Elsevier

Applied Ergonomics

Volume 35, Issue 4, July 2004, Pages 401-408
Applied Ergonomics

Assessing floor slipperiness in fast-food restaurants in Taiwan using objective and subjective measures

https://doi.org/10.1016/j.apergo.2004.01.006Get rights and content

Abstract

Slips and falls are major problems in occupational injuries in which floor slipperiness is a critical issue. Most of the studies on slipperiness assessments were conducted in laboratories. Field assessments are rarely reported in the literature. This study investigated floor slipperiness in seven kitchen areas of 10 western-style fast-food restaurants in Taiwan using both objective and subjective measurements which were conducted by friction measurements and by employees’ ratings of floor slipperiness, respectively. The friction measurement results showed that the sink area had the lowest average friction in the kitchens. Employees, however, rated both the sink and back vat (chicken fry) areas as the most slippery areas. The Pearson's and Spearman's correlation coefficients between the averaged friction coefficients and subjective ratings for all 70 evaluated areas across all 10 restaurants were 0.49 and 0.45, respectively, with p<0.0001 for both. The results indicate that average friction coefficient and perception are in fair agreement, suggesting that both might be reasonably good indicators of slipperiness.

Introduction

Slip and fall accidents are serious safety problems in work environments (Leamon, 1992; Swensen et al., 1992). In Taiwan, falls accounted for 14.5% of all occupational injuries in 2001, second only to traffic accidents (Council for Labor Affairs, 2002). Among these reported fall cases, 73.7% were falls on the same level. Statistics show that the majority of falls in the USA and European countries also occur on the same level with roughly 40–50% of same level falls attributable to slipping (Courtney et al., 2001). In addition to falls, slips likely contribute to many other occupational injuries. Hayes-Lundy et al. (1991), for example, reported that 11% of grease burns in fast-food restaurants were attributed to slips. Additionally, slips or trips while carrying a load were identified as a contributing factor for low back injuries in over 30% of all such cases (Leamon, 1992).

Contaminants such as grease and water are common on the floors of restaurant kitchens. Hence, slippery floors, which are a critical factor for falls on the same level, are common in restaurants (Chang et al., 2003). Leamon and Murphy (1995) reported that slips and falls resulted in the second most frequent claims and were the most costly claims in workers’ compensation within the restaurant industry in the USA. They reported that the incidence rate of falls on the same level over a 2-year period was 4.1 per 100 full-time equivalent restaurant employees, resulting in an annual per capita cost of US $116 per employee.

Measurement of friction between the shoe and floor is the most common method to assess floor slipperiness (Chang et al., 2001b). It is generally assumed that slips are more likely to occur on floors with a low coefficient of friction (COF), and mean COF values are often used to assess the potential risk of slip and fall accidents. In addition to the mean COF value, friction variation can also play a role in determining slipperiness. Strandberg (1985) indicated that local friction variation could increase the potential of slip and fall accidents. The slipperiness of a floor is initially judged subjectively by several mechanisms, which may include visual perception and proprioceptive recognition to maintain body balance. Discontinuities in friction across floor surfaces may result in unexpectedly encountering a low friction area without body posture adjustments, leading to a fall. People do manipulate gait when aware of walking on slippery surfaces, casting doubt on the validity of the mean COF value as the sole indicator of slipperiness (Leamon, 1992; Grönqvist et al., 2001).

The Brungraber Mark II, an inclined-strut slipmeter driven by gravity, is a friction measurement device commonly used in the USA (Grönqvist et al., 1999; Powers et al., 1999; Chang and Matz, 2001; Chang et al. (2001a), Chang et al. (2003); Chang, 2002). This slipmeter simultaneously applies forces parallel and normal to a floor surface with an impact of a footwear pad on the floor at an inclined angle in order to eliminate the dwell time problem with the static friction measurement.

The COF values measured using the Brungraber Mark II were compared with the tangential to normal force ratio (FH/FV) obtained from a force plate through the operation of the slipmeter on the force plate (Grönqvist et al., 1999; Powers et al., 1999). The results indicated that the COF obtained directly from the slipmeter and from the force plate measurements showed good agreement over different floor surfaces with different contaminants for non-slip conditions. The COF values measured with the Brungraber Mark II were shown to have a strong correlation (r>0.95) with those measured with a dynamic apparatus to simulate a slip, although the absolute COF values obtained from both devices were quite different (Grönqvist et al., 1999).

In addition to the friction measurements, perception of floor slipperiness is also essential to assessing slipperiness. Myung et al. (1993) compared the subjective ranking of slipperiness produced from paired comparisons after walking on surfaces, and the static COF of ceramic, steel, vinyl, plywood and sandpaper measured with a mechanical device to simulate a foot slip. They found that the higher the measured COF value, the less slippery the subjective ranking, with the exception of vinyl tile. Their results indicated that humans have a promising ability to subjectively differentiate floor slipperiness reliably, even though the measured static COF differences among these floor surfaces might not be prominent. They concluded that humans were reliable, but risky, discriminators of floor slipperiness.

The results from Cohen and Cohen (1994) were, however, somewhat different. In a laboratory experiment, their subjects visually compared 23 tested tiles to a standard tile with a COF of 0.5 and reported whether the tile was more slippery. They found a significant number of disagreements between subjective responses and the COF values of the tiles.

Swensen et al. (1992) conducted a study to collect both subjective rating and ranking of surface slipperiness of steel beams with different coatings from ironworkers and college students after walking on the surfaces. They found that the correlation between subjective rating and the measured COF of the beams were strong for both ironworkers (r=0.75) and college students (r=0.90). The subjective ranking of these surfaces, however, was consistent with the measured COF for ironworkers but not for college students (r=−0.14).

Grönqvist et al. (1993) compared the results of subjective ratings from walking experiments with objective measures of slipperiness using biomechanical and tribological approaches in the presence of a slippery contaminant. They reported a significant correlation between the subjective evaluation scores and the objective measurements such as slip distance (r>0.99, p<0.01) and the measured COF (r=0.97, p<0.05).

Most studies comparing friction measurement and perception of floor slipperiness published in the literature were conducted in laboratories with new floor surfaces and artificial contaminants. These conditions may not represent what most employees encounter daily. Field studies can better reflect realistic conditions of floor surfaces. However, field studies of floor slipperiness using both friction measurements and employees’ ratings of slipperiness are rare. The main objective of this study was to examine the relationship between point-in-time friction measurements and employee reports of floor slipperiness over major working areas in western-style fast-food restaurants in Taiwan.

Section snippets

Methods

Ten western-style fast-food restaurants participated in the study. The conditions in this type of restaurant during lunchtime represent one of the worst situations during their daily operation due to a large volume of customers over a short time period and contaminants on floor surfaces. Both friction measurements and subjective ratings were conducted concurrently in each restaurant during weekdays immediately after the lunch period, starting at approximately 1 p.m. and finishing before 5 p.m.

Friction measurement

The number of tiles measured per restaurant ranged from 35 to 47 with an average of 41.5. The numbers of tiles measured in each area had means and standard deviations of 4.1±0.87 (front counter), 6.7±0.82 (fryer), 6.5±0.71 (oven), 8.1±1.91 (back vat), 7.7±1.57 (sink), 4.6±0.84 (walkthrough), and 3.7±0.67 (beverage stand).

Table 1 presents the means and standard deviations of the friction coefficients for the seven areas in all 10 restaurants. In addition to the mean friction coefficient, it is

Discussion

Despite speculations that friction variation can play a significant role in the perception of slipperiness (Strandberg, 1985), the results from the current study indicate that the mean value of COF had fair agreement with the perception rating. However, the results from Chang et al. (2003) indicated a significant variation among the friction measured on four floor tiles in the same areas. Therefore, it is necessary to measure friction on several tiles in the area and use the average to

Conclusions

This study provided a unique opportunity to explore the relationship between the average friction coefficient and perception over seven major working areas in a restaurant field environment. The results of the current study showed that the levels of friction in different areas in the kitchens of fast-food restaurants were significantly different. This coincides with the general perception that certain areas in a kitchen are more slippery than others. The friction coefficients in the sink areas

Acknowledgements

The authors thank the participating restaurants for their support in this study. The authors also thank Chin Jung Chen, Terry Hsu and Yi-Ping Chen at Chung-Hua University, and Simon Matz and Margaret Rothwell at Liberty Mutual Research Institute for Safety for their assistance in the study. This study was completed during Dr. Li's tenure as the 2002 visiting scholar of Liberty Mutual Research Institute for Safety.

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