Exhibit 11: Cabinet Manufacturing Work Setting

The site was a cabinet manufacturing company in which basic work processes involved sawing rough lumber, planing cabinet panels and parts, sanding and painting, assembly, and packing and shipping. A total of 17 jobs representing one full production of a kitchen cabinet were first screened on the basis of job descriptions and walk-through observations for risk of both musculoskeletal disorders and traumatic injury. Five job tasks (three lifting tasks and two pushing and pulling tasks) were selected for more in-depth analyses because of their linkage with excessive back strain and sprain reports among the workers. Videotapes and still photos were taken of the job tasks, along with workstation measurements. (NIOSH protocols for analyzing videotapes of job operations are described in Tray 5-H of the Toolbox.) Frequencies, weights, and heights of loads lifted were noted together with measurements of initial and sustained push forces. Applying the NIOSH 1980 lifting equation formula for defining lift weight limits and the Michigan 2-dimensional static strength prediction program showed that the three lifting jobs presented conditions warranting control actions to reduce risk of overexertion or back injury. (Information about these two techniques is included in Tray 6 of the Toolbox.) Initial and sustained push forces for the other two jobs were rated against maximal acceptable values reported in the literature for 50% of the male and female population. One of these two tasks (pushing stacking bunks) exceeded these values and was judged potentially hazardous; recommendations for risk reduction were offered [HETA 88–384–2062].

Exhibit 12: Window Balance Systems Manufacturing Work Setting

The site was a plant that produced window balance systems. The product was made from either stamped, roll-formed aluminum or extruded vinyl. Both metal fabrication and extrusion operations were performed at the plant. All 12 jobs in the assembly department were targeted for analyses on the basis of earlier State inspection reports describing conditions associated with the development of carpal tunnel syndrome. These jobs were observed in a plant walk-through and videotaped for later analyses. Information was collected concerning the number of employees engaged, the task elements, the number of pieces assembled per work shift, the tools used, the difficulties workers perceived in the job, and worker suggestions for improvements. Measurements were also taken of work surface heights (both worktable and conveyor). A review of the videotape in real time and slow motion yielded data on repetitiveness of movements, awkward hand/wrist and shoulder postures, and indicators of muscular force requirements. The task cycle times were derived from these observations, along with the number of hand/wrist motions (flexion, extension, ulnar and radial deviation, pinching) and the number of unnatural shoulder positions. Particularly extreme postures were noted in the videotape analyses as one means for rating muscular force exerted. Other bases for rating force were the number of forceful manipulations in a given job cycle, the size and type of tool used, and the weight of the product handled.

Jobs were rated for ergonomic stress to prioritize interventions needed to eliminate the stress. The job ratings were determined by combining the observed level of repetitiveness or movements per day with the level of force. Three levels of repetitiveness were defined and assigned values. A value of "1" was given for jobs with low (fewer than 10,000) movements per day, "2" for jobs with medium (10,000–20,000) movements per day, or "3" for high (more than 20,000) movements per day. Average and peak levels of force were also judged by the investigators and given ratings of "1" or "2" (low force), "3" (medium force), or "4" or "5" (high force).

The total stress score for each job was determined by adding the assigned values for the repetition and force. Two jobs (pulling springs to attach them to window liners and hooking springs into window liners) were found to represent the greatest musculoskeletal stress when rated in this way. However, all of the assembly jobs were found to pose problems requiring ergonomic hazard control actions [HETA 88–361–2091].

Exhibit 13: Grocery Warehouse Setting

The site was a large grocery warehouse with the focus on order selector jobs. Order selectors load cases of grocery items from warehouse shelves to pallets according to a "picking order" (a listing of the items and quantities to be picked), the order of picking the items, and their locations (aisle and slot numbers) in the warehouse. In terms of job tasks, the order selector routine is to drive a pallet jack to the location of the items in the warehouse, lift the items from the shelves, carry them to the pallet, and lift or lower the items onto the pallet and place labels on the items. The order selector then proceeds to the next item on the order list, and the procedure is repeated. After the entire list of orders is picked, the order selector wraps or tapes the stacked cases together and places the loaded pallet on the loading dock for transport from the warehouse. Order selection is known as a physically demanding job. One objective of the NIOSH evaluation was to assess the potential risk associated with the manual lifting tasks just described. Before the evaluation, a standard incentive program was installed at this warehouse to establish a "fair amount of time" for order selecting activities. Achieving 100% of the standard was considered a "day's work." Order selector performance was averaged over a week, and employees were disciplined for performance that fell below 95% of the standard. Workers who exceeded the standard were rewarded with additional pay or paid time off.

Techniques used to assess the potential risk associated with the manual lifting tasks performed by the order selectors included the following:

• Weight measurements of the objects lifted
  
  
• Videotape, still photos, and angular measurements of the body postures of workers carrying out the lifting tasks
  
  
• Use of a motion monitor to record the motion of the trunk as it may affect the forces on the intervertebral joints of the spinal column
  
  
• Time activity analysis of the manual lifting routines of the order selectors, including work-rest cycles
  
  
• Use of portable heart monitors and oxygen consumption meters to measure the energy expenditure in the course of carrying out regular order selector activities

Information on load weights and body postures were systematically recorded for five representative lifting tasks that workers and the NIOSH investigators judged as having a high risk of potential for injury. These data served as input to the Michigan 3-Dimensional Static Strength Prediction Program for estimating compressive forces on the lower back and muscle strength requirements for designated lifts. The data were also used in the NIOSH revised lifting formula for recommending weight limits based on the characteristics of a specific lifting task. The evaluations for the five tasks by both the Michigan and NIOSH procedures found all loads to be clearly excessive. In addition, the lumbar movements constituting these tasks, as analyzed and measured in terms of flexion angle of the trunk and lateral and twisting velocity, combined with lifting rate and other factors, indicated a high risk of low back injury based on the models developed by Marras [Marras et al. 1993].

The mean metabolic rates as measured by oxygen consumption were above the value (5.0 kcal/min) recommended in the literature as an upper limit for young male workers during an 8-hour workday. Observed heart rates were also high. Two of the three workers had average heart rates exceeding 110 beats/min, the suggested maximum acceptable for the majority of healthy workers [Astrand and Rodahl 1986].

Time-motion analyses of the data collected indicated that the average frequency of lifts during the normal activities of the selectors was 4.1 lifts/min. This lifting rate, coupled with observed loads averaging 30.4 lb, would probably result in fatigued muscles, especially since a high percentage (53%) of the lifts required extreme trunk flexion and reaches above shoulder height. Calculations for these lifting conditions were well above the upper limits recommended by the NIOSH lifting equation [Waters et al. 1993].

Data collected in this evaluation provided for workers' perceptions of the physical effort required by their jobs and the job demand versus the control they felt they had in their work routines. Findings here indicated "hard physical effort" as the average response, which correlated well with the heart rate and oxygen consumption monitoring already described. Responses to the job demand and control questions, when compared with other worker groups, showed order selecting to be a high demand and low control job. Informal interviews with workers revealed their concern over the work standards and their inability to control the pace of their jobs. The literature associates this combination of job attributes with increased stress and job dissatisfaction [HETA 91–405–2340].

Exhibit 14: Office Setting

The sites were offices in two State governmental agencies in which more than 500 workers performed data entry tasks using VDTs. Questionnaires administered to the total sample of workers indicated a significant prevalence of constant musculoskeletal discomfort, with the greatest number localized to the trunk area, followed by the neck, buttocks, arm/shoulders (particularly on the right side), and, lastly, the lower legs. The specific design features of 40 workstations, representing a subsample of those used by this worker group, were analyzed to determine the extent to which they could account for the complaints. In all cases, the keyboard in these units was positioned immediately in front of the worker, with the document placed either to the left or right or between the keyboard and the display. Documents were manipulated mostly with the left hand, with the right hand used exclusively for keyboard operation. Wrist rests were not available, and flexibility in keyboard and video display placements was limited. Work tables and chairs lacked adjustable features. Various measurements and observations were made at these workstations during actual VDT work, including seat pan heights and compression seat back height, keyboard height, seated postures of the workers, upper arm angles, document distances, head tilt, gaze angle, and chair tilt and swivel. Statistical techniques were used to predict the amount of musculoskeletal discomfort from the aforementioned ergonomic variables. This analysis was performed by the region of the body affected and indicated the ergonomic factors, both singly and in combination, that could account for significant amounts of the reported discomfort in that area. The results showed, for example, that leg discomfort increased when the lower leg length exceeded the seat pan height and when the seat pan was soft. With regard to arm/shoulder discomfort, height discrepancy between the positions of the elbow and the keyboard proved to be a significant predictor as did long reaches to documents with the left arm. Less neck and trunk discomfort was found for erect sitting postures compared with stooped or slouched positions and as the height of the backrest was lowered in relation to the length of the operator's back. These and other findings served as the basis for offering suggestions about workstation configurations that could alleviate the discomfort problems [Sauter et al. 1991].

Exhibit 15: Engineering Controls—Beverage Delivery

NIOSH staff conducted an ergonomic study of soft beverage driver-sales jobs. Such job tasks as handling beverage cases for delivery were problematic for two reasons: the stacking of cases in the truck bay exceeded the normal reach limit of workers, and most of the beverage lifting tasks also exceeded the recommended weight limit of the 1993 NIOSH lifting equation. Heart rate measurements, as an indicator of the physical effort required for this work, were found to be high among the driver-sales workers, especially during peak periods. Estimates indicate that more than 35,000 lb of beverage products were handled daily by these driver-sales workers. The rate of musculoskeletal injuries for the affected workforce, in terms of days lost, was twice that of workers in general manufacturing jobs.

To relieve the above-mentioned problems, the following engineering controls were implemented:

• Pullout platform steps in the bay floors enabling the drivers to step up and work at bay level
  
  
• External handles between the bays for workers to grab to give them better mechanical leverage during removal of the beverage product
  
  
• Multilevel shelving units that provided compartments for different products, gave easier direct access, and eliminated the problem of having to lift or move different products around to find the ones slated for delivery to a customer
  
  
• Lubricated two-wheel hand trucks with proper tire pressure maintained to make pushing and controlling the load easier
  
  
• Plastic beverage containers instead of glass ones to reduce package weight
  
  
• Improved beverage cartons designed with larger handles and smooth, contoured bases that make them easier to handle when removing stacked cartons from the truck

Changes in work risk factors were documented through videotaping, modeling the stresses imposed on the body by the materials handling tasks, continuous monitoring of heart rate, and analyzing discomfort surveys. Data were compared before, during, and after the ergonomic interventions were implemented.

The benefits of the ergonomic interventions were in proportion to the amount of time such controls were used. Reductions in stressors for the back and shoulders were observed when pullout steps, external handles, and multilevel shelving were used. Heart rates decreased for six of nine driver-sales workers during the study period, despite an increase in the product volume handled. The ergonomic interventions reduced the multiple handling of beverage cases and the awkward postures during beverage handling, resulting in a reduced number of reports of fatigue [McGlothlin 1995; NIOSH 1996].

Exhibit 16: Engineering Controls—Motorcycle Manufacturing

NIOSH researchers conducted initial and follow-up evaluations of musculoskeletal disorders of the upper limbs and back at a motorcycle manufacturing company. The objectives of this evaluation were to identify the job tasks in the flywheel milling department thought to cause musculoskeletal injuries and to provide recommendations to decrease and prevent such injuries. NIOSH researchers reviewed OSHA Form 200 logs and workers' compensation data and conducted an ergonomic evaluation of four jobs in this department (two flywheel milling jobs, one flywheel truing job, and one flywheel balancing job). Data gathered on the initial site visit in the flywheel milling area showed that repeated manual transport, placement, and removal of the flywheels between milling processes resulted in more than 28,000 lb handled per 8-hour shift. In addition, repeated use of a handheld power grinder to remove metal burrs from milled flywheels proved to be inefficient and presented other accident risks. Analysis of data from the flywheel truing job showed that impact forces from the 5-lb brass hammer repeatedly striking the flywheel ranged from 25,000 to 92,000 lb. Using the NIOSH 1993 lifting equation to analyze the flywheel balancing job showed potential risk for back injury. NIOSH recommended engineering controls to reduce risk factors for musculoskeletal disorders, and the company effected a number of them through establishment of a management/labor ergonomic committee. The engineering controls included the following:

• Upgrading forging and milling machine processes and improving product flow to reduce the burden of flywheel handling from 28,000 to 17,500 lb per 8-hour shift
  
  
• Installing a customized 40-ton press to eliminate the use of brass hammers for truing the flywheels
  
  
• Using an overhead lift to eliminate manual handling of the 35-lb assembled flywheel unit, further reducing the total weight that had to be handled each day

During a 5-year period from 1989 through 1993, the efforts of the plant's management, engineers, and workers resulted in a reduction of WMSDs involving lost or restricted workdays from 27.6 per 100 workers in 1989 to 12.5 per 100 workers in 1993. The severity of musculoskeletal disorders decreased from 610 lost or restricted-activity workdays per 100 workers in 1989 to 190 workdays in 1993 [HETA 91-0208-2422].

Exhibit 17: Administrative Controls—Jewelry Manufacturing

NIOSH investigators were asked by a jewelry manufacturer to evaluate upper extremity musculoskeletal disorders among employees. Questionnaire surveys of employees indicated that 66% reported work-related upper extremity musculoskeletal symptoms. In the 2 years before the NIOSH evaluation, physicians diagnosed seven employees with carpal tunnel syndrome.

Besides making numerous specific engineering control recommendations, the NIOSH investigators also suggested the following administrative control strategies:

• Training new employees in proper craftsmanship, tool use, and maintenance—for example, emphasizing the need to keep cutting tools sharp to reduce force requirements and the need to keep power tools balanced and lubricated to minimize vibration
  
  
• For new employees, providing more frequent rest breaks at the outset to relieve fatigue and overexertion
  
  
• Rotating employees to jobs that require the use of different muscle or tendon groups (for example, NIOSH investigators suggested that employees using small handtools be rotated to inspection tasks)
  
  
• Providing more frequent breaks for those employees doing polishing, buffing, etching, and engraving tasks because they are engaged in manual tasks for long periods [HETA 90-273-2130]

Exhibit 18: Administrative Controls—Meat packing

In one meat packing case, an administrative control approach was used to address ergonomic problems in boning and trimming tasks. Physical stressors of this job included awkward wrist postures, high grip forces, and a high workload. Observations showed that the total boning task workload was 96% of the total task cycle, allowing 4% for rest. In contrast, the trimming task workload was 80% of the total task cycle, allowing 20% for rest. One suggestion was that the trimmers could trim more of the lean shank, reducing the boners' workload. A better balance was struck between these two tasks, and an increase in lean shank yield from this modified job was documented [Gjessing et al. 1994].

Exhibit 19: Evaluating Ergonomics Programs in Meat packing Plants

A variety of techniques were used in meat packing plant ergonomic case studies to evaluate and gauge the effectiveness and benefits of the ergonomic hazard control efforts:

• Symptom surveys Two of the case studies described administering symptom surveys to workers before implementation of the demonstration ergonomics programs. The symptom surveys were used to confirm findings from records, help identify problem jobs, and establish baseline data. These baseline data were compared with data from identical surveys administered after controls were implemented. Reductions in the number and severity of symptoms identified during the time period between the first and second survey would be expected if the controls implemented are effective.

  In one case, symptom surveys indicated a decline in the number of people reporting pain and a decline in pain severity. In the other case, symptom surveys showed an increase in the number of reported discomfort areas over the project period. The investigator in this case attributed the rise to increased employee knowledge of ergonomic hazards and WMSDs, as well as to seasonal increases in production.

• OSHA Form 200 Logs As with symptom surveys, two of the case studies referred to company-maintained OSHA Form 200 logs to identify problem jobs and establish incidence rates of WMSDs. Data maintained in these logs were used to gauge the plant-wide effects of the ergonomic interventions on overall and job-specific incidence rates of reportable WMSDs. In one case, plant-wide rates were calculated for the two 1-year periods before the study and for two 6-month periods after the interventions. The rates per 200,000 work hours were 55, 75, 80, and 59, respectively. The incidence rates continued to rise in the first 6 months of the post-intervention period, but they fell more than 27% in the second post-intervention period. Reductions in rates of 19%, 33%, and 42% for the second 6-month period were shown in three of the four departments, whereas the rate in the fourth department remained the same.
  
  
• Other records In these meat packing case studies, employee absenteeism rates, employee turnover rates (both overall and job-specific), and workers' compensation costs were used to judge ergonomics program effectiveness. In one of the cases, the investigators studied a plant for 7 years. During this period, workers' compensation costs declined to 20% of the pre-ergonomic program costs.
  
  
• Productivity and quality In one case study, an administrative control for a trimming job resulted in a $14,000 increase in product yield over 6 months. In the same case study, changes in the hog shackling task to reduce back injuries in workers were calculated to yield a $436,000 annual savings from reduced product (hog) loss.
  
  
• Task analysis and checklists The same techniques used to identify and evaluate the ergonomic risk factors of jobs and tasks were used to gauge the benefits of implemented controls. These were analyzed in terms of the risk factors that were reduced or eliminated from the original, unmodified job. In one case, risk factors such as awkward postures and heavy lifting were reduced or eliminated when mechanized lifts were installed to handle the 250-lb metal tubs while they were being washed [Gjessing et al. 1994].

Exhibit 20: Medical Management—Poultry Processing Plants

At the request of a State labor department, NIOSH determined the prevalence of WMSDs of the neck and upper extremities in workers employed at two poultry processing plants. OSHA reports and symptom data obtained via questionnaires and physical exams found workers in jobs requiring highly repetitive, forceful motions and awkward postures to have significantly more hand and wrist disorders than those employed in less physically demanding work. In the course of this study, NIOSH also assessed the medical management practices in the two plants with regard to injured workers and the company's WMSD prevention program. Based largely on the questionnaire data and other sources of information, the following areas were suggested as needing improvement or change:

• Increased nurse access: From 23% to 29% of employees in one plant who met the various case definitions of upper extremity musculoskeletal symptoms indicated that their foreman or supervisor refused to allow them to leave their workstation to see the plant nurse at some point during the course of the year.
  
  
• More efficient job rotation schemes: Nearly 30% of the workers in the high exposure jobs in one plant and almost 27% in the second were involved in a job rotation plan. Both plant groups reported spending at least 2 days a week in jobs other than their base jobs. The rotation, however, did not necessarily place them in less ergonomically stressful tasks. Rather, the jobs they temporarily filled were often vacancies on the production line in the same high exposure area.
  
  
• Questionable use of vitamins and anti-inflammatory drugs: The policy of one plant required all new hires to take ibuprofen tablets and Vitamins E and C several times a day during their probationary periods. Although use of these substances has been advocated as a way to prevent WMSDs, valid, scientific evidence to establish their effectiveness is not available. More importantly, this approach does not substitute for effective engineering or administrative controls. Also, consumption of therapeutic amounts of these drugs (e.g., ibuprofen) can pose a risk of other adverse health effects [HETA 89-307–2009].

Exhibit 21: Proactive Ergonomics at an Appliance Manufacturer

NIOSH, as a demonstration project, is assisting an appliance manufacturer in designing a new assembly line that, by incorporating ergonomic factors, can prevent musculoskeletal disorders without limiting production output. Steps in the project include the following:

• Evaluating musculoskeletal injury patterns associated with work on existing production lines, observing related risk factors, and determining engineering solutions for these risk factors
  
  
• In-house training of assembly line workers, engineers, and management to recognize, evaluate, and provide solutions to job risk factors
  
  
• Applying the above training information in the planning of a new assembly line with the goal of preventing musculoskeletal disorders
  
  
• Conducting a symptom survey of the assembly line workers at the beginning of the new line's production to establish baseline morbidity rates
  
  
• Fine tuning the production line with ergonomic controls as production increases and as workers become more knowledgeable and skilled in their jobs
  
  
• Conducting periodic follow-up symptom surveys to determine injury trends and outcomes

NIOSH interactions with the plant's design, manufacturing, and production engineers are aimed at shifting the engineers' thinking from just production issues to include ergonomic concerns. The following are some benefits resulting from these interactions:

• The design and use of a tool-balanced, in-line screw gun with torque control. The torque control is achieved by attaching an "L"-shaped handle called a "cheater bar" to the tool. This design allows the torque resulting from driving screws with this tool to be transferred to the bar, which is stabilized by holding it against the edge of the metal cabinet of the washer or dryer. In so doing, the torque force is not absorbed by the tool user.
  
  
• Using a pneumatic tool to open the hose clamps needed to attach hoses to the drain valves of washing machines. The original task was performed with a pair of pliers. This change reduces the static forces and awkward postures required for attaching the hose to the valve.
  
  
• Using height-adjustable worktables and height-adjustable shelving units, allowing workers of different heights and arm lengths to assemble parts with more ease and comfort.
  
  
• Using a pneumatic lift and rotation table to lift the washers to the desired standing height of the worker so they can drive in screws without stooping over, and rotating the tables so that all screws can be fastened from one workstation.
  
  
• Building an assembly line with these ergonomic workstation features may be less costly than retrofitting existing lines. Another advantage is that the worker is learning to do the job in ways that are more healthful and more productive [Estill and McGlothlin 1994].