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Casella USA Why Hearing Protectors are Important Why hearing protectors are important Why should we care about our hearing? It provides a link to the outside world One of the 5 basic human senses Taste Smell Touch Sight Hearing How do we hear?

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casella usa

Casella USA

Why Hearing Protectors

are Important

why hearing protectors are important
Why hearing protectors are important
  • Why should we care about our hearing?
    • It provides a link to the outside world
  • One of the 5 basic human senses
    • Taste
    • Smell
    • Touch
    • Sight
    • Hearing
how do we hear
How do we hear?
  • Pressure variations in the air caused by something moving and disturbing the air
  • Sound waves are collected by our outer ears
  • Mechanical vibrations are amplified by the small bones in the middle ear
  • Vibrations are turned into electrical impulses by the cochlea in the inner ear
  • Our brain sorts them out into meaningful sounds
damage to our hearing
Damage to our hearing
  • Our ears are very delicate
    • Can hear sounds over a very wide range of levels, frequencies and times
  • Damage to our ears can occur from a number of sources
    • Mechanical shock
    • Ototoxic drugs
    • Exposure to high noise levels
exposure to high noise levels
Exposure to high noise levels
  • Can occur socially
    • Gun shooting
    • Motor racing
    • Music concerts
  • Can occur at work
    • Exposure to high noise levels
    • Long exposure over a working lifetime
    • Results in a social impairment to hearing acuity
the equal loudness curves
The equal loudness curves
  • Lowest curve shows the threshold of hearing (audibility) for normal adult male
the inequality of human hearing loss
The inequality of human hearing loss
  • We do not loose our hearing in a linear fashion
  • Hearing loss is more pronounced at certain frequencies than others
  • The mid frequencies are lost first
    • 4 kHz dip
    • Then hearing loss spreads out across the range
    • Effect is to hear “muffled” sounds rather than just reduced in volume
the inequality of human hearing loss8
The inequality of human hearing loss

Graph of hearing loss after different exposure times taken from NIOSH web site

see for further information

how do we monitor noise exposure
How do we monitor noise exposure?
  • Use noise measurement instruments
  • Hand held sound level meters
    • Best where workers are at fixed locations or follow known patterns of work, e.g. process workers
  • Personal noise dosimeters
    • Best where workers have random job patterns or are mobile during the day, e.g. construction workers
what do we need to monitor
What do we need to monitor?
  • OSHA workplace noise regulations stipulate the Time Weighted Average noise level (TWA) in decibels
  • Notional equivalent noise level for a standard working day to ensure consistency across all industries
  • Permitted exposure level is set at 90 dB for 8 hours
  • Averages out the noisy times and the quieter periods
  • All the noise exposure at work during a shift must be included but result expressed as an 8 hour “standard day”
what if the noise levels are too high
What if the noise levels are too high?
  • More noise can be tolerated but the exposure duration must be reduced accordingly
  • Average of 90 dB for 8 hours = 100%
  • Average of 95 dB for 4 hours = 100%
  • Average of 100 dB for 2 hours = 100%
  • Anything above this must be reduced
how do we reduce noise exposure
How do we reduce noise exposure?
  • Make the noise source quieter
  • Increase the distance between the noise source and worker
  • Put up barriers between noise and worker
  • Put enclosure around noise source
  • Reduce exposure duration for worker
  • Reduce noise arriving at workers ears
how to limit personal noise exposure
How to limit personal noise exposure?
  • Must protect the ears to block the unwanted noise out
  • Can fit hearing protectors over the ears
    • Ear muffs
  • Can fit hearing protectors inside the ear canal
    • Ear plugs
are all hearing protectors the same
Are all hearing protectors the same?
  • NO!!
  • Some work better than others
  • More reduction at certain frequencies
  • Comfort
  • Weight
  • Size
  • Suitability for a specific task
how do we choose the right protector
How do we choose the right protector?
  • Must be acoustically capable of reducing high noise to below the required limit
  • Decibel reduction at different frequencies must be considered
  • Must be comfortable and acceptable to the worker to wear for the required period of time
  • Cannot be effective if it is not worn
rating hearing protectors
Rating hearing protectors
  • Reduction performance varies with frequency
  • Measure noise reduction at standard frequencies in 9 octave bands from 31 Hz to 8 kHz
    • Needs an octave band sound level meter
  • Use the Noise Reduction Rating (NRR) method
    • Simpler sound level meter or noise dosimeter can be used to measure the overall ‘C’ and ‘A’ noise levels
performance of hearing protectors
Performance of hearing protectors
  • Both methods are based on the different reductions achieved by ear plugs or ear muffs at different frequencies
  • Calculations provide a single number rating value for the hearing protector
  • Can estimate which models would be effective for a given source of noise
  • Allow the worker to choose which model based on personal choice, weight, size etc.
what happens if a protector is not worn
What happens if a protector is not worn?
  • All the good work obtained from making noise measurements will be wasted if the chosen hearing protector is not used!
  • Consider the example of a hearing protector that has a nominal noise reduction of 30 dB
  • If it is only worn for 50% of the required time the best reduction achieved by wearing the protector will be only 3 dB!!
  • 75% wearing will still only give 6 dB reduction
  • Hearing loss is a common feature of a modern work environment where there are many noisy machines
  • Risk is proportional to the average level and the exposure time
  • Best solution is to reduce the noise at source
  • More likely that personal hearing protection must be used in the short term
  • Hearing protectors must be suitable and effective
  • Protectors must be worn to achieve expected reduction
cel products to measure noise
CEL Products to measure noise
  • The CEL-200 series of sound level meters
    • 231 basic model
    • 254 with A and C
    • Type 2
    • No memory
    • Simple meters
cel products to measure noise21
CEL Products to measure noise
  • The CEL-300 series of noise dosimeters
    • 320 basic model
    • 360 data logging
    • Memory for storage
    • Direct printing
    • Type 2 accuracy
    • Calculates all required parameters for OSHA
cel products to measure noise22
CEL Products to measure noise
  • CEL-400 series sound level meters
    • 440 basic model
    • 480 data logging
    • Memory
    • Printing
    • Type 1 and 2
    • Frequency analysis by auto-scanning bands
cel products to measure noise23
CEL Products to measure noise
  • CEL-500 series real time analysers
    • 553 basic model
    • 573 data logging
    • 593 event logging
    • Memory & Printing
    • Simultaneous frequency analysis
    • Type 1
    • Upgradeable
casella cel inc in the usa
Casella CEL, Inc. in the USA

How to contact us –

Casella CEL, Inc. Western Office,

17 Old Nashua Road, #15 PO Box 1592,

Amherst, NH 03031 Vacaville, CA 95696

Tel 1 (800) 366 2966 1 (877) 299 2966

Fax 1 (603) 672 8053 1 (707) 446 4731


On the Web at