Hazard Analysis — Hand-Arm Vibration


Problem:

Workers who operate pavement cutters and concrete grinders may face hazards from hand-arm vibration.


Risk Description:

Repetitive use of power tools when tending pavement cutters and concrete grinders exposes workers to hand-arm vibration, and is a risk factor for hand-arm vibration syndrome and carpal tunnel syndrome.

Carpal Tunnel Syndrome (CTS)

Hand-Arm Vibration Syndrome (HAVS)

Hand-Arm Vibration Syndrome (HAVS)

Hand-Arm Vibration Syndrome is a condition associated with vibration exposure to the hands and arms. It is characterized by damage to blood vessels, nerves, and other musculoskeletal structures. The main work-related circulatory disorder is Vibration White Finger (VWF). Hand-Arm Vibration Syndrome may occur with carpal tunnel syndrome.

Work-Related Risk Factors

Hand-Arm Vibration Syndrome is caused by the frequent use of vibrating hand tools that have a frequency range between 8 Hz and 1500 Hz. The most hazardous frequencies are from 100 to 150 Hz. Examples of vibrating hand tools include grinders, chipping hammers, sanders, chain saws, and jackhammers.

Development and Progression

Initially, the nerves are irritated by the vibration, causing the feeling of tingling and numbness in the hand and fingers. Blood vessels may be irritated and spasm, causing the fingers (especially the tips) to feel cold and possibly painful. Eventually, the finger tips may intermittently blanch. Blanching is often brought on by use of vibrating tools in cold environments. The blanching may last until the fingers are rewarmed. Attacks of blanching, pain, or numbness generally increase in frequency over time, and they may involve several fingers. At first, the attacks are caused by cold temperatures, but over time they may occur during milder temperatures as well. In cooler climates, improvement in the condition is frequently seen during the summer. For milder cases, when exposure is decreased or eliminated, nearly 50% of patients improve to near their baseline within about five years post-exposure. Improvement is not as good when HAVS is well-established, and some nerve damage may be irreversible.

Common Symptoms

Individuals with HAVS complain of tingling, numbness, loss of feeling, and/or pain in the hands and fingers. They may experience a gradual decrease in hand strength, reduced dexterity, and hand and arm muscles that tire easily. Also, they may have a cold feeling of the fingers and possibly whitening (blanching) of the fingers beginning at the tips. In more severe cases, shrinking of the hand muscles (atrophy) is possible.

Common Treatment

Most treatment for HAVS focuses on reducing work exposure to vibration. Quitting smoking reduces the frequency and intensity of attacks. In cases where extensive blanching occurs in all fingers, it may be necessary to change occupations.

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 to several 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.


Level of Risk:

Work loads or activities are of such a magnitude and character that a significant number of workers risk developing an MSD in the short or long term.

A comprehensive review by NIOSH concluded there is strong evidence from epidemiology and biological studies that exposure to hand-arm vibration causes hand-arm vibration syndrome (HAVS). The risk increases as the magnitude and duration of exposure to vibrating tools increases. There is also a link between exposure to hand-arm vibration and carpal tunnel syndrome. The risk appears to be greater if exposure to hand-arm vibration is combined with other risk factors, such as work in a cold environment and use of nicotine.

The precise level of vibration that is harmful is not fully understood. There are, however, U.S. and international standards that describe doses currently regarded as "acceptable."  These standards include the International Standard (ISO) 5349 (1986), American National Standard (ANSI) S3.34 (1986), and the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) for Hand-Arm Vibration.  In general, the higher the acceleration level, the shorted the exposure time should be.

When operating a conventional vibrating tool, the tissues of the fingers and palm absorb more than 90% of the transmitted energy from the tool.  This energy absorption causes injuries to the nerves, resulting in deficits in touch and temperature sensation.  The small fiber nerve damage appears to be largely irreversible.  Large impact tools, such as jackhammers, produce low-frequency tissue waves that can also affect the shoulder and neck.


Assessment Info:

To assess exposure to vibration, determine the associated magnitude of acceleration (m/s2) and the primary frequency (Hz) of the vibration.  Also, visit Thomas Bernard's website for a host of practical ergonomic tools.

To determine the level of exposure, the vibration magnitude is measured in terms of the acceleration (m/s2) of the surface of the tool that is in contact with the hand, and the primary frequency (Hz) of the vibration. The risk of injury depends on both the magnitude of the vibration and the amount of time a worker is exposed to the vibration.

Specialized instruments (accelerometers) are needed for assessment of vibration. It is best to contact someone who has experience with measuring vibration to determine the level of vibration exposure.After the acceleration, primary frequency, and exposure time are known, various standards can be used to determine if the vibration is potentially harmful.These standards include ISO 5349, ANSI S3.34-1986, and the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) for Hand-Arm Vibration.

Thomas Bernard's website has a host of practical ergonomics tools, including the ACGIH-TLV for Hand-Arm Vibration.


Regulations & Standards:

There is no Federal OSHA standard specifically for exposure to hand-arm vibration. 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 prohibits employers from to work in surroundings or under working conditions which are unsanitary, hazardous, or dangerous to his health or safety.

The American Conference of Government and Industrial Hygienists (ACGIH) has a recommended exposure limit, called the Threshold Limit Value (TLV). Table 1 lists acceleration levels and exposure durations to which, ACGIH has determined, most workers may be exposed repeatedly without severe damage to fingers. ACGIH advises that these guidelines be applied in conjunction with other protective measures including vibration control.

Table 1
The ACGIH Threshold Limit Values (TLVs) for exposure of the
hand to vibration in X, Y, or Z direction*

Total Daily Exposure Duration (hours)

Maximum value of frequency weighted acceleration (m/s2) in any direction*

4 to less than 8 hours

4

2 to less than 4 hours

6

1 to less than 2 hours

8

less than 1 hour

12

The frequency-weighting is based on a scheme recommended in the international standard ISO 5349. Thomas Bernard's website has a host of practical ergonomics tools, including the ACGIH-TLV for Hand-Arm Vibration.

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: https://www.asse.org/cartpage.php?link=A10-40-2007.

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.