NOISE , VIBRATION THEIR EFFECT AND PREVENTION
NOISE &VIBRATION Their effect and preventionB.Arunachalam
Loud noises can cause hearing loss by damaging the delicate hair
cells in the inner ear. Most of the time this damage happens
gradually when prolonged exposure to loud sounds exhausts these
hair cells. As noise levels increase, the tiny cilia at the top of
the hair cells can be injured or broken off. Entire groups of these
hair cells can even be torn away. Hair cells don't repair
themselves. So when enough hair cells are damaged, a hearing loss
results.
A short, intense soundan explosion, for example may cause
immediate hearing loss. But usually hearing loss occurs gradually
after prolonged exposure to loud noise. It may occur so gradually
you may not even realize you are losing your hearing. Over time,
sounds may simply become muffled or distorted.
Tinnitus, a ringing or roaring sound, sometimes described as the
sound of crickets in one or both ears, can accompany both immediate
and gradual hearing loss. Tinnitus occurs when the damage to hair
cells hasn't gotten to the point where they produce nothing,.
Rather, the hairs produce ongoing sounds because they are partially
damaged. That is, they are constantly stimulated because they are
irritated. The brain perceives this constant irritation as
sound.
Hearing loss can be progressive if you continue exposing
yourself to the same noise, Today you may have a minor or moderate
hearing loss, but after further exposure, the loss may become more
severe. However, once you stop the exposure, the hearing loss won't
get worse.
The tenth conference on Safety in Mines under Para 4
Occupational Health Surveillance and Notified Diseases recommends ,
4.1 Noise mapping should be made mandatory of various work places
in the mine premises based on the various machines being used in
concerned mines along with personal noise dosimetry of individual
workmen exposed to noise level above 85 dbA. Sound is measured in
decibels. A normal conversation takes place at about 60 decibels. A
shop floor noise level is about 100 decibels, and a jack hammer
noise measures about 110 decibels.. Prolonged exposure to noise
above 85 decibels can cause hearing loss.Occupational hearing loss
includes acoustic traumatic injury and noise induced hearing loss
(NIHL) and can be defined as partial or complete hearing loss in
one or both ears as a result of ones employment. Exposure to
excessive noise is the major avoidable cause of permanent hearing
impairment.To see if you may be in an environment that could cause
hearing loss, ask yourself the following questions:
Is the noise at my workplace so loud that I have to raise my
voice significantly for someone an arm's length away to hear
me?
When I leave work and am in a quieter environment, do my ears
feel plugged? Or do I hear a mild ringing or whooshing noise that
goes away after an hour or two?
Is there trouble in normal and telephone conversations ? Is it
required to turn up the radio/television volume ? Do I feel
presence of Tinnitus ?If you answer yes to any of these questions,
get your hearing tested and protect your ears.
Muffle the roarImplement a noise monitoring program when
"information indicates that any employee's exposure may equal or
exceed an 8-hour average exposure of 85 decibels." When engineering
controls cannot eliminate or reduce hazardous noise, provide
hearing protectors and ensure workers wear them. Health effects of
hearing loss are Lack of concentration Irritation Fatigue Head ache
Sleep disturbance. Psychologically the individual feels neglected
in the society as more often people avoid communicating with them
Risk increases with intensity ,length of exposure and individuals
susceptibilityThe most effective way to prevent Noise Induced
Hearing Loss is to protect from hazardous noise. When all
engineering controls and work practices are not feasible for
reducing noise exposure to safe levels personal protection devices
should be resorted to .A personal hearing protection device is a
device designed to reduce the level of sound reaching the eardrum.
Ear muffs, ear canal caps, ear plugs are the main types of hearing
protectors. We should consider the following
1. The workers who will be wearing them
2. The need for compatibility with other safety equipment
3. Workplace conditions such as temperature, humidity and
atmospheric pressure
Common excuse for not using the protective device are
discomfort, interference with hearing,Protection devicesExpandable
foam plugs These plugs are made of a formable material designed to
expand and conform to the shape of each person's ear canal. Roll
the expandable plugs into a thin, crease-free cylinder. Whether you
roll plugs with thumb and fingers or across your palm doesn't
matter. What's critical is the final resulta smooth tube thin
enough so that about half the length will fit easily into your ear
canal. Pre-molded, reusable plugs Pre-molded plugs are made from
silicone, plastic or rubber and are manufactured as either
one-size-fits-most or are available in several sizes. Many
pre-molded plugs are available in sizes for small, medium or large
ear canals. A critical tip about pre-molded plugs is that a person
may need a different size plug for each ear. The plugs should seal
the ear canal without being uncomfortable. This takes trial and
error of the various sizes. Directions for fitting each model of
pre-molded plug may differ slightly depending on how many flanges
they have and how the tip is shaped. Insert this type of plug by
reaching over your head with one hand to pull up on your ear. Then
use your other hand to insert the plug with a gentle rocking motion
until you have sealed the ear canal. Advantages of pre-molded plugs
are that they are relatively inexpensive, reusable, washable,
convenient to carry, and come in a variety of sizes. Nearly
everyone can find a plug that will be comfortable and effective. In
dirty or dusty environments, you don't need to handle or roll the
tips.
Canal caps Canal caps often resemble earplugs on a flexible
plastic or metal band. The earplug tips of a canal cap may be a
formable or pre-molded material. Some have headbands that can be
worn over the head, behind the neck or under the chin. Newer models
have jointed bands increasing the ability to properly seal the
earplug.
The main advantage canal caps offer is convenience. When it's
quiet, employees can leave the band hanging around their necks.
They can quickly insert the plug tips when hazardous noise starts
again. Some people find the pressure from the bands uncomfortable.
Not all canal caps have tips that adequately block all types of
noise. Generally, the canal caps tips that resemble stand-alone
earplugs seem to block the most noise.
Earmuffs Earmuffs come in many models designed to fit most
people. They work to block out noise by completely covering the
outer ear. Muffs can be "low profile" with small ear cups or large
to hold extra materials for use in extreme noise. Some muffs also
include electronic components to help users communicate or to block
impulsive noises.
Workers who have heavy beards or sideburns or who wear glasses
may find it difficult to get good protection from earmuffs. The
hair and the temples of the glasses break the seal that the earmuff
cushions make around the ear. For these workers, earplugs are best.
Other potential drawbacks of earmuffs are that some people feel
they can be hot and heavy in some environments.
Still, the best hearing protector is the one that is comfortable
and convenient and that you will wear every time you are in an
environment with hazardous noise. When engineering or
administrative controls can't eliminate your exposure to hazardous
noise, you can wear hearing protection devices, such as ear plugs
or ear muffs.
Not every type of hearing protection is useful for every type of
noise. Disposable foam earplugs may be fine for some noise exposure
while earmuff-type protection may be suitable for another.
But hearing protection doesn't work if you don't use it.
According to a study, construction workers said they wear ear plugs
or ear muffs between 36 to 61 percent of the time when they are
necessary. Not surprisingly, more than half believed they developed
a hearing loss.
Some International Standards governing permitted Noise Levels of
Heavy Earth Moving Machines are as below
ISO 6394:2008 Specifies a method for determining the emission
sound pressure level of earth-moving machinery at the operator's
position, measured in terms of the time-averaged A-weighted
emission sound pressure level while the machine is stationary with
the engine operating at the rated speed under no-load conditions.It
is applicable to earth-moving machinery as defined in ISO 6165 and
specified in ISO 6393:2008
ISO 6395:2008
Specifies a method for determining the noise emitted to the
environment by earth-moving machinery, measured in terms of the
A-weighted sound power level while the machine is operating under
dynamic test conditions. It is applicable to earth-moving machinery
as specified in Annex A and as defined in ISO 6165.
ISO 6396:2008
Specifies a method for determining the emission sound pressure
level of earth-moving machinery at the operator's position,
measured in terms of the time-averaged A-weighted emission sound
pressure level while the machine is operating under dynamic test
conditions.It is applicable to earth-moving machinery as defined in
ISO 6165 and as specified in ISO 6395:2008, Annex A.
The tenth conference under Para 4.2requires Vibration studies of
various mining machinery required to be done before their
introduction in mining operations as per ISO standardsISO
5349:1986] for hand-arm vibration (HAV) and ISO 2631:1997] for
whole-body vibration (WBV) are two most important standards that
are widely used for evaluation of vibration exposure. Vibration
transmitted to the body through the supporting surfaces such as
feet, buttocks or back is known as whole body vibration (WBV).
There are various sources of WBV in the mining industry, such as
the seat-transmitted vibrations from dumper, dozer, shovel,
backhoes, load-haul-dump vehicles (LHD), road graders, etc.; WBV
transmitted through feet while standing on or moving near vibrating
machines like various types of crushers, vibrating screen or while
operating certain types of loadersEquipment-induced vibration is
widely recognized as a health hazard. It is a physical stressor to
which many people are exposed at workplace. An estimated 1 million
workers were engaged in the Indian mining industry in the year
2003. The actual figures could be much higher. Analysis of
employees database of several mines reveals that 18% employees in
the Indian mining industry are occupationally exposed to vibration.
Large-scale mechanization considerably adds to the severity and
complexity of the problem because of
1) increase in the percentage of exposed population and
2) longer duration of exposure.
Vibration is defined as oscillatory motion. Oscillatory
displacement involves alternate velocity in one direction and then
a velocity in the opposite direction. This change of velocity means
that the object is constantly accelerating, first in one direction
and then in the opposite direction.[ In 1977 the International
Labor Office (ILO) listed vibration as an occupational hazard and
recommended that measures have to be taken to protect employees
from vibration and the responsible authorities have to establish
criteria to determine the danger; when necessary, the exposure
limits must be defined by means of these criteria. Supervision of
employees exposed to occupational hazard as a result of vibration
at their places of work must also include a medical examination
before the beginning of this particular job, as well as regular
check ups later
ISO/TR 25398:2006 provides guidelines for those such as
employers, national authorities and manufacturers of earth-moving
machinery who are required to determine, assess and document the
daily whole body vibration exposure for ride-on machines as defined
in ISO 6165. It also provides guidelines for reducing vibration
levels on machines and for determining the vibration reduction from
machine improvements to reduce vibration levels. It is intended to
assist in establishing documentation for specific earth-moving
machinery under typical operating conditions.
Health impacts
The human responses to vibration depend on the part of the body
that is exposed. There are two broad types of vibrations that
workers are exposed to:
1) Vibration transmitted to the whole body (whole-body vibration
or WBV) through a supporting surface, for example, the feet of a
standing person or the buttocks of a seated person 2) Vibration
applied to a part of the body, i.e., segmental vibration. When
vibration is applied to the hand, it is termed as hand-arm
vibration or HAV.
Whole-body vibration and segmental vibration need to be studied
separately because they are measured and evaluated using different
standards. They also require different control measures and have
differing effects on the human body. The earliest literature
available on health impact of vibration chiefly refers to the
miners. The widespread use of jackhammers in the mining industry is
a potential source of hazardous vibration affecting limbs in the
human body. Jackhammers are used both in opencast and underground
mines; and the operators, popularly known as drillers, are
regularly exposed to hand-arm vibration (HAV). Vibrating hand tools
like hand drills, chipping machine, riveting guns; control systems
of modern large drill machines; and handheld grinders, scrapers,
etc, are other sources of HAV exposure in mines.
Regular exposure to vibration causes both vascular and neural
disorders. Involvement of arms manifest as vibration-induced white
finger (VWF) or hand-arm vibration syndrome (HAVS). The clinical
symptoms are:
1. Tingling and/or numbness in the finger(s) initially - similar
to but not same as Carpel Tunnel Syndrome (CTS).
2. As the exposure continues, the appearance of a single white
or blanched fingertip occurs - usually, but not always in the
presence of cold.
3. With further exposure, these attacks increase in number,
intensity and duration, especially in cold conditions. In the later
stages, HAVS attack will occur in all seasons. Simultaneous
combination of vibration, cold and nicotine (from smoking) are
particularly harsh since all three tend to act as synergistic
vasoconstrictors. Later stages of HAVS are generally
irreversible.
4. In extreme and rare cases, the loss of blood supply to the
fingers can lead to gangrene, which may require amputation.
The existence of sensory and vascular components in HAVS led to
the adoption of the Stockholm grading based on the subjective
history supported by the results of clinical tests to classify the
severity Stockholm workshop scale for classification of hand arm
vibration syndromeS.NoStageSymptoms
Cold-induced Reynauds phenomenon
0No attacks
1Mild Occasional attacks affecting only the tips of one or more
fingers
2Moderate Occasional attacks affecting distal or middle (rarely
also proximal) phalanges of one or more fingers
3Severe Frequent attacks affecting all phalanges or most
fingers
4Very severe As in stage 3, with trophic changes in the finger
tips
Sensor neural effects
S.NoStageSymptoms
10SNExposed to vibration but no symptoms
21SNIntermittent numbness, with or without tingling
32SNIntermittent or persistent numbness, reduced sensory
perception
43SNIntermittent or persistent numbness, reduced tactile.
discrimination and or manipulative dexterity.
.
Vibration levels of various mobile mining equipments were
measured by a study group. Track dozers in opencast mines were
studied in Australia. It was observed that the operators were at
health risk if they worked 6 h per day. There is strong
epidemiological evidence that occupational exposure to WBV is
associated with an increased risk of lower back pain, sciatic pain
and degenerative changes in the spinal system, including lumbar
inter vertebral disc disorders. Which parts of the body are most
likely to be injured during exposure to whole-body vibration
depends on the magnitude of vibration, distribution of the motion
within the body, body postures and the vibration frequency,
direction and duration. Ill effects of WBV are :
Diseases of spinal column: These are very common and associated
with long-term exposure to whole-body vibration. The back is
especially sensitive to the 4-8 Hz vibration range. WBV exposure
has been linked to severe lower back pain (lumbar spine) and
degeneration, bucking/ slipping of the lumbar discs. Chronic
exposure to WBV takes some time before lower back problems develop.
Poorly designed vehicle seats, awkward postures and manual cargo
handling in addition to WBV exposure tend to aggravate lower back
pain symptoms. Digestive system diseases are often observed in
persons exposed to whole-body vibration over a long period of time.
This is due to resonance movement of the stomach at frequencies
between 4 and 5 Hz. Prolonged exposure to whole-body vibration at
frequencies below 20 Hz affects cardiovascular system and results
in hyperventilation, increase in heart rate, oxygen intake,
pulmonary ventilation and respiratory rate. The Indian mining
scenario
National Institute of Miners Health, Nagpur, conducted vibration
surveys in various mines of the country. It was found that in
opencast mines, operators of heavy earth moving machineries (HEMM)
were at greater health risk from occupational exposure to
vibration. Records of two metal mines were examined to determine
the percentage of mining population regularly exposed to
occupational vibration . An average of 18% employees was found to
be exposed to vibration at work.
EmployeesNos. Percentage
Total No. of employees studied2106
No. of employees exposed to HAV1828.6
No. of employees exposed to WBV1949.2
Subjects exposed to occupational vibration in mining
industry
International standards and regulations are based on the
research work done in developed countries, where working conditions
are different and susceptibility of an individual to external
stimuli may considerably vary,
Principal resonance frequencies of human
bodyPosturePartResonancefrequency
(Hz)
Standing Whole body4-7
Head and shoulder1-2
Lower arm 15-30
Hand30-150
Legs2-20
Knees1-3
Foot16-31
Sitting/RecliningKnees Abdomen & Chest4-8
Eye balls20-25
Skull50-70
MEASURING VIBRATION
Evaluation of severity of exposure depends on measurement of
magnitude, frequency, direction and duration of vibration, followed
by comparison with scientific guidelines. All these parameters of
exposure can be measured simultaneously using modern digital
vibration monitors coupled with personal computers in field
conditions.
The duration of measurement may be for a few minutes if it
characterizes a repetitive cycle of operation throughout the day. A
typical instrument uses accelerometers as sensors (transducers)
which convert the mechanical energy of vibration into equivalent
electrical energy and integrates the varying quantities over the
period of measurement.
Acceleration values in three mutually perpendicular axes are
simultaneously obtained (i.e., up-down, side-to-side
and front-to-rear) for HAV and WBV.
The vibration results in each direction are then separately
weighted, calculated for comparison with the appropriate HAV or WBV
standard to determine if any exposure action value (EAV) or
exposure limit value (ELV) has been exceeded.
The result is expressed in terms of acceleration in individual
axis, summation of all three axes or vibration dose value (VDV),
etc, as per their definition and applicability described in
reference standards.
The run time history is recorded so that the varying magnitudes
and their characteristics such as presence of shocks, etc, can be
attributed to a particular operation.
The Bureau of Indian Standards (BIS) has adopted vibration
standards that are identical to corresponding ISO standards.
REFERENCES
1) The tenth conference on Safety in Mines2) Bibhuti B. Mandal,
Anup. K. Srivastava National Institute of Miners Health, Nagpur,
India , Risk from vibration in Indian Mines,
3) ISO standards on Ergonomics for Earth Moving Machinery
VibratioN
EMBED AcroExch.Document.7
Earth Moving Equipment Safety Round Table (EMESRT)
NOISE