Ergonomics is the science of fitting jobs to people.Ergonomics encompasses the body of knowledge about physical abilities and limitations as well as other human characteristics that are relevant to job design. Ergonomics design is the application of this body of knowledge to the design of tools, jobs and the workplace for safe and efficient use by workers. Good ergonomics design makes the most efficient use of worker capabilities while ensuring that job demands do not exceed those capabilities.
Ergonomics Muscular-Skeletal Disorders
Muscular-Skeletal Disorders from improper ergonomics are any injury or illness of soft tissues of the upper extremity (fingers through upper arm), shoulders and neck, low back, and lower extremity (hips through toes) that is primarily caused or exacerbated by workplace ergonomics risk factors, such as sustained and repeated exertions or awkward postures and manipulations. Included are disorders of the muscles, nerves, tendons, ligaments, joints, cartilage and spinal disks. Medical conditions that generally develop gradually over a period of time & do not typically result from a single instantaneous event. MSDs do not include injuries caused by slip, trips, falls, or other similar accidents. They can differ in severity from mild periodic symptoms to severe chronic and debilitating conditions.
Examples of MSDs from improper ergonomics include:
- Carpal tunnel syndrome
- Muscle strains
- Raynaud’s phenomenon
- Rotator cuff tendonitis
- De Quervains’ disease
- Carpet layers knee
- Trigger finger
- Low back pain
Signs of Muscular-Skeletal Disorders are objective physical findings.
Examples of signs of MSDs from improper ergonomics include:
- Decreased range of motion
- Decreased grip strength
- Loss of function
- Redness/loss of color
Symptoms of MSDs are physical indications that MSDs are developing. Symptoms can vary in their severity depending on the amount of exposure the employee has had. Often symptoms appear gradually as muscle fatigue or pain at work that disappears during rest. Usually symptoms become more severe as exposure continues (e.g., tingling continues when your employee is at rest, numbness or pain makes it difficult to perform the job, and finally pain is so severe that the employee is unable to perform physical work activities). Examples of symptoms MSDS from improper ergonomics include:
Stages of Musculoskeletal Injuries
Musculoskeletal injury may progress in stages: early, intermediate and late.
Early Stage: The body aches and feels tired at work but symptoms disappear during time away from work. Early warning signs, for example sore shoulders and neck pain, often occur after the work activity stops (e.g. when driving home after a day of work). The effects may also be noticed the next morning such as aches and stiffness in the limbs or hands.The injury does not interfere with the ability to work and should heal completely if appropriate precautions are taken.At this stage there are often no visible signs of a problem.
Intermediate Stage: The injured area aches and feels weak near the start of work and continues
until well after work has ended. Work becomes more diffi cult to do. However, the injury will still heal completely if dealt with properly. Visible signs may be present.
Late Stage: The injured area aches and feels weak, even at rest. Sleep disturbance is a common
complaint.Even non-demanding tasks are very difficult.The injury may not heal completely but
effects can be eased if dealt with properly. Visible signs may be present.
Not everyone goes through these stages in the same way. It may be diffi cult to say exactly when one stage ends and the next begins. The fi rst sign of pain is a signal the muscles and tendons should
rest and recover and that medical attention may be required. If there is no recovery an injury can become longstanding and sometimes irreversible.The earlier workers recognize signs & symptoms, the quicker the employer will be able to respond.
Ergonomics Muscular – Skeletal Disorder (MSD) Risk Factors
Risk hazards consist of numerous ergonomics elements such as conditions of a job process, work station, or work method. Not all the below listed risk factors will be present in every MSD-producing task, nor is the existence of one of these factors necessarily sufficient to cause a MSD from improper ergonomics.
- Repetitive and /or prolonged activities
- Forceful exertions
- Prolonged static postures
- Exposure to heat or cold
- Awkward postures, including reaching above the shoulders or behind the back.
- Twisting the wrists and other joints.
- Excessive vibration from power tools
- Inappropriate or inadequate hand tools.
- Continued bending at the waist.
- Continued lifting from below knuckles or above shoulders.
- Twisting at the waist, especially while lifting.
- Lifting or moving heavy objects.
- Lifting or moving asymmetric sized objects.
- Prolonged sitting, especially with poor posture.
- Lack of adjustable chairs, footrests, body supports, and work surfaces.
- Poor grips on handles.
- Slippery footing
MSD Hazard Control Methods
Ergonomics Engineering Controls, where feasible, are the preferred method for controlling MSD hazards. Engineering controls are the physical changes to jobs that control exposure to MSD hazards. Engineering controls act on the source of the hazard and control employee exposure to the hazard without relying on the employee to take self-protective action or intervention. Examples of ergonomics engineering controls for MSD hazards include changing, modifying or redesigning the following:
Ergonomics Work Practice Controls are controls that reduce the likelihood of exposure to MSD hazards through alteration of the manner in which a job or physical work activities are performed. Work practice controls also act on the source of the hazard. However, instead of physical changes to the workstation or equipment, the protection work practice controls provide is based upon the behavior of managers, supervisors and employees to follow proper work methods. Work practice controls include procedures for safe and proper work that are understood and followed by managers, supervisors and employees. Examples of work practice controls for improper ergonomics MSD hazards include:
Safe and proper work techniques and procedures that are understood and followed by managers, supervisors and employees.
Conditioning period for new or reassigned employees.
Training in the recognition of MSS hazards and work techniques that can reduce exposure or ease task demands and burdens.
Administrative Controls are procedures and methods, typically instituted by the employer, that significantly reduce daily exposure to MSD hazards by altering the way in which work is performed. Examples of administrative controls for MSD hazards from improper ergonomics include:
- Employee rotation
- Job task enlargement
- Adjustment of work pace (e.g., slower pace)
- Redesign of work methods
- Alternative tasks
- Rest breaks
Environmental Ergonomics Factors:
Heat/Cold: Excessive heat and humidity effects the body’s blood circulation and causes cramps, burns/rashes and general discomfort. Cold exposures also effects the body’s blood circulation and causes hypothermia, loss of flexibility, distraction and poor dexterity. A generally comfortable temperature range is 68 to 74 degrees Fahrenheit – +/-10 degrees depending on the physical work load – with humidity between 20 to 60 percent.
Noise Level/Peaks: Excessive noise levels above 90 decibels (dBA) and noise peaks above 100 decibels (dBA) cause headaches and increases blood pressure, muscle tension and fatigue. High exposure over a long period of time causes deafness and other audiological disorders. Short term exposure causes irritability and distraction.
Illumination: Under-and over-lighted areas causes headaches, muscle strains, fatigue and eye injury. It effects the body by reduced visual acuity, distractions, and glare interference. Poorly lighted areas also provides an atmosphere for trip/fall hazards and poor coordination. Illumination is measured with a light meter, similar to that used by a photographer. Recommended illumination (measured in foot-candles) by job type:
◦ General assembly 55 to 150
◦ Inspections 100 to 150
◦ Warehouse 50 to 100
◦ Storage 10 to 50
◦ Offices 100 to 200
Ergonomics Vibration: Excessive vibration causes pain to muscles, joints and internal organs; causes nausea and trauma to the hands, arms, feet and legs. Vibration is measured by its direction, acceleration and frequency on the body.
Ergonomics Environment: Otherwise known as work stress, included in this category are salary administration, job positions, rest breaks, Employee attitude, and boredom. Keeping the Employment Environment up-beat is difficult; however, light colored, well lighted, un-crowded and clean areas provide a positive environment. Employees should rest often depending on their work activity and temperature. Keeping the job moving and variation in activity reduces boredom.
Ergonomics Work Station Design
Using an old rule-of-thumb, if we try to design something that everyone can use, no one will be able to use it. The same principal holds true with ergonomic work station design. The idea of ergonomic work station design is to make it fit the user. It will have to be adjustable for many body heights, sizes, weights and reaches whether sitting or standing.
One of the first principals in Work Station Design is to consider the tallest Employee and the Employee with the shortest reach. The reason being is that we can not shorten an Employee’s height or lengthen an Employee’s reach. Platforms can be used to raise shorter Employees to the proper work height. Either sitting or standing, the Employee should be comfortable at his work station. The arms should rest at the Employees sides and the Employees back/neck should be kept straight; therefore, the work level must be waist-high.
Standing in one place for prolonged periods may lead to a host of injuries. Sit/stand work stations should be considered. If an Employee has to stand, providing something to lean on so the Employee will have the opportunity to rest. Also, providing a heavy rubber pad to stand on will help relieve neck, shoulder, back, and leg stress. Some common injury prone positions with the body effect are as follows:
Work Position Body Effect
Standing in one place Varicose veins, back stress pooling of blood in legs
Sitting without back support Low back stress
Chair too high Decreased circulation, (legs dangling over end) bruises
Shoulders rounded Upper/lower back stress, respiratory distress.
Leaning forward Lower back stress
Arms extended/over-reaching Stress to arm muscles, upper back stress
Elbows “winged” Joint stress at shoulder, poor use of bicep muscles
Stepping backwards Loss of balance, displaced gravity, muscle stress
Locking knees Stress to back of knee, poor blood circulation
With casual observation of work stations, each of these injury prone positions can be eliminated. Almost anytime an Employee has to raise a foot off of the floor to reach a moving or stationary object, they are hyper-extending and are in an injury prone position.
Ergonomics Tool Design
The last area of work station design is tool design. Many manufacturers are marketing tools that are “ergonomically designed”. However, just because a tool is ergonomically designed, it may do more harm than good. In many cases, just changing the way a toll is used may be and effective ergonomics solution.
Tools should be designed, modified or used in a manner which allows the hand to rest in a near neutral position. In some cases, heavy tools will need to be suspended from above, so the bulk of the weight is not supported by the Employee’s hands/arm. The handles of the tool should extend the full length of the palm, be soft/shock-resistant and large enough to be easily gripped. Trigger activated tools should be modified to allow multi finger operation which prevents the full required activation force from being applied by only one finger.
Ergonomics – Pro-Active Job Design
General Workstation Design Principles
1. Make the workstation adjustable, enabling both large and small persons to fit comfortably and reach materials easily.
2. Locate all materials and tools in front of the worker to reduce twisting motions. Provide sufficient work space for the whole body to turn.
3. Avoid static loads, fixed work postures, and job requirements in which operators must frequently or for long periods
— lean to the front or the side,
— hold a limb in a bent or extended position,
— tilt the head forward more than 15 degrees, or
— support the body’s weight with one leg.
4. Set the work surface above elbow height for tasks involving fine visual details and below elbow height for tasks requiring downward forces and heavy physical effort.
5. Provide adjustable, properly designed chairs with the following features
— adjustable seat height,
— adjustable up and down back rest, including a lumbar (lower-back) support,
— padding that will not compress more than an inch under the weight of a seated individual, and a
— chair that is stable to floor at all times (5-leg base).
6. Allow the workers, at their discretion, to alternate between sitting and standing. Provide floor mats or padded surfaces for prolonged standing.
7. Support the limbs: provide elbow, wrist, arm, foot, and back rests as needed and feasible.
8. Use gravity to move materials.
9. Design the workstation so that arm movements are continuous and curved. Avoid straight-line, jerking arm motions.
10. Design so arm movements pivot about the elbow rather than around the shoulder to avoid stress on shoulder, neck, and upper back.
11. Design the primary work area so that arm movements or extensions of more than 15 in. are minimized.
12. Provide dials and displays that are simple, logical, and easy to read, reach, and operate.
13. Eliminate or minimize the effects of undesirable environmental conditions such as excessive noise, heat, humidity, cold, and poor illumination.
Design Principles for Lifting and Lowering Tasks
1. Optimize material flow through the workplace by
- reducing manual lifting of materials to a minimum,
- establishing adequate receiving, storage, and shipping facilities, and
- maintaining adequate clearances in aisle and access areas.
2. Eliminate the need to lift or lower manually by
- increasing the weight to a point where it must be mechanically handled,
- palletizing handling of raw materials and products, and
- using unit load concept (bulk handling in large bins or containers).
3. Reduce the weight of the object by
- reducing the weight and capacity of the container,
- reducing the load in the container, and
- limiting the quantity per container to suppliers.
4. Reduce the hand distance from the body by
- changing the shape of the object or container so that it can be held closer to the body, and
- providing grips or handles for enabling the load to be held closer to the body.
5. Convert load lifting, carrying, and lowering movements to a push or pull by providing
- ball caster tables,
- hand trucks, and
- four-wheel carts.
PRIMARY RISK FACTORS
The force that a worker exerts on an object is aprimary risk factor. Muscles and tendons can be
overloaded when a strong (high) force is appliedagainst the object (load). A risk can also occur when a weaker (low) force is applied repeatedly (repetition) or continuously over a long period of time (duration). Exerting high or low muscle force can interfere with circulation, lead to muscle fatigue and tissue damage.
These conditions can result from:
- Gripping, pinching, holding
- Lifting, lowering
- Pushing, pulling, carrying
- Stopping a moving object or resisting the kickback from tools
Factors that affect the amount of force applied include:
- Size of the load
- Weight of the load
- Position of the load
- How often the load is handled
- How long of time the load is handled
Factors affecting grip force include:
- Grip Type – a pinch grip requires 5x the force of a power grip
- Wrist Posture – grip force decreases dramatically in flexion
- Grip Size – handle size will infl uence grip force
- Cold – results in increased force application
- Gloves – improperly fi tted gloves hinder the ability to have or maintain a good grip
- Vibration – vibrating tools cause an increase in the gripping force used to hold them
The effects of these forces can be made worse by:
- Slippery or odd shaped objects that are difficult to hold.
- Lack of handles or unsuitable handles on tools, or objects that are too small or too large.
- Awkward body positions, such as bending down or reaching forward or overhead.
- Vibrating tools or equipment.
- Poorly fi tted or inappropriate gloves.
Pinch grip Power grip
Repetition is the rate of recurrence with which a task or set of motions is performed. Using the same body part repeatedly to perform a task puts a worker at increased risk of MSI, as it does not allow for the rest or recovery of the affected muscles.
The effects of repetition can be made worse by:
- The task or motion is repeated at a high rate over long durations.
- There is not enough of a rest period to allow the stressed muscle or body part torecover.
- Repetition is combined with other risk factors such as high forces and/or awkward posture.
- When muscles and/or the body part is unaccustomed to task.
Contact stress occurs when a hard or sharp object comes in contact with a small area of the body.The tissues and nerves beneath the skin can be injured from the pressure. Local contact stress can
- Ridges on tool handles digging into fingers.
- Edges or work surfaces digging into forearms or wrists.
- Striking objects with the hand, foot, or knee.
The effects of local contact stress can be made worse if:
- The hard object contacts an area with minimal protective tissue,such as the wrist,palm,or fingers
- Pressure is applied repeatedly or held for a long time.
Examples of local contact stress. Local contact stress occurs when hard or sharp edges of tools or objects dig into the skin.