ERGONOMICS-2

Ergonomics

SECONDARY RISK FACTORS

Environmental Conditions:

Cold Temperatures

People who work outdoors – on construction sites, doing avalanche surveys, or work on loading docks – face additional risk of injury aggravated by cold. Cold temperatures produce a reduction in the hands ability to feel (tissue sensitivity), function (dexterity) and grip strength. It also makes muscles and joints stiffer, and increases reaction time. As a consequence, workers must use greater force to grip and hold hand tools, which increases the risk of an MSI.

The effects of cold temperatures can be made worse by:

  • Not dressing appropriately for the environment and activity e.g. for physically active work, wear layers of clothing that can be removed as the worker warms up. For less active work, more layers may be needed.
  • Not keeping the head covered to retain body heat and not keeping the feet warm and dry.
  • Lifting or forceful exertion when chilled; stiff joints and muscles increase the risk of injury.

Vibration

Vibration affects tendons, muscles, joints and nerves. Vibration to a specific body part can decrease sensitivity and result in unnecessary increases in muscle contraction, which may lead to injury or fatigue of that part. Localized vibration from machines and hand tools can damage the nerves and blood vessels of the hands and arms. Whole-body vibration, experienced by people who operate heavy equipment such as truck and bus drivers, increases the risk of lower back pain and damage to the spinal discs. The body’s response depends on the duration, frequency and extent of the vibration.

The effects of vibration can be made worse by:

  • Machines and power tools that are not maintained. Well-maintained equipment minimizes vibration.
  • Not limiting exposure to vibration by failing to implement work practices and administrative controls such as task rotation and rest breaks.
  • Not wearing appropriate personal protection equipment where required e.g. vibration dampening gloves.
  • Simultaneous exposure to cold temperatures.

Illumination

Appropriate lighting and elimination of glare in the work area allows for adequate depth perception and contrast by the worker(s) when handling material such as when lifting and carrying objects. Improper lighting can be a contributing factor to a musculoskeletal injury. For example, poor lighting could cause the worker to misjudge weight and object shape resulting in inappropriate or poor lifting techniques.

The effects of illumination can be made worse by:

  • Lighting is not maintained e.g. replacing burned out bulbs.
  • Lighting in the work area was not designed for the type of work tasks being performed.

Characteristics of the organization of work

Work recovery cycles and task variability:

The objective of planned work recovery cycles and task variability is to avoid the onset of fatigue of specifi c muscles or body parts, which can put workers at an increased risk of injury.

Work recovery cycles and task variably can include rotating jobs, performing tasks with different physical or mental demands, or a rest break. The need for recovery cycles and task
variability depends on:

  •  the nature of the task,
  •  worker characteristics, and
  •  environmental conditions.

Fatigue increases the risk of injury. Risk of injury depends largely on the ratio of work period to work recovery cycles/task variably, that is, the recovery time compared to exertion. Risk control for work

recovery cycles and task variably:

The demands of physical handling should be well below the normal exhaustion level for the worker. When developing work recovery cycles and task variability for a specifi ed task consider work rate, load weights and whether tasks involve vigorous or minor exertions.

To vary physical demands, consider alternating physical task with non-physical tasks, or long cycle tasks with shorter ones, or to a task where the demands on specifi c muscle and body parts are  sufficiently different. Ideally,workers should be given the flexibly to vary  type of tasks they perform.

Review the adequacy of work recovery cycles and task variability whenever there are changes in any
of these factors:

  •  The requirements of a task
  •  Environmental conditions
  •  The work process
  •  Physical capacity of workers

 

Work rate:

Individual workers vary in the rates at which they perform the same task. Some individuals need longer periods to recover from physical work to prevent injury.

The more critical or physically demanding the task, the more desirable it is to let the worker set the pace, where possible. Just as important, where possible, is to avoid sudden increase in workload.

Planning the work rate will also involve consideration of work recovery cycles/task variability and staffing schedules.

Other Considerations

Risk Factors can overlap:

More than one risk factor can be present in a task. The more risk factors in the task, the greater the
risk of injury. For example:

A worker bends forward from the waist to lift a box from the floor. The bending is an awkward posture (work posture) linked to the location of the box (out of proper lifting/bending* range?) on the floor (layout of the workplace). The box is wrapped with twine, which the worker grabs to lift the box (contact stress). If the worker repeatedly lifts boxes from the floor (repetition), or does similar lifting tasks all day (long duration, organization of work tasks), the risk of MSI is further increased.

Eliminating or Minimizing Risk Factors:

After identifying and assessing risk factors, the next step is to determine which control measures
should be implemented, and which ones eliminate or minimize the risk of MSI. Ask the following questions when considering control measures:

  •  Can exposure to the risk factor be eliminated?
  •  How can the intensity/magnitude of the job duty be reduced?
  •  Can frequency of the job function be reduced?
  •  Can duration be reduced?

Control measures for eliminating or minimizing risk factors:

  • Engineering Controls
  •  Administrative Controls
  •  Personal Protective Equipment (PPE) Controls

Engineering controls

The purpose of engineering controls is to design (or change by redesign) physical aspects of the workplace or tools to reduce or eliminate employee exposure to ergonomic risk factors. Engineering controls are preferred over other control methods. They are relatively permanent and benefit anyone performing the job – not just the individual who experienced an MSI.

Some examples are: adjusting work heights, minimizing reach distances, changing the layout of workstations, using adjustable or angled tools or equipment and the use of carts and other conveyors.

Administrative Controls

Administrative control functions include determining appropriate policy, procedures, education and training activities that affect the individual worker and the work environment. These actions are intended to reduce the workers’ exposure to MSI risks. This can be accomplished by reducing the duration of exposure and/or slowing the onset of fatigue and discomfort. For example, by ensuring that repetitive or demanding tasks incorporate opportunities for rest or recovery breaks (e.g. allow brief pauses to relax muscles; change work tasks; change postures or techniques).

To be effective, administration controls require:

  •  support by management,
  •  education and training,
  •  employee awareness of risk factors, and
  •  monitoring to ensure effectiveness of program and compliance of WCB requirements.

Personal Protective Equipment

Personal protective equipment may only be used as a substitute for reducing MSI risk factors where
engineering and administrative controls are not practicable. For example, workers may wear vibration-dampening gloves while using a chain saw or wear knee pads while working on their knees to install flooring.

 

MANUAL MATERIAL HANDLING:

Manual handling (i.e. lifting, carrying, pushing and pulling) of heavy, bulky, and/or irregularly shaped objects during work tasks) can lead to possible musculoskeletal injures. Under these circumstances a worker is more susceptible to injury as these type of tasks often require using awkward body postures, which can place considerable physical demands on the body, especially the back. The following information lists potential causes of MSI where such tasks are performed, as well as, examples of ways to prevent injuries (control measures) while performing these tasks.

Manual material handling examples:

  • manually loading and unloading material from vehicles, boxes or pallets
  • manually moving materials in warehouses, offices or outdoor work locations
  • stocking shelves, etc.

This section on material handling is divided into the following categories:

  • Lifting
  • Carrying
  •  Extended reaching
  •  Working heights
  •  Pushing/pulling

Lifting

Lifting of heavy, bulky, and/or irregularly shaped items can increase the risk of MSI’s. Lifting too
heavy a load puts unnecessary strain on the body, particularly the back.Proper lifting techniques play an important role in ensuring no injuries occur while performing these tasks (e.g. hold object close to the body and lift with the legs not the back). It is important that lifting be performed between the shoulder and knuckles height.

Knuckle height is when the arms are straight down in front of the worker, the height above the floor where the knuckles of the hands are located is the lowest height a worker should be lifting from or bending down to. Lifting and handling materials above shoulder level or below knuckle level (particularly while bending or twisting) adds unnecessary stress to the spine and back muscles.

In some cases lifting may have to be performed from the floor level. Where a mechanical lift is
unavailable and the material does not allow for the proper use of body mechanics, workers must be trained in proper lifting procedures (e.g. seek assistance from a co-worker).

Control Measures:

  • Restrict lifting to between knuckle and shoulder height.
  •  Minimize frequency of lift.
  •  Where possible separate the material into more manageable loads.
  • Don’t put a load(s) on the fl oor if it needs to be manually lifted again later.
  •  When moving an item, test its weight before lifting.
  •  Don’t overestimate your ability to handle heavy items.
  •  Get as close as possible to loads and get a firm grip before lifting.
  •  Position yourself so that you are facing your load.
  •  Avoid reaching, twisting and bending.
  •  Be sure of your footing before performing the lift.
  •  Where feasible, provide lifting aids (lift tables, mechanical or powered assists, hoists, etc.) to move heavy or bulky loads.
  •  Ask for assistance if in doubt.
  •  Establish safe lifting work procedures and ensure workers are trained in them.

Carrying

Depending on the distance an object is carried,it’s weight and size, there may be unnecessary strain placed on the body for long duration’s, which can attribute to an increase of MSI. It is important to be aware that the weight that can be safely carried by hand is less than the amount that can be safely lifted. This is due to the fact that carrying involves holding the object for a longer period in combination of having to physically move it. The longer the holding time (i.e.distance of travel while carrying object) the less weight that can be carried; the limiting factor is fatigue of the grip and shoulder muscles.

The grade of the floor is also a factor – carrying uphill or downhill increases the strain on the body, especially on stairways.

Control Measures:

Eliminate the need to carry by:

  • Using a cart, dolly, or pallet jack.
  •  Using a conveyor.
  •  Rearranging the work place.
  •  Providing slides or tables between workstations.

If elimination of carrying is not feasible:

Reduce the weight by:

  •  Reducing the size of the object.
  •  Using lighter material for the object.
  •  Reducing the capacity of the container.
  •  Reducing the weight of the container itself.
  •  If unable to reduce the weight, ask for assistance to move the object.

Reduce the distance material is carried by:

  • Moving the operation closer to the previous or following operation.
  •  Using conveyors or rollers.
  •  Changing the layout of the workplace.

Note: If carrying can not be eliminated, provide proper handles on object to ensure a good grip and proper positioning of object when carried by worker(s).

Extended Reaching

Extended reaching occurs when workers are required to reach to heights or distances outside of the range from knuckle to shoulder height, and more than about 18 inches from the front of the body. This can require bending, twisting, stretching, and holding the arms up high or other awkward postures. In such postures, the weight of objects (and even of the body itself) creates greater stress on muscles and tissues due to the “lever effect”. Extended reaching can cause musculoskeletal injuries to the neck and shoulders.

Control Measures:

  •  Adjust work stations, fi xtures, parts, tools, etc. to put the most-used items within easy reach.
  •  Keep workplaces clear of obstructions which increase reaching.
  •  Use platforms, step stools or other such aids to reach locations above shoulder height.
  •  Support or counter balance tools that are used above chest level.
  •  Limit or avoid reaching to full arms length for or with loads, or exerting force with the arm extended.
  •  Provide turntables, to allow easy access from all side.

 

Working Heights

Poor working heights in combination with any of the following can increase the risk of MSI:

  •  duration of work,
  •  repetition,
  •  high forces,
  •  weight,
  •  static loading, and
  •  cold.

If the work area is raised too high,the shoulders and arms must frequently be lifted upto compensate, which may lead to cramping and fatigue in the neck and shoulders.

If work heights are too low, the back and neck must be bent forward which can lead to neck and back pain or discomfort.

Ideally the height of work surfaces or the height of the worker’s position should be adjustable to
allow the employee to work from an appropriate neutral position at all times.

Control Measures:

Work at an appropriate height by using:

  •  False bottom bins and lift tables to change the product height and reduce the need to bend or stoop.
  • Adjustable working platforms, stools, and ladders to allow for neutral positions of the limbs, neck and torso.
  •  Tilt tables (e.g. drafting tables) to bring work closer.
  •  Extended handles on tools.

Reduce the demand on the body by:

Limiting the period of time required to perform an operation that is overhead, to the side, or down low. This can be accomplished by changing tasks frequently (e.g. paper work that may be normally completed at the end of the shift could be done in intervals through out the day to allow the body to recover).

The right work angle keeps the shoulder in a more comfortable position.

Pushing/Pulling

The greater the force required to push or pull an object, the greater the risk of developing an MSI.
In general, pushing a load is preferable to pulling a load. While pulling a load, arm and shoulder extension and abduction (working behind the mid-line of the body) and twisting may create an MSI risk factor.

Posture is a key factor in limiting how much force can be exerted in pushing and pulling. With extended reaches, or other awkward postures, less force can be exerted. On the other hand, by leaning into a push or away from a pull, the operator can apply more force. For example, pushing a heavy hand truck down a long corridor is usually possible because the large muscles of the legs and trunk can be used. Moving the same hand truck in a tight space where upright posture must be maintained is more difficult because the smaller arm muscles must be used to maneuver it.

Push or pull force is affected by:

  •  Body weight.
  •  Height of the work (height of handles).
  •  Distance of force application from body, or amount of trunk flexion/extension.
  •  The amount of friction between the worker’s shoes and the floor.
  •  How long the force must be applied.
  •  The distance the object must be moved.
  •  The availability of a brace or structure for the worker to push against.
  • The texture of the floor surface e.g. carpet, smooth, slippery.
  •  Debris on surface areas.

Control Measures:

Eliminate the need to push or pull by using:

  •  Conveyor system.
  •  Fork lift.
  •  Slide, chute, etc.
  •  Powered carts instead of hand carts.

Reduce the force by:

  •  Reducing the weight or size of the load.
  •  Using wheels and casters.
  •  Improving the size, composition, tread,maintenance and swivel properties of wheels on carts.
  •  Using ramps.
  •  Regular maintenance of equipment and floor surfaces e.g. lubrication of equipment; keep floor surfaces clean and clear of debris.
  •  Redesigning the work area to minimize how far items need to be moved.
  •  Installing automatic doors.
  •  Making friction work for the worker– minimize the friction on the object (i.e. don’t push on carpets) and maximize traction for the worker by wearing appropriate shoes.
  • Providing well-designed handles in appropriate locations.

ERGONOMICS 1

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
  • Epicondylitis
  • Synovitis
  • Muscle strains
  • Raynaud’s phenomenon
  • Sciatica
  • Tendonitis
  • 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
  • Deformity
  • Swelling
  • Cramping
  • 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:

  • Numbness
  • Burning
  • Pain
  • Tingling
  • Aching
  • Stiffness

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
  • Illumination
  • Vibration
  • 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:

  • Workstations
  • Tools
  • Facilities
  • Equipment
  • Materials
  • Processes

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:

Job Foot-candles

◦ 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

  • conveyors,
  • ball caster tables,
  • hand trucks, and
  • four-wheel carts.

PRIMARY RISK FACTORS

Force

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

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:

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
result from:

  •  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.