Article Text

Factors associated with worker slipping in limited-service restaurants
1. Theodore K Courtney1,
2. Santosh K Verma1,
3. Yueng-Hsiang Huang2,
4. Wen-Ruey Chang3,
5. Kai Way Li3,4,
6. Alfred J Filiaggi3
1. 1Center for Injury Epidemiology, Liberty Mutual Research Institute for Safety, Hopkinton, Massachusetts, USA
2. 2Center for Behavioral Sciences, Liberty Mutual Research Institute for Safety, Hopkinton, Massachusetts, USA
3. 3Center for Physical Ergonomics, Liberty Mutual Research Institute for Safety, Hopkinton, Massachusetts, USA
4. 4Department of Industrial Engineering and System Management, Chung-hua University, Hsin-Chu, Taiwan, ROC
1. Correspondence to Mr Theodore K Courtney, Center for Injury Epidemiology, Liberty Mutual Research Institute for Safety, 71 Frankland Road, Hopkinton, MA 01748, USA; theodore.courtney{at}libertymutual.com

## Abstract

Objective Slips, trips and falls (STF) are responsible for a substantial injury burden in the global workplace. Restaurant environments are challenged by STF. This study assessed individual and work environment factors related to slipping in US limited-service restaurant workers.

Methods Workers in 10 limited-service restaurants in Massachusetts were recruited to participate. Workers' occupational slip and/or fall history within the past 4 weeks was collected by multilingual written questionnaires. Age, gender, job tenure, work hours per week and work shift were also collected. Shoe type, condition and gross shoe contamination were visually assessed. Floor friction was measured and each restaurant's overall mean coefficient of friction (COF) was calculated. The logistic generalised estimating equations model was used to compute adjusted odds ratios (OR).

Results Of 125 workers, 42 reported one or more slips in the past 4 weeks with two reporting a resultant fall. Results from multivariable regression showed that higher restaurant mean COF was significantly associated with a decreased risk of self-reported slipping (OR 0.59, 95% CI 0.42 to 0.82). From the highest to the lowest COF restaurant, the odds of a positive slip history increased by a factor of more than seven. Younger age, male gender, lower weekly work hours and the presence of gross contamination on worker's shoe sole were also associated with increased odds of slip history.

Conclusion Published findings of an association between friction and slipping and falling in actual work environments are rare. The findings suggest that effective intervention strategies to reduce the risk of slips and falls in restaurant workers could include increasing COF and improving housekeeping practices.

• Coefficient of friction
• falls
• occupational
• restaurants
• slip

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Same-level slips, trips and falls (STF) are responsible for a substantial injury burden in the global workplace.1 2 In the USA, STF are associated with the most severely disabling, sudden-onset occupational injuries including fractures.3 Direct, per capita costs of STF workplace injuries have previously been estimated to range from US$50 to US$400 per worker depending on the industry group considered.4 More recently, the Washington State Department of Labor and Industries reported an average workers' compensation cost per claim for same-level falls of US\$6745.5 Substantial losses have also been reported in the UK, Finland and Sweden.6–10

Courtney et al2 examined national-level injury data systems from the USA, UK and Sweden to better describe the contribution of slipperiness to the overall burden of STF injuries in those countries. Whereas few systems actually differentiated between slipping, tripping and other antecedents of same-level falls, those systems that provided such data suggested that slipping contributed to between 40% and 50% of fall-related injuries.2 Similar results were recently reported by Verma et al.11 This proportion is somewhat lower than observations from field studies in the literature, which depending on the work population studied, report a range of between 60% and 85% of fall injuries being attributed to slipping.7 9 12

The field studies cited on workplace slipping and falling have generally taken the form of case follow-back studies in which only injured workers were interviewed and the potential causal factors were assessed retrospectively. There is also a considerable literature addressing slipping in controlled, laboratory environments.13 14 However, reports specifically observing and assessing risk factors for slipping in the workplace are relatively rare.

Restaurants are among the largest employers in the USA. Webster15 reported that eating and drinking places led all other industries in non-fatal occupational injury and illness case count for 7 of 8 years from 1992 to 1999.

The largest proportion of disabling restaurant injuries result from same-level falls (26%). Falls to the floor account for six of the 10 most disabling restaurant injuries in terms of the median number of days away from work (range 12–82 median days lost).16 Among the top 10 highest risk industrial classes for same-level falls in the state of Washington, full service restaurants had the highest frequency of same-level falls claims followed closely by limited-service (also known as ‘fast food’) restaurants from 1999 to 2003.17

In restaurants, STF can occur on wet or contaminated surfaces and at transitions in floor types or materials (eg, from a carpet in the dining area to ceramic tiles in the kitchen area). Common sources of contamination include dishwashing spray/run-off, leaking equipment/pipes, food debris and spillage from open container transport (such as those holding fryer grease/food waste).16

Despite slipping being a frequently attributed initiating event resulting in STF injuries, there is little information in the literature about workers' typical experience of slipping in the workplace. Work environment and individual factors associated with slipping in the restaurant environment are not well documented. As part of a series of studies examining human and environmental factors related to STF in active restaurant environments,18–22 the present study assessed the potential association between individual and work environment factors and workers' experience of slipping in US limited-service restaurants.

## Methods

This cross-sectional study was conducted in 10 limited-service restaurants in Massachusetts, USA. Workers who had worked in their location for a period of at least 4 weeks were eligible to participate. A total of 126 workers participated in the study for a response rate across all locations of 87.5%. Restaurant employees who volunteered to participate in the study were compensated for their time. The study was conducted under the supervision of the Liberty Mutual Research Institute for Safety Institutional Review Board for the Protection of Human Participants. Further details of the recruitment of sites and participants have been published previously.20 22

### Measures

Investigators developed a self-report survey to assess employees' recent slip and/or fall history. Workers were asked whether they had slipped, with or without a subsequent fall, while working at the restaurant within the previous 4 weeks. The survey also collected data on each worker's age, gender, ethnic group, tenure, work hours per week, work shift and shoe type.

Classification of shoe slip resistance was based on observed tread patterns (see figure 1 for an example of a typical resistant sole). Shoe condition (visible tread wear observed vs not), and gross shoe contamination (present/absent) were assessed by visual inspection by a study team member. These onsite assessments were later verified by comparison with digital photographs documenting the sole characteristics and condition of each participant's shoes by a panel of the investigators (TKC, W-RC, KWL, AJF). At least three panelists had to concur to confirm a classification as slip resistant.

Figure 1

Typical tread pattern of slip-resistant shoes.

Floor coefficient of friction (COF) was measured according to the F-1677-96 standard method published by the American Society for Testing and Materials23 along with protocol refinements recommended by Chang.24 COF values for a minimum of 39 tiles in the main areas of each restaurant kitchen were obtained using a Brungraber mark II slipmeter (Slip-Test Inc, Spring Lake, New Jersey, USA) with neolite test liners.18–22 Measurement results were averaged at the restaurant level to calculate each restaurant's overall mean COF.

### Procedure

Participants completed the survey questionnaire during their break outside the kitchen in a dining room location set aside for the survey. Surveys were typically collected during and immediately following lunch hours on weekdays as this provided the greatest concentration of active employees during the day. Participants completed the survey anonymously.

The survey was made available in three languages predominant among the restaurant workers in the region: English, Spanish and Portuguese. Study team members fluent in both Spanish and Portuguese were also available to assist non-English-speaking participants during data collection.

### Data analysis

Univariable and multivariable analyses were used to assess the associations between worker self-reported slip history, personal factors and floor and shoe conditions. As responses from participants within the same restaurants may be correlated, a logistic generalised estimating equation model with compound symmetry covariance structure was used to fit the model.25 Compound symmetry covariance structure assumes a constant correlation between any pair of participants within a restaurant. All statistical analyses were performed using the SAS system version 9.1. One participant was excluded from the analyses due to an excessive number of missing values.

## Results

Table 1 presents the results with respect to participant demographics, length of service, shift start and work hours per week. The mean age of participants was 30 years (range 14–71), and 60% of the participants were women. Forty-eight per cent of workers identified themselves as white, 44% as Hispanic, 4% as black and 4% as Asian.

Table 1

Self-reported participant demographics by slip history during previous 4 weeks (n=125)

Participants averaged 34.5 (SD 8.6) work hours per week and had worked in their restaurant location for an average of 34.5 months (median 17, SD 45.5). Forty-two workers (33.6%) reported experiencing a slip at work within the previous 4 weeks. Of these workers reporting slipping (n=42), two (4.5%) fell as a result.

Forty-four workers (35%) wore slip-resistant shoes. The majority of workers' shoes (60%) evidenced some degree of sole wear. Observable contamination (gross contamination such as embedded foodstuffs) were present on 13% of workers' shoes (see table 2). Overall mean COF across the 10 restaurants varied from a high of 0.81 to a low of 0.42, with both a mean and median of 0.64, and a SD of 0.11.

Table 2

Observed footwear slip resistance and condition by slip history during previous 4 weeks (n=125)

Table 3 presents unadjusted and adjusted odds ratios (OR) from univariable and multivariable generalised estimating equations models and their 95% CI. Lower mean restaurant COF was significantly associated with a positive history of slipping within the past 4 weeks in both the univariable and multivariable models (OR 0.65, 95% CI 0.47 to 0.90; OR 0.59, 95% CI 0.42 to 0.82, respectively). In the multivariable model, for each 0.1 increase in the overall mean COF, the odds of a positive slip history decreased by 41%. To put this in perspective, the odds of a positive slip history in the restaurant with the lowest overall mean COF was more than seven times higher compared with the restaurant with the highest overall mean COF, after controlling for other variables in the model.

Table 3

Unadjusted and adjusted OR and 95% CI from generalised estimating equations models

The use of slip-resistant shoes and shoe sole wear (worn or not) were not significantly associated with the risk of slipping. However, the presence of gross contamination on the shoe sole was associated with a more than three times increase in the risk of slipping (OR 3.25, 95% CI 1.33 to 7.94). For each 5-h increase in weekly work hours, the odds of slipping decreased by approximately 20% (OR 0.80, 95% CI 0.64 to 1.00).

Men reported a higher incidence of slipping in the previous 4 weeks than women (OR 2.3, 95% CI 1.09 to 4.95). Each 10-year increase in age was associated with a 17% reduction in the odds of slipping (OR 0.83, 95% CI 0.69 to 1.00).

## Discussion

### Work environmental factors

#### Coefficient of friction

Many laboratory studies have reported a lower COF to be associated with an increased risk of slipping.26 COF ranging from 0.2 to 0.6 have been suggested as ‘safe limits’ for walking.14 27 28 In the present study sites, the mean COF ranged from 0.42 to 0.81. These values were either within or above the literature's recommendations regarding ‘safe limits’. However, approximately 34% of study participants reported slipping at work in the previous 4 weeks. Moreover, an increasing mean overall COF value was associated with decreasing odds of slipping within this range of COF values across the study sites. These results highlight the importance of COF in relation to workers' experience of slipping on the job. The proper application of routine cleaning and housekeeping procedures may help to maintain COF. In addition, there are a variety of approaches to improving floor COF in restaurant environments, including the application of floor treatments that aim to restore roughness to tile surfaces chemically as well as the replacement of floor surfaces.16 29

#### Contamination

Gross contamination may reflect ineffective housekeeping and highlights the importance of proper floor cleaning and good work practices to reduce the presence of contamination sources on floor surfaces.30 The development and effective deployment of written floor cleaning protocols and food handling training to prevent floor contamination may help to reduce the odds of slips and falls in restaurant workers as a result of gross contamination.16

#### Work hours

Lower weekly work hours were marginally associated with an increased odds of slipping. This finding would seem somewhat counterintuitive as lower weekly work hours could be expected to be associated with a decreased risk of slipping at work. In this argument, workers spending fewer hours per week at work would have less time exposed to slip hazards. However, it is possible that workers with fewer hours are less familiar with the work environment and its hazards and are therefore less likely to adapt their behaviour to prevailing conditions.

#### Slip-resistant shoes

While there are many ‘slip-resistant’ shoes on the market, very few published studies have examined the association between slip-resistant shoes and the risk of slipping. Bell et al29 reported a comprehensive STF prevention programme in hospital employees in which slip-resistant shoes were one part of the intervention. While the overall intervention programme proved effective, their study design did not allow for the independent assessment of efficacy for individual components of the programme.

In the present study, the classification of shoes as slip resistant was based on observed tread patterns (eg, figure 1). This approach may have had limitations with respect to the correct classification. Second, workers who had experienced a slip or fall in the past may be more likely to wear slip-resistant shoes. For these reasons, the association between slip-resistant shoes and the odds of slipping could have been biased towards the null. Future studies could improve upon the exposure classification related to slip-resistant footwear (eg, by recording footwear brand and model type for shoes marketed as ‘slip resistant’) and examine the risk of slipping prospectively.

### Individual factors

#### Gender

In biomechanical laboratory studies, a slip is more likely to occur when the required COF approaches the available COF at the floor–shoe interface.31–33 Theoretically, if the required COF exceeds the available COF, a slip is probable.13 14 Therefore, given a constant level of available COF, the risk of slipping will increase with increasing required COF. Burnfield and Powers34 reported that men had higher required COF values compared with women at fast walking speeds. However, women had higher required COF at slow walking speeds. Auvinet et al35 also reported higher walking speeds, greater stride lengths and higher accelerations at heel strike, mid-stance and push-off in men than in women. It is also possible that reporting behaviour and/or sensitivity to detecting a slip could vary by gender. Bell et al29 recently indicated that that women may be at higher risk of STF-related injuries than men in the healthcare industry. This finding was consistent with those of Kemmlert and Lundholm9 in health care; however, they further reported that the overall STF injury rate across all the industries studied was higher for men than for women.

#### Age

Increasing age was marginally associated with decreased odds of self-reported slipping. Older adults may walk slower and with shorter step length, which is generally considered protective against slipping.36–38 In a study of workers compensation claimants, Verma et al11 reported that the proportion of injuries from slip-initiated falls compared with trip-initiated falls decreased with increasing age in female workers over 45 years age. However, there is evidence that older workers may not perceive the same environment to be as slippery as their younger counterparts, which also has implications for their ability to detect and report slipping.21 While older workers may report fewer slip episodes, they may also be less able to recover from a slip than younger workers, and may be at greater risk of tripping-initiated falls based on laboratory observations.39 Epidemiological evidence from the literature indicating a higher frequency of STF-related injury among older workers2 9 40 could partly reflect this more limited capacity for recovery of balance. Given the increasing proportion of older workers in the workforce,2 41 42 these results should be considered when developing and deploying workplace slip-prevention approaches.

#### Strengths

Chang et al43 have previously suggested that there is a need for research to assess the relationship between measures of environmental slipperiness and actual worker experience of slipping or falling on the job. The present study sought to address this gap, partly by assessing individual and environmental factors related to workers' experience of slipping and/or falling in US limited-service restaurants. The results provide empirical evidence from active workplace environments showing a strong relationship between COF and worker slipping experience. We were not able to locate another published study in the literature, to date, that had similar findings. As participants did not have information about the COF levels of their restaurants, it is unlikely that the recall of the slip experience could be systematically affected by this information. Investigators administering the surveys were also blinded to COF measurements.

One of the major challenges in studying risk factors and interventions for occupational injuries in active work environments is the rarity of the outcome. Slipping is one important precursor to falling and subsequent injury (although injuries can occur from both a subsequent fall or from bodily responses to loss of balance control and the threat of falling).3 Our results demonstrate that the prevalence of slipping in limited-service restaurant workers is sufficiently frequent to permit the application of epidemiological methods to assess the relative contributions of the observed exposures. Using slipping as an ‘upstream outcome measure’, it may be more feasible to examine risk factors for STF-related injuries and the effectiveness of potential interventions related to slipping.

#### Limitations

The COF measures in the current study could document the friction status only at the time of measurement, but COF can vary over time, partly based on the contamination level on the floor.24 44 45 The risk of slipping was ascertained in the previous 4 weeks. Point-in-time measurement of COF may not have adequately characterised friction levels during the previous 4 weeks. In addition, this study used mean restaurant COF values, although COF values can vary from floor location to floor location in the workplace.22 The potential misclassification that could arise from these limitations in the study measures is anticipated to be non-differential and would bias the association between COF and the risk of slipping towards the null. However, despite the potential influence of such variations in time and location, overall mean COF showed a strong association with self-reported slipping in the workplace.

Self-reported slips could be influenced by a variety of factors. Workers from restaurants that have taken the initiative to reduce slip hazards may have an enhanced sensitivity and situational awareness and thus may report a higher incidence of slipping. However, it is also possible that they may perceive peer or supervisory pressure to support intervention ‘success’ and report only major incidents of slipping. Similarly, workers wearing slip-resistant shoes may have a different threshold for reporting a slip. It was beyond the scope of the present study to examine how these factors could affect the threshold for reporting slips.

We used logistic regression to compute adjusted OR as the log-binomial model failed to converge. OR overestimate relative risks when the prevalence of outcome is not rare among the unexposed population.46 Therefore, actual relative risks may not be as high as the OR reported. In addition, the results of the study may not be generalisable to non-limited-service restaurant environments.

## Conclusions

A lower device-measured mean COF was associated with an increased risk of self-reported slipping in the limited-service restaurant environment. A significant proportion of participants reported slipping at least once in a 4-week period at mean COF levels that have been proffered as safe for walking based on laboratory observations. Gross contamination of worker footwear and male gender were also associated with an increased risk of slipping. Finally, younger age and fewer weekly working hours were marginally associated with an increased risk of slipping. Recommendations for future studies include employing longitudinal designs better to capture slip incidents and, potentially, variations in COF by time.

### What is already known on the subject

• Restaurants are one of the largest US employers, and STF-related injuries comprise the greatest proportion of worker injuries in restaurants.

• A considerable body of scientific literature documents strong associations between COF and slipping in controlled, laboratory settings.

• There is little information in the literature about workers' typical experience of slipping in the workplace, and work environment and individual factors associated with slipping in the restaurant environment are not well documented.

• There is a need for research to assess the relationship between measures of environmental slipperiness and actual worker experience of slipping and/or falling on the job.

• This study is among the first to provide empirical evidence from active workplaces showing a strong relationship between work environment factors such as COF and contamination and workers' self-reported experience of slipping.

• Potential countermeasures include enhancing COF and improving housekeeping practices.

• This study also demonstrates that the prevalence of slipping among restaurant workers is sufficiently frequent to permit the application of epidemiological methods to assess the relative contributions of the observed exposures.

• Using slipping as an upstream outcome measure, it may be more feasible to examine risk factors for STF-related injuries and the effectiveness of potential interventions related to slipping.

## Acknowledgments

The authors gratefully acknowledge the Liberty Mutual Research Institute for Safety technical and support staff, who contributed to the collection of data or study administration: Niall O'Brien, Lyn Dempsey, Debra Larnis, Danyel Tarinelli, Mary Dionne, Carmelina Lopes and Margaret Rothwell. The authors are also indebted to Marvin Dainoff and Ray McGorry for their constructive criticisms of earlier drafts of the manuscript.

## Footnotes

• Competing interests None.

• Ethics approval This study was conducted with the approval of the Institutional Review Board for the Protection of Human Participants, Liberty Mutual Research Institute for Safety, 71 Frankland Road, Hopkinton, MA 01748.

• Provenance and peer review Not commissioned; externally peer reviewed.