Examination of vibration characteristics and transmissibility properties of 'anti-vibration' mats for workers exposed to vibration via the feet

Miners are exposed to vibration at the feet when driving locomotives and standing on vibration drilling platforms. Case reports suggest these workers are reporting pain, discomfort and blanching in the toes more often than their co-workers who are not exposed to vibration via the feet (Thompson et al., 2010). The purpose of the field study was to document the frequency and amplitude characteristics of vibration experienced at the feet under typical mining equipment operation. Health guidance caution zone limits (ISO, 1997) were used to determine the potential health risk to the workers as a result of the vibration. Two categories of underground mining equipment, primary (locomotives) and secondary Gumbo drill, bolter, wood and metal raise platforms), were distinguished by their origin of vibration. Measurements were collected using a tri-axial accelerometer mounted according to the ISO 2631-1 standards, at the location where the worker stood to complete the required job task (ISO, 1997). Musculoskeletal disorder history, work history, and demographic information were also collected.;As a result of the field study, it was shown that miners are exposed to vibration levels at the feet that are above the ISO 2631-1 health guidance caution zone for an 8 hour shift (Leduc, 2011; ISO, 1997). Anecdotal evidence suggests mats could be used to attenuate vibration. The purpose of the laboratory study was to evaluate the transmissibility properties and comfort of 'anti-vibration' mats. Ten participants experienced four mat conditions and three vibration conditions. Three commercially available mats and a no mat condition were randomly evaluated while participants stood on a vibrating platform with an exposure set to 5.0 m/s2 (dominant frequency of 4 Hz) for V1a and 15 m/s2 (dominant frequency of 30 Hz) for V1b, and a no vibration condition, V2. Participants provided a discomfort rating on a 9 point scale following each mat condition. Vibration was measured at the feet using a tri-axial accelerometer according to ISO 2631-1 (1997) and ISO 5349-1(1986) standards.;During the high frequency vibration condition (V2), all mats provided some attenuation in the z-axis. Mat 2 had the lowest mean discomfort rating for both vibration conditions (V1 and V2) and the greatest attenuation of vibration in the z-axis. No significance was found in participant reported discomfort between mats; however, exposure to the high vibration profile (V2) significantly increased participant reported discomfort. Based on the lab findings, longer duration testing should take place in the field to determine if mats will attenuate vibration and decrease worker discomfort.;Vibration resulting from a primary source exposure had a dominant frequency below 6.3 Hz. However, the dominant frequency recorded from secondary source exposures were predominantly in the 31.5 to 40 Hz range. All workers reported discomfort in their lower limbs. The wooden raise platform and the metal raise platform exposed the workers to vibration levels at the feet that placed them above the ISO 2631-1 health guidance caution zone, when the 8-hour frequency-weighted root-mean-square acceleration exposure levels were considered (ISO, 1997). Workers standing on the jumbo drill and raise platforms experienced dominant frequency vibration known to be associated with hand-arm vibration syndrome. The jumbo drill operator and a raise miner have been diagnosed with vibration induced white feet. The dominant frequency recorded at the feet of the locomotive operators was in the range associated with resonance of the spine and pelvis. Further investigation is warranted to determine long-term health effects resulting from vibration exposure via the feet.