Slip & Fall


Friction Sled
Triodyne Safety Bulletin
Volume 2 No. 1, September 1995
Claudine P. Giebs, Ralph L. Barnett and Peter J. Poczynok

It's better to collapse than to topple over, it's better to be short than tall and it's best not to fall at all.


The Drunk, the Child and the Soldier - My, How They Fall
Triodyne Safety Bulletin
Volume 2 No. 2, September 1995
Ralph L. Barnett

Discussion of the Triodyne Friction Tester.


Hand Trajectories Under Free Fall
Triodyne Safety Brief
Volume 12 No. 2, January 1997
Ralph L. Barnett and Suzanne A. Glowiak

Can the hands elevate during a free fall scenario? This question arises in the design of fall intervention devices, during accident reconstruction and in the study of safe climbing strategies. This paper calculates the maximum simple reaction time that will enable the hands to elevate during a "drop" event.


Hand Motion During Trip and Fall Scenarios
Safety Engineering and Risk Analysis
Volume 7, 1997
Ralph L. Barnett and Suzanne A. Glowiak

The location of workplace hazards, the design of fall intervention systems, the development of climbing and walking strategies, and the forensic analysis of slip and fall accidents all benefits from a knowledge of hand motion under the combined effects of gravity and human response. This paper calculates the maximum simple reaction time that will enable the hands to elevate during a drop or trip event. Hand trajectories are characterized for both scenarios.


Hand Motion During Trip and Fall Scenarios
Triodyne Safety Abstract
Volume 2, No. 4, July 1997
Ralph L. Barnett and Suzanne A. Glowiak

The location of workplace hazards, the design of fall intervention systems, the development of climbing and walking strategies, and the forensic analysis of slip and fall accidents all benefits from a knowledge of hand motion under the combined effects of gravity and human response. This paper calculates the maximum simple reaction time that will enable the hands to elevate during a drop or trip event. Hand trajectories are characterized for both scenarios.


Falling: The Cook County Illinois Experience
Triodyne Safety Bulletin
Volume 7 No. 1, June 1998
Claudine P. Giebs Myers, Peter J. Poczynok

An analysis of fall behavior as reported in the Cook County Verdict Reporter from 1991 and 1997.


"Slip and Fall" Theory - Extreme Order Statistics
Triodyne Safety Brief
Volume 21 No. 3, September 2002
Ralph L. Barnett

Classical "slip and fall" analysis was reformulated in this paper to account for the stochastic nature of friction. As it turned out, the new theory, arising from this analysis, was a precise statement of the distribution function for the smallest value among n independent observations. This made it possible to invoke an important result from the asymptotic theory of extreme order statistics that reduced the theory to a simple and elegant relationship among the probability of slipping, the critical friction criterion, the distance traveled by the walker, and the average, spread and asymmetry of the distribution of friction coefficients. The new theory reveals that short walks lead to fewer falls; low friction floors are sometimes better than high friction ones.


Floor Reliability With Respect to "Slip and Fall"
Triodyne Safety Brief
Volume 24 No. 3, November 2003
Ralph Lipsey Barnett and Peter Joseph Poczynok

For a given community of walkers and a specific type of ambulation, force-plate studies have established the required level of horizontal resistance for stable locomotion. This stochastic floor loading is resisted by friction forces which must be great enough to prevent slipping. A statistical characterization of frictional resistance has recently been developed using extreme value statistics. Reliability theory provides a method for combining the floor loading and friction resistance which, for the first time, enables one to determine in a rational manner the probability of slipping. This paper presents a formula describing the "slip and fall" reliability of a floor/footwear couple.


Stochastic Theory of Human Slipping
Triodyne Safety Bulletin
Volume 22 No. 4, February 2003
Ralph L. Barnett, Suzanne A. Glowiak and Peter J. Poczynok

The conventional approach to human slipping is essentially deterministic; it states that no slipping will occur when the average friction coefficient is greater than some critical friction criterion. Under this condition, pedestrians will not slip when they encounter the average friction coefficient. On the other hand, to successfully negotiate a walk of n-steps they must not slip when they encounter the smallest of the n friction coefficients. Consequently, a new slip theory has been formulated as a problem in extreme value statistics. An elegant relationship is obtained among the probability of slipping, the critical friction criterion, the number of steps taken by the walker, and the central measure, scatter, and asymmetry of the distribution of friction coefficients. The new theory reveals the structure of human slipping in a startling way that introduces completely new concepts: the go/no go nature of classical slip predictions is replaced by a probability of slipping; low friction floor/footwear couples may lead to fewer slips than high friction ones; slipping can occur in any case where conventional theory predicts "no slip"; and the number of slips depends on the distance traveled by a pedestrian. Finally, this paper develops the idea that the slipperiness of a real floor must be evaluated for a duty-cycle. Duty-cycles can be represented as frequency histograms when a floor is homogeneous and isotropic.


Slip and Fall Characterization of Floors
Triodyne Safety Brief
Volume 26 No. 2, June 2004
Ralph L. Barnett and Peter J. Poczynok

During ambulation, every maneuver causes the feet to impose tangential loading at each contact with the floor. If the frictional resistance at the contact point is less than the associated tangential loading, slipping occurs and sometimes falling. There are five disciplines, some recently developed, that enable one to develop the general theory for predicting the number of walkers who will slip within a given time period on a statistically homogeneous and isotropic floor. These include force-plate studies, floor duty cycles, tribometry, extreme value theory of slipperiness, and floor reliability theory. When used with some additional bookkeeping notions, the general theory will be extended to real floors traversed by walkers with multiple ambulation styles and wearing a variety of footwear.


Extreme Value Formulation of Human Slip: A Summary
Triodyne Safety Brief
Volume 27 No. 4, April 2005
Ralph L. Barnett and Suzanne A. Glowiak

Conventional "slip and fall" theory establishes a go-no-go criterion that indicates whether or not a given floor has satisfactory slip resistance. Specifically, the theory states that no slip, and hence no fall, will occur whenever the average coefficient of friction between a floor and some "worst case standard footwear material," e.g. leather, is greater than a threshold friction coefficient. This threshold friction is not selected by some rational protocol; it is often established by legislative fiat or consensus. Using extreme value statistics, this paper reformulates classical "slip theory" to explicitly account for the stochastic nature of friction coefficients. By abandoning the traditional deterministic approach to slip in favor of a statistical formulation, fully integrated protocols are able to be developed which predict the number of pedestrians who will slip or, alternatively, who will violate a threshold slip criterion. A new theory emerges that embraces everything from a simple floor with a single walker to very complicated real floors traversed by a throng of pedestrians with multiple ambulation styles and wearing a variety of footwear. It must be emphasized that the new slip protocol merely provides a mathematical framework that enables walkway professionals to make quantitative estimates of slip propensity. Like conventional theory, it also suffers from the "garbage in-garbage out" syndrome. Accurate tribometers, for example, are still required for precise predictions. On the other hand, the concept of threshold criterion and worst case footwear surrogates are replaced by force-plate data obtained by gait laboratories using various communities of walkers. Reliability determination for real floors requires the introduction of floor duty cycles.


Slip, Trip and Fall
Center of Excellence

Ralph L. Barnett

Review of the subject of slips, trips, and falls as a safety topic.


Slipping on Concrete: A Case Study
Volume 29 No. 1, July 2007
Ralph L. Barnett, Adam A.E. Ziemba, and Theodore Liber

The ambulation of pedestrians claims more lives and produces more disabling injuries than warfare. Every year global statistics on Slip/Trip and Fall indicate that senior citizens and the general population have respectively achieved No. 1 and No. 2 status with respect to traumatic death and injury. The automobile is the only competition for this dubious distinction. This paper presents a forensic and safety study that focuses on slip and fall.


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