Reprinted with permission from:

American Industrial Hygiene Association Journal
A Publication for the Science of Occupational and Environmental Health

Although agriculture is generally recognized as the nation's most hazardous industry and displays high rates of musculoskeletal disorders with evidence to suggest that ergonomic risk factors are involved, there is very little history of application of ergonomic approaches in agricultural workplaces. A three-year National Institute for Occupational Safety and Health-supported study has been initiated in California nurseries to describe and design engineering interventions for priority musculoskeletal disorders. In this article are reported the results of the project's initial workplace job task screening for ergonomic risk factors and associated musculoskeletal disorder reports to define landmark ergonomic risk factors for the nursery industry and select priority job tasks for intervention.

Keywords:agriculture, ergonomics, nursery industry

For the past several years agriculture has been generally regarded as the nation's most hazardous industry. However, there is almost no history of work on ergonomic risk factors in agriculture. Review of reported occupational injuries in California agriculture for the period 1981-1990 by AgSafe(1) shows that sprains and strains predominate as major types of injury, accounting for 43% of all reported agricultural occupational injuries. Further, it was estimated by AgSafe(1) that nearly 40% of the reported sprain and strain injuries involved the back. Back injuries are generally acknowledged by agricultural employers and workers' compensation insurers as a significant problem from the perspectives of both incidence and cost. When these data were combined with a reported citation of overexertion as injury cause of 25% of all injuries, interest was stimulated in a search for practical, cost-effective ergonomic interventions that might begin to address this problem in agriculture.

For initial inquiry into the ergonomics of musculoskeletal disorders in agriculture, nurseries were chosen for three primary reasons: (1) nurseries feature a comparatively, stable workforce from year to year; (2) nurseries share many workplace characteristics with manufacturing industries, in which much previous ergonomic intervention research had been performed; and (3) nurseries constitute a major sector of California agricultural, and share many workplace and work force characteristics with other agric ultural commodities.

It should also be noted that according to the AgSafe data,(1) nurseries shared with other agricultural commodities a pattern of high rates of sprain and strain injuries. The AgSafe data(1) suggested that 48.9% of all reported injuries in horticultural specialties (including nurseries) were sprains and strains, slightly above the proportion for agriculture as a whole. Overexertion as a cause of injury for this area was cited for 30.2% of reported injuries, also above the general proportion for the Industry, as a whole.

AGRICULTURAL INDUSTRY COOPERATORS

Three nursery companies are formally cooperating in the project. All three specialize in container-grown outdoor bedding and ornamental plants, primarily for delivery to retail nurseries. These cooperators are all large operations by industry standards and between them account for some 1290 employees at the involved worksites. This industry is almost completely nonunion in California, and there is no active union representation at any of the cooperator sites. The majority of workers in these operations are Spanish-speaking, from Mexico or Central America. They earn an average of about $3.00 per hour. Nursery work is considered a comparatively good job by most California agricultural workers because it is year-round, relatively well paid, and at these sites includes health benefits. All of these cooperators have active and well-planned injury and illness prevention programs on site. Provision of workers' compensation insurance benefits is required in California.

NURSERY WORK ORGANIZATION

Operations at most California nurseries of this type followed a similar four-part organization.

(1) Propagation: New plants are started in a specialized area. Four different methods are commonly used--cuttings from mature plants, tissue culture, seeds, and grafting. Propagation includes greenhouse maturation. Propagation is characterized by highly repetitive, hand-intensive work (see Figure I).

(2) Canning: As plants grow they are replanted in individual plastic containers called "cans" (typically 2-3 times). A powered conveyor is used, from which cans are loaded onto trailers by hand for field transport (see Figure 2). Canning is characterized by repetitive pinching and other hand-intensive activities and repetitive upper extremity lifting and bending to off-load the conveyor.

(3) Field Work: Plants are held in outdoor groups until fully mature. During this period tasks include watering, pruning, fertilizing and weeding, tying-staking-shaping, and spacing as plants grow (see Figures 3 and 4). Fieldwork is characterized by prolonged stooping, frequent lifting, and hand-intensive tasks.

(4) Shipping: When plants are fully mature, they are moved to the shipping area, labeled, organized by order load, and loaded into trucks. This operation can also include truck unloading at retail sites. This work is characterized by frequent stooping, l ifting, and carrying.

METHOD

This project's overall goal is to develop and assess for agricultural work the preventive efficacy of applications of previously validated ergonomic approaches. The overall project will employ a pre-post design to collect and analyze data from injury/illness incidence, ergonomic risk factors, and productivity and worker acceptance measures. The necessary, first step of identification and analysis of injuries related to ergonomic causal factors and designation of priority intervention targets is highlighted here.

Specific objectives for this phase of the project included describing and prioritizing ergonomic risk factors and hazards for musculoskeletal disorders (including back injury and cumulative trauma disorders) in the nursery industry. Once this preliminary survey was completed, the project team and cooperators selected specific priority jobs or tasks for intervention. Continuing project work will include evaluation for nursery application previously validated task and tool modifications used in other industries with similar tasks; develop task and tool modifications that eliminate or significantly reduce the ergonomic hazards associated with that task; and conduct and evaluate cooperative on-site intervention trials (6-12 months) for each selected task with cooperating nursery operations. Final evaluation will include repeated detailed ergonomics and injury analyses and assessment of interventions as to their technical fit in the cooperating operations, industry acceptance, and impact on productivity.

To gain an overall assessment of the jobs and tasks involved the greatest ergonomic risk for musculoskeletal disorders, a triangulation strategy was evolved. Triangulation simply refers to the use of three points of reference instead of one or two to determine a location or trend. By extension, the comparison of three different and isolated means of identifying high-risk tasks is intended to strengthen confidence in a screening or survey exercise. In this workplace scale studio, preliminary to more detailed measurements, it was important to select economic methods both in terms of personnel time and equipment. Once high-risk job tasks were identified by each survey method, the three different lists were compared. Those job tasks that were identified by all survey methods made up the pool of priority job tasks for selected intervention.

The first method involved inquiry of managers and supervisors. These employees all had long experience in both the nursery industry and with the cooperating employers. Their assessments were based on personal work experience, accumulated employee opinion, and oversight of operations injury and illness records. Each supervisor was asked to cite jobs or tasks that in their experience constituted the highest level of risk for identified musculoskeletal disorders. The resulting list was summarized with their participation and approval into a single priority list.

The second survey method involved workplace screening of jobs for ergonomic risk factors. Because this involved three very large cooperating operations with some 1290 employees, a simple work site screening checklist approach as described by Keyserling(2) was selected. Three preliminary checklists were pilot tested, with one of the ANSI Z-365 checklists being finally selected, This ANSI Z-365 checklist proved among the quickest to apply in the work site setting and yielded results that allowed the most useful degree of distinction between close-scoring job tasks because it was not binary (a risk factor was either present or not). These jobs are "fluid" in their content, in that tasks required variation for many reasons, including weather and season. Job titles or descriptions are not precise since a worker may be assigned to do quite different tasks from day to day. For this reason the team decided to analyze each task falling' under the four functions described above. This approach may prove useful in other industries (such as construction) where job content varies within a given job title.

Two trained ergonomic evaluators used the checklist to evaluate the 50 identified job tasks on each of the three cooperating work sites. The evaluators' checklist practice was tested for interpreter error by comparing scores generated by both evaluators observing the same task performed by the same worker at the same time. As a result of the first-cut survey the highest scoring job tasks were selected and submitted to a more detailed checklist modified from validated checklists previously published by Keyserling, et al.(3) that were developed for use in manufacturing. The modifications made the checklists more appropriate for nursery work. The highest scoring job tasks from this set of checklists were submitted to the triangulation procedure.

The third survey method involved scrutiny of each cooperator's injury and illness records to identify those job tasks that were most frequently, associated with musculoskeletal disorders. Initial inquiry revealed that most of these employers maintained separate records for the Occupational Safety and Health Administration (OSHA) reportable injuries and for first aid (i.e., those not referred to medical care and returning to work). Because some musculoskeletal disorders may initially be present as more simple sprains or strains, it was determined to include scrutiny of the first aid records in this initial review. Cooperators made all records available, and a list Of musculoskeletal disorders and associated job tasks was developed.

RESULTS

Priority concerns as reflected by managers and supervisors are displayed on Table 1. These focused on lifting and carrying containers, repetitive hand tasks in cutting and pruning, and in slips and falls in fieldwork.

Results from the ergonomic risk factor checklist procedure at the three cooperating work sites resulted in similar identification of a set of jobs by job task as shown in Table II.

Review of the OSHA 200 injury report logs and non-required first-aid report data for 1993 and 1994 at each of the three cooperative sites suggested a list of 85 musculoskeletal disorders involving 1246 lost work days as displayed in Table III. By analyzing type of injury and descriptive information on situation and cause, those injuries that appeared to be cumulative in nature were selected. Those with clearly acute causes such as slips, falls, or vehicle incidents were excluded.

The resulting job tasks with the highest risk of musculoskeletal disorders by this indicator are shown on Table IV.

As the project proceeds, this information on musculoskeletal outcomes will be supplemented by extensive pain and symptom surveys of employees performing specific tasks selected for intervention.

Triangulation across the three methods resulted in a list of candidate tasks for intervention planning. Among the three cooperating nurseries, there are variations in tasks and how they are performed. Some nurseries have more powered equipment (e.g., forklift trucks, pruning equipment) than others, which modifies the risk factors to which workers are exposed. The Following descriptions delineate the most common risk factors for the development of work-related musculoskeletal problems in the seven candidate tasks for intervention planning.

Plant Cuttings (Propagation)
The worker stands or sits at a worktable, empties a basket of plant cuttings, and uses hand shears to cut them into smaller pieces for propagation. The shears are held in the dominant hand; plant material is grasped with the non-dominant hand. After each piece of plant material is cut, the shears must be disinfected by dipping them in a solution in a small container on the workbench.

When cutting, the right hand is engaged in very repetitive gripping, with an average of 50-60 cuts per minute. Mild to moderate wrist flexion and ulnar deviation are present throughout the cutting cycle.

The left hand is used to hold the cuttings, orient them for cutting, and discard the remains in a bin. Moderate wrist extension and ulnar deviation are present throughout the cycle.

Additional risk factors include contact stress on the front of the thighs from the edge of the worktable, contact stress-from the handles of the clippers, and poorly fitting latex gloves.

Handling Cans for Transport to Field (Canning)
In transporting plants from the conveyor belt to the trailer the worker grasps three or four 1-gallon containers in each hand and places them on a trailer located either to one side of him or behind him. This job cycle is repeated 13-20 times per minute. Risk factors include highly repetitive gripping; high pinch forces (estimated to be in excess of 66% of predicted maximum voluntary contraction); contact stress from the edges of cans on the lateral surfaces of the fingers; contact stress from the edge of the trailer against the thighs; high energy demand; and cold ambient temperatures (in the early mornings).

An additional risk factor is awkward posture. A worker experiences up to 60 degrees of trunk flexion when placing cans on the trailer (an a verage of 40 degrees of peak lumbar flexion as measured by the Lumbar Motion Monitor). A worker experiences up to 90 degrees of shoulder flexion when placing cans on the trailer. This represents high biomechanical stress on the shoulder when combined with trunk flexion.

Transporting Plants from Trailer to Planting Bed (Field Work)
The worker grasps three or four 1-gallon containers in each hand, carries them up to 55 feet, and places them on the ground along a predetermined row. This job cycle is repeated 3-5 times per minute. Risk factors include highly static gripping with both hands for periods of 10-15 seconds; high pinch forces (estimated to be in excess of 66% of predicted maximum voluntary contraction); frequent trunk flexion (up to 100 degrees of trunk flexion, or an average of 50-60 degrees of peak lumbar flexion as measured by the Lumbar Motion Monitor); contact stress from the edges of the cans on the lateral surfaces of the fingers; contact stress from the edge of the trailer against the thighs; and cold ambient temperatures (in the early mornings).

Field Pruning (Field Work)
The pruner works with various shears to remove unwanted or dead parts from the tops and sides of plants. He or she is usually standing or bent over to reach plants. The dominant hand holds the shears and is engaged in very repetitive gripping, with an average of 40-50 cuts per minute. The fingers of the right hand are also used to pinch off small twigs or other plant parts. The non-dominant hand grasps the can for a rapid pick-and-place and also holds the cuttings in a static grip, with moderate wrist flexion and ulnar deviation present throughout the cutting cycle.

Risk factors include prolonged trunk flexion (up to 90 degrees of trunk flexion, 50 degrees of lumbar flexion); awkward posture of both wrists, primarily flexion and ulnar deviation; contact stress from the edge of the can, left hand; contact stress from the handle of the shears, right hand; cold ambient temperatures (in the early mornings).

Spacing (Field Work)
As the plants grow they must have adequate room to expand. Thus, spacing must be done periodically, which involves grasping and lifting 3-4 plants in each hand, carrying them a short distance, then placing them on the ground in rows. This cycle is repeated 3-5 times per minute.

Risk factors include repetitive gripping; high pinch forces (in excess of 66% of predicted maximum voluntary contraction); frequent trunk flexion (an average of 60-65 degrees of peak lumbar flexion); and cold ambient temperatures (in the early mornings).

Weeding (Field Work)
The worker examines each plant, checks for weed growth, and removes them. He or she pulls the weed by hand or uses a tool called a 'spoon' to scoop them out.

Risk factors include repetitive gripping (5-6/min); high pinch forces; contact stress on the non-dominant hand from the plant and on the dominant hand from the tool; prolonged trunk flexion (90-100 degrees); and cold ambient temperatures (in the early mornings).

Plant Labeling (Shipping)
This operation consists of counting containers and moving each one out from its row into the furrow. The worker grabs the edge of a container in each hand and places the containers in the furrow. The worker peels a label from its backing with the dominant hand and places it on the outside of the can.

Risk factors include repetitive pinching of labels (dominant hand, 13/min); repetitive gripping (non-dominant hand, 13/min); high pinch forces (left hand); prolonged trunk flexion (70-100 degrees); contact forces on the dominant hand when wiping off dirt and water to place the label; and cold ambient temperatures (in the early mornings).

Load/Unload Truck (Shipping)
Each worker lifts three to four containers per hand (total weight 16 to 80 lb. per hand) to a flatbed trailer truck. Up to 400 plants must be moved by 1-2 workers in a period of 1-3 hours. The workers then remove the plants (3 to 4 at a time) onto crates on the floor of the dock according to the order form to be filled. Each crate holds up to 40 plants. The crates are moved by hand truck or forklift from the holding dock and placed into the trailer of the truck. Another worker then removes each container and places it on racks in the truck.

Risk factors include repetitive gripping (10-12/min); high pinch forces (in excess of 66% of predicted maximum voluntary contraction); frequent trunk flexion (90 degrees. 7/min); contact stress from the edges of the cans on the lateral surfaces of the fingers; very high energy demand; cold ambient temperatures (in the early mornings); and contact forces on the dominant hand when wiping dirt from the can to place the label.

All of these should be considered to involve a high degree of ergonomic risk for musculoskeletal disorders. Further, this list of tasks and the identified risk factors also leads to identification of landmark risk factors for this industry, which are now described as (1) repetitive hand work (clipping, cutting, pruning, etc.); (2) stooped working postures; and lifting, carrying, and moving loads with awkward postures (stoop, reach, twist pinch grip, etc.).

To narrow the list of priority job tasks to 3-5 feasible areas for inter vention, each of the seven job tasks was reviewed using the Following criteria: (1) number of workers regularly exposed, (2) duration of exposure usually involved, (3) feasibility of intervention strategy, and (4) degree of risk reduction anticipated from intervention strategy.

This exercise required the engineering group to present intervention strategy ideas graphically. A set of four jobs/tasks were selected as involving high risk for musculoskeletal disorders and as presenting likely targets of opportunity for ergonomic intervention. That list is in Table V.

DISCUSSION

None of the survey screening methods used in this study is particularly complicated and none requires expensive instrumentation. At the same time, these methods do facilitate priority setting for intervention. Conceptually, the research team attempted to improve on large-scale screening efforts by using multiple methods and selecting priorities through triangulation to increase confidence. This approach can overlook a job that has a high degree of illness or injury incidence that for some reason is not mentioned in the reporting period scrutinized. It can also eliminate a job that scores high on ergonomic risk factor checklists but for some reason is not reflected on the other measures. However, this type of criticism will apply to virtually any general workplace screening method that is also practical enough to be used in similar circumstances. By using three different measures, insulating the screening teams, and then comparing the different results, a set of priorities was reached that reflected high scores on each separate method and that met the expectations of cooperating workers and supervisors, ergonomists, and occupational health experts.

Additionally the resulting priority job tasks involve the ergonomic risk factors one would expect in this type of workplace: stooping, lifting and carrying loads, and repetitive hand tasks. These risks do not differ from those found in other industries. Because they result from a multi-method survey of the nursery workplace, and because all assessment groups agree on their priority, the team felt confident in identifying these as generally critical or "landmark" ergonomic risk factors for this industry. This is an important distinction for the industry group and for longer-term agricultural research planning.

Engineering strategies in the prototype stage at this time include (1) lightweight handles for lifting and carrying cans that eliminate pinch grip and minimize stooping; (2) handles for cans mounted on hand trucks for larger cans and greater through-put; (3) raised working platforms in the canning offloading area to facilitate use of handles; (4) hydraulic tilting trailers to minimize can lifting when loading and unloading; and (5) powered clippers and cutters for use in prudence and cutting tasks.

As the project moves into its second phase, these priority tasks are being analyzed in detail using research scale instrumentation. Health outcomes will be assessed using structured employee interviews with well-tested symptom batteries, and analysis of hours worked before and between musculoskeletal symptom occurrences. Ergonomic risk factors are being assessed using the Lumbar Motion Monitor,(4) the Greenleaf System for WristSystem,(5) the National Institute for Occupational Safety and Health (NIOSH) Lifting Equation, and metabolic demands through the use of priority heart rate monitoring and the University of Michigan Energy Expenditure Prediction Program.(7)

Work on engineering alternatives for each of the targeted tasks is underway using the engineering design process. Multiple potential alternatives will be generated by the engineering team, and each will be evaluated for (1) degree to which it reduces risk of, or risk factors for, work-related musculoskeletal disorders; (2) interaction of the intervention with other nursery activities; (3) acceptability of the intervention by the workers; (4) capital cost associated with implementation; and (5) changes in productivity associated with the intervention.

Nursery management and selected workers are involved in the design evaluation process, and the engineering team recognizes that any intervention that is not acceptable to management and the workers has little chance of being implemented.

Initial design has concentrated on tools to allow workers to do their jobs with improved postures, better hand grips, less energy consumption than currently required. They have also concentrated on developing simple inexpensive alternatives rather than automation. The purpose of this approach is two-fold: to reduce prevention costs and to contribute to job preservation. The intervention phase of the project is just starting, and time will judge the wisdom of this approach.

CONCLUSIONS

This study provides evidence that agricultural work demonstrates types of musculoskeletal disorders and ergonomic risk factors similar to those already reported in other industries. It also provides preliminary evidence that the same approach of ergonomic risk factor analysis and intervention using known principles and demonstrated methods is readily applicable to agriculture. Finally, this phase of the project has resulted in a set of general or landmark risk factors for longer-term research and prevention consideration. Future similar projects in different agricultural commodities are expected to reinforce the importance of these risk factors in agricultural work.

The agricultural industry has long been insulated from much of traditional occupational health and safety approaches. Further, agricultural audiences are quick to cite genuinely special work circumstances and situations that militate against applying remedies from other sectors. In this light, demonstration of how ergonomic methods apply to agricultural workplaces and can lead to practical, productive, and safe designs for agricultural tools and tasks is well worthwhile. Finally, this study suggests that a multi-method approach to workplace survey screening for high intervention targets is both productive and practical.

The preliminary research reported here is an essential first step to ergonomic improvement of agricultural work settings. Such work is of critical importance in demonstrating to the industry the value of ergonomic methods in practical and effective prevention of musculoskeletal disorders. The value of doing so via cooperative demonstration trial with selected companies that are acknowledged as industry leaders should not be understated.

ACKNOWLEDGMENTS

The project team is led by Dr. John A. Miles, Biological & Agricultural Engineering, UC Davis. Other team members are Dr. Julia Faucett, Occupational Health Nursing, UC San Francisco; Dr. James Meyers, Center for Occupational & and Environmental Health, UC Berkeley; Mr. Ira Janowitz, Ergonomics Program, UC San Francisco; Mr. John Kabashima, UC Cooperative Extension, Orange County; and Ms. Diana Tejeda, Biological & Agricultural Engineering, UC South Coast Research & Extension Center.

REFERENCES

1. AgSafe: "Occupational Injuries in California Agriculture 1981-1990." Oakland, CA: UCDANR, 1992.
2. Keyserling, W., M. Brouwer, and B. Silverstein: A checklist for evaluating ergonomic risk factors resulting from awkward postures of the legs, trunk and neck. Int. J. Ergon. 9:283-301 (1992).
3. Keyserling, W., et al.: Postural risk factors associated with back pain: findings of a case-referent study. Appl. Ind. Hyg. 3(3):89 (1988).
4. Garg, A., D. Chaffin, and G. Herrin: Prediction of metabolic rates for manual materials handling jobs. Am. Ind. Hyg. Association. J. 39:661-674 (1978).
5. Meyers, J., L. Bloomberg, J. Faucett, I. Janowitz, et al.: Using ergonomics in the prevention of musculoskeletal cumulative trauma injuries in agriculture: learning from the mistakes of others. Journal of Agromedicine. 2(3):11-24 (1995).
6. Armstrong, T.J., J.A. Foulde, S. Goldsein, and B. Joseph: "Analysis of Cumulative Trauma Disorders and Work Methods." (Technical report) Cincinnati, OH: NIOSH, Center for Ergonomics, 1981.
7. Ayoub, M. and A. Mital: Manual Materials Handling. Lon don: Taylor & Francis, 1989.

FIGURE 1. Cutting activity (monitored by Greenleaf WristSystem)
FIGURE 2. Workers removing cans from the canning line
FIGURE 3. Field work, pruning
FIGURE 4. Field work spacing

James M. Meyers
Center for Occupational & Environmental Health, University of California, Berkeley, 1301 South 46th Street, Building 112, Richmond, CA 94804-4603

John A. Miles
Biological and Agricultural Engineering Department, University of California at Davis, Davis, CA 95616

Julia Faucett
Occupational Health Nursing Program, University of California, San Francisco, CA 94143-0608

Ira Janowitz
Center for Occupational & Environmental Health, University of California, Berkeley, 1301 South 46th Street, Building 112, Richmond, CA 94804-4603

Diana G. Tejeda
University of California South Coast Research & Extension Center, 7601 Irvine Boulevard, Irvine, CA 92781

John N. Kabashima
University of California South Coast Research & Extension Center, 7601 Irvine Boulevard, Irvine, CA 92781