اثرات بهداشتی ارتعاش
Vibration-induced white finger (VWF) is the most common condition among the operators of hand-held vibrating tools. Vibration can cause changes in tendons, muscles, bones and joints, and can affect the nervous system. Collectively, these effects are known as Hand-Arm Vibration Syndrome (HAVS). The symptoms of VWF are aggravated when the hands are exposed to cold.
Workers affected by HAVS commonly report:
- attacks of whitening (blanching) of one or more fingers when exposed to cold
- tingling and loss of sensation in the fingers
- loss of light touch
- pain and cold sensations between periodic white finger attacks
- loss of grip strength
- bone cysts in fingers and wrists
The development of HAVS is gradual and increases in severity over time. It may take a few months to several years for the symptoms of HAVS to become clinically noticeable.
What are the symptoms of hand-arm vibration syndrome (HAVS)?
Hand-arm vibration exposure affects the blood flow (vascular effect) and causes loss of touch sensation (neurological effect) in fingers. One of the earliest methods used for identifying the severity of these symptoms was the Taylor-Pelmear classification method. Table 1 shows the Taylor-Pelmear classification of the clinical stages of vibration induced white finger. This classification was widely used in the past.
Taylor-Pelmear classification of vibration-induced white finger by stages
A common method that is used to classify VWF is the Stockholm Workshop classification scale.
The Stockholm Workshop classification scale for cold-induced vascular
(blood flow) symptoms in fingers with hand-arm vibration syndrome
The Stockholm Workshop classification scale for sensorineural
changes in fingers due to hand-arm vibration syndrome
Source: Gemne, G., et al. Scandinavian Journal of Work, Environment and Health. Vol. 13, no. 4 (1987). p. 275-278.
The severity of hand-arm vibration syndrome depends on several other factors, such as the characteristics of vibration exposure, work practice, personal history and habits. Table 3 summarizes these factors.
Factors that influence the effect of vibration on the hand
Individual FactorsAcceleration of vibration Grip forces - how hard the worker grasps the vibrating equipment Operator's control of tool Frequency of vibration Surface area, location, and mass of parts of the hand in contact with the source of vibration Machine work rate Duration of exposure each workday Hardness of the material being contacted by the hand-held tools, for example metal in grinding and chipping Skill and productivity Years of employment involving vibration exposure Position of the hand and arm relative to the body Individual susceptibility to vibration State of tool maintenance Texture of handle-soft and compliant versus rigid material Smoking and use of drugs.
Exposure to other physical and chemical agents.Protective practices and equipment including gloves, boots, work-rest periods. Medical history of injury to fingers and hands, particularly frostbite Disease or prior injury to the fingers or hands
What is Raynaud's phenomenon of occupational origin?
Hand-arm vibration syndrome is also known as Raynaud's phenomenon of occupational origin. Vibration is just one cause of Raynaud's phenomenon. Other causes are connective tissue diseases, tissue injury, diseases of the blood vessels in the fingers, exposure to vinyl chloride, and the use of certain drugs. The resulting reduced blood flow can produce white fingers in cold environments. Raynaud's phenomenon is discussed in more detail in another document on this site.
What are the health effects of whole-body vibration?
Whole-body vibration can cause fatigue, insomnia, stomach problems, headache and "shakiness" shortly after or during exposure. The symptoms are similar to those that many people experience after a long car or boat trip. After daily exposure over a number of years, whole-body vibration can affect the entire body and result in a number of health disorders. Sea, air or land vehicles cause motion sickness when the vibration exposure occurs in the 0.1 to 0.6 Hz frequency range. Studies of bus and truck drivers found that occupational exposure to whole-body vibration could have contributed to a number of circulatory, bowel, respiratory, muscular and back disorders. The combined effects of body posture, postural fatigue, dietary habits and whole-body vibration are the possible causes for these disorders.
Studies show that whole-body vibration can increase heart rate, oxygen uptake and respiratory rate, and can produce changes in blood and urine. East European researchers have noted that exposure to whole-body vibration can produce an overall ill feeling which they call "vibration sickness."
Many studies have reported decreased performance in workers exposed to whole-body vibration.
How much vibration exposure has to accumulate before people are affected?
As in all occupational exposures, individual sensitivity to vibration varies from person to person.
Three important factors affect the health effects that can result from exposure to vibration:
- the threshold value or the amount of vibration exposure that results in no adverse health effects
- the dose-response relationship (how the severity of the ill health effects is related to the amount of exposure)
- latent period (time from first exposure to appearance of symptoms
The threshold value of vibration is the level below which there is no risk of vibration syndrome. In other words, it is the maximum intensity of vibration to which most healthy workers can be exposed every workday for their entire full-time employment without developing numbness, paleness or chill of fingers. Workers will not develop vibration-related injuries or disease if their exposure to vibration is maintained at sufficiently low levels.
What has been observed is that the number of affected people increases as the intensity and duration of vibration exposure increases. This type of exposure-response relationship indicates a possible link between health effects and the total amount of vibration energy entering the hands or body. Depending on the intensity of exposure, the symptoms may appear months or years after the start of the exposure.
The latent period for VWF is the time from the first occupational exposure to hand-arm vibration until the onset of symptoms. The latent period depends on the intensity of exposure. The higher the intensity, the shorter the latent period. Table 4 shows typical latent periods reported for workers in some occupations.
Average latent periods for vibration-induced
diseases in different occupations
Stage of VWF
Latency (years)Foundry worker Tingling
Source: Vibration effects on the hand and arm in industry. Edited by A.J. Brammer et al. New York : John Wiley and Sons, 1982.
Why is it not easy to diagnose vibration related diseases?
The acceptance of vibration syndrome as an industrial disease is hindered mainly because:
- Not every physician is trained to diagnose vibration-induced white finger (VWF) or other vibration-related diseases.
- The causes of VWF cannot always be identified.
- There are no objective clinical tests to measure the impairment.
- The disease progresses for years before the symptoms become severe enough to affect a worker's ability to do her or his work.
Are there any studies about the combined effect of noise and vibration?
Since most vibrating machines and tools produce noise, a vibration-exposed worker is likely to be exposed to noise at the same time. Studies of hearing loss among lumberjacks revealed that, for equal noise exposure, those with vibration-induced white finger (VWF) had greater hearing loss than those without VWF. The reason for this effect is not clear.
Studies of the effect of separate and simultaneous exposure to noise and whole-body vibration have concluded that whole-body vibration alone does not cause hearing loss. However, simultaneous exposure to noise and vibration produces greater temporary hearing loss than noise alone.
Are there exposure standards for vibration?
Following is a list of exposure limits (TLV®) recommended by the American Conference of Governmental Industrial Hygienists. There are other regulations and standards. Workplaces should try to maintain exposures as much below the limits as possible.
In some international jurisdictions, the exposure limit is also given as threshold limit and exposure limit. Threshold limit is lower than exposure limit and warrants the initiation of control measures. Following is an example of such limits.
Document last updated on October 21, 2008