How hard do avalanche practitioners tap during snow stability tests?

Abstract

This study examines the impact force applied from hand taps during extended column tests (ECTs), a common method of assessing snow stability. The hand-tap loading method has inherent subjectivity and inconsistencies across US, Canadian, Swiss, and Norwegian written standards. We developed a device, the “tap-o-meter”, to measure the force-time curves during these taps and collected data from 286 practitioners, including avalanche forecasters and mountain guides in Scandinavia, Central Europe, and North America. The mean, median, and inner-quartile peak forces are distinctly different for each loading step (wrist, elbow, and shoulder), and the peak force approximately doubles from one loading step to the next. However, there is considerable overlap across the range of measurements and examples of participants with higher-force wrist taps than other participants' shoulder taps. This overlap challenges the reliability and reproducibility of ECT results, potentially leading to dangerous interpretations in avalanche decision-making, forecasting, and risk assessments. Our results provide an answer to the question “How hard do avalanche practitioners tap?” but not necessarily to the question “How hard should avalanche practitioners tap?” These data and insights are intended to facilitate discussion among the tests' creators, the scientific community, and the practitioner community to update thresholds, guidelines, and test interpretation.