CURRENT PRIORITIES IN FALL PREVENTION RESEARCH AT
THE LIBERTY MUTUAL RESEARCH INSTITUTE FOR SAFETY
Ian Noy, Ph.D., CPE
Liberty Mutual Research Institute for Safety,
71 Frankland Road, Hopkinton, MA 01748, USA

At the Liberty Mutual Research Institute for Safety (LMRIS), our approach to fall
prevention research recognizes the importance of integrating diverse perspectives
across a multiplicity of relevant disciplines, including tribology, biomechanics,
epidemiology, and behavioral sciences. This paper is an update of our paper
presented at ICFPP2010, providing a brief overview of current LMRIS research
efforts aimed at advancing our understanding and prevention of falls.

Introduction
Since its inception nearly 60 years ago, the Research Institute’s mission has been theadvancement of scientific knowledge in workplace and highway safety, and work disability.
The scientific research conducted at the Institute is predicated on Liberty Mutual’s creed “tohelp people live safer, more secure lives.” Consistent with this non-proprietary mission, theresearch findings are published in the peer-reviewed scientific literature. Thus, Liberty Mutual
Insurance (LMI) is distinguished as the only property and casualty insurer with a world-classresearch program dedicated to safety and disability research that adheres to the highest objective
standards of scientific integrity.
Until very recently, the research conducted by the Institute has been primarily concernedwith occupational safety and related work disability. The focus on occupational safety reflects
the historical standing of Liberty Mutual as a workers compensation carrier. Liberty Mutual
today is a highly diversified carrier and as part of the Institute’s strategic realignment, the scopeof research is diversifying to address non-occupational injuries.
Falls represent the leading cause of nonfatal unintentional injury in the U.S. In 2007, there
were 8 million reported cases (NEISS, 2007), accounting for 28% of among adults aged 18-64.
Falls also represent a leading cause of severe occupational injuries, representing over 25% ofcompensable losses. According to the 2012 Liberty Mutual Workplace Safety Index (2012), themost disabling workplace injuries and illnesses that occurred in 2010 (the latest year for whichdata are available) amounted to $51.1 billion in direct U.S. workers compensation costs. Fall onsame level ranked second as a leading cause of disabling injury. With direct costs of $8.61
billion, this category accounted for 16.9% of the total injury burden. Fall to lower level ranked
fourth at $5.12 billion. Together, the cost of slips and falls on same level and to lower level in2010 amounted to $13.7 billion, representing 26.9% of the total burden (see Figure 1). The
burden would actually be about 5% higher if bodily injury were to be included, representing
slips and trips without falling.
According to the Bureau of Labor Statistics data, over the period 1998 to 2010 thefrequency of falls on same level and falls to lower level that resulted in more than 5 days awayfrom work declined by 17% and 31%, respectively. It is remarkable that while the frequency of- 41 -

work-related falls has declined over the 12 years, the burden associated with falls has grownconsiderably over this same period. The cost burden associated with falls on same level andfalls to lower level actually increased by 42.3% and 3.7%, respectively. In fact, the cost burden
associated with falls grew substantially more than any other injury category.
Overexertion
Fallonsamelevel
Bodilyreaction
Falltolowerlevel
Struckbyobject
Struckagainstobject
Repetitivemotion
Highwayincident
CaughtinorcompressedbyAssaults&violentactsbypersons

1.3
0

4.1
4.0
3.9
3.5
5

11.4
10.0
8.0

10

15

26.8

16.9

20

25

30

Figure 1. 2012 Liberty Mutual Workplace Safety Index: Top ten causes and % of burden
Slips, trips and falls occur as a result of the confluence of factors, and a comprehensive
program of research must bring together engineering, biomechanical, epidemiological andcognitive and sociotechnical systems perspectives. A unique strength of the Institute is its
ability to engage a broad range of disciplines in addressing the key domains of research interest- slips, trips and falls being a core domain. The Institute’s four research centers, specializing ininjury epidemiology, physical ergonomics, behavioral sciences and return-to-work, provide
complementary perspectives to falls-related research. The studies described below provide abrief overview of current research on falls.

Falls on same level
Slips and falls among limited-service restaurant workers

A multi-disciplinary field study of slips and falls among limited-service restaurant workers was
conducted in conjunction with research partners at the Harvard University School of Public
Health. In this study, we examined the slip and fall experiences of workers from 36 limitedservice restaurants in six U.S. states. The study investigated how factors such as floor surface
characteristics, slip-resistant shoes, floor cleaning practices, safety climate, and transient risk
factors (e.g., contamination, distraction and rushing) affect the risk of slipping. A total of 475
workers participated in the study. For each restaurant surveyed, participants completed abaseline survey that gathered information on demographics, perceptions of floor slipperiness,
slip-resistant shoe use, floor cleaning practices, and number of slips experienced in the fourweeks prior to the start of the study. In addition, restaurant managers provided information on
floor cleaning protocols and shoe policies. During the subsequent 12 weeks, participants
reported their slip experiences.
The data indicated a high rate of slipping in these restaurants, with an overall rate of 22 slips
annually per full-time worker. (Verma, Chang et al., 2010) The mean individual slipping ratevaried among the restaurants from 0.02 to 2.49 slips per 40 work hours. Liquid and grease
were implicated in more than 70% of slips, and the highest numbers of slips occurred in the sinkand fryer areas. The rate of slipping decreased by 21% for each 0.1 increase in the meancoefficient of friction (COF).
About 70% of the restaurants used enzyme-based floor cleaners. In these restaurants,
however, 63% of study participants reported that they used hot/warm water to dilute the cleaner,
which is contrary to the manufacturers’ instructions to use cold water and may decreasecleaning effectiveness. Other findings are described below under separate headings. These- 42 -

findings will be used to inform safety recommendations and guidelines with respect to floor
selection, floor cleaning protocols, slip-resistant shoe use, and safety policies related to fall
prevention.

Slip-resistant shoes and risk of slipping (Verma, Chang et al., 2011)

A strong association was observed between the use of slip-resistant shoes and the rate ofslipping. A shoe was considered slip-resistant if it bore the manufacturer’s “slip-resistant”
marking on the sole. After adjusting for age, gender, body mass index, education, primarylanguage, job tenure, and type of restaurant chain, the use of slip-resistant shoes was associatedwith a 54% reduction in the reported slipping rate. These results support the use of slip-resistantshoes along with measures to increase COF as preventive interventions to reduce slips, falls, andrelated injuries.

Factors influencing the use of slip-resistant shoes among limited-service restaurant
workers (Verma, Courtney et al., 2012)
To understand the factors that influence an individual’s use of slip-resistant shoes at work,
researchers examined demographic and job characteristic data from the study’s 475 participants.
Restaurant managers were asked whether the employer provided and paid for slip-resistantshoes; and, if not, whether the employer had given any guidance regarding slip-resistant shoeuse. A multivariate analysis indicated that slip-resistant shoe use was lowest in the 15- to 19year-old age group. Education level, job tenure, and the mean COF had no significant effects on
the use of slip-resistant shoes. Women were 18% more likely than men to wear slip-resistantshoes. Workers whose employers provided slip-resistant shoes were 52 percent more likely towear them and these workers had the highest proportion of use (91%), as compared to workers
who received no shoes and no guidance regarding slip-resistant shoe use. These results suggestthat employer provision of slip-resistant shoes was the strongest predictor of their use. Given
their effectiveness and an average cost of about US $30, slip-resistant shoes can be a costeffective intervention to reduce slips and falls. Impact of transient risk factors on slipping (Verma, Lombardi et al., 2011)

A nested case-crossover design was used to examine the association between certain transient
risk factors—rushing, distraction, and walking on a contaminated floor— and the rate ofslipping. The data included average work hours, average weekly duration of exposure to eachtransient risk factor, job tenure at the current location, weekly slip experience, and whether anyof the three transient risk factors were present at the time of slipping. The results indicate thatthe rate of slipping when workers were rushing was 2.9 times higher than when they were
working at a normal pace. Distraction and walking on a contaminated floor also significantly
increased the rate of slipping by 1.7 and 14.6 times, respectively. Slip-resistant shoe use
decreased the effects of rushing and walking on a contaminated floor, and the effects of all threetransient factors (rushing, distraction, and contamination) decreased monotonically as job tenure
increased. Participants on average reported walking on a contaminated floor for about one thirdof their work time. These findings suggest that rushing, distraction, and floor contamination
have significant effects on slipping rates among restaurant workers. Reducing the transient
exposures of rushing, distraction, and floor contamination; encouraging the use of slip-resistantshoes; and establishing a greater safety focus may help reduce the incidence of slipping.

Perceived versus actual risk of slips and falls (Courtney et al., 2013)

To examine the association between subjective measures of risk and the actual risk of slippingin the workplace, participants were asked to rate floor slipperiness using a four-point scale ineight functional areas of the restaurant kitchen: front counter, drive-through, sandwich
assembly, fryer, grill, sink, cooler/freezer, and ice machine at the baseline. Participants reported
their slip experience every week for the following 12 weeks. The results indicated that each 1point increase in mean restaurant-level perception of slipperiness (on the 4-point scale) was
associated with a 2.71 times higher rate of subsequent slipping. These data indicate that- 43 -

perceptions of slipperiness and the subsequent rate of slipping were strongly associated,suggesting that worker perceptions of slipperiness could be used as a leading indicator to
identify slipping hazards and assess intervention effectiveness.

Risk of slips, trips, and falls in full-service restaurants
This study extends the work described above to study the effects of floor surface, shoe type, andfloor cleaning practices on the risk of slips and falls in full-service restaurants. It also aims toinvestigate the impact of restaurant design and other factors related to slip, trip, and fall risk. In
each of the 48 restaurants that participated in the study, researchers measured the COF on
selected floor tiles in the kitchen and dining areas. They also gathered data on floor types,
transitions from one floor type to another, and lighting. During working hours, researchers
recorded practices or designs that could affect the risk of slipping and tripping. They also
examined workers’ shoes to determine slip resistance and collected data from managers on
floor-cleaning frequency, products, and protocols. Interviews held with over 750 participants
gathered basic demographic data, as well as information on job tasks, responsibilities, and priorexperiences related to slips, trips, and falls. Specific questions related to fatigue were included,
such as information on working hours, break times, double shifts, personal sleeping patterns,
and levels of alertness during the workday. Following the interviews, study participants
submitted weekly reports of their slip, trip, fall, and injury experiences and hours worked over a
12-week period. Analyses are underway and should enhance our understanding of worker slip,
trip, and fall risks in the kitchen and dining areas of full-service restaurants. The information
gained is expected to have significant safety implications for restaurant workers and patrons.

Multidisciplinary approaches toward the measurement of slipperiness in alaboratory environment
This study is part of a larger project aimed at understanding the relationships among perception,
gait and related mechanisms involved in falls due to slips. Figure 2 represents a simplified
conceptual model of the perception-action cycle of a pedestrian walking on a floor surface. The“Perception” box represents a version of the original Brunswik Lens Model (Brunswik, 1952) inwhich multiple inputs are differentially weighted. In this case, visual and proprioceptive cuesare evaluated with weightings dependent on exposure. That is, early gait adjustments are based
primarily on visual information and subsequent adjustments incorporate both visual andproprioceptive feedback.


Floor
AffordanceACOFContiguity
Grade,etc.

IndividualCharacteristicsandCognitiveAttributes
Motivation
Attention
Experience
MentalWorkload
Age
PriorknowledgeExpectation
Etc.

Perception

SlipPotential
UCOF
BalanceGaitparameters

V
P

ResponseͲGait
GRFUCOF
Stridelength/width
Speed,etc.

V=visualinput
P=proprioceptiveinput

Figure 2. Conceptual model of perception-action cycle in walking- 44 -

In this first study, we were interested in the principal components of the measurement ofslipperiness. Participants were exposed to 15 conditions of different degrees of slipperiness(five floor surfaces and three conditions: dry, water, glycerol) and were asked to walk as fast as
possible without a slip. The five floor surfaces were selected from 37 common floor types dueto their distinctive features that represented different combinations of friction levels andperceptual cues to slipperiness. Preliminary multiple and bivariate regression analyses examined
the relationships among perception ratings of slipperiness, gait parameters and COF. The results
indicated that the frictional demand, heel angle and perception ratings of slipperiness had thehighest adjusted R2 in the multiple linear regression analyses. 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. Additional analyses will examine theinterrelationships among behavioral, biomechanical and tribological mechanisms.

A statistical model to predict slip probability (Chang et al., 2012)
The probability of a slip can be estimated using a statistical model by comparing the available
coefficient of friction (ACOF) with the required coefficient of friction (RCOF). The models
available in the literature use mean values to estimate the risk of slips. However, it may bepossible to derive more accurate estimates by determining the stochastic properties of thesevariables. This study investigated the stochastic distributions of the ACOF of five different
floor surfaces under three conditions; dry, water and glycerol. The results of 50 participants
showed that in 86% of the time the RCOF can be represented by the normal distribution, thoughin 76% of the cases the distributions for the left and right foot were different. The distributionsof the ACOF could only be represented by the normal curve in 20% of the cases. In practice,
the ACOF can be considered a constant when it is near zero or much higher than the RCOF.

Falls to lower level
Risk factors for work-related portable ladder falls (Lombardi et al., 2011)

A field study designed to identify ways to prevent or reduce the risk for work-related falls fromportable ladders, which account for the majority of disabling ladder-related injuries, wasconducted in collaboration with the Harvard University School of Public Health, the U.S.
Consumer Product Safety Commission (CPSC), the National Institute for Occupational Safety
and Health, and the Center for Construction Research and Training (CPWR). Using cases
identified from the National Electronic Injury Surveillance System (NEISS) – a stratified
national probability sample of all injuries reported in US emergency rooms, we interviewed 306
workers who had experienced and were treated for a ladder-fall injury. Initial analyses focusedon specific, modifiable factors that may trigger portable ladder falls. Secondarily, we evaluatedthe risk of fractures—the most frequent and severe outcome from ladder falls—as a function ofseveral variables related to work environment, equipment, and the workers themselves. The
injured workers were most often employed in construction, installation, maintenance and repair,and sales-related fields. The falls originated from a step, trestle, extension, straight, or rolling
ladder, at an average height of 7.5 feet (35% of falls originated from <5 feet, and 5% from >20feet). The most frequent bodily injury sites were the arm, elbow or shoulder; the head, neck or
face; and the lower trunk. Diagnoses were primarily fractures, strains or sprains, and contusions
or abrasions. Typically, workers were most often standing or sitting while working on the ladderwhile installing or hanging an item or performing repairs and maintenance tasks preceding theirfalls. Ladder movement was an important mechanism; in 40% of the cases studied (varying byladder type), the bottom of the ladder moved before the fall. The study found a significant
monotonic relationship between increasing fall height and fracture risk, and this relationshipwas also influenced by an increase in worker age, and increased when working on the ladder, as- 45 -

compared to climbing up or down. The findings have particularly important implications forolder workers, who comprise the fastest-growing segment of the U.S. workforce. 

Effect of rest breaks on injury risk for ladder falls (Arlinghaus et al., 2012)

Additional analyses of the 302 cases from the NEISS examined whether workers who take rest
breaks are able to work longer into the workday without injury than workers without rest breaks,
and, if so, whether a longer accumulated rest-break time has a greater protective effect (i.e., alonger time-to-injury) than a shorter total break time?
The findings indicated that longer accumulated rest break time exhibited a significant
protective effect allowing for a prolonged time spent on task without injury (see Figure 3). Thisfinding suggests that rest-break design could be used to inform fatigue management strategies
aimed at improving workplace safety.

Figure 3. Effect of rest breaks on time to injury stratified by rest break duration

lateral reaching while on stepladders: Balance control and risk perception
In 2010, falls from ladders accounted for 5.5% of injuries involving days away from workin the U.S. construction industry sector (Bureau of Labor Statistics, 2011) and are also a major
cause of injury in other industries. Several laboratory experiments examined factors affecting
lateral reaching while on stepladders. For example, one study examined the effect of ladderexperience and risk perception on lateral reaching distance and stability. Twenty-four
experienced and 24 novice male ladder users performed lateral reaches while standing on 6- and
12-foot stepladders. Participants stood on the third rung from the top of the ladder and reached
for a target as researchers measured lateral reach distances, ground reaction forces, postures, andkinematics. The study also examined the effect of motivation on maximum reach, induced byplacing a reach-to target at the extreme lateral position for the participant (as opposed to theunmotivated condition where no target was presented). The data indicated that the average
maximum lateral reach distance was 66 mm shorter on the 12-foot stepladder than on the 6-footladder. Acclimation led to a 35 mm increase in unmotivated reach distances. Motivation brought
about a further increase of 66 mm. Across all conditions, the sum of the forces under the twoladder legs furthest from the target decreased from approximately 50% to 12–18% of the total
vertical forces created by the individual and ladder. After a short period of acclimation, users
were able to reach further without significantly affecting the forces underneath the ladder.

Straight ladder set-up and use in a field environment
Prior research has explored ladder setup methods and friction requirements in laboratory
settings (Chang et al., 2004). However, few studies have observed individuals set up and use
ladders in real-world settings. In this research, we studied a group of utility workers whoroutinely use ladders, following each worker as they proceeded to various worksites during the- 46 -

course of a normal workday. We collected information on climbing behavior, the use of
personal protective equipment, ladder-carrying, and ladder setup angle, as well as relevant
ground and weather conditions. At the end of each workday, participants completed aquestionnaire assessing their knowledge of ladder setup. The results are currently being
analyzed to determine the relationships between setup behavior, training, and setup outcomes.
In addition, the data are being analyzed to ascertain the impact of safety climate on ladder use
and injury outcomes. Study findings will provide insight into the effectiveness of training on
ladder use and setup, and will be used to inform and update ladder safety recommendations.

Summary
The LMRIS program comprises both field and laboratory studies to identify risk factors andunderlying mechanisms associated with falls. The program is focused on falls on same level
due to slips and falls from ladders. Our program is leveraged through joint research withseveral partners including the Harvard University School of Public Health. Findings from thesestudies provide a scientific basis for the development of cost-effective interventions andstrategies for reducing the incidence of work and non-work related slip and fall-related injuries.

References
Arlinghaus, A., Lombardi, D.A., Courtney, T.K., Christiani, D.C., Folkard, S., & Perry, M.J. (2012). The
effect of rest breaks on time to injury - a study on work-related ladder-fall injuries in the UnitedStates. Scand J Work Environ Health, 38(6),560-7.
Brunswik, E. (1952). The conceptual framework of psychology. International Encyclopedia of Unified
Science, 1 (10), The University of Chicago Press.
Bureau of Labor Statistics (2011). Table R64. Number of nonfatal occupational injuries and illnesses
involving days away from work1 by event or exposure leading to injury or illness and industry sector,
private industry, 2010. Bureau of Labor Statistics, U.S. Department of Labor. Available at:
http://www.bls.gov/iif/oshwc/osh/case/ostb2888.pdf. Accessed 9/13/13.
Chang, W.R., Chang, C.C., Matz, S., & Son, D.H. (2004). Friction requirements for different climbing
conditions in straight ladder ascending. Safety Science, 42 (9), 791-805.
Chang, W.R., Matz, S., & Chang, C.C. (2012). Stochastic distribution of the required coefficient offriction for level walking – an in-depth study. Ergonomics, 55 (8), 937-945.
Courtney, T.K., Verma, S.K., Chang, W.R., Huang, Y.H., Lombardi, D.A., Brennan, M.J., & Perry, MJ.
(2013). Perception of slipperiness and prospective risk of slipping at work. Occup Environ Med,70(1), 35-40.
Liberty Mutual Research Institute for Safety (2012). 2012 Workplace Safety Index. available at
http://www.libertymutual.com/researchinstitute. From Research to Reality, 15 (3), Hopkinton, MA.
Lombardi, D.A., Smith, G.S., Courtney, T.K., Brennan, M.J., Kim, J.Y., & Perry, M.J. (2011). Workrelated falls from ladders--a follow-back study of US emergency department cases. Scand J Work
Environ Health, 37(6), 525-32.
National Electronic Injury Surveillance System (NEISS). (2007). Retrieved June 30, 2013, fromhttp://www.cpsc.gov/Research--Statistics/NEISS-Injury-Data/.
Verma, S.K., Chang, W.R., Courtney, T.K., Lombardi, D.A., Huang, Y.H., Brennan, M.J., Mittleman,
M.A., & Perry, M.J. (2010). Workers' experience of slipping in U.S. limited-service restaurants. J
Occup Environ Hyg, 7(9), 491-500.
Verma, S.K., Chang, W.R., Courtney, T.K., Lombardi, D.A., Huang, Y.H., Brennan, M.J., Mittleman,
M.A., Ware, J.H., & Perry, M.J. (2011). A prospective study of floor surface, shoes, floor cleaningand slipping in US limited-service restaurant workers. Occup Environ Med, 68(4), 279-85.
Verma, S.K., Courtney, T.K., Corns, H.L., Huang, Y.H., Lombardi, D.A., Chang, W.R., Brennan, M.J., &Perry, M.J. (2012). Factors associated with use of slip-resistant shoes in US limited-service restaurant
workers. Inj Prev, 18(3), 176-81.
Verma, S.K., Lombardi, D.A., Chang, W.R., Courtney, T.K., Huang, Y.H., Brennan, M.J., Mittleman,
M.A., Ware, J.H., & Perry, M.J.. (2011). Rushing, distraction, walking on contaminated floors andrisk of slipping in limited-service restaurants: a case--crossover study. Occup Environ Med, 68(8),575-81.

- 47 -

- 48 -