ERGONOMICS OF MANUAL MATERIALS HANDLING - Environmentally Conscious Materials Handling - page 45

depending on origin of lift and duration of lifting. In the revised guide,
F max values as low as 8 lifts/min are used for long-duration, low (below
knuckle height) origins of lift.
A special procedure was developed for situations in which the worker did
not lift continuously during the 15-minute observation period. For example,
if a worker lifts at a rate of 10 lifts per minute for 8 minutes, followed
by 7 minutes of light work, the frequency F would be calculated as F =

5 . 33 lifts/min. The analyst should be careful to ensure that the
15-minute observation period was representative of the total task demand
of the worker.
• Coupling component . The nature of the coupling, as well as the location of
the origin of lift, were used to determine the coupling multiplier (CM). The
coupling multiplier ranges from 0.90 to 1.0. Table 2.6 is used to classify
the nature of the couplings.

10 ( 8 )/ 15 =

2.4.3 Assumptions of the Revised Guide
Waters et al. (1993) described five limitations of the revised lifting equation:
1. It assumes that manual materials handling activities other than lifting are
minimal and do not require significant energy expenditure.
2. It assumes no unpredicted conditions such as unexpected heavy loads or
slips or falls.
3. It assumes no one-handed lifting or lifting while seated or kneeling, lifting
in a confined workspace, shoveling, lifting people, lifting hot or cold loads,
or high-speed lifting tasks.
4. It assumes worker shoe/floor static coefficient of friction of 0.4 (preferably
> 0.5).
5. It assumes that lifting and lowering tasks have the same level of risk.

2.4.4 Using the Revised Guide
In using the revised guide, the RWL equation was simplified somewhat by empha-
sizing the modifiers rather than presenting a numerical equation, as was done
to calculate the AL of the 1981 guide. Even though the 1981 guide equation
was relatively simple mathematically, many practitioners had difficulty prop-
erly calculating the AL. Therefore, the RWL was presented more simply as:
RWL LC ( HM )( VM )( DM )( AM )( FM )( CM ) . The multiplier factors could be

calculated or looked up in a provided table, but NIOSH felt that inclusion of a
set of six tables (one for each of the six multiplier factors) would reduce the
errors in calculating the RWL. The primary advantage of using the tables to find
the six modifier factors is that the table values range from only 0.0 to 1.0, so
factors greater than 1.0 are eliminated and there is no possibility for a negative
factor entering the calculation.

=