The Changing World of Slip-and- Fall Defense

Transcription

1 Retail and Hospitality A Robust Analysis By John P. Leffler, K. Marc Barré, Jr., and Andrae P. Reneau The Changing World of Slip-and- Fall Defense Expert opinions should be informed by awareness of relevant research and methodologies that correlate tribometer test measurements to actual human slip experiences. 18 For The Defense February 2013 Pedestrian fall events are frequently linked to allegedly slippery walkway surfaces. Building codes and accessibility regulations require adequate walkway slip resistance, but unfortunately, without specifying how it is to be confirmed. Thus, actually proving that a walkway surface provides insufficient traction is a complex task requiring expertise and (where appropriate) the use of tribometer devices for post- incident field traction measurement. In fact, numerous state and federal courts have held that matters of slip resistance and surface friction are beyond the understanding and experience of the average lay citizen. Rosenfeld v. Oceania Cruises, Inc., 654 F.3d 1190, 1194 (11th Cir. 2011) (internal quotation omitted). See also Michaels v. Taco Bell Corp., 2012 U.S. Dist. Lexis , at *16 *17 (D. Or. Sep. 27, 2012); Sanders v. Anderson, 2007 Wash. App. Lexis 2429, at *3 *4 (Wash. Ct. John P. Leffler PE is a forensic mechanical engineer with FORCON International in Atlanta. He specializes in product and vehicle incidents and premises liability. He is a leader in the ASTM F13 pedestrian safety committee and teaches at Georgia Tech. K. Marc Barré, Jr., is a partner and Andrae P. Reneau is an associate of Swift Currie McGhee & Hiers LLP in Atlanta. Their practice areas include premises liability, automobile litigation, insurance coverage, and product liability DRI. All rights reserved. App. Aug. 14, 2007) (unpublished opinion); Leonard v. Bearcat Corp., 2002 U.S. Dist. Lexis, at *4 (E.D. Mo. Aug. 20, 2002). Notably, the past five years have seen major advances in the scientific foundations for traction analysis and specifically correlating tribometer measurements to actual human slip experiences. The nuances of these scientific advancements are not trivial, however, and no scientifically defensible and universally applicable recipe exists for differentiating safe walkway materials from among the various types and markets. Perhaps as a result, during this same time period, there have been efforts to sidestep the complexity of human slip analysis and instead promote analysis methods that are much easier to understand but that are (upon closer inspection) less technically robust. Regardless, it has become a very different world in slip-andfall defense than it was five years ago as a result of these advancements. Slip Events and the Shoe- Walkway Interaction There are generally three types of slip events: heel strike, toe-off, and front-rear split. A heel strike slip is the most common cause of a slip- related fall. During the stride, as the leading heel contacts the

2 walkway, the heel slides forward. The forward momentum of the pedestrian exacerbates the slip, and the leading leg can no longer support its share of the body weight. A toe-off slip occurs when the trailing foot slips as the toes push off. A toe-off slip rarely results in a fall, since the majority of body weight will already have been shifted to the leading leg. The elderly are the most susceptible to a front-rear split slip event. In these slip events, the lower extremities are not strong enough to keep from spreading apart into an increasingly longer stride and a fall to the side is typical. These types of slip events can be caused by a walkway surface that lacks sufficient available traction for that particular coupling of pedestrian and footwear, especially given the contaminants and other extrinsic factors that may be present. Thus, analyzing pedestrian traction involves the empirical study of friction the factor that complicates most interactions of adjacent objects in contact. Due to variables that include adjacent surface roughness, slope, contours, contact force magnitude, contact velocity and acceleration, hysteresis, damping, mechanical and molecular bonding, deformation, wear, contaminants, and other factors, every measurement of friction will be slightly different. Accordingly, effective measurement of pedestrian traction involves tribometers that attempt to reduce the variability of these factors. It is not reasonably possible to quantify pedestrian traction objectively through informal methods such as a visual inspection, scuffing one s shoes on the surface, or rubbing the surface with one s fingertips. Repeatable and defensible analysis requires a tribometer measurement. It is true that some walkway surfaces such as unfinished bare concrete are so rough that someone may be able to judge traction without a tribometer. But slips on these surfaces are not typically the subject of litigation. It is also true that some walkways have surface features such as large stylized contours that preclude reliable traction measurement with tribometers by either litigating party. In such cases, competent experts can provide useful advice on alternate analysis methods. Pedestrian Traction Testing Terms The topic of traction testing encompasses both coefficient- of- friction testing and slip resistance testing though both are frictional measurements. Coefficient of Friction Many tribometers claim to measure the coefficient of friction (COF). From physics, the COF is a ratio between the horizontal force necessary to slide an object and the vertical weight of the object. See Figure 1 below. The maximum COF between two surfaces will typically be at the threshold of movement. For static coefficient of friction (SCOF), the maximum value will be just at the point of incipient relative movement, and for dynamic coefficient of friction (DCOF), the maximum value will typically be when the moving surface has minimal velocity. As COF is between two surfaces, testing wet or contaminated walkway surfaces is often called slip resistance testing. Slip Resistance The term slip resistance is defined in ASTM F1646, a terminology standard, as The relative force that resists the tendency of the shoe or foot to slide along the walkway surface. Slip resistance is related to a combination of factors including the walkway surface, the footwear bottom, and the presence of foreign materials between them. Additional discussion in ASTM F1646 includes reference to the capabilities of the pedestrian and other factors. As such, it is clear that slip resistance is not technically the same as COF, although the terms are frequently used interchangeably. It is important to note, however, that a tribometer is a mechanical device, and as such it cannot tangibly account for individual pedestrian gait peculiarities or other intrinsic factors. Overview of Laws and Standards The three primary codified regulations relevant to walkway traction are the National Fire Protection Association (NFPA) 101 Life Safety Code, the federal American with Disabilities Act (ADA) Accessibility Guidelines for Buildings and Facilities, and the International Code Commission International Building Code. These regulations all require that walkway surfaces be slip resistant, but they do not identify a methodology for quantifying slip resistance. The past five years have seen major advances in the scientific foundations for traction analysis and specifically correlating tribometer measurements to actual human slip experiences. As for voluntary consensus standards, several organizations have developed standards related to pedestrian safety. As reference, ANSI is the American National Standards Institute, an organization that accredits standards development organizations but does not write standards. ASTM International, formerly the American Society of Testing and Materials, Technical Committee F13: Pedestrian/Walkway Safety and Footwear ANSI/American Society of Safety Engineers (ASSE), A Subgroup: Standards for Slip Resistance and Prevention of Slips, Trips and Falls ANSI/National Floor Safety Institute (NFSI), B101: Committee on Slip, Trip and Fall Prevention ANSI/International Code Commission (ICC), A117: Architectural Features and Site Design of Public Buildings and Residential Structures for Persons with Disabilities The ICC A117 Consensus Committee on Accessible and Usable Buildings Figure 1. Coefficient of Friction COF = F horiz F gravity F horiz F gravity For The Defense February

3 Retail and Hospitality and Facilities administers the A117.1 standard that formed the basis for the ADA regulations for walkways. Traditional Requirements for Traction There is a popular understanding that a value of 0.5 is the threshold for adequate traction on a walkway. This 0.5 value has It is not reasonably possible to quantify pedestrian traction objectively through informal methods such as a visual inspection, scuffing one s shoes on the surface, or rubbing the surface with one s fingertips. 20 For The Defense February 2013 been commonly referenced for over 60 years by both experts and courts, despite the lack of a reliable scientific foundation, and despite constant evolution in test methods and research. See, e.g., Phelps v. Stein Mart, Inc., 2011 U.S. Dist. Lexis (W.D. La. April 7, 2011); Sanders, 2007 Wash. App. Lexis 2429 (Wash. Ct. App. Aug. 14, 2007) (unpublished opinion). However, at this time there are no codified standards or laws that establish 0.5 or any other value as the minimum required COF or slip resistance value for a walkway. Specific COF values have been required in the past. For example, the Occupational Safety and Health Administration (OSHA) structural steel walkway traction regulation, 29 C.F.R (c)(3) was codified in 66 Fed. Reg (2001), which required a COF of 0.5 as measured by an English XL or equivalent tribometer, with such testing conducted per the English XL- specific ASTM standard test method F1679. However, F1679 was withdrawn by ASTM in 2006 due to a lack of an agreed-upon precision statement of the statistical performance of the tribometer and for including reference to proprietary apparatus where alternatives exist. When F1679 was withdrawn, OSHA s regulation was withdrawn in 71 Fed. Reg (2006). In fact, for various reasons, all specific traction requirements have been withdrawn, and laws and standards from the above entities only describe specific values for traction in advisory and nonmandatory sections. As measurements are meaningless without an established reference, codification of target minimum traction levels would require agreements about which tribometer and methodology to use for testing and which reference surface or surfaces to use for baseline values, and there currently are no such agreements. Facilitating such agreements would require overcoming factionalism among different organizations that have competing interests, but more importantly, it would require accommodating the fact that friction measurement is highly instance- specific. Previous requirements for a single target traction value ignore how friction measurement works and how humans slip. The following discussion may be complex, but this is a complex topic. How Much Traction Do Humans Need? Proactive methods to evaluate walkway traction will often involve human subject testing. Human subject laboratory testing offers the opportunity to accommodate the numerous variables involved in pedestrianwalkway traction more consistently. Before we worry about how much traction is available, we should consider how much traction is required by pedestrians. Many pedestrian traction research studies over the past three decades have involved devices called force plates. A force plate is an electronically instrumented walking surface plate set into a recess in the floor of a test walkway in a laboratory. The force plate is typically about two feet square and consists of a thick metal plate supported by force sensors. Three-axis force plates will simultaneously measure the forces imparted to it by pedestrians in the vertical, lateral, forward, and backward directions. Recalling the concept of COF, these force measurements can be used to calculate the actual required COF (RCOF) for that pedestrian. Another term in use, similar to RCOF, is utilized COF (UCOF). The difference is that the term utilized implies the availability of that amount of traction while required does not. Yet another similar term in use is traction demand. Notably, force plate RCOF testing typically does not involve the pedestrian slipping adequate traction is facilitated on the force plate surface. Numerous multisubject force plate studies have been done with male and female pedestrians of various ages and body types involved in various walking activities. For normal walking, studies show that the average RCOF for typical pedestrians ranges between 0.17 and M.S. Redfern et al., Biomechanics of Slips Ergonomics (2001). Slip Testing with Humans and Tribometers With a foundation for understanding how much traction pedestrians require, we can analyze how much traction is available. A reactive way to determine whether a walkway surface has adequate traction is to testinstall the surface in a pedestrian traffic area and track how many people slip on it, but this would be an unreasonable risk to public safety. Note that tribometers provide measurements of the available traction of a surface, but tribometers don t slip and fall. Human subject testing can be used to test the limits of traction, specifically to find the thresholds of slipping. Typically such testing is done on a laboratory test walkway with various configurations of potentially slippery surfaces randomly placed underfoot, with test subjects harnessed to a track-mounted overhead trolley for safety. As with RCOF testing, variations in human slip testing include people of different ages, body types, and gender. Many different elements of the shoe- walkway interface can be varied in analyzing potential contributors to slipping, such as shoe tread patterns and sole materials, walkway surface materials and coatings, or contaminants. This information, if reliably determined, approximates real world knowledge about the actual thresholds for human slipping without the risks associated with conducting test installations with unaware pedestrians. This is the standard of care: there are no superior or merely comparable alterna-

4 tives to human subject testing that are simpler or less complex. It is, however, impractical to conduct human subject testing with every new walkway surface material or shoe design. Periodic traction audits of installed flooring would also be impractical if that flooring needed to be ripped out and sent to a lab. Thus, tribometers are sold based on their stated ability to field test walkway surfaces and find the thresholds of traction. However, as tribometers are machines and not humans, a defensible tribometer would measure as slippery only those surfaces objectively found slippery by humans. This concept, while it may sound obvious, is a recent advancement. In the past, there was poor correlation between tribometer measurements and actual human slips. Research and the ASTM F2508 Standard In 2007 Dr. Christopher Powers of the University of Southern California (USC) Musculoskeletal Biomechanics Research Laboratory, in collaboration with the ASTM F13 pedestrian safety committee, published a paper that created a unified methodology for correlating human slip research results to tribometer measurements. C.M. Powers et al., Assessment of Walkway Tribometer Readings in Evaluating Slip Resistance: A Gait-Based Approach, J. Forensic Sci. 52, (Mar. 2007). The methodology was further refined in a subsequent paper published in C.M. Powers et al., Validation of Walkway Tribometers: Establishing a Reference Standard, J. Forensic Sci. 55, (Mar. 2010). The later research involved 80 human test subjects who walked across four different walkway reference surfaces. These specific surfaces were chosen for their consistency of manufacture and for their predicted differences in traction. The surfaces were an unglazed ceramic tile, a vinyl composite tile, a glazed porcelain tile, and a polished black granite tile. They were tested wet. As groups of test subjects walked across the four tiles the number of slips were recorded, and the final results ranked the tiles in order of decreasing traction, as listed above. Additionally, there was statistically significant differentiation between the numbers of recorded slips for each tile. The next step in the USC testing, once the test subjects had reliably ranked the tiles by slip experiences, was to see if tribometers could also rank these reference surfaces in the same order of decreasing traction and with statistically significant measurement differentiation. Eleven tribometer designs were tested, and four were able to rank and differentiate the reference tiles correctly in the same way as the humans had. In effect, these four tribometers measured as slippery only those surfaces objectively found slippery by humans. One of the USC research participants, a member of ASTM F13, then wrote ASTM F2508, Standard Practice for Validation and Calibration of Walkway Tribometers Using Reference Surfaces, which was released in The F2508 standard provides the consensus- approved methodology to validate whether a tribometer can properly rank and differentiate those same four reference surfaces (now available for purchase from ASTM), based on the USC research. Notably the 11 tribometer designs evaluated in the USC research were each represented by one individual device, which would not necessarily be representative of other production units of each design. For higher confidence in a tribometer design s ability to rank and differentiate the reference tiles, an interlaboratory study is recommended to verify whether other production units and operators can also be expected to achieve reliable results. ASTM has a proven interlaboratory study procedure available, which is widely used across many fields of scientific analysis, and the ASTM F2508 standard has recently been updated to provide for this additional layer of statistical rigor. It is also important to note that ASTM F2508, while the most defensible methodology currently in place, would benefit from a broader variety of reference tiles and corresponding human slip research. Tribometers and the Significance of Their Results The tribometers described below are common in the United States. The tribometer contacts the walkway surface with a testfoot. Most tribometers use a laboratorygrade standardized rubber called Neolite as the testfoot material. Some tribometers still use leather despite leather s inconsistency as an organic material. Some walkway surfaces and contaminants cannot be tested reliably with a particular tribometer. A competent expert will know the limitations of the tribometer that he or she uses and of the tribometer used by an opposing expert. There are many other tribometer designs and methodologies in use around the world. Repeatable and defensible analysis requires a tribometer measurement. Drag Sleds Drag sleds involve dragging a weighted testfoot across the walkway surface of interest. As discussed above, the peak value for COF will be at the thresholds of motion, and in operation the testfoot will be brought to the point of sticking to or slipping on the walkway surface. This point typically will represent the maximum traction measurement for the surface. Drag sleds typically are used in a manner (SCOF testing) in which the testfoot momentarily rests motionless against the walkway surface, which has been known for decades to affect accuracy of measurement due to bonding or adhesion of the testfoot to the walkway surface while stationary. R. Brungraber, An Overview of Floor Slip- resistance Research with Annotated Bibliography, National Bureau of Standards Technical Note 895 (1976). Figure 2. Slip-Test Mark III Tribometer For The Defense February

5 Retail and Hospitality Adhesion is particularly problematic in wet surface testing; it results in artificially high measurement values, meaning that walkways will test as being safer than they may actually be. Horizontal Dynamometer Pull-Meter This device is described in ASTM C and is still referenced for COF testing Human subject laboratory testing offers the opportunity to accommodate the numerous variables involved in pedestrian-walkway traction more consistently. of ceramic tile. It is hand-pulled along the walkway surface and is an assembly of a digital force gauge, a thick aluminum plate with Neolite pads glued to the underside, and a 50-pound weight. RSI BOT 3000 This device is a motorized drag sled, which uses small powered wheels to travel across the walkway. The device can be used in both static and dynamic COF modes. Figure 3. English XL Tribometer 22 For The Defense February 2013 ASM 825 This device, formerly the ASM 725, contains electronics but is hand-pulled across the surface by the user. It uses three small Neolite discs as testfeet. Articulated-strut Tribometers Tribometers of this type apply loads to an angled strut that kicks out when a slip occurs. These designs avoid adhesion by thrusting an initially suspended testfoot down to the walkway surface, which applies the horizontal and vertical components of the walkway surface load to the testfoot simultaneously. Slip-Test (Brungraber) Mark II and Mark III Portable Inclinable Articulated- Strut Slip Tester (PIAST) These tribometers use a sliding 10-pound weight (Mark II) or compression spring (Mark III) for actuation of a Neolite testfoot. The Mark III can be used on sloped walkways. See Figure 2 on page 21. English XL Variable Incidence Tribometer The device uses a pressurized CO 2 cylinder for pneumatic actuation of its Neolite testfoot. This tribometer can be used on sloped walkways. See Figure 3, this page. The Effect of Differing Tribometer Operation Methods Given the variety of operational methods that exist with different tribometers, it is perhaps unsurprising that each tribometer can be expected to provide somewhat different numerical measurement values from the other tribometers when testing the same walkway surface. Indeed the four tribometers able to rank and differentiate the ASTM reference surfaces correctly (in the USC research) each provided different measurement values for the same surface. In the past this type of situation was a great source of controversy in expert testimony and a subject of Daubert challenges: Brand X tribometer measures 0.43 for this surface but Brand Y measures 0.55! Which one is correct? Until the advent of the USC research and ASTM F2508 methodology, it was difficult to deal with this because typically the robust context provided by human slip research was not in place to back up an expert s tribometer measurements. Now, if Brand X and Brand Y are each validated to ASTM F2508 and properly used, the answer to which measurement is correct would be both are correct. It then becomes the job of the experts to reliably correlate those measurements to the research- proven propensity for a human slip. Given the context of human slips, the tribometer measurement s actual numerical value becomes unimportant. It doesn t really matter whether an ASTM F2508 validated tribometer design displays a measurement value of 0.5, or 347, or on a marginally slippery surface since the tribometer has been reliably correlated to human slips. Revisiting the withdrawn OSHA structural steel traction regulation that required a COF measurement of 0.5 using an English XL tribometer or equivalent, it can be seen that there really is not an equivalent if a single target COF value (0.5) is to be required. Competing Methodologies Certainly the preceding discussion is not for the faint of heart. Reliably correlating tribometer measurements to actual human slips is complex, and this information does not typically translate well to professionals involved in specifying walkway materials such as architects and contractors. Ideally, such professionals would be able to look at a manufacturer s sales literature for flooring and see some stamp of approval that the flooring has adequate traction for foreseeable pedestrian activity, or there would be a simple- to- use tribometer that did not require much experience or judgment to use it properly, and the user would feel confident in the universal suitability of the device for reliably testing all common walkway materials. But neither of these scenarios is supported by the preceding discussion. There are, however, recent methodologies in place that offer this simplified approach. For example, traction testing services are offered to flooring manufacturers for their walkway materials and to property owners for their installed floors, and certificates of approval are issued, provided that certain traction thresholds are met. The tribometer used with these services is well-made though it is of a design known to have issues with certain types of testing and on certain surfaces. Further, certification classes are offered on the use of the tribometer, and the testing and train-

6 ing methodologies are backed by consensus standards from an accredited standards committee. There is an implied correlation of this traction testing to actual human slip testing though the technical specifics of this correlation are elusive. Inquiries and formal technical challenges to the validity and statistical reliability of the methodologies are carefully rebuffed (so as to not lose accreditation). In the absence of technically robust yet simple methodologies, such competing methodologies will find a market, but at the same time, competent opposing experts should be able to discredit such approaches. Going forward, there are efforts in place within the ASTM F13 pedestrian safety committee to create an F2508-backed traction rating system for use by flooring manufacturers (and specifiers), but an elegant solution to this non-trivial task has yet to be developed. Slip Resistance Expert Testimony Admissibility As mentioned above, numerous state and federal courts have held that matters regarding slip resistance are beyond the understanding and experience of the average lay citizen and thus, expert testimony is required. Such testimony would then of course be analyzed for the qualification, reliability, and helpfulness factors in Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579 (1993). In light of this, courts have generally ruled one of two ways on the admissibility of expert testimony regarding slip resistance: (1) an expert failed to present a standard for determining when certain flooring would create a safety hazard and thus, the expert s opinions were not admissible; or (2) competing methodologies of testing slip resistance by the parties respective experts were admissible if they were relevant and reliable, and any questions about the sufficiency of such tests applied to the weight of such opinions, and the trier of fact must decide the weight. For example, in Mincey v. Parsippany Inn, 2010 N.J. Super. Unpub. Lexis 2690 (N.J. Sup. Ct. App. Div. Nov. 8, 2010) (unpublished), the plaintiff filed a lawsuit for injuries that she sustained when she slipped and fell on a wet bathroom floor while she and her husband were staying at the defendant motel. Id. at * 1. Arguing that it breached no duty owed to the plaintiff, the defendant moved for a summary judgment, which was subsequently granted by the trial court. On the appeal the plaintiff argued that her expert s report was sufficient to create a material factual dispute to defeat the summary judgment. The New Jersey Superior Court Appellate Division affirmed the trial court s judgment. In reaching its holding, the court explained that the plaintiff s expert, a licensed engineer, performed [s]lip resistance measurements on the bathroom tile once while the tile was dry and again with the tile wet with distilled water. Id. at *4. He measured the dry slip resistance at 0.74 and the wet slip resistance at 0.24 and essentially opined that the floor at issue was not slip resistant and would become more slippery when wet. Id. The court noted that during the oral argument the trial court asked at what point along the spectrum from 0.24 to 0.74 would a safety hazard come into existence, however, the plaintiff s expert conceded that there is no number for him to rely on because no such number exists. Id. at *5 6. Accordingly, the court hearing the appeal concluded: the trial judge properly concluded that it constituted a net opinion. [The expert] essentially opined that a dry tile floor will have greater slip resistance than a wet tile floor. He was, however, unable to posit any opinion, to a reasonable degree of engineering certainty, as to a standard for determining when the tile floor at issue would create a safety hazard. Id. at *9 10. See also Fedor v. Freightliner, Inc., 193 F. Supp. 2d 820 (E.D. Pa. 2002) (excluding the opinion of plaintiff s expert in a slip and fall case because he offered no discernible methodology upon which he had based his opinion regarding a decrease in surface friction). Unlike Mincey, in Phelps, 2011 U.S. Dist. Lexis 4112 (W.D. La. Apr. 7, 2011), expert testimony regarding COF was not excluded due to an insufficiently reliable methodology. Rather, the court concluded that the competing methodologies of testing slip resistance presented by the parties respective experts were admissible because each was relevant and reliable, and any questions about the sufficiency of such tests dealt with the weight of such opinions, and the trier of fact needed to decide this. Id. at *12. In Phelps, the plaintiff slipped and fell on tile in the entrance to a department store. Id. at *1. The plaintiffs and the defendant each retained experts that conducted drag sled tests on the tiles to determine the COF of the tiles. Id. at *1 *2. The court noted that that the ASTM requires a coefficient of friction of 0.50 or greater for flooring. Id. at *2. Regarding this last statement by the court, ASTM in fact only references a COF of 0.50 (as being adequate ) in standard D2047, which is for testing floor polishes in a laboratory using a bulky and antiquated tribometer. ASTM D2047 was not relevant to Phelps U.S. Dist. Lexis 4112 (W.D. La. Apr. 7, 2011). The plaintiffs expert used a phenolic material from the sole of the shoe one of the plaintiffs was wearing at the time of the accident as the testing material, and a dynamometer with whole and half-pound gradations. Id. at 3. Based on his dry drag sled tests that produced an average coefficient of friction of 0.48, the plaintiffs expert opined that the tiles were dangerous at the time of the accident and six months previously. Id. The defendant s expert used leather from a new dress loafer as the testing material and a dynamometer with one-sixteenth-pound gradations. Id. Based on his dry drag sled tests that produced an average coefficient of friction of 0.52, the defendant s expert opined that the tiles were not defective at the time of the accident. Id. Subsequently, each party moved to exclude the other s expert opinion arguing that the opinions were not products of reliable principles and methods. Id. at *3 4. The court subsequently admitted both of the parties expert testimony and explained that each of the experts conducted drag sled tests, which is a well-known and accepted method of testing, in a reliable manner and in accordance with the facts of the case. Id. at *6, 10. The court concluded that while neither expert considered other factors, such as degree of wear on the shoe or flooring material, presence of foreign material, or other human factors, it was not persuaded that the expert testimony should be excluded on that basis alone. Id. at *11. Rather, the court concluded that the experts respective tests were admissible and any deficiencies were relevant to the weight of the testimony, and the jury should decide the weight questions. Id. at For The Defense February

7 Retail and Hospitality *12. See also Great Am. Ins. Co. v. Cutrer, 298 F.2d 79, (5th Cir. 1962) (finding allowing testimony from the parties expert witnesses appropriate when the defendant s expert conducted COF testing based on a government test and the plaintiff s expert conducted COF testing using the plaintiff s shoes because the weight assigned to such expert testimony was for A competent expert will know the limitations of the tribometer that he or she uses and of the tribometer used by an opposing expert. the jury to decide); Rosenfeld, 654 F.3d at 1190 (allowing the plaintiff s expert s testimony although the defendant argued that the expert s COF testing methods failed to accurately test for wet conditions, were imprecise, and failed to test the exact location of the plaintiff s fall because such attacks dealt with the weight and persuasiveness of the expert testimony and not the admissibility). The decision in Phelps, 2011 U.S. Dist. Lexis 4112 (W.D. La. Apr. 7, 2011), instructively frames the advances in traction testing. Though the case is recent, the two opposing Ph.D. experts relied on legacy tribometer analysis methods that did not have reliable correlation to human slips so they were not relevant to the facts of the case. Further, their measurements were within four percent of each other on a measurement scale of , yet one expert claimed danger at 0.48 and the other claimed safety at This approach treated the anecdotal 0.50 safety threshold as an absolute without apparently considering the complexities of human traction demand, recent human slip research, or tribometry. 24 For The Defense February 2013 Confronting Complexity As exemplified in Phelps, 2011 U.S. Dist. Lexis 4112 (W.D. La. Apr. 7, 2011), experts, as well as courts, have typically disregarded the human factors associated with slip resistance testing. However, correlating tribometer testing to actual human slips is now both possible and necessary, and experts and investigators should become familiar with the complex issues described above to inform triers of fact reliably. Tribometer manufacturers do offer training courses, which have varying levels of technical depth and rigor, but manufacturers do not require that users take them. Also, many successful experts continue to rely on indefensibly simplistic methodologies or reveal (in testimony) large gaps in their knowledge about tribometry, human falls, and walkway surfaces. Often, as in Phelps, 2011 U.S. Dist. Lexis 4112 (W.D. La. Apr. 7, 2011), competent opposing experts do not counter these experts. In the interests of at least familiarizing experts and other interested parties with the myriad issues involved in slip-and-fall investigation, the ASTM F13 committee is about to publish a new standard, F2948 Standard Guide to Walkway Auditor Qualifications. This standard outlines dozens of knowledge topics to consider (where applicable) in a slip-and-fall investigation or in proactive auditing of installed flooring. The standard does not attempt to specify what someone should know about these topics, however, because the technical knowledge base continually advances due to ongoing research. Notably, one legal decision seems to indicate that some experts and courts may not accept ASTM F2508 even though it outlines the only reliable method of correlation to human slips. Michaels v. Taco Bell Corp., 2012 U.S. Dist. Lexis (D. Or. Sept. 27, 2012). In that case, a plaintiff slipped and fell on a wet floor near the front entrance of a Taco Bell restaurant. Id. at *1. The plaintiff s expert, a consulting engineer, performed slip resistance testing using an English XL tribometer using the withdrawn ASTM F1679 test method and found that the tiles had a wet slip resistance of 0.15 and a slip resistance of 0.14 after the tiles were damp mopped with Taco Bell cleaning solution. Id. at *7. Taco Bell moved to exclude the proffered expert testimony arguing, among other things, that the plaintiff s expert used the ASTM F1679 test method, which was withdrawn in 2006, and did not use the newer F2508 validation methodology. Id. at *11. Specifically, Taco Bell argued that (1) the F1679 standard only provides instructions on how to use a tribometer, not how to calibrate it; and (2) before publication of F2508, there was no standard at all against which tribometers could be calibrated uniformly relative to human slips; and (3) the English XL manufacturer acknowledged that F2508 was the applicable standard. Id. at *19. Conversely, the plaintiff argued that despite ASTM s withdrawal of F1679 for a violation of form and style and for referring to proprietary apparatus where alternatives exist, it continued as the recognized industry standard for using a tribometer. Id. at * Further, the plaintiff argued that when her expert conducted his testing, F2508 was not generally accepted in the industry because only two months had passed between ASTM s adoption of F2508 and her expert s testing. Id. at *20. Finally, the plaintiff argued that her expert s tribometer was calibrated by the manufacturer, to F1679, just two days before he conducted his testing and thus, his tribometer was capable of making reliable measurements. Id. The court concluded that whatever its shortcomings lack of correlation to human slips F1679 was in general use to calibrate tribometers at the time of the expert s testing. The court also explained that the defendant failed to establish that F2508 was generally accepted in the industry as the standard for calibrating tribometers when the plaintiff s expert performed his testing. Id. at *21. Thus, the court concluded that at the time of plaintiff s expert s testing in May 2011, F2508 had not gained the general acceptance that Federal Rule of Evidence 702 required and that the methodology used by the plaintiff s expert was reliable to determine if the tribometer slips, but not the human. Id. at *22. The court concluded, however, that the plaintiff s expert testimony failed to apply his methods to the facts of the case adequately. Among other things, the court stated that the expert failed to explain in his report how his various testing methods were relevant to the conditions of the floor at the time of the plaintiff s fall. Id. at *24. Accordingly, even though it appears that the court erroneously concluded that F2508 Slip-and-Fall, continued on page 78

8 Slip-and-Fall, from page 24 should not have applied to the plaintiff s expert s testing, especially considering that F2508 was an active consensus- approved standard and the only standard that allowed for correlation to human slips, the court did, in the end, properly exclude the plaintiff s expert testimony. Intrinsic Considerations Stepping away briefly from this discussion, it is worth recalling that pedestrian fall events involve humans. Traction testing involves considering a multitude of extrinsic factors. The intrinsic factors pertaining to an individual pedestrian include fall kinematics, expected and unexpected injuries, preexisting medical conditions, and medications, as well as plaintiff or witness statements and depositions. These intrinsic factors may have at least as much relevance as the extrinsic factors in a case. Conclusions Traction testing has many complexities that cannot be robustly accommodated by a simplistic binary slippery or not slippery determination. Laws, codes, and standards do not provide the recipe for reliable analyses across all likely scenarios. The use of a tribometer is only part of a robust analysis. Thus, an expert must have an understanding of the limitations of the tribometer, and of the limited ability to test certain surfaces and contaminants. The expert s opinions should be informed by awareness of relevant research and methodologies that correlate tribometer test measurements to actual human slip experiences. Recent developments in human slip research and standards development have enhanced the standard of care. 78 For The Defense February 2013