The Institute for the Study of Human Vibration

OCCUPATIONAL VIBRATION: A BRIEF OVERVIEW
by Donald E. Wasserman* * & Jack F. Wasserman**

INTRODUCTION

In the United States alone there are some 8-10 million workers who daily are exposed to occupational vibration'. These vibration exposures are usually categorized into two groups2. Whole Body Vibration (WBV), or head-to-toe exposure, affecting such employees as truck, bus, heavy equipment, farm vehicle, fork-lift, and overhead crane operators. The second group is Hand-Arm Vibration (HAV), or localized vibration exposure, mainly, but not exclusively, affecting employees who use all manner of vibrating pneumatic, electrical, hydraulic, and gasoline powered hand-tools. Rarely does one speak of "crossover exposures" between WBV and HAV except in the case of certain hand-tool usage such as road-rippers or jackhammer type tools where the worker can choose either to grasp the tool with their hands, extending the tool away from the torso (HAV exposure) or let the tool rest against the torso (WBV exposure) in an attempt to damp the vibration3. Sometimes both can occur simultaneously, such as in motorcycling or mountain bike use. The medical effects of HAV and WBV are distinctly very different, as are their vibration exposure patterns and physical characteristics such as acceleration levels, vibration frequencies, pathways into the human body. Thus it is common practice to discuss HAV & WBV separately; although they share a common physics, they do not share a common physiology nor do they share the same safety and health effects.

*Copyright, 1999, D.E. Wasserman & J. F. Wasserman, All rights reserved.
* *From: The Institute for the Study of Human Vibration, University of Tennessee, College of Engineering, Knoxville, TN 3 7996.
(The opinions expressed herein are those of the authors and not necessarily those of the University of Tennessee ).

SYNOPSIS: HEALTH & SAFETY EFFECTS OF OCCUPATIONAL VIBRATION EXPOSURE

Hand-Arm Vibration exposure has been causally linked to a generally irreversible condition of the fingers and hands called Hand-Arm Vibration Syndrome 5 (HAVS). HAVS was discovered in the U.S. and characterized more than eight decades ago by the famous pioneering occupational physician, Alice Hamilton, during an early investigation of hand-arm maladies stemming from the daily use of vibrating pneumatic hand tools by workers in the quarrying, cutting, and carving Oolitic limestone in Indiana6 . In 1918, Dr. Hamilton termed this condition Raynaud's Phenomenon of Occupational Origin, later the name would be changed to Vibration White Finger or "dead hand" disease, finally this condition became known as Hand-Arm Vibration Syndrome.

Major symptoms of HAVS5 are initially characterized by tingling and/or numbness in the fingers; similar to but not the same as Carpal Tunnel Syndrome. As vibration exposure continues the appearance of a single "white" or blanched fingertip occurs, usually, but not always in the presence of cold. This seemingly innocuous attack of "white finger" marks the beginning of the dreadful later irreversible finger blanching process. Often these attacks are mistaken by workers who think they have frostbite. Initial finger blanching attacks last about 5-15 minutes and are widely spaced apart. As vibration exposure continues, especially in cold conditions, these attacks increase rapidly 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 non-work 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 helps trigger HAVS attacks; the simultaneous combination of vibration, cold, and nicotine from smoking is particularly deadly since all three tend to act as vasoconstrictors and thus help "close down" blood vessels. In extreme conditions, 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 HAVS is irreversible. Workers are advised to cease vibration exposure and seek medical attention immediately if they notice 114 VS signs and symptoms. Prevalence of HAVS in the US tool users have been reported as high as 50% 7,8. Medical treatment is generally palliative and can include the use of blood pressure control medications known as calcium channel blockers5.

Whole-Body Vibration exposure is quite different from HAV exposure and enters the human body through different pathways, such as via spine while an operator drives a vehicle, for example. There can be potential acute safety effects as well as chronic health effects resulting from WBV exposure. WBV exposure has been causally linked, but not limited to, severe low back pain9 (lumbar spine), and degeneration, moisture loss, bucking, and slipping of the lumbar discs. Generally WBV chronic exposure take some time before low back problems develop. Sometimes workers have reported they have kidney pain from WBV exposure; simulated animal studies have shown this mostly to be referred pain from the lumbar spine10. Finally, 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 female workers who become pregnant and are exposed to WBV can possibly have added risk factors such as miscarriages and other gynecological disorders 11,12.

The WBV safety issue concerns vehicles operators who are subjected to whole-body resonant conditions while driving vehicles and the possibly of their loosing 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 wheel2.

Finally, recently there have been attempts to use WBV as part of the so-called return to work regimes called "work hardening"; at this writing, neither we nor our colleagues know of any scientific/therapeutic value of using WBV exposure and thus we strongly advise against it us in rehabilitation medicine13.

VIBRATION MEASUREMENTS2

It is not the intent of this brief presentation to discuss the details of occupational vibration measurements in any great depth herein, because we authors2 and a few others14 have extensively presented this information elsewhere over the past several years and the interested reader is advised to investigate these in depth presentations. Here are just a few basics.

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, or velocity, or displacement) and a direction the motion moves. Vibration at any given point is defined by six vectors; three mutually perpendicular "linear" motions which move in a line (i.e. front-to-back, up-down, side-to-side) and three rotational vectors ( i.e. pitch, yaw, roll ). For occupational vibration, rotational motions are not measured, only the three (triaxial) linear axes are simultaneously measured; 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 measure of vibration intensity is usually acceleration, more precisely a form of average acceleration known as "rms, or root-mean-squared, acceleration" as separately, and simultaneously, measured for each of the three mutually perpendicular axes. There are uniform coordinate systems and measurement methods described in both HAV and WBV standards, and followed, usually allow HAV or WBV measurements to be directly compared.

Finally, there is the concept of resonance, or natural frequency, wherein the human body as well as other physical structures respond by acting as a sort of a vibration "tuner" rejecting certain impinging vibration frequencies and responding or "tuning" to other vibration frequencies by actually amplifying and exacerbating these impinging vibration frequencies. For example, human WBV resonance occurs in the vertical (up-down) direction from 4-8 Hertz. What's the concern? Simply this: if a vehicle, for example, contains spectral components of 4-8 Hz frequencies and these vibrations reach the operator's spine via the driver's seat, then the spine will most likely involuntarily respond by actually amplifying and exacerbating the effects of the WBV exposure. In other words, our body has the ability to select, accept, and amplify certain vibration frequencies over others in doing so it can worsen the effects of the vibration. The various vibration standards attempt to define & compensate for these unwanted and potentially troublesome human resonant frequencies. Resonance may seem unusual to many, but it affects virtually all physical structures, such as bridges, for example; this is the reason why soldiers never march across a bridge, lest it will absorb the vibration excitation from marching and then internally amplify the vibration causing the bridge to sway and eventually collapse.

OCCUPATIONAL HAND-ARM & WHOLE-BODY STANDARDS USED IN THE US

Currently there are numerous and varied consensus occupational HAV and WBV standards used throughout the World2,5,14 The US Government has not issued either regulatory HAV nor WBV standards as of this writing. The major consensus occupational HAV and WBV standards used in the US as of this writing are as follows:

HAV: American Conference of Governmental Industrial _Hygienists (ACGIH) standard for Hand-Ann Vibration (1984-99); American National Standards Institute (ANSI), S3.34 (1986-99); National Institute for Occupational Safety & Health (NIOSH Criteria for a Recommended Standard for Hand-Ann Vibration #89-106 issued in 1989); WBV: International Standards Organization (ISO) 2631 (1972-85); ANSI S3.18 (1979-99 ACGIH standard for Whole-Body Vibration (1996-99)

NOTE: For each of the HAV standards and similarly for each of the WBV standards there are prescribed uniform/universal methods for collecting and computer analyzing so-called triaxial linear vibration acceleration data; however, these standards are not uniform in their presentation nor interpretation of said data and what values of acceleration and vibration frequencies constitute an exceedence of a given HAV or WBV standard. Thus, you the reader are cautioned not to attempt vibration by any measurements before obtaining the actual standard and reading/understanding it thoroughly.

OCCUPATIONAL HAND-ARM & WHOLE-BODY VIBRATION CONTROL

Controlling workplace 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 control2,7 in vehicles such as trucks, buses, heavy equipment, etc. usually centers around the use of so-called "air-ride seats" which are designed primarily for maximum 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 good 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 Control5 is primarily concerned with replacing conventional vibrating-hand tools, with so-called 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 so-called "neutral position" thus minimizing the tendency towards Carpal Tunnel Syndrome, not HAVS. In order to minimize the vibration generated by the tool it should be internally mechanically damped and/or isolated. Thus in our view the proper tool to seek is one which is both antivibration AND ergonomically designed. The use of so-called "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. In our view, the problems with wraps are basically twofold: they tend to increase tool handle diameter, 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, the use of only full-finger antivibration (A/V) gloves is recommended to help protect the worker from HAVS. A/V gloves generally reduce vibration, keep the fingers and hands warm and dry and help prevent cuts & lacerations. However, these gloves must be properly fitted. Using finger exposed AIV 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 include: letting 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 hands; consider vibration free breaks, about 10 minutes/vibration per hour; and if signs and symptoms of HAVS appear seek medical help immediately.

We hope this brief overview of occupational vibration has been helpful. Please contact us at ISHV should you need assistance with human vibration problems.

Cited References l."Industrial Vibration-An Overview", D. Wasserman, D. Badger, T. Doyle, L. Margolies, Journal of the American Society of Safety Engineers, 19, 38-43, 1974. 2."Human Aspects of Occupational Vibration", D. Wasserman, Elsevier Pub., Amsterdam, 1987. 3."Primary Torsion of the Omentum in a Jackhammer Operator: Another Vibration Injury", P. Shields & K. Chase, Journal of Occupational Medicine,30, 892-894, 1988. 4."Jackhammer Usage & The Omentum", D. Wasserman, Journal of Occupational Medicine,3 1, 563,1989. 5. "Hand-Arm Vibration: A Comprehensive Guide for Occupational Health Professionals-2nd. Edition", P. Pelmear & DE Wasserman, OEM Medical Publishers, Beverly Farms, MA, 1998. 6. "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 Labor Report 236, No. 19, 1918. 7. "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. 982-101, 1982. 8. Current Intelligence Bulletin #38: "Vibration Syndrome", NIOSH Pub. #83-110,1983. 9. "Vibration-Chapter 4", D. Wilder, D. Wasserman, M. Pope, W. Taylor (In Physical & Biological Hazards of the Workplace, P. Wald, MD & G. Stave, MD, eds.), Van Nostrand Reinhold Pub., New York, 1994. 10. "Serum & Urine Changes in Macaca Mulatta Following Prolonged Exposure to Whole-Body Vibration", D. Badger, D. Sturges, R. Slarve, & D. Wasserman, AGARD Conference on Vibration, Oslo, Norway, Paper 1310-1, Pub. #AGARD-CPP-145,1974. I l."Sound & Vibration in Pregnancy", R. Abrams, Seminars In Perinatology, Part 11, 273-334, Saunders Pub., Philadelphia, 1990. 12. "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, 174,552-556,1996. 13. "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. 14. "Handbook of Hunan Vibration", M. J. Griffin, Academic Press, London, 1990.

OCCUPATIONAL VIBRATION A BRIEF OVERVIEW
*by DE WASSERMAN" & J. F. WASSERMAN
Date: August, 1999
Copyright, 1999, DE Wasserman & J.F. Wasserman.
All rights reserved. (Used with permission )
From: The Institute for the Study of Human Vibration
University of Tennessee,
College of Engineering,
Knoxville, TN

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