Chimich DD, Elkin BS, Siegmund GP (2020). Variability of Friction Measurements Using Three Common Walkway Tribometers. Journal of Testing and Evaluation 49. doi: 10.1520/JTE20190637.
Walkway tribometers are used to assess the slip resistance of flooring surfaces. To yield valid measurements, the ASTM F2508-16e1, Standard Practice for Validation, Calibration, and Certification of Walkway Tribometers Using Reference Surfaces, standard practice requires an annual calibration to show a tribometer’s test results fall within the 95th percentile confidence intervals (CI) of its supplier’s validation test results on 4 reference surfaces. Many users, however, report difficulty meeting this requirement.
Here we examine the variability within and between multiple calibrations to evaluate the current calibration procedure and assess whether field measurements of a surface can be directly compared to calibration test results. We performed multiple calibrations with three common walkway tribometers on one set of reference surfaces. We then simulated field tests on each reference surface and compared these results to the calibration test results.
Overall, all three tribometers ranked and differentiated the reference surfaces in all calibrations; however, none of the calibrations fell within the supplier’s CIs for all four surfaces. The between-calibrations variance ranged from 15 % to 90 % of the total variance in the data set, and only 25 % of the “field” test results fell within the 95th percentile CI of our calibration values.
Our findings show that the current ASTM F2508 calibration requirement does not adequately account for measurement variability. Moreover, our findings indicate that field measurements should not be compared directly to calibration measurements without factoring in measurement uncertainty. Overall, our results show the need for an improved calibration procedure and more research to establish a valid method for estimating slip risk on field surfaces.