|
102-275
Broadway |
MFL Occupational Health Centre, Inc. |
Vibrating hand tools can transmit vibration to the body. Over a period of time this may be harmful and lead to a condition referred to as hand/arm vibration syndrome (HAVS).
Vibration is characterized by its frequency, amplitude, and acceleration.
Frequency refers to how often the vibrating object moves back and forth about its resting position. The number of cycles that a vibrating object completes in one second is referred to as the frequency. The unit of frequency is Hertz, Hz. One hertz equals one cycle per second.
Amplitude refers to the maximum distance that the object moves on either side of the resting position. The intensity of the vibration depends on its amplitude.
Table 1 - Factors That Influence the Effect of Vibration on the Hand*
|
Physical
and Worksite Ergonomic Factors
|
Individual
Factors
|
| Acceleration of vibration | Operator's control of tool |
| Grip forces - how hard the worker grasps the vibrating equipment | Skill and productivity |
| Frequency of vibration | |
| Surface
area, location and mass of parts of the hand in contact with the source
of vibration |
Individual susceptibility to vibration |
| Duration of exposure each work day | Smoking and use of medication |
| Hardness
of the material being contacted by the hand-held tools, for example (metal
in chipping and grinding) |
Exposure to other physical and chemical agents |
| Years of
employment involving vibration exposure |
Disease or prior injury to the fingers or hands |
| State of tool maintenance | |
| Machine work rate | |
| Position of the hand and arm relative to the body | Medical history of injury to fingers and hands, particularly frostbite |
| Protective
practices and equipment, including gloves and work-rest periods |
|
| Texture of handle - soft and compliant versus rigid material | |
*Modified from original table published in ref.
Acceleration refers to how quickly the speed of the vibration object changes with time and is measured in m/s2. The speed of vibrating object is not constant; it is maximal as the object passes through the resting position moving toward the extremes. A vibrating object slows down as it approaches the extreme position where it stops and moves in the opposite direction.
Occupational exposure to vibration was first reported to affect workers in 1911. Since then a large number of workers employed as rock drillers, stone cutters, chippers, grinders and chainsaw and jackhammer operators have been shown to develop hand/arm vibration syndrome. Basically, any worker using compressed air tools and gasoline or electric-driven tools is at risk.
One of the major symptoms of HAVS is Raynaud's phenomena, an intermittent constriction of the blood vessels in the hand causing changes in colour. Vibration induced Raynaud's phenomena has also been called Vibration White Finger (VWF), or White Hand. The current terminology, however, is HAVS. The syndrome can be divided into vascular effects and sensory and neurologic effects. Table 2 describes the currently used staging system for HAVS.
Vascular effects occur after a variable period of time, depending on the amount of vibration and the individual's sensitivity. Blanching of the fingertips occurs following exposure to cold. Blanching attacks may be accompanied by numbness and may be precipitated by cold, cramp conditions, after handling cold objects or immersion in water. Blanching attacks typically last for minutes to an hour and end with the hands turning red and with considerable pain in the fingers. During an attack, touch, pain and temperature sensation are often reduced. Although initially blanching is localized to the tips of the fingers following extensive exposure, it eventually spreads to involve all fingers to the knuckles and to the tips of the thumbs. The palms of the hands are rarely affected. Blanching does not usually occur at work, but more often happens during rest periods. However, in some individuals, vibration may bring on the blanching if the fingers are cold. Approximately 30% of individuals under age 50 who have HAVS no greater than stage 2V will improve if further vibration exposure is avoided. Older workers and those with higher staged disease will tend to remain stable if vibration exposure is stopped, although some may deteriorate.
Table 2 - Hand Arm Vibration Syndrome Classification System†
|
Stage* |
Signs
and Symptoms
|
Interference
with Activities
|
| Vascular | ||
| OV |
No signs or symptoms | None |
| 1V | Episodic blanching of one or more fingertips | None |
| 2V | Episodic blanching of one or more fingers, usually confined to winter | Some interference with social activities |
| 3V | Extensive finger blanching, frequent episodes summer and winter | Restriction of hobbies and social activities to avoid vasospasms |
| Sensory/Neurologic | ||
| OSN | No signs or symptoms | None |
| 1SN | Intermittent tingling | None |
| 2SN | Intermittent numbness; reduced skin perception | Possible interference with activities involving fine tasks |
| 3SN | Reduced skin perception and/or dexterity; intermittent numbness | Interference with activities involving fine tasks at work and at home |
†Original table published
in ref. 3.
*Staging is done separately for each hand.
Abnormal sensations in the fingers are most common after the use of a vibrating tool and at night. There may also be numbness, impaired skin sensitivity and a decreased ability to sense vibration; occasionally, there is a loss of hand dexterity. Recovery of nerve function after discontinuation of vibration exposure is less likely than the reversal of vascular effects. The vibration exposure is thought to damage nerves and nerve endings. Workers may also complain of muscle fatigue and weakness. Although it has been said that hand/arm vibration can affect other body systems, this remains to be confirmed.
Most Canadian jurisdictions do not have formal vibration exposure regulations and tend to use the American Conference of Governmental Industrial Hygienists Threshold Limit Values (ACGIH-TLVs) as guidelines. These and other standard setting organizations base their values of allowable exposure on a combination of duration of exposure and the acceleration of the vibrating tool. There is controversy on the appropriate technical way to measure exposure.
Although some individuals have recommended immersion of the blanched fingers in warm water, swinging the arms along with warmth of the body may be more useful at the onset on the attack. For the prevention of blanching, it is most important to wear warm, dry clothes and maintain a raised body temperature.
The key for preventing HAVS is improved engineering of vibrating hand tools and their maintenance measures, which will allow for a reduction of vibration at the source of transmission. The use of alternative work practises whenever feasible, should also be pursued. The use of anti-vibration gloves may help to remove some of the vibration while keeping the hands warm and dry. Critical in controlling HAVS are improved work practises, such as minimizing vibration exposure time, using minimum grip strength by guiding the tool and letting it do the work, keeping the body warm and early recognition of symptoms and reporting them to a healthcare provider. Due to the effects of smoking on the circulatory system - individuals working with powered hand tools should be encourage to stop smoking.
In 1918, Dr. Alice Hamilton reported that "stonecutters who used air hammers developed a spasmodic contraction of the blood vessels of certain fingers, making them blanched, shrunken and numb... The trouble seemed to be caused by three factors - long continued muscular contraction of the fingers in holding the tool, the vibration of the tool, and cold. It is increased too by continuous use of the air hammer, by grasping the tool too tightly, by using a loose, air hammer, and by cold in the working place. If these factors can be eliminated, the problem could probably be decidedly lessened."4
References
August 1992
