A robotic system that can perform rebar-tying operations autonomously without exposing workers to health and safety risks from manually tying rebar and being in the environment.
Hazard Analysis — Stressful hand & wrist activity
Problem:
Workers who tie or cap rebar (bridge construction) may face hazards from stressful hand & wrist activity.
Risk Description:
Performing stressful hand activities while tying or capping rebar can lead to tendon inflammation (tendonitis) in the hand, wrist, or shoulder, or carpal tunnel syndrome.
Carpal Tunnel Syndrome
Hand/Wrist Tendonitis and Trigger Finger
- forceful hand use
- repetitive hand use
- awkward postures during hand use (postures in extreme joint positions)
- sharp tool handle edges
Double jointedness (hyperlaxity) of the wrist, thumb, or fingers is a risk factor for tendonitis near the double joint.
Specific areas of tendonitis may be traced back to specific activities that use the affected muscle or tendon. For example:
- Work involving repetitive hand motion with frequent thumb extension, or extreme lateral wrist movements is risk factor for deQuervain's syndrome (thumb tendonitis).
- Repetitive wrist flexion against resistance is a risk factor for tendonitis of the wrist flexor tendons.
Wrist flexor or extensor tendonitis is more likely to occur when workers are not accustomed to doing a task that involves force, repetition, or awkward postures.
Development and Progression
Tendonitis is an inflammatory condition. This inflammation can then lead to small tears in the tendon. The group of disorders referred to commonly as hand or wrist tendonitis may actually be one of four different types of tendonitis: paratendonitis (tenosynovitis), tendonosis, tendonitis, or peritendonitis crepitans. Paratendonitis is inflammation of the paratenon layer that is between the tendon and its sheath. Tendonosis is a degeneration of the tendon fibers that may also be characterized by an increase in blood supply, some cell death, or hardening of tissues due to calcium deposits. Tendonitis can range from a tendon strain due to inflammation, to degeneration or even tears in the tendon. Lastly, peritendonitis crepitans is when the musculotendinous junctions become inflamed.
The muscles that bend the fingers are connected to the bone with tendons. These tendons slide through a narrow tunnel. When the tunnel opening becomes irritated and narrows, or the tendon itself becomes inflamed, the tendons can become stuck in the tendon. When this happens, people may not be able to straighten the finger, appropriately called "trigger finger."
In some people these conditions may become chronic and limit life and work activities.
Common Symptoms
Individuals with hand/wrist tendonitis have pain, swelling, warmth, redness, or discomfort of the hand or forearm. Individuals with de Quervain's syndrome have pain during thumb movement due to tendon irritation at the thumb.
Trigger finger is a condition in which the finger makes a snapping sound when the person tries to straighten it. The finger may become locked in a flexed position and the clicking sound can be alarming, but the condition is not usually very painful.
Common Treatment
Nonsteroidal anti-inflammatory drugs (NSAIDs, e.g. ibuprofen or naproxen) are often helpful. Other treatments include rest, occupational or physical therapy, ice or heat applications. Injections of corticosteroids ("cortisone injections") may be beneficial in the short term. Stretching and strengthening exercises for the hand and wrist are recommended after the pain improves. Work should be modified to limit intense hand and wrist activity. Recovery can be a slow process taking from six months up to two years.
In extreme cases of trigger finger, surgery may be required to release the tendon that became stuck in a flexed position. Trigger finger is not very common.
Carpal Tunnel Syndrome
Carpal tunnel syndrome is compression of the median nerve within the carpal tunnel of the wrist. The condition is characterized by numbness and tingling in the palm side of the thumb, index finger, and middle finger.
Work-Related Risk Factors
- Forceful exertions of the wrist and hand
- Highly repetitive activities of the wrist and hand
- Prolonged use of vibrating tools
- Awkward postures of the wrist
Age, body mass index (BMI; a measurement of the relation between body weight and height), and gender are also risk factors for carpal tunnel syndrome. Individuals who are older, obese, or female may be at greater risk of developing the condition.
Development and Progression
The carpal tunnel is in the wrist, bordered by the carpal bones on the back of the wrist and the transverse carpal ligament on the palm side of the wrist. Tendons that flex (bend) the fingers go through the carpal tunnel, along with the median nerve. The median nerve provides nerve supply to the skin over the palm side of the thumb, index finger, middle finger, and part of the ring finger. The median nerve also connects toseveral muscles that move the thumb and part of the fingers. Anything that increases pressure in the carpal tunnel can reduce the function of the median nerve as it passes through the carpal tunnel. Increased pressure in the carpal tunnel can occur from the previously mentioned risk factors. Additionally, trauma, such as a wrist fracture, can increase pressure in the carpal tunnel. Nerve conduction studies are often used to determine if the median nerve function is reduced.
Common Symptoms
Individuals with carpal tunnel syndrome have numbness and tingling (and occasionally pain) over the palm side of the thumb, index finger, middle finger, and occasionally the ring finger. Symptoms are often worse at night and may wake the person at night. Symptoms may be worse if the wrist is held in extreme flexion or extension.
Common Treatment
Conservative treatment for carpal tunnel syndrome includes resting splints and nonsteroidal anti-inflammatory drugs (NSAIDs, e.g. ibuprofen or naproxen). Injections of corticosteroids ("cortisone injections") may be beneficial in the short term. Stretching and strengthening exercises for the elbow and wrist are recommended after initial symptoms improve. Work activities should be modified to minimize extreme positions of the wrist.
When median nerve function is reduced and symptoms are severe, surgery is often needed to release the pressure in the carpal tunnel. In severe cases of carpal tunnel syndrome, loss of hand function may be permanent.
Assessment Info:
To assess exposure to stressful hand and wrist activities, observe the task to determine the: 1) time spent in awkward postures (wrist is bent >20°); 2) repetitive nature of the task; and 3) force demands on the hands from lifting, carrying, pushing, or pulling heavy objects (>10 lbs) or tools/parts (>5.5 lbs).
To assess the exposure to stressful hand and wrist activities, it is necessary to observe a worker constructing suspended ceiling interior systems. Look for:
- Time spent with the wrist bent more than 20° in any direction for >1/3 of the cycle time
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Repetition as defined by either:
- Use of the hand, wrist, or finger with a cycle time of < 30 seconds.
- More than half of the cycle time is spent performing similar hand or wrist motions.
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Hand force:
- Use of one hand to lift, carry, push or pull objects weighing > 10 pounds (4.5 kg).
- One-handed use of a tool or part weighing > 5.5 lbs (2.5 kg) for > 1/3 of the cycle time
- Using a pinch grip in which the thumb and fingertip are <5 cm apart to hold something for > 1/3 of the cycle time.
There is an ACGIH® TLV® guideline for assessing levels of hand activity called the "Hand Activity Level" (HAL). This tool does require some training before it can be used properly. Links to a version of the Hand Activity Level tool and other practical ergonomics tools are available on Thomas Bernard’s website at http://personal.health.usf.edu/tbernard/ergotools/index.html.
Quantitative methods of measuring hand force are available (e.g. surface electromyography) but require technical expertise.
Regulations & Standards:
There is no Federal OSHA standard specifically for this hazard. However, hazardous work activities or exposures that are not covered by a specific standard are covered by the general duty clause, which requires each employer to provide a safe and healthful workplace.
Regulations adopted by a state must be at least as protective as the corresponding federal standard. Work may also be subject to rules of other federal, state and local agencies. Even where there is no hazard specific standard, OSHA provides a general duty for the employer to provide a work site free from recognized hazards.
The American National Standards Institute (ANSI) has a standard which applies to construction work where there may be risk factors for musculoskeletal disorders. ANSI standard A10.40 is not a regulation, but implementing this standard can help reduce the risk of MSDs. The standard is available for purchase from the American Society of Safety Engineers: http://www.asse.org/departments/standards/.
Federal OSHA Standards are enforced by the U.S. Department of Labor in 26 states. There are currently 22 states and jurisdictions operating complete State plans (covering both the private sector and state and local government employees) and 5 - Connecticut, Illinois, New Jersey, New York and the Virgin Islands - which cover public employees only. If you are working in one of those states or jurisdictions you should ensure that you are complying with their requirements.
