From The Ergoweb® Learning Center

Slip, Trip, Fall Research Gaining Pace

Miss America, Rachel Smith, slipped and fell while sashaying across the stage in the 2007 Miss Universe competition. She regained her feet – and her poise – in an instant. Few people are that agile. Slip, trip and fall (STF) accidents often claim lives or livelihoods. A snapshot of current STF research shows several institutes around the world focused on finding solutions, and according to Wen-Ruey Chang, Ph.D., Senior Research Scientist at the Liberty Mutual Research Institute for Safety (LMRIS) in Massachusetts, “overall STF research is growing stronger each year.”

Medications, muscle weakness and poor vision can all increase the odds of a fall for elderly people, already a high-risk population. Author Kurt Vonnegut, 84, died after a fall at home in 2007, and diet guru Robert Atkins, 72, died in 2003 after a spill on ice. The federal government says about one third of Americans 65 and older fall each year. Of some 1.8 million people over 65 who were treated in emergency rooms in 2003, 13,700 died.

Workers are another high-risk population. According to the United States Department of Labor, injuries from falls are serious enough to require time off work for some 250,000 employees each year. Federal statistics also show some 30,000 employees suffer sprains or strains each year from arresting their fall, which carries the risk of wrenched muscles and joints.

Killer Falls

A now venerable study by Ralph L. Barnet, chairman of Triodyne Inc. and a professor at the Illinois Institute of Technology’s Department of Mechanical, Materials and Aerospace Engineering, helps explain why even same-level falls can be fatal. “The Drunk, the Child and the Soldier – My, How They Fall” was published as a Safety  Bulletin of Triodyne, an engineering consulting firm in Illinois, in September 1995.

The professor explains that it is better to collapse [like a drunk] than to topple over, …  better to be short than tall and … best not to fall at all” because the head strikes the ground at “killer” speeds. Professor Barnet calculated the speed at which drunks, small children and soldiers are likely to hit the ground, and showed mathematically that toppling produces greater impact speeds than free fall.

Response to the STF Challenge

Liberty Mutual’s research institute is one of some 12 facilities around the world that are wrestling with the physical, psychological and environmental factors that contribute to STF incidents.

A Senior Scientist at LMRIS, Dr. Chang has investigated shoe and floor interfaces with the goal of finding ways to reduce occupational slips and falls. His projects involve identifying preferred, higher-friction microscopic geometric features of floors, evaluating commonly used slipmeters and observing shoe-to-floor interfaces under various contaminated conditions. His work complements the research of epidemiologists, psychologists and engineers at the Institute who are working to develop interventions and guidelines to reduce slip and fall incidents.

Dr. Chang told The Ergonomics Report™ in April that researchers at the Institute recently completed a 10-year longitudinal study in collaboration with the National Institute for Occupational Safety and Health (NIOSH) in the United States and the Finnish Institute of Occupational Health. Private and public hospitals participated. “The study evaluated the effectiveness of a comprehensive slip, trip, and fall prevention program in three acute-care hospitals,” he explained, [and] “included on-site hazard assessments, changes to housekeeping procedures and products, introduction of products and procedures, slip-resistant footwear, general awareness campaigns, and other prevention measures.”

Measurable Benefits

The study led to measurable benefits. Dr. Chang said the hospitals’ total STF workers’ compensation claims rate declined by 58 percent “from the pre-intervention (1996-1999) to the post-intervention (2003-2005) time period (adjusted rate ratio=0.42, 95%CI: 0.33-0.54).” He pointed out that the research suggests “sensible implementation of a broad-scale prevention program, using available control approaches, can significantly reduce STFs in hospitals and potentially other environments.”  If we apply what we know, he added, “it can have a measurable impact.” 

According to Dr. Chang, LMRIS researchers’ projects include a prospective study to examine the association between the kitchen floor surface coefficient of friction, use of slip resistant shoes, floor cleaning methods, and risk of slip among fast food restaurant workers.

In collaboration with the School of Public Health at Harvard University, he said, LMRIS scientists have undertaken a descriptive and case-crossover analytic study of transient risk factors for portable ladder falls. “We hope to identify risk factors that can trigger falls on portable straight ladders to better inform safety practices and interventions,” he explained. The US Consumer Products Safety Commission, the Center for Construction Safety Research and Training and NIOSH are participating in the project.

LMRIS is also working to develop a “statistical model to estimate the probability of having a slip incident when unexpectedly encountering a slippery area,” said Dr. Chang. 

In another project, Institute researchers are “using multi-disciplinary approaches in tribology, biomechanics, and psychology to identify promising methods to assess slipperiness,” he explained. In its early years LMRIS was a pioneer in the field, developing tools such as the horizontal-pull slipmeter to measure floor slipperiness.

Some Liberty Mutual research focuses on subtleties of walking. "Microslips" are routine, tiny skids forward of the heel. Researchers want to find out if large unnoticed microslips indicate a floor that could be dangerous.

Shared Research

The International Ergonomics Association (IEA) Technical Committee on Slips, Trips, and Falls was founded in 2006 and is currently chaired by Dr. Chang. The panel has set up a STF contact group at The 2007 International Conference on Slips, Trips, and Falls was its first major enterprise. The event brought more than 70 academics and government and industry representatives from seven countries to LMRIS to share their research findings. “The diversity of topics covered reflects the complexity of slip, trip, and fall incidents and reinforces the fact that we have much to learn about their causes,” notes Dr. Chang, who is chair of the committee.

Parallel Investigations

Researchers from the Human Movement and Balance Laboratory at the University of Pittsburgh Department of Bioengineering in Pennsylvania are looking for better ways to stop people falling after they slip or trip. Led by Mark Redfern, Ph.D., CPE, a professor in the Department of Bioengineering and two other departments at the university, they are investigating how some people save themselves from falling, how aging affects that response and whether older people can be trained to recover from a slip without falling.

Professor Redfern was one of three editors who collaborated with Dr. Chang on the book, “Measuring Slipperiness: Human Locomotion and Surface Factors.” One reviewer describes the book, which was published by CRC Press in 2002, as “the most comprehensive treatment of the subject ever compiled.”

The book covers basic concepts and definitions of terms related to the ‘measurement of slipperiness,’ from the onset of a foot slide to a gradual loss of balance and a fall. It includes group perspectives on human-centered (biomechanical, locomotive, perceptual, and cognitive), and environmental (roughness, friction) aspects and approaches. It addresses the injury burden of slipperiness, globally reviews existing slipmeters, and summarizes areas of consensus in the field of slipperiness measurement.

Dr. Redfern’s research focuses on human postural control and ergonomics. The goal of the first is the prevention of injuries from falling by investigating factors that influence balance. He wants to develop a greater understanding of the normal function of the postural control system so better ways can be developed to diagnose, treat and rehabilitate patients with balance disorders. He also wants to develop new design criteria for the workplace and elsewhere to minimize the potential for falls. His main test subjects are Individuals with vestibular disorders and the elderly 

Using an engineering approach to investigate the postural control system, he is looking at the ergonomics of fall prevention and the influence of postural factors in back injuries.

Balance is a complex, non-linear control problem with feedback from the vestibular, visual and proprioceptive sensory systems, he explains. “All this information is integrated by specific areas in the brain to determine where a person is in space and what movements are required to maintain balance. By applying an engineering analysis approach, specific parts of the system can be probed to determine any problems that may be occurring.”

In one of the projects, the group is examining the influence of visual and proprioceptive cues in the environment on balance in the elderly. The findings from Dr. Redfern’s team indicate that elderly are dependent on these cues for balance. Elderly people at risk for falls may be particularly reliant on these sensory inputs, according to the findings.

Slip test subjects at the Pittsburgh lab are protected from collapsing or toppling by a harness. They wear sensors on the legs to record muscle activity. And tiny balls stuck to various parts of the body serve as landmarks so a computer can analyze movement in three dimensions.

The experiments will soon be expanded from slipping incidents to tripping so the researchers can study how they adjust their gait if they expect trouble.

Slipping research focuses on a very brief moment. Rakie Cham, co-director of the Pittsburgh lab, said in a recent Associated Press article about the lab’s recent research. She noted that a severe slip leaves only about a quarter-second to save oneself from falling.

One-tenth to two-tenths of a second after your foot hits a slippery spot, she said, your knee and hip joints react to try to bring the skidding foot back. And you try to push your hip forward to regain your balance. If that doesn’t work, you whip your other foot forward. That happens between about one-fifth and one-quarter of a second after the skid starts.

"If you’re a little late," Dr. Redfern said, "you’re way late." And if it doesn’t work, you’re going down. It sounds simple, but scientists are still unraveling the details.

Cleveland Clinic Research

The Lerner Research Institute in the Department of Biomedical Engineering at the Cleveland Clinic in Ohio is working to characterize the physiological and biomechanical mechanisms underlying the increased incidence of life and lifestyle-threatening falls in older adults, and to design and validate technologies and interventions aimed at reducing this incidence.

Mark Grabiner, Ph.D., a staff scientist at the Institute, recently sent 52 old and young adults for a stroll over artificial ice, to see what reactions make a difference between falling and just wobbling.

Two things stood out. People who were able to slow down the slipping foot were more likely to recover, Dr. Grabiner said in the Associated Press article. More surprising was a finding about the other foot. The most crucial thing about its placement is how far to the left or right from the center it is.

He explained that study analysis implies that "if I can improve the location of that foot in the sideways direction by only four centimeters (about 1.5 inches), I increase the likelihood of this person recovering by 50 percent."

But can people be trained to react differently to an event that happens so quickly and unexpectedly? Dr. Grabiner said he’s had success in training older women to keep from falling after tripping. So he believes the new data will help his efforts to train older men to recover from slips.

Studies suggest that people who’ve practiced recovery moves can improve their reactions to slipping, but the question is how long that effect persists after the training is over.

Challenges to Conventional Theories

The Ergonomics Report™ asked Dr. Chang if any of the new STF research challenges accepted theories or has surprised him.

It has been suspected that [sudden changes in friction] within a working area could be a more critical factor in slip and fall incidents than the average friction coefficient,” he replied. “Our team’s results published in Applied Ergonomics, based on a field study conducted in fast food restaurants, indicated that friction variation only had a slightly higher correlation with employees’ perception of slipperiness than the level of friction coefficient over six major working areas in the kitchen.” He said a high correlation was found between the level of friction and friction variation based on friction coefficient measured in these major working area across 10 fast food restaurants in the study. He cautioned that this is only a single study on this issue, and a more extensive effort will be needed to assess this question. “Due to a strong correlation between friction variation and the level of friction coefficient and only slightly higher correlation for the friction variation with the perception than the level of friction coefficient,” he added, “for the time being, the mean friction coefficient of an area is still a reasonably good indicator of slipperiness in practice.” 

Sources: Dr. Wen-Ruey Chang; Liberty Mutual Research Institute for Safety; Triodyne Inc.; University of Pittsburgh Department of Bioengineering; Lerner Research Institute, Cleveland Clinic

This article originally appeared in The Ergonomics Report™ on 2008-05-02.