A comprehensive framework for physical evaluation of manual

Int. J. Manufacturing Technology and Management, Vol. 24, Nos. 1/2/3/4, 2011

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A comprehensive framework for physical evaluation of manual material handling tasks Ratri Parida* and Pradip Kumar Ray Department of Industrial Engineering and Management, Indian Institute of Technology, Kharagpur-721 302, West Bengal, India E-mail: [email protected] E-mail: [email protected] E-mail: [email protected] E-mail: [email protected] *Corresponding author Abstract: While designing a worksystem for manual material handling (MMH) tasks, consideration of physical evaluation is of paramount importance in order to identify and minimise both short-term and long-term risks. In this context, assessment of occupational risk factors associated with the physical environment of a worksystem is a critical research need. In this paper, a generic framework for physical evaluation of MMH tasks is proposed. Four kinds of physical environment may be considered in this approach. This framework has been applied for a typical masonry job in a construction site located in Eastern India particularly with respect to effect of thermal environment. Representative sample of 23 male workers were examined. The metabolic rate among mason workers was calculated to be 602.633 W for an average temperature and humidity of 35.9°C and 55.5% RH, respectively. However, relevant solutions for improvements, such as introduction of rest allowances, etc., were suggested. Keywords: manual material handling; MMH; physical evaluation; thermal environment; occupational hazards; short-term and long-term risks; worksystem. Reference to this paper should be made as follows: Parida, R. and Ray, P.K. (2011) ‘A comprehensive framework for physical evaluation of manual material handling tasks’, Int. J. Manufacturing Technology and Management, Vol. 24, Nos. 1/2/3/4, pp.153–166. Biographical notes: Ratri Parida is presently a Research Scholar in the Department of Industrial Engineering and Management, Indian Institute of Technology, Kharagpur, India. She is currently working on Ergonomic Design of Manual Material Handling Tasks. Her research interests include biomechanics, ergonomics, etc. She obtained her BTech in Mechanical Engineering and MTech in Industrial Engineering from Biju Patnaik University of Technology (BPUT), Odisha, India. Pradip Kumar Ray is a Professor in the Department of Industrial Engineering and Management, Indian Institute of Technology (IIT), Kharagpur, India. He received his PhD and MTech degrees from IIT, Kharagpur, and Bachelor of Mechanical Engineering degree from B.E. College, Shibpur, India. He has about 30 years of diversified experience – eight years in industry and 23 years of teaching and research experience at IIT Kharagpur. He has published around 120 papers in international and national journals of repute and conferences. His

Copyright © 2011 Inderscience Enterprises Ltd.

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R. Parida and P.K. Ray areas of interest and research include productivity modelling, quality engineering, ergonomics, safety engineering and JIT-based operations management.

1

Introduction

Recent decades have seen major changes in the nature of industrial work as human muscle power has been increasingly replaced by machines. Inspite of automation in industrial settings, there exists manual material handling (MMH) in many kinds of worksystems. According to the European 90/269/CEE guideline, MMH has been defined as any transporting or supporting of a load, by one or more worker, including lifting, lowering, pulling, pushing, carrying, or moving of a load, which by reasons of its characteristics or of unfavourable ergonomic conditions, involves a risk, particularly of back injury to workers (Social Europe, 1994). The methods of carrying out such jobs may have severe adverse consequences on physical fitness of the persons involved. Besides biomechanical, physiological and psychological evaluation, physical evaluation of a worksystem (Maiti and Ray, 1994; Maiti and Bagchi, 2006; Maiti, 2008) becomes critical particularly for the jobs which are carried out in an open environment like construction-related jobs and activities. The main objective of such an evaluation is to improve the method of working as well as the working environment so that best possible performance is consistently achieved. Moreover, consideration of physical evaluation results in appropriate ergonomic design of a worksystem with the purpose of reducing incidents of musculoskeletal disorders through modification of task parameters, such as lift frequency, weight of the lift and lift distance of MMH tasks based on levels of thermal, auditory, visual and vibratory factors. Although several researchers have contributed to the design of worksystems involving manual handling of tasks under different working conditions, there is a constant need to study the effect of physical environment on the performance of the persons engaged in MMH jobs in both open and closed environments and workplaces from the perspective of ergonomic design of such jobs and the workplaces. As manual handling involves considerable physical work demands with considerable risk of physical stress and deterioration of health and fitness, a evaluation of physical environment in this context assumes significance for a better ergonomic design of workplace for the development or exacerbation of musculoskeletal symptoms (Elders and Burdorf, 2001; Hoozemans et al., 2001; Kramer et al., 2010). As environmental conditions vary widely across the workplaces, it is imperative that empirical investigative research is needed for development of a general approach. There exists a scope for enormous study and research in certain opportunities and issues for design improvement of jobs for effective minimisation of long-term and short-term hazards (occupational and health) and development of a measurement procedure with a considerable level of accuracy that may be applicable for workers involved in various MMH tasks. A variety of tools and techniques have been used in the analysis of ergonomic hazards in the occupational environment and hence, it is important to point out that manual handling activities may lead to a variety of problems/injuries and these problems may be classified as ‘musculoskeletal disorders’ which occur as a result of ‘micro-trauma’ (Putz-Anderson, 1988). Micro-trauma is the result of the

A comprehensive framework for physical evaluation of manual material

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associated work-related risk factors, such as enormous physical stress, poor level of human performance due to adverse environmental conditions, awkward postures, repetitive movements, and excessive force on links and joints of the human body in the workplace. Therefore, development of a comprehensive approach to assess the effect of micro-trauma is a prime necessity. Among the type of evaluations named, physical evaluation has become more essential as it leads to a design of the worksystem resulting in enhanced safety and comfort of the concerned workers. In this paper, a comprehensive and generic research framework is proposed for physical evaluation of the jobs, in moderate to heavy category, under diverse work environments, based on a review of literature. The application of such a framework with respect to certain MMH jobs commonly occurring in construction workplaces, such as bricklaying and masonry work is discussed in detail. Also mentioned are the advantages of the framework, and identified research issues to be taken up for continuous updates of the research framework.

2

Physical evaluation of worksystems in construction: a literature review

The ergonomic criteria for constructing a well-maintained and sound physical environment in a worksystem are to help workers in achieving their objectives with substantial reduction in effort, stress and errors within tolerable limits. A physical environment may be classified as in the following categories: 1

thermal

2

auditory

3

vibratory

4

visual.

Hancher and Abd-Elkhalek (1998) introduced a model that utilises a heat stress index, called the wet-bulb globe temperature (WBGT) to evaluate the combined effect of climatic conditions on the physiological and sensory responses of the human body. WBGT is considered to be a reliable one based on the effect of environmental factors (ACGIH, 1993). The basic underlying principle of thermal environment is that the human body must maintain thermal equilibrium in order to have a safe and efficient workplace (Corlett and Clark, 1995). Environmental variables like wind velocity, temperature and level of ultraviolet light increase successively with the change in workload and elevation and may affect workers visual sensitivity while working at higher heights (Hsu et al., 2008). Noise is the most persistent contaminant in human environment and its accumulation may lead to an obvious physical, psychic and social deterioration (Fernandez, 2009). Surveys in industries have shown that it is the primary source of dissatisfaction and annoyance (Ballesteros et al., 2010). Therefore, determination and minimisation of the short-term and long-term risk factors caused due to noise while carrying out MMH activities is the prime focus for evaluation of auditory environment. The use of vibratory tools may impose higher stresses on the anatomical structures of the hand-arm system and impedes peripheral circulation which may result in cumulative trauma disorders (CTDs) like carpal tunnel syndrome (NIOSH, 1997; Armstrong et al., 2002; McDowell, 2006), etc. The major reason for assessing vibratory environment is to

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evaluate the effect of hand-arm vibration impinging on the workers and hence minimising its effect (Tayyari and Smith, 1997). Hopkinson and Collins (1970) opine that a well-designed illumination system is important for industrial productivity and quality, as well as operator performance, comfort and convenience. Construction industry is considered to be a potential risk area because it is highly labour-intensive with constantly changing jobs (Koningsveld, 1997; Hsie et al., 2009). Poor safety measures, awkward postures, and improper and inadequate rest periods with higher workload result in an unsafe working condition, particularly in building construction industry (Maiti, 2008; Kramer et al., 2009). Construction workers are exposed to hazards, such as hand-arm vibration, repetitive movements, holding heavy tools and frequent MMH in their routine jobs (Chang et al., 2009). Although ergonomic principles follow fit-job-to-man (FJM) approach, fit-man-to-job (FMJ) is applicable when the workers are engaged in MMH tasks in an adverse open environment compatible with adverse consequences in terms of safety, comfort, health and fitness in the long run. Therefore, continuous monitoring and immediate actions, such as designing a better work-rest schedule, providing protective clothing, etc. are required to be taken up for keeping the situation under control.

3

Objectives of the proposed research framework

A critical review of the existing literature with regard to physical environment and the related ergonomic principles for MMH tasks results in the identification of a number of research issues, which are required to be addressed for improved ergonomic design of worksystems for MMH tasks. In this regard, the following objectives for a comprehensive physical evaluation of MMH tasks were set: 1

to study the effect of physical work environment on the performance of workers

2

to study the short-term as well as long-term impacts of physical work environment on the safety, fitness and health of the workers

3

to develop norms and guidelines tailored to specific situations, particularly under constraints and unavoidable extreme conditions.

The proposed research framework addresses these objectives in a logical and systematic manner. In this paper, the details of the proposed research framework and its application for certain MMH tasks at a construction site are discussed.

4

Proposed research framework

Assessment of the physical environment has been proposed in the framework as shown in Figure 1 for carrying out various MMH activities. The basic inputs for physical evaluation include anthropometric variables (providing stature, age, etc.), characteristics of the task to be carried out (including work posture, nature of the job, force required, duration, and frequency of work) and the environment itself affecting the productivity of the workers. The first and foremost step is to select a job, i for an age-group, j where i = 1, …, n and j = 1, …, m and as per the given job, i and age-group, j, a sample size of subjects is selected. For carrying out the physical evaluation of man-machine interaction,


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the methodology consists of the following steps, may be divided into five respective parts: part 1 dealing with evaluation for thermal environment, part 2 dealing with evaluation for vibratory environment, part 3 dealing with evaluation for auditory environment, part 4 dealing with evaluation for visual environment, and part 5 dealing with the improvement potential. Part 1

Evaluation for thermal environment

•

Step 1: Collect the sets of data as per job-wise and age-group-wise.

•

Step 2: Calculate WBGT index using three variables, viz. dry bulb temperature (DBT), wet-bulb temperature (WBT) and relative humidity.

•

Step 3: Measure heat exposure threshold limit in WBGT.

Part 2

Evaluation for vibratory environment

•

Step 1: Select the sets of data as per job-wise and age-group-wise.

•

Step 2: Measure the duration of exposure and acceleration components in x-, y- and z-directions are with the help of an accelerometer.

•

Step 3: Calculate root mean square (RMS) value of frequency-weighted acceleration.

•

Step 4: Measure the threshold limit values for joints and whole body.

Part 3

Evaluation for auditory environment

•

Step 1: Select and collect the sets of data as per job-wise and age-group-wise.

•

Step 2: Calculate allowable noise dose and sound pressure level using the following equations.

•

Step 3: For a given range of job, i and age-group, j, calculate permissible exposure limit, action limit time and threshold limit values as per the noise level.

Figure 1

A generic framework for physical evaluation of MMH tasks Manual material handling (MMH) Activities

Constraints Humans

Biomechanical modelling

Select a manual material handling activity (relevance, priority and return/impact)

Physical evaluation

C

Job Workplace

Physiological evaluation

1. Lifting 2. Lowering 3. Carrying 4. Pulling 5. Pushing 6. Shovelling 7. Combination

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Figure 1

A generic framework for physical evaluation of MMH tasks (continued)

Human

Physical evaluation of worksystem

Task characteristics

Environment

Select a job, i for an age group, j where i = 1, …, n and j = 1, …, m

1. Physical workload 2. Ambient temperature 3. Clothing 4. Humidity

Select the sample size of persons for a given i and j

Evaluation for thermal environment

Select sets of data (job-wise and age group-wise)

Calculation of WBGT (with or without solar load)

For job, i = i + 1 For age-group, j=j+1

Measurement of heat exposure threshold limit value in WBGT

Evaluation for vibratory environment

Evaluation for visual environment

Evaluation for auditory environment

1. DBT 2. WBT 3. Relative humidity


Determination of, 1. Duration of exposure 2. Acceleration components in x, y and z directions

Measurement of RMS value of frequency-weighted acceleration


Calculation of allowable noise dose, sound pressure level and noise level

Measurement of illumination level of the workplace for job, i and age-group, j

For job, i = i+1 For age-group, j = j + 1 Comparison with standard /recommended levels

For job, i = i + 1 For age-group, j = j + 1

Measurement of threshold limit values for joints and body members


Calculation of permissible exposure limit, action limit time and threshold limit values for a range of sound levels for job,i and age-group, j

For job, i = i + 1 For age-group, j=j+1

Assessment of degree of comfort

1. Identification of short-term and long-term risk factors 2. Feedback from workers

Identification of 1. Technical solutions 2. Operation-based solutions

A comprehensive framework for physical evaluation of manual material Part 4

Evaluation for visual environment

•

Step 1: Select and collect the sets of data as per job-wise and age-group-wise.

•

Step 2: Measure the level of illumination (in lux) and assess its effect on a particular job, i and age-group, j while doing MMH activities.

•

Step 3: Compare the estimated value with standard/recommended levels.

•

Step 4: Assess the degree of comfort in the workplace.

Part 5

5

159

Improvement potential

•

Step 1: Identify different short-term and long-term risk factors for the given job and their criticality.

•

Step 2: Feedback is taken from the workers engaged in MMH activities to understand the criticality of the problem.

•

Step 3: Identify and recommend technical as well as operation-based solutions.

Characteristic features of the proposed research framework

The research framework as proposed is a comprehensive one in the sense it is generic. It focuses on both online and offline data collection applicable to various engineering systems. As it is very solution-oriented, it may be implemented for potential improvement of the various kinds of worksystems where the workers are engaged in MMH activities in both open and close environments. Therefore, the proposed research framework can be applied to any worksystem for physical evaluation of the MMH tasks. The potential benefit of the framework in respect of construction-related material handling tasks are manifold: work design based on ergonomic principles and interface-related variables as well as development of norms and guidelines for workers exposed to adverse open environment enhancing concerned workers’ safety and comfort in the long run.

6

Application of proposed framework for MMH tasks in construction worksystem

The proposed framework may be applied to evaluate varying environmental conditions in any construction workplace. Conditions such as, extreme heat, high levels of peak noise, segmental vibration and improper lighting can be considered for evaluation. Heat stress is often a serious problem when MMH tasks are undertaken in an open environment (Srinavin and Mohamed, 2003). Even hand-arm or segmental vibration may be induced while using several types of hand-held tools, like power drills, saws, jack hammers, concrete vibrators, pneumatic wrenches, etc. In a typical construction site, some of the critical construction-related MMH jobs are as follows: 1

excavation and land movements

2

foundations and erection of structures

3

loading and unloading of materials like bricks, sand, cement bags, etc. at site

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4

pouring and filling concretes

5

scaffold erection

6

shovelling work for cement-sand slurry or mortar preparation

7

carrying and placing plywood panels for shuttering jobs.

With the help of the proposed framework, a step-by-step measurement approach may be followed to determine the effect of physical condition on job performance and to develop norms and requirements for ergonomic design of construction jobs and work environment (Fernandez, 2009). Evaluation of thermal environment is a prime necessity, as per construction industry is concerned. Compared to other physical environments, thermal environment severely affect the physical and physiological condition of the construction workers resulting in health disorders and loss of work productivity as most of the work is carried out in an open worksystem. Therefore, evaluation of thermal environment has been taken up for application of the proposed research framework.

7

Data collection and analysis of thermal environment

Ergonomics of the physical environment is basically concerned with analysing the effects of thermal, auditory, visual, vibratory and other factors on the health, comfort and performance of the workers (Parsons, 1995). As majority of the construction activities are carried out in an open environment in hot and humid conditions during day time, evaluation of thermal environment is considered to be very critical as working in extreme high temperature and humidity over long duration may have both physiological and psychological effects on workers thereby reducing productivity and increasing rate of accidents (Zhao et al., 2009). In a construction worksystem, workers of several occupations are engaged in various MMH tasks and therefore, the physical effort of the workers also varies. During construction work, the workplace keeps on changing and hence, the workers become unfamiliar with the workplace (Hsu et al., 2008). This variability in work and workplace along with extreme environmental conditions in an open environment is a key factor for increasing the metabolic rate and influencing productivity of the workers (Thomas et al., 1999; Aynur and Serdar, 2004). Heat stress and strenuous physical jobs may increase metabolic rate (M) of the workers that may provoke irritability, discomfort from sweating, affecting physiological systems and death in extreme situations (McIntryre, 1980; Hancher and Abd-Elkhalek, 1998; Miller and Bates, 2007; Perez-Alonso et al., 2011). In this context, metabolic rate is one of the important factors for determination of thermal comfort, defined as the physical state of the body rather than environmental conditions (Fanger, 1970; ISO, 1984) or strain resulting from exposure to the thermal environment (ISO 8996, 2001). Data pertaining to the study carried out at LD3 and TSCR construction site of a large integrated steel plant located in Eastern India were collected and analysed. A step-by-step approach has followed as mentioned in part 1 and part 5 of Section 5 for the evaluation of thermal environment.


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Step 1

Several data pertaining to the evaluation of the thermal environment were collected. Input data, such as anthropometric data were collected and the characteristic and nature of the task (masonry work) has been identified and defined. A representative sample of 23 construction workers engaged in masonry and bricklaying work has been selected for the study. The mean stature, whole body weight, and age of the mason workers are 156.1 cm, 51.1 Kg, and 25.2 years, respectively as shown in Table 1.

Step 2

The average ambient temperature and average relative humidity at the construction site were recorded to be 35.9°C and 55.5% RH, respectively which are quite high as working environment above 32°C and relative humidity above 60% is considered as high-temperature-and-humidity environment (Zhu and Zhao, 2006).

Step 3

Metabolic rate (M) for each of the worker engaged in masonry work has been calculated using the following formula. Metabolic rate, M = (Number of mets for masonry) × Askin × CF

where CF

conversion factor

Askin skin surface area Metabolic rate of masonry occupation measured in mets is 7 (Ainsworth et al., 1993). Skin surface area has been computed using Du Bois approximation formula as follows:

Askin = (0.202) × ( W 0.425 ) × ( H 0.725 ) where Askin skin surface area in m2 W

body weight of the person in Kg

H

stature of the person in m.

The following conversion factors have been used. CF1 = 50 Kcal/hour * m 2

and CF2 = 58 watts/m 2

Masonry/ bricklaying

Occupation

23

156.2

Avg

Min 1.41

Max 1.65

Skin surface area, A (in square-metres)

144.8

Min

Stature (in Cms) 170.2

Max

1.48

Avg

57.0

Max 51.1

Avg 27

Max 22

Min

Age (in years)

579.6

Max 495.8

Min

519.5

Avg

Metabolic rate, M (in Kcal/hr)

52.0

Min

Whole body weight (in Kg)

Specific anthropometric dimensions

3

Max

1

Min

672.3

Max

575.0

Min

602.6

Avg

4

Avg

Work experience (in years)

Metabolic rate, M (in Watt)

25.2

Avg

Table 1

Number of workers

162 R. Parida and P.K. Ray

Specific anthropometric dimensions (stature, whole body weight, age) and metabolic rate for masons


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Using the abovementioned formula, the average metabolic rate for the masons has been found to be 602.633 Watts (considering mean skin surface area of 1.48 m2) as given in Table 1 which shows that masonry and bricklaying work is very intense physical activity involving very high metabolic rate and WBGT at the site was recorded to be 35.9°C which is also quite high as and when compared to the safe values for an average healthy person is given in Table 2 (ISO 7243, 1989; ISO 8996, 2001; Olesen, 1995; Ainsworth et al., 2000). Table 2

Reference values of WBGT (ISO 7243)

Metabolic rate class 4

Part 5

Metabolic rate, M (in Watts)

Reference value of WBGT Person acclimatised to heat (°C)

Person not acclimatised to heat (°C)

25

20

M > 468

Improvement potential

Working continually in an adverse environment, such as hot and humid climate, loud noise, less illumination, etc. for an extended period of time may aggravate fatigue and hamper the physiological system of the workers. In this context, a proper work-rest schedule should be designed for the construction workers so as to avoid the critical short- and long-term consequences of fatigue, such as discomfort, loss of concentration, nervous fatigue due to less illumination and loud noise, increase in heart rate and energy expenditure rate, reduced efficiency and performance leading to the risk of overexertion and injuries among the workers exposed to such environments (Mital et al., 1991). With the help of Murrel’s (1965) formula, using standard basal rate and standard metabolic rate, rest time has been defined as: Rest time (R) = (B − S) / (B − 1.5)

where B

energy expenditure in Kcal/min

S

standard metabolic rate (5 Kcal/min for males and 4.2 Kcal/min for females)

1.5 average energy expenditure at rest (standard basal rate) in Kcal/min. Using the above formula, rest time, R was found to be 51% of the total working time. This concludes that workers should work intermittently and take about four hours rest in their eight-hour work shift for improved man-machine interface.

8

Results and discussion

Based on the above-mentioned observations and analysis, it may be inferred that the masons are applying more effort to carry out their task in an open, hot and humid environment as a result of which metabolic rate is very high. It has been studied that most of the workers who work in hot and humid environment are likely to be acclimatised to heat, therefore with the increase of temperature, heart rate does not vary. As a result,

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metabolic rate has been considered to be one of the most important factors while estimating rest periods. High metabolic rate disturbs thermal balance of the body resulting in heat disorders, such as heat cramps of muscles, exhaustion, heat rash, transient heat fatigue, etc. were found to be very common among the workers. In order to reduce fatigue and stress under the given environmental conditions, work schedules should be revised, rest periods and work durations should be constantly monitored. Improvement in the form of adequate rest allowances, job rotations and an appropriate work-rest proportion need to be suggested so that the level of physical exertion is within acceptable limits. Therefore, design of physical environment is very important in order to provide better worksystem conforming to both physiological, personal requirements and limitations of the workers. Such a design simultaneously increases work efficiency and maintains health status of the workers with minimum or acceptable work stress. This may lead to designing an appropriate man-machine interface. Furthermore, physiological data, such as sweat rate, total sweat loss, heat storage and skin wetness may be collected and analysed to evaluate whether a given environment is acceptable for continuous work. Similar studies needs to be undertaken for assessing the effect of prevailing auditory, vibratory and visual environments. However, evaluation of thermal environment is a priority as it is a significant influencing factor for various kinds of health risks that vary among workers across industries and locations (Beriha et al., 2011a, 2011b; Madanmohan et al., 2008; Whitt et al., 2008).

9

Conclusions

The proposed framework for physical evaluation is generic and comprehensive in nature, and hence can be applied to assess physical environments of any worksystem, focusing on the risks and hazards the workers encounter while doing MMH jobs. Additionally, appropriate technical and operation-based remedial measures may be identified for designing an appropriate man-machine interface. By using this framework, it is emphasised that an in-depth study of the physical environment (i.e., thermal, auditory, vibratory and visual) is needed for assessment of a construction workplace where workers are exposed to extreme conditions in open environment. Assessment of physical environment results in identification of deficient areas and subsequent implementation of preventive and remedial measures for physical work environment improvement.

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