Best Practice Engineering Control Guidelines to Control Worker Exposure to Respirable Crystalline Silica During Asphalt Pavement Milling

This document represents more than ten years of collaborative research among labor, industry and government where they found asphalt milling machines with well-designed dust controls can reduce worker exposure to respirable crystalline silica during asphalt milling operations.

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 provides recommendations to industry for controlling silica-containing dust.   They include:

• Placing ventilation controls on all new half-lane and larger asphalt milling machines
• Maximizing enclosure around the cutter drum and conveyor belts of milling machines
• Designing a ventilation control with an outlet that releases dust at a high speed in an upward orientation located near the top of the secondary conveyor or in another location away from workers, if the ventilation control on the machine does not already include a dust collector
• Retrofitting watersprays that are used to prevent or suppress dust on milling machines if ventilation dust controls are not available

The NIOSH Best Practices document additionally provides guidance for manufacturers of asphalt milling machines so that they can evaluate current and future dust controls.