Workplace ERGONOMICS

What is the meaning of ERGONOMICS???

Ergonomics is the process of designing or arranging workplaces, products and systems so that they fit the people who use them. Ergonomics applies to the design of anything that involves people – workspaces, sports and leisure, health and safety.

Ergonomics is a branch of science that aims to learn about human abilities and limitations, and then apply this learning to improve people’s interaction with products, systems and environments. Ergonomics aims to improve workspaces and environments to minimize risk of injury or harm. So as technologies change, so too does the need to ensure that the tools we access for work, rest and play are designed for our body’s requirements.

What is the necessity of ERGONOMICS???

According to NIOSH, the total economic cost of work-related injuries and illnesses is estimated to be ?41151 crore. Recent research has shown that lower back pain is the world’s most common work-related disability – affecting employees from offices, building sites and in the highest risk category, agriculture. Ergonomics aims to create safe, comfortable and productive workspaces by bringing human abilities and limitations into the design of a workspace, including the individual’s body size, strength, skill, speed, sensory abilities (vision, hearing), and even attitudes.

How ERGONOMICS works???

Ergonomics is a relatively new branch of science, but relies on research carried out in many other older, established scientific areas, such as engineering, physiology and psychology.

To achieve best practice design, Ergonomists use the data and techniques of several disciplines:

• Anthropometry: body sizes, shapes; populations and variations
• Biomechanics: muscles, levers, forces, strength
• Environmental physics: noise, light, heat, cold, radiation, vibration body systems: hearing, vision, sensations
• Applied psychology: skill, learning, errors, differences
• Social psychology: groups, communication, learning, behaviours.

The word "Ergonomics" comes from two Greek words "ergon", meaning work, and "nomos" meaning "laws". Today, however, the word is used to describe the science of "designing the job to fit the worker, not forcing the worker to fit the job." Ergonomics covers all aspects of a job, from the physical stresses it places on joints, muscles, nerves, tendons, bones and the like, to environmental factors which can effect hearing, vision, and general comfort and health.

Physical stressors include repetitive motions such as those caused by typing or continual use of a manual screwdriver. Other physical stressors could be tasks involving vibration such as using a jackhammer, or tasks which involve using excessive force, such as lifting boxes of heavy books. Working in an awkward position, such as holding a telephone to your ear with your shoulder, can also cause problems. Repetitive motions, vibration, excessive force, and awkward positions are frequently linked to ergonomic disorders; however, the majority of "Cumulative Trauma Disorders "(CTDs) or "Repetitive Strain Injuries" (RSIs), are caused by repetitive motions that would not result in undue stress or harm if only performed once. Carpal tunnel syndrome, Tendonitis, Tenosynovitis, DeQuarvain's Syndrome, Thoracic Outlet Syndrome, many back injuries, and several other conditions may result from repetitive motions.

Environmental factors could include such things as indoor air quality or excessive noise. "Sick building syndrome", with its accompanying headaches, congestion, fatigue and even rashes, can result from poor air quality in a building or office. Excessive noise around heavy machinery or equipment can cause permanent hearing loss. Improper lighting can cause eyestrain and headaches, especially in conjunction with a computer monitor.

Over time, poor posture may be caused by habits from everyday activities such as sitting in office chairs, looking at the computer, driving, standing for long periods of time, or even sleeping. Poor posture can easily become second nature, causing or aggravating episodes of back pain and damaging spinal structures. Fortunately, the main factors affecting posture and ergonomics are within one’s ability to control and are not difficult to change. The following guidelines suggest several ways to improve posture and ergonomics, especially for people who work sitting in an office chair for most of the day. Ergonomics is the study of improving the fit between the worker and the physical demands of the workplace. Ergonomics can be used to reduce injuries, improve productivity, and reduce the costs of doing business.

The construction industry suffers from debilitating and costly occupational injuries primarily to workers’ backs, necks, shoulders, hands, and arms. These types of injuries or traumas are commonly called repetitive motion injuries (RMIs) and are caused by activities that are repeated on a regular basis. Symptoms of RMIs may include chronic pain, numbness, tingling, weakness, and limited range of motion. RMI symptoms may not be noticeable for months or even years after exposures or may appear to be acute after a sudden and severe onset.

1. Factors that can contribute to RMIs:
2. Awkward postures
3. Forceful exertion, including heavy lifting

• Repetitive work

1. Vibration from tools and equipment
2. Pinching (contact stress) during tool use and material handling
3. Temperature extremes

• Lack of recovery time to affected body parts

1. Knowledge of ergonomic principles can be used to produce simple changes in the workplace and work activities which in turn can avoid injury, improve productivity, and make jobs easier.

• Employers must establish and implement a program designed to minimize RMIs if more than one person is diagnosed with RMIs as follows:

1. The RMIs are work related.
2. The employees incurred the RMIs while performing a job process or operation of identical work activity.

• The RMIs were reported in the past 12 months.

1. A licensed physician objectively identified and diagnosed the RMIs.

• The program must include the following:

1. A work site evaluation
2. Control of exposures that caused the RMIs

• Training of employees.
• Some ways to eliminate or reduce RMIs:

1. Proper lifting and material handling
2. Use of equipment to reduce load and strain

• Employee rotation for repetitive tasks

1. Use of ergonomically designed tools
2. Use of personal protective equipment
3. Appropriately timed rest periods

Some key points need to understand before you think of ergonomics:-

• Knowing the warning signs of back pain caused by poor ergonomics and posture:-

 Back pain may be the result of poor ergonomics and posture if the back pain is worse at certain times of day or week (such as after a long day of sitting in an office chair in front of a computer, but not during the weekends.); pain that starts in the neck and moves downwards into the upper back, lower back and extremities; pain that goes away after switching positions while sitting or standing; sudden back pain that is experienced with a new job, a new office chair, or a new car; and/or back pain that comes and goes for months.

• Get up and move:-

 As muscles tire, slouching, slumping, and other poor postures become more likely; this in turn puts extra pressure on the neck and back. In order to maintain a relaxed yet supported posture, change positions frequently. One way is to take a break from sitting in an office chair every half hour for two minutes in order to stretch, stand, or walk. Stretching really helps ease muscle tension.

• Keep the body in alignment while sitting in an office chair and while standing:-

 Distribute body weight evenly to the front, back, and sides of the feet while standing. While sitting in an office chair, take advantage of the chair’s features. Sit up straight and align the ears, shoulders, and hips in one vertical line. Any single position, even a good one, will be tiring. Leaning forward with a straight back can alternate with sitting back, using the back support of the office chair to ease the work of back muscles. Also be aware of and avoid unbalanced postures such as crossing legs unevenly while sitting, leaning to one side, hunching the shoulders forward or tilting the head.

• Use posture-friendly props and ergonomic office chairs when sitting:-

 Supportive ergonomic “props” can help to take the strain and load off of the spine. Ergonomic office chairs or chairs with an adjustable back support can be used at work. Footrests, portable lumbar back supports, or even a towel or small pillow can be used while sitting in an office chair and while driving. Using purses, bags, and backpacks that are designed to minimize back strain can also influence good posture. Proper corrective eye-wear, positioning computer screens to your natural, resting eye position can also help to avoid leaning or straining the neck with the head tilted forward.

• Use exercise to help prevent injury and promote good posture:-

Regular exercise such as walking, swimming, or bicycling will help the body stay aerobically conditioned, while specific strengthening exercises will help the muscles surrounding the back to stay strong. These benefits of exercise promote good posture, which will, in turn, further help to condition muscles and prevent injury. There are also specific exercises that will help maintain good posture. In particular, a balance of trunk strength with back muscles about 30% stronger than abdominal muscles is essential to help support the upper body and maintain good posture.

• Wear supportive footwear when standing:-

 Avoid regularly wearing high-heeled shoes, which can affect the body’s center of gravity and change the alignment of the entire body, negatively affecting back support and posture. When standing for long periods of time, placing a rubber mat on the floor can improve comfort.

• Remember good posture and ergonomics when in motion:-

Walking, lifting heavy materials, holding a telephone, and typing are all moving activities that require attention to ergonomics and posture. It is important to maintain good posture even while moving to avoid injury. Back injuries are especially common while twisting and/or lifting and often occur because of awkward movement and control of the upper body weight alone.

• Create ergonomic physical environments and workspaces, such as for sitting in an office chair at a computer:-

It does require a small investment of time to personalize the workspace, home, and car, but the payoff will be well worth it. Undue strain will be placed\ on the structures of the spine unless the office chair, desk, keyboard, and computer screen, etc. are correctly positioned.

• Avoid overprotecting posture:-

Remember that it is important to maintain an overall relaxed posture to avoid restricting movements by clenching muscles and adopting an unnatural, stiff posture. For individuals who already have some back pain, it is a natural tendency to try to limit movements to avoid the potential pain associated with movement. However, unless there is a fracture or other serious problem, the structures in the spine are designed for movement and any limitation in motion over a long period of time create more pain and a downward cycle of less motion and more pain, etc.

1. Ergonomics in Lifting:-

Lifting of any object without following ergonomics rules can end up with different type of musculoskeletal diseases. So there is equation which is called lifting equation developed by the NIOSH to calculate the manual material handling risk associated with the lifting and lowering task in the workplace. It may help to calculate the job task variables to determine safe lifting practices and guideline.

Recommended weight limit:-

Recommended weight is the maximum acceptable weight (load) that nearly all healthy employees could lift over the course of their shift of 8 hours without increasing the risk of musculoskeletal disorders (MSD) to the lower back.

Lifting index:-

Lifting index is calculated to provide a relative estimate of the level of physical stress and MSD risk associated with the manual lifting tasks evaluation.

                                       LI<1.0 (Nominal risk to healthy employees)

                                       LI>1.0 (High risk to healthy employees)

                                       LI is directly proportional to low back injury

So the aim of the lifting equation is to reduce the value of lifting index < 1.0.

Recommended weight limit lifting equation:-

                          RWL= LC*HM*VM*DM*AM*FM*CM

Where,

LC= load constant

HM= horizontal multiplier

VM= vertical multiplier                                 

DM= distance multiplier

AM= asymmetry multiplier

FM= frequency multiplier

CM= coupling multiplier

Multiplier:- the term multiplier refers to the reduction coefficients that serve to decreases the load constant.

Lifting index:- Lifting index is a term that provides a relative estimate of the level of physical stress associated with a particular manual lifting task. Lifting task with a lifting index greater than 1.0 posed an increased risk for lifting related low back injury. If the magnitude of lifting index increases, then

• The level of the risk for the worker performing the job would be increased.
• A greater percentage of the workforce is likely to be at risk for developing lifting related low back injury.
• If lifting index is 3.0 then work is highly stressful lifting tasks.

 Task data variables:-

1. Horizontal location:-

Horizontal Location (H) Horizontal Location (H) is measured from the mid-point of the line joining the inner ankle bones to a point projected on the floor directly below the mid-point of the hand grasps (ie. load center), as defined by the large middle knuckle of the  hand.

Horizontal Location (H) should be measured. In those situations where the H value cannot be measured, then H may be approximated from the following equations:

• for V = >25 cm H = 20 cm + W/2

 

• V <25 cm H = 25 cm + W/2

 

Where: W is the width of the container in the sagittal plane and

                V is the vertical location of the hands from the floor.

1. Vertical Location (V):-

Vertical Location (V) is defined as the vertical location of the hands above the floor at origin of lift. V is measured vertically from the floor to the mid-point between the hand grasps, as defined by the large middle knuckle.

• Vertical Travel Distance (D):-

The Vertical Travel Distance (D) is defined as the vertical travel distance of the hands between the origin and destination of the lift.

D = V destination – V origin

The vertical distance (D) is assumed to be at least 25 cm, and not greater than 175 cm. If the vertical travel distance is less than 25 cm, then D should be set to the minimum distance of 25 cm.

1. Asymmetric Angle (A):-

Asymmetry refers to a lift that begins or ends outside the mid-sagittal plane. The asymmetry line is defined as the horizontal line that joins the mid-point between the inner ankle bones and the point projected on the floor directly below the mid-point of the hand grasps, as defined by the large middle knuckle. The sagittal line is defined as the line passing through the mid-point between the inner ankle bones and lying in the mid-sagittal plane, as defined by the neutral body position (ie. hands directly in front of the body, with no twisting at the legs, torso or shoulders). The asymmetric angle is not defined by foot position or the angle of torso twist, but by the location of the load relative to the worker's mid-sagittal plane.

1. Lifting Frequency (F):-

Average number of lifts per minute, as measured over a 15 minute period. If the worker does not lift continuously for 15 minutes, we need to use a special procedure to determine the appropriate lifting frequency. This procedure is presented below:

1. Compute the total number of lifts performed for the 15 minute period Lifting rates x work time Lifting rate: the number of actual lifts per minute
2. Divide the total number of lifts by 15: Total number of lifts 15

Lifting above the maximum frequency results in RWL of 0.0. (Except for the special case of discontinuous lifting discussed above, where the maximum frequency is 15 lifts/minute.)

1. Coupling (C):-
   • Coupling refers to the relationship between the hands and the Coupling Classification Coupling must be classified as good, fair, or poor dependent on the nature and dimensions of the object and gripping method.

GOOD Containers of optimal (boxes, crates, etc.) with handles or hand-hold cut-outs of optimal. Loose parts or irregular objects (castings, stock, and supply materials): comfortable grip in which the hand can be easily wrapped around the object FAIR Containers or/objects of optimal with handles or hand-hold cut-outs less than optimal design. Containers of optimal with no handles or hand-hold cut-outs. Loose parts or irregular objects: coupling classified as FAIR if the hand can flex about 90 degrees when gripping. POOR Containers of less than optimal design. Non-rigid bags, sagging bags. The effectiveness of the coupling may vary with the distance of the object from the ground, so that  a good coupling could become a poor coupling during a single lift. The entire range of the lift   should be considered when classifying hand-to-object couplings, with classification based on overall effectiveness.

A container is considered less than optimal if it has a frontal length less than 40 cm, height less than 30 cm, rough or slippery surface, sharp edges, asymmetric center of mass, unstable contents, or requires the use of gloves. An optimal hand-hold cut-out has the following approximate characteristics: less than or equal to 3.8 cm height, 11.5 cm length, semi-oval shape, less than or equal to 5 cm clearance, smooth non- slip surface, and less than or equal to 0.60 cm container thickness (e. g. double thickness cardboard). Significant Control Significant control is defined as a condition requiring precision placement of the load at the destination of the lift. This is usually the case when the worker has to : (1) re-grasp the load near the destination of the lift, or (2) momentarily hold the object at the destination,  or (3) carefully position or guide the load at the destination.

Coupling classification:-

1. Good
2. Fair
3. Poor
4. Good:- contains of optimal design (boxes, crates etc.) with handles or hand hold cut outs of optimal design (40*30).
5. Fair:- Loose parts or irregular objects (castings, stock, supply materials) comfortable grip in which the hand can be easily wrapped around the object.

• Frequency independent recommended weight limit:-

FIRWL=23*HM*VM*DM*AM*CM

• Single task recommended weight limit(STRWL) for each task:-

STRWL=FIRWL*FM

• Frequency independent lifting index(FILI) for each task:-

FILI=object weight*FIRWL

• Single task lifting index(STLI):-

STLI=object weight*STRWL

RAPID ENTIRE BODY ASSESSMENT(REBA):-

This ergonomic assessment tool uses a systematic process to evaluate whole body postural MSD and risks associated with job tasks. A single page worksheet is used to evaluate required or selected body posture, forceful exertions, type of movement or action, repetition, and coupling. REBA is a postural targeting method for estimating the risk of work related entire body disorders. A REBA assessment gives a quick and systematic assessment of the complete body postural risk to a worker.

RAPID UPPER LIMB ASSESSMENT(RULA):-

RULA was developed to evaluate the exposure of individual workers to ergonomic risk factors associated with upper extremity MSD. The RULA ergonomic assessment tool considers biomechanical and postural load requirements of job tasks/demands on the neck, trunk and upper extremities. A single page worksheet is used to evaluate required body posture, force, and repetition. Based on the evaluations, scores are entered for each body region in section A for the arm and wrist, and section B for the neck and trunk. After the data for each region is collected and scored, tables on the form are then used to compile the risk factor variables, generating a single score that represents the level of MSD risk.

The RULA was designed for easy use without need for an advanced degree in ergonomics or expensive equipment. Using the RULA worksheet, the evaluator will assign a score for each of the following body regions: upper arm, lower arm, wrist, neck, trunk, and legs. After the data for each region is collected and scored, tables on the form are then used to compile the risk factor variables, generating a single score that represents the level of MSD risk as outlined below:

In a comprehensive MSD prevention process: 

• Ergonomic issues are systematically identified and resolved with cost effective solutions.
• Employees are educated on proper lifting techniques, ergonomic principles, body mechanics and self-care tools and
• Costly injuries are averted with a proactive, prevention-focused approach (early intervention) that seeks out and eliminates worker fatigue and

Suzanne Rodgers:-

The Muscle Fatigue Analysis was proposed by Rodgers as a means to assess the amount of fatigue that accumulates in muscles during various work patterns within 5 minutes of work. The hypothesis was that a rapidly fatiguing muscle is more susceptible to injury and inflammation. With this in mind, if fatigue can be minimized, so should injuries and illnesses of the active muscles. This method for job analysis is most appropriate to evaluate the risk for fatigue accumulation in tasks that are performed for an hour or more and where awkward postures or frequent exertions are present. Based on the risk of fatigue, a Priority for Change can be assigned to the task.

Using the task identification sheet, divide a job into tasks and determine what percent of the shift each task is done. Identify which tasks are perceived as “difficult” by people on the job. Do the analysis on the primary tasks performed (those done for more than 10% of the shift) and on any tasks considered “difficult”, no matter how much of the job they constitute.

Use a separate Task sheet for each task. For a task and for each body region, assess the three job risk factors by assigning each factor a rating by category. The task data sheet provides a format for this process. Descriptions of Effort Levels for the different body regions, Continuous (single) Effort Duration and Effort Frequency are provided on the data collection form. Within a body region, once an Effort Level is chosen to represent the task, the assignment of Continuous Effort Time and Efforts per Minute should be associated with the chosen effort. Notes: If the effort level is high enough that most workers cannot accomplish it, if the continuous effort duration is greater than 30 sec, or if the frequency is greater than 15 / min, then there is sufficient reason to assign a Very High priority for change.

The Priority for Change is found by locating the combination of scores in the various categories in the table on task identification data sheet. Note: A combination of 3 and 3 for Duration and Frequency is not possible. The table provides an indication of relative risk for fatigue within a category. The earlier the combination of categories is in the list the lower the fatigue should be (i.e., it is better).

In this method three factors are evaluated

1. Effort
2. Duration
3. Frequency

 

 

Results:-

The results is a number with three digits. The first digit represents effort. The second digit represents effort duration and the third digit represents effort frequency.

The priority of change is found on the table:-

Green zone- low priority for change

Yellow zone- moderate priority for change

Purple zone- high priority for change

Red zone- very high priority for change

 

Moore and Garg (strain index):-

The Strain Index was proposed by Moore and Garg as a means to assess jobs for risk of work-related musculoskeletal disorders (WRMSDs) of the distal upper extremities (hand, wrist, elbow). Divide a job into tasks. For each task and for each hand, assess the six job risk factors by assigning it to a category. The following data sheet provides a format for this process. For each category, note the rating. The Strain Index is the product of the six ratings.

Strain index has six factors those are:-

1. intensity if exertion
2. duration of exertion
3. efforts per minute
4. hand/wrist posture
5. speed of work
6. duration of task

LEHMAN information:-

Lehman information is used to calculate the body metabolism of the worker depending upon the type of work the worker is doing.

Metabolism= Metabolism (position of the body)+ metabolism (description of the work)

 

Anthropometry:-

Anthropometry is the study of human body measurement and can be used for the design of the office furniture and work benches to fit for the worker not the worker to fit in the working environment. The design value obtained from the software can be taken as a reference and according to that value we can design the office assets for the workers or employees.

Anthropometry covers the following charactericts;-

1. The distance between the elbow and floor-typing
2. Distance between the surface of the table and floor-typing
3. Recommended height for the seat
4. Length of forearm and hand (normal reach limit)
5. Distance between thigh and toes-sitting (minimum space for the legs under the table)
6. Distance between the surface of the tables and eyes
7. Width of the shoulders
8. Height
9. Distance between floor and eyes
10. Distance between floor and foot(thigh should be 900)
11. Distance between elbow and floor
12. Length of arm and hand to thumb
13. Maximum reachable hand to thumb (arm: 450)
14. Width of the hand
15. Length of the hand
16. Length of the foot
17. Width of the foot
18. Length of forearm and hand to thumb(optimum distance from coupling)
19. Width of thigh
20. Distance between seat and the lower part of the table
21. Distance between the top of the head and shoulders
22. Distance between shoulder and forearm
23. Distance between forearm and knee
24. Distance between knee and heel
25. Distance between floor and heel
26. Distance between the top of the head and the surface of the seat
27. Length of upper arm

Calculation of force:-

In many case it is important to calculate the force to carry an object. We have to calculate the force in different situations.

• Lifting
• Pulling/pushing (horizontal plane)
• Pulling/pushing (inclined plane)

Before calculating the force in pulling or pushing an object the following data’s are required:-

• Mass of the object
• Coefficient of friction

This above mentioned information are mandatory but the aerodynamic force may be needed for the calculation. In the aerodynamic drag method the following data may be needed.

• Speed(m/s)
• Cross sectional area (m2)
• Coefficient of drag
• Density of air (1.176kg/m3)

Heat stress-measurement of WBGT:-

WBGT is the wet bulb globe temperature index. Indoor or outdoor with no solar load.

 WBGT= 0.7*NWB+ 0.3*GT

Outdoors with solar load

WBGT= 0.7*NWB+ 0.2*GT+ 0.1*DB

Where NWG= natural wet-bulb temperature

GT- globe thermometer temperature

DB- dry-bulb(air) temperature

Noise exposure:-

The time duration (T) is calculated by the following formula

                                                           

 

Where T= time duration

             L= sound level

Typing evaluation:-

Typing evaluation is done by the following formula

If the number of keys typed per hour is more than maximum number of keys per hour then it is bad, which is not acceptable number of keys. The number of keys per hour must be lower than the maximum number of keys per hour.https://www.youtube.com/watch?v=QeDUCXfzl6U