1. Work Related Hazards Physical Chemical Biological

2. Pysical Hazards Sound Radiation Electricity Temperature

3. Sound

4. Sound Waves

5. Sound Spectrum S pectrum of the Salvatore Mundi bell, Salzburg.

6. Sound Propagation

7. Hearing

8. Cochlea

9. Hair Cells

10. Graph showing HEARING LOSS as a function of FREQUENCY Work Induced HEARING LOSS Audiogram Measured by an AUDIOMETER. 0 dB denotes the hearing threshold level Points below 0 denote louder threshold levels

11. Work Related Hearing Loss

12. PRESBYCUSIS

13. Men

14. 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.

15. TINNITUS A 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.

16. Measurement of Sound Sound Intesity The 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

17. Intensity (Power) Level The measurement of the INTENSITY of one sound in comparison to another sound or fixed level Expressed in DECIBELs.

18. 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)

19. 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.

20. 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

21. 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 dB 1000Watts / M2 causes an increase of 30 dB 10 Watts / M2 causes an increase of 60 dB

22. EQUAL LOUDNESS CONTOURS The ear is not equally sensitive to all frequencies,

23. 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)

24. NOISE CRITERION (NC)

25. Permissible Noise Levels

26. The End