As Originally published by M.A.S.E. LLC, October-November 2013.
By: John Ryan
Tel: (855) 627-6273
Email Mr. Ryan
A significant number of elderly persons experience falls every year. In 2010, 2.3 million nonfatal fall injuries involving elderly people were treated in emergency rooms around the country. In the same year, 21,700 elderly people died as the result of unintentional falls. Falls for elderly people are extremely hazardous as they may not recover from fractures and other injuries. While a majority of these injuries were unrelated to mobility aids, mobility aids do fail, resulting in falls. This Clues will examine different mobility aids, and how they can fail in accidents.
There are various types of mobility aids - wheelchairs, transport chairs, rollators, walkers, canes, gait trainers, crutches, and motorized scooters. Wheelchairs can be manual or motor powered, and come in various configurations including folding and non-folding. There are also wheelchairs for rough terrain. Wheelchairs can be very stable, or poorly constructed and unstable. Transport chairs are lightweight versions of wheelchairs designed for moving people short distances. These are much less stable, and are typically constructed of structural components of lower strength than wheelchairs. Walkers typically have a four-legged frame, either in a fixed leg configuration or with wheels on the front legs.
Figure 1: The original Rollator
Rollators are a type of walker with wheels on each leg. They are sometimes equipped with a sitting surface to rest on. They usually have brakes on two or more of the wheels. Rollators are at times combined with a transport chair.
Figure 2: Rollator/Transport Chair
What can go wrong with these devices that allow elderly people to continue to be mobile during their advanced years? There are multiple failure modes for mobility devices including structural failure, tipping, adjustment or folding mechanism failure, and brake failure.
Structural failure of mobility device components can cause the mobility device to collapse. This can be due to inadequately designed structural components that cannot support the weight of use. The design of the frame may result in high stresses at locations where forces act on a lever arm. Failure can also be due to fatigue failure, which occurs from repeated use and forces acting repeatedly over extended periods of time. Welds can fail to securely adhere to structural components, resulting in weld failure. When any of these failures occur, the mobility aid can collapse, resulting in injuries or death.
Wheelchairs, transport chairs, and rollators can give the occupant a false sense of security if they are not designed adequately. Improperly designed sitting mobility aids and wheeled walkers can become unstable and cause the device to tip. A tipping mobility aid can result in head trauma or other severe injuries. These types of accidents can be prevented easily with proper engineering design and analysis.
Chairs that are designed to be mobile to put in vehicles often feature a folding design of some sort. Design or manufacturing flaws can result in these folding mechanisms to collapse, causing the device to collapse and the occupant to fall to the ground. The units must also be able to withstand bumps and drops without collapsing. Walkers and rollators have adjustable handles to accommodate users of different heights. The adjustment mechanism can fail, causing the adjustable mechanism to collapse and the user to fall.
Failure of the brakes on wheelchairs, rollators, and other devices can result in unanticipated movement of the device, and result in a fall, or uncontrolled motion of the device. If a seated unit with wheels experiences a brake failure on a slope, the unit can impact a fixed object at high speeds.
Voluntary industry standards outline performance criteria for many of these mobility aids. Some relevant standards include:
ISO 7176-1 1999 Wheelchairs - Part 1: Determination of Static Stability
ISO 7176-1 1999 Wheelchairs - Part 2: Determination of Dynamic Stability of Electric Wheelchairs
ISO 7176-1 1999 Wheelchairs - Part 3: Determination of Effectiveness of Brakes
ISO 7176-1 1999 Wheelchairs - Part 6: Determination of Maximum Speed, Acceleration and Deceleration of Electric Wheelchairs
ISO 7176-1 1999 Wheelchairs - Part 8: Requirements and Test Methods for Static, Impact and Fatigue Strengths
ISO 11199-1 Walking Aids Manipulated by Both Arms-Requirements and Test Methods-Part 1: Walking Frames
ISO 11199-1 Walking Aids Manipulated by Both Arms-Requirements and Test Methods-Part 2: Rollators
Testing can be performed on mobility aids involved in accidents to determine if they meet industry criteria for strength, stability, and safety. Tests defined in the standards are performed both on unloaded units and different tests are run involving a test dummy.
Figure 3: Stability testing with a test dummy
At MASE, we have experience with analyzing and testing mobility aids, as well as extensive experience dealing with structural failures and design defects. Call us at (855) 627-6273 or email us at info@mase.pro to discuss your accident case.
Please call us to discuss any questions you have about unsafe products. (855) 627-6273
John L. Ryan, BSME, P.E. is a Mechanical Engineer who provides general Mechanical and Structural Engineering expertise. Mechanical and Safety Engineering (MASE) provides full service analysis and accident reconstruction of products involved in accidents. Mr. Ryan's services have been requested for attorneys and insurance companies needing forensic engineering expert witness testimony to determine whether machinery and products involved in injury cases were adequately designed or whether they have a Design, Manufacturing, or Material Defect. All products are lab-tested on site to determine adherence to industry standards and engineering design protocol. Alternate preventative designs are developed when none exist commercially.
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