The role of friction in the measurement of slipperiness, Part 2: survey of friction measurement devices

Machine learning prediction of footwear slip resistance on glycerol-contaminated surfaces: A pilot study

Slippery surfaces due to oil spills pose a significant risk in various environments, including industrial workplaces, kitchens, garages, and outdoor areas. These situations can lead to accidents and falls, resulting in injuries that range from minor bruises to severe fractures or head trauma. To mitigate such risks, the use of slip resistant footwear plays a crucial role. In this study, we aimed to develop an Artificial Intelligence model capable of classifying footwear as having either high or low slip resistance based on the geometric characteristics and material parameters of their outsoles. Our model was trained on a unique dataset comprising images of 37 indoor work footwear outsoles made of rubber. To evaluate the slip resistant property of the footwear, all samples were tested using a cart-type friction measurement device, and the static and dynamic Coefficient of Frictions (COFs) of each outsole was determined on a glycerol-contaminated surface. Machine learning techniques were implemented, and a classification model was developed to determine high and low slip resistant footwear. Among the various models evaluated, the Support Vector Classifier (SVC) obtained the best results. This model achieved an accuracy of 0.68 ± 0.15 and an F1-score of 0.68 ± 0.20. Our results indicate that the proposed model effectively yet modestly identified outsoles with high and low slip resistance. This model is the first step in developing a model that footwear manufacturers can utilize to enhance product quality and reduce slip and fall incidents.

The effect of tread patterns on slip resistance of footwear outsoles based on composite materials in icy conditions

INTRODUCTION

Falls on icy surfaces are the leading cause of injuries for outdoor workers. Footwear outsole material and geometrical design parameters are the most significant factors affecting slips-and-falls. Recently, composite materials have been incorporated into outsoles to improve traction, yet the best design parameters are not fully understood.

METHOD

In this effort, based on Taguchi orthogonal array design, 27 outsole prototypes were fabricated with different tread pattern features using our patented composites and tested in a simulated winter condition.

RESULTS

An analysis of variance (ANOVA) showed that surface area (p = 0.041, Contribution = 15.63%) was the only factor significantly affecting the slip-resistance of our prototypes. The best performance was observed for the maximized surface area covered by our composite material with circular and half circular plugs laid obliquely, mostly in the forefoot area.

PRACTICAL APPLICATIONS

These findings suggest that some tread design features of composite-based footwear have a great role in affecting slip-resistance properties of composite-based footwear.

Validating the ability of a portable shoe-floor friction testing device, NextSTEPS, to predict human slips

Measuring shoe-floor friction is critical for assessing the safety of footwear products. Portable devices for measuring coefficient of friction (COF) are needed. This study introduces such a device and evaluates its ability to predict human slip events across shoe designs. A portable device (18 kg) was utilized to measure 66 unique shoe-floor-fluid coefficients of friction (COF). Consistent with the shoes, flooring, and fluid contaminants from the COF tests, participants (n = 66) were unexpectedly exposed to the fluid while walking. Slip predictions were made based on a separate training data set. Slip predictions were made prospectively and using logistic regression analyses. The slip predictions were valid (p < 0.001), 91% sensitive, and 64% specific. The logistic regression fit also revealed that the COF values predicted slip outcomes (p = 0.006). This device is expected to expand the capacity of researchers, product developers, forensic engineers, and safety professionals to prevent slips and enhance human safety.

Relationship between Friction Coefficient and Surface Roughness of Stone and Ceramic Floors

Slips and falls are common occupational incidents worldwide. The friction on a floor surface is one of the critical environmental factors affecting the risk of a slip. In this research, we conducted friction measurements on stone and ceramic floor tiles under dry, wet, and water–detergent (WD) solution covered conditions using a horizontal pull slip meter (HPS). Our purposes were to quantify the slip resistance of commonly used stone and ceramic floors under different surface conditions and to validate the curvilinear relationship between the coefficient of friction (COF) and surface roughness of the floors proposed in the literature. The COF data were analyzed together with a surface profile parameter (Ra) of the floor samples. The results showed that the COFs of the stone floors were significantly (p < 0.0001) higher than those of the ceramic floors. All the floors under the dry conditions were slip resistant when adopting the ANSI 1264.2 criterion. Two and five ceramic floors were not slip resistant under the wet and WD solution covered conditions, respectively. Three polynomial regression equations were established to describe the relationship between the COF and Ra. The curvilinear functions of these models indicate that the three-zone (initial growth, steady-growth, and plateau) concept concerning the COF–Ra relationship in the literature was valid when static COF values measured using an HPS were adopted. In addition, the three-zone concept was valid not only on WD solution covered surfaces but also on dry and wet surfaces.

Evaluation of Winter Footwear: Comparison of Test Methods to Determine Footwear Slip Resistance on Ice Surfaces

The use of slip-resistant winter footwear is crucial for the prevention of slips and falls on ice and snow. The main objective of this paper is to evaluate a mechanical testing method to determine footwear slip resistance on wet and dry ice surfaces and to compare it with the human-centred test method introduced by researchers at KITE (Knowledge, Innovation, Talent, Everywhere)-Toronto Rehabilitation Institute-University Health Network. Phase 1 of this study assessed the repeatability and reproducibility of the mechanical method by evaluating ten different occupational winter boots using two SATRA Slip resistance testers (STM 603, SATRA Technology Centre, Kettering, UK). One tester is located in Toronto and one in Montreal. These boots were chosen based on the needs of the IRSST (Institut de Recherche Robert-Sauvé en Santé et en Sécurité du Travail, Montréal, Quebec, Canada), who were primarily interested in providing safe winter footwear for police, firefighters and municipal workers. In Phase 2, the results of the human-centred test approach were compared with the mechanical results. In Phase 3, two of these boots with conflicting results from the previous phases were tested using a second human-centred method. In Phase 1, the mechanical testing results obtained in the two labs showed a high linear correlation (>0.94) and good agreement on both ice surfaces; however, they revealed a bias (~0.06) between the two labs on the dry ice condition. The mechanical and human-centred tests (phase 2) were found to be better correlated in the wet ice condition (R = 0.95) compared to the dry ice condition (R = 0.34). Finally, the rating of the footwear slip resistance based on the number of slips counted in phase 3 was consistent with the rating by the human-centred test method (phase 2), but not the mechanical method (phase 1). The findings of this study provide a better understanding of the limitations of the SATRA ice tray for measuring footwear slip resistance and demonstrate that the mechanical method must be further refined to make it more comparable to the human-centred methods to achieve better agreement with real-world performance.

An observational ergonomic tool for assessing the worn condition of slip-resistant shoes

Worn shoes are known to contribute to slip-and-fall risk, a common cause of workplace injuries. However, guidelines for replacing shoes are not well developed. Recent experiments and lubrication theory suggest that the size of the worn region is an important contributor to the shoe tread's ability to drain fluid and therefore the under-shoe friction. This study evaluated a simple test for comparing the size of the worn region relative to a common object (AAA and AA battery) as a means of determining shoe replacement. This study consisted of three components involving slip-resistant shoes: Experiment #1: a longitudinal, mechanical, accelerated wear experiment; Experiment #2: a longitudinal experiment where the same shoes were tested after each month of worker use; and Experiment #3: a cross-sectional experiment that exposed participants to a slippery condition, while donning their own worn shoes. The COF (Experiments #1 and #2); under-shoe fluid pressure (all experiments); and slip severity (Experiment #3) were compared across outcomes (fail/pass) of the battery tests. Larger fluid pressures, lower coefficient of friction, and more severe slips were observed for shoes that failed the battery tests compared with those passing the tests. This method offers promise for assessing loss in friction and an increase in slip risk for slip-resistant shoes.

Traction performance across the life of slip-resistant footwear: Preliminary results from a longitudinal study

INTRODUCTION

Slips, trips, and falls are a major cause of injury in the workplace. Footwear is an important factor in preventing slips. Furthermore, traction performance (friction and under-shoe fluid drainage) are believed to change throughout the life of footwear. However, a paucity of data is available for how traction performance changes for naturally worn, slip-resistant footwear.

METHOD

The presented research is a preliminary analysis from an ongoing, larger study. Participants wore slip-resistant footwear while their distance walked was monitored. Friction and under-shoe fluid pressures were measured using a robotic slip tester under a diluted glycerol contaminant condition after each month of wear for the left and right shoes. The size of the worn region was also measured.

RESULTS

Friction initially increased and then steadily decreased as the distance walked and the size of the worn region increased. Fluid pressures increased as the shoes were worn and were associated with increased walking distance and size of the worn region.

DISCUSSION

Consistent with previous research, increases in the size of the worn region are associated with increased under-shoe fluid pressures and decreased traction. These trends are presumably due to reduced fluid drainage between the shoe-floor interface when the shoe becomes worn.

CONCLUSIONS

Traction performance changes with natural wear. The distance walked in the shoe and the size of the worn region may be valuable indicators for assessing loss of traction performance. Practical Applications: Current shoe replacement recommendations for slip-resistant shoes are based upon age and tread depth. This study suggests that tools measuring the size of the worn region and/or distance traveled in the shoes are appropriate alternatives for tracking traction performance loss due to shoe wear.

A Biomechanical Investigation of Athletic Footwear Traction Performance: Integration of Gait Analysis with Computational Simulation

Evaluations are vital to quantify the functionalities of athletic footwear, such as the performance of slip resistance, shock absorption, and rebound. Computational technology has progressed to become a promising solution for accelerating product development time and providing customized products in order to keep up with the competitive contemporary footwear market. In this research, the effects of various tread pattern designs on traction performance in a normal gait were analyzed by employing an approach that integrated computational simulation and gait analysis. A state-of-the-art finite element (FE) model of a shoe was developed by digital sculpting technology. A dynamic plantar pressure distribution was automatically applied to interpret individualized subject conditions. The traction performance and real contact area between the shoe and the ground during the gait could be characterized and predicted. The results suggest that the real contact area and the structure of the outsole tread design influence the traction performance of the shoe in dry conditions. This computational process is more efficient than mechanical tests in terms of both cost and time, and it could bring a noticeable benefit to the footwear industry in the early design phases of product development.

Influence of averaging time-interval on shoe-floor-contaminant available coefficient of friction measurements

Available coefficient of friction (ACOF) is a common metric of footwear traction performance. ACOF is the ratio of friction to normal force, often averaged over a time-interval. The time-interval needed to achieve repeatable and valid ACOF is unknown. A post-hoc analysis was performed on nine shoe-floor-contaminant combinations to assess the repeatability and bias of data averaged across 4 time-intervals (2 ms, 50 ms, 100 ms, 200 ms) after the target normal force was reached. The ability to predict human slips was assessed for ACOF across these intervals. Differences in repeatability and validity across the four intervals were small. However, statistically significant differences were observed for the shortest compared with the longest interval (lower repeatability yet modestly improved predictive ability). Given the limited impact of time-interval on the results, a shorter interval of 50 ms is recommended to enable testing of smaller floor samples.

Prediction of coefficient of friction based on footwear outsole features

Traction testing of footwear is expensive, which may create barriers for certain users to assess footwear. This study aimed to develop a statistical model that predicts available coefficient of friction (ACOF) under boundary lubrication conditions based on inexpensive measurements of footwear outsole features. Geometric and material hardness parameters were measured from fifty-eight footwear designs labeled as slip-resistant. A robotic friction measurement device was used to quantify ACOF with canola oil as the contaminant. Stepwise regression methods were used to develop models based on the outsole parameters and floor type to predict ACOF. The predictive ability of the regression models was tested using the k-fold cross-validation method. Results indicated that 87% of ACOF variation was explained by three shoe outsole parameters (tread surface area, heel shape, hardness) and floor type. This approach may provide an assessment tool for safety practitioners to assess footwear traction and improve workers' safety.

Slip and Fall Incidents at Work: A Visual Analytics Analysis of the Research Domain

Slip and fall incidents at work remain an important class of injury and fatality causing mechanisms. An extensive body of safety research has accumulated on this topic. This article presents an analysis of this research domain. Two bibliometric visualization tools are applied: VOSviewer and HistCite. Samples of 618 slip and fall related articles are obtained from the Web of Science database. Networks of institutions, authors, terms, and chronological citation relationships are established. Collaboration and research activities of the slip and fall research community show that most contributors are from the United States, with the (now closed) Liberty Mutual Research Institute for Safety the most influential research organization. The results of a term clustering analysis show that the slip and fall research can be grouped into three sub-domains: epidemiology, gait/biomechanics, and tribology. Of these, early research focused mainly on tribology, whereas research on gait/biomechanics and epidemiological studies are relatively more recent. Psychological aspects of slip and fall incident occurrence represent a relatively under-investigated research topic, in which future contributions may provide new insights and safety improvements. Better linking of this research domain with other principles and methods in safety science, such as safety management and resilience, may also present valuable future development paths.

Changes in under-shoe traction and fluid drainage for progressively worn shoe tread

Shoe wear is known to increase slipping risk, but few studies have systematically studied this relationship. This study investigated the impact of progressive shoe wear on the available coefficient of friction (ACOF) and under-shoe fluid dynamics. Five different slip-resistant shoes were progressively worn using an accelerated, abrasive, wear protocol. The ACOF and fluid forces (the load supported by the fluid) were measured as shoes were slipped across a surface contaminated with a diluted glycerol solution. As the shoes became worn, an initial increase in ACOF was followed by a steady decrease. Low fluid forces were observed prior to wear followed by increased fluid forces as the worn region became larger. Results suggest that traction performance decreases particularly when the heel region without tread exceeds a size of 800 mm2. This study supports the concept of developing shoe replacement guidelines based upon the size of the worn region to reduce occupational slips.

Vinyl Composite Tile Surrogate for Mechanical Slip Testing

BACKGROUND

Vinyl composite tile (VCT), which is a common flooring in workplaces, is sometimes utilized as the standard floor material for mechanical slip testing experiments. Unfortunately, VCT is a sub-optimal standard test material, since it changes over time and is difficult to manufacture consistently.

PURPOSE

This study aimed to identify a durable laboratory-grade substitute flooring that could provide traction results that are representative of footwear performance on VCT.

METHODS

Eight polymer tiles (cast nylon, polyethylene, polycarbonate, acetal, Delrin, PTFE, polypropylene, and nylon) were tested and the available coefficient of friction (ACOF) was measured and compared with that of two VCT designs. First, a screening test was performed to identify good material candidates based on six shoes and two contaminants (water and oil). Two surrogate candidate tiles were then tested across 17 shoes and three contaminant conditions (water, sodium laurel sulfate, and oil).

RESULTS

Cast nylon tile was found to be the most generalizable VCT surrogate, exhibiting strong correlations with both VCTs for oil contamination. None of candidates were representative of the VCTs for other contaminants.

CONCLUSIONS

Cast nylon may be a useful alternative for VCT for standard slip testing of footwear in oily conditions.

Analysis of required coefficient of friction in running and walking

The popularity of running has increased over the past few years. However, just a few studies in running have focused on the friction between surface and shoe/foot. Changes in friction can affect aspects of human motion, such as safety, motion pattern and efficiency among others. The aim was to investigate the effects of cadence (walk, self-selected running and imposed-running), stance sub-phases (absorption and propulsion) and footwear (barefoot and shod) on the required coefficient of friction (RCOF) of regular runners. Twenty healthy runners (12 males, 8 females, 29.4 ± 4.9 years, 70.4 ± 9.6 kg) participated in this study. Two force plates were used to measure the ground reaction forces (GRF) in order to calculate the RCOF for each condition and the stance phase was divided in sub-phases. In walk, the RCOF was smaller in the absorption than in propulsion phase (p < 0.001). Results evidenced effects of the cadence (p < 0.001), stance sub-phases (p < 0.001) and footwear (p < 0.001) on the RCOF. There was interaction effect in cadence with stance sub-phases (p < 0.001) and footwear with stance sub-phases (p < 0.001). Our results show RCOF is influenced by cadence and footwear condition in the absorption phase.

Predicting slips based on the STM 603 whole-footwear tribometer under different coefficient of friction testing conditions

Assessing footwear slip-resistance is critical to preventing slip and fall accidents. The STM 603 (SATRA Technology) is commonly used to assess footwear friction but its ability to predict human slips while walking is unclear. This study assessed this apparatus' ability to predict slips across footwear designs and to determine if modifying the test parameters alters predictions. The available coefficient of friction (ACOF) was measured with the device for nine different footwear designs using 12 testing conditions with varying vertical force, speed and shoe angle. The occurrence of slipping and the required coefficient of friction was quantified from human gait data including 124 exposures to liquid contaminants. ACOF values varied across the test conditions leading to different slip prediction models. Generally, a steeper shoe angle (13°) and higher vertical forces (400 or 500 N) modestly improved predictions of slipping. This study can potentially guide improvements in predictive test conditions for this device. Practitioner Summary: Frictional measures by the STM603 (SATRA Technology) were able to predict human slips under liquid contaminant conditions. Test parameters did have an influence on the measurements. An increased shoe-floor testing angle resulted in better slip predictions than test methods specified in the ASTM F2913 standard.

A Novel Method of Assessing Floor Friction in Cowsheds and Its Association with Cow Health

Simple Summary

The objective of this paper was to test a simple method of measuring the extent of the slipperiness of different types of floors in cow shelters. Excessively slippery floors, which are less abrasive, are known to reduce a cow’s ability to walk, lie down, and get up without slipping and causing injury to herself. A moderate level of friction between the cows’ hooves and the floor is required for cow comfort and prevention of foot disease and injuries. This study developed a rapid method that welfare assessors can use to measure the slipperiness of floors in cowsheds. The data obtained were then validated by comparing them with the various animal-based and resource-based welfare parameters assessed in each shelter. The analyses done in this study show that there is a link between excessively slippery floors and various parameters such as frequency of cleaning the floors, the gradient of floors, wounds on the bodies and joints of the cows, and the presence of dirty hind limbs. All of these ultimately affect the welfare of cows in shelters. These results suggest that this simple measure of floor friction could be useful in cow welfare assessments. Further work on the repeatability of this method is recommended.

Abstract

Measurement of friction of cowshed floors to determine slipperiness potential is important for cow comfort. Existing methods require elaborate equipment and procedures. A quick method for assessment of friction characteristics is proposed. Friction was measured in 54 cattle housing and yard facilities with earth, brick, concrete, and stone floors, and its association with cattle health parameters was investigated through assessment of 30 animals per facility. A 156 g cuboidal wooden block attached to a spring balance was pulled over 3 m, and the coefficient of friction was recorded as the force required to move the block at a constant speed. The coefficient of friction ranged from 0.3 to 0.7 and was lowest for concrete and highest for earth floors. A multivariate analysis found that cows were standing more and could be more easily approached when they were on floors with high friction levels. The proportion of cows with dirty hind limbs declined with increasing friction of the floor, probably reflecting the fact that they felt more confident to stand rather than lie on high friction floors. This simple measure of frictional characteristics of cattle floors offers promise to be included in welfare measures as an indicator of cow welfare.

Generalizability of Footwear Traction Performance across Flooring and Contaminant Conditions

Background

To prevent slip and fall events at the workplace, mechanical slip testing is conducted on shoes. Such experiments may involve redundant testing across floorings and contaminant conditions, causing wasted time and effort.

Purpose

Quantify the correlations between shoe traction across different contaminant-flooring conditions to reduce redundant slip testing efforts.

Methods

The available coefficient-of-friction (ACOF) was quantified for 17 shoes across five floorings and three contaminant conditions. Redundant testing conditions were identified when the shoe ACOF values for one floor-contaminant condition were highly correlated with a second floor-contaminant condition.

Results

High correlations were observed among quarry floorings across different contaminants and among vinyl (composite tile) floorings with the same contaminant. However, vinyl floorings exhibited low correlations with quarry floorings. Low correlations were also observed across contaminants within vinyl tiles.

Conclusions

This study was able to determine the generalizability of traction performance of shoes across vinyl and quarry floorings. This information is anticipated to reduce redundant traction testing of shoes across vinyl and quarry floorings.

Coefficient of friction testing parameters influence the prediction of human slips

Measuring the available coefficient of friction (ACOF) of a shoe-floor interface is influenced by the choice of normal force, shoe-floor angle and sliding speed. The purpose of this study was to quantify the quality of slip prediction models based on ACOF values measured across different testing conditions. A dynamic ACOF measurement device that tests entire footwear specimens (Portable Slip Simulator) was used. The ACOF was measured for nine different footwear-contaminant combinations with two levels of normal force, sliding speed and shoe-floor angle. These footwear-contaminant combinations were also used in human gait studies to quantify the required coefficient of friction (RCOF) and slip outcomes. The results showed that test conditions significantly influenced ACOF. The condition that best predicted slip risk during the gait studies was 250 N normal force, 17° shoe-floor angle, 0.5 m/s sliding speed. These findings can inform footwear slip-resistance measurement methods to improve design and prevent slips.

Relationship among several measurements of slipperiness obtained in a laboratory environment

Multiple sensing mechanisms could be used in forming responses to avoid slips, but previous studies, correlating only two parameters, revealed a limited picture of this complex system. In this study, the participants walked as fast as possible without a slip under 15 conditions of different degrees of slipperiness. The relationships among various response parameters, including perceived slipperiness rating, utilized coefficient of friction (UCOF), slipmeter measurement and kinematic parameters, were evaluated. The results showed that the UCOF, perceived rating and heel angle had higher adjusted R² values as dependent variables in the multiple linear regressions with the remaining variables in the final pool as independent variables. Although each variable in the final data pool could reflect some measurement of slipperiness, these three variables are more inclusive than others in representing the other variables and were bigger predictors of other variables, so they could be better candidates for measurements of slipperiness.

Performance testing of work shoes labeled as slip resistant

The variability in friction and slip propensity across slip resistant (SR) shoes is poorly understood. This study aimed to quantify the impact of shoe design features on the available coefficient of friction (ACOF) across shoes labeled as SR. Differences in ACOF and the slipping rate across SR shoes were also quantified. Twelve shoes were tested across five types of flooring and three contaminant conditions using a whole shoe mechanical slip tester. Geometric and hardness parameters were measured to determine the effect of heel outsole design on ACOF. The rate of slipping was evaluated for three of the shoes on vinyl tile with canola oil using human subjects. Differences in ACOF were significant across shoe outsole designs (p < .001). ACOF was correlated with geometrical and hardness parameters. Rate of slipping was lower for the highest ACOF shoe (p < .001). This information can be used to guide SR shoe selection and design.

Shoe-Floor Interactions in Human Walking With Slips: Modeling and Experiments

Shoe-floor interactions play a crucial role in determining the possibility of potential slip and fall during human walking. Biomechanical and tribological parameters influence the friction characteristics between the shoe sole and the floor and the existing work mainly focus on experimental studies. In this paper, we present modeling, analysis, and experiments to understand slip and force distributions between the shoe sole and floor surface during human walking. We present results for both soft and hard sole material. The computational approaches for slip and friction force distributions are presented using a spring-beam networks model. The model predictions match the experimentally observed sole deformations with large soft sole deformation at the beginning and the end stages of the stance, which indicates the increased risk for slip. The experiments confirm that both the previously reported required coefficient of friction (RCOF) and the deformation measurements in this study can be used to predict slip occurrence. Moreover, the deformation and force distribution results reported in this study provide further understanding and knowledge of slip initiation and termination under various biomechanical conditions.

Predictive multiscale computational model of shoe-floor coefficient of friction

Understanding the frictional interactions between the shoe and floor during walking is critical to prevention of slips and falls, particularly when contaminants are present. A multiscale finite element model of shoe-floor-contaminant friction was developed that takes into account the surface and material characteristics of the shoe and flooring in microscopic and macroscopic scales. The model calculates shoe-floor coefficient of friction (COF) in boundary lubrication regime where effects of adhesion friction and hydrodynamic pressures are negligible. The validity of model outputs was assessed by comparing model predictions to the experimental results from mechanical COF testing. The multiscale model estimates were linearly related to the experimental results (p < 0.0001). The model predicted 73% of variability in experimentally-measured shoe-floor-contaminant COF. The results demonstrate the potential of multiscale finite element modeling in aiding slip-resistant shoe and flooring design and reducing slip and fall injuries.

Slip safety risk analysis of surface properties using the coefficients of friction of rocks

This study was conducted to determine the most appropriate surface processing techniques (SPT), environmental conditions (EC) and surface roughness (SR) to minimize the risk of slipping when pedestrians walk on a floor covering of rocks barefoot and with shoes. Coefficients of friction (COFs) and values of SR were found using five different types of rocks, four SPT and two (ramp and pendulum) tests. Results indicate that the parameters which affect the COF values of rocks include SR, EC and SPT. Simple linear regression was performed to examine the relationship between the values of the COF and the SR. The value of the COF was identified as R² ≥ 0.864. Statistical results, which are based on experimental measurements, show that rocks are classified according to their safe use areas depending on their COF and SR values.

Gait adaptation on surfaces with different degrees of slipperiness

Gait adaptation to employ different ways to avoid a potential slip is needed to continue walking safely on a new surface, especially when transitioning to a slippery surface. In this experiment, participants walked back and forth five times (trials) on surfaces with different degrees of slipperiness. The results show that trial 1 was significantly different from other trials for most of the dependent variables, especially for the low and high friction conditions. Kinematics on high and medium friction surfaces were very similar, but more adjustments were needed for low friction surfaces. The data for the first trial reflect gait after walking for 2.4 m on the walkway, not the first step onto the walkway. The current data show that gait adaptation continued beyond the first trial. Since participants in this experiment were aware of the floor conditions, the results could have important safety implications that user awareness alone might be insufficient for safe floor designs.

Multidimensional Aspects of Slips and Falls

The study of slips and falls has traditionally focused on body kinematics and tribology. However, this strictly mechanical approach does not allow scientists to assess the importance of each component in relation to the complete system, and thus it lacks integration. The purpose of this chapter is to present and demonstrate the components of a broad analysis for in-depth understanding of slips and falls while walking on level surfaces. In most slip-and-fall studies, balance analysis is simplified and attributed to the point of heel contact. To determine sufficient fall prevention strategies, however, one must analyze balance before the critical moment of lost control. Such an approach requires the sciences of biomechanics, mechanics, anatomy, and neuromuscular control, as well as tribology. Causes of slips and falls are complex, and prevention approaches are often reactive, driven by high-injury trends and lawsuits. Prevention strategies need to be more proactive: Understanding the causes of accidents can help in identifying and correcting hazards before they cause problems. Examples include reporting incidents, selecting the right flooring, selecting footwear, and implementing proper floor-cleaning procedures. A combined effort among all members of the organization, including communication across the entire work system, is critical to the success of slip-and-fall prevention efforts.

State of science: occupational slips, trips and falls on the same level

Occupational slips, trips and falls on the same level (STFL) result in substantial injuries worldwide. This paper summarises the state of science regarding STFL, outlining relevant aspects of epidemiology, biomechanics, psychophysics, tribology, organisational influences and injury prevention. This review reaffirms that STFL remain a major cause of workplace injury and STFL prevention is a complex problem, requiring multi-disciplinary, multi-faceted approaches. Despite progress in recent decades in understanding the mechanisms involved in STFL, especially slipping, research leading to evidence-based prevention practices remains insufficient, given the problem scale. It is concluded that there is a pressing need to develop better fall prevention strategies using systems approaches conceptualising and addressing the factors involved in STFL, with considerations of the full range of factors and their interactions. There is also an urgent need for field trials of various fall prevention strategies to assess the effectiveness of different intervention components and their interactions. Practitioner Summary: Work-related slipping, tripping and falls on the same level are a major source of occupational injury. The causes are broadly understood, although more attention is needed from a systems perspective. Research has shown preventative action to be effective, but further studies are required to understand which aspects are most beneficial.

Required coefficient of friction during level walking is predictive of slipping

The required coefficient of friction (RCOF) is frequently reported in the literature as an indicator of slip propensity. This study aimed to further develop slip prediction models based on RCOF by examining slips under moderately slippery conditions where the RCOF was approximately equal to the available coefficient of friction. Baseline RCOFs were found for normal walking trials and then an unexpected slip was introduced with a moderately slippery boot-floor contaminant combination for thirty-one subjects. Slip outcomes (i.e., whether a subject experienced a slip) were assessed based on the displacement of a marker placed on the heel. A logistic regression analysis was used to model the impact of RCOF on slipping. Results showed that subjects who walked with a greater RCOF were found to have a higher probability of slipping. The predicted probability of a slip across the RCOF ranged from 3% to 95% and an increase of 0.01 in RCOF was associated with a slipping odds ratio of 1.7. Thus, modest differences in RCOF can have a dramatic impact on slip propensity. This study shows that RCOF can be a sensitive and valid predictor of slipping in realistic frictional environments.

Prospective gait changes as a function of shifting perceptions of slipperiness: effects of visual and somatosensory cues

Forty participants, ages 18-45 years, rated perceived slipperiness before and after walking on five different floors under three different surface conditions. The before-ratings were taken as a proxy for visual cues to slipperiness, while after-ratings were taken as a proxy for somatosensory feedback received while walking on the surface. Before and after ratings of slipperiness were used to predict gait parameters, as a function of trial, during repeated walking. Effects of after-ratings of slipperiness were observed beginning on the second trial, and continued through the fifth trial, while effects of before-ratings of slipperiness were most apparent on the first trial. When perceived slipperiness increased (or decreased) from before to after walking on the surface, gait became more (or less) protective across trials. It is concluded that both visual cues, as well as somatosensory feedback, are used in the prospective control of gait. Practitioner Summary: Effects of visual and somatosensory cues to slipperiness on gait were disentangled using floor surfaces varying in the slipperiness suggested by those cues. Visually based ratings of slipperiness predicted gait parameters on earlier trials, while somatosensory-based ratings predicted gait parameters on subsequent trials. Flooring design should provide reliable information regarding slipperiness.

Assessing the performance of winter footwear using a new maximum achievable incline method

More informative tests of winter footwear performance are required in order to identify footwear that will prevent injurious slips and falls on icy conditions. In this study, eight participants tested four styles of winter boots on smooth wet ice. The surface was progressively tilted to create increasing longitudinal and cross-slopes until participants could no longer continue standing or walking. Maximum achievable incline angles provided consistent measures of footwear slip resistance and demonstrated better resolution than mechanical tests. One footwear outsole material and tread combination outperformed the others on wet ice allowing participants to successfully walk on steep longitudinal slopes of 17.5° ± 1.9° (mean ± SD). By further exploiting the methodology to include additional surfaces and contaminants, such tests could be used to optimize tread designs and materials that are ideal for reducing the risk of slips and falls.

The influence of footwear tread groove parameters on available friction

The purpose of this study was to determine how footwear tread groove parameters influence available friction (COF). Utilizing a whole shoe tester (SATRA STM 603), 3 groove parameters (width, depth and orientation) were evaluated. Groove orientation had 3 levels (parallel, oblique and perpendicular), width had 3 levels (3, 6 and 9 mm) and depth had 3 levels (2, 4 and 6 mm). In total, the COF of 27 shoes, each with a distinct groove combination, was assessed on wet porcelain tile. The 27 groove combinations produced a wide range of COF values (0.080-0.344). Groove orientation had the greatest impact on COF, explaining the greatest variance in observed COF values (ŋ(2) = 0.81). The most slip resistant groove combination was an oblique orientation, with 3 mm width and 2 mm depth. The least slip resistant groove combination was a parallel orientation, with a 6 mm width and 6 mm depth.

SURFACE MODIFICATION OF TPR SOLE: AN APPROACH TO IMPROVE SLIP RESISTANCE ON QUARRY AND CERAMIC TILES

Human slip on smooth surfaces is a common accident, even though the footwear soling materials are designed with cleats and treads to provide more friction with the floor. About 20% of footwear is made with thermoplastic rubber (TPR; styrene-butadiene-styrene) soles. The slip resistance property under wet-flooring conditions of this kind of sole is poor because of the nonionic nature of the polymer. Chemical surface modification can be exploited to improve the slip-resistance property of TPR soles. The surface is chemically modified with trichloroisocyanuric acid in a methyl ethyl ketone medium (TCI/MEK; at 1, 2, and 3%) to introduce chlorinated and oxidized moieties to the rubber surface. The extent of surface modification produced in TPR with this change can be tested using attenuated total reflectance–Fourier transform infrared spectroscopy, scanning electron microscopy, and contact angle and surface roughness measurements. The improvement in slip resistance can be evaluated by measuring the coefficient of friction using a dynamic slip-resistance tester. The extent of the change in the functional physical properties, such as surface roughness, contact angle, work adhesion, in slip resistance can be improved by optimizing the concentration of trichloroisocyanuric acid. Physicomechanical properties of unmodified and modified soles that are essential for wear performance can be tested and compared. Quantitative changes on the surface of modified rubber soles increases surface roughness, reduces contact angles, and increases work energy, so there is a considerable increase in the coefficient of friction, especially under wet floor conditions. The chemical surface treatment tends to reduce the bulk mechanical properties, such as tensile strength, elongation at break, and abrasion resistance, because cyanuric acid attacks the sole. The coefficient of friction produces a positive trend at 1 and 2% TCI/MEK treatments, but the trend is negative at a 3% concentration. The optimum surface treatment level for surface modification to enhance the slip resistance of TPR is 2% TCI/MEK.

A Method for Measuring Fluid Pressures in the Shoe-Floor-Fluid Interface: Application to Shoe Tread Evaluation

Background

Fluid contaminants cause slipping accidents by reducing shoe-floor friction. Fluid pressures in the shoe-floor interface reduce contact between the surfaces and, thus, reduce friction between the surfaces. A technological gap for measuring fluid pressures, however, has impeded improved understanding of what factors influence these pressures.

Purpose

This study aimed to introduce a technique for measuring fluid pressures under the shoe and to demonstrate the utility of the technique by quantifying the effects of tread depth and fluid viscosity on fluid pressures for two different shoes.

Methods

A fluid pressure sensor embedded in the floor surface was used to measure fluid pressures, while a robotic slip-tester traversed the shoe over the floor surface. Multiple scans were collected to develop 2D fluid pressure maps across the shoe surface. Two shoe tread types (an athletic shoe and a work shoe), two fluids (high-viscosity diluted glycerol and a low-viscosity detergent solution), and three tread depths (full tread, half tread, and no tread) were tested, while fluid pressures were measured.

Results

Untreaded shoes combined with a high-viscosity fluid resulted in high fluid pressures, while treaded shoes or low-viscosity fluids resulted in low fluid pressures. The increased fluid pressures that were observed for the untreaded shoes are consistent with tribology theory and evidence from human slipping studies.

Conclusions

The methods described here successfully measured fluid pressures and yielded results consistent with tribological theory and human slipping experiments. This approach offers significant potential in evaluating the slip-resistance of tread designs and determining wear limits for replacing shoes.

The stochastic distribution of available coefficient of friction for human locomotion of five different floor surfaces

The maximum coefficient of friction that can be supported at the shoe and floor interface without a slip is usually called the available coefficient of friction (ACOF) for human locomotion. The probability of a slip could be estimated using a statistical model by comparing the ACOF with the required coefficient of friction (RCOF), assuming that both coefficients have stochastic distributions. An investigation of the stochastic distributions of the ACOF of five different floor surfaces under dry, water and glycerol conditions is presented in this paper. One hundred friction measurements were performed on each floor surface under each surface condition. The Kolmogorov-Smirnov goodness-of-fit test was used to determine if the distribution of the ACOF was a good fit with the normal, log-normal and Weibull distributions. The results indicated that the ACOF distributions had a slightly better match with the normal and log-normal distributions than with the Weibull in only three out of 15 cases with a statistical significance. The results are far more complex than what had heretofore been published and different scenarios could emerge. Since the ACOF is compared with the RCOF for the estimate of slip probability, the distribution of the ACOF in seven cases could be considered a constant for this purpose when the ACOF is much lower or higher than the RCOF. A few cases could be represented by a normal distribution for practical reasons based on their skewness and kurtosis values without a statistical significance. No representation could be found in three cases out of 15.

A multivariable model for predicting the frictional behaviour and hydration of the human skin

BACKGROUND

The frictional characteristics of skin-object interactions are important when handling objects, in the assessment of perception and comfort of products and materials and in the origins and prevention of skin injuries. In this study, based on statistical methods, a quantitative model is developed that describes the friction behaviour of human skin as a function of the subject characteristics, contact conditions, the properties of the counter material as well as environmental conditions.

AIMS

Although the frictional behaviour of human skin is a multivariable problem, in literature the variables that are associated with skin friction have been studied using univariable methods. In this work, multivariable models for the static and dynamic coefficients of friction as well as for the hydration of the skin are presented.

MATERIALS & METHODS

A total of 634 skin-friction measurements were performed using a recently developed tribometer. Using a statistical analysis, previously defined potential influential variables were linked to the static and dynamic coefficient of friction and to the hydration of the skin, resulting in three predictive quantitative models that descibe the friction behaviour and the hydration of human skin respectively.

RESULTS AND DISCUSSION

Increased dynamic coefficients of friction were obtained from older subjects, on the index finger, with materials with a higher surface energy at higher room temperatures, whereas lower dynamic coefficients of friction were obtained at lower skin temperatures, on the temple with rougher contact materials. The static coefficient of friction increased with higher skin hydration, increasing age, on the index finger, with materials with a higher surface energy and at higher ambient temperatures. The hydration of the skin was associated with the skin temperature, anatomical location, presence of hair on the skin and the relative air humidity.

CONCLUSION

Predictive models have been derived for the static and dynamic coefficient of friction using a multivariable approach. These two coefficients of friction show a strong correlation. Consequently the two multivariable models resemble, with the static coefficient of friction being on average 18% lower than the dynamic coefficient of friction. The multivariable models in this study can be used to describe the data set that was the basis for this study. Care should be taken when generalising these results.

A Novel Method for Evaluating the Effectiveness of Shoe-Tread Designs Relevant to Slip and Fall Accidents

Slip and falls account for a large share of occupational accidents. Slips are typically initiated when an insufficient amount of friction is present between the shoe and floor surfaces during walking. Shoe tread is thought to enhance the friction by channeling fluid contaminants away from the shoe and floor surface thus mitigating the fluid’s ability to lubricate the two surfaces and reduce friction. This study presents a novel method for evaluating the effectiveness of shoe tread by measuring fluid pressures during simulated slips. Sensors embedded into the floor measured fluid pressure while a robotic slip-tester simulated a human slip. A work shoe with three different tread depths (no, medium and full tread) was tested against a vinyl floor using a diluted (90%) glycerol and diluted detergent (2% detergent, 98% water) contaminant. Fluid pressures were high in the no tread condition but negligible in the other two tread depth conditions for the diluted glycerol and were negligible for all diluted detergent conditions. The no tread (COF: 0.005) also had lower friction coefficient values than treaded conditions (COF: 0.08-0.38). This study suggests that the effectiveness of tread to reduce the lubricating quality of the fluid can be directly measured using a robotic slip-tester and a fluid pressure sensor embedded in the floor. This method has the potential for developing tread depth recommendations and in evaluating the validity of slip-testers to simulate under-shoe conditions.

Stochastic distribution of the required coefficient of friction for level walking--an in-depth study

This study investigated the stochastic distribution of the required coefficient of friction (RCOF) which is a critical element for estimating slip probability. Fifty participants walked under four walking conditions. The results of the Kolmogorov-Smirnov two-sample test indicate that 76% of the RCOF data showed a difference in distribution between both feet for the same participant under each walking condition; the data from both feet were kept separate. The results of the Kolmogorov-Smirnov goodness-of-fit test indicate that most of the distribution of the RCOF appears to have a good match with the normal (85.5%), log-normal (84.5%) and Weibull distributions (81.5%). However, approximately 7.75% of the cases did not have a match with any of these distributions. It is reasonable to use the normal distribution for representation of the RCOF distribution due to its simplicity and familiarity, but each foot had a different distribution from the other foot in 76% of cases.

PRACTITIONER SUMMARY

The stochastic distribution of the required coefficient of friction (RCOF) was investigated for use in a statistical model to improve the estimate of slip probability in risk assessment. The results indicate that 85.5% of the distribution of the RCOF appears to have a good match with the normal distribution.

Friction variation in common working areas of fast-food restaurants in the USA

Friction variation has been related to employees' perception of slipperiness in a field study conducted in fast-food restaurants. However, details of friction variation in actual workplaces have not been reported in the literature. This field study investigated friction variations in 10 fast-food restaurants in the USA. The results indicated that friction reductions in a step exceeding 10% were proportional to the ages of the floor tiles in most restaurants. There were more friction reductions exceeding 10% in the sink areas than the other five areas measured, but all the areas had more than 10% friction reductions in at least one of the restaurants. As expected, significant relative friction reductions are common on older floors. A small portion of the newer tiles had significant relative friction reductions, despite their overall higher friction levels. Therefore, slip and fall preventions should not be overlooked in restaurants with newer floors. Friction variation is speculated to be a significant contributor to slip and fall incidents. However, friction variation has not been quantified in the literature. Understanding of potential friction variations in field environments helps identify potential issues for interventions. This field study investigated friction variations in fast-food restaurants in the USA.

Impact of joint torques on heel acceleration at heel contact, a contributor to slips and falls

Slips/falls are a health burden in the workplace. Previous research has implied a relationship between foot dynamics at heel contact and slips/falls; however, heel acceleration has received little attention. Heel acceleration as the heel contacts the ground is the result of the combined effort of the leg joint torques to control motion of the foot. This study aims to examine the association of heel acceleration with fall risk, and explore the main joint torque determinant of heel acceleration at contact. Sixteen young and eleven older adults walked on known dry floors and in slippery environments expected to be dry. Heel acceleration at heel contact in the direction of motion, i.e. anterior/posterior, was compared between slip-recovery and slip-fall outcomes. Results showed that subjects that recovered contacted the floor with a greater heel deceleration (p < 0.05) than fall subjects. Knee torque alone explained 76% of the heel acceleration variability (p < 0.01). These data suggest that walking with reduced knee flexion torque at heel contact results in a reduced heel deceleration, a potential risk factor for slip-initiated falls.

The effect of contact area on friction measured with the portable inclinable articulated strut slip tester (PIAST)

A portable inclinable articulated strut slip tester (PIAST) measures friction at the shoe and floor interface. The squeeze-film effect with the PIAST is excessive in representing a human strike. The goal of this study was to investigate the effect of the contact area size on friction for reducing the squeeze-film effect. The footwear pad area of this slip meter was sequentially reduced from 7.62 cm square to 2.54 cm square. Five walkways were constructed. Friction was measured on each walkway under three surface conditions. Thirty-five participants rated their perceptions of slipperiness. The results indicated that the friction increased and plateaued as the size of the contact area was reduced. The effect of the pad size on the friction coefficient was statistically significant. The correlation coefficients between the friction and perception rating did not give a clear indication of what pad size might have a better correlation with human perception. Friction measurement at the shoe and floor interface is a critical issue in assessing potential interventions and identifying potentially dangerous locations for slip and fall incidents. This paper addresses a potential improvement in measuring friction on liquid-contaminated floor surfaces.

Stepping over obstacles of different heights and varied shoe traction alter the kinetic strategies of the leading limb

This study aims to investigate the effects of shoe traction and obstacle height on friction during walking to better understand the mechanisms required to avoid slippage following obstacle clearance. Ten male subjects walked at a self-selected pace during eight different conditions: four obstacle heights (0%, 10%, 20% and 40% of limb length) while wearing two different pairs of shoes (low and high traction). Frictional forces were calculated from the ground reaction forces following obstacle clearance, which were sampled with a Kistler platform at 960 Hz. All frictional peaks increased with increases in obstacle height. Low traction shoes yielded smaller peaks than high traction shoes. The transition from braking to propulsion occurred sooner due to altered control strategies with increased obstacle height. Collectively, these results provided insights into kinetic strategies of leading limb when confronted with low traction and high obstacle environments. This study provides valuable information into the adaptations used to reduce the potential of slips/falls when confronted with environments characterised by low shoe-floor friction and obstacles. It also provides the necessary foundation to explore the combined effects of shoe traction and obstacle clearance in elderly people, more sensitive to slippage.

A methodology to quantify the stochastic distribution of friction coefficient required for level walking

The required friction coefficient is defined as the minimum friction needed at the shoe and floor interface to support human locomotion. The available friction is the maximum friction coefficient that can be supported without a slip at the shoe and floor interface. A statistical model was recently introduced to estimate the probability of slip and fall incidents by comparing the available friction with the required friction, assuming that both the available and required friction coefficients have stochastic distributions. This paper presents a methodology to investigate the stochastic distributions of the required friction coefficient for level walking. In this experiment, a walkway with a layout of three force plates was specially designed in order to capture a large number of successful strikes without causing fatigue in participants. The required coefficient of friction data of one participant, who repeatedly walked on this walkway under four different walking conditions, is presented as an example of the readiness of the methodology examined in this paper. The results of the Kolmogorov-Smirnov goodness-of-fit test indicated that the required friction coefficient generated from each foot and walking condition by this participant appears to fit the normal, log-normal or Weibull distributions with few exceptions. Among these three distributions, the normal distribution appears to fit all the data generated with this participant. The average of successful strikes for each walk achieved with three force plates in this experiment was 2.49, ranging from 2.14 to 2.95 for each walking condition. The methodology and layout of the experimental apparatus presented in this paper are suitable for being applied to a full-scale study.

Slipping of the foot on the floor when pulling a pallet truck

Workers pulling pallet trucks are likely to slip when pulling and stepping on a low-friction floor. This study investigated the slipping of male participants when pulling a pallet truck, walking backward, and stepping on either a dry, wet, or glycerol-contaminated vinyl surface. The weight of the load on the truck was either low (0 kg), medium (295 kg), or high (568 kg). A motion-tracking system was used to collect the three-dimensional coordinates of the markers on the shoes. It was found that subjects might slip either upon landing of the leading foot on the toe (slip I) or before taking off of the lagging foot on the heel (slip II). The results indicated that the slip distances for both types of slip were significantly affected by the load and surface conditions and their interactions. Micro-slips (slips between 0.1 and 3 cm) and midi-slips (slips between 3 and 10 cm) were more common in slip I than in slip II. On glycerol-contaminated surfaces, the probabilities of a slide, or a slip more than 10 cm, for both slips I and II were over 40%. The implications of the results were discussed.

Assessing slipperiness in fast-food restaurants in the USA using friction variation, friction level and perception rating

Although friction variation is speculated to be a significant contributor to slip and fall incidents, it has not been related to a measurement of slipperiness in the literature. This field study investigated the relationship among multiple friction variations, friction levels and the perception ratings of slipperiness in six major working areas of 10 fast-food restaurants in the USA. The mean perception rating score for each working area was correlated with various friction reduction variables across all the restaurants in comparison with its correlation with the mean friction coefficient of each working area. The results indicated that the absolute and relative reductions in friction over the whole working area, among 12 friction reduction variables evaluated, could have a slightly better correlation with the perception rating score (r=0.34 and 0.37, respectively) than the mean friction coefficient of each working area (0.33). However, in friction measurements, more effort and time are needed to quantify friction variations than to obtain the mean friction coefficient. The results of the multiple regression model on the perception rating indicated that adding friction reduction variables into the regression model, in addition to the mean friction coefficient, did not make a significant impact on the outcomes. The results further indicated a statistically significant correlation between the mean friction coefficient and the maximum relative friction reduction over the whole area in each working area across all the restaurants evaluated (r=0.80). Despite a slightly lower correlation with perception rating than the friction variation, the mean friction coefficient of an area is still a reasonably good indicator of slipperiness.

Effects of slip testing parameters on measured coefficient of friction

Slips and falls are a major cause of injuries in the workplace. Devices that measure coefficient of friction (COF) of the shoe-floor-contaminant interface are used to evaluate slip resistance in various environments. Testing conditions (e.g. loading rate, timing, normal force, speed, shoe angle) are believed to affect COF measurements; however, the nature of that relationship is not well understood. This study examines the effects of normal force (NF), speed, and shoe angle on COF within physiologically relevant ranges. A polyvinyl chloride shoe was tested using a modified industrial robot that could attain high vertical loads and relatively high speeds. Ground reaction forces were measured with a loadcell to compute COF. Experiment #1 measured COF over a range of NF ( approximately 100-500 N) for two shoe angles (10 degrees and 20 degrees ), four speeds (0.05, 0.20, 0.35, and 0.50 m/s), and two contaminants (diluted detergent and diluted glycerol). Experiment #2 further explored speed effect by testing seven speeds (0.01, 0.05, 0.20, 0.35, 0.50, 0.75, and 1.00 m/s) at a given NF (350 N) and shoe angle (20 degrees ) using the same two contaminants. Experiment #1 showed that faster speeds significantly decreased COF, and that a complex interaction existed between NF and shoe angle. Experiment #2 showed that increasing speed decreased COF asymptotically. The results imply that COF is dependent on film thickness separating the shoe and the heel, which is dependent on speed, shoe angle, and NF, consistent with tribological theory.

The use of a heel-mounted accelerometer as an adjunct measure of slip distance

A human-centered measure of floor slipperiness could be useful as an adjunct to conventional tribologic measures. This paper reports on the development and evaluation of a measure of slip distance based on variables derived from the signal of a heel-mounted accelerometer. Twenty-one participants walked on a laboratory runway under several surface slipperiness conditions at three walking speeds during a protocol designed to produce a wide range of slip distances at heel strike. Analysis of variance showed significant effects of slip distance (no-slip, micro-slip and slide), walking speed (1.52, 1.78 and 2.13 m/s) and their interactions on peak forward acceleration, peak vertical acceleration and deceleration time of the heel following heel strike in 704 trials. Regression analysis of slip distance and deceleration time showed the strongest relationship with R2=0.511. Large individual variation in the strength of this relationship was observed. The heel-mounted accelerometer may have utility as an adjunct measure in the evaluation of floor slipperiness, particularly for field applications where direct measurement may not be feasible.

Assessment of Walkway Tribometer Readings in Evaluating Slip Resistance: A Gait-Based Approach

The purpose of this study was to assess the viability of using slip risk (as quantified during human subject walking trials) to create a reference standard against which tribometer readings could be compared. First, human subjects (N=84) were used to rank objectively the slipperiness of three different surfaces with and without a contaminant (six conditions). Second, nine tribometers were used to independently measure and rank surface slipperiness for all six conditions. The slipperiness ranking determined from the walking trials was considered the reference against which the tribometer measurements were compared. Our results revealed that only two of the nine tribometers tested (Tortus II and Mark III) met our compliance criteria by both correctly ranking all six conditions and differentiating between surfaces of differing degrees of slipperiness. These findings reinforce the need for objective criteria to ascertain which tribometers effectively evaluate floor slipperiness and a pedestrian's risk of slipping.