# Psyc 552 Ergonomics & Biomechanics by BevHde9

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```									Psyc 552 Ergonomics &
Biomechanics
Lecture 14
Evaluating Lifting with NIOSH
   National Institute of Occupational Health &
Safety.
   Created Lifting Equation in 1994.
   The multiplicative model that computes a
Lifting Index (LI).
   LIs > 1.0 pose greater risk of low back pain.
NIOSH Equation Components

Container characteristics
Vertical location
Horizontal location
NIOSH Equation Components
Asymmetry angle

 Frequency of lifts
 Lifting duration
Components to Multipliers
RWL = LC x HM x VM x DM x AM x FM x CM
   RWL = Recommended Weight Limit
   LC = Load Constant (51 lbs)
   HM = Horizontal Multiplier
   VM = Vertical Multiplier
   DM = Distance Multiplier
   AM = Asymmetry Multiplier
   FM = Frequency Multiplier
   CM = Coupling Multiplier
Variables – Horizontal Component
   Horizontal Location (H) is measured from the mid-
point of the line joining the inner ankle bones to a
point projected on the floor directly below the mid-
point of the hand grasps (i.e., load center), as defined
by the large middle knuckle of the hand.
   H = 8 + W/2 for V => 10 inches
   H = 10 + W/2 for V < 10 inches
   W = width of the container in the sagittal plane and
V is the vertical location of the hands from the floor.
Variables – Horizontal Multiplier
   HM = 10/H
   When H < 10, HM = 1
   When H >25”, HM = 0
Variables – Vertical Component
   The vertical location should be measured at
the origin and the destination of the lift to
determine the travel distance (D)
Variables – Vertical Multiplier
   VM is based on the absolute deviation of V
from the optimal or knuckle height of an
average worker.
   VM = 1(.0075|V-30|) – for inches
   When V is at 30 inches (75 cm), the vertical
multiplier (VM) is 1.0.
   If V is greater than 70 inches, then VM = 0
Variables – Distance Component
   Vertical Travel Distance variable (D) is
defined as the vertical travel distance of the
hands between the origin and destination of
the lift.
   DM = (.82 + (1.8/D)) – for inches
   The DM is 1.0 when D is set at 10 inches;
DM is 0.85 when D = 70 inches
Variables – Asymmetry Component
   Asymmetric angle (A) defined as the angle
between the asymmetry line and the mid-
sagittal line. The asymmetry line is the
horizontal line that joins the mid-point
between the inner ankle bones and the point
projected on the floor directly below the mid-
point of the hand grasps, as defined by the
large middle knuckle.
Variables – Asymmetry Component
   The asymmetry angle (A) must always be
measured at the origin of the lift. If significant
control is required at the destination, however,
then angle A should be measured at both the
origin and the destination of the lift.
Variables – Asymmetry Multiplier
   AM = 1-(.0032A)
   The range is from a value of 0.57 at 135
degrees of asymmetry to a value of 1.0 at 0
degrees of asymmetry.
   If A is greater than 135 degrees, then AM = 0
Variables – Frequency Component
   Frequency is:
   The number of lifts per minute (F)
   The amount of time engaged in lifting (duration)
   The vertical height of the lift from the floor.
Frequency Special Considerations
   Lifting frequency is the average number of
lifts per minute over a 15 minute period.
   When work does not require lifting for 15
minutes and the lifting frequency does not
exceed 15 lifts per minute then:
   Compute the total number of lifts for a 15 minute
period – (lift rate X work time)
   Divide the total number of lifts by 15
   Use the quotient as the frequency F for the table.
Lifting Example
   A job requires:
   Lifting for 8 minutes
   Light work for 7 minutes
   Lift rate for the 8 minutes is 10 lifts/min
   The lift frequency F would be:
   (10 x 8)/15 = 5.33 lifts/minute
Lifting Duration – Short
   Short: <1hour, followed by a recovery time
equal to 1.2 times the work time (Rest time /
Work time = 1.2).

   To be classified as short-duration, a 45-minute
lifting job must be followed by at least a 54-
minute recovery period prior to initiating a
subsequent lifting session.
Lifting Duration – Moderate
   Moderate: > 1 hour < 2 hours, followed by a recovery period
of at least .3 times the work (Rest time / Work time = .3).

   If a worker continuously lifts for 2 hours, then a recovery
period of at least 36 minutes would be required before
initiating a subsequent lifting session. If the recovery time
requirement is not met, and a subsequent lifting session is
required, then the total work time must be added together. If
the total work time exceeds 2 hours, then the job must be
classified as a long-duration lifting task.
Lifting Duration – Long
   Long: 2 to 8 hours, with standard breaks
(morning, lunch, and afternoon).
Variables – Frequency Multiplier
   The FM value depends upon the average
number of lifts/min (F), the vertical location
(V) of the hands at the origin, and the duration
of continuous lifting. For lifting tasks with a
frequency less than .2 lifts per minute, set the
frequency equal to .2 lifts/minute. For
infrequent lifting (i.e., F < .1 lift/minute),
however, the recovery period will usually be
sufficient to use the 1-hour duration category.
Variable – Coupling Component
   An optimal handle design            An optimal hand-hold cut-
has                                  out has the following
   .75 - 1.5 inches diameter,       approximate
   > 4.5 inches in length,          characteristics:
   2 inches clearance,                 > 1.5 inch height,
   cylindrical shape,                  4.5 inch length,
   smooth, non-slip surface.           semi-oval shape,
   > 2 inch (5 cm) clearance,
   smooth non-slip surface,
   > 0.25 inches container
thickness (e.g., double
thickness cardboard).
Variable – Coupling Component
   An optimal container         A worker should be
design has:                   capable of clamping
   < 16 inches frontal       the fingers at nearly 90
length,                   degrees under the
   < 12 inches height,       container, such as
   a smooth non-slip         required when lifting a
surface.                  cardboard box from the
floor.
Variable – Coupling Component
   A container is considered             A worker should be able to
less than optimal if it has:           comfortably wrap the hand
   A frontal length > 16”             around the object without
   height > 12”                       causing excessive wrist
   rough or slippery surfaces,        deviations or awkward
   Sharp edges,                       postures, and the grip
   asymmetric center of mass,         should not require
   unstable contents,                 excessive force.
   requires the use of gloves.
   A loose object is considered
easily be balanced between
the hand-grasps.
Variable – Coupling Multiplier
   The coupling multiplier (CM) is determined
from decision tree and a tabled value.
Tabled Values
Tabled Values (cont.)
Tabled Values (cont.)
Coupling Quality
23”
30”

44#

63”
15”

23”
Manufacturing
Punch Press

44   44   23 15 23 63     48   0   0       <.2   <1   Fair
Origin Destination
Computing RWLs

.44   .89   .86   1.0   1.0   .95   16.3
.44   .75   .86   1.0   1.0   1.0   14.5

•The RWL for the origin and destination is
computed because significant control is required.

•Significant control: Precision placement where
the worker 1) re-grasps the near the destination, 2)
momentarily holds object at destination, or 3)
Computing Lifting Index

44
16.3
2.7
44
3.0
14.5

•LIs > 1 indicate increased risk of low back pain.
Redesign the Job

.44   .89   .86   1.0   1.0   .95   16.3
.44   .75   .86   1.0   1.0   1.0   14.5

   Bring load closer to the body – rotate it 90
degrees.
   Lower destination height.
   Reduce travel distance.
   Eliminate significant control.
23”          The reel is 12” wide.

30”

44#

63”

15”

23”
Modifications

1.0   .89   .86   1.0   1.0   .90     35.1
.83   .75   .86   1.0   1.0   .90     24.6

44
35.1
1.3
44
1.8
24.6
NIOSH Equation Limits
   The model DOES NOT apply when lifting or
lowering:
   With one hand
   Over 8 hours
   While seated or kneeling
   In restricted work space
   Unstable objects
   Wheelbarrows or shovels
   With high speed motion
   With unreasonable foot to floor friction
   In unfavorable environments (66-79 degrees and 33 to
50% humidity)

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