In-depth survey report: field evaluation of Dynapac engineering controls designed to reduce occupational exposures during asphalt paving operations at Dynapac, Inc., San Antonio, Texas, report no. CT-208-23a.
On April 29 - May 2, 1998, researchers from the National Institute for Occupational Safety and Health (NIOSH) evaluated a first-generation engineering control designed to capture and remove fugitive asphalt emissions during asphalt paving. The Dynapac engineering control evaluation was completed as part of a Department of Transportation (DOT) project to evaluate the effectiveness of engineering controls on asphalt paving equipment. NIOSH researchers conducted the research through an interagency agreement with DOT's Federal Highway Administration (FHWA). Industry, labor, and governmental participation in the project was fostered through a research partnership which included NIOSH, FHWA, the National Asphalt Pavement Association (NAPA), the Asphalt Institute, six manufacturers of asphalt paving equipment, the International Union of Operating Engineers (IUOE), the Laborers' International Union of North America (LIUNA), and the Laborers' Health and Safety Fund of North America (LHSFNA). The asphalt paving engineering control study consisted of two major phases. During the primary phase, NIOSH researchers visited each participating manufacturer and evaluated their engineering control designs under managed environmental conditions. The indoor evaluation used tracer gas analysis techniques to quantify the control's exhaust flow rate and to determine the control's capture efficiency. Results from the indoor evaluations provided equipment manufacturers with the necessary information to maximize engineering control performance prior to the second phase of the study; performance evaluation of the engineering controls under "real life" paving conditions. Throughout each manufacturer's phase two evaluation, NIOSH researchers focused primarily on the ability of the engineering control to capture and remove airborne contaminants generated within the asphalt paver's auger area. Secondary measurements were collected at screed and paver operator positions located on the asphalt paver. Since no prescribed methods exist to evaluate engineering controls under the unique physical constraints of the asphalt paving environment, the NIOSH researchers developed a multifaceted evaluation strategy that included tracer gas testing, industrial hygiene sampling, and real-time sampling for particulate (PM10), organic vapor, and temperature. All of these methods were incorporated into a control-on vs. control-off field evaluation protocol in order to quantify the engineering control's performance. The scope of this report is limited to the Dynapac phase two (field) evaluation of a single engineering control installed on a Dynapac Model F30W Wheeled Paver with screed model VB 1000 V. The exhaust hood measured 94 inches long and was centered behind the paver and over the augers. The plenum inlet was a 1-inch slot, located on the bottom of the plenum and running the approximate length of the hood. The 8-inch wide plenum varied in height from 11 inches at the two ends to 5 inches at the center to allow clearance for the auger assembly. Five-inch flanges extended from the leading and trailing edges of the exhaust hood across the full length of the hood. The open space between the leading flange and the rear of the paver measured 5 inches. The hood position was fixed with the augers placed in a typical paving height (position #4). The bottom of the hood measured 46 inches above the ground and approximately 26 inches above the top of the augers. A partition, located within the exhaust plenum, separated the right and left halves of the plenum. Two hydraulically-driven exhaust fans, one for each half of the plenum, provided the negative pressure and exhaust capacity to the exhaust hood. Each fan is rated at approximately 590 cubic feet per minute (cfm) [1000 cubic meters per hour]. The exhaust volumes indicated by the tracer gas tests were 1207 cfm for the two fans combined. Test results indicate that the Dynapac engineering control design was successful in capturing and removing an average of 31 percent of the asphalt fume released from the auger area. This source reduction led to an average worker-area reduction of 5 percent. One way to circumvent the mathematical impact of background concentrations and the variability resulting from ambient conditions, as well as the frequent interruptions in the paving process, was to evaluate the engineering control's ability to prevent higher-level (top 25%) contaminant concentrations at both the auger and the screed operator and paver operator positions. Using this approach, the Dynapac engineering control produced an average reduction in higher-level exposures of 61 percent at the auger and 47 percent at the screed and operator workstations. The Dynapac evaluation was the last of six field evaluations to be conducted as part of the engineering controls research partnership. Many of the environmental and process variables were unique to the Dynapac evaluation. For example, the Dynapac field evaluation was the only evaluation conducted largely in a parking lot. This limited the amount of continuous paving that could be done and made the evaluation more difficult. The reported performance results should not be used to predict future results under different conditions or to compare performances with those obtained by other paver manufacturers. The implementation of engineering controls on asphalt paving equipment will continue to be an iterative process. NIOSH encourages Dynapac to incorporate the following recommendations into their engineering control implementation process: (1) Investigate ways to increase the existing level of auger-area enclosure, especially over the center portion of the auger area; (2) Monitor the worker/contractor acceptance of the current/future auger-area enclosure design and incorporate design changes if undesirable field-modifications are observed; (3) Monitor field conditions of asphalt paver engineering controls to determine how well the control design stands up to the rigorous demands of a paving environment; and, (4) Modify or supplement the existing hood enclosure to minimize escaping fume when the screed is extended beyond the width of the tractor.
Asphalt-fumes; Asphalt-industry; Control-technology; Engineering-controls; Equipment-design; Equipment-operators; Exhaust-gases; Exhaust-hoods; Exposure-limits; Occupational-exposure; Organic-vapors; Particulate-sampling-methods; Construction-equipment; Region-6; Road-construction; Road-surfacing; Polycyclic-aromatic-hydrocarbons