An Evaluation of the NIOSH Lifting Equation: A Psychophysical and Biomechanical Investigation
Using the results of psychophysical and biomechanical experiments, NIOSH (National Institute for Occupational Safety and Health) Recommended Weight Limit (RWL), the Lifting Index (LI), the form of the asymmetry multiplier, and the criterion for compression force were investigated. Analysis of the results indicated a significant difference between the NIOSH RWL and the reported Maximum Acceptable Weight of Lift (MAWL). Contrary to the NIOSH lifting equation, the form of the asymmetry multiplier was found to be non-linear. The overall average of peak compression force on the L5/S1 was 3685 N. Fifty-eight percent of all compression forces reported in the biomechanical experiment were found to exceed the suggested 3400 N set by NIOSH guidelines. These results support previous research findings on the validity of NIOSH guidelines.
Implications of the Proposed Revisions in a Draft of the Revised NIOSH Lifting Guide (1991) for Job Redesign: A Field Study
The main objective of this research project was to compare the recommended load limits for lifting tasks derived based on the NIOSH (1981) Lifting Guide and the proposed NIOSH Draft Revisions of (1991). The study involved the following steps: 1) Identification of a total of 15 manual lifting tasks from 8 different jobs performed at the industrial site, with different tasks characteristics in order to cover most of the possible lifting conditions considered under the Draft Revisions to the NIOSH Guide (1991), 2) Description of the lifting tasks variables for the identified jobs, 3) Calculation of the RWL values for the identified jobs per 1991 Lifting Guide, as well as the AL and MPL values according the 1981 Lifting Guide, 4) Comparison of the actual loads lifted (L) with the values of RWL, AL and MPL, and calculation. The results showed that the Draft Guide of 1991 was much more restrictive with respect to defining the lifting acceptable jobs. Under this Guide, 10 out of 15 tasks analyzed in this study (66.7%) were found unacceptable, and required redesigning. For comparison, under the NIOSH (1981) Guide, as many as 8 of 15 (53.3%) of the tasks were found fully acceptable (below the action limit or AL level), while 6 tasks (40%) required application of administrative controls, and only 1 of the 15 tasks analyzed (6.7%) was found unacceptable.
Endurance time and physiological responses to prolonged arm lifting.
The main objective of this study was to examine the effects of prolonged arm lifting tasks on endurance time and physiological responses. Ten male college students participated in the study. The independent variables were the frequency of handling and weight of load. The dependent variables were endurance time, oxygen consumption, minute ventilation, heart rate, and ratings of perceived exertion of the shoulder, arm, back, leg and overall body. The results indicated that: (1) endurance time decreased with an increase in frequency or load; (2) oxygen consumption and heart rate limits were dependent on the interaction of frequency and load; (3) oxygen consumption and heart rate limits for arm lifting were generally lower than limits for leg lifting tasks; and (4) for arm work, average physiological responses recorded over short durations were not significantly different from those based on long durations.