WEEK 4

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FACULTY OF HEALTH SCIENCES - HLSC 4676U Occupational Ergonomics and Work Disability Prevention - Winter, 2023 Sessional Lecturer Dr. Heather Matchett B.Kin (Hons), D.C. WEEK FOUR January 29, 2024 Outline  Occupational Health Hazards Continued o Biomechanical  NIOSH  MHH  Biomechanical Models  MSK System and LBP  Posture (Seated work and Chair Design)  Cumulative Trauma Disorders/Repetitive Strain Injuries BIOMECHANICAL Revised NIOSH Lifting Equation – Assessing Relevant Handling Factor  Revised in 1994 to improve upon prior 1981 lifting equation  The determination of whether a lift is too heavy can be made by using the NIOSH lifting equation, which considers various factors in lifting tasks that contribute to the risk of injury.  These factors include the weight of the load, as well as other variables such as the frequency of lifts and the distance of the load from the body. By applying this equation, a recommended weight limit (RWL) can be calculated, which takes into account these variables and helps determine if a lift is within safe limits.  To calculate the recommended weight limit (RWL), you need to measure or assess several variables related to the lifting task. These variables include the horizontal distance (H) the load is lifted, the starting height of the hands from the ground (V), the vertical distance of lifting (D), the time between lifts or frequency of lifting (F), the angle of the load in relation to the body (A), and the quality of the grasp or handhold (C).  Each variable is assigned a numerical value from reference tables, and the NIOSH equation uses these values to calculate the RWL.

Figure 1. F=Frequency, A=Angle of load, H=Horizontal, C=Coupling, D=Distance travelled, V=Vertical location Figure 2. Figure 2 illustrates the AM (Asymmetric Multiplier) and its body angle in relation to the load. The proximity of the multiplier factors to the pick up location indicates a Recommended Weight Limit (RWL) of approximately 23kg (or 51 lbs), which is called the load constant. On the other hand, if the multiplier factors deviate from 1, the RWL should be reduced. To determine the appropriate multiplier value, you will need to measure the distance in centimeters for each factor. For the horizontal multiplier, measure the distance from the person's ankles to their hands while holding the object. Record this measurement and refer to the "horizontal distance" chart in the Calculating Recommended Weight Limit (RWL) to find the corresponding multiplier factor. Use this factor in the lifting equation. Please note, if the measured value does not match any figures in the table, NIOSH allows for extrapolation or using the next higher value from the table for more protection. Repeat this process for the other five factors (vertical multiplier,

distance multiplier, frequency multiplier, asymmetric multiplier, and coupling multiplier). Once all of these values are obtained, you can use the Revised lifting equation calculator to determine the recommended weight limit. Finally, to assess the weight of the object, and thus the safety of the lifts, compare it with the recommended weight limit. If the actual weight exceeds the limit, identify the factor(s) posing the greatest risk and make adjustments to the lifting process. A special hint: The factors with the lowest multiplier values indicate the highest level of risk. The Revised NIOSH Lifting equation is not applicable in various scenarios. It does not apply when lifting with one hand, lifting for more than 8 hours, lifting while seated or kneeling, lifting in a restricted work space, lifting unstable objects like buckets or containers of liquids, lifting while pushing or pulling, lifting with wheelbarrows or shovels, lifting with high speed motion greater than 0.76m/s (or 30 inches/second), lifting extremely hot or cold objects or in extreme temperatures, or lifting with poor foot/floor coupling that poses a high risk of slip or fall.  NIOSH Lifting Equation and its factors  The equation is: RWL = LC x HM x VM x DM x AM x FM x CM  LC, Load constant - A "load constant" (LC) of 23 kg (about 51 lb) was established by NIOSH as a load that, under ideal conditions, is safe for 75% of females and 90% of males to lift.  AM, Asymmetric Multiplier Factor - Twisting angle of the body while lifting, measured in degrees A = Angle (degrees) AM Factor 90° 0.71 60° 0.81 45° 0.86 30° 0.90 0° 1.00  HM, Horizontal Distance Multiplier Factor - Horizontal distance in cm, from the midpoint between the ankles to the hands while holding an object H = Horizontal Distance (cm) HM Factor 25 or less 1.00 30 0.83 40 0.63 50 0.50 60 0.42

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 VM, Vertical Distance Multiplier Factor - Vertical distance in cm, of the hands from the ground at the start of the lift V = Starting Height (cm) VM Factor 0 0.78 30 0.87 50 0.93 70 0.99 100 0.93 150 0.78 175 0.70 >175 0.00  CM, Coupling Multiplier Factor - Quality of grasp (classified as good, fair, or poor), and depends on the body position (standing or stooping). C = Grasp CM Factor: Standing Stooping Good (handles) 1.00 1.00 Fair 1.00 0.95 Poor 0.90 0.90  FM, Frequency Multiplier Factor - Frequency of lifts and the duration of lifting (in minutes or seconds) over a given workshift F = Time Between Lifts FM Factor Lifting While Standing: OR Lifting While Stooping: One Hour or Less Over One Hour One Hour or Less Over One Hour 5 min 1.00 0.85 1.00 0.85 1 min 0.94 0.75 0.94 0.75 30 sec 0.91 0.65 0.91 0.65 15 sec 0.84 0.45 0.84 0.45 10 sec 0.75 0.27 0.75 0.27 6 sec 0.45 0.13 0.45 - 5 sec 0.37 - 0.37 -

 DM, Distance Multiplier Factor - Vertical distance in cm, that the load travels D = Lifting Distance (cm) DM Factor 25 or less 1.00 40 0.93 55 0.90 100 0.87 145 0.85 175 0.85 >175 0.00  RWL, Recommended Weight Limit Canadian Centre for Occupational Health and Safety EXAMPLE 1 - considering HM Factor: Determine whether this person is lifting under or over their RWL for this particular task. A worker lifts 13 kg boxes from the table to the shelf five times for one hour or less. In this example, there is a barrier between the worker and the box. The revised NIOSH Lifting Equation is: RWL = 23 Kg x HM x VM x DM x AM x FM x CM H (Horizontal Distance) - 50 cm V (Vertical Distance) - 70 cm D (Lifting/Carrying Distance) - 40 cm F (Frequency) - 12 min A (Angle) - 0° C (Coupling/quality of grip) – fair, standing Look up the values for HM, VM, DM, AM, FM, CM in respective charts above and calculate RWL. 23 Kg x 0.50 x 0.99 x 0.93 x 1.00 x 1.00 x 1.00 = 10.59 kg Therefore, they are over the RWL and are at risk for a lifting related injury. Workspace design revisions: Remove the barrier so the worker can get closer to the box they are lifting. Now the horizontal distance will be changed to 30cm. The revised NIOSH Lifting Equation is: RWL = 23 Kg x HM x VM x DM x AM x FM x CM 23 kg x 0.83 x 0.99 x 0.93 x 1.00 x 1.00 x 1.00 = 17.58 kg Compare weight of the load against Weight Limit in new workspace. The weight of the load at 13 kg is now lower than the recommended weight limit of 17.58 kg. Therefore, most workers can safely perform the task.

Canadian Centre for Occupational Health and Safety EXAMPLE 2 - considering VM Factor: A worker lifts an 18 kg load from piled pieces of metal from the floor to the table five times in an hour. H (Horizontal Distance) - 30 cm V (Vertical Distance) - 0 cm D (Lifting/Carrying Distance) - 115 cm F (Frequency) - 12 min A (Angle) - 0° C (Coupling/quality of grip) – poor The revised NIOSH Lifting Equation is: RWL = 23 Kg x HM x VM x DM x AM x FM x CM 23 Kg x 0.83 x 0.78 x 0.85 x 1.00 x 1.00 x 0.90 = 11.39 kg ** Please note: * The distance was 115 cm. By looking at the reference tables, the distance factor was greater than 100cm, so the value of 0.85 was instead selected in order to be more protective. Since the weight of the load is 18 kg, it is significantly higher than the calculated RWL. This task will therefore likely increase the chance of a lifting related injury. Workspace design revisions: If the metal collection area (starting height) is raised off the floor, D (lifting distance) is decreased from 115 cm to 40 cm, while increasing V (vertical distance) from 0 cm to 75 cm. The revised NIOSH Lifting Equation is: RWL = 23 Kg x HM x VM x DM x AM x FM x CM 23 kg x 0.83 x 0.93* x 0.93 x 1.00 x 1.00 x 0.90 = 14.86 kg * Please note that the vertical distance is 75 cm. Since VM was greater than 70 cm, 0.93 was selected as the value in order to be more protective. In this example, the load at 18 kg is still higher than the new recommended weight limit of 14.86 kg. Therefore, the worker is still at risk for a lifting related injury, and more workspace design revisions must be made. Further revisions could include supplying the working materials in containers with handles, or by reducing the weight of the lift to lower than 14.86 kg. Canadian Centre for Occupational Health and Safety EXAMPLE 3 - considering Frequency Factor: A worker lifts 6 kg boxes from the conveyor to the cart ten times every minute for two-hours. H (Horizontal Distance)- 20 cm V (Vertical Distance) - 75 cm D (Lifting/ carrying Distance) - 0 cm F (Frequency) - 6 sec over 1 hour, standing A (Angle) - 90° C (Coupling/quality of grip) - fair, standing The revised NIOSH Lifting Equation is: RWL = 23 Kg x HM x VM x DM x AM x FM x CM 23 kg x 1.00 x 0.93 x 1.00 x 0.71 x 0.13 x 1.00 = 1.97 kg

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* The vertical distance provided is 75 cm. Since VM was greater than 70 cm, 0.93 was chosen in order to be more protective. The weight of 6 kg is much larger than the recommended weight limit of 1.97 kg. Therefore, this task is likely to increase the risk of a lifting related injury. Workspace design revisions: Shorten the frequency to lifting while standing, one hour or less, 10s (FM reference table) The revised NIOSH Lifting Equation is: RWL = 23 Kg x HM x VM x DM x AM x FM x CM 23 kg x 1.00 x 0.93 x 1.00 x 0.71 x 0.75 x 1.00 = 11.39 kg The newly calculated RWL post-design revisions is 11.39kg, which is higher than the load of 6 kg that the worker has to lift. In this case, most workers can safely perform the task. Manual Materials Handling (MMH)  The NIOSH lifting equation serves as both a job analysis tool for assessing lifting demands and a guide for optimizing workplace and device design for material handling. It highlights seven key design parameters that job designers should aim to optimize.  The horizontal and vertical multipliers in the NIOSH equation serve as a reminder to job designers that loads or material handling devices (MHDs) should be kept close to the body and positioned at thigh or waist height whenever possible. Placing large packages on or near the floor poses a particular hazard, as they cannot be easily kept close to the body. This requires individuals to lean their torsos forward, resulting in a significant increase in low-back disc compression force.  Hence, it is important to avoid presenting large packages to workers at a height lower than mid-thigh level, approximately 30 inches above the floor (Chaffin, 1997). To facilitate the handling of heavy or bulky objects, adjustable lift tables can be utilized. These lift tables not only assist workers but also reduce the vertical distance that an object needs to be lifted, as suggested by the distance multiplier.  The asymmetric multiplier serves as a reminder for designers to minimize torso twisting during materials handling. A simple and thoughtful redesign of the workplace layout can eliminate unnecessary torso twisting movements, thereby significantly reducing the risk of worker discomfort and injury. To minimize torso

twisting, lifting tasks should be designed in a manner that requires the use of both hands in front of the body and ensures a balanced load distribution between the hands.  ** Extra caution should be exercised when lifting bags of powdered materials, as the contents may shift during the lifting process. If possible, this type of lifting should be avoided altogether.  The NIOSH lifting equation also emphasizes the importance of minimizing the frequency of lifting by implementing appropriate lifting techniques and work-rest schedules. Whenever possible, frequent and heavy lifting should be performed with the assistance of material handling devices (MHDs). Additionally, the loads or MHDs should be designed to be easily grasped and handled. Efforts should be made to minimize the weight of the load by selecting lightweight materials, if feasible.  It is evident that the design parameters mentioned above do not encompass all possible causes of musculoskeletal issues in manual materials handling. There are additional factors that play a significant role in determining the occurrence and intensity of low back pain, such as whole body vibration, psychosocial factors, age, health, physical fitness, and nutrition conditions. It is important to consider these factors as well when engaging in the process of workspace design.  Moreover, it should be noted that lifting-related low-back pain represents only a portion of the overall cases of low-back pain in work environments. This is supported by studies conducted by Frymoyer et al. in 1980 and the National Safety Council in 1990. Furthermore, the discussion on seated work highlights another common cause of low-back problems.  Prior to lifting, it is important to assess the availability of mechanical aids and seek assistance for heavy or awkward loads. Additionally, one should evaluate and determine the weight of the load, ensuring that it can be lifted without straining oneself. It is crucial to ensure that the load is free to move and that its contents are stable and balanced. If necessary, repack items to prevent shifting, as shifting contents greatly increases the risk of injury. Before proceeding, check that the planned location is clear of obstacles and debris, as they can lead to slips and falls. Different types of loads or materials may require specific handling and lifting techniques, so it is important to be aware of these variations. Lastly, if there is any uncertainty about safely handling the load, it is best to refrain from lifting it altogether.  Prior to lifting, it is also important to warm up/stretch your muscles. Position yourself near the load and face the direction you plan to move. Maintain a wide stance to ensure balance. Ensure you have a secure grip on the load. Keep your arms straight during the lift. Engage your abdominal muscles/core by tightening them. Protect your neck by tucking your chin into your chest. Begin the lift by using your body weight. Lift the load as close to your body and as centered as possible. Lift smoothly without any sudden jerking movements. Avoid twisting or bending to the side while lifting. Refrain from carrying loads with only one hand. Biomechanical models  Biomechanical models are mathematical representations of the mechanical properties of the human body, specifically the musculoskeletal system. This system is analyzed as a series of mechanical links, with bones and muscles acting as levers.  By utilizing established methods of physics and mechanical engineering, biomechanical models can predict stress levels on specific musculoskeletal components. This makes them an extremely valuable analytical tool for job designers to identify and avoid hazardous job situations.  The foundation of biomechanical modeling is based on Newton's three laws, which state that a mass remains in uniform motion or at rest until acted on by an unbalanced external force, force is proportional to the acceleration of a mass, and any action is opposed by a reaction of equal magnitude.

Musculoskeletal System and Low Back Pain  The musculoskeletal system comprises the bones, muscles, and connective tissues, including ligaments, tendons, fascia, and cartilage. Bone can sometimes also be classified as a connective tissue. The primary functions of the musculoskeletal system are to provide support and protection to the body and its parts, maintain posture and facilitate body movement, and generate heat while regulating body temperature.  The human body consists of 206 bones, which form the sturdy skeletal framework responsible for major support and protection. The skeleton serves as the structural foundation that holds all other body parts together. Certain bones have the specific role of safeguarding internal organs, such as the skull protecting the brain and the rib cage shielding the lungs and heart from external harm. Additionally, certain bones, like the long bones in the upper and lower extremities, collaborate with attached muscles to facilitate body movement and various activities.  Each of the remaining four types of connective tissues possesses its own distinct roles. Tendons, for instance, are dense fibrous connective tissues responsible for linking muscles to bones and transmitting the forces generated by the muscles to the connected bones. Ligaments, on the other hand, are also dense fibrous tissues, but their primary function is to connect the articular ends of bones and aid in stabilizing the

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joints formed by these bones. Cartilage, a translucent elastic tissue, can be found on certain articular surfaces of bones as well as in body parts like the nose and ear. Lastly, fascia serves as a covering for various body structures, effectively separating them from one another.  According to the National Council on Compensation Insurance's estimates, cases of low back pain typically make up approximately one-third of all workers' compensation payments. It is also believed that occupational and other unknown factors may cause low back pain in as high as 50-70 percent of the general population (Andersson, 1981; Waters et al., 1993).  The main cause of work-related low back pain and disorders is manual material handling, which involves lifting, bending, and twisting motions of the torso, as mentioned prior. This type of pain is prevalent both in terms of occurrence rate and severity. However, low back problems are not limited to these situations. Low back pain is also common in sedentary work environments that require prolonged static sitting postures. Therefore, the analysis of the biomechanics of the back becomes crucial in both manual handling and seated work scenarios.  The weight of the upper body and the load exert considerable pressure on the structures in the lower back, particularly on the disc between the fifth lumbar and the first sacral vertebrae, known as the L5/S1 lumbosacral disc.  When performing a lifting task, there are multiple factors that affect the stress exerted on the spine. Among these factors, the weight and the position of the load in relation to the center of the spine are crucial in evaluating the potential risk of injury in the workplace. Additionally, other factors such as the degree of torso twisting, the size and shape of the object, and the distance the load is transported also play a significant role in determining the strain on the spine. Posture (Seated work and Chair Design)  It is highly recommended to use a seated workplace whenever possible for long-duration jobs. This is because maintaining a seated posture is much easier and less straining on the body. Additionally, it allows for better control of arm movements, provides a stronger sense of balance and safety, and improves blood circulation. However, it is important to note that the sitting posture does have its drawbacks, particularly

when it comes to low-back problems. Seated work environments where no lifting or manual handling activities occur are often associated with common low-back pain.  The main cause of low-back disorders in seated work is the loss of the lordotic curvature in the spine and the corresponding increase in disc pressure. When a person sits down, the pelvis rotates backward, changing the lumbar lordosis into a kyphosis. This is especially true when a person sits with a slumped posture. Without proper body support, most people tend to adopt a slumped sitting posture shortly after sitting down. This compresses the front part of the intervertebral discs and stretches the back part, causing the discs to protrude backward and put pressure on the spinal soft tissues and nerve roots. This can result in back pain and eventual disc herniations.  Various studies have demonstrated that the pressure on the discs is significantly lower (at least 35-40%) when in an upright standing posture compared to sitting (Nachemson & Morris, 1964; Chaffin & Andersson, 1991). Among different unsupported sitting postures, the lowest disc pressure is observed when sitting with a straight back. As depicted in Figure 3, the disc pressure is much lower in an erect sitting posture compared to a slumped sitting posture. Therefore, it is clear that sitting posture greatly influences the variation in disc pressure. Fig. 3  To reduce the occurrence and severity of low back pain in individuals who work while seated, it is crucial for workplace designers to give special attention to seat design. A well-designed seat can assist individuals in adopting a less straining posture and alleviate the load placed on the spine. In this regard, there are several seat-design parameters that prove effective in achieving this objective, including the inclination angle of the backrest, provision of lumbar support, and the presence of armrests.  The backrest plays a significant role in reducing stress on the lower back. The inclination angle of the backrest is a crucial parameter in its design. A 90° back-inclination angle (a seat with a straight back) is unsuitable as it encourages individuals to adopt a slumped posture. An increase in the inclination of the backrest leads to an increase in the transfer of body weight to the backrest and a decrease in disc pressure. According to Hosea et al. (1986) and Andersson et al. (1974), the ideal inclination angle should range between 110° and 120°. To alleviate low-back stress, it is recommended to equip the backrest with a lumbar support pad, which helps maintain lordosis and is particularly crucial when the back inclination angle is small.

 Chaffin and Andersson (1991) found evidence that a lumbar support is equally effective as a full back support. The thickness of the lumbar support should be approximately 5 cm. Additionally, it is preferable for the lumbar support to be adjustable in height and size to ensure maximum comfort for individuals of different sizes.  Arm rests can assist in supporting a portion of the body weight while seated, thereby reducing the load on the spine. Although there is no conclusive evidence that a tiltable seat surface significantly alters spinal load (Bendix et al., 1985), it is still desirable as it allows for posture variations throughout the worker’s shift .  Properly adjusting the seat height, utilizing cushioned seat surfaces, and providing adequate leg space can all contribute to minimizing back stress. However, it is important to note that regardless of how well- designed the seats are, individuals should not maintain a static sitting posture for extended periods. Sedentary workers should take regular breaks to stand up and walk around.

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Cumulative Trauma Disorders (CTDs) / Repetitive Strain Injuries (RSIs)  The occurrence of these disorders can be primarily attributed to the progressive impact of repetitive and prolonged physical strain and stress.  CTDs encompass a range of soft tissue disorders affecting various parts of the upper extremities, such as the fingers, hand, wrist, upper and lower arms, elbow, and shoulder.  Common examples include: tendonitis, neuritis, ischemia (circulatory restrictions), bursitis, vibration- induced white fingers or Raynaud’s phenomenon, game keeper’s thumb, carpal tunnel syndrome, medial and lateral epicondylitis, tenosynovitis, and impingement syndromes.  Causes and prevention of CTDs o It is evident that Cumulative Trauma Disorders (CTDs) can be caused by various work-related factors. These factors include repetitive motion, excessive force application, unnatural posture, prolonged static exertion, fast movement, vibration, cold environment, and pressure of tools or sharp edges on soft tissues. CTD issues are more likely to occur when forceful exertions are involved, as the increased tension in muscles and tendons can exacerbate the problem. o Unnatural joint postures, such as bent wrists, elevated elbows, or raised shoulders, can put strain on the soft tissues and cause the tendons to rub against the bones, increasing friction. Additionally, using a short tool handle against the base of the palm, gripping sharp objects, or placing the arm on a sharp edge can obstruct blood flow and potentially irritate the nerves. These issues can also arise in vibrational or cold environments. In many job situations, these factors often combine, further increasing the risk of developing CTDs, and ergonomic design specialists should seek to remedy this whenever possible. o Human factors professionals and ergonomists need to work with the management and related worker organizations to establish continuing education programs to increase the workers' awareness and knowledge of the risks, causes, and preventive methods of CTDs. Attention to worker health conditions, establishment of regular exercise programs and facilities, and creation of a desirable social environment are some of the approaches that the management can adopt to minimize the risk of work-related CTDs. o Job schedules should be carefully evaluated and designed to reduce time and pace pressure and provide great flexibility. Warm-up exercises before the start of the work and the adoption of adequate work-rest cycles are effective ways of conditioning and relaxing the body in a work environment. o Workers are forced to adopt an awkward posture when the workplace is not designed according to the anthropometric characteristics of workers. Elevated elbows and raised arms are required when using a high work surface. Static postures are unavoidable when the work space is too small to allow any movement, or when the job task requires hours in front of a computer. Neck and shoulder pain are likely to develop when the visual displays are located either too high or too low. Therefore, anthropometric design of workplaces is also an important method for preventing work-related CTDs. o Automated equipment, supporting devices, and well-designed work tools can contribute to the reduction of CTD risks. In instances where tasks are highly repetitive or require forceful exertions, it is advisable to utilize automated equipment. When designing work tools, it is crucial to carefully analyze the required joint postures and avoid unnatural positions such as bent, twisted, or overextended joints. For individuals using computer keyboards, the inclusion of wrist rests with a suitable surface contour and soft cloth material can promote a more natural wrist posture and minimize contact with potentially cold and sharp table edges.

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