Attenuation of Continuous Vibration Transmission in the Hand and Arm Using Composite-Based Tool Designs

Abstract

Exposure to high noise levels may be the most common occupational hazard. Recent estimates suggest that as many as 30 million Americans are exposed to noise levels greater than the current safe limits for workplaces. At current durations of exposure, it is expected that 25% of these workers will develop permanent, noise-induced hearing loss. In many of these industrial environments, high levels of vibration also exist that can lead to several injuries and ailments. To address the adverse effects associated with the use of high noise emission impact tools, a study was initiated to develop and evaluate alternate tool designs that reduce the potential for hearing loss and vibration-related injuries. Recent work has focused on integrating advanced engineering polymers (composites) into tool designs for the purpose of eliminating direct metal-to-metal impact. This approach has several significant performance advantages including reduced operator discomfort due to hand-arm mechanical shock, reduced noise, and less danger from flying metal fragments. To quantify sound emission characteristics of these new designs, continuous sound pressure, maximum sound pressure, and maximum sound pressure level were measured using an array of five precision microphones each located 1 meter from the tool. Data was sampled at 40 kHz while test subjects operate both pneumatic tools and hand-struck tools. Frequency spectra of the sound pressure signals were examined for all tool treatments, and indicate that the addition of a polymer insert between metal impact components significantly reduces noise emission, especially at higher frequencies. Sound pressure levels were reduced by as much as 4 dBA compared to conventional tool designs. Similar reductions were observed in vibration transmission in the hand and arm. As a result, tools that integrate polymer-based components may be operated for longer daily exposure times without inducing hearing loss or vibration-related injuries. Data from this study may also help auditory and ergonomic specialists in understanding impulse noise characteristics and exposure.