Dust Control Handbook for Industrial Minerals Mining and Processing

silica. Quartz is the most common single mineral in the earth's crust, and many miningoperations involve direct contact with overburden and ore containing quartz. Thus, workersthroughout much of the mining industry are potentially exposed to respirable crystalline silicathrough routine mining activities such as drilling, crushing, sizing, transporting, and loading.When workers inhale respirable dust, the particles can penetrate the body's defense mechanismsand reach the alveolar region of the lungs. Crystalline silica particles that deposit in the alveolarregion can stimulate an inflammatory and toxic process that can ultimately develop intoclinically recognizable silicosis. Depending on the concentration of respirable crystalline silicaand duration to which they are exposed, workers may develop any of several forms of silicosis[NIOSH 2002]:chronic—resulting from long-term excessive exposures, and first clinically apparent 10–30 years after first exposure;accelerated—resulting from exposure to higher concentrations of crystalline silica, firstclinically apparent 5–10 years after the initial exposure;acute—resulting from exposure to unusually high concentrations of crystalline silica,clinically apparent within weeks to 5 years after the initial exposure.Chronic silicosis, the most common form of the disease, results in characteristic nodular scarringin the lungs and occurs after many years of inhaling respirable crystalline silica dust. Over time,the initial small nodules can eventually coalesce into large fibrotic masses, a condition calledprogressive massive fibrosis. Accelerated silicosis is much less common than chronic silicosisbut progresses more rapidly, and acute silicosis, a rarely occurring form of the disease, is themost serious and most rapidly fatal form. Unlike chronic and accelerated silicosis, where a chestx-ray examination typically reveals scattered discrete small (and possibly also large) opacities,the chest x-ray appearance of acute silicosis resembles that of a diffuse pneumonia. Thisappearance results from extensive damage to the lining of the air spaces of the lungs, causing thealveoli to become filled with an abnormal fluid containing protein, degenerating cells, and othermaterials [Davis 2002].Not all workers diagnosed with silicosis will be symptomatic; some with chronic disease willhave no notable symptoms despite characteristic abnormalities on their chest radiograph.However, many workers with chronic silicosis will develop symptoms over time and essentiallyall those with accelerated and acute forms of the disease will be symptomatic even before theyare diagnosed. Though silicosis is incurable, various symptoms, including chest irritation withuncontrollable coughing and shortness of breath, can be debilitating and warrant therapeuticintervention. Additionally, those with silicosis are at substantial risk for developing tuberculosis3or other mycobacterial diseases [NIOSH 2002; Davis 2002].This introduction has highlighted the need to control exposures to respirable silica dust. Thecontrol technologies discussed in this handbook for lowering dust levels below permissible orrecommended occupational exposure limits are designed to control exposures not only to silicadust, but also to other types of dust. Also, while this handbook is focused on protecting workers3Additional information on silica and silica-related diseases can be found at the National Institute for OccupationalSafety and Health (NIOSH) website at http://www.cdc.gov/niosh/topics/silica/.Introduction 3