ERGONOMICS OF MANUAL MATERIALS HANDLING - Environmentally Conscious Materials Handling - page 42

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2 NIOSH Work Practices Guide

2.4 Revised NIOSH Guide

In the late 1980s, another committee was formed by NIOSH (several members
were also members of the original committee) to address the shortcomings of the
1981 guide and to explore revisions to the guide. The result of the committee's
efforts was the publication of the “Revised NIOSH Equation for the Design
and Evaluation of Manual Lifting Tasks” (Waters et al 1993) and Applications
Manual for the Revised NIOSH Lifting Equation (Waters et al. 1994). The major
changes of the revised guide included adding factors for couplings (handles) and
accounting for asymmetry during lifting. The concepts of the action limit (AL)
and the maximum permissible limit (MPL) were replaced with a recommended
weight limit (RWL) and a lifting index (LI). The RWL is similar to the AL
calculation in that it consists of a load constant that is then modified by six
adjustment factors: horizontal factor, vertical factor, distance factor, frequency
factor, coupling factor, and asymmetry factor. The LI is a ratio of task demand
(load weight) to the RWL. With the inclusion of asymmetry, one of the original
assumptions of the 1981 guide of symmetric sagittal plane lifting was removed.
From three of the approaches outlined in the 1981 guide, the criteria in
Table 2.2 were used to develop the revised guide lifting equations (Waters
et al. 1993). When the criteria for the revised guide are compared to the AL
criteria from the 1981 guide, similarities can be noted (see Table 2.3).
As can be seen in the tables, the biomechanical criteria remained the same
(although the more proper force units of newtons were used), the 1981 phys-
iological criteria is the midpoint of the range found in the revised guide, and
the psychophysical criteria remained unchanged. The revised guide lowered the
load constant but then decreased the adjustments due to the horizontal factor, the

Ta b l e 2 . 2 Criteria for Revised Lifting Guide
Approach (revised) Design Criteria Cut-off Value

Biomechanical Max disc compression force 3.4 kN (770 lbs)

Physiological Max energy expenditure 2.2 to 4.7 kcal/min

Psychophysical Max acceptable weight Acceptable to 75% of female

workers and 99% of male workers

Ta b l e 2 . 3 Criteria for Original Lifting Guide
Approach (1981)

Design Criteria Cut-off Value

Biomechanical Max disc compression force 350 kg (770 lbs)

Physiological Max energy expenditure 3.5 kcal/min

Psychophysical Max acceptable weight Acceptable to 75% of female

workers and 99% of male workers