Assessment of walkway tribometer readings in evaluating slip resistance: a gait based approach.

Introduction: Tribometers are mechanical instruments which purport to measure the slip resistance of walkway surfaces. However, it has been well documented that different tribometers yield different measurements of friction for the same flooring material. Purpose: To assess the viability of using slip risk (as quantified during human subject walking trials) to create a reference standard against which tribometer readings could be compared. Methods: Part I: Human subject slip events during walking were used to objectively rank the slipperiness of three different surfaces with and without a contaminant (6 conditions). Eighty four subjects (42 males, 42 females; mean age 25.9 [+ or -] 3.8 years) were randomly assigned to one of the six floor surface conditions: High pressure laminate (HPL) (dry and wet); Delrin (dry and wet), and Teflon (dry and wet). All subjects wore a pair of Oxford style shoes and a fall-arresting body harness attached to an overhead trolley. Subjects first performed 3 to 6 non-slip walking trials followed by a single trial in which the floor panel of interest was inserted into the walkway. The ranking of surface slipperiness was based on the number of slip events (combination of heel and toe slips) observed in each group. Part II: Nine tribometers were used to independently measure and rank surface slipperiness for all six conditions (Horizontal Pull Slipmeter, C-1028, Tortus II, Universal Walkway Tester, Sigler Pendulum, Wessex Pendulum, Mark II, Mark III, English XL). The ranking of the floor surfaces for each tribometer was based on the friction values obtained. The slipperiness ranking determined from the walking trials was considered the reference against which the tribometer measurements were compared. The results of the tribometer measurements were then compared to the gait-based ranking of surface slipperiness using two criteria: 1) Did the tribometer measurements correctly rank the slipperiness of the different surfaces? 2) Did the tribometer measurements differentiate between surfaces with significantly different levels of slipperiness? Results: The nine different tribometers produced widely varying friction measurements for the six surfaces. Across all tribometers and surfaces, friction measurements varied from a low of 0.06 [+ or -] 0.02 for the English XL on wet Delrin to a high of 2.06 [+ or -] 0.28 for the Tortus II on dry HPL. A comparison of the tribometer measurements of friction to the gait-based ranking of surface slipperiness showed that only two of the nine tribometers tested (Tortus II and Mark III) met our compliance criteria. Discussion: The results of the tribometer measurements were consistent with the conclusions of previous studies in that different tribometers give varied friction values for the same surface. In the current study, only two of the nine tribometers tested (Tortus II and Mark III) met our compliance criteria by both correctly ranking all 6 conditions and differentiating between surfaces of differing degrees of slipperiness as established by the walking trials. These findings reinforce the need for objective criteria to ascertain which tribometers effectively evaluate floor slipperiness and a pedestrian's risk of slipping. Moreover, this experimental protocol demonstrates that human gait-based measures of slipperiness can be used to create reference standards against which the output of tribometers can be compared.

Tsai YJ, (1) Powers CM, (1) Stefanou MA, (1) Brault JR, (2) Siegmund GP (2)

(1) Musculoskeletal Biomechanics Research Laboratory, Department of Biokinesiology and Physical Therapy, University of Southern California., Los Angeles, CA.

(2) MacInnis Engineering Associates, Lake Forest, CA