Mobility Device Accidents
First published Summer of 2020
Accidents Involving Mobility Aids
Mobility aids are devices that help people with difficulty walking whether due to age, injury, or disease, continue to be able to move around. These devices include a variety of styles for specific applications. Users of these devices rely on the stability and strength of the mobility aids, and trust that the device they are using is safe, and will continue to be safe. Due to the difficulties that users experience that require the use of mobility aids, users are often less able to protect themselves in the event of a device failure or tipover, and can be more likely to suffer more significant injuries. The weight of the user can often be a factor as well, as due to a lack of mobility some users can be near the weight limit of these devices or even over the weight limit. This issue of Forensic Clues will examine the different types of mobility devices, some common failure modes, and how we can help you with your client’s accident case.
Walkers, Canes, Crutches
Mobility devices without
wheels include walkers, canes, and crutches which are typically support aids
that users lean on to help them walk.
Walkers typically have four legs to them, with some designs having two
legs. The four-legged versions typically
have two legs with wheels, and two legs with rubber stoppers on them. Canes and crutches have singular legs.
Wheelchairs / Powered
Scooters
Wheelchairs are one of the
most common types of mobility aids, and are mobile chairs that can be
self-propelled or motor-driven, for the purpose of locomotion of the user. Wheelchairs provide full support for the
weight of the individual, and motion is generated by someone pushing it, the
user rolling the large wheels to provide
locomotion, or with a motor of some sort. These usually have some sort of braking
system.
Rollators
Rollators are a type of walker with wheels on each leg.
They are sometimes equipped with a sitting surface to rest on, that is not
intended to be used while the unit is in motion. Rollators provide stability, balance,
and support for the user. While normally equipped with four wheels
there are three-wheel versions. They usually
have brakes on two or more of the wheels. Rollators are at times combined with
a transport chair.
Rollator/Transport Chair
The primary difference
between a rollator, and a rollator/transport chair is that the
rollator/transport chair is designed to allow motion of the device with the
user in it, compared to a rollator being designed to help the user walk, and stop
to rest when needed.
Knee Scooters
A knee scooter is typically a four-wheeled device that
allows a user to place one or both of his or her knees on the device to
facilitate movement. It can have brakes,
as well as all-terrain versions with larger wheels.
Support Aids
Some devices are not intended to help facilitate movement,
but rather stationary support. These can
include lift assist devices intended to help a person to their feet from a
seated position, or can include chairs that are intended for bath use. There are also bath transfer chairs and
benches which have a seated position on the
exterior of the bath as well as in the bath itself, to help with transitioning
between the bath and the floor.
What Can Go Wrong?
Mobility aids typically
have designs that make them stowable, involving folding or retractable legs and
other structural members. While this facilitates transport in vehicles,
this also introduces a failure mode of the device collapsing. If these devices had fixed structural
members, this failure mode would be eliminated.
Collapse can occur due to the failure of connections that keep the
device in the weight-supporting mode, including bolts that fail, are loose, or
fall out. Other connection failures can
include pins that are spring-loaded, and come out of their corresponding hole,
or is assembled such that the pin is not engaged. Some designs are safer than others, with
failures of connections or loading in an atypical manner not causing
collapse. Collapse can be due to
design failure, failure to maintain,
incorrect assembly, or human error.
Tipover
Tipover is a very common
mode of failure with mobility devices.
Tipovers can occur to either side, to the front, or to the rear. While some tipovers are unavoidable, many are
due to designs that are not adequately stable. Manufacturers at times design their
products to meet industry standards, which does not necessarily mean that the
design will be safe, due to arbitrary industry standards, standards that do not
encompass all conditions a mobility
aid will face, and corrupt standards that are developed by product
manufacturers to protect themselves. One
accident we see often is tipovers due to hitting a bump. This scenario is not adequately covered by
industry standards, as standards call for static (not-moving) stability tests
unless the device is an electric-powered wheelchair. Tipovers can be due to a poor, unstable
design, overreaching on the part of the user, a user being overweight, being on
an angled surface, the occupant holding extra weight, or hitting a bump.
Brake Failure
Brake failure can result
in collision or tipover accidents, and can be due to a failure to maintain,
incorrect assembly of the mobility device, design defects, or due to the brakes
being inadequate to slow or stop the device.
Structural Failure
Another common cause of
mobility device accidents is structural failure of the device, which can
include the main structural components collapsing, buckling, or rupturing. This can be due to design defects resulting
in inadequate strength, the weight of the user being greater than the rated
strength of the device, deterioration of the device, or loose connections that
result in unanticipated forces that the structure cannot withstand.
Assembled Incorrectly
Incorrect assembly is
often noted prior to use, but can go undetected, and can include a variety of
failures such as not using all bolts or other connectors, or having components
reversed or mounted in the incorrect location.
User Exceeding Capacity of
Device
We often see devices fail with users that are either
slightly under, or slightly over the rated capacity of the device. While a lay person may think that a failure
of a device when used by someone who his ten pounds heavier than the rated
capacity is the user’s fault, this does not correlate with engineering design
principles, that require a factor of
safety for any design where the health and welfare of an individual is at
stake. A failure of a device due to the
user being heavy, is a failure to properly design the device with adequate
factors of safety. Dynamic loading
occurs whenever motion is involved, such as hitting a bump in a
wheelchair. This bump can magnify the
weight of the user over four times, resulting in potential failure of the
device if it does not have adequate factors of safety. This literally means that a 300-pound user
can generate 1200 pounds of force when motion is involved.
How We Can Help
At MASE, we can determine if an accident involving a
mobility aid is due to a design defect, failure to maintain, or human
error. We offer full service mechanical
engineering expert witness services. The
first step is a free review of basic case information and photographs, at which
point you will be informed of our thoughts on the case, the mode of failure if
identifiable at this point, and the validity of a potential liability or
premises claim. Data and conclusions can be drawn from the failed
device itself, and exemplars are often purchased, examined, and tested.
Call
us at (855) 627-6273 / email info@mase.pro