OCCUPATIONAL VIBRATION: Who is at Risk?

Introduction

Have you ever personally experienced or watched a heavy equipment construction crew get tossed around by vibration; or a truck driver moving a heavy rig down the highway; or someone using a power hand-tool and observed the intense ripples of vibration motion beginning at the operator’s hands, moving up through the forearms to the shoulders? Do you think this daily human exposure to vibration is harmless? Think again, because what you don’t know about daily vibration exposure can seriously and irreversibly hurt those who are exposed!

In the U.S.A. alone there are some 8-10 million people who are regularly exposed each day to occupational vibration and many more world-wide2. These vibration exposures are usually divided into two different major groups depending on the job.

• One major exposure type is called Whole Body Vibration (WBV), or head-to-toe exposure, affecting truck, bus, heavy equipment, farm vehicle, fork-lift, railroad, and overhead crane operators, etc.
• The second major exposure type is called Hand-Arm Vibration (HAV), or localized vibration exposure,mainly, but not exclusively, affecting people who regularly use all types of vibrating pneumatic, electrical, hydraulic, and gasoline powered hand-tools.
• On rare occasions there can be daily “crossover exposures” between WBV and HAV, depending on the job. For example, in the case of certain hand-tool usage such as pneumatic pavement breakers or demolition type tools where the operator can choose either to grasp the tool with their hands extended away from their torso (HAV exposure) or letting the tool rest against their torso (WBV exposure) in an attempt to damp the vibration. Sometimes both WBV and HAV exposures occur simultaneously, such as in motorcycling or mountain bike use.

Health and Other Effects

The health effects of HAV and WBV are distinctly very different, as are their vibration exposure patterns and their physical characteristics of vibration intensity, duration, vibration frequencies, and pathways into the human body. Thus it is common practice to discuss HAV and WBV separately; although they share common physics, they do not share a common physiology nor do they share the same safety and health effects.

Hand-Arm Vibration exposure has been causally linked to a generally irreversible condition of the fingers and hands called Hand-Arm Vibration Syndrome (HAVS). HAVS was first discovered in the U.S. and characterized in 1918, during an early medical study stemming from the daily use of vibrating pneumatic hand tools by workers quarrying, cutting, and carving Oolitic limestone in Indiana. In 1918, the condition was called Raynaud’s Phenomenon of Occupational Origin, later the name changed to “dead hand” or Vibration White Finger disease, finally this condition became known as Hand-Arm Vibration Syndrome in the 1970s. Since 1918 there have been numerous studies linking HAV exposure to HAVS, usually with, but not limited to, the concurrent presence of cold temperatures.

Symptoms With HAV exposure, typical major symptoms

of HAVS first characterized by tingling and/or numbness in the finger(s); similar to, but not the same as Carpal Tunnel Syndrome (CTS,a compression syndrome of the hands). As vibration exposure continues, the appearance of a single “white” or blanched fingertip occurs, usually, but not always in the presence of cold. This “white finger” attack can mark the beginning of the socalled finger blanching process. Often these attacks are mistaken by workers who think they have frostbite. Initial finger blanching attacks last a few minutes and are widely spaced apart. As vibration exposure continues, especially in cold conditions, these attacks increase in number, intensity, duration, and finger pain. In the later stages of HAVS, attacks can and do occur in all seasons and off-the-job as well as on the job. There is interference in both the patient’s work and nonwork lives; the latter while doing tasks like mowing the lawn and touching cold objects such as a vehicle steering wheel early in the morning, or cold water striking the fingers, etc. Cold can help trigger HAVS attacks; the simultaneous combination of vibration, cold, and nicotine [from smoking] is particularly harsh since all three tend to act as vasoconstrictors and thus help “close down” blood vessels. In extreme and rare cases, the loss of blood supply to the fingers can lead to gangrene, which may require finger amputation. Thus HAVS can quickly become a serious occupational disease. For the most part doctors and scientists have found HAVS to be generally irreversible. Workers are advised to stop all vibration exposure and seek medical attention immediately if they notice HAVS signs and symptoms. Prevalence of HAVS in U.S. tool users has been reported as high as 50%. Medical treatment is generally palliative and can include the use of certain blood pressure control medications to minimize the effects of the HAVS attacks.

Whole Body Vibration exposure is quite different from HAV exposure and enters the human body through different pathways, such as via the spine while an operator drives a vehicle. There can be potential acute safety effects as well as chronic health effects resulting from WBV exposure.

WBV exposure has been casually linked, but not limited to, severe low back pain (lumbar spine), and degeneration, moisture loss, bucking, and slipping of the lumbar discs. Generally WBV chronic exposure takes some time before low back problems develop. Poor vehicle seating, awkward postures, and manual cargo handling in addition to WBV exposure tend to exacerbate low back pain misery. Recent studies have indicated that WBV exposed female operators who become pregnant can possibly have added risk factors such as miscarriages and other gynecological disorders. The WBV safety issue concerns vehicle operators who are subjected to WBV “resonant” conditions while driving vehicles and possibly losing control of their vehicle due to the mechanical decoupling action between the steering wheel and the driver’s hands as he or she attempts to hold and safely control the steering wheel.

Vibration Measurements & Standards

Vibration is a description of motion; as such vibration is called a vector quantity which simply means motion is described by both a magnitude intensity (i.e. acceleration) and a direction the motion moves. For occupational vibration, three mutually perpendicular measurements,are simultaneously obtained (i.e. up-down, side-to-side, front-to-rear); for HAV, from tool handles, where the worker grasps the tool; for WBV, from the top of seat cushion where a vehicle driver sits. The vibration results in each direction are then separately “weighted”, calculated and compared to the appropriate HAV or WBV standard to determine if a standard has been exceeded. There are numerous occupational vibration consensus standards used worldwide for HAV and WBV. Currently in the U.S. the occupational standards used are: HAV: ANSI S3.34, ACGIH-HAV standard, and NIOSH #89-106. For WBV:ANSI S3.18 and ACGIH-WBV standard. Current international occupational standards used are: European Union Directive 2002/44/EC for HAV and WBV. For HAV: ISO5349. For WBV: ISO 2631—1997.

Finally, the reader needs to know about an important concept, called “resonance”, or natural frequency; wherein the human body involuntarily and selectively reacts to vibration by behaving as a sort of a “tuner” rejecting certain impinging vibration frequencies and responding or “tuning” to other vibration frequencies. For example, human WBV resonance occurs in the vertical (updown) direction from 4-8 Hertz. In the side-to-side and front-to-rear directions, WBV resonance occurs at 1-2 Hertz. At these resonant frequencies many scientists believe humans are most vulnerable over other vibratory frequencies. Various occupational vibration standards attempt to define and compensate for these unwanted and potentially troublesome human resonant frequencies.

Controlling Occupational Vibration

Controlling occupational vibration is usually multifaceted and assumes that vibration measurements have been made and that the appropriate vibration standard has been exceeded thus requiring vibration control methods be used. Whole-Body Vibration control in vehicles usually centres around the use of “air-ride seats”, which are designed primarily for maximum up-down vertical vibration control in attenuating the particularly hazardous 4-8 Hz resonance frequencies. Some manufacturers also offer seats for not only vertical vibration control, but also front-to-back and side-to-side control too. Seats alone are not necessarily a panacea and should be supplemented where possible in vehicles with suspended cabs, properly inflated tires, and goodfunctioning shock absorbers. In plant situations where vibrating machinery is used, air-ride seats are a possibility, as well as mechanically isolating the vibrating equipment from the floor, where possible remote operation also should be considered using inexpensive closed circuit TV. Try to keep workers away from WBV exposure.

Hand-Arm Vibration Control is primarily concerned with replacing conventional vibratinghand tools, with reduced vibration “antivibration” (A/V) tools. A word of caution: power tools advertised as “ergonomically designed” are not necessarily vibration reduced! An ergonomically designed power tool is usually a product where the tool handle’s characteristics allow the tool to be used with the hand-wrist maintained in the socalled “neutral position” thus minimizing the tendency towards Carpal Tunnel Syndrome not necessarily HAVS. To minimize the vibration generated by a power tool it should be internally mechanically damped and/or isolated. Thus the proper tool to seek is one which is both antivibration AND ergonomically designed. The use of “tool wraps” around the handles of conventional tools is not recommended and should only be considered as a last resort measure and only for the shortest-time possible. The problems with wraps are: they tend to increase tool handle diametre, thus creating the possibility of introducing other cumulative trauma disorders into the hand; and wraps do not necessarily attenuate enough (lower frequency) vibration to bring the tool(s) into compliance with the HAV standards. Next, to help protect workers from HAVS, only full-finger protected antivibration (A/V) gloves will reduce vibration, but they must also:

a. keep the fingers and hands warm and dry
b. help prevent cuts and lacerations
c. must be properly fitted.

Remember: Using finger exposed A/V gloves is not recommended, since HAVS usually begins at the finger tips moving downward towards the palm.

Finally, good work practices should be used, which includes: let the tool do the work by gripping it as lightly as possible, consistent with safe work practices; do not use the tool more than necessary; do not smoke, keep the fingers and hands warm and dry to avoid HAVS attacks, keep (cold) tool exhaust away from both hands, consider vibration free breaks,about 10 minutes/ vibration hour, and if signs and symptoms of HAVS appear seek medical help immediately.

Cited References

1. “The Nuts & Bolts of Human Exposure to Vibration”, D.Wasserman & J.Wasserman, Sound & Vibration, 36,1,40-41,2002.
2. “Industrial Vibration-An Overview”, D. Wasserman, D. Badger, T. Doyle,L.
3. “Human Aspects of Occupational Vibration”, D.Wasserman, Elsevier Pub., Amsterdam, 1987.
4. “Handbook of Human Vibration”, M. Griffin, Academic Press London, 1990.
5. Primary Torsion of the Omentum in a Jackhammer Operator: Another Vibration
6. “Jackhammer Usage & The Omentum”, D. Wasserman, Journal of Occupational Medicine, 31,563,1989.
7. “Hand-Arm Vibration: A Comprehensive Guide for Occupational Health Professionals- 2nd Edition”, P. Pelmear & DE Wasserman, OEM Medical Publishers, Beverly Farms,MA,1998.
8. “A Study of Spastic Anemia in the Hands of Stonecutters: The Effect of the Air Hammer on the Hands of Stonecutters”, A. Hamilton, US Dept of Labour Report
9. “Vibration White Finger Disease In US Workers Using Chipping & Grinding Hand Tools”,Vol.1, Epidemiology, D.Wasserman,W. Taylor,V. Behrens, et al, NIOSH Pub. 82-101,1982.
10. Current Intelligence Bulletin #38 :”Vibration Syndrome” NIOSH Pub.#83-110,1983.
11. “Occupational Vibration Exposure” D.Wilder, D.Wasserman, & J.Wasserman (In Physical & Biological Hazards of the Workplace, 2nd Ed., P.Wald, MD & G Stave,MD,eds.) Wiley Publishers, New York,2002.
12. “Sound & Vibration in Pregnancy”, R. Abrams, Seminars in Perinatology, Part 11, 273-334, Saunders Pub., Philadelphia, 1990.
13. “Acceleration of the Fetal Head Induced by Vibration of the Maternal Abdominal Wall in Sheep”, A. Peters., R. Abrams., K. Gearhardt, & D.Wasserman, American Journal of Obstetrics & Gynecology, 74,552-556,1996.
14. “Whole-Body Vibration & Occupational Work Hardening”, D.Wasserman, D.Wilder, M. Pope, M. Magnusson, A. Alekslev, & J.Wasserman, Journal of Occupational & Environmental Medicine, 39,403-407,1997

This IH bulletin is an excerpt from “Occupational Vibration: Are You at Risk?” by Don Wasserman
and reprinted with permission of Quest Technologies.

About the Author

Donald Wasserman, MSEE, MBA
Mr.Wasserman is an internationally known Biomedical Engineer and a recognized expert in the area of occupational vibration where he has been working for over three decades.