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Donald E. Wasserman, MSEE, MBA*, Human Vibration Consultant,
Cincinnati, Ohio
Bedford, Indiana, 1918:
"Among men who use the air hammer for cutting stone there
appears very commonly a disturbance in the circulation of the
hands which consists of spasmotic contraction of the blood vessels
of certain fingers, making them blanched, shrunken, and numb.
. .these attacks come on under the influence of cold, and are
most marked, not while the man is at work with the hammer, but
usually in the early morning or after work. . .the fingers affected
are numb and clumsy while the vascular spasm persists. . .the
condition is undoubtedly caused by the use of the air hammer.
. .stonecutters who do not use their hammer do not have this
condition of the fingers. . .the trouble seems to be caused by
three factors - long continued muscular contraction of the fingers
in holding the tool, the vibrations of the tool, and cold. It
is increased by too continuous use of the air hammer, and by
cold in the working place. If these features can be eliminated
the trouble can be decidedly lessened.".
Alice Hamilton, MD (1).
Cincinnati, Ohio, 1983:
"In light of a recently completed, comprehensive study
by the National Institute for Occupational Safety & Health
(NIOSH), the Institute concludes that vibrating handtools can
cause vibration syndrome, a condition also known as vibration
white finger and as Raynaud's phenomenon of occupational origin.
Vibration syndrome has adverse circulatory and neural effects
in the fingers, the signs and symptoms include numbness, pain,
and blanching (turning pale and ashen). Of particular concern
is evidence of advanced stages of vibration syndrome after exposures
as short as one year. . .".
NIOSH, Current Intelligence Bulletin #38, (2).
INTRODUCTION
During the harsh winter of 1918 a famous occupational physician,
Dr. Alice Hamilton, found herself in the small midwestern town
of Bedford, Indiana. Why? Because Bedford and vicinity is the
heart of the U.S. Oolictic limestone belt. As a Federal Government
physician, Dr. Hamilton was summoned to this area at the request
of numerous limestone quarry cutters and carvers who used vibrating
pneumatic hammers and related tools. Without the aid of modern
technology Dr. Hamilton examined several of these workers, who
after daily use of these air tools complained of tingling and/or
numbness in their fingers (paraesthesia) followed by daily painful
attacks of finger blanching/whitening which increased in severity,
number, and duration with increased hand-arm vibration (HAV)
exposure. These attacks usually occurred int the presence of
cold temperatures (1).
In 1862, Dr. Maurice
Raynaud, a Paris physician, first descried the paraesthesia followed
by finger blanching attacks in females
who were exposed to cold temperatures, but not vibration; this
condition became known as Primary Raynaud's Disease (3). In 1911
Loriga in Italy (4) first briefly described these symptoms in
miners using vibrating pneumatic hand-tools. But it was not until
the famous Hamilton study appeared in 1918 that the association
between the use of vibrating tools and disease (called Raynaud's
Phenomenon of Occupational Origin) became apparent. Over the
past eighty years many studies linking tool vibration to the
so-called "vibration white finger" disease have been
reported; this condition is now called "Hand-Arm Vibration
Syndrome" (HAVS) because hand-arm vibration appears to cause
damage not only to the blood vessels, but also the bones, muscles,
and tendons of the hands (5). HAVS is a universal problem in
the U.S. alone there are nearly 2 million workers exposed to
HAV, mostly from pneumatic, electrical, and gasoline-powered
vibrating hand-tools (6).
HAVS MEDICAL AND EPIDEMIOLOGY
(5)
HAVS must be differentially diagnosed form Raynaud's Disease
of other causation by a qualified physician because:
a) Primary Raynaud's occurs for unknown reasons in a small
number of non-vibration cold exposed persons (mostly females).
b) Raynaud's can occur
as a so-called "presenting condition" in diseases such
as: scleroderma, lupus, and other connective tissue diseases
as well as from exposure to vinyl chloride (acro-osteolysis);
and various obstructive arterial diseases.
c) In its early tingling and numbness stages of HAVS Raynaud's
can be confounded/confused with Carpal Tunnel Syndrome (CTS).
(Note: Both HAVS and CTS can occur when using vibrating tools.)
The medical severity scale for HAVS uses the so-called Stockholm
system (modified Taylor-Pelmear system) where the patient is
examined for both neurological and peripheral vascular impairment
and each hand is separately assessed into impairment stages.
Unfortunately, HAVS is for the most part irreversible unless
it is detected in the very earliest of finger blanching stages
and the vibration exposure ceases. Fig. 1 shows a Stage 3 case
HAVS for a pneumatic tool operator; Fig. 2 shows a rare case
of Stage 4, tissue necrosis/gangrene unfortunately required digit
amputation for this pneumatic tool operator.
Figure1:
A vibrating pneumatic hand-tool operator in the
later stages of Hand-Arm Vibration
Syndrome (HAVS). 
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Figure 2: A rare case
of tissue necrosis/gangrene in a vibrating pneumatic hand-tool
operator at the terminal stage of Hand-Arm Vibration Syndrome
(HAVS).
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Unfortunately, current
medical treatment is palliative (not curative) and usually involves
the use of blood pressure control
medicines called "calcium channel blockers", which
seem to work well to reduce HAVS symptoms in mostly older workers.
Young HAVS workers do not generally tolerate these medications
very well.
In the late 1970's my vibration group at the National Institute
for Occupational Safety and Health (NIOSH) conducted a series
of comprehensive (medical, epidemiological, engineering) studies
of vibrating pneumatic tool workers in foundries and shipyards
(7, 8), limestone cutters/carvers (9), and underground uranium
mining workers (10). The results of the chipping and grinding
workers foundry/shipyard studies are summarized in the Table,
namely that 41 - 47% of the vibration exposed workers examined
were afflicted with the HAVS/VWF finger blanching stages; blanching
in these workers appeared in a mere 1.1 - 2.4 years (called the
latent interval). Yet when shipyard workers using the same pneumatic
tools were examined the prevalence of HAVS/VWF decreased to 17.5%
and increased in latency to 19.4 years. Why the differences in
HAVS prevalence and latency? The answer: "piecework".
Under the pressure of the piecework incentive system in these
foundries the workers worked very hard, very fast, and gripped
the tools tighter and stronger with tense muscles thus increasing
the "vibration coupling" and more efficiently moving
the vibration from the tool(s) into their hands causing HAVS
to appear more rapidly than did the shipyard workers who were not on piecework.
NIOSH Hand-Arm Vibration Studies
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Prevalence of VWF in Chipping & Grinders
& Controls |
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Workers Tested |
Foundry #1 |
Foundry #2 |
Shipyard |
Total |
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Chippers & Grinders |
119 |
66 |
92 |
277 |
|
Controls |
----------------- |
79 |
30 |
109 |
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______________________________________________________ |
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Totals |
119 |
145 |
122 |
386 |
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VWF Prevalence |
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| Stage 1,2,3 |
47% |
41% |
17.5% |
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(Mean) Latent Interval |
1.1 years |
2.4 years |
19.4 years |
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The results of our 1978 repeat of the Alice Hamilton study
in Bedford, sadly showed that the prevalence of HAVS was virtually
the same (about 80%) as what Dr. Hamilton had found some 60 years
before. Only the HAVS victims had changed. . .nothing else. Our
uranium miners study who used pneumatic tools showed about a
20% prevalence of HAVS. Many studies have been reported world-wide,
most show significant prevalences of HAVS.
HAND-ARM VIBRATION STANDARDS
AND MEASUREMENTS (11)
The purpose of HAV measurements is to assess what vibration
intensity hazard level(s) impinging on the hands of a worker
operating a given tool; and subsequently comparing these measurements
to existing HAV health and safety standards to determine if they
have been exceeded. This process is not easily described
without great detail and thus the reader is referred elsewhere
to other texts by this author for details (5, 11). The process
will only be briefly described here: Vibration is a 'vector quantity",
thus it is necessary to measure both its acceleration intensity and direction.
Normally this requires
six independent measurements to be simultaneously made at any
one vibrating point; three mutually
perpendicular "linear directions: up-down, side-to-side,
front-to-rear; and "three rotational directions": pitch,
yaw and roll. In virtually all human vibration measurements,
only the three "triaxial" linear measurements are made.
For HAV, three measurements per hand are simultaneously obtained,
tape recorded and computer analyzed for their vibration "frequency
and corresponding intensity content" in accordance with
the guidelines set forth in each of the HAVS standards usually
used here in the U.S., namely ISO 5349, ANSI S3.34, ACGIH-TLV
for HAV, NIOSH #89-106.
The frequency content
of vibration impinging on the body is of particular importance
since human response to vibration over
a wide frequency range is not uniform or linear, thus a special
mathematical "weighting function" is applied to the
vibration data. This mathematical treatment of the data tries
to account for the so-called "human resonance" phenomenon
exhibited at certain frequencies where the body actually internally
and involuntarily amplifies and exacerbates impinging vibration.
Once this description of the vibration hazard levels in relation
to these standards have been determined for each hand position
on the tool, the stage is set for the control measures which
will need to be adopted in order to minimize worker exposure
to HAV.
CONTROLLING HAND-ARM VIBRATION
(2, 5, 11, 12)
Controlling HAV in the workplace usually requires a comprehensive
approach since a variety of measures are available and should
be tailored to specific needs; here is what is currently available:
anti/vibration (A/V, i.e. reduced vibration) tools, ergonomically
designed tools, tool handle wraps, antivibration gloves and glove
standards, work practices and (as appropriate) administrative
controls.
I) A/V TOOLS AND ERGONOMICALLY
DESIGNED TOOLS
A/V tools and ergonomically designed tools are not
necessarily the same. A/V tools are principally designed to internally
reduce vibration, usually by two methods: damping and/or isolation.
Damping is the conversion of mechanical vibration motion into
a small amount of heat caused by the deformation of a damping
material; usually a viscoelastic material. Isolation removes
vibration by the intentional mismatch of the pathway between
the vibration source and the receiver (i.e., the human hand).
An ergonomically designed
hand-tool tries to optimize the tool handle interface between
the operator's hand and the tool
handle, irrespective of the internal vibration generated by the
tool. Thus the tool handle is usually designed with a nominal
1.5 inch diameter and angled such that the handle allows the
hand to be operated in the so-called "neutral position" to
minimize stress on the carpal tunnel. Tools are also designed to
have a high power-to-weight ratio.
The problem is simple this: if a n ergonomically designed
hand-tools is used on the job and the internal tool vibration
has not been reduced, this results in better coupling
of the vibration energy into the hand! Thus an ergonomically
designed hand-tool alone without internal vibration reduction
could be worse (from a HAV standpoint) that a tool not ergonomically
designed. The reverse is true too, and A/V tool without an ergonomically
designed handle might reduce HAVS but could cause CTS. The solution
is simply this: PURCHASE ONLY ANTIVIBRATION TOOLS WHICH ARE
ERGONOMICALLY DESIGNED; BOTH ARE NEEDED FOR MAXIMUM WORKER
PROTECTION.
II) TOOL HANDLE WRAPS
Tool handle wraps consist of simply wrapping a conventional
vibrating hand-tool with a commercially available viscoelastic
material. These wraps are inexpensively available in do-it-yourself
kits from a variety of manufacturers. At first glance it would
appear that tool handle wraps might be a good idea for inexpensively
reducing vibration: they really are not! This big problem
with wraps is: wraps can significantly increase the tool handle
diameter thus presenting the distinct possibility of introducing
Cumulative Trauma Disorders (CDT) into the hands with perhaps
some unknown amount of vibration reduction. Our advice, if a
wrap must be used: use it only as a very temporary measure
and replace it with an ergonomically designed A/V tool with known
benefits ASAP.
III) ANTIVIBRATION GLOVES AND
GLOVE STANDARDS
The need for antivibration gloves became very apparent in
the early 1980's when our NIOSH studies confirmed high prevalences
of HAVS in the U.S. Many conventional gloves with damp higher
frequency vibration present in some tools. The real problem is
to develop A/V gloves which damp and attenuate the lower vibration
frequencies present in many tools such as pneumatic chipping
hammers and jack hammers, for example. For the most part, conventional
gloves cannot help very much.
In the late 1980's
the first A/V gloves were introduced in the U.S. and elsewhere.
They were mostly conventional outer skin
gloves with so-called viscoelastic glove liners. These materials
became well known for their initial applications in the shoe
industry to combat the familiar "heel strike" problem,
which studies have shown contains mostly high frequency vibration
components. Next, a Japanese firm introduced an A/V glove design
using an air bladder inflated with a small bellows pump; it was
awkward to use and not very effective and was subsequently removed
from the market. Through the years there have been steady and
effective improvements made and introductions in both viscoelastic
materials (such as GELFOM made by Chase Ergonomics Co.) and A/V
glove design in an effort to not only reduce high vibration frequencies,
but also the insidious lower vibration frequencies found in many
tools.
Circa 1988, ANSI introduced in the U.S. the first A/V glove
testing standard (ANSI S3.40). Today, we rely on an excellent
international A/V glove standard (EN ISO 10819) which is very
stringent and attempts to evaluate the effectiveness of gloves
to attenuate HAV over a wide frequency band. Gloves meeting this
tough new standard are not only desirable but are vastly improved
in their ability to damp vibration over early version A/V gloves
where there were no uniform testing methods.
Lest the reader be aware, A/V gloves must do much more
than simply damp vibration! Namely, in addition to vibration
reduction, a truly effective A/V glove must do the following:
1) Keep the fingers and hands warm, to minimize cold-triggered
HAVS attacks.
2) Keep the fingers dry by wicking hand perspiration.
3) The glove must fit correctly so that proper tactile feedback
is maintained, thus permitting workers to safely and effectively
operate the tool with minimum, but safe, grip strength.
4) ONLY full-finger A/V gloves should be used, not
gloves where the fingers are exposed to vibration and cold and
the palm is protected; exposed fingers are not protected
from HAVS. This disease virtually always begins at the finger
tips and works its way down towards the palm.
THE BOTTOM LINE WITH REGARD TO A/V GLOVES IS: WHERE POSSIBLE,
TO USE FULL-FINGER PROTECTED GLOVES THAT FIT WELL AND ARE IN
CONFORMANCE WITH EN ISO 10819.
IV) WORK PRACTICES (2, 5, 11,
12)
Good work practices make sense. Workers are advised to:
1) Use only Antivibration-ergonomically designed power tools.
2) Use only full-finger protected, good fitting, AntiVibration
gloves, preferably those with have passed EN ISO 10819.
3) Let the tool do the work, grasping it as lightly as possible
consistent with safe work practices.
4) Keep your hands (and body) warm and dry to avoid possible
HAVS attacks.
5) Use power tools only as necessary and at reduced tool speed
if possible.
6) Use overhead tool balancers or supports where possible.
7) Do NOT SMOKE while operating power tools. Nicotine, cold
and vibration ALL CONSTRICT BLOOD VESSELS.
8) Avoid using power tool wraps.
9) Keep power tools and related hardware (grinding wheels,
bits, chisels, etc.) well maintained.
10) See a physician immediately if signs and symptoms appear
(i.e. tingling/numbness or whitening in fingers).
11) Keeps your wrists in the neutral position as much as possible
while working with power tools.
__________________________________________________________________
*Footnote: Donald E. Wasserman was the first Chief, Occupational
Vibration Section, NIOSH from 1971-84 where he was responsible
for and conducted virtually all occupational Hand-Arm and Whole
Body Vibration studies. He has been a private Human Vibration
and Biomedical Engineering Consultant for many years. He has
authored or co-authored more than 100 publications on this subject;
these include three books, numerous book chapters, and papers.
He has actively participated in the development and review of
numerous occupational vibration standards/guides both internationally
and nationally. He is a consultant to the Federal Government,
state and local governments, private industry and the legal profession.
*Copyright 1998, Donald
E. Wasserman, Inc. & Chase Ergonomics,
Inc., All Rights Reserved.
For further information on this subject, please contact:
Donald E. Wasserman
Human Vibration Consultant
7910 Mitchell Farm Lane
Cincinnati,Ohio 45242 U.S.A.
__________________________________________________________________
CITED REFERENCES
1) Hamilton, A: "A Study of Spastic Anemia in the Hands
of Stonecutters, Effects of the Air Hammer on the Hands of Stonecutters",
Bulletin #236. US Bureau of Labor, Industrial Accident and Hygiene
Series, #19, 1918.
2) National Institute
for Occupational Safety & Health,
Current Intelligence Bulletin #38 "Vibration Syndrome",
NIOSH Pub. #83-110, 1983.
3) Raynaud, M: "Local Asphyxia and Symmetrical Gangrene
of the Extremities" (Paris, 1862), Translated in: Selected
Monographs, London, New Sydenham Society, 1888.
4) Loriga, G: "Pneumatic Tools",
1911. Quoted by Teleky, L. Occupational Health Supplement, ILO,
pp. 1-12, 1938.
5) Pelmear, P., and
Wasserman, D. (Contributing Editors): "hand-Arm Vibration:
A Comprehensive Guide for Occupational Health Professionals -
2nd Edition, OEM Press, Beverly Farms,
MA, 1998.
6) Wasserman, D et
al: "Industrial Vibration - An Overview",
Journal American Society of Safety Engineers, 19, 6, pp. 38-43,
1974.
7, 8) Wasserman, D.,
Taylor, W., Behrens, V., et al: "Vibration
White Finger Disease in US Workers Using Chipping and Grinding
Hand-tools." Vol. I - Epidemiology, NIOSH Pub. #82-118;
Vol. II - Engineering, NIOSH Pub. #82 - 101, 1982.
9) Taylor, W., Wasserman,
D., Behrens, V., et al: "Effects
of the Air Hammer on the Hands of Stonecutters, The Limestone
Quarries of Bedford, Indiana Revisited", British Journal
of Industrial Medicine, 41 pp. 289-95, 1984.
10) Wasserman, D.,
Behrens, V., Pelmear, P., et al: "Hand-Arm
Vibration Syndrome in a Group of US Uranium Miners Exposed to
Hand-Arm Vibration", Applied Occupational and Environmental
Hygiene, 6, pp. 183-7, 1991.
11) Wasserman, D. "Human Aspects of Occupational Vibration",
(Textbook), Elsevier Science Publishers, Holland 1987.
12) Wasserman, D.: "The Control Aspects of Occupational
Hand-Arm Vibration", Applied Industrial Hygiene, 4,8, pp.
F22-26, 1989.
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