Ergonomic Assessment
Josh Prince
Keith Heerdegen
Mary Cook
Stacking
We measured 3 types of boxes that are most common it the warehouse.
We recorded the dimensions and more importantly the force the box exerts.
Box1
Height-15 in Length-24 in Width-14 ½ in Weight-18 kg Force- 50 lbs/sq. in
Box2
Height- 20 ½ Length-25 ½ Width-17 ½ Weight-14 kg Force-24 lbs/sq. in
Box3
Height-22 Length-20 ½ Width-9 ½ Weight-12 kg Force-22 lbs/sq. in
Job description
NIOSH recommended weight is 23 kg (225 N).
Employees commonly are either stacking these boxes off pallets or back on them.
Can stack anywhere from 5 boxes to hundreds of boxes in a given job.
Lift boxes overhead
Evaluation and Risk Factors
Bending– Greater than 15°
Twisting– Greater than 15° in some
incidences
Head and Neck– Ideal
Energy consumption increases 50% when working bent over
Can cause over-exertion (account for ¼ of all reported occupational injuries)
Will cause increase stress on discs in back (up to 225%)
Evaluation and Risk Factors
Arms– Reaching overhead – Over extending
Elbows– Out of position– Not at 90° angle
Wrists– In and out of neutral
position– Extended greater than 10°
Back and disc problems
Shoulder pain
Tendinitis in elbow or shoulder
Arthrosis (joint degeneration)
Evaluation and Risk Factors
Standing– Knees are straight and not
locked Repetition
– Lifting can occur more than 20 times in an hour
Force– Boxes can weigh over
25lbs. Grip
– Moderate pinch grip– Awkward handle
Muscle strain
Arthritis
Fatigue
Muscular- lactic acid build up and shortage of oxygen
General (weariness)
Solution
Lift with legs, not with back Keep arms at sides and elbows at 90 degrees (less
strenuous) Wrists should be in neutral position at all times. Keep the boxes on pallets to avoid extra stacking Take breaks to avoid fatigue Be as efficient as possible (human body only
converts 30% to energy)
Solution
Use a scissor lift with pallet
Use a vacuum lifting system
Pallet Jacks
Dimensions of a stacked pallet:
– Height- 82 ½ inches
– Width- 43 ½ inches
– Length- 49 inches
– Weight- 789lbs
Using Pallet Jacks
Employees use pallet jacks to move pallets that can range from 300 lbs to 1400 lbs.
Use both push and pull forces.
Distances vary but can end up pushing for an extended period of time (up to 1 minute without stopping)
Using Pallet Jacks
Pull Force- 26 lbs/sq. in
Push Force- 58 lbs/sq. in
Evaluation and Risk Factors
Back and Neck– Straight and upright– No bending involves
Twisting– Minor twisting when
turning the pallet jack
Standing– Knees are straight and
not locked
Injuries will most likely occur at the shoulder, arm, or upper back.
Causes a lot of muscle strain especially in the legs. Pulled muscles Muscle strains
Evaluation and Risk Factors
Arms– Extended in front of body
when pulling– In good position when
pushing
Elbows– In front of body and not
at 90° when pulling– At sides and close to 90°
when pushing
Tendinitis
Arthrosis (joint degeneration
Fatigue
Possible CTS
Evaluation and Risk Factors
Wrist– In neutral position when
pulling– Extended greater than
10° when pushing Repetition
– Can be exerting force for up to a minute without rest
– Usually frequent stops (times for rest)
Evaluation and Risk Factors
Grip– Slight pinch grip
Evaluation and Risk Factors
Static effort in the arms (prolonged state of contraction of the muscles). This causes:
– Less oxygen to the muscle Lactic acid builds up Muscle can’t recover
– Fatigue– Higher heart rate– Higher energy consumption– Longer rest periods needed– Less efficient
Solutions
Pull the pallet jack instead of push since it creates less of a force.– It keeps the wrists in neutral position.
Keep the elbows at sides and at 90° while pulling.– More efficient.– Less stress on the arms and shoulders.
Solutions
Take frequent rest break to avoid fatigue.– Will also help limit the static effort.
Avoid twisting the body when turning. – Turn with the arms
Try to install a more adequate handle on the jack.
Use a automatic power jack
References
Kroemer, K. H. E. and E. Grandjean. “Fitting the Task to the Human: Fifth Edition.” Taylor and Francis. 1997