis,(12,13) and airway diseases.(14,15) These concerns prompted a local construction union to request assistance from the National Institute for Occupational Safety and Health (NIOSH) for health hazard evaluations concerning exposures to dust and silica among roofers in Phoenix, Arizona. In response to these requests, NIOSH performed field studies to evaluate roofers’ exposures to silica. Health Effects Associated with Silica Exposure Silicosis is a disease of the lung caused by the deposition of fine crystalline silica particles (10 μm or less in diameter) in the lungs. The deposition of silica particles in the lungs triggers a chronic inflammatory response resulting in normal lung tissue being replaced with scar tissue (fibrosis). Symptoms of silicosis may include cough, shortness of breath, chest pain, early fatigue with exertion, and wheezing. Silicosis usually occurs after years of exposure (chronic) but may appear in a shorter period of time (acute) if exposure concentrations are very high. Acute silicosis is typically associated with a history of high exposures from tasks that produce small particles of airborne dust with a high silica content.(16) The International Agency for Research on Cancer (IARC) in 1996 concluded that there was “sufficient evidence in humans for the carcinogenicity of inhaled crystalline silica in the form of quartz or cristobalite from occupational sources.”(17) Workers diagnosed with silicosis are also at an increased risk of developing tuberculosis due to silica particles disabling the macrophages.(18) For a diagnosis of occupational silicosis, workers must have a history of exposure to respirable silica and a confirmatory test such as a chest X-ray, chest computed tomography (CT), or lung biopsy.