Effect of Shoe Tread Depth on Hydrodynamic Pressures in the Shoe-Floor Interface During Slipping

Details

• Personal Author:
  Beschorner K ; Chambers AJ ; Redfern MS
• Description:
  INTRODUCTION: Fall accidents accounted for 15% of nonfatal occupational accidents in 2010. Shoe tread has been found to affect coefficient of friction. Shoe tread is thought to provide drainage channels that prevent pressurized fluid from building up between the shoe and floor. In addition, inadequate tread has been linked with slipping accidents in mail delivery industry. While tread has been linked with higher friction, a gap currently exists regarding whether shoe tread can prevent pressurized fluid buildup during walking and slipping events. Several studies have theorized that hydrodynamic pressures are the critical mechanism causing a slip but no study to date has confirmed their existence during human slipping events. The purpose of this study is to measure hydrodynamic pressures during human slipping events using fluid pressure sensors embedded in the floor. Hydrodynamic pressures and slip outcomes will be compared between treaded and untreaded shoes. METHODS: Seventeen participants (10 female, mean +/- standard deviation: age 23.5 +/- 4.0 years, height 1.71 +/- 0.072m, weight 70.0 +/- 11.8 kg) were unexpectedly slipped while wearing either treaded or untreaded shoes. Subjects experienced one slip while wearing a treaded and an untreaded shoe. The shoes were advertised as slip-resistant footwear. Treaded shoes had the full tread intact (tread depth = 3 mm), while non-treaded shoes had the tread completely abraded from the shoe. Shoe order was randomized. Slips were induced using a 90:10 glycerol: water solution that was applied to a 24" x 24" vinyl floor tile. At least five dry trials were collected before participants were unexpectedly slipped wearing the first type of shoes. After the first unexpected slip, at least fifteen dry trials with the second pair of shoes were collected to ensure participants returned to a normal gait. Participants listened to music between trails to prevent them from noticing the fluid contaminant being applied to the floor. Motion data were collected at 120 Hz using a 14 camera Vicon motion capture system. Hydrodynamic pressures were measured by fluid pressure sensors that were embedded just beneath the surface of the floor (Setra). The sensors were set up in a 3x3 grid and sensors were spaced 30 mm apart from each other. The starting point for the subject was aligned so that their foot would hit just behind the first row of sensors and slip or step across the sensors. Subjects wore a safety harness to prevent injury. The primary variables of interest were the hydrodynamic pressures and the peak slip-velocity. Specifically, the maximum hydrodynamic pressure from each sensor was calculated. To more completely describe the hydrodynamic pressure profile, onset durations of hydrodynamic pressures were calculated. Onset was the first moment that the hydrodynamic pressure signal exceeded 5 standard deviations of baseline and offset was when it first dropped below 5 standard deviations of baseline. Peak slip velocity (PSV) was calculated as the maximum resultant velocity of the heel between the beginning and end of the slip. The beginning of the slip was defined as the first local minimum of the heel velocity after heel strike. Slip stop was defined as the first local minimum of the heel velocity after the slip. An ANOVA was performed to determine the effect of tread (independent variable) on the hydrodynamic pressures (dependent variable) and slip-severity (dependent variable). To determine whether hydrodynamic pressures varied mediolaterally across the shoe or during the progression of the slip, another ANOVA was performed with peak pressure as the dependent variable and sensor location as the independent variable. RESULTS AND DISCUSSION: Untreaded shoes had higher hydrodynamic pressures and led to more severe slips. The average (standard deviation) peak hydrodynamic pressure was 124 kPa (75 kPa) for the untreaded shoes and 1.1 kPa (.29 kPa) for treaded shoes. The average PSV was 1.57 +/- 0.80 m/s for untreaded shoes and 0.063 +/- 0.017 m/s for treaded shoes. Hydrodynamic pressures were characterized by a single peak and durations were 86 ms (65 ms) in the untreaded conditions (Figure 1). In treaded conditions, hydrodynamic pressures were only observed in one slip for one sensor with duration of 36 ms. Assuming a sliding velocity of 1-1.5 m/s, this duration would correspond with a hydrodynamic pressures occurring over approximately 10 cm of the shoe surface. These results confirm the existence of hydrodynamic pressures in the shoe-floor interface during actual slipping events. Furthermore, shoe tread has a demonstrated effectiveness in reducing hydrodynamic pressures. Based on the duration of hydrodynamic pressures, tread over the posterior 10 cm of the heel appears to be critical to preventing slipping accidents. Previous researchers have suggested that slip-testing devices should be tribologically fidelic as part of being "biofidelic" (i.e., relevant to human slips). Comparing hydrodynamic pressures of slip-testing devices to human slips may be an approach for testing the devices' tribological fidelity. Neither the sensor position nor the PSV were significantly correlated with peak hydrodynamic pressures. One explanation for a lack of correlation between sensor position and the hydrodynamic pressures is that the sensors were mapped to the flooring location as opposed to the shoe. Previous research by our group has shown that the highest hydrodynamic pressures occur centrally near the back of the foot. Future analyses may benefit by correlating the position of the sensors to the foot during slipping to the hydrodynamic pressures. In addition, using the instantaneous velocity of the foot when over the sensor as well as other factors (vertical force, for example) may yield better correlation than peak slip velocity. [Description provided by NIOSH]
• Subjects:
  Accidental Falls Accidents Biomechanical Phenomena Occupational Health Occupational Injuries Safety
• Keywords:
  Biomechanics Floors Occupational Accidents Slips, Trips, And Falls STF Walking Surfaces
• Publisher:
  American Society of Biomechanics
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Abstract or Summary
• Place as Subject:
  Nebraska ; OSHA Region 3 ; OSHA Region 5 ; OSHA Region 7 ; Pennsylvania ; Wisconsin
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-2
• NIOSHTIC Number:
  nn:20055609
• Citation:
  Proceedings of the 37th Annual Meeting of the American Society of Biomechanics, September 4-7, 2013, Omaha, Nebraska. Newark, DE: American Society of Biomechanics, 2013 Sep; :407
• Email:
  beschorn@uwm.edu
• Federal Fiscal Year:
  2013
• NORA Priority Area:
  Manufacturing ; Services
• Performing Organization:
  University of Pittsburgh at Pittsburgh
• Peer Reviewed:
  False
• Start Date:
  20100801
• Source Full Name:
  Proceedings of the 37th Annual Meeting of the American Society of Biomechanics, September 4-7, 2013, Omaha, Nebraska
• End Date:
  20140731
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:36b882c836b9087ef16f4ed9f97d32fa3380beb0fe1ebe691001585a14214c1d4414c81db5e4c1fc49ec6d0847611ef399afbdaa98b6507646e1dec4814a8f55
• Download URL:
  https://stacks.cdc.gov/view/cdc/213421/cdc_213421_DS1.pdf
• File Type:
  [PDF - 48.13 KB ]