Slip Resistance Testing Conducted by Biomechanical Engineering Expert Witness Deemed Reliable

Slip Resistance Testing Conducted by Biomechanical Engineering Expert Witness Deemed Reliable

The Plaintiffs alleged that on December 24, 2020, Dr. Bruce Bunting slipped and fell outside the automatic exit doors at the CVS Store. Bunting claimed that he slipped on “slick and wet concrete that resulted from a mixture of salt and water.” The Plaintiffs alleged that CVS Pharmacy, LLC created the slick surface by “spreading the salt on a wet and warm day, which caused it to make the ground unsafe and slippery.” According to the Plaintiffs, the CVS Store was “negligently kept, maintained, and operated, creating an unreasonable risk of injury to invitees,” including Bunting. As a result of the fall, Bunting allegedly suffered a “closed fracture dislocation of his right ankle” that required surgery. The Plaintiffs further alleged that CVS’ negligence caused Bunting to suffer “serious bodily and emotional injuries and damages, including physical pain, suffering, emotional distress, inconvenience, loss of the enjoyment of life, and medical expenses.”

One of CVS’ designated expert witnesses was Alexandra Maddox, a mechanical engineer and biomedical engineer. Maddox’s expert report detailed her investigation, including slip resistance testing she conducted on January 19, 2023, on the incident walkway surface at the CVS Store, and provided her opinions regarding the slip resistance of the walkway surface. According to Maddox, the salt and water solution that Bunting described slipping on “was less lubricating than water on a walking surface, and created greater slip resistance than water alone.” She stated that the incident walking surface was reasonably safe for pedestrian traffic and concluded that there was lack of sufficient evidence to support the claim that the incident walkaway caused Bunting’s fall.

As part of her slip resistance testing, Maddox used an English XL Variable Incident Tribometer (“VIT”), a device used for slip resistance testing in different environments. A VIT is designed to yield coefficient of friction (“COF”) measurements that correlate to the likelihood of slip incidents occurring on a given surface. Maddox used a VIT that Excel Tribometers, the manufacturer of the English XL VIT, calibrated three days before her field test. Maddox then field calibrated the VIT the day before her field test. According to CVS, Maddox’s VIT was validated and calibrated in accordance with American Society for Testing and Materials (“ASTM”) standard F2508. Maddox also applied American National Standards Institute (“ANSI”) standard A1264.2, which recommends a COF of 0.5 or greater for walking surfaces in the workplace under dry or wet conditions. CVS asserts that Maddox “obtained slip resistance measurements under both wet and dry scenarios” pursuant to ANSI A1264.2. Consistent with the VIT device manual, Maddox used only water for the wet testing. Maddox concluded that the walkway surface had a COF of 0.64 ± .03 when dry and 0.51 ± .03 when wet.

Plaintiffs’ filed a motion to strike all opinion testimony of Defendant’s Expert Witness Alexandra Maddox.

Biomechanical Engineering Expert Witness

Alexandra Maddox holds a Bachelor’s degree in Biomedical Engineering and is in the process of completing her Doctorate in Aerospace Engineering at the University of Cincinnati. During her tenure at Boston Scientific as a Biomedical Engineer, she gained comprehensive experience in medical device production, covering development, design, manufacturing, and production phases. In her undergraduate research, Maddox specialized in tissue biomechanics related to airway collapse during sleep apnea, earning recognition with the University of Cincinnati’s Biomedical Engineering Student Award for exceptional research. Additionally, she provided technical expertise to the U.S. Government as a Post-Doctoral Researcher at the University of Maryland Applied Research Lab for Intelligence and Security, focusing on testing and evaluating voice analytic tools and other biometric devices for personal vetting purposes. She works as a Biomechanical Engineer for CED Technologies, Inc.

Discussion by the Court

The Plaintiffs argued that Maddox was not qualified under Rule 702 to provide expert testimony regarding the slip resistance of the walkway surface at the CVS Store citing his lack of qualifications as a licensed professional engineer, a certified safety specialist, a certified Variable Incidence Tribometrist, or even a human factors expert, besides being inexperienced in testing
or evaluating walking surfaces for slipperiness. Plaintiffs added that neither Maddox’s ongoing work as a PhD. student pertained to walkway surfaces or testing of materials nor did her Occupational Safety and Health Administration (“OSHA”) accreditations in general industry standards reflect an expertise
in walkway safety because they were minimally focused on walkway safety and fall protection.

CVS argued that Maddox was qualified under Rule 702 to offer expert opinions on the slip resistance and reasonable safety of the walkway surface because he did qualify as a Certified English XL Tribometrist (“CXLT”) besides possessing a valid CXLT Certificate. CVS added that it was illogical for the Court to deem Maddox unqualified to perform slip resistance testing using a VIT when the company that manufactures the very device that she used has certified that she is qualified to do so.

It was worth noting that Maddox had a bachelor’s degree in biomedical engineering, had nearly completed her Ph.D., and has completed two accredited courses in OSHA general industry standards, including walkway safety leading the Court to conclude that Maddox was qualified under Rule 702 to offer opinion testimony regarding the slip resistance of the walkway surface at the CVS Store. Maddox obtained her CXLT certification “following
classroom and field training provided by” the manufacturer of the VIT that Maddox later used to perform a field test of the walkway surface at the CVS Store. The Court held that Maddox’s status as a CXLT rendered her able to help the jury determine the slip resistance of the walkway surface at the CVS Store and, in turn, whether CVS was negligent in its treatment of the walkway surface.

Plaintiff called Maddox’s VIT testing methodology “unreliable flawed science”. Plaintiff argued that ASTM F2508 failed to establish a safe threshold value for a walkway surface because it was based on VIT measurements from young adults walking in a straight path on a level surface,whereas the incident involved Bunting who was 73 years old at the time of the incident and was stepping over a door onto a slanted surface; its test subjects walked in shoes that were not representative of all shoes; its use fell short of implying proper validation and calibration under all combinations of test materials and walkway surfaces; and it failed to purport to address all safety concerns associated with its use. In addition to citing recent studies and publications, the Plaintiffs also pointed that ASTM withdrew ASTM F1679—a VIT testing standard that ASTM originally published in 2004—because it lacked precision and bias testing back in 2006. Plaintiff added that Maddox did not demonstrate that she complied with ASTM’s calibration requirements to use a VIT. CVS rejected the Plaintiff’s suggestion that ASTM F2508 cannot be used to determine the reasonable safety of a walking surface, considering ASTM F2508 did not purport to establish what did and what did not constitute a safe walking surface.

CVS also argued that the studies relied upon by the Plaintiffs to assert the unreliability of VIT testing merely recommended accounting for variability in slip resistance measurements, as Maddox’s measurements did. As for the Plaintiffs’ argument about the withdrawal of ASTM F1679, CVS noted that Maddox did not depend on this standard, and a federal court had previously rejected this argument, affirming the reliability of VIT testing. CVS further asserted, contrary to the Plaintiffs’ suggestion, that the manufacturer of Maddox’s VIT had calibrated the device three days before her field test, and Maddox herself had field-calibrated the same device the day before the test. Moreover, CVS argued that Maddox had conducted her testing in accordance with the VIT manual and her training, producing “reliable” and “reproducible” results. CVS concluded that the Plaintiffs’ challenge to Maddox’s conclusions was more appropriately characterized as cross-examination material and not a valid basis for seeking to exclude her opinions under Rule 702 and/or Daubert.

The Court noted that the Plaintiff could not successfully identify any such instance where the federal court found VIT testing to be an unreliable methodology. The Court found that various arguments made by the Plaintiffs regarding VIT testing went to the weight of the evidence instead of its admissibility. For example, Maddox’s reliance on ASTM F2508 did not render her methodology unreliable considering ASTM F2508 is an international standard that is intended to establish the procedures for validation,
calibration, and certification of VITs or the studies and publications cited by the Plaintiffs to raise concerns about VIT testing did not establish her testimony to be excludable. These sources discussed the need to
consider measurement uncertainty when interpreting VIT testing results which Maddox accounted for by testing the surface at different locations and presenting the slip index values as “mean ± standard deviation.”


The Court denied the Plaintiff’s motion to strike all opinion testimony of Defendant’s Expert Witness Alexandra Maddox.

The Court has not arrived on an outcome for this case since the remaining issues involved in this case still await resolution.

Key Takeaways:

The Court closely examined Alexandra Maddox’s qualifications under Rule 702 to provide expert testimony, recognizing her background in biomedical and aerospace engineering, ongoing pursuit of a PhD, and completion of accredited courses in OSHA standards as sufficient qualifications despite lacking specific certifications like a licensed professional engineer or certified safety specialist. Maddox’s certification as a Certified English XL Tribometrist (CXLT) was deemed significant, bolstering her credibility in slip resistance testing, especially given the manufacturer’s training and certification process. While Plaintiffs critiqued Maddox’s methodology, particularly regarding calibration and adherence to standards such as ASTM F2508, CVS defended her approach, highlighting compliance with manufacturer guidelines and industry standards. The Court distinguished between challenges to the admissibility of Maddox’s testimony and arguments regarding the weight of the evidence, considering concerns about reliability and adherence to standards as affecting the latter. Maddox’s reliance on ASTM F2508, despite its limitations, was deemed acceptable as it aimed to establish procedures for validation and calibration of Variable Incidence Tribometers (VITs), which Maddox followed in her testing methodology. Moreover, the Court noted Maddox’s efforts to address measurement uncertainty by testing surfaces at different locations and presenting slip index values with statistical measures like mean and standard deviation, demonstrating awareness of and mitigation against potential sources of error in her testing. Overall, the Court’s ruling underscores the importance of evaluating expert testimony based on qualifications, methodology, adherence to standards, and consideration of measurement uncertainties while recognizing the distinction between challenges to admissibility and weight of evidence.

Case Details

Case Caption:Bunting Et Al V. District Of Columbia Cvs Pharmacy, LLC
Docket Number:1:22cv766
Court:United States District Court, District of Columbia
Citation:2024 U.S. Dist. LEXIS 21129
Order Date:February 7, 2024


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