State-of-the-Science Review of the Occupational Health Hazards of Crystalline Silica in Abrasive Blasting Operations and Related Requirements for Respiratory Protection

Abstract

Excessive exposures to airborne crystalline silica have been known for over 100 years to pose a serious health hazard. Work practices and regulatory standards advanced as the knowledge of the hazards of crystalline silica evolved. This article presents a comprehensive historical examination of the literature on exposure, health effects, and personal protective equipment related to silica and abrasive blasting operations over the last century. In the early 1900s, increased death rates and prevalence of pulmonary disease were observed in industries that involved dusty operations. Studies of these occupational cohorts served as the basis for the first occupational exposure limits in the 1930s. Early exposure studies in foundries revealed that abrasive blasting operations were particularly hazardous and provided the basis for many of the engineering control and respiratory protection requirements that are still in place today. Studies involving abrasive blasters over the years revealed that engineering controls were often not completely effective at reducing airborne silica concentrations to a safe level; consequently, respiratory protection has always been an important component of protecting workers. During the last 15-20 yr, quantitative exposure-response modeling, experimental animal studies, and in vitro methods were used to better understand the relationship between exposure to silica and disease in the workplace. In light of Occupational Safety and Health Administration efforts to reexamine the protectiveness of the current permissible exposure limit (PEL) for crystalline silica and its focus on protecting workers who are known to still be exposed to silica in the workplace (including abrasive blasters), this state-of-the-science review of one of the most hazardous operations involving crystalline silica should provide useful background to employers, researchers, and regulators interested in the historical evolution of the recognized occupational health hazards of crystalline silica and abrasive blasting operations and the related requirements for respiratory protection.

Outbreak of silicosis in Spanish quartz conglomerate workers

“…9 More than three million European workers were exposed to crystalline silica at the beginning of the 1990s. 10 Despite the decline in silicosis incidence observed in developed countries in the following decades, mainly due to the improvement of prevention measures such as protective equipment, 8 additional efforts to reduce dust exposure by strict compliance with existing regulatory standards are still considered necessary. 11 In Spain, silicosis incidence appears to be increasing.…”

“…6 In recent years, clusters of cases have been reported in relation to new occupational exposures in several countries. [7][8][9] Some of them are related to mechanization procedures (cutting, calibration, and polishing) used in the manufacturing and installation of kitchen countertops made of quartz conglomerates, materials with a high content of crystalline free silica (70-90%). These workers are exposed to high concentrations of silica, resulting in disease after relatively short latency periods.…”

Evaluation of the Approach to Respirable Quartz Exposure Control in U.S. Coal Mines

“…(2)(3)(4) Non-respiratory disease has also been associated with respirable quartz exposure, including scleroderma, rheumatoid arthritis, and renal disease. (5)(6)(7) Miners, including coal miners, are occupationally exposed to respirable quartz during the extraction and processing of ore. (8)(9)(10) In coal miners, exposure to respirable quartz occurs when rock above, below, or within the coal seam is disturbed as the coal is extracted. Exposure can also occur when ground control methods are implemented in underground coal mines (e.g., installation of roof bolts) and when drill holes for exploration or placement of blasting agents are installed.…”

Immunological Effects of Silica and Related Dysregulation of Autoimmunity

“…Silicosis is known as environmental and occupational pulmonary fibrosis and the most typical form of pneumoconiosis results from long-term exposure (ten years or more) to relatively low concentrations of silica dust and usually appears ten to thirty years after the first exposure (Hoffman & Wanderer, 2010;Madl, 2008;Rimal, 2005). Patients with this type of silicosis, especially in the early stages, may not have obvious signs or symptoms of disease, but abnormalities may be detected by x-ray.…”