Hand-Arm Vibration Controls for Jackleg Rock Drills: A Pilot Study Assessing Ergonomic Hazards.

Jackleg drill operators are exposed to harmful levels of hand-arm vibration (HAV). Anti-vibration handles and gloves provide modest reductions in HAV exposures and forearm muscle exertion from the use of AV handles and gloves by jackleg drill operators. The goal of this pilot study was to investigate changes in HAV with the use of anti-vibration gloves and handles compared to forearm muscle exertion experienced by operators and measured with surface electromyography (EMG). Five subjects operated the drill under four different cases: no anti-vibration controls, anti-vibration gloves only, anti-vibration handle only, and simultaneous anti-vibration handle and glove use. Muscle exertion was expressed as a percent of maximum voluntary contraction (%MVC) and was compared using Welch's ANOVA with Games-Howell post-hoc comparisons. The case with both anti-vibration controls in use simultaneously (largest grip diameter) was associated with a mean %MVC of 36.13% during operation for all forearm muscles combined, which was significantly higher than the other cases (p < 0.05). There were no statistically significant differences in mean HAV exposures. The anti-vibration handle with anti-vibration glove case only increased the maximum allowable exposure time by eight minutes as compared to the control case without any anti-vibration controls. These results suggest that the modest HAV exposure reductions from the use of anti-vibration handles and gloves may pale in comparison to the increased muscle exertion resulting from their use, and this tradeoff among jackleg drill operators is a potential concern that warrants further investigation.

Are hard hats a risk factor for WRMSD in the cervical-thoracic region?

OBJECTIVES: To investigate the effect of wearing hard hats on the lower cervical and upper thoracic region using surface electromyography (sEMG) and possible link to work-related musculoskeletal disorder (WRMSD). METHODS: Twenty study subjects wore sEMG sensors placed on the upper trapezius muscle on their dominant side to assess muscle activity while wearing different hard hats. Study subjects were asked to don six different hard hats and assume varied neck postures. A repeated-measures design was used to analyze the results for difference and similarities in muscle activity. RESULTS: There was a small, significant effect of wearing a hard hat on muscle loading in the upper trapezius (p = 0.038). Post-hoc analyses revealed the only statistically significant difference was between wearing no hard hat at all and wearing head protection (without accessories) in the flexed posture (p = 0.006). CONCLUSION: The results demonstrated that there was little difference in lower cervical and upper thoracic muscle activity while donning hard hat and assuming various neck postures. Wearing a sample of commonly used hard hats in this study does not appear to substantially increase muscle activity that would cause fatigue in the lower cervical and upper thoracic region among young, healthy volunteer subjects.