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Donald E. Wasserman, MSEE, MBA*, Occupational Vibration Consultant,
D.E. Wasserman & Associates, Inc., Cincinnati, Ohio 45242. Email:
dewasserman@juno.com
INTRODUCTION: The Problem
There are some 1.5-2 million U.S. workers, and millions more worldwide,
who are regularly exposed to Hand-Arm Vibration (HAV) (1,2).
For the most part, these workers regularly use pneumatic, hydraulic,
electrical, or gasoline-powered hand tools as part of their jobs.
First described in the U.S. in 1918 (3,4), regular HAV exposures
have been shown to be inextricably, medically linked to an irreversible,
non-curable medical condition of the hands originally called
Raynaud's Phenomenon, later called Vibration White Finger, and
now known as Hand-Arm Vibration Syndrome (HAVS) (1,2,5).
HAVS is characterized initially by tingling and/or numbness in
one or more fingers in either or both hands. With increasing and
prolonged HAV exposure, usually in the presence of cold temperatures,
blanching (whitening) attacks of one or more or the HAV exposed
finger(s) begins. These discrete attacks usually last five to fifteen
minutes. As the HAV exposures continue, the number and frequency
of HAVS attacks both progressively increase: the exposed worker
next becomes progressively debilitated and can no longer work.
The prognosis can even worsen in some instances, since one or more
fingers may become gangrenous, and amputation may be required (2).
As a rule, even if a worker is removed from a vibration related job, the HAVS
problem does not go away, remaining even in the absence of vibration exposure.
HAVS attacks continue, now triggered solely by cold temperatures.
In the U.S. alone, typical prevalence of HAVS can be as high as 50% of a HAV
exposed work force, with white-finger attacks beginning as early as one to two
years after the start of HAV exposures (called "blanching latency period")
(1,6). Medical professionals dealing with HAVS usually use an internationally
recognized evaluation criterion called "The Stockholm Scale" to evaluate
the severity of HAVS in one or both hands. Current HAVS medical treatment is
palliative and does not cure the disease (2). Note that HAVS is not Carpal Tunnel
Syndrome (CTS). Prevention is the keyword if we are to minimize the risk of workers
acquiring HAVS. Prevention is multifaceted and includes the following basic elements
including the need for and use of appropriate HAV workplace standard(s) (1,2).
- Use only
anti-vibration/ergonomically designed power tools (whenever
and wherever possible) that meet or exceed appropriate HAV
standard(s). A description follows.
Use only certified full-finger protection anti-vibration gloves which meet
or exceed A/V glove standard ISO 10819 (7).
- Use HAV-prevention
work practices which include the following: Keep fingers and
hands warm and dry at all times; do not smoke, because nicotine,
cold temperatures, and vibration are all blood vessel vasoconstrictors;
let the tool do the work: grasp the tool as lightly as possible
consistent with safe work practices; take vibration rest breaks,
nominally ten minutes per continuous vibration work hour; keep
the tools properly maintained; operate tools at reduced speed
if possible.
- Be aware
that ergonomically designed power tools alone or certified
A/V gloves alone will not necessarily reduce exposure to mandated
levels. A combination of all prevention methods will yield
the best results.
- Immediately
seek medical help if signs and symptoms of HAVS occur.
HAND-ARM
VIBRATION MEASUREMENT BASICS (2,8,9,10)
A Must Know: Virtually all HAV health/safety
standards require vibration measurements to be performed.
During the late 1970's, the International Standards Organization
(ISO, Geneva) produced one of the first accepted HAV standards,
ISO 5349 (11). ISO 5349 provided a measurement template for
all other standards to follow, thus there has been great
uniformity and international acceptance as to how HAV measurements
are to be performed. Here are some important basics followed
by a brief discussion of the HAV health/safety standards
used in the U.S:
- By definition,
vibration is called a "vector quantity", which simply
means vibration motion has both a direction and a magnitude
or intensity.
- In all
Hand-Arm (and Whole-Body) vibration work the universally accepted
vibration magnitude (or intensity) quantity measured and/or
evaluated is "acceleration," in particular, root-mean-squared
[rms] acceleration. Acceleration is measured in gravitation
'g' units in the U.S. Elsewhere, it is expressed as 'meters/sec/sec',
where 1g = 9.81 m/sec/sec. The HAV frequency bandwith range
for most power tools is nominally 5 Hz - 1400 Hz.
- To classically
define vibration at any one point normally takes an astounding
six mutually perpendicular simultaneous vibration acceleration
measurements. These measurements consist of three motions which
move up-down, side-to-side, and front-to-back (called "linear
motions" because they move in a line) and three twisting
or "rotational movements" called pitch, yaw, and
roll. To simplify human vibration measurements, the three rotational
motions are not made, thus, only the three linear acceleration
measurements are simultaneously obtained and each motion direction
is evaluated.
- Universally,
each of the three simultaneous (triaxal) HAV measurement directions
has a specific designation: acceleration motion parallel to
the long bones of the forearm is designated as the z axis acceleration
direction; motion moving back and forth across the knuckles
of the hand is designated the y axis acceleration direction;
and motion moving into and out of the palm is designated the
x axis acceleration direction.
- HAV measurements
are simultaneously made using three lightweight transducers
called accelerometers. Each accelerometer is mounted mutually
perpendicular on a single lightweight metal cube. This cube
is then mounted to a device such as an adjustable diameter
auto hose clamp. Finally, this combination of clamp, cube and
three accelerometers is tightly clamped to the power tool handle
being tested, with the mounting position of the test device
located very close to where the tool is grasped by the tool
operator.
If two hands are used to grasp and operate the tool, then (optimally) two
test devices are needed, and will be positioned close to where each hand
grasps and operated the tool. Each accelerometer must be individually and
appropriately calibrated. Cables leading from each accelerometer/transducer/axis
are plugged into portable electronic equipment, which simultaneously enables
each accelerometer to capture each acceleration signal (providing an ISO-HAV
weighting function) and process, store and analyze each vibration axis signal
separately. Finally, the vibration axis results can be individually displayed,
or mathematically combined into a single, total ISO weighted rms acceleration "sum
value," to determine if a given HAV standard has or has not been exceeded.
In certain instances, control engineers trying to eliminate specific workplace
vibration hazards may employ a "1/3 Octave Band Fourier vibration spectrum
analysis" using these HAV measurements, to enhance the understanding
of vibration data. Usually the total ISO weighted rms sum value is easily
derived from the spectrum analysis.
U.S.
HAND-ARM VIBRATION HEALTH AND SAFETY STANDARDS
ISO 5349 provides an excellent measurement template, but since ISO 5349 does
not prescribe daily acceptable HAV dose values, virtually all other standards
(including all U.S. standards) use this same HAV data collection/analysis method,
but differ as to the interpretation of the analyzed HAV data.
The First HAV Standard was published and promulgated in
1984 (to the present) by the American Conference of Government Industrial
Hygienists (ACGIH, Cincinnati, OH)(12). AACGIH requires the weighted HAV
measurement process described above and separate evaluation of each x,
y, and z vibration axis measured. If one or more vibration axes rms weighted
acceleration values exceed the ACGIH recommended standard, then the standard
has been exceeded for that number of daily vibration does hours worked.
In particular, the ACGIH standard states that for each vibration axis:
For 4<8 hrs/day, 4 meters/sec/sec should not be exceeded. For 2<4
hrs/day, 6 meters/sec/sec should not be exceeded. For 1<2 hrs/day, 8
meters/sec/sec should not be exceeded. For exposures less than 1 hr/day,
12 meters/sec/sec should not be exceeded.
The Second HAV Standard was published and promulgated in 1986
(through April, 2006) by the American National Standards Institute (ANSI, New
York, NY)(13) and was designated ANSI S3.34-1986. This standard, too, required
the weighted HAV process described above and also a Fourier vibration spectrum
analysis for each tested vibration axis. Each axis results are graphically
compared/overlaid onto a family of weighted, exposure time-dependent curves.
This system allowed precise determination of which (if any) of the weighted
curves' daily exposure time curves had been exceeded, and determination of
which vibration frequencies within the measured tool were the culprits. The
standard was very precise and accurate, and was used for many years. Unfortunately,
it became too cumbersome for many, since a Fourier spectrum analyzer was needed
to evaluate the HAV data.
In May 2006, ANSI replaced S3.34 with an easier to use, easier to understand
HAV standard called ANSI S2.70-2006, which will be described later in this paper.
The Third HAV "criteria for a recommended standard" was published
by the National Institute for Occupational Safety and Health (NIOSH) in 1989
and is designated #89-106. It is rarely if ever used, because it is an interim
document that does not establish hand-arm vibration numerical limits, although
NIOSH fully recognized the need for a HAV standard, and the gravity of the HAVS
problem in the U.S. NIOSH 89-106 has become an HAV/HAVS information document
(15).
The Fourth HAV Standard used in the U.S. is not a health and
safety standard per se, but is a test certification standard for full-finger
protected anti-vibration gloves. Known as ISO 10819-1996, the standard was
later adopted by ANSI as ANSI S3.40-2002: ISO 10819. The procedures under this
standard are unique to A/V glove testing and are accepted worldwide (7).
Finally, at this writing, the U.S. Occupational Safety and Health Administration
(OSHA) has adopted no HAV standard, but does recognize the HAVS problem.
THE NEW ANSI S2.70-2006 HAV STANDARD (14, 16)
Background, EU: In 1989, the European Union (EU) in Brussels
issued a Directive (89/391/EEC) informing its member nations that it planned
to take measures to protect its member nation workers from various occupational "physical
agents" found in the workplace. These included Hand-Arm Vibration and
Whole-Body Vibration. In a later 2002 Directive (2002/44/EEC) (17) to its member
nations, the EU further declared its intention to begin establishing firm health
and safety criteria for these physical agents by developing criteria "on
the minimum health and safety requirements regarding the exposure of workers
to the risks arising from physical agents-vibration."
Finally, in July 2005, these HAV and WBV criteria were actually enacted into
law by the EU, thus affecting millions of vibration-exposed workers and their
employers in all EU nations.
The legislative action of the EU represents the most profound and far-reaching
protective standards activities ever undertaken in the area of occupational vibration.
The effects of the EU Directive are being felt worldwide not only by EU workers
and employers, but also by international manufacturers whose products vibrate,
including all types of power tools and chain saws (HAVS) and all types of heavy
construction equipment, farm vehicles, trucks and buses (WBV).
Background, ANSI Working Group 39 and S2.70-2006: Some four
decades ago the American National Standards Institute formed a working group
committee (ANSI S2/Working Group (WG) 39) under the administrative auspices
of the Acoustical Society of America. This group of human vibration scientists,
engineers, and physicians tackled the task of developing ANSI human vibration
consensus standard documents, and this same committee also functions as the
ANSI United States Delegation to the International Standards Organization (ISO)
in Geneva, Switzerland. The WG 39 committee (numbering approximately 15 members)
is currently chaired by D. Reynolds, and this author DW has been an active
member of WG39 for the past 35 years.
WG 39 has been responsible for virtually every ANSI and ISO human vibration standard
(and revision) since its inception, including HAVs related standards ISO 5349
and ANSI S.3.34-1986. Fully cognizant of international human vibration standards
activity and the need to revise the 20 year-old ANSI S3.34 standard, the committee
began developing ANSI S2.70, to replace S3.34. After much work, drafting and
consensus voting/resolution, in May 2006, ANSI S2.70 was finally approved.
Both the EU HAV Directive and ANSI S2.70 are, to a significant extent, in harmony
with one another, and provide a single global HAV standard.
IMPORTANT NOTES:
I. Please recognize that although similar, the EU Vibration Directive is
a legal binding document being implemented by the EU member nations. The same
is NOT true in the U.S. for ANSI S2.70-2006, which is a voluntary, legally nonbinding,
consensus HAV standard.
II. The reader is strongly advised to obtain a complete copy of ANSI S2.70-2006*
and thoroughly read and understand the standard before attempting to implement
it in the workplace. The brief discussion provided below is intentionally simplified
and informative, not an attempt to replace the complete version of the HAV
standard.
Here is a
brief summary of the important, common, and harmonized parts
of both ANSI S2.70-2006 and the EU Directive. Both require the
following:
- The employer
is the designated party responsible for the health and safety
of its workers; thus the employer must provide a safe workplace
for its employees. Thus the employer needs to purchase reduced
vibration tools and ISO 10819 compliant/certified anti-vibration
gloves; institute safe work practices; and provide workplace
prevention programs, etc. to keep their workers safe.
- If Hand-Arm
Vibration workplace acceleration values (ISO frequency weighted
rms acceleration sum value) for a given tool or product exceed
2.5 meters/sec/sec for 8 hrs/day (this is called the "Daily
Exposure Action Value" or DEAV), employers must begin
implementing HAV safety and health measures to protect exposed
workers.
- In the
extreme case, for 8 hrs/day, workers shall not be exposed above
5.0 meters/sec/sec. This is the "Daily Exposure Limit
Value" or DELV for HAV (ISO frequency weighted rms acceleration
sum.)
Note that "ISO
frequency weighted sum value" simply means the following:
I. Triaxial vibration acceleration measurements are simultaneously made on the
tool or product being tested in accordance with ISO 5349, Parts 1 and 2;
II. The ISO frequency weighted rms acceleration values are next separately calculated
for the x, y, and z axes, respectively;
III. The resulting "x axis ISO frequency weighted rms acceleration value" is
squared, the resulting "y axis ISO frequency weighted rms acceleration value" is
squared, and the resulting "z axis ISO frequency weighted rms acceleration
value" is squared.
IV. Next, sum each of these three squared ISO frequency weighted rms acceleration
values obtained in the previous step, and finally, calculate the square root
of this ISO summed value.
This final numerical answer is what is needed: the "total daily ISO frequency
weighted rms acceleration sum."
a. For an
8 hr/day work shift, if this final value is less than 2.5 meters/sec/sec,
the tool can be operated over the work shift.
b. If this final value is greater than 2.5 meters/sec/sec, then the "action
value" has been exceeded, and the HAV protective measures must be instituted
by the employer.
c. If this final value exceeds 5.0 meters/sec/sec, workers may not use the tested
tool until this ISO frequency weighted rms acceleration sum value can be reduced
to below 5.0 meters/sec/sec for an 8-hour day.
ANSI
S2.70-2006 TERMINOLOGY
The following will be helpful to potential users of ANSI S2.70. Again, the user
is urged to obtain a complete copy of this document* before attempting HAV work.
- ANSI S2.70
is a 17-page document consisting of three "normative" annexes.
The term normative means these annexes are considered an actual
part of this standard, as opposed to an "informative annex," which
is not.
- Daily Exposure
Action Value (DEAV) is defined by this standard as the "health
risk threshold," or the HAV dose sufficient to produce
abnormal signs, symptoms, etc. in the hands and arms of some
exposed persons. DEAV = 2.5 meters/sec/sec for 8 hrs/day HAV
exposures. A graph is provided in this document if DEAV exposures
are other than 8 hrs/day.
- Daily Exposure
Limit Value (DELV) is defined by this standard as the "high
health risk threshold." or the HAV dose sufficient to
product abnormal signs, symptoms, etc. in the hand and arms
of a high proportion of exposed persons. DELV = 5.0 meters/sec/sec
for 8 hrs/day HAV exposures. A graph is provided in this document
if DELV exposures are other than 8 hrs/day.
- Once triaxial
HAV measurements have been made, processed, ISO weighted, etc.
for a tested tool, and the final "total ISO weighted rms
acceleration values" have been determined, it is possible
to roughly statistically predict when in time a percent of
the HAV exposed population using that tested tool might expect
to enter into the vascular or early finger blanching stage.
This time duration is called the "latent period".
This standard provides a graph that can help predict the latent
period for 10% of the HAV exposed population.
- The ANSI
S2.70 HAV standard recommends that only certified anti-vibration
gloves that have passed or exceeded the ANSI S3.40/ISO 10819,
EU compliance anti-vibration glove testing standard(s) be used
in the workplace. Note: ANSI S2.70 does not change or modify
testing procedures and other criteria now required by S3.40/ISO
10819.
*The
ANSI S2.70-2006, HAV Standard is available from the Acoustical
Society of America, Standards Secretariat,
35 Pinelawn Rd.,
Suite 114E, Melville, NY 11747; phone (631) 390-0215; FAX (631)
390-0217;
email asastds@aip.org.
Copyright
2006 by D.E. Wasserman, all rights reserved.
REFERENCES
1. National Institute for Occupational Safety and Health: "Vibration Syndrome." Current
Intelligence Bulletin #38, NIOSH Publication #83-110, NIOSHTIC Number 20000268,
1983.
2. Pelmear, P.L. & Wasserman, D.E. Hand-Arm Vibration: A Comprehensive
Guide for Occupational Health Professionals, 2nd Edition, OEM Medical Press:
Beverly Farms, Mass, 1998.
3. Hamilton, A. "A Study of Spastic Anemia in the Hands of Stonecutters." U.S.
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White Finger Disease in U.S. Workers Using Pneumatic Chipping and Grinding
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00171557, 1982.
6. Wasserman D., Beherns, V., et al. "Vibration Syndrome in Chipping and
Grinding Workers." Journal of Occupational Medicine, 26, 10, Special Supplement,
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7. International Standards Organization (ISO, Geneva) and American National
Standards Institute (ANSI, New York): ANSI S3.40-2002: ISO 10819-1996: "Method
for the Measurement and Evaluation of The Vibration Transmissibility of Gloves
at the Palm of the Hand." (Co-adopted by: ISO-1996 and ANSI-2002.)
8. Wasserman, D. Human Aspects of Occupational Vibration, Elsevier Publishers,
Amsterdam, 1987.
9. Griffin, M. Handbook of Human Vibration, Academic Press, London, 1990.
10. Wasserman, D., Reynolds, D., Beherns, V., Taylor, W., Samueloff, S, Basel,
R. "Vibration White Finger Disease in U.S. Workers Using Pneumatic Chipping
and Grinding Hand Tools II: Engineering Testing." NIOSH Publication #82-101,
NIOSHTIC Number 00121181, 1982.
11. International Standards Organization: ISO 5349-1986. "Guidelines for
the Measurement and the Assessment of Human Exposure to Hand-transmitted Vibration" Revised
as ISO 5349, Part 1, "General Requirements" and Part 2, "Practical
Guidance for the Measurements at the Workplace." Geneva, 2001 to present.
12. American Conference of Government Industrial Hygienists (ACGIH). "Standard
for Hand-Arm Vibration." Cincinnati, 1984 to present.
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the Measurement and Evaluation of Human Exposure to Vibration Transmitted to
the Hand " New York, 1986 to April 2006.
14. American National Standards Institute. (revision/replacement of ANSI
S3.34-1986) "ANSI
S2.70-2006: Guide for the Measurement and Evaluation of Human Exposure to Vibration
Transmitted to the Hand." New York, May 2006.
15. National Institute for Occupational Safety & Health. "Criteria
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Publication #89-106, NIOSHTIC Number 20000288, 1989.
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for the Measurement and Evaluation of Human Exposure to Vibration Transmitted
to the Hand." Proceedings of the NIOSH First American Conference on Human
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Exposure of Workers to the Risks Arising from Physical Agents: Vibration." [16th
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Brussels, Belgium.
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