8.3 Ergonomics & MSD Risk Factors

Ergonomics & MSD Risk Factors

Ergonomics is the scientific study of designing and arranging workplaces, equipment, systems, and tasks so that they fit the physical capabilities and limitations of the human body. In short, ergonomics is the practice of "fitting the job to the worker," rather than forcing the worker to adapt to a poorly designed job. The primary goal of ergonomics is to prevent Musculoskeletal Disorders (MSDs), which are injuries that affect the body's movement or musculoskeletal system.

While there is currently no specific federal OSHA standard for ergonomics in general industry, employers are legally obligated under Section 5(a)(1) of the Occupational Safety and Health Act (the General Duty Clause) to provide a workplace free from recognized hazards, which includes severe ergonomic hazards.

Musculoskeletal Disorders (MSDs)

Musculoskeletal Disorders represent a major category of occupational illnesses and injuries, accounting for approximately 33% of all lost-workday injuries in U.S. general industry. MSDs affect muscles, tendons, ligaments, nerves, joints, cartilage, and spinal discs. They develop gradually over weeks, months, or years, and can lead to permanent disability if left unaddressed.

Common occupational MSDs include:

• Carpal Tunnel Syndrome (CTS): Compression of the median nerve as it passes through the wrist, causing pain, numbness, and tingling in the hand and fingers. It is often caused by repetitive wrist motion or awkward wrist bending.
• Tendonitis: Inflammation or irritation of a tendon, the thick fibrous cord that attaches muscle to bone. It commonly affects the wrist, elbow, or shoulder due to repetitive strain.
• Rotator Cuff Syndrome: Damage to the tendons and muscles that stabilize the shoulder joint, frequently caused by repetitive overhead reaching or lifting.
• Trigger Finger: A condition where a finger becomes locked in a bent position due to inflammation of the tendon sheath, often caused by repetitive pinching or using hand tools with sharp pressure points.
• Epicondylitis (Tennis or Golfer's Elbow): Inflammation of the tendons in the elbow joint, caused by repetitive twisting of the forearm or forceful gripping.
• Lower Back Injuries: Including muscle strains, ligament sprains, and herniated or ruptured spinal discs. These are primarily caused by improper lifting, heavy lifting, or twisting while carrying loads.

Core Ergonomic Risk Factors

Ergonomic hazards are characterized by five primary physical risk factors. The risk of developing an MSD increases significantly when two or more of these risk factors occur simultaneously (for example, lifting a heavy load while in an awkward posture).

1. Repetition: Performing the same motion or motion pattern continuously or frequently throughout a shift. Tasks that require repeating the same cycle of motions every few seconds (such as manual assembly, packaging, keyboarding, or sorting) do not allow muscles and tendons sufficient time to rest and recover, leading to fatigue and tissue damage.
2. Forceful Exertion: The amount of physical effort required to perform a task. High force requirements place mechanical stress on muscles, tendons, and joints. Examples include lifting heavy parts, pushing or pulling heavily loaded carts, pinching small components, or using heavy manual tools.
3. Awkward Postures: Body positions that deviate significantly from the "neutral posture" (the natural, relaxed alignment of the joints where muscles operate most efficiently). Awkward postures put extra strain on joints and soft tissues. Examples include: * Reaching overhead or behind the body. * Bending forward at the waist or twisting the neck and torso. * Bending the wrists up, down, or sideways while gripping objects. * Kneeling or squatting for extended periods.
4. Contact Stress: Localized physical pressure exerted on soft tissues when a body part presses against a hard or sharp edge. Common sources of contact stress include: * Resting the wrists on the sharp edge of a desk or workstation table. * Using tools with hard, unpadded handles that press directly into the palm. * Kneeling on hard concrete floors without knee protection.
5. Vibration: * Hand-Arm Vibration (HAV): Transmitted from vibrating hand tools (such as jackhammers, grinders, or chainsaws) to the hands and arms. Chronic exposure can damage blood vessels and nerves, leading to Hand-Arm Vibration Syndrome (HAVS) or Raynaud's phenomenon ("white finger"). * Whole-Body Vibration (WBV): Transmitted through the feet or buttocks when standing or sitting on vibrating surfaces, such as driving forklifts, delivery trucks, or heavy earthmoving equipment over rough terrain. WBV is strongly linked to chronic lower back pain.

Hazard Identification and Job Analysis

Employers must proactively identify ergonomic hazards before they result in injuries. Methods for identifying hazards include:

• Reviewing OSHA 300 Logs and Injury Records: Analyzing historical injury data to identify departments or job roles with high rates of sprains, strains, or carpal tunnel cases.
• Employee Surveys and Feedback: Workers are often the first to experience discomfort or pain. Conducting surveys or setting up safety committees allows employees to report early symptoms of MSDs.
• Job Hazard Analysis (JHA) and Ergonomic Assessments: Observing employees as they perform their tasks, measuring reach distances, weights lifted, forces required, and frequency of repetitive actions.

Hierarchy of Controls for Ergonomics

Once ergonomic hazards are identified, employers must apply the Hierarchy of Controls to eliminate or reduce the risks:

1. Engineering Controls (Most Effective): Physical changes to the workplace, equipment, or tools that design out the hazard. Examples include: * Installing adjustable-height workstations so workers of different heights can maintain neutral postures. * Utilizing mechanical lifting assists (such as vacuum lifts, overhead hoists, scissor lift tables, or conveyor belts) to eliminate manual lifting. * Redesigning tool handles with ergonomic curves and textured grips to keep wrists straight and reduce the required grip force. * Positioning materials within the worker's "comfort reach zone" to eliminate overhead reaching or bending.
2. Administrative Controls: Changes in how work is organized, scheduled, and performed. Examples include: * Job Rotation: Alternating workers through different tasks that use different muscle groups, allowing fatigued muscles time to recover. * Work-Rest Cycles: Incorporating scheduled stretch breaks and rest periods to prevent cumulative fatigue. * Job Enlargement: Combining multiple distinct tasks to vary the physical demands on the body throughout the shift. * Training: Training workers on ergonomic principles, proper body mechanics, and how to identify and report early signs of MSDs.
3. Personal Protective Equipment (PPE): The least effective control method because it does not eliminate the hazard. Examples include: * Vibration-dampening gloves to absorb hand-arm vibration. * Knee pads for workers who must kneel on hard surfaces. * Shoulder pads to cushion loads carried on the shoulder. * Important Note on Back Belts: Back belts (or back braces) are NOT considered PPE by OSHA or NIOSH. Extensive research has shown that back belts do not prevent back injuries in uninjured workers, and they may actually increase risk by giving workers a false sense of security or weakening core abdominal muscles.

Principles of Safe Manual Lifting

To prevent back injuries, which are the most common and costly MSDs, workers must use proper lifting techniques and stay within their "Power Zone."

• The Power Zone: The region between mid-thigh and mid-chest height, close to the body. Lifting objects within this zone puts the least amount of mechanical stress on the spine.
• Steps for a Safe Lift:
  1. Plan the Lift: Check the path for obstructions and test the weight of the object by tipping it slightly. If it is too heavy, seek help (team lift) or use a mechanical assist.
  2. Establish a Wide Base: Stand close to the load with feet shoulder-width apart, providing a stable foundation.
  3. Bend the Knees, Not the Waist: Keep the back straight and bend at the knees and hips. Never bend forward at the waist with straight legs.
  4. Tighten Core Muscles: Keep your abdominal muscles tight to support your spine.
  5. Lift with the Legs: Use the strong muscles of the thighs and buttocks to push up, keeping the back straight throughout the lift.
  6. Keep the Load Close: Hold the object as close to your body as possible. Carrying a load far from your body multiplies the force exerted on your lower back.
  7. Do NOT Twist: Keep your shoulders aligned with your hips. If you need to change direction, pivot your feet rather than twisting your torso.