The document describes the development of an ergonomic waste container for hospitals. The current waste container design requires lifting garbage bags overhead, which can cause shoulder and back injuries. The researchers designed a new waste container that rotates to 30 and 45 degrees, allowing bags to be removed without overhead lifting. Testing showed the new design significantly reduced shoulder abduction by about 9-10 degrees compared to the old design, which may decrease injury rates for custodial workers.

1. Development of an Ergonomic Waste Container for Hospitals
Rosa Padilla, Jennifer Baltich, and Fadi Fathallah
Biological Systems Engineering Program
Department of Biological and Agricultural Engineering
University of California, Davis
The current waste container design at most hospitals, including the UC Davis Medical
Center, requires an individual to raise the garbage bag up and out of the container, which involves
shoulder flexion above the head and flexion at the waist for most individuals. Overuse injuries
due to lifting are very common to the muscles of the shoulder and result in high costs for treating
injured workers. The aim of this study was to design a new waste container that will limit the
amount of shoulder and trunk flexion required to remove the garbage bags from the container. A
waste container was developed, which rotates about two pins on each side to 30 and 45 degree
angles from the upright position so that the bags can be removed without lifting them over your
head. The degree of shoulder and trunk flexion for the new and old waste container was
measured using electrogoniometers. The most important result was that the average degree of
shoulder abduction decreased by about 9 degrees from the new bin at 30 degrees and 10 degrees
to the new bin at 45 degrees. There also was a significant reduction in sagittal flexion between
the old bin and the new bin. The reduction in the level of shoulder abduction and sagittal flexion
with this new design may reduce the incidence of injury and improve working conditions for
custodial staff in hospital environments.
INTRODUCTION
The large range of motion of the shoulder makes it
vulnerable for several injuries to the muscles and tissues
of this area. Overuse injuries due to lifting are very
common to the muscles of the shoulder. Rotator cuff
impingement is especially common with repetitive
overhead action (Keyserling, 2000; Keyserling, Stetson,
Silverstein, & Brouwer, 1993). This will cause great
irritation to anyone with this problem and pain with
overhead lifting. There is also the general risk of tearing
or straining a muscle in the shoulder region when lifting
weights above the head (Keyserling, 2000; Keyserling et
al., 1993).
The custodial staff of the UC Davis Medical Center
in Sacramento is currently having shoulder and back
problems as a result of the current design for the waste
containers in the facility. The containers that are used at
the moment require the individual who is emptying the
trash to lift the trash bag up and out of the container,
which often requires lifting their arms above their head.
Injuries to the back and shoulder are the most expensive
injuries among parts of the body of U.S. healthcare
workers, whose injuries and illnesses are estimated to
cost in excess of $3 billion annually (Waehrer, Leigh, &
Miller, 2005). Such injuries are detrimental not only to
the custodial staff, but also to the medical center, and
ultimately its patients.
It was hoped that a waste container that limits the
amount of lifting and stress on the shoulder and back
muscles, will help reduce the incidence and cost of
injuries. This will improve the working conditions for
the custodial staff and provide them with a safer working
environment so that they can enjoy their work and be as
productive as possible.
The ultimate goal of this project is to design a waste
container that will limit the amount of overhead lifting
required to remove the trash bag from the container, so
as to reduce back and shoulder stress for the custodial
workers. The waste containers are in hospital settings, so
the new waste container must be leak proof. The solution
must also not be too time-consuming since several bags
are removed on a daily basis. Finally, the new waste
container must not change the dimensions of the current
bin and must have a hands free method of opening.
METHODS
Container Design
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2. The leak-proof requirement of the design removed
the possibility of developing a waste container with a
side door to eliminate overhead lifting. As a result, a
rotating waste container was designed (Fig. 1). It
consists of a metal frame that stands upright at all times
with two pivot points connected to a metal basket. This
basket holds the waste container. There is a lever
locking mechanism connected to one of the pivot points.
Figure 1. Picture of fabricated final design
When the user wants to remove the garbage bag
from the waist container, they step on the foot pedal and
squeeze the lever on the locking mechanism. The basket
is then free to rotate and the user can pull the lever
towards them. As they do so, the basket containing the
waste container will rotate about the two hinges towards
the user. When the user releases the locking mechanism
lever at a desired angle, the basket containing the waste
container will lock into that position. The user is then
able to remove the garbage bag from the waste container
inside of the basket by pulling the bag towards them
rather than lifting it straight up above shoulder height.
There are four options of angles to lock the basket
into. This allows for a variety of individuals of various
heights to use the prototype comfortably and effectively.
Once the trash has been removed, the user once again
squeezes the handle on the lever and rotates the basket
containing the waste container back to its upright
position and releases the lever to lock it back in place.
This design remains leak proof and still limits
overhead lifting by allowing the user to slide the trash
out towards them rather than lifting it above their heads.
Subjects
Seven subjects participated in the study, five of
whom were women and two men since there are more
female custodial workers than male at the UCD Medical
Center. Heights requirements for the test subjects were
based on anthropometric data for the average American
male and American female. The female subjects were
selected between 5’ and 5’8”, and male subjects were
between 5’6” and 5’10” to be as close as possible to the
5th to 50th percentile range of heights (NASA, 1995)..
The subjects had no prior shoulder injuries.
Apparatus
The Lumbar Motion Monitor (LMM) (Chattecx
Corp. Hixon, TN) was used to measure the position,
velocity, and acceleration of the spine in the sagittal,
lateral, and twisting planes (Marras, Allread, & Ried,
1999).
The motion of the shoulder was monitored using a
Biometrics electrogoniometer (Biometrics Ltd, UK)
placed on the left shoulder. This provided joint range of
motion, angular position, velocity and acceleration of the
shoulder joint in two planes (Abduction/Adduction and
Flexion/Extension) during the removal of a trash bag
from each waste bin.
The pulling force required by the user to remove the
trash bag from each waste container was measured using
a digital force gauge (Chatillon DFS-500, AMETEK,
Largo, FL).
Procedure
For both the new and old bin, 3-D motion of the
back and the 2-D motion of the shoulder during the
process of removing the various weights of trash bags
from the bins were measured using electrogoniometers.
The force required to remove each weight condition
from the old and new waste bins were also recorded to
determine the pulling force.
For the old waste bin, each of these measurements
could only be completed from one angle, since the bin
stands in only one upright position. For the newly
developed container, kinematic variables were measured
at the two peak angles that the new waste bin prototype
can be tilted to, namely 30 and 45 degrees from vertical.
In order to show variation in the weight of the trash bag,
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3. subjects handled bags weighing 5, 7, and 10 pounds at
each of the two tilting angles, and at 0 degrees (old
waste bin).
Experimental Design
Table 1 gives a list of the experimental conditions
tested in this evaluation. To avoid possible learning or
carry-over effect, conditions were randomly presented to
the subject. For each condition, shoulder angle, sagittal
flexion angle, and time to remove trash bag were. For
each experimental condition, three trials were collected
and their average was used to represent that condition.
ANOVA tests were performed to test differences among
the old system and the newly developed waste container.
Table 1: Experimental conditions.
Waste
Bin
Trash
Weight
(lbs)
Angle of
Inclination from
Upright
(degrees)
Old 5 0
New 5 30
New 5 45
Old 7 0
New 7 30
New 7 45
Old 10 0
New 10 30
New 10 45
RESULTS
The average degree of shoulder abduction,
adduction, flexion, and extension for the old bin, the
new bin at 30 degrees and the new bin at 45 degrees can
be found in Table 2. The changes in the degree of
shoulder flexion and extension were not significant, as
was shown by the ANOVA results.
Table 2: Average angles of shoulder abduction,
adduction, flexion, and extension.
Bin
Average
Degree of
Abduction
Average
Degree of
Adduction
Average
Degree of
Flexion
Average
Degree of
Extension
Old 39.84 1.08 26.03 26.24
New 30 31.05 2.99 23.02 24.42
New 45 29.44 2.74 23.43 22.27
(Only the angles for abduction and adduction were proven to be significantly
different using ANOVA with a p value of 0.05. The degrees of flexion and
extension were not found to be significant.)
The results for the shoulder showed a significant
decrease in the level of shoulder abduction from the old
bin compared to the new bin angled at 30 and 45
degrees.
The average degree of shoulder abduction decreased
by about 9 degrees from the new bin at 30 degrees and
10 degrees to the new bin at 45 degrees (Figure 2). The
degree of shoulder adduction, however, increased
slightly from the old bin to the new bin at 30 and 45
degrees. Reducing the shoulder abduction is important
in reducing the risk during removing trash from a waste
bin. There was only about a 2-degree increase in the
level of adduction, however, which is of little practical
significance (Figure 3).
Old New 30 New 45
BIN
15
20
25
30
35
40
45
50
55
60
Abbduction(Deg)
Figure 2. Average (+/- std dev.) abduction angles for the
old bin, the new bin tilted to 30 deg. and the new bin
tilted to 45 deg.
Old New 30 New 45
BIN
-4
-3
-2
-1
0
1
2
3
4
5
6
7
Adduction(Deg)
Figure 3. Average (+/- std dev.) angles of adduction for
the old bin, the new bin tilted to 30 degrees, and the new
bin tilted to 45 degrees.
The pulling force proved to decrease with the new
bin at 30 and 45 degrees. This can be seen in Figure 4
below. This is due to the fact that the individual is
pulling the garbage bag out of the new waste container
rather than lifting the bag straight up above their head as
found with the old waste container. The pulling force
shall decrease even more if the UCD Medical Center
continues with their plan to implement trash liners with
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4. ridges to allow more air flow between the bag and the
liner, reducing the contact between the waste container
and the garbage bag.
Pulling Force
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
Old New 30 New 45
Waste BIn
AveragePullingForce(lbs)
5 pounds
7 pounds
10 pounds
Figure 4. Average pulling force at each weight option
for the old waste container, the new waste container at
30 degrees, and the new waste container at 45 degrees.
The ANOVA results for sagittal position showed
that for the old bin, the weight has no significant effect
on the shoulder and back motion. There was; however, a
significant difference between the old bin and the new
bin. The degree of sagittal flexion with the old container
was 9 degrees greater than the new container. With the
old design the user had to bend at the waste more to get
the trash bag out of the bin. A rotating waste container
reduced sagittal position by allowing the person to pull
the bag out and step back without having to bend at the
waist to try to get the bag out of the container.
The ANOVA results for the lateral position showed
that lateral position for the old container was
significantly higher than the container. The old waste
container produced an average of 4 degrees of lateral
bending whereas the new container produced -1 degrees
of lateral bending. This may be contributed to the
design of the lever for the locking mechanism, which is
on the left side of the new bin. The user would have to
lean to the left, producing a negative lateral flexion, to
see the lever position required for the angle they are
seeking.
The ANOVA results for sagittal velocity showed
that the weight does not seem to be a factor in the
amount of sagittal velocity for the new or the old
container, but that there was a significant difference
between the old bin and the new bin in the degree of
sagittal flexion velocity. The old container goes from
about 8 to 10 degrees per second whereas the new
container remains steady at around 4 degrees per second.
This observation indicates that using the old trash bin is
causing the user to increase their sagittal velocity. This
may be explained by the need of the user to generate
more momentum in the upright bag so as to compensate
for reduced shoulder strength due to needing to lift the
upright bag higher than the inclined condition. The
reduction in sagittal velocity given by the new design
reduces the dynamic component of the bag lifting, which
is a risk factor for low back injuries (Marras et al.,
1993).
DISCUSSION
Ergonomics is a field that is expanding greatly.
Overuse injuries have become more of a concern in the
work place. The results of this study show a great
potential in the suggested design for reducing the level
of shoulder awkward postures involved in waste
removal. The only motion that showed an increase was
shoulder adduction and the increase was minimal and
overshadowed by the great decrease in shoulder
abduction. The trunk kinematic results also showed a
great decrease in the sagittal flexion and velocity, which
is the primary plane of motion of concern. The waste
container can be used in other settings outside of the
hospital as well.
There are a few recommendations that would be
made to the UC Davis Medical Center or any hospital
that would be interested in this new design for their
waste bins. First of all, a mechanism that would allow
for the lid to remain open while the trash bag was being
removed is recommended. One idea could be analogous
to the mechanism of a retractable ballpoint pen. If the
mechanism that is used in a retractable ballpoint pen
were placed on the hinges of the lid that attached to the
foot pedal, this would allow the user to press the foot
pedal once and allow the lid to open and stay open.
Once they were done removing the trash bag, they would
simply have to push the foot pedal again to release the
lid and allow it to close. This would make it easier for
the user to remove the trash. Since the angled bin brings
the top of the trash bin close to the user, it is slightly
difficult to remove the trash and keep your foot on the
foot pedal at the same time to keep the lid open.
Another further improvement is a locking
mechanism that does not require as much precision as
the current design. This would make the task of tilting
and locking the bin in position a lot faster.
Another suggestion would be to secure the bin to the
basket better so that when it is at an angle and the user is
removing the trash bag the bin does not come out with
the bag. Whatever method is chosen for securing the
bin, holes cannot be drilled into the liner because that
would break the requirement of maintaining a leak proof
liner.
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5. Limitations
This intervention effectively achieved the goals set out
to reach; however, there were some limitations with the
testing of this intervention. First, the test was performed
in a laboratory setting and using students; further testing
on actual custodial staff would further validate the
potential for the intervention. Second, the new device
showed promise in reducing risk factors for the shoulder
and lower back; however, further implementation of this
approach in hospital rooms, and a follow up
epidemiological study to test its effectiveness in
reducing musculoskeletal injuries among hospital
custodial staff would be desired.
CONCLUSION
Hospital custodial staff suffers from high prevalence of
back and shoulder musculoskeletal disorders. One task
that has been identified as a potential source of risk for
these disorders is the trash bag removing task in hospital
rooms. This study introduced an alternative waste
container that holds promise in reducing risk factors for
shoulder and lower back risk factors. Further testing is
needed to validate the effectiveness of the intervention
during actual trash bag removing in hospital rooms.
ACKNOWLDGEMENT
This work was part of an undergraduate senior design
project. The authors would like to thank professor Ken
Giles for his support and guidance during this effort.
We would also like to thank Dr. Mir Shafii for all his
efforts and assistance in the building the new container.
A special thank you is due to Brandon Miller for his help
in editing and formatting this manuscript,
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