“Slippery” work surfaces: Towards a performance definition and quantitative coefficient of friction criteria

There have been 50 years of research in walking/working surface slipperiness and coefficient of friction (COF) measurements. Nevertheless, numerous standards address slip/fall accidents only in terms of requiring surfaces to be qualitatively “nonslippery.” The literature useful for establishing quantitative criteria for “slippery” vs. “slip-resistant” have been summarized here. A performance definition for “slippery work surfaces” is proposed. Recommendations applicable to standards-making organizations are made, including changing terms such as “non-slip” to “slip-resistant” and defining “slippery” in terms of quantitative COF values. For persons walking unloaded on level surfaces, a COF standard of 0.5 would be reasonable. Research is recommended to determine if “slip-resistance” requirements and accident prevention could be achieved more easily be controlling the type of shoe, type of task, or amount of surface contaminant rather than controlling only the COF of the basic surface and its coating.     

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.     

Development of an objective determination of a slip with a portable inclineable articulated strut slip tester (PIAST)

A portable inclineable articulated strut slip tester (PIAST) is a slipmeter that is widely used in the USA to measure coefficient of friction (COF) at the shoe sole and floor interface. A determination of a slip at the measurement interface, which is currently judged subjectively by operators, plays a crucial role in deciding the outcomes of a PIAST measurement. The goal of this study was to develop an objective determination of a slip based on the movement of the weight used by the slipmeter. The displacement of the weight and the time duration of consecutive strikes in a measurement were used to derive the objective slip criterion. Various footwear materials, floor materials and surface conditions were used to cover a wide range of COF values. The results of the regression analysis indicated that the objective COF predicted by the method developed in the current study was significant (R² = 0.997, β = 0.991, p < 0.001) in predicting the subjective COF determined by the operator.     

Slip initiation in alternative and slip-resistant footwear

Slips occur as a result of failure of normal locomotion. The purpose of this study is to analyze the impact of alternative footwear (Crocs?, flip-flops) and an industry standard low-top slip-resistant shoe (SRS) under multiple gait trials (normal dry, unexpected slip, alert slip and expected slip) on lower extremity joint kinematics, kinetics and muscle activity. Eighteen healthy male participants (age: 22.28?±?2.2 years; height: 177.66?±?6.9?cm; mass: 79.27?±?7.6?kg) completed the study. Kinematic, kinetic and muscle activity variables were analyzed using a 3(footwear)?×?4(gait trials) repeated-measures analysis of variance at p?=?0.05. Greater plantar flexion angles, lower ground reaction forces and greater muscle activity were seen on slip trials with the alternative footwear. During slip events, SRS closely resembled normal dry biomechanics, suggesting it to be a safer footwear choice compared with alternative footwear.     

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.     

The Surface Roughness of a Rubber Soling Material Determines the Coefficient of Friction on Water-Lubricated Surfaces

For more than a decade, evidence has been accumulating that points to the fact that the microscopic roughness of the footwear soling surface is a major determinant of slip-resistance on lubricated surfaces, but conclusive experimental proof has been lacking. This article describes an experiment in which five pairs of shoes were soled with the same rubber compound. Four of the pairs were abraded by different grades of grit to produce a range of roughness values. The coefficient of friction (CoF) of the five solings was then measured repeatedly by the walking traction method on wet surfaces including glazed wall tiles, vinyl asbestos coated with the wax floor polish, and both sides of a sheet of float glass. The Kruskal-Wallis statistical test proved beyond doubt that the soling roughness is a major factor in determining the CoF of this rubber soling material; p < 10⁻⁵. Nearly all of the grip was due to surface roughness of the soling material on these atypically smooth floors, although the surface roughness of the floors also had a significant effect on CoF; p < 0.003. Float glass is shown to be a promising reference floor material for the measurement of CoF of footwear; there was no statistical difference between results for the two sides of the glass sheet. Float glass could be used in the development of a standard CoF test method because new sheets of glass from the same manufacturer are identical and extremely smooth. The specification of CoF values for solings/floors combinations in lubricated conditions is of little value unless associated with roughness measurements and knowledge of how wear will affect the surface roughness of the sole. This article reports the first evidence that any specification of flooring by measuring CoF based on dry surfaces could lead to an increase in the number of injuries caused by slipping on the wet surfaces. Published by Elsevier Science Ltd     

Friction measurements on “anti-slip” floors under shoe sole,contamination, and inclination conditions

Friction measurements were conducted to study the effects of shoe sole, floor, contamination, and inclined angle of the floor surface on friction coefficient. The shoe sole samples included composite rubber outsole samples with and without V-shaped tread design. Unglazed ceramic tiles of both flat and tiles with molded profile design were tested. The contamination conditions included dry, wet, and glycerol-contaminated conditions. The inclined angles included 0°, 5°, and 10°. A Brungraber Mark II slipmeter was used. The results showed that all the four factors affected friction coefficient significantly (p < 0.0001). Flat rubber soles had higher friction coefficients than the soling samples with V-shaped tread design on all tested floors and inclined angles under wet conditions. Flat soles, however, had extremely low friction when tested on flat floors under glycerol-contaminated conditions. The floors with molded grooves perpendicular to friction measurement direction had the highest friction coefficients than all other floor conditions under both the wet and glycerol-contaminated conditions except the wet/flat sole/10° condition. A regression model with a cosine function was established to describe the relationship between friction coefficient and inclined angle of the floor under the experimental conditions. This model is statistically significant at p < 0.0001 with an R² of 0.97.     

Subjective assessments of floor slipperiness before and after walk under two lighting conditions

A gait experiment was performed. The participants were tested under shoes, floors, surface and lighting conditions. They gave floor slipperiness ratings before and after a gait trial. The perceived sense of slip (PSOS) was collected. It was found that the perceived floor slipperiness (PFS) before walking was affected significantly by the lighting, floor and surface conditions. Relative low PFS values were recorded under wet and detergent-contaminated conditions in the normal daylight condition as compared with those in the dimmed condition. The PFS after the gait was significantly affected by the floor and surface conditions. The PSOS was highly correlated with the PFS after trial. The regression analyses results indicated that both the coefficient of friction (COF) of the floor and lighting were primary predictors of the PFS before a gait. The COF and walking speed were the primary predictors of the PFS after a gait.     

Roughness and slipperiness of floor surface: Tactile sensation and perception

The slipperiness of floor is one of the risk factors affecting the occurrence of slipping and falling. The purpose of the study was to compare the roughness and slipperiness of five floor surfaces based on tactual sensations from different body segments for human subjects. The perceived roughness and perceived floor slipperiness of five floors based on tactual sensation from 20 male and 20 female subjects were collected and compared. The female subjects tended to give higher subjective ratings on both perceived roughness and slipperiness than their male counterpart. Both index fingertip and palm were more sensitive than foot in the sensation of floor roughness. The differences among fingertip, palm, and foot in the perceived floor slipperiness were not statistically different. The regression analysis results indicated that floor roughness parameter R_a is a better predictor in predicting both the perceived floor roughness and perceived floor slipperiness than the COF of the floor.     

Heel contact dynamics during slip events on level and inclined surfaces

This study describes heel contact dynamics during slip events, information that must be known to develop biomechanically relevant shoe-floor coefficient of friction measurement systems. Sixteen subjects walked on a level, 5 and 10° ramp with two possible contaminants (dry, oil). Foot motion was recorded at 350 Hz and compared among no-slip, slip-recovery and slip-fall events. For all trials, the foot rotated to foot-flat, even during slip and fall trials. Heel sliding patterns recorded upon and shortly after heel contact were similar for all conditions. Slip distances, sliding velocities and heel acceleration profiles varied across trials. During the fall trials, the slipping motion of the foot was found to decelerate approximately 200 to 300 ms into stance before accelerating again, eventually leading to the fall. This deceleration was believed to be an attempt by the subject to recover from the slip. Recovery attempts on inclined surfaces were less successful than on level floors. In general, the slip distance and peak forward sliding velocity associated with fall trials were greater than or equal to 10 cm and 0.8 m/s, respectively. These complex motions at the shoe-floor interface during slipping should be taken into account for improving slip resistance measurement systems.     

Slip and fall accident prevention: A review of research, practice, and regulations

This paper summarizes current research, practices, and regulations regarding walking/working surface slipperiness and coefficient of friction (COF) measurements. The literature and data are reviewed from three aspects:

1. (a) the biomechanics of walking and psychophysiological factors involved in slips and falls studied by the scientific community,

2. (b) various measuring devices and methods developed in an attempt to quantify the “slipperiness” of walking/working surfaces, and

3. (c) an acceptable quantitative standard for the “slipperiness” of surfaces and the impact of the Americans with Disabilities Act (ADA) on such a standard.

Unresolved issues related to slip-resistance are identified. A multifaceted approach and synergy from researchers, the building industries, standards organizations, and government are needed to obtain concensus on such issues.     

Evaluation of two models of a slipmeter

The aim of the study was to compare the performances of the Brungraber Mark II (BM II) and Mark III (BM III) slipmeters. Friction measurements with the two slipmeters were conducted in a laboratory using four footwear materials, four floor types, and three surface conditions. Both the coefficient of friction (COF) values obtained with the slipmeters and the force platform-based COF values were measured. The COF measured with the BM II was slightly higher than that measured with the BM III with a R² of 0.83. A comparison of the averaged normal force between the two slipmeters showed that the BM II generated a significantly higher normal force than the BM III at a low COF and the difference of the normal force between the two slipmeters decreased when the COF value was increased. The regression analysis results in this study showed that the force platform-based COF values were closer to the COF values obtained with the BM III than with the BM II. The R² values for the regression model between the COF values obtained from the slipmeter and the force platform were 0.90 and 0.79 for the BM II and BM III, respectively.     

CAERvest® – a novel endothermic hypothermic device for core temperature cooling: safety and efficacy testing

Introduction. Cooling of the body is used to treat hyperthermic individuals with heatstroke or to depress core temperature below normal for neuroprotection. A novel, chemically activated, unpowered cooling device, CAERvest®, was investigated for safety and efficacy. Methods. Eight healthy male participants (body mass 79.9?±?1.9?kg and body fat percentage 16.1?±?3.8%) visited the laboratory (20 °C, 40% relative humidity) on four occasions. Following 30-min rest, physiological and perceptual measures were recorded. Participants were then fitted with the CAERvest® proof of concept (PoC) or prototype 1 (P1), 2 (P2) or 3 (P3) for 60 min. Temperature, cardiovascular and perceptual measures were recorded every 5 min. After cooling, the CAERvest® was removed and the torso checked for cold-related injuries. Results. Temperature measures significantly (p?Conclusion. This study demonstrates that the CAERvest® is an effective device for reducing body temperature in healthy normothermic individuals without presence of cold injury. Further research in healthy and clinical populations is warranted.     

Comparison of Canadian firefighters and healthy controls based on submaximal fitness testing and strength considering age and gender

Introduction. Few studies have addressed whether firefighters are fitter than the general population and possess sufficient levels of aerobic capacity and muscle strength to perform on-duty tasks in a safe and efficient manner, considering age and gender. We aimed to evaluate the fitness levels of Hamilton firefighters, and to determine the effects of age and gender. Methods. In total, 89 participants were recruited. The modified Canadian aerobic fitness test was used to determine participants’ estimated maximal oxygen consumption (V_O2max) levels. For upper and lower body strength levels, a calibrated J-Tech hand-held dynamometer and a National Institute for Occupational Safety and Health (NIOSH) lifting device was used respectively. Results. Firefighters’ mean (SD) V_O2max level was 40.30?±?6.25?ml·kg^?1·min^?1. Age proved to have a statistically significant impact on V_O2max (p?<?0.001). Gender displayed statistically significant effects on strength levels. Firefighters’ age was the only statistically significant independent variable, and accounted for 61.00% of the variance in firefighters’ aerobic capacity levels. Conclusions. Firefighters possessed somewhat similar aerobic capacities but much higher levels of body strength when compared with the general population. With age, firefighters’ aerobic capacities decreased; however, their upper and lower body strength levels remained the same.     

Investigation into effects of work-related quality of life and some related factors on cognitive failures among nurses

Objective. Cognitive failure is one of the factors which can be influenced by personal and professional characteristics. This research was carried out to study the effect of work-related quality of life (WRQoL) and some related factors on cognitive failures (CF) among nurses. Methods. This cross-sectional study was conducted among nurses working in intensive care units, critical care units and emergency units in 2014. Results. In total, 750 nurses participated in the study. The mean?±?SD for the total CF and WRQoL was 40.5?±?12.7 and 75.8?±?13.7 respectively. The results show that CF have a statistically significant difference among the age groups, experience groups and working units. Multiple regression tests show that age, income and WRQoL have a significant effect on CF. Based on the results, for a unit increase in WRQoL we expect a 0.26 unit decrease in CF. Analysis of variance results show that the emergency ward had changed the overall effect of WRQoL on CF, after the effect of WRQoL was controlled. Conclusions. Overall results from the present research indicated that, despite the high level of WRQoL among the studied nurses, the rate of CF was not at an appropriate level. Development of supportive and interventional strategies is highly recommended.     

Human walks carefully when the ground dynamic coefficient of friction drops below 0.41

This study investigated the available and utilized friction during non-slip gait in level walking, and determined the limit which human starts to walk carefully to adapt to slippery surface. Sixteen floor–footwear-contaminant conditions with different slipperiness (dynamic coefficient of friction, DCOF, from 0.11 to 1.06) were employed. Fifteen harnessed Chinese male performed ten self-paced walking trials in each condition without slips. The utilized friction (COF_u) was obtained from the maximum value of shear to normal ground reaction force ratio during the first 25% stance. ANOVA and Tukey tests showed three subsets with similar COF_u, and confirmed the hypothesis that the utilized friction drops gradually when the available friction drops below a certain critical limit. Non-linear regression models were applied to the data to determine the COF_u to be 0.20 and the limit of available ground friction which human starts to walk carefully to adapt to slippery surface (DCOF_limit) to be 0.41.     

Effects of physical exercise on musculoskeletal disorders,stress and quality of life in workers

Background. The effect of physical exercise in the workplace (PEW) on health promotion of workers is contradictory. Objective. To evaluate the effects of the PEW in musculoskeletal disorders (MSDs), perception of stress and quality of life in workers. Methods. The participants were divided into two groups: control group (n?=?46) including non-participant workers of the PEW program, and PEW group (n?=?50) including workers who regularly participate in the exercise program. All workers answered the Nordic general questionnaire, the perceived stress scale and the quality-of-life questionnaire. Results. The PEW group reported a lower prevalence of MSDs for the trunk in the last 7 days and 12 months (p?=?0.021 and p?=?0.001, respectively), and for the upper limbs in the last 12 months (p?=?0.001) compared with the control group. The results for the perception of stress and quality of life showed no significant differences between the groups. Conclusion. PEW is a potential method to reduce MSDs in workers, but it was not efficient in reducing stress levels or improving the quality of life of the workers.     

Measures of health,fitness, and functional movement among firefighter recruits

Aim. The purpose of this study was to examine the associations between various health and fitness measures and Functional Movement Screen? (FMS?) scores among 78 firefighter recruits. Methods. Relationships between FMS? scores and age, body mass index (BMI), sit and reach (S&R) distance, estimated maximal aerobic capacity (V˙_O2max), estimated one-repetition maximum squat (1RM-Squat_max), and plank endurance (%Plank_max) were examined. Results. Total FMS? scores were significantly correlated with BMI (r?=??0.231, p?=?0.042), estimated 1RM-Squat_max (r?=?0.302, p?=?0.007), and %Plank_max (r?=?0.320, p?=?0.004). Multiple regression analyses indicated that this combination of predictors significantly predicted (F(3, 74)?=?5.043, p?=?0.003) Total FMS? score outcomes and accounted for 17% of the total variance (R²?=?0.170). In addition, logistic regression analyses indicated that estimated 1RM-Squat_max also significantly predicted (χ²?=?6.662, df?=?1, p?=?0.010) FMS? group membership (≤14 or ≥15). Conclusion. These results suggest that the health and fitness measures of obesity (BMI), bilateral lower extremity strength (estimated 1RM-Squat_max), and core muscular endurance (%Plank_max) are significantly associated with functional movement patterns among firefighter recruits. Consequently, injury prevention programs implemented among firefighter recruits should target these aspects of health and fitness.     

The cut-off point for tympanic temperature as a heat strain index for evaluation of outdoor workers: a field study

Objectives. The aims of this study were (a) to assess the agreement coefficient between tympanic temperatures and the most popular and valid heat stress index, wet bulb globe temperature (WBGT), in outdoor environments; (b) to determine a cut-off point for tympanic temperature as a heat strain index for evaluation of outdoor workers. Methods. 1452 measurements of WBGT index and tympanic temperature were recorded for outdoor workers from nine different climatic regions. Consistency of the WBGT and tympanic temperature were tested. The cut-off point for tympanic temperature in outdoor environments regarding WBGT evaluation was suggested based on obtained sensitivity and specificity from a receiver operating characteristic curve. Results. The results showed that there were numerous situations in which WBGT exceeded the reference value, whilst the measured values of tympanic temperature rarely reached a permissible value for core temperature (38?°C). Therefore, appropriate consistency of results between the heat stress and strain indices was not achieved. Conclusion. The criterion of tympanic temperature equaling 37?°C was suggested as a cut-off point for tympanic temperature as a heat strain index for outdoor environment evaluation.