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