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Friction Sled
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
Discussion of the Triodyne Friction Tester.
Hand Trajectories Under Free Fall
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
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
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
An analysis of fall behavior as reported in the Cook County Verdict Reporter from 1991 and 1997.
"Slip and Fall" Theory - Extreme Order Statistics
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"
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
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
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
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
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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