Letting
autoworkers sit while they reach into a car’s interior could help
prevent shoulder and back strain—but another solution might be to tilt
the entire car so that workers can stand up.
That’s the finding of two recent studies, which tested two ways to protect autoworkers from injury.
Sitting
on a cantilevered chair reduced the stress on the workers’ backs and
shoulders for three common installation tasks. But a different
strategy—tilting a car sideways on a carriage so that workers could
access the interior while standing—reduced the stress for nine different
tasks.
The chair study appears in the July issue of the journal Applied Ergonomics, and the carriage study appears in a previous issue.
The
car carriage appears to be a better overall option for preventing
injuries, explained William Marras, professor and Honda Endowed Chair in
the Department of Integrated Systems Engineering at Ohio State
University.
“Under
these conditions, if you can tilt the car, the chair becomes
unnecessary,” said Marras, who directs Ohio State’s Center for
Occupational Health in Automotive Manufacturing (COHAM), where the tests
took place.
Honda
Motor Co. asked the COHAM team to test the commercially available chair
as well as the car carrier, both of which are already used in some of
its plants and by other manufacturers around the country.
To
use the chair, workers sit on a padded seat at the end of an L-shaped
steel beam that is locked into a track above. The “L” slides back and
forth as workers use their legs to pull the chair across the floor and
into the car.
The
researchers tested 10 men and women, five of whom were experienced
autoworkers. The other five were college student volunteers, intended to
represent first-time, untrained autoworkers. They rode the chair into
and out of a car frame while they tightened bolts and installed seat
belts, shoulder slides, roof consoles, and dome lights. Wired with
sensors to monitor muscle strain, the subjects performed these tasks
over a simulated eight-hour workday.
In
only three situations—installing the roof console and insulation and
tightening bolts in the center of the car—did sitting in the chair
reduce loads on the spine and shoulder stress.
The
chair didn’t help much when workers had to reach the sides or back of
the car, either. For installation tasks at the edge of the vehicle,
sitting in the chair reduced spine load but did nothing to reduce
shoulder stress.
“We
thought that sitting down inside the car would make installing the
seatbelt easier, but it turned out that you’d need two right hands,”
said Sue Ferguson, senior research engineer at COHAM and lead author of
the study.
Originally,
the cantilever chair came with a bucket seat that prevented workers
from moving freely. The researchers replaced it with a flat seat and
simplified the cantilever system overall. The new design was more
practical than the original, and much less expensive: it cost $4,000 to
build compared to the original’s $100,000.
In
the car carriage study, the researchers had 12 people install equipment
in a car’s interior, underbody, and engine room while standing. They
measured stresses on the people’s bodies when the car was tilted at
different angles.
Of
nine different installation tasks, seven became much less strenuous
when the car was tilted on its side 45 degrees. The other two showed
similar improvements when the car was tilted completely sideways at 90
degrees.
Because
of the modification that the researchers made to the seat in the chair
study, they began to think about ways to improve seats in general. They
are now working with a seat manufacturer to discover more features that
make a seat comfortable and functional.
Meanwhile,
Honda is using the Ohio State team’s discoveries to improve the
ergonomics of their factories. In 2007, the company reported that it was able to reduce injuries by 70% over five years by adopting these strategies.
Source: Ohio State University
