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Engineering Controls Database

Best Practices for Dust Control in Metal/Nonmetal Mining –
Mineral Processing Operations – Background Issues – Housekeeping Practices

Respirable crystalline silica dust exposure has long been known to be a serious health threat to workers in many industries and occupations. Workers with high exposure to crystalline silica include miners, sandblasters, tunnel workers, silica millers, quarry workers, foundry workers, and ceramics and glass workers Overexposure to respirable crystalline silica dust can has been associated with development of silicosis, lung cancer, pulmonary tuberculosis, and airways disease.

The International Agency for Research on Cancer (IARC) reviewed the published experimental and epidemiologic studies of cancer in animals and workers exposed to respirable crystalline silica and concluded that there was sufficient evidence to classify silica as a human carcinogen [IARC 1997]. Silicosis is also a fibrosing disease of the lungs caused by the inhalation, retention, and pulmonary reaction to the crystalline silica. When silicosis becomes symptomatic, the primary symptom is usually dyspnea (difficult or labored breathing and/or shortness of breath), first noted with activity or exercise and later, as the functional reserve of the lung is also lost, at rest. Once contracted, there is no cure for silicosis. The goal, therefore, is to limit worker exposure to respirable dust to prevent development of these diseases.
Silica refers to the chemical compound silicon dioxide (SiO2), which occurs in a crystalline or noncrystalline (amorphous) form [NIOSH 2002]. Silica is a common component of rocks; and; throughout the mineral processing cycle, mined ore goes through a number of crushing, grinding, cleaning, drying, and product-sizing sequences as it is processed into a marketable commodity. Because these operations are highly mechanized, they are able to process high tonnages of ore and generate high levels of silica.
Although good housekeeping practices seem to be a minor or common-sense issue, it can be a significant factor in a worker’s respirable dust exposure at mineral processing operations. When housekeeping is performed properly and on a scheduled time frame, it can play a key factor in minimizing respirable dust exposure to workers at processing plants. When it is not performed, or performed improperly, it can have just the opposite effect. One example of this was documented when a worker was dry sweeping the floor with a push broom at a mineral processing operation. In this instance, the exposure of a coworker located one floor up from the person sweeping the floors increased from 0.03 mg/m3 before sweeping occurred to 0.17 mg/m3 during and immediately after the occurrence. Dry sweeping is an unacceptable method of cleaning because of the dust it liberates into the work environment [USBM 1986]. The most effective method of housekeeping is to wash down the plant with water on a regular basis. For the ideal system, floor drains and floors that are sloped correctly toward the drains should be incorporated into the structure’s design during construction.

Housekeeping should be performed at the end of each shift so that workers coming on to the next shift start with a clean work environment. A final component of effective housekeeping is proper upkeep and maintenance of plant equipment and processes. When product is observed building up on the floors of the plant, it indicates that some function or process is leaking ore. In some cases, visible dust can be seen leaking from holes or damaged equipment and this must be quickly corrected to minimize dust leakage.
NIOSH [2010]. Information circular 9517. Best practices for dust control in metal/nonmetal mining. Morgantown, WV: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2010-132.
IARC [1997]. IARC monographs on the evaluation of carcinogenic risks to humans: silica, some silicates, coal dust and para-aramid fibrils. Vol 68. Lyon, France: World Health Organization, International Agency for Research on Cancer.

NIOSH [2002]. NIOSH hazard review: health effects of occupational exposure to respirable crystalline silica. Cincinnati, OH: U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 2002-129.

USBM [1986]. Impact of background sources on dust exposure of bag machine operator. Cecala AB, Thimons ED. Washington, DC: U.S. Department of the Interior, U.S. Bureau of Mines, IC 9089.
dust control
metal/nonmetal mining
mineral mining
mineral processing