A Primer Based on Workplace Evaluations of Musculoskeletal Disorders
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Elements of Ergonomics Programs A Primer Based on Workplace Evaluations of Musculoskeletal Disorders |
Table 4. Reference levels used in rating job risk factors for musculoskeletal disorders
risk condition |
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| Based on body measurement data indicating comfortable or normal seated and standing arm reach distances for the majority of the male and female population (see Tray 6 of the Toolbox). | |
| NIOSH Work Practices Guide first used in defining acceptable loads to be lifted [NIOSH 1981]. Revised NIOSH lifting equation for recommended weight limits proposed in 1993 [Waters et al. 1993; Waters et al. 1994]. Applies to standing, two-handed, smooth lifting and lowering of stable objects in unrestricted spaces. Calculations take account of the horizontal distance of load from the body, vertical locations of hands at the beginning and end of lift, vertical distance of the load moved, frequency rate of lifting, balance, and coupling factors (see Tray 6 of the Toolbox).
Michigan 2- and 3-Dimensional Static Strength Prediction Program which estimates, for lifting tasks, the amount of compressive force at the lumbo-sacral disc [Chaffin and Andersson 1991] (see Tray 6 of the Toolbox). Model of risk of low back disorders as a function of workplace characteristics and trunk motion characteristics (e.g., lift rate, trunk bending, twisting motion) [Marras et al. 1993, 1995] (see Tray 6 of the Toolbox). |
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loads |
Initial and sustained forces of loads pushed or pulled at variable rates that are judged acceptable for 90% of the female work population [Snook and Ciriello 1991] (see Tray 6 of the Toolbox). |
vibration |
International Standards Organization (ISO) Dose System for Whole Body Vibration indicating vibration levels in three dimensions with limiting times for fatigue decreased proficiency [ISO 2631/1, 1985] (see Tray 6 of the Toolbox). |
vibration |
American National Standards Institute (ANSI) daily exposure limits [ANSI S3.34. 1986] and American Conference of Governmental Industrial Hygienists (ACGIH) [ACGIH 1996] values for judging whether estimated worker task exposure levels are excessive (see Tray 6 of the Toolbox). |
| Both the number of hand manipulations per 8-hour work shift and the task cycle time have been used to rate this factor. Task cycle times of 30 sec or less were defined as high repetition; cycle times greater than 30 sec as low repetition. For hand manipulations, high repetitiveness was described as more than 20,000 manipulations per 8-hour work shift; medium repetitiveness as between 10,000 and 20,000 manipulations per 8-hour work shift, and low repetitiveness as less than 10,000 manipulations per 8-hour work shift [HETA 88 361 2091; HETA 88 180 1958]. A recent proposed repetition guideline believed to be more protective is cited by Kilbom [1994] (see Tray 6-B of the Toolbox). This guideline also considers other areas of the upper extremity. Each area may have a different ability to tolerate repetitious activity. At the same rate of repetitions some specific acts such as pinching may be less well tolerated than others. This is an example of complexities that current guidelines may not address adequately. | |
demands of work tasks |
Relative ratings on a 5-point scale used to classify task performance as
requiring high, medium, and low levels of force [HETA 88 180 1958;
HETA 88 361 2091].
Criterion of 5.0 kcal/min as measured by oxygen consumption used as a limit for energy expenditure [Astrand and Rodahl 1986] (see Tray 6 of the Toolbox). |