Plant-Wide Hazards Ergonomics

When motions are repeated frequently (e.g., every few seconds) for prolonged periods, such as several hours without any break or over an entire workshift, there may be inadequate time for muscles and tendons to recover. If the repetitive tasks also involve other ergonomic risk factors, muscles and tendons become extremely strained or fatigued more quickly.

Highly repetitive tasks often involve the use of only a few muscles or body parts while the rest of the body is unaffected. To reduce the strain that repetitive tasks pose to those body parts, a number of employers in the poultry processing industry have done the following:

• Job rotation — Rotating employees into several different jobs during the course of a workshift is a way to distribute work so that each employee spends less time performing the same repetitive tasks. In order for job rotation to reduce muscle/tendon strain and provide adequate recovery time, the different jobs into which workers rotate need to involve the use of different muscles or body parts.
• Job enlargement — Designing jobs so they include a wider variety of tasks (or a longer motion pattern) is another way to reduce the frequency and duration of repetitive motions.
• Micro breaks or rest pauses — Building short micro pauses between motions or tasks is another way to give muscles and tendons recovery time.

Awkward postures

Working with various parts of the body (e.g., limbs, joints, back) in bent, extended or flexed position rather than in a straight or neutral position. Working in awkward postures increases the exertion and muscle force an employee must apply to complete a task and compresses tendons, nerves and blood vessels. In general, the more extreme the postures the more force is needed to complete the task. Examples of awkward postures include performing overhead work, bending or twisting to lift an object, typing with bent wrists, and squatting.

Extended Reaching

Elevated and long reaches are a problem in all phases of poultry processing. A number of jobs and tasks require employees to work with their hands above their head or shoulders, their arms extended to arm's length, or their elbows raised out from their body. These kinds of tasks and jobs place stress on the shoulders, elbows and back, and can result in an ergonomic injury.

Elevated reaches — Examples of jobs and tasks that require employees to repeatedly reach or work with their hands above their head or their elbows above their shoulders include:

• Hanging live birds onto elevated shackle conveyors.
  • Hanging live birds involves lifting birds from about waist height and placing them into shackles on conveyors that are above shoulder height.
• Rehanging birds onto elevated shackle conveyors.
  • Product is placed on the elevated shackle conveyor at least twice during processing.
• Reaching inside carcasses on the elevated conveyor to inspect and removing entrails that were missed.
  • Stacking boxed product above shoulder height for shipment.

Extended reaches — Employees also have to perform extended reaches when conveyors are too wide or there is not adequate access to the work area.

• Most poultry processing conveyors are 18 - 24 inches wide. That means employees must reach their arms forward 20 inches or more to access product that is at the far edge of the conveyor.
• Long reaches across conveyors can force some employees, particularly shorter employees, to bend their backs to reach the product. Most people must support up to 50% of their total body weight when they bend over 90 degrees.

Extended elbows —Tasks that require employees to work with their elbow(s) away from the body also place stress on the elbow and shoulder.

• Lifting large or bulky objects often requires employees to hold their elbows away from the body.
• Providing improper hand tools can force employees to raise their elbows away from the torso in order to prevent wrist deviation.
• Using in-line knives on horizontal surfaces can force shorter employees to lift their elbows as high as shoulder height in order to keep their wrists straight.

General controls to reduce reaching hazards:

• Raised working platforms to reduce elevated reaches.
• Narrower conveyors and cutting surfaces to reduce extended reaches.
• Ramping conveyor height to reduce extended reaches across conveyors for shorter employees.
• Bent handled knives that allow cuts to be made with straight wrists and elbows close to the body.

Bent Wrists

Working with wrists in a bent rather than straight position can result in ergonomic injuries, especially where the task also involves high hand force. Working with bent wrists puts stress on the tendons and tendon sheaths in the hands and wrists. When the wrists are bent the tendons and sheaths rub against hard bones and ligaments. If this happens repeatedly, the tendons and sheaths can become irritated and inflamed, resulting in injury such as tendonitis. The inflamed tendons and sheaths can also press against the nerves that run through the wrist to the hand, resulting in carpal tunnel syndrome.

A number of tasks in the poultry processing industry require employees to work with their wrists bent, including:

• Inspection of body cavities — Employees often must bend their wrists to inspect body cavities or birds and remove missed material, especially if they must work at heights that are too high or low.
• Boning, cutting/trimming — Using in-line knives often forces employees to bend their wrists in order to exert the finger and hand force necessary to hold and control the knife.
  • Boning tasks can force employees to bend their wrists 30 - 40 degrees, especially if they are working on a flat, horizontal surface.
  • Grip strength can be reduced by 25 - 55% when work must be performed with bent wrists.
• Trimming — When employees hold meat during trimming, they often must bend the wrist toward the body so the meat is properly aligned for scissor use.

General controls to reduce awkward wrist postures:

• Bent handle knives to allow cuts to be made with straight wrists.
• Raised working platforms to allow employees to inspect body cavities of birds with straight wrists.

Force

Performing essentially the same motion or motion patter over and over again with little variation in task assignment. Repetitive motion task often involve the use of only a few muscles, tendons and body parts, which can become strained when the same motion is repeated frequently (i.e., every few seconds) for prolonged periods (e.g., several house at a time, the entire workshift, day after day) without adequate recovery time. The severity of risk depends on how often the motions are repeated, the speed of the motions, the force required to perform the motions, and the number of muscles involved.

High hand force

Most poultry processing jobs and tasks involve intensive hand activities that may expose employees to high hand forces; for example, gripping hand tools and squeezing scissors. This is especially true where employees are not provided with proper hand tools. Using improper hand tools usually requires employees to exert greater force to control and operate them. Applying high hand force repeatedly for prolonged periods can cause muscle fatigue, tendon inflammation, and contact trauma.

Factors that can increase the amount of hand force employees must exert to perform a task include:

• Weight of hand tool — Employees must use more force to hold and operate heavy hand tools.
• Size of hand tool — Employees must use more force to operate tools that do not have good weight distribution because they cannot hold the tool at the center of gravity.
• Handle or grip size — Tool handles that are too small or too big reduce the employee’s grip efficiency. Improperly sized handles force employees to exert more finger force just to hold it. Continual or prolonged exertion of finger force can lead to tendon inflammation and injury, especially if the wrist is bent.
• Tool activation — The way tools are activated can also increase the amount of hand force employees must exert.
  • Manual knives generally require employees to use more hand force to cut through meat than electric knives.
  • Tools with squeeze triggers, such as scissors and staple guns, may require employees to apply a lot of muscle contraction in the hand and fingers, especially if the object to be cut is thick or dense.
  • If the trigger of a tool is too small the employee may only be able to use one finger to activate it. Where all the force to squeeze the activation trigger must be generated by one finger, the tendons may be overused to the point where fluid builds up, making it difficult to bend the finger to squeeze the tool.
• Vibration — Employees may have to use increased grip force to maintain control when operating vibrating power tools. Vibration can also desensitize the hand, requiring increased grip force to achieve the same feel of control.
• Tool maintenance — Improper maintenance of tools can increase the amount of force employees must use when operating hand tools.
  • Dull knives require exertion of more force to cut through meat than properly sharpened knives.
  • Poorly-maintained power tools may expose employees to more vibration.
• Cold — Working in cold temperatures or with cold air blowing across the hands reduces the blood flow to the hands and fingers, making the fingers stiff and less dexterous. When this occurs, employees must apply more force in order to maintain the same feel of control over tools and product.
• Gloves — Using gloves can make grasping a hand tool or object more difficult because they may change the friction, decrease dexterity or interfere with sensory feedback. Gloves can reduce grip strength by as much as 20%.
• In poultry processing, employees usually wear at least one glove on the knife hand and two on the non-knife hand.

General controls to reduce excess hand force:

• Provide electric and power scissors and knives.
• Provide tools with power grip rather than pinch grip.
• Provide tools with appropriate size handle/grip–longer handles and wider grips.
• Implement knife sharpening and maintenance program.

Heavy Lifting

Many jobs and tasks in poultry processing can require workers to lift, push, pull and carry heavy loads. Heavy lifting can result in overexertion and injury to the lower back.

Some of the poultry processing tasks that involve heavy lifting include the following:

• At some plants live birds are delivered in small cages that workers must manually unload from trucks and manually empty.
  • A small cage of live birds can weigh more than 50 pounds.
• Because of line breakdowns or other process demands, sometimes workers must manually unload semi-processed birds from transport tubs to conveyor or rehang lines.
  • Workers usually lift more than 1 bird at a time — 3 birds in a hand creates a load of 20 pounds.
    • Lifts can be made from almost floor height as the tub empties to above shoulder height, depending on the height of the rehang conveyor.
• Often workers must manually move scraps and parts around the plant.
  • Totes of scrap meat and skin can easily weigh more than 50 pounds.
• Workers must manually load packed boxes of product onto pallets and move loaded pallets.
  • A box of processed chicken typically weighs between 40 to 80 pounds.
    • Lifting frequencies as high as 10 per minute are possible.
  • A loaded pallet can easily weigh more than 1500 pounds.

How much weight a worker can safely lift depends on a number of factors. When the factors are such that the worker can assume an “ideal” body posture during the lift, the worker is able to lift greater loads. However, when the body posture is not ideal (e.g., back is bent or arms are outstretched), then the amount of weight the worker can safely lift is reduced. Factors affecting how much weight a worker can safely lift include:

Lifting factors	More weight can be safely lifted when:	The amount of weight that can safely be lifted is reduced when:
How far from the body the load is held (horizontal distance).	The load is close to the body and not too large/bulky, which allows the arms and elbows to be close to the torso during the lift.	The load is farther away from the body or is large/bulky, forcing the arms and elbows away from the torso during the lift.
How high or low is the lift (vertical distance).	The lift is at waist height.	The lift must be made from below the knees or above the shoulder.
How much the worker must twist to lift and move the load.	The lift is performed in front of the body.	The worker must twist the torso to lift and move the load.
How often the lift is repeated.	The lift is performed only occasionally.	The lift is performed repeatedly (several times a minute).
How far the load is carried.	The lift does not involve carrying.	The load must be carried a distance (more than 3 feet).
How the load is gripped.	The load has handles.	The load does not have handles or is slippery.

General controls to reduce lifting hazards:

• Use lift assists (hand dollies, carts, lift tables, forklifts).
• Reduce size of product boxes to lighten load.
• Arrange work space so employee can move closer to load and perform lifts with arms close to body.
• Use adjustable palletizers that allow loading at waist height.
• Use pallets that can rotate.
• Use tubs with adjustable bottoms to reduce need for bending over to remove product.
• Put objects to be lifted at waist level.
• Arrange workstation so lift is done in front and without twisting.
• Use chutes and slides to move loads across conveyors or in new direction.
• Put handles or grips on boxes.
• Use gloves that aid in holding slippery objects.

NIOSH Lifting Guidelines and Calculators

Vibration

Although using powered hand tools may help reduce employee exposure to ergonomic risk factors such as repetition and force, they can expose employees to vibration. Vibration restricts the blood supply to the hands and fingers, which, depending on the vibration level and duration of exposure, can contribute to an ergonomic injury. Signs and symptoms of vibration-induced injury, such as Reynaud's phenomenon, start with occasional numbness or loss of color in the fingertips. They progress to more frequent and persistent symptoms affecting a larger area of the fingers and resulting in reduction in feeling and manual dexterity.

Factors that increase the amount of employee exposure to vibration include:

• Bad power tool design — Even new tools can expose employees to excessive vibration if they are not designed with devices that dampen or shield employees from vibration.
• Poor power tool maintenance.
• Old power tools.

General controls to reduce vibration:

• Use low vibration tools.
• Use vibration dampeners or shields to isolate source of vibration from employee.
• Inspect and maintain power tools regularly.

Contact Stress

Contact stress results from continuous contact or rubbing between hard or sharp objects/surfaces and sensitive body tissue, such as soft tissue of the fingers, palms, thighs and feet. This contact creates localized pressure for a small area of the body, which can inhibit blood, nerve function, or movement of tendons and muscles.

Some of the contact stress problems in poultry processing include:

• Using manual scissors in cutting and trimming tasks.
  • Each motion to open the jaws of the scissors brings the hard surface of the handle into contact with the unprotected sides of the fingers where nerves are located. Employees do thousands of cuts during the course of a workday.
• Working on conveyor/assembly lines.
  • Employees' thighs can press or rub against conveyor/assembly lines, especially if tasks require reaching across the conveyor, or if the work area is too small.
• Standing on steel slat working platforms for long periods of time.
  • In many poultry processing plants employees work on platforms made of narrow steel slats that allow meat and fat to fall through the steel grids. While these platforms help reduce slips and allow for easy clean up, they expose employees to localized pressure in their feet. The slats, which may be no more than 1/4" wide, act like a knife edge, concentrating contact when employees are standing for a long time.
  • Another problem related to standing for long periods of time is the “static load” placed on the legs and back. Circulation is reduced, blood pools, and localized fatigue increases the longer employees must stand. Muscles and tendons become more susceptible to strain as they become fatigued from prolonged standing.

General controls to reduce contact stress:

• Use electric or power tools, knives and scissors.
• Use spring-loaded scissors.
• Attached well-designed handles to tools.
• Wrap of coat tool handles and grips with cushioning material.
• Use palm pads.
• Use sit stand stools to reduce static loading on legs and back.
• Use shoes with thick or cushioned soles.

The likelihood of injury from these hazards is increased because many tasks must be performed in cold environments or at workstations which limit and isolate movement.