Transcript Sound Hazards

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
Work Induced
HEARING LOSS
Audiogram
Graph showing HEARING LOSS as a function
of FREQUENCY
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
PRESBYCUSIS
Is this loss caused by noisy modern living or
is it natural aging?
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.
TINNITUS
A ringing sound heard in the ear
Caused by:
prolonged exposure to loud sound,
or short exposure to very loud sound.
Taking drugs such as aspirin.
Temporary or chronic,
Measurement of
Sound
Sound Intesity
The units
ergs per second per square cm,
or the watts per square meter.
THRESHOLD OF HEARING:
10
-12
WATTS / M,
PAIN THRESHOLD:
2
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 bel
One 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 of
10,000 units,
Has a difference of Intesity level
of 4 bels or 40 decibels.
Range of Sound
Intensities
Threshhold of pain (1 watt/m2)
to
Threshhold of hearing (10-12 watts/m2),
I decibells it is 0 to 120 dB.
An increase of Sound intesity of
10 Watts / M2 causes an increase of 10 dB
Increase of Sound intesity
An increase of Sound intesity : of
10 Watts / M2 causes an increase of 10 dB
100 Watts / M2 causes an increase of 20 dB
1000Watts / M2 causes an increase of 30 dB
6
10 Watts / M2 causes an increase of 60 dB
To double Sound Intestiy causes an
extra 3 dB
Two sounds each with 70 dB add up to 73 dB
EQUAL LOUDNESS
The ear is not equally
sensitive
to
all
frequencies,
CONTOURS
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
Excellent listening conditions
Sleeping, residential, private
office, library & classroom
Large offices, stores, cafeterias
and restaurants
Lobbies, laboratory,
engineering and secretarial
spaces
dB(A)
less than 30
34 - 47
42 - 52
47 - 56
Maintenance, equipment,
kitchen and laundry rooms
52 - 61
Shops, garages, power-plant
control rooms, etc
56 - 66
Permissible
Noise Levels
The End