Project P4: Improving Wheelchair and Wheelchair Seating Crashworthiness  

Task Leaders: Miriam Manary, MSE, Gina Bertocci, PhD

Co-investigators: Nichole Ritchie, MSE, Patricia Karg, MS, Lawrence Schneider, PhD

Other Participants: Tom Whelan (manufacturer), Sue Johnson (manufacturer), Jill Kolczynski (manufacturer), Mike Barner (clinician), Virginia Nelson (clinician), Bette Cotzin (clinician, transportation provider), Nathaniel Madura (researcher), Jennifer Whalen (student), wheelchair seating manufacturers, wheelchair users.

Overview

This is a development project that is aimed at improving wheelchair and wheelchair seating crashworthiness through three tasks:

• Task P4.1 - Completion of a Rear Impact Standard for Occupied Forward-Facing Wheelchairs and Demonstration of Feasibility in Prototype Designs
• Task P4.2 - Enhancement of the Surrogate Wheelchair Base (SWCB)
• Task P4.3 - Development and Validation of a Surrogate Wheelchair Seating System (SWCSS)

This activity will support the long-term outcome of improved safety for wheelchair users, particularly in the van and minivan environments.  The standard and test devices (SWCB and SWCSS) developed in this project will support the intermediate outcomes of increased availability and use of wheelchair bases and seating systems that are suitable and safe for occupancy in motor vehicles.

Expected Project Outputs and Short-term Outcomes

Expected outputs

• A completed wheelchair rear-impact standard with associated test methods
• Rear impact design/performance criteria for wheelchairs
• Prototypes of modified commercial wheelchairs that demonstrate compliance with the rear-impact standard, 
• An enhanced SWCB for use in frontal crash testing of a wider range of wheelchair seating systems with varying occupant restraint and wheelchair securement configurations,
• A surrogate wheelchair seating system (SWCSS) for use in testing the frontal crashworthiness performance of wheelchair bases independent of specific seating systems,
• Publications that document the results of the project tasks.

Expected short-term outcomes

• Increased wheelchair and seating manufacturer knowledge regarding design of wheelchair frames and seating systems for improved performance in rear impacts
• Increased availability of wheelchair seating systems and wheelchair base frames that are crashworthy under frontal and rear impact conditions
• Improved wheelchair user safety and crash protection due to innovative changes to commercial wheelchair components

Project Updates

• Project P4.1: July 2007
• Project P4.1: July 2007
• Project P4.1: July 2007
• P4 Annual Report 2007 (2.8 MB pdf)

Task P4.1: Completion of a Rear Impact Standard for Occupied Forward-Facing Wheelchairs and Demonstration of Feasibility in Prototype Designs

This task will begin with the revision and improvement of draft design guidelines for wheelchairs that provide enhanced occupant protection in rear impact.  These draw on the work from the previous RERC and on-going complementary studies.  The design guidelines will define wheelchair characteristics, head/back support geometries, and seatback and attachment hardware strengths associated with good wheelchair performance in a moderate-to-severe rear impact test. It is possible that solutions that incorporate rear-impact protection features would only be acceptable for wheelchair users who already need or use head back support during motor-vehicle travel, although rear-impact protection is an important feature for all travelers.   If head/back support structures on the wheelchair are determined to interfere with the comfort and function of users, a vehicle mounted head/back support may be more appropriate, and these solutions will be explored in Project P3.

Unlike the development process for the frontal impact standards where many lightweight commercial wheelchairs already had sufficient frame strength to perform well under the frontal crash conditions, it is anticipated that most wheelchairs will require enhancements to meet the proposed forward-facing rear impact criteria.  Therefore, the project will facilitate commercial wheelchair product improvement by identifying and demonstrating how wheelchairs can meet these proposed standards. Input from wheelchair manufacturers will be incorporated into the standards development process.

 Specifically, the research team will work with the collaborating manufacturers to identify a set of candidate wheelchairs that represent the nominal characteristics of groups of wheelchair types (i.e., stroller-type, standard manual, pediatric power, adult power, etc).  Wheelchairs that are more often used by populations that cannot easily transfer to OEM seating during motor vehicle travel, and thus can benefit most from rear-impact protection features, will be the focus.   Based upon previous efforts related to identification of failure mechanisms in rear impact and determination of seat back loading in rear impact the design of the wheelchair, (particularly the seatback and head support features) will be enhanced to improve rear-impact crash performance. The improved performance will be verified using the dynamic test methods in the draft standard.  The information gleaned from the process will be used to improve the forward-facing rear-impact draft standard and provide manufacturers with real solutions on how to achieve compliance.

This exercise will provide insight into the feasibility of creating successful designs, determine the potential impact on other wheelchair features/functions, and give a clearer idea of which wheelchair types are likely to be amenable to having rear-impact protection features built into the product.   The activity will conclude with revision of both the design guidelines and draft forward-facing rear-impact standard to reflect new knowledge gained from the development process.

Update July 2007: P4.1 Completion of a Rear Impact Standard for Occupied Forward-Facing Wheelchairs and Demonstration of Feasibility in Prototype Design

During the reporting period, the draft rear-impact wheelchair standard has been revised twice. The test methods in the improved standard has been used to conduct new tests and the revised performance criteria have been used to evaluate all rear-impact test data available to date. Two RESNA papers have resulted from this work. The draft standard was discussed at the last two ISO meetings and the group has decided to support an ISO new work item that will propose incorporating the draft as an informative annex to 7176-19.

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Task P4.2: Enhancement of the Surrogate Wheelchair Base

This task will focus on improving the existing SWCB to expand its utility and scope of its application. The initial effort will be a sled test series to address the issues of the mass of the SWCB, particularly in the case where a seating system has a fully integrated seatback frame and attaches to the wheelchair base only through the hardware connected to the seatpan.  A set of worst-case scenarios for seating failure modes and the concerns that have been identified by the wheelchair manufacturers to date will be fully defined, and a sled test series will be used to explore the key issues of, and solutions to, effective testing of these systems.  Also, computer modeling will be used to investigate the effects of SWCB mass on seat attachment hardware shear loading and relative motion between the seating system and SWCB.

A second activity will use computer modeling and sled testing to explore the effect of anchoring the lap belt to the vehicle floor, the wheelchair base, and the wheelchair seating system to determine which test modes produce worst case outcomes and are therefore most appropriate for SWCB test protocols.  The analysis will also assess differences in outcomes that may warrant additional tests to be added to the standard, or lap belt anchoring configurations that should be discouraged.   The knowledge gained in the two activities above will be used to improve SWCB design, SWCB drawings, and relevant standards.

Update July 2007: P4.2 Enhancement of the Surrogate Wheelchair Base (SWCB)

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Task P4.3: Development and Validation of a Surrogate Wheelchair Seating System

The success and promise of the SWCB has led to the complementary issue of how to test wheelchair frames independent of a specific seating systems, so that there are commercial products to accept the seating systems tested using the SWCB in accordance with ANSI/RESNA WC20 and ISO 16840-4.  The solutions must provide wheelchair base/frame manufacturers of wheelchair frames/bases the same level of confidence and ease of testing afforded to the seating system manufacturers. The objectives of this task are to design, develop and validate a surrogate seating system for these purposes.  While the primary function of the SWCSS will be to test wheelchair frames and bases, the SWCSS will also be used as a platform for limited testing supplemental postural supports. The following steps will be used in the development of a SWCSS:

• development of SWCSS Design Criteria,
• development of SWCSS Design Criteria, and
• SWCSS Validation.

Update July 2007: P4.3 Development and validation of a surrogate wheelchair seating system (SWCSS)

During the reporting period, the process of developing a preliminary design for a surrogate wheelchair seating system was initiated through discussions with other researchers, wheelchair users, clinicians, and wheelchair seating manufacturers to determine how such a device is likely to be used and what types of commercial products will be most effected. An in-depth retrospective survey of over 500 dynamic tests was begun that will yield information on how commercial wheelchair frames fail during WC19 frontal impact tests. These data will provide information as to how surrogate seating should load wheelchair frames in order to represent a nominal worst-case seating system under frontal impact conditions. In addition, plans are underway to meet with a group of manufacturers and clinicians in the Fall of 2007 to review project findings and design ideas to date.

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Last updated: December 4, 2007