Lesson 2: CAUSES OF HEARING DAMAGE ARC 507: ENVIRONMENTAL CONTROL III (ACOUSTICS AND NOISE CONTROL ) Department of ar

1. Lesson 2: CAUSES OF HEARING DAMAGE ARC 507: ENVIRONMENTAL CONTROL III (ACOUSTICS AND NOISE CONTROL) Department of architecture Federal university of technology, akure

2. Contents • Introduction. • Noise Induced Hearing Damage. • Acoustic Trauma • Temporary Threshold Shift • Permanent Threshold Shift • Biologic Variability • Tinnitus • Other Causes of Hearing Loss • Ototoxic Agents • Diseases • Ageing • Socioacusis

3. SUMMARY This topic explains the main adverse health effects of noise: damage to the hearing mechanism, known as noise– induced hearing loss (NIHL); and tinnitus. Also covered are other agents that can damage hearing: ototoxic substances; diseases; and the ageing process.

4. agents of hearing damage • Hearing damage may result from several agents – both occupational and non – occupational: • Noise – occupational (called occupational noise-induced hearing loss). • Noise–non – occupational (called Sociocusis) • Ageing – (Presbyacusis). • Diseases and infections (collectively called Nosoacusis). • Ototoxic hazardous substances in the work place.

5. NOISE – INDUCED HEARING DAMAGE • Noise can affect hearing in four main ways: • Acoustic trauma • Temporary threshold shift (TTS) • Permanent threshold shift (PTS) • Tinnitus

6. NOISE – INDUCED HEARING DAMAGE • Acoustic Trauma • It is defined as damage to the ear resulting from a single exposure or relatively few exposures to a very intense level of sound (peak level greater than 140-150 dB), usually impulsive in nature, e.g. explosions. • Acoustic trauma may cause: • damage to the eardrum; • damage to the ossicles; and • mechanical damage to the hair cells.

7. NOISE – INDUCED HEARING DAMAGE Temporary Threshold Shift (TTS) It is defined as a temporary change in hearing level that recovers between exposures, resulting from sound levels over about 70 - 75dB(A).

8. Growth and Recovery of TTS NOISE – INDUCED HEARING DAMAGE

9. TTS for Different Noise level NOISE – INDUCED HEARING DAMAGE

10. NOISE – INDUCED HEARING DAMAGE Permanent Threshold Shift (PTS) This is permanent damage to the ear as a result of continued or repeated exposure to excessive noise over a period of time.

11. Progression of NIPTS for 90 and 100db(A) NOISE – INDUCED HEARING DAMAGE

12. NOISE – INDUCED HEARING DAMAGE Tinnitus This is the term given to noises which are heard in the ears’ or ‘in the head’ – ringing, buzzing, hissing, whistling, pulsing or other sounds which do not come from an external source

13. OTHER CAUSES OF HEARING LOSS • Ototoxic Agents • This means ‘toxic to the ear’. • Certain medications or chemical agents in the workplace can damage the ear cells in the inner ear. • Over 200 agents have been reported as ototoxic. • These include: • antibiotics such as streptomycin; • quinine; and • salicylates such as aspirin.

14. OTHER CAUSES OF HEARING LOSS • Ototoxic Agents continues... • Workplace ototoxic agents include: • solvents such as benzene, toluene, butanol, trichloroethylene; and • arsenic, lead, cobalt, mercury, and lithium.

15. OTHER CAUSES OF HEARING LOSS Diseases Nosoacusis is defined as hearing damage resulting from diseases and infections, ototoxic medications, or trauma (blows) to the head. Many systemic and hereditary diseases can cause hearing loss. Among these are: rubella, meningitis, diabetes, renal disease, rheumatoid arthritis and Meniere's disease.

16. OTHER CAUSES OF HEARING LOSS • Ageing • Presbyacusis is defined as progressive loss in sensitivity at the high frequencies occurring with increasing age. • A series of changes occur in the auditory system as humans age. These include: • loss of hair cell. • degeneration of the striavascularis. • loss of spiral ganglion cells in the auditory nerve. • degenerative changes in the central auditory nervous system.

17. OTHER CAUSES OF HEARING LOSS Median audiogram for male

18. OTHER CAUSES OF HEARING LOSS Median audiogram for female

19. OTHER CAUSES OF HEARING LOSS Sociocusis This is defined as noise – induced hearing loss from non-occupational noise, for example, high level music, recreational shooting, and other noisy hobbies such as carpentry and drag racing.