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The Effect of Subject Awareness in Assessing the Probability of Slip and Fall Accidents
RS2001/02-028
Final Report Date: May 2005
| Principal Investigators: |
Gunter Siegmund (University of British Columbia , MEA Forensic Engineers & Scientists) |
| Co-investigators: | David Sanderson, Timothy Inglis (University of British Columbia); John Brault (MEA Forensic Engineers & Scientists) |
For more information about this study, please contact Dr. Gunter Siegmund.
Issue
Slips and slip-related falls often result in musculoskeletal injuries. Although slips usually occur when surfaces are unexpectedly slippery, most laboratory studies of slips and falls use human subjects who know in advance they will be walking on slippery surfaces, and change the way they walk as a result.
This research examined whether the likelihood of a study participant slipping or falling on low-friction surfaces in laboratory tests is affected by knowing about the possibility of slipping or experience of a slip or fall. The findings have implications for using human subject data to validate tribometers, devices that measure shoe/floor friction.
Key findings
- Participants adjust their gait and are less likely to slip when they are aware of the possibility of slipping, compared with participants who are unaware. However, after participants have slipped once, their risk of further slips is comparable to those who are unaware of the possibility of slipping.
- The results of the study indicate that data acquired from human subjects who have prior experience slipping in the laboratory is not biased and can be used to validate tribometers.
Objectives
To examine how human subject awareness and prior slip experience affect the probability of slipping on low-friction surfaces in laboratory tests.
To provide validation data for two common tribometers and examine whether experiments designed to validate tribometers need to control their experimental conditions or correct their data for subject awareness and slip experience.
Method
Sixty-eight participants walked over non-slip surfaces, with three different low-friction surfaces inserted periodically. Participants wore a safety harness tethered from each shoulder to an overhead trolley.
Three increasing levels of prior knowledge and experience were used: deceived, aware, and experienced. At the first level, participants were deceived into thinking that there would be no slippery surfaces. At the aware level, participants had been told of the possibility of slippery surfaces, but had not yet experienced slipping. At the experienced level, participants had slipped before, and therefore had both awareness and prior slip experience.
Measurements taken included proportion of slips, slip distance, and required friction. Two tribometers were used to measure surface friction levels. Statistical analyses were conducted to assess how levels of prior knowledge affected the probability of slipping (the slip risk curve).
Results
Slips occurred in 17% of low-friction trials. No falls occurred in this study.
Participants changed the way they walked once they became aware of the possibility of slipping, and changed yet again after experiencing a slip.
Having awareness of the possibility of slippery surfaces decreases the likelihood of slipping. However, after participants experienced a slip, their risk of slipping was comparable to that of unaware subjects.
Conclusions
The results of the study show that subject awareness biases the slip risk curve toward underestimating the actual risk of slipping, but that having at least one prior slip experience subsequently eliminates this bias. Therefore, data from subjects with prior slip experience can be used to determine the risk of slipping (but not falling) for unaware subjects.
These results also suggest that data acquired from subjects who have slipped multiple times in laboratory tests do not need to be corrected to be used to generate slip risk curves for a tribometer. The researchers note, however, that other issues related to tribometers, such as repeatability, reproducibility and ability to measure contaminated surfaces still need to be addressed before tribometers can be used to reliably predict slips.
Future directions
Additional work is needed to determine if the findings observed here using three low-friction surfaces and two tribometers would apply to other tribometers and other surfaces — particularly contaminated surfaces, which are responsible for many slips and falls. Future work is also needed to address the risk of falling, as well as other tasks such as running, turning, and pushing, which were outside the scope of this project.
Publications and conference presentations
Journal articles
Siegmund GP, Heiden TL, Sanderson DJ, Inglis JT, Brault JR (2005). The effect of subject awareness and prior experience on tribometer-based predictions of slip probability. Gait & Posture doi:10.1016/j.gaitpost.2005.08.005.
Heiden TL, Sanderson DJ, Inglis JT, Siegmund GP (2005). Adaptations to normal human gait on potentially slippery surfaces: the effects of awareness and prior slip experience. Gait & Posture, doi:10.1016/j.gaitpost.2005.09.004.
Conference Presentations/Abstracts
Siegmund GP, Heiden TL, Sanderson DJ, Inglis JT, Brault JR (2005). Subject awareness and prior slip experience affect different aspects of normal human gait. 19 th Annual International Occupational Ergonomics and Safety Conference, Las Vegas, June 27-29, 2005.
Heiden TL, Sanderson DJ, Inglis JT, Siegmund GP (2004). Experience, rather than knowledge, of a slip induces gait adjustments. 34 th Annual Meeting, Society for Neuroscience, Abstract 415.10, San Diego, CA, October 23-28, 2004.