The Case of the Collapsing Seat: Weak Standards and No Oversight Led to a Fatal Defect

A renown seat safety expert has called on the U.S. Consumer Product Safety Commission and the Veterans Administration to institute random spot checks to ensure that mobility scooter and other powered wheelchair devices intended for the disabled meet minimum voluntary safety standards – and publicize any compliance failures to warn the public. Dr. Kenneth J. Saczalski, who has been at the forefront of seat strength issues for decades, made his call to action today at a meeting of the Society for the Advancement of Materials and Process Engineering meeting in Fort Worth, Texas.

Saczalski was retained by Miami attorney David Bianchi on behalf of the family of Carolyn Sorenson to determine what caused a scooter seat back to break in a products liability case against the U.S. distributors of the Daytona GT3 Electric Scooter. In January 2009, 64-year-old Sorenson died from positional asphyxiation in the trash room of her condominium building, when the plastic molded seat of her mobility scooter fractured and collapsed, causing her to fall backwards. Sorenson’s lower half remained belted in what was left of the seat, while her upper torso was wedged behind her against the door frame, according to police reports.

Mobility scooters, like thousands of other consumer products, are not subject to any mandatory standards. The Daytona GTS3 Electric Scooter with the folding seat system that failed in the Sorenson incident was allegedly designed and manufactured to ISO standard 7176-8 and WC-08 of ANSI’s Rehabilitation Engineering and Assistive Technology Society of North America (ANSI/RESNA). But as design and materials tests on exemplar seats showed, the standard’s static and dynamic compliance tests do not directly address the real-world stresses to which the seats are subjected. And, contrary to the claims of the company that sold the scooter, the plastic materials used in the seat were not the pure polypropylene, but a mixture of polypropylene and recycled plastic that weakened it.

Saczalski noted that “after initial certification there is no requirement for periodic recertifications. Consequently, after a period of use and time on the market, injury risk problems may arise from design flaws, such as failure to address potential stress concentration issues associated with handicapped user tasks related to rearward loading on the plastic seat systems.”  And “in addition, increased occupant/seat injury risks of plastic seat designs may also occur in later productions of the initially certified devices due to quality control issues and manufacturing flaws associated with the use of recycled moldable plastic materials that may contain high stress concentrations introduced through material impurities and foreign particle contaminates, often found in the recycled plastic materials.”

“It’s a cheaper way to go, but you get occlusions and imperfections, and when you lean on it, the seat tends to fracture in critical areas,” Saczalski said. “The regulators should make sure the manufacturers don’t change the quality after the fact. That’s what happened here. Once they certified it, they started changing the properties of the plastic in the seat.”

Attorney Bianchi settled the case against Medical Depot and Florida Home Medical.   Bianchi submitted Saczalski’s report to the CPSC and the FDA.

Scooters and off-road vehicles – of any configuration – that are not medical devices fall under the CPSC jurisdiction.  Many mobility scooters that are marketed and sold as a medical device fall under FDA jurisdiction.

Sorenson’s seat suffered two fractures on either side of the seat base near the rear mount bolts. Saczalski tested an exemplar mobility scooter to ISO 7176-8, and found that it broke in the same spot. He also used Finite Element Analysis to examine “the stress concentration and displacement patterns associated with rearward loading of the seat.” The FEA study again verified that that those areas of the seat were high-stress regions.

“The FEA also indicated that the likely failure regions were predictable and could have been virtually eliminated with minimal changes,” Saczalski said.

While the ISO and ANSI/RESNA WC-8 standards include a pendulum impact test for seatbacks, he notes: “these standards do not explicitly consider the typical handicap normal uses such as the rearward leaning function associated with the fatal injury case, and leaning on the seatback for stability while the handicapped individual is exiting or getting off the seat. This slow loading rearward process occurs thousands of times over the use of the device and must be addressed.”

Compounding such design standards was the use of adulterated plastics in the seat. Plastics expert Dr. Duane Priddy performed a microscopic evaluation of Sorenson’s seat and the exemplar and found that the seat material was contaminated by recycled plastic mixed with the polypropylene.

According to testimony by Florida Home Medical, Sorenson’s scooter was manufactured in 2008, but it was last tested in 2003. The certification process typically occurs before the product is introduced to the market, and there is no requirement for periodic re-certifications, so design flaws discovered through use and time in service are discovered through tragedies like the death of Sorenson.