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Ergonomics
News – January 2008 |
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Welcome to Ergonomics
News, a monthly electronic newsletter designed to help Ergonomists and
Safety Managers find the right solutions to a host of ergonomic-related
challenges - from manual material handling to office ergonomics. The
newsletter will include a column written by a veteran ergonomist, plus
several other articles linked to
http://www.occupationalhazards.com. |
In This
Newsletter:
1. Ergonomics and
Measurements
2. Get in Shape
... at Your Desk
3. AAOHN: Employers
Can Give Workers a Healthy Start in the New Year
4. New Database
Contains Aging Workforce Information
1. Ergonomics and
Measurements
By William H. Kincaid, P.E., CSP
It seems every ergonomics conference includes a session on quantifying
and measuring ergonomic stressors. This reflects the importance of
measurements to ergonomics.
Certainly in many situations, measurements of ergonomic stressors are
useful. Measurements give us our points of comparison to standards,
recommendations, regulations or the theoretical "ideal." It makes sense
to know how and why to take them.
First, what are we measuring? We need to take measurements of our basic
ergonomic stressors -- force, posture and repetition -- and in some
cases, factors such as vibration, temperature, lighting, etc.
We may weigh lifted items, measure the angle of a worker's back or count
the number of task cycles in a time period. Relatively simple tools are
used, such as a tape measure, a scale, an inexpensive device to measure
angles such as a protractor or a more expensive tool called a
goniometer, and a stopwatch. Anyone doing ergonomics work should have a
kit of these tools handy to use when needed.
Some measurements are estimates at best, such as a grip force
measurement taken with a hand dynamometer. The usual practice is to have
an operator squeeze the dynamometer with about the same force as
required to lift the object. It's not telling us the force required to
grip an object so much as it's measuring the operator's perception of
that force as applied to the dynamometer. Unlike weighing the object on
a scale, it's a degree of separation from an actual measurement of the
stressor.
It's not easy to measure hand grip force directly without affecting that
force. When someone picks up an object, particularly with a pinch grip,
the surface friction is a factor in grip force required to hold it, as
well as the angles of the fingers. If there was some way to measure the
actual force applied to the surface of the object, it would have to do
so without altering the friction or taking up much space between the
object and the finger surfaces. Someday, new technology may make this
practice obsolete, but for now it's the usual way to do the job.
It's good to know someone lifts a 12-pound weight 900 times a shift, but
what does that mean in terms of injury prevention? There are a number of
formulas and calculations such as the NIOSH "Lifting Equation," the Job
Strain Index, Humantech's excellent "BRIEF" checklist and the Rapid
Entire Body Assessment, which can be used to crunch these numbers into
something more meaningful.
Why Monitor?
That's the short version of the "how" of ergonomic measurement, and
here's the "why": Once we have measurements, we can compare them
against recommendations from many existing studies of the effects of
stressors. But studies of broad populations give us broad
results.
The NIOSH Lifting Equation is aimed at safe limits for 99 percent of men
and 90 percent of women. Given the wide variation of human
susceptibility, a measurement that gives us a safe limit for 99 percent
of men and 90 percent of women isn't necessarily going to work for us
when our workforce is specifically chosen to be stronger and sturdier
than those broad groups. For example, UPS has a process to maintain a
physically fit workforce, and gets good results using a maximum
individual lifting limit about 40 percent higher than the NIOSH maximum.
Why limit work activities with a broad standard when you hire only
workers in the higher fitness percentiles?
We might find our own in-house standards are a better point of
comparison. There aren't a lot of companies actually living by NIOSH or
other criteria. Many do have in-house standards or goals, simple or
otherwise, which allow heavier loads, stronger forces, more repetition
or more awkward postures than published criteria.
Since an ergonomics improvement process usually is a progressive path
rather than an overnight transformation, these companies may get closer
to published recommendations in the future. Or, in some cases, such as
UPS, propelled by a competitive marketplace to build a stronger than
average workforce, companies successfully may allow higher limits. With
some expertise, trial and error and educated guesswork, we might arrive
at our limits more tailored to our workers.
Ergonomics often relies on measurements, and knowing how to do them is
just the beginning. Finding good criteria to compare them to also is
important, and may mean striking out on our own. Regardless of what
stressors are measured or what the measurements mean, the ability to
take usable ergonomic measurements is a good skill for anyone working in
ergonomics.
William H. Kincaid, P.E., CSP, is a senior loss control consultant
with Lockton Companies, LLC.
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If you have
any comments or feedback about the content or format of IH
Insights, please share them with Editor Sandy Smith at ssmith@penton.com.
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