Evaluation of cut-off saw exposure control methods for respirable dust and crystalline silica in roadway construction.

Dust reduction equipment adapted for single-person operation was evaluated for gas-powered, commercially available cut-off saws during concrete curb cutting. Cutting was performed without dust control and with two individual exposure control methods: wet suppression and local exhaust ventilation (LEV). The wet suppression system comprised a two-nozzle spray system and a 13.3-L hand-pressurized water supply system with an optimum mean flow rate of 0.83 L/min for 16 min of cutting. The LEV system consisted of a spring-loaded guard, an 18.9-L collection bag, and a centrifugal fan with an estimated exhaust rate of 91 ft(3)/min. Task-based, personal filter samples were obtained for four saw operators during cutting durations of 4 to 16 min on five job sites. Seventeen filter samples were collected without dust control, 14 with wet suppression, and 12 with LEV, yielding a geometric mean respirable dust concentration of 16.4 mg/m(3), 3.60 mg/m(3), and 4.40 mg/m(3), respectively. A dust reduction of 78.0% for wet suppression and 73.2% for LEV was observed vs. no dust control. A statistically significant difference (p < 0.001) was also revealed for wet suppression and LEV when compared with no dust control; however, a significant difference (p = 0.09) was not observed between wet suppression and LEV. Despite these significant dust reductions, workers are still projected to exceed the ACGIH 8-hr time-weighted average threshold limit value for quartz (0.025 mg/m(3)) in less than 1 hr of cutting for both dust control methods. Further research is still needed to improve dust reduction and portability of both control methods, but the current LEV system offers important advantages, including a drier, less slippery work area and year-round functionality in cold weather.

Evaluation of noise attenuation and verbal communication capabilities using three ear insert hearing protection systems among airport maintenance personnel.

The goal of this project was to determine whether one type of earplug would allow a user to hear communication in a noisy environment better than two other types of earplugs. The three types of earplugs studied are newly available on the market. Sonomax SonoCustoms are custom fitted to the user. E-A-R Push-Ins are the newest form of foam earplugs, and Howard Leight SmartFits have an adaptable shape. One of the earplug manufacturers claimed to have improved verbal communications due to the design of the earplug. We hypothesized that the type of earplug providing better communication properties would have lower attenuation around the communication frequencies compared with the other types. To test this hypothesis, we used speech intelligibility and attenuation tests in the laboratory on 26 subjects, and real-time video exposure monitoring in the field (airport maintenance personnel) for visual communication cues. ANCOVA was used to analyze the data from the laboratory study. The type of earplug worn was not significant in the model (p-value 0.0849), nor was attenuation of the earplug (p-value 0.2379). Further analysis showed that attenuation did not differ significantly among earplugs (p-value 0.5903). Logistic regression was used to analyze the data from the field study. Again, the type of earplug was not significant in the model (p-value 0.0965). A comfort questionnaire determined that Howard Leight SmartFits and the E-A-R Push-Ins were more comfortable and easier to use than the Sonomax HPDs (p-value <0.0001). We found a definite difference between manufacturers' attenuation data and our attenuation data, especially in the frequencies for 125-1000 Hz. Also, there was no difference in frequency and overall attenuation among the HPDs. This resulted in no difference in communication abilities among the types of HPDs.