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Professional Biography

John Leffler is a Senior Managing Engineer at YA Group with over 1,200 forensic cases of experience, including 550+ product cases and 500+ cases involving premises liability and pedestrian falls. An experienced testifying expert and peer-reviewed author, John brings a uniquely hands-on foundation to his practice — having worked as an IndyCar mechanic, fabricator, and machinist before operating his own product design engineering firm for eight years, following five years designing machines, consumer products, and commercial products for several manufacturers. He also taught product design, materials, and manufacturing processes at Georgia Tech’s College of Design for 15 years.

John has extensive experience in standards development, having been heavily involved for over 20 years with ASTM International and several other ANSI-accredited organizations. He is the primary author of ASTM E2713 (forensic engineering) and both ASTM F2948 and F3539 (pedestrian walkway safety), and serves as Chair of ASTM subcommittees on bathing surface safety and walkway friction. He is internationally recognized as a leader in standards development across multiple organizations.

In 2021, John initiated and led a groundbreaking federally funded research project supporting the replacement of the obsolete ASTM standard for bathing surface friction. John has also manufactured research-proven walkway friction test tribometers since 2010, with devices in use by insurance companies, theme parks, research labs, and forensic professionals worldwide. His additional specializations include vehicle wheel/hub separations as well as product/machine design, manufacturing, and mechanical failures.

Credentials & Certifications

  • Professional Engineer (PE)
  • OSHA Occupational Safety & Health Standards for General Industry (30 hour)
  • OSHA Occupational Safety & Health Standards for Construction (30 hour)
  • FAA Certified Drone Pilot
  • ASE Certified Automobile Technician
  • NRPA Certified Playground Safety Inspector

Representative Consulting Assignments

  • Orange farm | St. Johns County FL — Worker fatality – Worker was mowing a grove with a farm tractor and was run over by the tractor & mower. The lack of a seatbelt was blamed. Analyzed the tractor controls and patterns of grass cutting, opining that the worker was boarding the tractor in the incident.
  • Paper mill | Milner GA — Trip/fall – A subcontractor fell into process wastewater. A 2” hose placed by another subcontractor was blamed. Analyzed the roles of the subcontractors and paper mill in the incident.
  • Highway crash | Canton GA — Wheel separation – A wheel from a new trailer came off and struck a vehicle. Analyzed the liability of the trailer wheel, axle, and fastener manufacturers. Designed a stud tension testing apparatus for use in biaxial wheel tests.
  • Rental condo | Gatlinburg TN — Slip/fall – A guest slipped on a terrycloth bathmat when exiting a bathtub. Analyzed the myriad deficiencies in the opposing expert’s friction testing of an exemplar bathmat and his cited “standards” of care.
  • Highway crash | Atlanta GA — Hub separation – A wheel hub/brake drum from a new trailer came off and struck a motorcycle. Analyzed causative deficiencies in the trailer manufacturer’s component stocking & assembly practices.
  • Hospital | Covington GA — Slip/fall – A nurse slipped while wearing medical shoe covers over her shoes. The hall carpet had sheet plastic covering to protect from construction dust. Conducted testing using a whole-shoe tribometer to compare the friction of shoe covers to uncovered shoes, on plastic-covered carpet.
  • Rural Texas — Runover of toddler - A manual-transmission vehicle was started in gear, due to failure of springs in the clutch interlock switch. Analyzed the liability contributions of the spring manufacturer, switch manufacturer, clutch system supplier & vehicle manufacturer.
  • Additional Case Types: — Design/manufacturing/usage of windows, furniture, playground/fitness equipment, tools, ladders, doors, lifts, and vehicle components.

Professional Experience

  • Senior Managing Engineer | YA Engineering Services | 2023 - Current
  • Forensic Mechanical Engineer | Reality Forensics LLC | 2022 - 2023
  • Forensic Mechanical Engineer | Forcon International | 2003 - 2022
  • Lead Engineer & Owner | Precistems Incorporated | 1998 - 2006
  • Contract Mechanical Engineer | Panasonic MMCD | 1998 - 1998
  • Contract Mechanical Engineer | Motorola Energy Systems Group | 1997 - 1998
  • Mechanical Engineer | Firearms Training Systems | 1996 - 1997
  • Mechanical Engineer | Decibel Products | 1996 - 1996
  • Project Engineer | Herman Miller Incorporated | 1994 - 1996
  • Mechanical Engineer | Firearms Training Systems | 1993 - 1994

Practices & Skillsets

  • ADA Compliance Assessment
  • Plumbing Systems
  • Premises Liability
  • Products Liability
  • Drone Pilot
  • Slip and Fall Evaluations
  • Failure Analysis of Materials and Components
  • Tort Liability
  • Human Factors

Publications and Presentations

  • Leffler JP, Mantilla DC, Powell D. The Effect of Surface Texture Variations on DCOF Measurements of Ceramic Tiles using the BOT-3000E Tribometer. Proceedings of the IEA 2026 Slips, Trips, and Falls International Conference. Huntsville, Alabama, June 2026.
  • Mantilla DC, Tranum A, Leffler JP, Powell D. Effects of Added Body Mass on Utilized Coefficient of Friction during Stair Descent. Proceedings of the IEA 2026 Slips, Trips, and Falls International Conference. Huntsville, Alabama, June 2026.
  • Leffler J, Edwards M, Pritchett D. New Milestones in Slip & Fall Science & Standards. For The Defense 66(1), Defense Research Institute. September 2024.
  • Lockhart TE, Leffler JP et al. Factors influencing slip/fall risk while entering and exiting bathing surfaces (Task 3). US Consumer Products Safety Commission Project 61320621Q0068. June 2023.
  • Leffler JP. Bath Surface Contract Report on Tribometer Values of Reference Surfaces (Task 2). US Consumer Products Safety Commission Project 61320621Q0068. June 2023.
  • Leffler JP. Bath Surface Contract Report on Tribology (Task I). US Consumer Products Safety Commission Project 61320621Q0068. June 2023.
  • Leffler JP, Blanchette MG. Effects of Bathing Surface Drainage Contouring on Tribometer Friction Testing. J. Testing and Evaluation 50(3). February 2022.
  • Leffler JP. Forensic Engineering Analysis of Design and Manufacturing Practices for an Automotive Spring. J. National Academy of Forensic Engineers 34(1). June 2017.
  • Leffler JP. Effects of Evidence Spoliation on Forensic Engineering Analysis of Alleged Brake Servicing Defects. J. National Academy of Forensic Engineers 33(2). December 2016.
  • Leffler JP, Blanchette MG. Forensic Considerations Regarding Traction and Tribometry of Bathing Surfaces. J. National Academy of Forensic Engineers 33(1). June 2016.
  • Leffler JP, Barré KM, Reneau AP. The Changing World of Slip-and-Fall Defense. For The Defense 55(2), Defense Research Institute. February 2013.
  • Leffler JP. Forensic Engineering Investigation of Vehicle Hub Separations. J. National Academy of Forensic Engineers 28(1). June 2011.
  • Leffler JP, Schlender EH. Forensic Engineering Analysis of Reliance on Standards in a Multi-Defendant Cross Claim Case. J. National Academy of Forensic Engineers 27(2). December 2010.
  • Leffler JP. Forensic Engineering Investigation of an Alleged Plastic Chair Failure. J. National Academy of Forensic Engineers 27(2). December 2010.
  • Leffler JP. Forensic Engineering Investigation of Vehicle Wheel Separations. J. National Academy of Forensic Engineers 26(1). June 2009.
  • Leffler JP. Forensic Engineering Use of Walkway Traction Testing. J. National Academy of Forensic Engineers 26(1). June 2009.
  • Extrinsic Analysis of Same Level Fall Incidents
  • Product Failures and Subrogation
  • Effective Use of Surrogates in Investigating Bodily Injury Claims
  • Subrogating the Slip and Fall Claim
  • Pedestrian Slips - Proactive & Reactive Things to Consider
  • Pedestrian Safety - Specific Exposures
  • Use and Misuse of Codes, Standards, and Regulations
  • Friction or Fiction: The Changing World of Slip-and-Fall Analysis
  • Prevent Slips, Trips and Falls With ANSI/ASSP A1264 Walking/Working Surface Standards
  • Hot Wheels: Tips and Strategies for Successfully Subrogating Vehicle Product Liability Claims
  • Product Failures: Potential Layers of Liability
  • Walkway Auditor Training Course: ASTM F2948
  • A New Suite of Tribometer Standards
  • The ‘Conditioning Clip’ for Slider 55 preparation
  • The ‘Shim Method’ for testing 3D-profiled bathing surfaces
  • Pendulum friction testing of patterned 3D-profiled bathing surfaces
  • British Pendulum Slider 55 lifespan considerations versus EN 16165 preparation requirements
  • Premises Liability: Tips for Slips & Trips
  • Useful Tech for Premises Liability Claims & Litigation
  • Proving That Your Subrogation Target Breached an Accepted Standard of Care
  • The Tipping Point with Manufacturer Representations: Workers Comp Subrogation

Education

  • Bachelor of Engineering, Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia

Training Courses

  • Design for Manufacture and Assembly, Designing Plastic Parts for Assembly, University of Wisconsin
  • Plastic Injection Molded Part Design & Molding Processes Workshops, GE Plastics
  • Advanced Plastic Gear Design, Universal Technical Systems
  • The Bolted Joint, American Society of Mechanical Engineers
  • Photogrammetry and Analysis of Digital Media, SAE
  • Understanding Slip & Fall Events: A Biomechanical Perspective, University of Southern California
  • Multifactorial Analysis of Slip and Fall Events: Implications for Forensic and Safety Professionals, ASTM
  • Advanced Safety Management, Georgia Tech
  • Injuries, Anatomy, Biomechanics & Federal Regulation, SAE
  • Occupant and Vehicle Kinematics in Rollovers, SAE
  • Commercial Vehicle Braking Systems, SAE
  • Certificates in Recon-3D and Cloud Compare usage, Ai2-3D Forensics
  • OSHA 2045 Machinery & Machine Guarding Standards, Mid-Atlantic OSHA Training Institute

Affiliations

  • American Society of Safety Professionals (ASSP)
  • • Member, ANSI A1264 Accredited Standards Committee on Slip and Trip Prevention
  • • Vice-Chair, Subcommittee A1264.2 Missteps on Walking-Working Surfaces
  • ASTM International
  • • Officer, Technical Committee F13 - Pedestrian/Walkway Safety & Footwear
  • • Chair, Subcommittee F13.10 - Traction
  • • Chair, Subcommittee F15.03 - Safety Standards for Bathtubs & Shower Structures
  • • Former Chair, Technical Committee E58 - Forensic Engineering

Professional Licenses

  • Professional Engineer (PE) - District of Columbia - License #PE40000848
  • Professional Engineer (PE) - Delaware - License #27766
  • Professional Engineer (PE) - Florida - License #64099
  • Professional Engineer (PE) - Georgia - License #PE024560
  • Professional Engineer (PE) - Louisiana - License #44910
  • Professional Engineer (PE) - Maryland - License #59621
  • Professional Engineer (PE) - New Jersey - License #24GE05941500
  • Professional Engineer (PE) - New York - License #107016
  • Professional Engineer (PE) - Pennsylvania - License #074801
  • Professional Engineer (PE) - South Carolina - License #26271
  • Professional Engineer (PE) - Tennessee - License #120823
  • Professional Engineer (PE) - Texas - License #134138
  • Professional Engineer (PE) - Virginia - License #0402046335