by

IRA JANOWITZ University of California, San Francisco Ergonomics Program

JAMES M MEYERS University of California, Berkeley

JULIA FAUCETT University of California, San Francisco

DIANA G TEJEDA University of California, Davis

JOHN A MILES University of California, Davis

VICTOR DURAJ University of California, Davis

JOHN N KABASHIMA University of California, Irvine

The University of California is conducting a four year intervention trial in cooperation with three large commercial nurseries to use engineering controls to reduce the incidence of work-related musculoskeletal disorders (WRMSD’s) among workers performing selected highly repetitive lifting and carrying tasks. The UC team identified eighty-five such injuries involving 1246 lost workdays among the cooperating pool of 1290 workers for the years 1993 and 1994. The team and cooperators then selected specific high-risk jobs for intervention, involving the manual handling of plants in 1-gallon and 5-gallon plastic containers. A set of handles for carrying and moving plant containers was developed, and is now being subjected to a twelve month intervention trial, after which their effect on incidence of musculoskeletal disorders and related symptoms associated with these jobs will be evaluated.

This paper reports on the impact these handles have on specific ergonomic risk factors identified in these tasks and associated with the targeted disorders. The Revised NIOSH Lifting Equation, the Lumbar Motion Monitor, and a protocol to compare the effect of the change from a pinch to a power grip were all used to assess the effect of the intervention. All measures indicate large magnitude reductions in targeted risk factor exposures including, extreme stooped postures, repetitive finger pinch grip, and repetitive lifting and lowering of containers. A trend towards a reduction in energy consumption was also noted.

This project is supported by NIOSH Cooperative Agreement U05/CCU911435-01

For further information, contact Ira Janowitz at UCSF Ergonomics Program, 1301 South 46 St., Building 112, Richmond, CA 94804; Tel: 925-256-0628

INTRODUCTION

Review of reported injury data for a ten year period for California agriculture by AgSafe (AgSafe, 1990) suggested that a high incidence of sprain/strain type injuries (48.9% of reported injuries) and overexertion (30.2% of reported injuries) as a cause of injury across all crops and commodities. A multi-disciplinary team of UC researchers was formed to apply ergonomics methods to the analysis and prevention of these injuries. Plant nurseries were selected as an initial intervention site because they offer a stable workforce, are a significant and growing sector of the California agricultural economy, and share some characteristics with field agriculture, construction, and manufacturing industries (Saloniemi; Schneider, et al). A previous ergonomics column in this journal (Grant and Habes) cited a long list of studies that demonstrated the effectiveness of engineering controls in reducing risk factors for WRMSD’s.

Three large 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.

PROCEDURES TO IDENTIFY HIGH RISK JOB TASKS

In order to identify high risk job tasks, cooperator’s injury (OSHA 200 logs) and first aid records were reviewed, all jobs were described and screened for ergonomic risk factors using a two-tiered checklist method, and workers and supervisors were asked to identify difficult job tasks (Keyserling, et al). Together with the cooperators, the project team selected job tasks identified as involving high risk for musculoskeletal injury for intervention. Among high priority job tasks were:

1. Handling plant containers for transport to field

a. Transporting plants from conveyor belt to trailer

The worker grasps one 5-gallon container in each hand, or 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.

b. Transporting containers from a trailer to a planting bed

The worker grasps one 5-gallon container in each hand, or 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 is repeated 3-5 times per minute.

2. Spacing Plants

As the plants grow they must have adequate room to expand. Thus, plant containers must periodically be moved and spaced farther apart in a ground-to-ground transfer. Workers grasp one 5-gallon container in each hand, or three or four 1-gallon containers in each hand, carry them up to 55 feet, and place them on the ground in new rows. This job cycle is repeated 3-5 times per minute.

The following risk factors for the development of work-related musculoskeletal problems are present in these tasks:

INTERVENTIONS

Once priority job tasks for intervention were agreed upon, design constraints for intervention development were agreed upon by management and labor at the nurseries. Among these constraints were the following:

1. Identification of tasks which all parties agree are problems

2. Concentration on engineering interventions by providing tools and procedures which will not require extensive training or behavior modification for workers.

3. Focus on inexpensive solutions with the potential for short pay back periods, because of industry concerns about the costs associated with re-engineering of their operations.

4. Limitations on job displacement for nursery workers involved in the tasks selected for intervention.

In focusing on manual materials handling, it was helpful for us to look for opportunities to do things which will have a positive effect on risk factors for WRMSD’s (Marras, 1993) and the modifiers used to calculate the Revised NIOSH Lifting Equation (Waters, et al, 1993). These were:

a. improve coupling (grip), changing it from a pinch to a power grip if possible

b. reduce moments by getting the load closer when lifting and carrying

c. improve trunk and upper extremity posture

d. reduce the speed and/or acceleration of lifting movements

e. reduce the amount of force required (change the weight of the load)

The initial primary intervention was the use of a handle for picking up and moving the 1- and 5-gallon plastic containers in which plants are grown. The handle is essentially a hand grip attached to a vertical stem which has at its base a system for coupling the tool to the container. These handles substitute a power grip for a pinch grip, and allow the containers to be placed on the ground without stooping. For 5-gallon containers, a tool in each hand is used to pick up one container each. Multi-container handles for 1 gallon containers were developed to pick up 3 containers with each tool, so as to maintain production at current levels.

Because container lip structures differ it has not been possible to design a universal coupling system which would work with all. Instead there are a total of six unique coupling systems. The handles are generally constructed of aluminum to maintain minimum tool weights, but some steel has been utilized where material strength is imperative, such as in parts of the 5-gallon tool, which must carry up to 25 pounds (11.36 kg).

Two handle shapes have been utilized, each with different advantages. A T-shaped hand grip for 5-gallon containers (see Figure X) helps protect the worker from prickly plants when gripped on the far side from the plant. When the plant is small or not prickly, it can be gripped nearer to the plant, resulting in a lower potential torque on the wrist. Left and right-hand grips for 1-gallon containers are angled in both vertical and horizontal planes to achieve neutral postures of the wrist while carrying the containers.

A curved handle has also been developed. It allows for either a low grip, near the bottom of the curve, when containers are elevated, as on a trailer, or a high grip when they are on the ground. There is no standard trailer design among the cooperating nurseries, and some features, such as steel lips welded around the edge of the trailer, are presenting obstacles that have yet to be overcome.

DATA COLLECTION METHODS

In order to control for variables such as ambient temperature, fatigue changes during the day, and differing plant maturity, 3 minutes of data collection for both the "before" and "after" conditions were carried out on the same day for each worker, within a few minutes of each other. All testing was carried out in a typical field with actual workers from that location. The same plants were handled during each 3-minute test and moved the same distance.

Revised NIOSH Lifting Equation: Measurements for the Revised NIOSH Lifting Equation were carried out according to the Applications Manual (U.S. Department of Health and Human Services). The product of the NIOSH equation is the "Recommended Weight Limit" or RWL. A Lifting Index is generated by dividing the actual weight by the RWL. A Lifting Index of 1 indicates that the load is one that nearly all healthy industrial workers could perform over an 8-hour shift.

Forward Bending: Dynamic postural data was collected using the Lumbar Motion Monitor (Marras, Sudhakar, Lavender, 1989). An in-field calibration method was developed to assure that the LMM would yield accurate results after having been transported over rough terrain. To analyze the effect of using the handle throughout the job cycle, we calculated the percentage of the cycle that each worker’s lumbar spines were bent forward more than 20 degrees.

Energy Expenditure: Heart rate was monitored as an indicator of the metabolic load of the task, using chest leads and a telemetry system. The percentage of aerobic capacity was then estimated from the heart rate, using the approach outlined in Eastman Kodak (1984). The objective here was to assure that the use of the handles would not increase the metabolic load on the workers.

Grip: A protocol was developed to compare the effects of the handles in substituting a power grip for a pinch. In the pre-intervention condition, workers routinely lift three 1-gallon containers or one 5-gallon container in each hand using a finger pinch grip. A platform was outfitted with a Chatillon force measurement dynamometer to measure upward pull force capability under the pre- and post-intervention conditions. Actual plants in containers were connected to the dynamometer with workers pulling upward on plant containers with and without the handles.

The object weight was divided by the maximum upward pull force to generate a ratio of weight to maximum upward pull with a given container. The determination of overall actual-to-maximum lift force ratios for the pre- and post-intervention task requirements are expressed as percentage of grip capability. EMG studies are planned for the Fall of 1997 to further analyze the percentage of maximum voluntary contraction required under pre- and post-intervention conditions.

RESULTS

Results from the above measurements of ergonomic effects of interventions are very positive. The handles are significantly reducing the risk factors targeted.

The Average Lifting Index for 1-gallon containers was reduced from 2.27 to 1.20, and from 5.20 to 3.26 for lifting 5-gallon containers. The percentage of job cycle bent forward more than 20 degrees was reduced from 64.46% to 43.95% with 1-gallon containers. This percentage was reduced from 22.00 to 11.15% in 5-gallon container handling. All of these results were significant (t test, p<0.005). There was no statistically significant change in energy expenditure, but there was a trend towards reduction in percent of aerobic capacity utilization with the handles that fell just short of significance.

Our grip testing protocol indicated that, when using handles for 1-gallon containers, workers had to exert an average of 9% of their grip capability whereas when not using the handles, they had to exert 48% of their grip capacity. When using handles for 5-gallon containers, workers had to exert only about 12% of their grip capability whereas when using a pinch grip they had to exert 25% of their grip capacity.

RESULTS OF ERGONOMICS MEASURES

Without handles With handles

1-gallon 5-gallon 1-gallon 5-gallon

Lifting Index 2.27 5.20 1.20 3.26

Forward Bending 64.46% 22.00% 43.95% 11.15%

Aerobic capacity 51.4% 46.5% 50.3% 50.0%

Grip Capacity 48% 9% 25% 12%

DISCUSSION

In a complex work setting there are any number of complicating or intervening elements or occurrences with potential for affecting data collection. In most cases, we have found approaches such as the Revised NIOSH Lifting Equation and the Lumbar Motion Monitor to be acceptable and effective in the nursery workplace. It does require removing a worker from regular work for a period, but does allow for performance of the targeted job task in the field setting.

The use of the Revised NIOSH Lifting Equation allowed us to integrate changes in the horizontal and vertical location of the load with respect to the worker, and changes in the type of grip used, into a singe variable that could be used to evaluate the effect of our interventions.

Subsequent planned data collection using the full capabilities of the Lumbar Motion Monitor will include analysis of twisting and side bending and include consideration of dynamic motion (velocity and acceleration), using the Ohio State University model proposed by Marras, et al (Marras, 1993).

It must be reiterated that despite concern for potential sources of error in methods employed, the large, statistically significant differences in results in each area for task performance with and without handles inspires confidence that a measurable effect is occurring as described.

CONCLUSIONS

This project has three primary goals. The first was to demonstrate that ergonomics methods and approaches developed in other industries have practical application to agricultural work. The second was to demonstrate that ergonomics risk factors identified can be targeted and either eliminated or significantly reduced through engineering intervention acceptable to workers and employers. The final goal was to demonstrate that reduction of exposure to selected ergonomics risk factors will result in reduced incidence of musculoskeletal disorders and symptoms.

The first goal was readily achieved in the practical and useful description of risk factors for WRMSD’s associated with nursery jobs and the productive use of this information to design tools to reduce the risk factors. The second goal is addressed by this paper. The third goal will be addressed in the project’s final reports in which final data on WRMSD incidence and symptoms are analyzed and reported.

While the data reported here are largely preliminary and will be supplemented and augmented by further data collection and analysis still underway, they do show persuasive evidence of the impact of the designed intervention tools and strategies on the targeted risk factors.

Repetitive or sustained stooping is a serious risk factor for chronic back injury that is present in much agricultural field work. Stooped posture or trunk inclination is reduced in all nursery workers using the tools. In an industry where "stooped" posture frequently reaches or exceeds 90 degrees, this is important progress.

One of the nursery industry’s most serious and unique ergonomic risk factors is the pinch grip required to handle plant containers. Use of the handles completely eliminates this grip, substituting a power grip. These are important improvements with respect to hand, arm, and other upper extremity WRMSD’s.

All of these ergonomics risk factor reductions are important, both individually and in combination. However, for this work to have an industry-wide impact it is important that the interventions be low-cost, fit with predominant work practices, and at least not increase worker energy expenditure or reduce current productivity levels. The 5-gallon handles appear to meet all of these criteria. They are of low complexity and involve little material or production costs. They fit well with current container handling practices and current equipment investments. Perhaps most importantly for eventual field impact is the fact that workers anecdotally reported that they liked the handles, especially for ground-to-ground transfers. While their effective use does require a period of adaptation, once achieved, workers report a clear preference for handling containers with the tools. Further development is needed for the 1-gallon tools. Lack of control over the varieties of 1-gallon containers used in some of the nurseries has impaired our ability to fully develop and test the use of the 1-gallon handle. Some intermediate size (2-2.5-gallon) containers have been recently introduced for flowers. Minor modifications of the present handle designs should work well for these containers.

These are important results. They tell us that agricultural field jobs which involve serious risk factors for musculoskeletal disorders can be effectively addressed using accepted ergonomics approaches. Further, they suggest an under-realized opportunity for intervention in these jobs using small tools. For the past several decades, engineering development in agriculture has concentrated on large machines, leaving small tools used throughout the industry largely untouched and unconsidered. It is time to take another look at many of the jobs and tasks which are routine in agriculture and which are largely taken for granted as immutable.

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