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Best Practices Recommended to Reduce Silica Exposure During Asphalt Pavement Milling

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March 24, 2015

The National Institute of Occupational Safety and Health (NIOSH) has developed a new document titled “Best Practice Engineering Control Guidelines to Control Worker Exposure to Respirable Crytalline Silica during Asphalt Pavement Milling.” Developed through the Silica/Asphalt Milling Machine Partnership, the document provides best practices to help reduce respirable silica exposures during asphalt pavement milling in highway construction.

“Inhalation of respirable crystalline silica can cause silicosis, a debilitating and potentially fatal lung disease, and other possible adverse health outcomes,” said NIOSH Director John Howard, M.D. “This collaborative effort by labor, industry, and government reflects the current knowledge of best practices and a partnership that has succeeded in developing recommended engineering controls for these worksites.”

Approximately 367,000 U.S. workers are employed in highway, street, and bridge construction, and are at risk of exposure to respirable crystalline silica. Workers use a variety of machinery when removing and recycling asphalt pavement; a number of them use cold-milling machines with toothed, rotating cutters that grind and remove the pavement, or work in close proximity to them. Dust generated from the cold-milling machines often contains respirable crystalline silica which can be transported by currents to the air workers breathe.

The NIOSH document of best practices, which represents more than ten years of collaborative research between partners working under the Silica/Asphalt Milling Machine Partnership, provides recommendations that include ventilation controls in addition to water sprays used to cool the cutting teeth of milling machines, lessening silica dust exposure.

The collaborative research began when the Silica/Asphalt Milling Machine Partnership was formed at the 2003 National Asphalt Pavement Association (NAPA) Annual Meeting, and studies on milling machine dust controls began later that year. The Silica/Asphalt Milling Machine Partnership is coordinated by NAPA and includes all U.S. and foreign manufacturers of heavy construction equipment that currently sell pavement-milling machines to the U.S. market.

In their studies, NIOSH and partners collected 42 worker personal breathing zone air samples at 11 different highway construction sites. They discovered that machines that adopt the dust control approach reduced worker exposures to respirable crystalline silica from asphalt milling operations.

NIOSH and the Silica/Asphalt Milling Machine Partnership including the following as recommendations to reduce worker exposure to respirable crystalline silica:

  • Placement of ventilation controls on all new asphalt milling machines
  • Maximizing cover around the cutter drum and conveyor belts of milling machines
  • Designing an outlet that releases dust at high speed away from the worker, if the ventilation control on the machine does not already include a dust collector
  • Water sprays that are used to prevent or suppress dust on milling machines if ventilation dust controls are not available.

In addition to NAPA and the equipment manufacturers, the Silica/Asphalt Milling Machine Partnership includes numerous paving contractors, the International Union of Operating Engineers; the Laborers International Union of North America; the Association of Equipment Manufacturers (AEM); and government organizations including the Occupational Safety and Health Administration (OSHA), the Federal Highway Administration (FHWA), and the Centers for Disease Control and Prevention’s (CDC) National Institute for Occupational Safety and Health (NIOSH).

The document additionally provides machine manufacturers guidance for evaluating current and future dust controls, and can be accessed here.

To learn more about engineering controls for silica in construction, visit:


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