Revised NIOSH Lifting Equation - Fundamentals and Assessment Tools for Occupational Ergonomics - page 883

TABLE 46.7 Coupling Multiplier

Coupling Multiplier

Coupling Type V , 30 in. (75 cm) V 30 in. (75 cm)

Good 1.00 1.00

Fair 0.95 1.00

Poor 0.90 0.90

46.5 Procedures

Prior to data collection, the analyst must decide (1) if the job should be analyzed as a single-task or
multi-task manual lifting job and (2) if significant control is required at the destination of the lift.
This is necessary because the procedures differ, depending on the type of analysis required.
A manual lifting job may be analyzed as a single-task job if the task variables do not differ from task to
task, or if only one task is of interest (e.g., single most stressful task). This may be the case if one of the
tasks clearly has a dominant effect on strength demands, localized muscle fatigue, or whole body fatigue.
On the other hand, if the task variables differ significantly between tasks, it may be more appropriate to
analyze a job as a multi-task manual lifting job. A multi-task analysis is more difficult to perform than a
single-task analysis because additional data and computations are required. The multi-task approach,
however, will provide more detailed information about specific strength and physiological demands.
For many lifting jobs, it may be acceptable to use either the single- or multi-task approach. The single-
task analysis should be used when possible, but when a job consists of more than one task and detailed
information is needed to specify engineering modifications, then the multi-task approach provides a
reasonable method of assessing the overall physical demands. The multi-task procedure is more compli-
cated than the single-task procedure, and requires a greater understanding of assessment terminology
and mathematical concepts. Therefore, the decision to use the single- or multi-task approach should
be based on: (1) the need for detailed information about all facets of the multi-tasked lifting job; (2)
the need for accuracy and completeness of data regarding assessment of the physiological demands of
the task; and (3) the analyst's level of understanding of the assessment procedures.
The decision about control at the destination is important because the physical demands on the worker
may be greater at the destination of the lift than at the origin, especially when significant control is
required. When significant control is required at the destination, for example, the physical stress is
increased because the load will have to be accelerated upward to slow down the descent of the load.
This acceleration may be as great as the acceleration at the origin of the lift and may create high loads
on the spine. Therefore, if significant control is required, then the RWL and LI should be determined
at both locations and the lower of the two values will specify the overall level of physical demand.
To perform a lifting analysis using the revised lifting equation, two steps are undertaken: (1) data is
collected at the worksite as described in Step 1 (described next); and (2) the RWL and LI values are
computed using the single- or multi-task analysis procedures described in Step 2 (described later).

46.5.1 Step 1: Collect Data
The relevant task variables must be carefully measured and clearly recorded in a concise format. As men-
tioned previously, these variables include the horizontal location of the hands (H), vertical location of the
hands (V), vertical displacement (D), asymmetric angle (A), lifting frequency (F), and coupling quality
(C). A job analysis worksheet, as shown in Figure 46.4 for single-task jobs or Figure 46.5 for multi-task
jobs, provides a simple form for recording the task variables and the data needed to calculate the RWL
and LI values. A thorough job analysis is required to identify and catalog each independent lifting task
that comprises the worker's complete job. For multi-task jobs, data must be collected for each individual
task.