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noise source. path of propagation. reduce the strength. impede the acoustic energy along its transmission path. Noise Control (A System Approach). protect the individual at the receiving end from exposure to the noise. individual receiving the noise. Principle:

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noise control a system approach

noise source

path of propagation

reduce the strength

impede the acoustic energy along its transmission path

Noise Control(A System Approach)

protect the individual at the receiving end from exposure to the noise

individual receiving the noise

  • Principle:
  • Plan with noise control consideration
  • Reduce at source
  • Attenuation during transmission
  • Receiver Personal Protection (by ear protectors, hearing conservation programme and exposure control:
  • ear plugs, ear muffs, communication headsets and helmets)



Noise Control starts at Planning Stage

1. Noisy operations should be grouped in one area. (Why?)

2. The machines purchased should be those with low noise output.

3. Noisy areas where workers spend time should have adequate sound absorption materials on the ceiling and the walls.

4. Noisy equipment should be fastened on a rigid and heavy base with adequate isolating elements to avoid propagation of vibration.

5. Noise sources (machines) should be enclosed with structures which supply adequate sound insulation.

6. Offices and other places where mental work is carried out should be situated far from the noise source. The intervening rooms, which will act as buffers, should be used for parking, stores etc. .


Attenuation during transmission

  • Positioning the source to increase the distance between the noise source and the individual)
  • Planning of the layout of the building to reflect the energy back towards its source
  • Using barriers, enclosures and absorption materials with good sound absorption coefficient(the fraction of the incident energy which is absorbed by the material)
  • Controlling of vibration by vibration isolators or by increasing the rigidity and mass of the item to be protected.

Good Practice:

  • Noise Labeling: in a noisy environment display the measured noise levels of the sources at different positions.
  • For mobile machines and equipment display noise level at the bye standers location at 7 m distance
  • Measure noise levels and divide the exposed areas into noise class like:
    • 76-85 Class I
    • 86-95 Class II
    • 96-105 Class III
    • Above 105 or Lpeak >140 dB (lin) Class IV
  • Maintain exposure duraction under different noise levels as:


Noise level (LAeq,T) dB(A) Time to reach noise exposure (LAeq,8h) of 85 dB(A)

85 8.0 hours

86 6.4 hours

87 5.1 hours

88 4.0 hours

89 3.2 hours

90 2.5 hours

91 2.0 hours

92 1.6 hours

93 1.3 hours

94 1.0 hour

95 48 min

96 38 min

97 30 min

98 24 min

99 19 min

  • Noise level (LAeq,T) dB(A) Time to reach noise exposure (LAeq,8h) of 85 dB(A)
  • 100 15 min
  • 101 12 min
  • 102 10 min
  • 103 8 min
  • 104 6 min
  • 105 5 min
  • 106 4 min
  • 107 3 min
  • 108 2 min
  • 109 115 sec
  • 110 90 sec
  • 111 72 sec
  • 112 58 sec
  • 113 47 sec
noise control
Noise Control
  • Administrative Control
  • Engineering Control
  • Personal Protective Equipment ( hearing protective devices)
administrative controls
Administrative Controls
  • Operate noisy equipment on second or third shifts.
  • Rotate employees through high-noise areas.
  • Modify existing machinery.
  • Place noise limit specs. on new equip.
  • Maintain equip. in good condition.
  • Use noise control when installed.
  • Reporting noisy equip. to supervisor for repair.
engineering controls
Engineering Controls
  • Reduce noise at the source.
  • Interrupt the noise path.
  • Reduce reverberation and structural vibration.
personal protective equipment hearing protection devices hpd
Personal Protective Equipment (Hearing Protection Devices - HPD)
  • Employers shall provide to employees exposed to 8 hr TWA of 85 dB at no cost.
  • Employers shall ensure being worn:
    • by employees exposed to 8 hr TWA of 90dB or greater
    • by employees exposed to 8 hr TWA of 85dB or greater and:
      • Whose baseline audiogram has not been established
      • Who have experienced a threshold shift
hearing protection device hpd noise reduction
Hearing Protection Device (HPD)Noise Reduction
  • HPD must reduce employee noise exposure below PEL e.g. below 8 hr TWA of 90 dB.
  • Employees with standard threshold shift (STS), HPD must reduce employees noise exposure below an 8 hr TWA of 85 dB.
  • Noise Reduction Ratio (NRR)
    • Convert dose to TWA; subtract 7 from NRR; subtract remainder from TWA to obtain the est.TWA under ear protector
    • Subtract 7 from NRR; subtract remainder from TWA to obtain the est. TWA under ear protector
hearing protection use
Hearing Protection Use
  • Voluntary Use
    • Exposed to an 8 hr TWA of 85 dB
  • Mandatory Use
    • Exposed to an 8 hr TWA of 90 dB
    • Exposed to an 8 hr TWA of 85 dB but have not had a baseline hearing test
    • Employees who have suffered STS hearing loss and are exposed to an 8 hr TWA of 85 dB
employee responsibility
Employee Responsibility
  • Understand the need for hearing protection devices.
  • Wear HPDs and seek replacements.
  • Encourage co-workers to wear HPDs.
  • Communicate problems to supervisors.
management responsibility
Management Responsibility
  • Provide occupational noise training.
  • Provide hearing protection devices.
  • Demonstrate commitment – wear HPDs.
  • Enforce the use of HPDs.
  • Keep up to date with HPD selection and use.
  • Encourage questions and resolve problems.
purpose of hearing protectors
Purpose of Hearing Protectors
  • Reduction of sound waves traveling to the inner ear
attenuation of different types of hearing protectors
Attenuation of Different Types of Hearing Protectors
  • Ear Plugs
    • Reduce noise by as much as 30 decibels
  • Ear Canals
    • Reduce noise by as much as 30 decibels
    • Used when individual is unable to use traditional ear plugs
  • Ear Muffs
    • Reduce noise by as much as 15-30 decibels
    • Use in conjunction with ear plugs when exposed to high noise levels (105+ decibels)
instructions on selection fitting use and care of hearing protectors
Instructions on Selection, Fitting, Use, and Care of Hearing Protectors

Ear plugs

    • Keep clean and free of materials
      • Wash in mild liquid detergent and warm water
      • Squeeze excess water and air dry
    • Discard plugs when hardened or do not re-expand
  • Ear Canals
    • Clean like normal ear plugs
    • Do not tamper with the headband and the acoustic seal
instructions on selection fitting use and care of hearing protectors1
Instructions on Selection, Fitting, Use, and Care of Hearing Protectors
  • Ear Muffs
    • Keep clean and free of debris
      • Clean cushions with warm soapy water
    • Do not tamper with the acoustic seal between the cushions and the headband
    • Do not modify the ear muffs in any way
    • Do not stretch or abuse the headband
audiometric testing
Audiometric Testing
  • Conducted by a qualified audiologist.
  • Baseline Audiogram/Test
    • Shows initial hearing status
    • For comparison to future audiograms
  • Periodic (Annual) Audiogram/Test
    • To determine if HCP is effective and if non-noise factors affects hearing
    • Recheck audiogram or professional referral necessary if significant hearing change occurs
purpose of audiometric testing
Purpose of Audiometric Testing
  • To measure hearing by sending tones to each ear through headphones.
  • To show how one’s hearing compares to normal hearing based on age.
  • To determine whether hearing is being conserved.
  • To alert employee and employer for noise, age or medical related hearing loss.
explanation of test procedures
Explanation of Test Procedures
  • Audiometer sends tones to each ear through headphones.
  • Listen carefully and respond each time you hear a tone.
  • Levels at which you can barely hear the tones is your hearing threshold levels.
  • Audiogram records threshold (dB) for different pitches or frequencies (Hertz).
evaluation of audiogram
Evaluation of Audiogram
  • Annual audiogram compared to baseline audiogram to determine threshold shift
  • If threshold shift
    • Employee must be notified in writing within 21 days
  • If threshold shift from occ. noise exp.
    • Employee fitted with hearing protectors, trained in use and care, required to use them.
    • Employee refitted with better attenuation hearing protectors and retrained in hearing protector use
    • Refer employee to eval/exam if add. testing necessary or if medical pathology is caused by hearing protectors
    • Inform employee of need to eval/exam if medical pathology unrelated to hearing protectors is suspected
evaluation of audiogram con t
Evaluation of Audiogram (con’t)
  • If subsequent audiogram to noise exp. less than 8 hr TWA of 90dBA indicates that threshold shift is not persistant:
    • Inform employee of new audiogram
    • May discontinue required use of hearing protectors

Normal Hearing

Mild Hearing Loss

Moderate Hearing Loss

Severe Hearing Loss

Profound Hearing Loss

standard threshold shift
Standard Threshold Shift
  • Hearing ability changed by an average of 10 decibels.
  • Employee notification within 21 days.
  • Revised hearing protection required.
  • Further medical evaluation.
  • Allowance may be made for the contribution of aging.
audiometric test requirements
Audiometric Test Requirements
  • Test shall be pure tone, air conduction, hearing threshold exam.
  • Test frequencies from 500 to 6000 Hz in each ear.
  • Audiometers shall meet ANSI S3.6 and Appendix B
  • Audiometric exams administered in room shall meet Appendix C
audiometer calibration
Audiometer Calibration
  • Audiometer functional operation shall be checked daily.
  • Audiometer calibration shall be checked acoustically annually per Appendix D
  • Provide annually to employees who are exposed to noise at or above 8 hr TWA of 85 dB.
  • Topics must include:
    • Effects of Noise on Hearing
    • Purpose of Hearing Protectors
    • Advantages and Disadvantages of Different Types of Hearing Protectors
    • Attenuation of Different Types of Hearing Protectors
    • Instructions on Selection, Fitting, Use, and Care of Hearing Protectors
    • Purpose of Audiometric Testing
record keeping
Record Keeping
  • Employee Exposure Measurements
  • Audiometric Tests
    • Audiogram/Noise Exposure Assessment
    • Job classification
    • Audiometer calibration date
  • Hearing Protection Devices Used
  • Audiometric Test Rooms
    • Background sound pressure level in test room
  • Constant exposure to noise over 85 dB can cause hearing damage.
  • Hearing loss can not be cured or repaired.
  • Hearing tests should be conducted annually.
  • Hearing protection devices include ear plugs, ear muffs, and canal caps.