Anthropometry and Ergonomics Workplace Psychology - Paper II By Stephen Kingsford Boamah Abstract In the construction industry, employers use heavy equipment for their operations. Some of such equipment are loaders, various types of haul trucks, dozers and scrapers. The operators of these equipment experience rough and uneven road surfaces, vibrations, noise and smoke (carbon monoxide) inhalation. These exposures could lead to elevated ergonomic discomfort, resulting in musculoskeletal disorders and respiratory complications. The approach of ergonomics in this regard is to reduce musculoskeletal injuries during equipment operations, which automatically require static sitting, awkward postures, jarring and whole body vibration. Effective seat design, cab layout, maintenance, operator work habit, equipment suspension technique and work rotation and schedules should be considered by the user. These, if well thought through and effectively managed, is likely to improve the health and safety of the operator, as well as performance. 1.0 Introduction Constructional equipment include loaders, backhoe, heavy haul trucks, dozers and scrapers, graders and haul trucks. These equipment are used for undertaking tasks such as earth moving, paving, excavating, loading, hauling etc. by trained and certified operators, who often report high level of musculoskeletal disorders (Jorgensen et al., 2007). There is a wide range of health hazards encountered by the operators of these equipment such as exposure to awkward postures due to placement of controls and monitors, whole-body vibration, diesel exhaust, noise, dust, psychosocial health risks such as time/attendance (pressures and shift work), and extreme temperatures (Kittusamy and Buchholz, 2004). Work related risk factors need to be observed through a systemic approach that focuses on health, safety, production and performance of employees. Ergonomics is simply a study of work which deals with work and human interaction and its impeding environment. This helps to identify hazards associated with the use of equipment, tools, environment and the job design which can subject employees to stress and other related fatigue issues (Jorgensen et al., 2007). This paper therefore seeks to discuss the ergonomic analysis of a workstation or task-related musculoskeletal disorders (MSD), associated with the use of heavy mobile equipment and recommend practical controls to prevent such injuries. 2.0 Heavy Mobile Equipment Operation and Musculoskeletal Injuries (MSI) An MSI is a dysfunction of muscles, nerves, tendons, cartilages, ligament, bones, spinal discs and/or joints including hernias, tears, carpal tunnel syndrome, strains, soreness, sprains, pain, and tissue injuries. Musculoskeletal injuries can be acute or long term, with the long term kind starting as body discomfort, pains and irritation. If appropriate measures are not taken to curtail through effective reengineering situation, the condition of the operator will worsen, causing pain affecting him/her at both work and home. A number of factors have been associated with MSI. Works related to MSI are repetitive awkward postures, duration of exposure, vibration force, extreme temperatures and mechanical stressors (exposure to hard edges), however, there are other contributing factors such as gender (male or female), body weight, size, segment, height, overall fitness, physiological response to accident or injuries, human machine interface, previous injury records, competency and task assignment. Zimmerman (1997) explains that often, long service operators are absent from work or visit the hospital for treatment than new operators, and again, operators operating older equipment often absent themselves from work or have a higher rate of visiting the hospital and complaining of signs and symptoms of MSI as compared to new equipment operators. Heavy mobile equipment operations require high level of body movement, awkward posturing, twists and turns, exposure to noise, dust and repetitive climbing and descending from cabin, etc. A case where an operator complains of lower back pain, the association between a prolonged sitting body posture and vibration effect is considered as a significant factor to precipitate the lower back pain of the operator as compared to only vibration or awkward posture (Okunribido et al., 2006). It is important to note that both vibration and posturing affect operators of mobile equipment and there is the need to put in place control measures which will help reduce MSI. In 2001, Donati stated that, body posturing and body vibrations can be mitigated by engineering controls (seat, cab and engine design). 2.1 Body Posture Zimmerman et al. (1997) indicates that job factor challenges in mobile equipment operations, that is; twist, turn and bending of the body and working in a repetitive position for long hours can be influenced by so many factors such as the orientation of work, environment, workstation layout, the workers’ individual work methods and anthropometric features (Kittusamy and Buchholz, 2004). Below are some factors that aid body posturing when operating heavy mobile equipment:  Height, size and fit of the seat as it correlates to the operator’s stature.  Operating Posture – correlates to jarring and twist turning and bending.  Placement of controls – correlates to both foot and hand coordination. As stated earlier, the suspension of older equipment seat adjustment for lowering and rising or bending forward and backwards is dependent on the seat. Height often plays a key role, as shorter operators adjust their seat to gain or have vertical advantage and to have better vision to undertake their task. Visual clearance is critical in the operation of heavy mobile equipment, this often compromises the recommended seat arrangement as operators adjust seat randomly, ignorant of the effects of wrong body posture which has the tendency to aggravate MSI (National Institute for Occupational Safety and Health, 1997). (Okunribido et al., 2006; Jorgensen et al., 2007), states respectively that operators undertaking twist, turn and bending positions have an increase load and pressure build up on their neck, shoulders and vertebral disc. 2.2 Anthropometry The study of the anthropometry indicates every individual body has a unique dimension (Parkinson et al., 2007). It is important not to consider the design of work stations using an average person’s dimension (Kroemer and Grandjean, 2003). When equipment is to be used by multiple users, the equipment design should factor all this and be able to accommodate reference point optimization for the individual. Figure 1: Dimension and Optimizing Vehicle Occupant Packaging. (Parkinson and Reed 2006) To accommodate and allow room for multiple users, the cabin should be designed to have adequate space and seat equipped with adjustable features which accommodate all range of postures, behaviours and statures (Kroemer and Grandjean, 2003). Human characteristics is very important during design stage and it should be given the needed consideration (Parkinson and Reed 2006). Anthropometry emphasises on body measurements instead of the body’s physical action/output such as working capacity, shape, mobility size, flexibility and strength (Pheasant and Haslegrave, 2006). However, there are a lot of factors that impact the latter, and this includes age, weight, gender, ethnicity, occupational selection and secular trend and other contributing factors such as personal protective equipment (PPE), the tasks that need to be undertaken and operating posture. The cabin and its interior design is one of the key factors which is of primary concern due to human body shape, size and height (Parkinson et al., 2007). The location of hand controls, seat, foot pedal and other accessories are sometimes a challenge due to the cab size and various equipment placements in relation to driving or visual task. 2.3 Operating Posture According to Parkinson et al. (2007), the interior design of a truck or vehicle can be affected significantly by the body posture of the operator, as individuals with same body size often drive or operate equipment with different postures during their shift. Varying body postures cannot be achieved when the seat and its accessories for adjustment are not present or are faulty. Also, substandard cabin design in heavy mobile equipment may result in poor body posturing, which can lead to increase in stress, pain, fatigue and MSI. 2.4 Visibility Visibility is very essential in operating heavy mobile equipment. Whenever an operator sits in a cabin to perform any task, the first thing he/she does is to check for vision before adjusting his/her seat, and if vision or visibility is inadequate, he/she cannot undertake the assigned task. Visibility is important, creates a safe working environment for the operator and should not be compromised (Donati, 2001). 3.0 Control Measure for Awkward Postures Poor visibility of an operator, inadequate room in the operator cabin, seat design, foot pedal, and positions of other workstation controls are underlying factors to awkward posture (Kittusamy and Buchholz, 2004). There are several literature work done on this subject which provide vital information that will help minimize operator posture stress. The cabin design can factor or design to suit the operator needs by providing side mirrors, reverse camera, swivel chairs with adjustable facilities to eliminate intermittent twist to view task. Donati (2002) elaborates significant information on good body posture as a safe way of minimizing effect of vibration and MSI. Below is a breakdown of this approach to minimize exposure to operator posture; 1. Effective operator cabin design to improve visibility (without operator having to struggle to gain visibility), and proper positioning of controls and other accessories. 2. Effective design of operator’s seat with correct adjustable and swivel sitting settings which fits operator work environment, size, etc. 3. Competency through training on how to operate in the operator cabin. Seats should be designed in such a way that it can be multi-directional and accommodate different kinds of persons as indicated in the vehicle occupant package for users. A total lockable or partial swivel seat is an advantage for tasks which require multiple viewing of all the 4 cardinal points (Donati, 2002). Controls and other accessories such joy stick should also provide flexibility in terms of its operation and a comfort room for the relaxation of the arm, for easy reach without any force or stretch. Many designers nowadays provide similar control features at both directions in the operator cabin which aid in proper posturing and good coordination without twisting and turning. In order not to put stress on the legs, cabins of equipment with steering wheel or consoles present on either side of the operator must be designed to create enough space for the operators to have free leg movement. Failure to provide enough space will result in the operator bending the legs to make space or adjusting the seat downwards to create space below the steering wheel. Seat sizes and modifications should cater for operators as indicated in vehicle occupant package. The seat should be adjustable in all four cardinal points and also adjustable to suit different body weights. Cabs should be designed to allow front and back movement of the seat. The seat should be able to provide literal support and should not restrict body movement. New designs provide the luxury of hip and thigh adjustment on various degrees of literal support. This takes away the pressure on the knee and supports the upper leg as well. The seat should provide support to the operator’s back and shoulders, and should have a mechanism to adjust the lumber region for the lower back. The seat should be able to rotate in order for the operator to turn and have overall contact with the task at hand. Figure 2: Arm rest and support for the operator including seat belt Figure 3: No seat belt, arm rest and support for the operator including It is important to remember that, covers should have rough smooth surfaces, not smooth - to prevent slips during operation. The suspension of seat is very important and should also be discussed. Lastly, it should be easy to know and use controls of the seat. The controls should be easily reachable, suitably positioned and should be operated with ease, consistency and safety. Controls should not pose injury threat to the hands and fingers of operators. Operators of equipment that are controlled by joysticks or levers are often exposed to the hazard of repetitive movement of the arm and consideration should be the provision of forearm support when operating such equipment. An adjustable arm support, in terms of angle, height and width is preferable to suit different operators and should be comfortable with no sharp edges. The feet of the operator should not be hanging whilst seated and there should be adequate space between the operator’s head and the roof. Access and egress from the cab is very important and should be considered. The cab and seat design should provide safety and comfort to the operator when entering or exiting the seat. To aid mounting and dismounting of the cab, hand rails and steps should be available on the cab and it should be designed such that the operator can always maintain a three point contact when mounting or dismounting. Education and training of heavy mobile equipment operator’s seat adjustment is key to eliminate workplace MSI as this will influence their behaviours on body posturing throughout the shift and training should also place emphasis on job rotation and operators avoiding static work for long hours. During selection and purchase of new equipment, all concerns of existing equipment by the operator and their hospital records need to be considered and factored into account. This review should consider the number of operators, age, gender, stature, and body weight as presented in the vehicle occupant package for users. Sampling of questions can be sort from experienced operators and collated to give judgement and recommendation for the equipment to be bought. 3.1 Vibration This is one of the highest in terms of heavy mobile equipment operation risk profile. The operators are exposed to excessive vibration when undertaking tasks and it is directly associated or linked to MSI in operators (Tiemessen et al., 2007). The effect of body vibration is dependent on the duration of exposure. Over the years, the mining industry have operated fleets of heavy mobile equipment due to mechanised mining methods, and this has resulted in increased exposure to whole body vibration in these operators. Kumar (2004) suggested after his investigation that, the magnitude of vibration exposure exceeds the exposure limit of ISO, and poses a significant risk to the operators of these fleets. 3.2 Seat Most seats are designed to absorb shock in terms of vibrations, and as stated in the previous paragraph, a lot of study has been done on seats that give guidelines about seat suspension and belting systems which focus on minimizing vibration rather than the seat response. In some instances, the suspension system affects the intensity of vibration by amplifying it. This increases the risk to the operator, and hence, selection of seat should be left to professionals. 3.3 Planned Maintenance There should be a system in place to check the condition of trucks, including their accessories and seats - this will help reduce exposure to whole body vibration. Regular maintenance will prevent deterioration of the truck and ensure seat is well positioned. The engineering of roadways should consider the road design, layouts, signage, windrows/berms, traffic segregation, speed monitoring/limiting, positive control of access to active mining areas (puck/barrier/delineators), change management for traffic changes, parking, extreme weathers, dust control, floating requirements, emergency crash and break-down. All these in place will ensure seat suspension remains solid and MSI is minimised. 3.4 Operator One of the critical control measures of mitigating MSI are fatigue management training and reducing drivers’ driving periods and exposure by taking intermittent breaks during the shift and having enough rest after close of work. Supervisors should observe and schedule operators work rosters to ease them from long term exposure. Task rotation should be encouraged (Tiemessen et al., 2007). 4.0 Conclusion Work related hazards such as vibrations, noise, dust, and poor body posturing precipitate MSI at the workplace, and these hazards confront heavy mobile operators’ daily, particularly poor body posturing while operating equipment. These hazards, if not managed well, could elevate both direct and indirect loss for the company. Companies should purchase equipment with well-designed operator cabin which fit the worker, to avoid instances where the worker compromises on his comfort to adjust to the cabin design. This will minimize or reduce the effect of vibration and other associated hazards. References 1. Jorgensen, M., Kittusamy, N.K., and Aedla, P. 2007, Repeatability of a checklist for evaluating cab design characteristics of heavy mobile equipment, Journal of Occupational and Environmental Hygiene, 4, 913-922. 2. Kittusamy, N. and Buchholz, B. 2004. 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