Tribological concepts involved in slipping accident analysis

Development of high slip-resistant footwear outsole using rubber surface filled with activated carbon/sodium chloride

High slip-resistant footwear outsoles can reduce the risk of slip and fall on wet and icy surfaces. Falls on wet and icy surfaces can cause serious life-threatening injuries, especially for older adults. Here we show that footwear outsoles using the rubbers filled with activated carbon or sodium chloride produce higher friction force and reduce the slip rate in walking. We have identified that small depressions were formed on outsole materials filled with activated carbon or sodium chloride during friction between the rubber and surface leading to some air ingress into the interface. While there are air bubbles between the rubber and surface, real contacts are surrounded by water with negative pressure (Laplace pressure). It is considered that the negative pressure promotes real contact formation, which causes high friction. We consider that the outsole materials filled with activated carbon or sodium chloride can reduce the risk of slip-and-fall accidents.

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.

Development of a high slip-resistant footwear outsole using a hybrid rubber surface pattern

The present study examined whether a new footwear outsole with tread blocks and a hybrid rubber surface pattern, composed of rough and smooth surfaces, could increase slip resistance and reduce the risk of fall while walking on a wet floor surface. A drag test was performed to measure static and dynamic coefficient of friction (SCOF and DCOF, respectively) values for the footwear with the hybrid rubber surface pattern outsole and two types of commercially available boots that are conventionally used in food factories and restaurant kitchens with respect to a stainless steel floor covered with glycerol solution. Gait trials were conducted with 14 participants who wore the footwear on the wet stainless steel floor. The drag test results indicated that the hybrid rubber surface pattern sole exhibited higher SCOF (≥0.44) and DCOF (≥0.39) values than the soles of the comparative footwear (p<0.001). Because of such high SCOF and DCOF values, the slip frequency (p<0.01), slip distance (p<0.001), and slip velocity (p<0.001) for the footwear with the hybrid rubber surface pattern outsole were significantly lower than those for the comparative footwear, which resulted in no falls during trials.

The effect of shoe sole tread groove depth on the friction coefficient with different tread groove widths, floors and contaminants

Slipping and falling are common phenomena in both workplaces and our daily activities. The risks associated with slipping and falling are related to the materials of footwear/floor, contamination condition, and geometric design of the sole. Shoe soles of various tread design are very common. Tread pattern of the shoe affects friction especially under liquid-contaminated conditions. Verification of the effects of tread groove depth is significant in assisting designers in designing proper footwear for workers exposed to slippery floor conditions. In this study, we measured the friction coefficients using the Neolite footwear pads on the terrazzo, steel, and vinyl floors under three liquid-contaminated conditions. A Brungraber Mark II slipmeter was used. The footwear pads had tread grooves with a width of either 3 or 9mm. The depth of the tread grooves ranged from 1 to 5mm. The results showed that tread groove depth affected the friction coefficients significantly. Higher friction values were recorded for footwear pads with deeper tread grooves on wet and water-detergent-contaminated floors. The averaged coefficient of friction (COF) gain per tread groove depth increase in millimeter under these two surface conditions ranged from 0.018 to 0.108, depending on the tread groove width, floor, and contaminant.

The effect of shoe soling tread groove width on the coefficient of friction with different sole materials, floors, and contaminants

Tread groove design is very common in footwear. However, coefficient of friction (COF) measurements between the footwear material and floor using a slipmeter were commonly performed using flat footwear pads. Such measurements might underestimate the actual slip resistance of the footwear pad. This research investigates the effects of the tread groove width on the measured COF using four footwear materials, three floors, and four liquid-contamination conditions using a Brungraber Mark II slipmeter. The analysis of variance results indicated that the footwear material, floor, contamination conditions, and groove width were all significant (p < 0.0001) factors affecting the measured COF. The hypothesis that wider tread grooves result in higher COF values was true with some exceptions especially on oil contaminated floors. A regression model, with an R2 of 0.91, was established to describe and predict the relationship between the COF and the tread groove width under footwear material/floor/contamination conditions.

Falls and working individuals: role of extrinsic and intrinsic factors

Falls are frequent occupational accidents involving workers and lead to important social and economic consequences both for the individual and for the employer. Different factors can modify balance control and lead to falling, especially environment-related and individual factors. The literature would appear to indicate that there have been few studies on the intrinsic factors involving the mechanisms of generating falls. This review determines the main factors involved in the mechanisms of falling, whether related to the environment, work or the individual. Knowledge of the extrinsic and intrinsic factors contributing to the fall could allow securer environment planning and occupational conditions for employers, and the use of balance rehabilitation methods for individuals to reduce the risk of falls.

The role of friction in the measurement of slipperiness, Part 1: friction mechanisms and definition of test conditions

Friction has been widely used as a measure of slipperiness. However, controversies around friction measurements remain. The purposes of this paper are to summarize understanding about friction measurement related to slipperiness assessment of shoe and floor interface and to define test conditions based on biomechanical observations. In addition, friction mechanisms at shoe and floor interface on dry, liquid and solid contaminated, and on icy surfaces are discussed. It is concluded that static friction measurement, by the traditional use of a drag-type device, is only suitable for dry and clean surfaces, and dynamic and transition friction methods are needed to properly estimate the potential risk on contaminated surfaces. Furthermore, at least some of the conditions at the shoe/floor interface during actual slip accidents should be replicated as test conditions for friction measurements, such as sliding speed, contact pressure and normal force build-up rate.

The locomotion of dairy cows on concrete floors that are dry, wet, or covered with a slurry of excreta

Six dairy cows were trained to individually walk down a concrete aisle for a food reward. Their locomotion was then examined in a switchback experiment as the floor surface of the aisle was changed from dry to wetted concrete or concrete covered by shallow (5 cm) or deep (12.5 cm) slurry from cattle excreta. The static and dynamic frictional coefficients were measured by a tribometer, but did not give a clear indication of the risk of slipping. Cow locomotion was measured over the second half of the aisle, and limb angles recorded as the cow passed a video camera. Wetting the floor did not affect the walking or stepping rate, but it reduced the arc made by the joints of the hindlimb during the supporting phase. Slurry caused the cows to keep their legs more vertical at the end of the support phase, probably to aid lifting the limb out of the slurry. It also caused the cows to place their forelimbs down less vertically at the start of the support phase, probably because of the reduced risk of slip in the slurry. When the floor was covered with either the deep or, to a lesser extent, the shallow slurry, the cows' walking and stepping rates were reduced, and on the floor covered with deep slurry their step length was increased. Therefore slurry reduces the cow's walking speed and alters limb angles during the support phase, producing a different walking pattern from cows on dry or wetted concrete.

A descriptive analysis of nonfatal occupational injuries to older workers, using a national probability sample of hospital emergency departments

An estimated 136,985 nonfatal, work-related injuries to workers 55 years of age and older were presented for treatment in hospital emergency departments across the United States during 1993. Men accounted for 63.7% of the injuries and had an injury rate of 1.06 per 100 workers, compared with a rate of 0.76 among women. Among the oldest workers (65+ years), injuries were more likely to be fractures or dislocations, to result from falls on the same level, or to involve hospitalization. The services industry had the largest number of injuries (31.9%), whereas the highest injury rate occurred in the agriculture/forestry/fishing industry (1.50 per 100 workers). The types of injuries most frequently requiring hospitalization were fractures or dislocations that resulted from a fall. Because older workers' employment demographics and injury patterns differ from the remainder of the labor force, interventions need to be developed which are specific to the workplace for this older working population.