overloading. This allowed the fabricator to move
materials from outside to anywhere inside the
plant, which in this situation was a better, safer
The Big Picture
Ergonomics is about looking at the whole picture, not just a certain lifting load at one machine or workstation. Consider a press brake
operator who forms parts and places them on
a custom-fabricated mobile scissor-lift cart. The
table’s large enough to accommodate large panels along with several smaller components and
can be adjusted depending on who’s operating
the brake that day.
Then the material handler pushes that scissor-lift cart to the powder coating department.
There, a short employee needs to extend her
reach to grasp a medium-sized part in the center
of the large cart. She does that again. And again.
And by the end of her shift, her back is aching.
In this case, would two carts—large parts in one,
smaller parts in another—have been a better solution? It could well have been, but not without
extensive observation and analysis.
Because everyone’s physiology is di;erent,
what’s safe for one employee may not be safe
for another. People’s height and weight have an
e;ect, as do their reach and the frequency of
particular movements. For instance, if a person
(like the operator in the powder coat department) needs to extend his or her arms laterally
beyond a comfortable distance when grasping
an object, the employee might feel a brief ping
in the back.
They do this repeatedly, and they’ll probably
feel the pain and remember it. But people might
not feel the pain all the time. Say someone needs
to perform an awkward, “long reach” lift maybe
once or twice a shift. She might feel a ping in her
back, but it goes away, so she doesn’t complain.
Still, over time it gets worse. And worse. Eventually she’s receiving physical therapy.
Because everyone’s body is di;erent, we have
to make some general assumptions when combatting MSDs. The same group of researchers at
Liberty Mutual also discovered that when workplaces accommodate the physical ability of 75
percent of the female population, two-thirds of
all back-pain claims can be avoided regardless of
the gender makeup of a given workplace. Using
this benchmark, they created tables for push,
pull, and lifting limits that any industry can use.
When first assessing MSD risk at any facility, engineers and ergonomics experts often start by
referencing the Liberty Mutual tables.
When an operation chooses to begin addressing workplace MSDs, facing the music is nowhere near as time- and resource-consuming
as ignoring the problem altogether. When accounting for medical care, employee turnover,
work stoppage, increased insurance premiums,
and regulatory fines, the consequences of overlooked MSD risks are steep. According to OSHA’s report on the financial impact of MSDs, a
musculoskeletal injury can cost an employer
anywhere from $48,000 to $67,000 per incident
in both direct and indirect costs.
What Makes a Cart Safe?
After a company’s safety team identifies a workplace safety vulnerability, many well-intended
fabricators will turn to material handling equipment to alleviate the overexertion their employees experience. Usually the equipment of choice
will be a heavy-duty flatbed cart robust enough
to carry a range of materials in high-product-mix environments. Unfortunately, some of these
carts still will leave employees vulnerable to injury, particularly when they’re not adequately
motorized. Especially creative fabricators might
also put their welding skills to use and construct
their own equipment to aid in the pushing, pulling, and lifting of essential materials, such as
sheet metal, piping, and steel support beams.
Some mistakes fabricators make include using
wheel casters that are too small for the load, pil-
ing too much material onto a single cart, and not
realizing when it’s time to motorize a manual cart.
How do you identify these problems? Again,
it starts with the plant walk-through. Are opera-
tors needing to lean and push excessively to give
a cart momentum? That might mean the load is
too heavy or the casters are too small, a partic-
ular problem for an uneven floor. Rolling those
small casters over a crack in the floor creates a
violent jostle, which in turn can throw a load o;
balance—not the safest of situations.
Put the right caster on these carts, and the
situation might improve. Larger-diameter caster
wheels make carts easier to push. The swivel ac-
tion makes a di;erence too. A well-made caster,
with precision-ground and sealed raceways, will
add stability to turns. So too will the swivel lead,
or the distance between the center of the wheel
and the center of the swivel action. A long swivel
lead increases the rotation distance and creates
a mechanical advantage, making turns easier.
Determining the wheel size is just the beginning. Another factor is the center of gravity. A
cart must be wide enough to be stable while carrying a variety of loads, but not too wide or it will
be di;cult to maneuver in tight spaces, whether
or not it’s motorized.
» This motorized custom cart with large wheels is designed to take very heavy loads.
» This motorized cart has a wide base and low center of gravity for optimal stability.