Ergonomics CS 1 PDF

IEN09 ERGONOMI CS 1 Prepared by: MARIA CORAZON B. ABEJO, PhD, PIE, ASEAN Eng.  NIOSH Lifting Equation: RWL = LC (51) x HM x VM x DM x AM x FM x CM The NIOSH Lifting Equation is widely accepted as valid in the field of occupational ergonomics, providing occupational health and...

IEN09 ERGONOMI CS 1 Prepared by: MARIA CORAZON B. ABEJO, PhD, PIE, ASEAN Eng.  NIOSH Lifting Equation: RWL = LC (51) x HM x VM x DM x AM x FM x CM The NIOSH Lifting Equation is widely accepted as valid in the field of occupational ergonomics, providing occupational health and safety professionals an objective ergonomic risk assessment tool for manual material handling tasks. The NIOSH Lifting Equation is a great way to identify ergonomic opportunities and prioritize ergonomic improvement efforts, and it also provides an objective baseline from which you can document ergonomic improvements. 2  NIOSH Lifting Equation Outputs: Recommended Weight Limit (RWL): Answers the question… “Is this weight too heavy for the task?” Recommended Weight Limit (RWL), which defines the maximum acceptable weight (load) that nearly all healthy employees (90%) could lift over the course of an 8-hour shift without increasing the risk of musculoskeletal disorders (MSD) to the lower back. NOTE: The smaller the RWL, the greater the potential strain on the person. Lifting Index (LI): Answers the question… “How significant is the risk?” Lifting Index (LI) is calculated to provide a relative estimate of the level of physical stress and MSD risk associated with the manual lifting tasks evaluated. A Lifting Index value of 1.0 or less indicates a nominal risk to healthy employees. A Lifting Index greater than 1.0 denotes that the task is high risk for some fraction of the population. As the LI increases, the level of injury risk increases correspondingly. Therefore, the goal is to design all lifting jobs to accomplish an LI of 1.0 or less. 3  NOTES: NIOSH lifting guide is limited to lifting activities that do not involve lifting or lowering under the following conditions: - With one hand - for more than 8 hours - While seated or kneeling - in a restricted workspace - unstable objects - while carrying, pushing or pulling - with wheelbarrows or shovels - with high-speed motion (faster than about 30 minutes (0.75 m)/second ) - on slippery floors - in hot, cold, dry or humid work environment. 4  Uses of RWL and LI: The RWL and LI can be used to guide or engineer lifting task design in the following ways:  Individual multipliers that determine the RWL can be used to identify specific weaknesses in the design.  The LI can be used to estimate the relative physical stress and injury risk for a task or job. The higher the LI value, the smaller the percentage of workers capable of safely performing these lifting job demands. So using the LI, injury risk of two or more job designs could be compared.  The LI can also be used to prioritize ergonomic redesign efforts. For example jobs can be ranked by LI and a control strategy can be implemented based on a priority order of the jobs or individual lifting tasks. 5  The NIOSH Lifting Equation always uses a load constant (LC) of 51 pounds (23 kg), which represents the maximum recommended load weight to be lifted under ideal conditions. From that starting point, the equation uses several task variables expressed as coefficients or dimensionless multipliers (In the equation, M = multiplier) that serve to decrease the load constant and calculate the RWL for that lifting task. Task variables needed to calculate the RWL:  H = Horizontal location of the object relative to the body (measured from the hands to the midpoint of the ankles- the greater the distance, the greater the stress on the spine) NOTE: Optimally, the load should be carried out as close to 10 inches as possible and should not exceed to 25 inches maximally. HM = 10 / H  V = Vertical location of the object relative to the floor (the vertical distance of the hands above the floor at the beginning of the lift. Lifts significantly below or 6 above knuckle height (30 inches) increases stress on spine.   D = Distance the object is moved vertically – factors in the vertical travel distance of the object between origin and destination. “D” is the absolute distance traveled form origin to destination. Must be a positive number. DM = ( 1.8/ D ) + 0.82  A = Asymmetry angle or twisting requirement in degrees. Twist increases the amount of force the spine can withstand without injury AM = 1 - 0.0032 x A NOTE: Each of the above multipliers can also be determined by referencing the data in the look-up Tables in Fig. 4-29 including the next two multipliers.  F = Frequency and duration of lifting activity- the frequency of lift per minute based on the average 15-minute samples. It is based on three variables effected  In the column of Frequency sub-Table in Fig. 4-29. 7 F =the average number of lifts per minute during a 15- minute period   C = Coupling or quality of the workers grip on the object - the quality of handles or hand holds. “C” is the quality of interaction between hands and the load. Good handles make the load easier to hold and support less risk of injury. Subjectively estimate the coupling (CM) value based on the height of the lift (V) relative to 30 inches (75 m) using the Table in Fig.4-29. Additional task variables needed to calculate LI:  Average weight of the objects lifted  Maximum weight of the objects lifted 8 9 10 11  NIOSH lifting equation RWL = LC × HM × VM × DM × AM × FM × CM LC = load constant of 23 kg HM = horizontal multiplier = (25/H) VM = vertical multiplier = 1 − (0.003IV − 75I) DM = distance multiplier = 0.82 + (4.5/D) AM = asymmetric multiplier = 1 − (0.0032A) FM = frequency multiplier (from Table 6.12) CM = coupling multiplier (from Table 6.13) Where: H = horizontal distance of the hands from midpoint (0) of the ankles V = vertical distance of the hands from the floor D = distance through which the load is lifted A = angle of asymmetry (Figure 6.4) F = frequency of lifting (lifts/min every 1, 2 or 8 hours) 12 13 14  INTERPRETING THE LIFTING INDEX *** The design objective is to achieve a Lifting Index (LI) less than 1.0. An LI less than 1.0 does not necessarily require further intervention. For jobs with an LI between 1.0-2.0, administrative controls (and possibly simple engineering controls) should be considered and judgment should be exercised, depending on the situation. If a group of healthy, young and uninjured males work on a job with a calculated LI of 1.5, then the complex engineering controls may not be necessary. However, as the LI exceeds 2.0 and approaches 3.0, simple to complex engineering controls (and possibly supplemental administrative controls should be considered ). 15 16 17 18 19 20 21 22 23  DESIGN OF LIFTING TASK Ayoub (1982) has summarized many of the guidelines for the design of lifting tasks. These are presented, in modified form, in Tables 6.7, 6.8 and 6.9 Table 6.7 How to minimize the weight to be handled: 1. Assign the job to more than one person. 2. Use smaller containers. 3. If possible, mechanise the process. 4. Machines, rather than employees, should transfer loads between surfaces. 5. Change the job from lifting to lowering, from lowering to carrying, from carrying to pulling, and from pulling to pushing. 6. Use handles, hooks or similar features to enable workers to get a firm grip on objects to be lifted.b 7. Reduce the weight of containers used to transfer objects. 8. Balance and stabilise the contents of containers to avoid sudden shifts in load during a lift. 9. Design containers so that they can be held close to the body. 10. Treat work surfaces to allow for ease of movement of containers. 24  Table 6.8 How to minimize reach and lift distances: 1. Increase height at which lift is initiated; decrease height at which it terminates. 2. Stack objects no higher than shoulder height. 3. Store heavy components on shelves between shoulder and knuckle height. 4. Avoid deep shelves. 5. Avoid side to side lifting from seated position. 6. Provide access space around components to cut down on the need for manual repositioning. 7. Storage bins or containers should be fitted with spring-loaded bottoms. 8. Use sloped surfaces to gravity-feed items to the point of lifting. 9. Provide free space around and under the work surface to increase functional reach. 25  Table 6.9 How to increase the time available for lifting: 1. Increase the time by relaxing the standard time for the job. 2. Reduce the frequency of lifts. 3. Introduce job rotation to parcel out lifting between workers. 4. Introduce appropriate work–rest cycles. 26