Mining Project: Reducing Silica and other Respirable Hazards in the Industrial Minerals and Metal/Nonmetal Mining Industries

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Principal Investigators
Start Date 10/1/2014
End Date 9/30/2019

To develop control interventions to reduce occupational exposure to silica and other respirable dusts in metal/nonmetal mines and mills.

Topic Areas

Research Summary

Occupational exposures to respirable crystalline silica are associated with the development of silicosis, lung cancer, pulmonary tuberculosis, and airway diseases such as chronic obstructive pulmonary disease, which includes chronic bronchitis and emphysema. MSHA’s compliance sampling results indicate that overexposure to respirable silica dust has continued to occur at high rates for select occupations in both underground and surface mining operations, including mobile workers, bagging operators, and stone polishers.

While the MSHA standard is unchanged at 100 µm/m3,  the Occupational Safety and Health Administration (OSHA) issued a final rule, which took effect on June 23, 2016, containing two standards on respirable crystalline silica that, among other things, lowered the permissible exposure limit (PEL) from 100 to 50 µm/m3 as an 8-hour time-weighted average concentration in the construction, maritime, and general industry sectors.  The final rule was fully implemented over a period of five years across the construction, general, maritime, and oil and gas industries.

This project had five research aims, as follows:

  1. Optimize pressurization/filtration systems for control rooms and operator compartments to reduce silica exposures to miners working in these types of enclosures.
  2. Use Helmet-CAM assessment technology on mobile workers to identify high respirable dust exposure job duties and tasks, then develop engineering controls and behavioral interventions to reduce these exposures.
  3. Identify, evaluate, and improve the effectiveness of engineering control technologies and interventions currently being used to reduce respirable dust levels at bagging operations.
  4. Determine effective control techniques and interventions to reduce silica exposures of miners while performing the thermalling process in dimensional stone operations.
  5. Determine a simplified and accurate correction tool for various light-scattering nephelometers/instruments to more closely represent compliance dust sampling in the metal/nonmetal industry using Helmet-CAM technology.

This project developed, implemented, and evaluated engineering controls to minimize respirable dust exposures at targeted job classifications. In order to develop feasible and successful engineering control technologies, NIOSH performed the following tasks: (1) Conceptualized, designed, and fabricated dust control systems; (2) Conducted laboratory testing of the dust control systems at NIOSH laboratory facilities over a wide range of representative operating controls and parameters that closely represented real mining conditions; (3) Optimized laboratory designs were taken into the field and real-world evaluations of those interventions were performed.

NIOSH's strong working relationship with metal/nonmetal mining industrial associations, as well as with individual companies, helped solve other mineral industry dust problems in the past and has led to wide-scale industry adoption of developed technologies. This research along with other related efforts in the mining program have resulted in the successful adoption of engineering controls by industry and helped to lower dust levels at occupations with historically high rates of overexposures. Ultimately this research has contributed to a reduction of silicosis and other respirable diseases in the metal/nonmetal mining industry.

Related Handbooks

Dust Control Handbook for Industrial Minerals and Processing, second edition

Design, Testing, and Modeling of Environmental Enclosures for Controlling Worker Exposure to Airborne Contaminants

Best Practices for Dust Control in Metal/Nonmetal Mining

Key Design Factors of Enclosed Cab Dust Filtration Systems

Related Journal Articles

Comparison of MERV 16 and HEPA Filters for Cab Filtration of Underground Mining Equipment

Air Cleaning Performance of a New Environmentally Controlled Primary Crusher Operator Booth

Dust Suppression Hopper Reduces Dust Liberation During Bulk Loading: Two Case Studies

Analysis of the Silica Percent in Airborne Respirable Mine Dust Samples from U.S. Operations

Assessing Noise and Dust

Related Project Research

Emerging Respirable Dust Sensing and Control for M/NM Mining

Advancing Exposure Monitoring for Airborne Particulates in Mining

Related Workshop

Silica Dust Control for Metal/Nonmetal Mining

Page last reviewed: February 18, 2020
Page last updated: February 18, 2020