Civil Engineering Reference
In-Depth Information
46.2.1 Recommended Weight Limit
The recommended weight limit (RWL) is the principal product of the revised NIOSH lifting equation.
The RWL is defined for a specific set of task conditions as the weight of the load that nearly all healthy
workers could perform over a substantial period of time (e.g., up to 8 h) without an increased risk of
developing lifting-related LBP. By “healthy workers,” we mean workers who are free of adverse health
conditions that would increase their risk of musculoskeletal injury.
The concept behind the revised NIOSH lifting equation is to start with a recommended weight that is
considered safe for an “ideal” lift (i.e., load constant equal to 51 lb) and then reduce the weight as the task
becomes more stressful (i.e., as the task-related factors become less favorable). The precise formulation of
the revised lifting equation for calculating the RWL is based on a multiplicative model that provides a
weighting (multiplier) for each of six task variables, which include the: (1) horizontal distance of the
load from the worker (H); (2) vertical height of the lift (V); (3) vertical displacement during the lift
(D); (4) angle of asymmetry (A); (5) frequency (F) and duration of lifting; and (6) quality of the
hand-to-object coupling (C). The weightings are expressed as coefficients that serve to decrease the
load constant, which represents the maximum recommended load weight to be lifted under ideal con-
ditions. For example, as the horizontal distance between the load and the worker increases from
10 in., the recommended weight limit for that task would be reduced from the ideal starting weight.
The RWL is defined as follows:
RWL ¼ LC HM VM DM AM FM CM
where
Metric
U.S. Customary
LC, Load constant
23 kg
51 lb
HM, Horizontal multiplier
(25
H)
(10
H)
/
/
VM, Vertical multiplier
1
(0.003
j
V
75
j
)
1
(0.0075
j
V
30
j
)
2
2
2
2
DM, Distance multiplier
0.82
þ
(4.5
D)
0.82
þ
(1.8
D)
/
/
AM, Asymmetric multiplier
1
2
(0.0032 A)
1
2
(0.0032 A)
FM, Frequency multiplier
From Table 46.5
From Table 46.5
CM, Coupling multiplier
From Table 46.7
From Table 46.7
The term “task variables” refers to the measurable task-related measurements that are used as input
data for the formula (i.e., H, V, D, A, F, and C), whereas the term “multipliers” refers to the reduction
coefficients in the equation (i.e., HM, VM, DM, AM, FM, and CM).
46.2.2 Measurement Requirements
The following list briefly describes the measurements required to use the revised NIOSH lifting equation.
Details for each of the variables is presented later in this chapter (Section 46.4):
H—Horizontal location of hands from midpoint between the inner ankle bones. Measure at the
origin and the destination of the lift (cm or in.)
V—Vertical location of the hands from the floor. Measure at the origin and destination of the lift
(cm or in.)
D—Vertical travel distance between the origin and the destination of the lift (cm or in.)
A—Angle of asymmetry — angular displacement of the load from the worker's sagittal plane.
Measure at the origin and destination of the lift (
8
)
Search WWH ::
Custom Search