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Work Related Hazards
Physical
Chemical
Biological
Pysical Hazards
Sound
Radiation
Electricity
Temperature
Sound
Sound Waves
Sound Spectrum
S pectrum of the Salvatore Mundi bell, Salzburg.
Sound Propagation
Hearing
Cochlea
Hair Cells
Graph showing HEARING LOSS as a function of FREQUENCY
Work InducedHEARING LOSS
Audiogram
Measured by an AUDIOMETER.
0 dB denotes the hearing threshold level
Points below 0 denote louder threshold levels
Work Related Hearing Loss
PRESBYCUSIS
PRESBYCUSIS
Men
Is this loss caused by noisy modern living or is it natural aging?
PRESBYCUSIS
Rosen discovered almost no signs of presbycusis among the Mabaan tribe of the Sudan
May be due to their Relatively Noise-Free environment and generally healthy condition.
TINNITUSA ringing sound heard in the ear
Caused by: prolonged exposure to loud sound,
or short exposure to very loud sound.
Temporary or chronic,
Taking drugs such as aspirin.
Measurement of Sound
Sound IntesityThe units
ergs per second per square cm, or the watts per square meter.
THRESHOLD OF HEARING:
10 WATTS / M,2-12
PAIN THRESHOLD: 1 WATTS / M,2
Intensity (Power) Level
The measurement of the INTENSITY of one sound in comparison to another sound or fixed level
Expressed in DECIBELs.
DECIBEL (dB)
The decibel is defined as one tenth of a belOne bel is the difference in level between two intensities X and Y where one is ten times greater than the other.
Intensity level (dB) = 10 log10 (X /Y)
DECIBEL (dB)
The difference between 10-8 watts/m2 and 10-4 watts/m2, an actual difference of Sound Intesity of10,000 units,
Has a difference of Intesity levelof 4 bels or 40 decibels.
Threshhold of pain (1 watt/m2) to
Threshhold of hearing (10-12 watts/m2),
Range of Sound Intensities
I decibells it is 0 to 120 dB.
An increase of Sound intesity of 10 Watts / M2 causes an increase of 10 dB
An increase of Sound intesity : of 10 Watts / M2 causes an increase of 10 dB
6
Increase of Sound intesity
To double Sound Intestiy causes an extra 3 dB
Two sounds each with 70 dB add up to 73 dB
100 Watts / M2 causes an increase of 20 dB1000Watts / M2 causes an increase of 30 dB
10 Watts / M2 causes an increase of 60 dB
EQUAL LOUDNESS CONTOURS The ear is not equally sensitive to all frequencies,
SOUND LEVEL
Measured with a Sound Level Meter
Sound level meters usually contain different weighting networks ( A, B, C, D)
The A network discriminated against, The very low frequencies similar the ear (see EQUAL LOUDNESS CONTOURS)
Such measurements are called dBA (see NOISE LEVEL)
NOISE CRITERION (NC)LOCATION dB(A)Excellent listening conditions less than 30
Sleeping, residential, private office, library & classroom 34 - 47
Large offices, stores, cafeteriasand restaurants 42 - 52 Lobbies, laboratory,engineering and secretarial 47 - 56 spaces Maintenance, equipment,kitchen and laundry rooms 52 - 61
Shops, garages, power-plantcontrol rooms, etc 56 - 66
Permissible Noise Levels
The End