Chapter 22

Noise and Vibration Hazards

Major Topics

• Hearing loss prevention terms• Hazard levels and risk• Standards and regulations• Worker’s compensation and noise hazards• Noise control strategies• Vibration hazards• Evaluating hearing loss prevention

programs

Sound

• Sound is any change in pressure that can be detected by the ear. Typically sound is change in air pressure. However it can also be change in water pressure or any other pressure sensitive medium.

Difference between Sound and Noise

• Noise is unwanted sound.

• Consequently the difference between noise and sound is in the perception of the person hearing it.

Differentiate between sound and vibration

• Sound typically relates to a sensation that is perceived by the inner ear as hearing.

• Vibration on the other hand is inaudible and is perceived through the sense of touch.

Relationship between pitch and cycles of sound waves

• Normal atmospheric pressure is represented by a straight line (see fig 22-1 page 499).

• Sound is represented by a wavy line that crosses above and below the straight line.

• The more frequently the sound waves cross the normal atmospheric pressure line (the shorter the cycle), the higher the pitch of the sound.

• The greater the vertical distance above and below the atmospheric pressure line, the louder or more intense the sound.

Types of industrial noise

• Wide band noise: is noise that is distributed over a wide range of frequencies. Most noise from manufacturing machines is wide band noise.

• Narrow band noise: is noise that is confined to a narrow range of frequencies. The noise produced by power tools is narrow band noise.

• Impulse noise: consists of transient pulses that can occur repetitively or non repetitively. The noise produced by a jackhammer is repetitive impulse noise.

Physiological problems associated with excessive noise

• The fundamental hazard associated with excessive noise is hearing loss.

• Exposure to excessive noise levels for an extended period can damage the inner ear so that the ability to hear high frequency sound is diminished or lost altogether.

• Additional exposure can increase the damage until even lower frequency sounds cannot be heard.

Risk of hearing loss from exposure to excessive noise

• A number of factors affect the risk of hearing loss associated with exposure to excessive noise:

• Intensity of the noise (pressure level)• Type of noise (wide band, narrow band, impulse)• Duration of daily exposure• Total duration of exposure (number of years)• Age of the individual• Coexisting hearing disease• Nature of the environment in which exposure occurs• Distance of the individual from the source of noise• Position of the ears relative to the sound waves

Sound level for personal protection

• Of the various factors the most critical are the sound level, frequency, duration and distribution of noise.

• The unprotected human ear is at risk when exposed to sound levels exceeding 115 dBA (decibels).

• Exposure to sound levels below 80 dBA is generally considered safe.

• Prolonged exposure to noise levels above 80 dBA should be minimized through the use of appropriate personal protective devices.

• To decrease the risk of hearing loss, exposure to noise should be limited to a maximum 8 hour time weighted average of 85 dBA (without protection).

ANSI S12.13-1991• In 1991 ANSI published ANSI Standard S12.13-1991 titled

“Evaluation of Hearing Conservation Programs”. This standard is designed to help safety and health professionals determine if hearing conservation programs work as they are intended.

• The advantage of the ANSI methods are:• Results of tests are compared in sequence. For example results of

year 4 are compared with results of year 3. The results of the earlier test are used as a baseline for comparison.

• Test results from several employees in a given work unit are examined individually and compared with past results sequentially. If enough employees show hearing loss, the conclusion may be that the work unit’s hearing conservation program is ineffective.

OSHA 29 CFR 1910.95

• The basic requirements generated from this OSHA standard for hearing conservation programs are as follows:

• Hearing hazards monitoring• Engineering and administrative controls• Audiometric evaluation• Personal hearing protection devices• Education and motivation• Record keeping• Program evaluation

Factors medical professionals consider in determining causal relationship of hearing loss

• The most common measurements are area surveys, dosimetry, and engineering surveys:

• In an area survey, environmental noise levels are measured using a sound level meter to identify work areas where exposures are above hazardous levels.

• Dosimetry involves the use of body worn instruments (dosimeters) to monitor an employee’s noise exposure over the work shift.

• Engineering surveys typically employ more sophisticated acoustical equipment in addition to sound level meters. These measurements are used to assess options for applying engineering controls.

Follow up, noise survey, audiometric testing

• Noise surveys involve measuring noise levels at different locations in the workplace. A sound level meter produces an immediate reading that represents the noise level at a specific instant in time. A dosimeter provides a time weighted average over a period of time such as one complete work shift.

• Audiometric testing: measures the hearing threshold of employees. For employees found to have a standard threshold shift – a loss of 10 dBA or more averaged at 2000, 3000, and 4000 Hz in either ear – the employer is required to fill out an OSHA 200 form in which the loss is recorded as a work time illness.

• Follow up: is critical. Failure to take prompt corrective action at the first sign of hearing loss can lead to permanent debilitating damage.

Appropriate follow up activities to initial hearing loss test

• Administering a retest to verify the hearing loss• Changing or improving the type of personal

protection used• Conducting a noise survey in the employer’s

work area to determine if engineering controls are sufficient.

• Testing other employees to determine if the hearing loss is isolated to the one employee in question or if other employees have been affected.

Engineering and Administrative Controls

• Engineering controls: are steps taken, other than administrative or personnel protection procedures, to reduce the sound level at the source or within the hearing zone of workers. All of these controls are designed to reduce noise at the source, along its path, or at the receiver.

• Administrative Controls: are controls that reduce the exposure of employees to noise rather than reducing the noise. Administrative controls should be considered a second level approach with engineering controls given top priority.

What is HAV?

• The most common vibration related problem is known as hand-arm vibration syndrome (HAV).

• Prevention strategies:• Purchase low vibration tools.• Limit employee exposure: NIOSH recommends no more

than 4 hours per day, two days per week.• Change employee work habits: wear properly fitting thick

gloves that can partially absorb vibration, take periodic breaks (at least 10 minutes each hour), use a loose grip on the tool and hold it away from the body, keep tools properly maintained (replace vibration absorbing pads regularly), keep warm, and use vibration absorbing floor mats and seat covers as appropriate.

Classification of HPDs

• The following 4 classifications of HPDs (hearing protection devices) are widely used: enclosures, ear plugs, super aural caps, and earmuffs.

• Enclosures are devices that completely cover the employees head, much like helmets.

• Earplugs (aurals) are devices that fit into the ear canal.• Superaural caps fit over the external edge of the ear

canal and are held in place by a headband.• Earmuffs cover the entire ear with a cushioned cup that

is attached to a headband.• Earplugs and earmuffs are able to reduce noise by 20 to

30 dB. By combining earplugs and earmuffs and additional 3 to 5 dB of blockage can be gained.

Evaluation of a hearing loss prevention program

• Hearing loss prevention programs should be evaluated periodically to ensure their effectiveness. Such evaluations should have at least the following components:

• training and education: training at least once a year, provided by qualified instructor, evaluation of training, content revised periodically, manager and supervisor involvement, posters, handouts, personal counseling sessions.

• supervisor involvement: supervisors provided with knowledge, wear hearing protectors in appropriate areas, discipline employees who repeatedly refuse to wear hearing protectors.

• noise measurement: noise exposed employees notified of exposure and apprised of auditory risks, results transmitted to supervisors, entered into health and medical records.

• engineering and administrative controls: most effective means of controlling or eliminating the hazard.

• monitoring and record keeping: audiometric technician adequately trained, certified, records complete, OSHA standards, NIOSH recommendations, results communicated to supervisors, managers, and employees.

• referrals: to outside sources for consultation or treatment• hearing protection devices: made available to all employees whose daily average noise

exposure is 85 dBA or above.• Administration: keeping organized and current on any changes in federal or state

regulations.

Summary• Sound is change in pressure that can be detected by the ear. It is

measured in decibels (dBA).• Noise is excessive sound.• Noise levels less than 80 dBA are considered safe.• Standards and regulations: ANSI S12.13, Evaluation of hearing

conservation programs and OSHA 29 CFR 1910.95, the hearing conservation amendment.

• Identifying hazardous noise: noise surveys, audiometric tests, record keeping, and follow up.

• Vibration can cause spinal injury due to hand arm vibration syndrome (HAV).

• Hearing loss prevention programs should include: training and education, supervisor involvement, noise measurement, engineering and administrative controls, monitoring and recordkeeping, referrals, hearing protection devices, and administration.

Home work

• Answer questions 8, 9 , 10, 15 and 16 on pages 520- 521.

• 8. At what sound level is it necessary to begin using some type of personal protection?

• 9. Give a brief description of ANSI S12.13.• 10. Give a brief description of OSHA 29 CFR

1910.95, Hearing Conservation Amendment.• 15. What is HAV? How can it be prevented?• 16. Explain the four classifications of HPD’s that

are widely used.