Journal - International Journal of Industrial Ergonomics
Author - Gary A. Mirka, Christy Smith, Carrie
Shivers, James Taylor
Summery
The objectives
of this intervention
research project were
to develop and
evaluate engineering controls
for the reduction of low back
injury risk in workers in the
furniture manufacturing
industry. An analysis
of injury/illness records
and survey data
identified upholsterers and
workers in the
machine room as
two occupations within
the industry at elevated
risk for low back injury. A detailed
ergonomic evaluation of the activities performed
by these workers was then performed
and the high risk subtasks were
identified. The analysis for upholsterers
revealed:
(1) High forces during
the loading and unloading of the
furniture to and from the
upholstery bucks,
(2) Static awkward
postures (extreme flexion > 501; lateral bending > 201; twisting >
201) during the upholstering of the furniture.
(3) Repetitive bending
and twisting throughout the operation.
For
machine room workers,
this ergonomic evaluation
revealed repetitive bending and twisting (up to 5 lifts/min and sagittal
flexion > 801; lateral bending > 151; twisting > 451) when
getting wooden components
from or moving
them to the shop carts
that are used
to transport these materials. Engineering interventions were
then developed and evaluated in the laboratory to document the reduction of
exposure to these stressors. The
height-adjustable upholstery buck system
eliminated the lifting and lowering
requirements and affected trunk
kinematics during the upholstery operation by reducing peak
sagittal angles by up to 79% (average:52%; range: 27–79%), peak sagittal
accelerations by up to 42% (average: 71%; range: 0–74%) and peak lateral
position by up to 31% (average: 20%; range: 12–31%), and showed no impact on
time to complete the task. The machine room lift reduced peak sagittal angle by
up to 90% (average: 76%; range: 64–90%), peak sagittal accelerations by up to
86% (average: 72%; range: 59–86%) and had a positive impact on the time to
complete the task (average reduction:
19%).
Introduction
About 75% of these establishments are
producers of household furniture
making up 88%
of the furniture manufacturing workforce As with
many manufacturing industry sectors, the furniture manufacturing industry has struggled
with problems associated
with work-related low back
pain and other
musculoskeletal illnesses. This is
compared to the
incidence rates of low back pain
cases of private industry as
a whole
and for general
manufacturing industry. The residential furniture manufacturing industry
can be broken
into three separate categories:
(1) Upholstered furniture (sofas, chairs,
loveseats, etc.),
(2) Case
goods (tables, desks, bookshelves, dressers, etc,)
(3) Hardwood chairs (such as dining room
chairs sometimes upholstered, sometimes
not).
Methods
The first step in this ergonomic intervention
process was to identify those jobs that
posed the greatest risk
for low back
injury Incidence and severity
rate data from OSHA
Form 200 Logs
were gathered from
a group of 29 casegoods facilities and 11 upholstered furniture facilities. The review of the OSHA Log data from upholstery facilities indicated
that a significant percentage of the low
back problems in these facilities were located in the upholstery department.
On-site ergonomic assessments
Fourteen different furniture
manufacturing facilities (both
casegoods and upholstered furniture) were visited over a period of six months
to conduct a high-level ergonomic
task analysis of the work activities performed in these facilities. The differences in
equipment and work technique among the
facilities manufacturing the
same product type were documented.
Engineering design of
prototypes
The research
and design team
employed an iterative prototyping process, wherein
each ergo- nomic
intervention prototype was
subjectively evaluated in the lab
by the research team and in
the field by furniture workers
and the results
of these assessments were
used to improve
on the design of the intervention. The principle
component of the intervention for
the upholstery operation is a
height-adjustable upholstery buck system
Result
As was hypothesized, the height adjustability
provided by the two interventions had a considerable impact on the trunk
kinematics required to perform these simulated furniture manufacturing
activities. Similarly, the results
of the laboratory evaluation of the shop cart lift show consistent improvements in trunk
posture as well
as significant changes in the
dynamics of the
lifting activity. The lift also showed a significant decrease in the
movement times required to perform the activity, a productivity benefit that we
anticipate will increase the likelihood
that the intervention is adopted by the industry.
Conclusion
This paper describes two lift-assisting interventions for the furniture manufacturing industry. Both generated considerable improvements
in the trunk postures and trunk kinematics required to perform the
requisite tasks. Productivity benefits from these
interventions were also found, but it is felt that
these productivity improvements
may only be a fraction of those that may come from the long-term utilization
of these interventions by skilled workers attempting to maximize
their productivity.
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