Techniques to Control and/or Prevent Vibration in the Workplace
By: Ken Zans
Before being considered as a nuisance, vibration was known to alleviate pain, and its therapeutic effects were used by the Chinese, the Greeks and the Romans. These beneficial effects are still used for pain relief and functional rehabilitation. Throughout the following centuries, a large diversity of vibrating machines were invented and their utilization was almost exclusively reserved for medical application.
However, in the early 18th century, Ramazzini, the first occupational physician, pointed out that vibration exposure had noxious effects. These harmful effects have actually emerged with industrialization.
Effects of Vibration on the Human Body
Vibration, in relation to its effect on the human body, is measured in three distinct patterns or ranges. These patterns range from Low Frequencies (zero to 2 HZ), Middle Frequencies (2 to 15-20 HZ), and High Frequencies (greater than 20 HZ). These figures are important in the study of the effects of vibration on the body because of the harmful effects of the lower ranges. It is well documented that the Low and Middle frequencies can cause more cumulative harm to the human body than vibrations at the higher frequencies.
The human body can (in these lower frequencies) amplify the vibration that exists from an outside source. We know, for instance, that the musculoskeletal system (muscles, tendons and bones) can "be a path" for vibration and actually amplify the vibration as it moves through the body. Let's say you are using a pneumatic tool that has a vibration frequency rating in the lower, more harmful ranges. If you were to measure the vibrations at the source (at the point where the tool touches the hand) and at the shoulder, you could see that the vibration was actually stronger at the shoulder.
The cumulative effects on the body can be wide and varied. Some of the more common disorders are White Finger Disease (Raynaud's Syndrome), Hand-Arm Vibration Syndrome, Carpal Tunnel Syndrome, tendonitis, and various bone and joint disorders. Long term exposure to vibration can also cause nausea, impaired vision, hyperventilation, raised blood pressure, impaired cardiac rhythm, and increased energy dissipation leading to exhaustion.
To Glove or Not To Glove? That Is The Question
Even though the effects of vibration are widely recognized, very little has been done in the average workplace to alleviate this concern. Traditionally, safeguards against vibration have taken place at the worksite using job rotation to limit exposure times and the use of after-market devices such as gloves and handle wraps.
The use of anti-vibration gloves has been the most prevalent preventive measure taken by most industries. This is due to the ease of implementation and the relative low cost of the glove. Unfortunately, for the most part, this measure is proving to be ineffective. We know that the vibration levels that effect the body most are those in the lowest frequencies. The anti-vibration gloves on the market are effective only in the high frequency ranges. In fact, recent studies show that most anti-vibration gloves actually amplify vibrations below 75 Hz while dampening the higher frequencies. It has been found that handle wraps or foam have this same effect.
Care should be taken to determine both the vibration levels of the tools being used and the dampening characteristics of the gloves purchased so that the preventive measures can be successful. Most glove manufacturers will provide this information, but tool manufacturers in the United States are not mandated by law to measure levels or provide vibration statistics to the end user.
However, American tool manufacturers have been faced with new directives in the European community that prevent them from selling tools without thresholds permanently printed on the equipment. Since January 1, 1995, the International Standards Organization has been instrumental in assuring that the end user is aware of vibration levels of all equipment purchased. Although this has not yet been established in the United States, this can be helpful here. For instance, if a manufacturer is selling their product overseas, they may be willing to provide the results of their studies upon request.
Techniques for Vibration Reduction and Control
1. Source Control - As noted above, care should be taken to match the vibration dampening effects of an after market device, such as wraps or gloves, to the vibration levels to of the tool being used. Goals for controlling vibration at its source should include:
-
Reduce vibration intensity/avoid resonance
-
Regulate tool speed/ tool balancing
-
Careful tool selection
2. Path Control
-
Limit exposure time
-
Reduce vibration transmission
-
Rotate personnel
-
Provide rest periods/minimize weight
-
Use balancers
-
-
Reduce vibration transmission
3. Receiver Control
-
Use vibration isolators/adapt posture
-
Reduce grip and push forces/reduce contact area
Conclusion
Whereas there has been a tremendous push in the after-market sales of vibration dampening devices such as handle wraps and anti-vibration gloves, studies have shown that unless these devices are carefully matched to the vibration frequencies of the tools used, there is very little benefit. In fact, under certain circumstances, the vibration levels are actually intensified by the use of these products. The best preventive measure for the control of vibration is through careful selection of tools and a proactive practice of job rotation to limit exposure times.
By Ken Zans
© 2015 Alliance Training and Consulting, Inc.
