Proceedings of the Human Factors and Ergonomics Society Annual Meeting

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1 Proceedings of the Human Factors and Ergonomics Society Annual Meeting Risk Exposure Assessment of Dairy Parlor Workers Anuja Patil, David Gilkey, John Rosecrance and David Douphrate Proceedings of the Human Factors and Ergonomics Society Annual Meeting : 1916 DOI: / The online version of this article can be found at: Published by: On behalf of: Human Factors and Ergonomics Society Additional services and information for Proceedings of the Human Factors and Ergonomics Society Annual Meeting can be found at: Alerts: Subscriptions: Reprints: Permissions: Citations: >> Version of Record - Sep 1, 2010 What is This? Downloaded from pro.sagepub.com at COLORADO STATE UNIV LIBRARIES on October 2, 2013

2 PROCEEDINGS of the HUMAN FACTORS and ERGONOMICS SOCIETY 54th ANNUAL MEETING Risk Exposure Assessment of Dairy Parlor Workers Anuja Patil, David Gilkey, John Rosecrance and David Douphrate The Department of Environmental and Radiological Health Sciences Colorado State University Modern dairy operations have evolved into a highly specialized and precise industrialized process timed critically for maximum milk production. Milking cows is a series of carefully sequenced work tasks that can be characterized as rapid, repetitive, forceful and include awkward postures of the hands, wrists, forearms, arms and shoulders. Exposure assessment using Strain Index (SI) and HAL (Hand Activity Level) was conducted in six dairy parlors at five locations throughout the Colorado region for this pilot study to evaluate the utility of these ergonomic assessment methods in dairy parlors and to estimate risk for upper extremity (UE) musculoskeletal disorders (MSDs) among dairy parlor workers. Results from our pilot study suggest that dairy parlor work is stressful to the UE with increased risk for developing MSDs. Copyright 2010 by Human Factors and Ergonomics Society, Inc. All rights reserved / X INTRODUCTION Force, repetition, and awkward posture are risk factors that have been found to be associated with the development of UE MSDs (NIOSH, 1997). In recent decades, there has been a growing body of evidence that establishes work related exposures and the risk for MSDs (Hagberg et al., 1995; NIOSH, 1997; NRC and IOM, 2001; Walker-Bone and Cooper, 2005). For example, Silverstein, Fine, and Armstrong (1987) found that the prevalence of carpal tunnel syndrome was associated with jobs characterized as highly forceful and repetitive. In another study investigators found that the prevalence of hand and wrist tendinitis in workers who performed highly repetitive and forceful jobs was 29 times greater than compared to those who performed less forceful and repetitive work (Armstrong, et al., 1987). Dairy parlor workers are exposed to many of these risk factors on a daily basis. Gustafsson and colleagues (1994) reported 80% of Swedish dairy workers reported having some musculoskeletal complaint in the previous 12 months. In the US, approximately 400,000 workers were employed at 60,000 dairy farms that produced 189 billion pounds of milk in 2009 (Dairy Mgt. Inc., 2010) The nation s herd of cows has grown to more than 9 million animals (Blythe, 2010) and adds $31 billion to our nation s economy (Dairy Mgt. Inc. 2010). Overall production declined slightly compared to 2008 levels while productivity per cow has increased 1.7% due to many possible factors including enhanced parlor methods. Milk comprises 88% of the revenue stream on modern dairy farms forcing expansion of herd sizes. These larger operations compel owners to employ newer, integrated, industrialized production processes to manage and stay profitable (Tylutki and Fox, 2002). This industry trend has led to herd sizes greater than 500 cows and many into the thousands of Cows with multiple parlor designs that achieve the necessary increases in productivity through systematic work tasks and the use of automation. The success of the larger operations is significant considering that 13% of the herds produce 78% of the milk (Hoppe and Banker, 2006). The dairy farm environment and production process is evolving with many of the new job tasks being highly repetitive, forceful in nature, and requiring awkward postures of the UE for those working in the milking parlors. Throughout the Colorado region, the majority of the workers performing milking tasks are immigrant Latino workers. It is common for parlor workers to perform their repetitive job tasks 8 to 10 hours each day working with few rest breaks to keep the operations in production 24/7/365. In addition to being exposed to risk factors for musculoskeletal disorders, the dairy workers are also exposed to other ergonomic risk factors such as loud noises, hot and cold temperatures, biologic pathogens and a host of animal handling events, stresses, and resulting injuries (Cecchini et al., 2005). Prior research evaluating dairy operations had identified upper extremity stresses using ergonomic exposure assessment methods such as electromyography (EMG) (Arborelius et al., 1986) and electrogoniometry (Pinzke et al., 2001; Stal et al., 2003), oxygen uptake, VO 2 max (Ahonen et al., 1990) as well as the Ovako Working Posture Analysis System (OWAS) (Lundqvist et al., 1997). Swedish investigators have identified musculoskeletal risk factors related to dairy operations with female milkers (Stal et al., 1998), milking machines (Stal et al., 1999; 2000), cluster support arms (Stal et al., 2003), and the newer rotary system for milking (Stal et al., 2003). A review of the literature did not reveal published articles where others had used the SI (Moore and Garg, 1995) and/or the HAL (ACGIH, 2001) ergonomic assessment tools. The SI has been used successfully to classify jobs by estimating risk for UE disorders with good sensitivity and specificity (Moore and Garg, 1995; Rucker and Moore, 2002). The investigators found a positive relationship between SI scores of five and greater and occurrence of upper limb disorders (Moore and Garg, 1995). The SI yields an index score based on multiplicative interactions of task variables, consistent with physiological, biomechanical, and epidemiological principles (Moore and Garg, 1995). The index score incorporates the intensity and duration of exertion, number of efforts per minute, hand and wrist postures, speed

3 PROCEEDINGS of the HUMAN FACTORS and ERGONOMICS SOCIETY 54th ANNUAL MEETING of work, and duration of task per day. It has been established that scores greater than five suggest increased risk and scores greater than seven are characterized as hazardous. The American Conference of Governmental Industrial Hygienists (ACGIH) TLV (Threshold Limit Value) for Hand Activity (2001) has also provided an evaluation approach to estimate job risk factors associated with musculoskeletal disorders of the hand and wrist. This approach was intended for a mono-task job performed more than fours hours per day. The ACGIH evaluation method is based on hand activity and effort level while performing a short cycle task (Latko, 1997; ACGIH, 2001). The sentinel literature review on musculoskeletal disorders and occupational exposures published by NIOSH in 1997 concluded that there was adequate evidence for causal relationships between musculoskeletal disorders and repetitive motion, forceful exertions, awkward postures, vibration, and combinations of occupational exposures. Latko (1997) used further epidemiological literature to establish a TLV process for the exposure levels to risk factors. The ACGIH TLV considers the worker s hand activity level (HAL) and peak hand force. Peak force is normalized on a scale of 0 to 10, which corresponds to 0% to 100% of the applicable population reference strength. Peak force can be estimated by a trained observer or rated by workers reporting their perceived exertion using the Borg scale, or measured using direct reading instrumentation (Wurzelbacher et al., 2009). The research team hypothesized that low cost and less technical methods embodied in the SI and HAL tools could yield meaningful results that correlated with direct reading instrumentation and that findings could be used for risk estimation, task design, intervention development, and verification of risk reduction. The purpose of this pilot study was to evaluate the utility of the SI and HAL for dairy parlor operations and to estimate risk levels for developing UE MSDs among milkers. To test our hypothesis, we designed this pilot study to apply the SI and HAL in six dairy parlors at five different dairy farms in the region. The design of the diary parlors varied with five having parallel arrangements and one with a herringbone orientation. The parallel parlor design requires that the Cows stand on an elevated platform at 90-degrees facing away from the operator area offering access to the udder and teats between the rear legs. In the herringbone parlor, the cows stand on an elevated platform that is angled or herringbone fashion facing away from the operator area. This orientation exposes enough of the back side half of the cow to allow the operator access to the teats to milk her from the side. This configuration also allows for enough room to use supporting equipment that assists in managing the weight of the pump cluster for both attaching and detaching. The job of milking cows can be categorized into five major subtasks: 1) dipping the cow s teats, 2) cleaning the teats, 3) stripping the teats, 4) attaching the milking cluster to the teats, and 5) post-dipping the teats. Dipping encompasses the application of a disinfection solution to the Cow s teats to reduce transmission of biologic contaminant to the milk. This is accomplished using a variety of hand held application devices filled with solution. The worker reaches forward to the teats and applies the disinfection agent. Milkers then use fresh towelettes or a cloth to clean and remove the disinfection agent from the teats before attaching the pump cluster. Stripping is a manual process of firmly squeezing and pulling down on the teat to stimulate the udder for milk production. Attaching the milking cluster of four individual pumps, one to each teat, on the cow s udder begins the actual milking process. Approximately three gallons or 25 lbs. of milk is pumped from each cow during a single session, two to three times per day (Prichard, 2010). After the milking process is complete, the cluster of pumps automatically releases and drops away. The dipping process is repeated to prevent infection. This entire job requires the worker to use frequent forceful and repetitive exertions at the wrist, arm and shoulder and takes about 10 minutes. METHODS Dairy farms within the region with herds greater than 500 were contacted through the university Agricultural Extension Agent and Dairy Veterinarian Specialist partnered with researchers in the Department of Environmental and Radiological Health Sciences at Colorado State University and the High Plains Center for Agricultural Health and Safety (HICAHS). The Human Research Board at the university approved all investigation protocols. Field sampling visits were scheduled at each dairy location. Three parlor workers were recruited at each site for the pilot study. The majority of the participants observed were Latino males with the exception of one Latino female. No personal information was collected on workers. The milking tasks were observed through multiple job-task cycles in six parlors at five different dairy farms in Colorado. The SI evaluation form was completed by two trained graduate students for the evaluation of the five major subtasks for milking; whereas, the ACGIH HAL tool was used to evaluate the overall task of milking in the parlor. The evaluators estimated peak force based upon observation of the worker, no direct reading instrumentation was employed to verify percent of maximum voluntary contraction. Following the SI evaluation, the same analyst then completed the ACGIH HAL form for each worker. Evaluation forms were returned to the ergonomics laboratory at Colorado State University for completion and data entry. The SI index scores were calculated and the ACGIH HAL ratings and peak force estimates were used to evaluate exposure relative to the TLV using the ACGIH TLV Booklet (2007). For this pilot study, descriptive statistics were generated to include overall means and standard deviations for SI scores by subtasks. Individual means were also generated for each subtask for each dairy parlor. Where both hands were being used while performing the subtasks, SI index scores were generated for both the right and left hands. The ACGIH HALs and peak force were used to estimate exposure relative to the TLV.

4 PROCEEDINGS of the HUMAN FACTORS and ERGONOMICS SOCIETY 54th ANNUAL MEETING RESULTS Results of our pilot study indicate that SI scores on average were higher than recommended thresholds, see Table 1. Table 1 SI Index Scores by Dairy and Subtask Note: SI > 5= some risk, > 7= hazardous Variability was seen among the six dairy parlors evaluated. Dairy 1 had the overall lowest SI scores ranging from 4.5 to 9 with lowest scores noted in left hand use in cleaning and stripping. Diary 2 SI scores ranged from 4.5 to 24 with the highest scores for cleaning, stripping and attaching pump clusters. Diary 3 had two parlors with observed differences in SI scores. Parlor 1 appeared to have lower SI scores overall ranging from 4.5 to 12; whereas, parlor 2 scores ranged from 9 to 24 with the highest score obtained for attaching the pump cluster. Diaries 4 and 5 had very similar SI scores ranging from 4.5 to The overall subtask means indicate that attaching the pump clusters produces the highest SI index score of 15.8 for both right and left hands. The lowest overall means SI score for the right hand was for cleaning the teat at 7 and for the left hand was for stripping at 6.5. The ACGIH HAL evaluations yielded less variability between dairy parlors. HAL scores were uniformly estimated at 7 for all six parlors, see Table 2. Table 2 HAL and Peak Force by Dairy Note: HAL 1 10, where 6 is steady motion with exertions and infrequent pauses. The Action Limit (AL) suggests that controls should be engaged. The right hand dominant activity was rated at 7 while the left hand was rated at 5. Normalized peak force was slightly greater for the right dominant activity at the 30%-40% effort range. The left hand peak force was estimated to be less at Dairies 1, 3 - parlor 1, and 5. Dairies 2 and 3 - parlor 2 had the highest peak force rating for both right and left hands. All parlors exceeded the TLV for the dominant right hand. Dairies 2 and 3 parlor 2 exceeded the AL for the left hand. DISCUSSION We believe that this pilot study has demonstrated the utility of these two low-technology, low-cost ergonomic tools for ergonomic risk assessment in dairy parlor work. Our findings seem to corroborate with prior research that found extreme positions of the UE, rapid movements, and high level of muscular load (Stal et al., 2003) were associated with high levels of MSDs among this population of diary workers (Gustafsson et al., 1994; Lundqvist, 1997; Pinzke et al., 2001; Stal et al., 2003). Prior research has employed direct reading exposure assessment instrumentation that may not be available to all persons interested in evaluating diary parlor operations. We propose that using these widely available, less technical and costly tools, may be an acceptable alternative when beginning the process of characterizing exposures in the parlor. These two ergonomic assessment tools have been applied to a variety of industrial and agricultural settings. The investigative team clearly recognizes that direct reading instrumentation is better if available. The SI and ACGIH HAL tools are indirect exposure assessment methods entirely based upon observations and judgments of the evaluator. The skill level of the evaluator is a major factor in the final results. Wurzelbacher and colleagues (2009) recently conducted a study and found that evaluators could not estimate peak force with consistency and accuracy when compared to direct reading instrumentation; this is a significant limitation of the ACGIH HAL. Despite this limitation, the SI and ACGIH HAL have been found to have good sensitive, specificity and predictive validity and should be considered for use in this environment (Rucker and Moore, 2002; Latko, 1995). Our findings have revealed that job tasks in the parlor are high risk for MSD with most SI scores above 5 and many above 7 (Moore & Garg, 1995). The ACGIH HAL scores are all at 7 and exceed the TLV; this is supportive of increased risk and consistent with SI scores and prior direct reading equipment findings. These findings clearly suggest that increased risks for MSDs are associated with dairy parlor milking operations. This pilot study has significant limitations that include small sample size, selection bias, observer bias, and indirect measurement data. The study population was not random but selected by convenience through prior relationships with the university. These dairies may be unique to Colorado and not represent the average dairy across the nation or elsewhere and results should not be externalized to other operations. The diary parlors in the US may be different than those is Sweden where much previous research has been conducted. The sample size is small and should only be interpreted as an indicator for future research. We suggest that future researchers estimate sample size using power calculations to determine effect size and select parlor sites randomly. This pilot study only evaluated the activities specific to milking; future research should evaluate all jobs and tasks within the dairy farm. The graduate students performing the ergonomic evaluations had training but lacked extensive experience with both tools. They may have over-estimated activities, forces and postures associated with the tasks and evaluation methods; we provided no comparison evaluations by

5 PROCEEDINGS of the HUMAN FACTORS and ERGONOMICS SOCIETY 54th ANNUAL MEETING experienced faculty. The methods selected for this pilot study are inherently limited in that indirect measures and estimates were used rather than direct reading instrumentation. We did not measure physiological reactions to exposures and therefore can t characterize actual responses that might better indicate the probability of MSDs. The industry is a significant contributor to our agricultural economy with many employed and at risk for MSDs. The industry has demonstrated a trend of expansion of the large herd operations with increasing numbers of immigrant workers employed. Diary parlor work is hard; herringbone and parallel parlors often hold cows for each milking cycle and operations are active around the clock. The milkers must execute a carefully timed sequence of tasks to obtain maximum production and in so doing are exposed to significant ergonomic stressors. 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6 PROCEEDINGS of the HUMAN FACTORS and ERGONOMICS SOCIETY 54th ANNUAL MEETING the neck and upper limb. Annals of Rheumatology Disorders, 64, Wurzelbacher, S., Burt, S., Ramsey, J. Crombie, K., Jin, Y. (2009). Comparison of Assessment Methods of Hand Activity and Force for Use in Calculating the ACGIH HAL TLV. Conference Proceedings. Monday, June 3, AIHCE Toronto, Canada.