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