5.0 GENERAL DISCUSSION
The six apple packing jobs assessed in this pilot study were found to be at risk for work related musculoskeletal disorders. Fifty-three percent of the workers reported a work related symptom in at least one body site. The criteria used to define a symptom as work related were conservative, including frequency and duration (occurred at least once a week or lasted one week or more), a continuing problem (occurred in the last year ), job-related (was first noticed on the current job), and of a chronic nature (did not start as the result of an acute trauma). There is probably at least some misclassification of work-related symptoms. One example would be sorters who had worked as packers and reported fairly severe symptoms (workers compensation claims, medical aid), but these symptoms were not classified as work-related because they did not start on the current (sorting) job. Many packers are reassigned to sorting as a light-duty job.
Packers reported more than half of the back, hand/wrist, neck, and shoulder problems that met the criteria of being work-related (62%, 64%, 57%, and 68% respectively), although very few workers' compensation claims had been filed (3%, 4%, 10%, and 0% respectively) (Table 15). This suggests that there is great potential for increasing workers’ compensation costs associated with this job. Sorters had a high rate of work-related back, hand/wrist, neck, and shoulder problems (45%, 22%, 11%, and 45% respectively) that resulted in workers' compensation claims rate of 27%, 22%, 0%, and 20% respectively. This represented about half of the claims. In addition to workers' compensation costs, nearly 30% of the packers and 36% of the sorters reported than their injuries affected their pace of work, potentially contributing to higher production costs.
Manual packing is highly repetitive, with packers handling approximately 13,000 apples per shift. Semi-automatic packing is highly repetitive, and it also has a high force component (baggers hold bags outstretched and tray packers use pinch grips to pull trays). Silverstein (1986) found that workers in high-repetition/low-force jobs had a 3 times greater risk of cumulative trauma disorders of the hand and wrist than workers in low repetition/low force jobs; the risk increased to 30 times for high-repetition/high-force jobs. This may, in part, explain the higher discomfort scores for semi-automatic packers.
Packing tasks performed by workers in the packing house industry are characterized by repetitive hand and wrist movements and static postures of the neck, arm, and shoulder muscles. Both static posture and repetition can produce injury when there is no break from muscle contraction (Putz-Anderson, 1988), Ohlsson (1994). When these packing house subjects (79% female) are compared to a reference group (Battevi, 1998) of female workers not exposed to repetitive tasks of the upper limbs, 13% of the reference group reported some upper limb pain compared to 68% of packing house subjects. Muscles become fatigued when there is no opportunity for blood flow to nourish the muscles and remove waste products. Micro-breaks from continual motion should be instituted by: a) encouraging workers to frequently make conscious minor changes in their posture and to use any breaks that occur due to equipment malfunction or other production changes to significantly change position and stretch; and b) briefly stop the conveyor system a few times per hour and encourage packers and sorters to change position and stretch.
Manual vs. Semi-automatic
Manual packing is more repetitive than semi-automatic packing; however, it also involves more continual and dynamic body movement. Packers have a high force component and a greater degree of static postures. The only two survey tools that could differentiate between manual or semi-automatic packing were job task observations and the across shift discomfort map. In looking at the findings of these two tools in combination, the highest hazard motions could be identified. No studies were found that addressed the effect of increased automation on musculoskeletal risk, self-reported discomfort, or injury. Jonsson (1988) found reallocation of female electronic workers from a job with highly repetitive tasks to more varied work tasks was a strong predictor of reduced symptoms in the neck, shoulder, and arm regions. Changing the job decreased static loading and increased the dynamic pattern of movements of the workers. Haider (1981) found increased pulse rates and longer reaction times for machine-paced work compared with self-paced work, especially early in the shift. Increased automation may affect a worker’s sense of discomfort because of greater restriction of movement, a sense of loss of control of the work process, and greater monotony reducing motivation.
Musculoskeletal disorders are multifactorial in nature, and certain studies have taken into account individual factors (e.g. age, gender, body mass index) to control for their confounding or modifying effects when looking at the strength of work-related factors. Buckwalter (1993) reported that musculoskeletal impairments are among the most prevalent and symptomatic health problems of middle and old age. The prevalence of neck and neck/shoulder disorders tends to increase with age (NIOSH, 1997). The mean age in this study population is 40 (ranging from 18-75). Our findings do not indicate higher symptom reporting or discomfort in older packers. The manual packers were generally older (mean age 47) than semi-automatic packers (mean age 36) and one would expect greater, rather than less, discomfort in an older population since recovering from muscle fatigue takes longer for older workers (deZwart, 1995). This may be due to the role of “survivor bias” (workers who have health problems leave their jobs, and the remaining population includes only those workers whose health has not been adversely affected by their jobs). Ohlsson (1989) found that for younger subjects, the odds of neck and shoulder pain increased significantly as the duration of employment increased, but for older workers no statistical change was found with the length of employment. Older workers with longer periods of employment reported fewer symptoms than did younger workers. Survivor bias underestimates the true risk of developing work-related musculoskeletal disorders.
This study was designed with a three-pronged approach using management records, worker self-reported symptoms, and risk factor observation. Findings from each evaluation tool are summarized in Table 29. There is general agreement among the assessment methods with regard to the hazardous areas for each job.
Although the OSHA 200 logs identified the same body sites as other tools, they were not all completed with the same degree of detail from year to year and company to company, so it was not possible to differentiate between jobs. These management records could provide a good source of information for a company to assess and manage work-related musculoskeletal disorders (WMSD) injury rates if attention is paid to details when recording injuries. A strong motivator for reducing the number and severity of WMSD claims could be lower workers' compensation payroll costs.
Observations using the checklist tool identified risky body postures, particularly of the upper body. Repetition, high force, and high muscle loading, especially for the back, were not particularly well assessed with the visual observation checklist used in this study. The checklist approach also lacked an exposure time element, so the assumption that an item checked on the checklist occurred for the entire cycle overestimates the actual exposure. The observational checklist used in this pilot study was useful as a quick, inexpensive screening tool to identify the greatest risk factors. Li and Buckle (1999) report that observational methods are limited but most applicable for static jobs, where body postures are held for longer periods of time or the body movements follow a simple pattern that is repeated during work. The checklist was most appropriate for observing sorter and packer jobs in this study. It was a poor tool for assessing simultaneous load/force, repetition, and duration, or for weighing or quantifying the interactions of checklist factors. We found the checklist to be least appropriate for assessing the segregator job. The NIOSH lifting equation focused on the risk of low back pain related to lifting activities and the 3-D Static Strength Test was used to assess forces and stresses of the shoulder that occur during lifts above shoulder height. We found these tools to be more sensitive in identifying injury risk than was the observation checklist.
Table 29 Summary of Hazard by Body Site Evaluation Tool Sorters Packers
|OSHA 200||back, hand/wrist, shoulder, neck*|
|Observations||neck, hand/wrist, forearm, elbow||neck, hand/wrist, back, elbow||back, wrist, elbow|
|3-D Static Strength||NA||NA||shoulder, back|
|Symptoms||survey back, shoulder, hand/wrist, neck||back, hand/wrist, shoulder, neck||shoulder|
|Risk Perception||upper body||upper body||none noted|
|Body Discomfort Map- Pre/Post Shift Change||shoulder, back, neck, hand/wrist, elbow||back, shoulder, hand/wrist, neck, elbow||none noted|
|Body Discomfort Map – Pre Shift||hand/wrist for manual baggers, low back for semi-auto tray packers||shoulder|
|Industry (gender studied)||Reference||All Low Back Pain||Occup. Low Back Pain||Non-Occup. Low Back Pain|
|Nurses (female)||Cust, 1972||34.6%||19.9%||14.8%|
|Teachers (female)||Cust, 1972||30.0%||12.8%||17.2%|
|Construction (male)||Latza, 2000||50.1%|
|Packing House (79% female)||48.5%*||26.5%*|
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