In-Depth Evaluation: Dust-Control Technology for Asphalt Pavement at Milling at New York State Thruway (Interstate Highway 90) Resurfacing Project, Donegal Construction, Contractor, Hamburg, New York, September 25 and 26, 2006

摘要

As part of an ongoing study to evaluate the effectiveness of dust-control systems on pavement milling machines, a field survey was performed during milling of asphalt on a rural, limited access, four-lane divided toll highway. The objective of this survey was to estimate the reduction in respirable dust emissions and workers' exposures that could be achieved through the use of higher water-flow rates through the milling machine's water spray system. The effectiveness of the dust controls examined in this study was evaluated by measuring the reduction in the respirable dust and respirable quartz exposures in personal and area samples collected during this typical milling job. Increasing the total water flow to the water-spray nozzles from about 12.5 gallons per minute (gpm) to about 20 gpm did not result in overall reductions in measured respirable dust concentrations at area air monitoring locations around the machine. Instead, the results were quite anomalous, and revealed large differences in the change in concentrations at the sampling locations on one side of the machine compared to the other. Specifically, on the left side of the machine, mean respirable dust concentrations from three sampling and data analysis techniques ranged from 70% to 87% lower during operation at the high water-flow rate than at the low-flow rate, but on the right side of the machine, comparable mean respirable dust concentrations ranged from 4 to 16 times greater at high water flow than at low flow. These anomalous results have been considered carefully by NIOSH researchers and machine manufacturer representatives, and an adequate explanation has not been developed. Clear conclusions cannot be reached from these data. Given the unexplained increases in respirable dust levels associated with the periods of high water flow, the personal breathing-zone exposures measured during the high water-flow periods may be unreliable. However, the measurements did reveal crystalline silica exposures in excess of the NIOSH recommended limit for during low water-flow periods. Ongoing NIOSH research is expected to lead to recommended measures to better control respirable dust and crystalline silica exposures from pavement milling.