Environmental Factors

1. Environmental Factors Industrial Noise Hardianto Iridiastadi, Ph.D.

2. Introduction • Industrial growth • Increases volume of noise • Incidence of hearing loss • Found in a number of industrial settings • Workshop • Steam boilers • Stamping machines • Forging

3. Basic Concepts Sound “ vibration through air which stimulates auditory sensation”

4. Basic Concepts The Ear • Outer • Auricle, pinna, auditory cannal, eardrum • Collects sound waves • Channeled along the canal • Vibration of sound according to intensity and frequency • Resonance effects amplify the intensity (10-15 dB)

5. Basic Concepts The Ear • Middle • Ear bones (hammer, anvil, stirup) • Mechanical transmissions to the oval window • Amplification of up to 25dB • Filled with air, with pressure that can be equalized via Eustachian tube

6. Basic Concepts The Ear • Inner • Filled with fluid • Sound waves propagate as fluid shifts from oval window to the round window • Through the cochlea, along basilar membrane • Stimulates sensory hair cells in the organs of Corti • Impulse transmitted along the auditory nerve to the brain

7. Basic Concepts • Sound • Frequency (Hz) • Intensity/amplitude (dB) • Audible : 20 Hz – 20 kHz • Subjective perception • Loudness • Curves of equally perceived loudness

8. Basic Concepts • Sound intensity level (dBA) • 100 : deafening (jet engine, explosion, rivet) • 80 : very loud (machinery, busy street) • 60 : loud (street activity) • 40 : moderate (conversation) • 20 : faint (soft background music) • 0 : quiet (whisper in soundproof room)

9. Basic Concepts Noise “ unwanted sound by listener” Hearing loss “ a hearing impairment of one or both ears, partial or complete, arising in or during the course of, but as the result of one’s employment”

10. Basic Concepts • Noise-induced hearing loss (NIHL) • Cumulative • Permanent • Loss of hearing • Develops over months or years • Hazardous exposure • Typically affect both ears

11. Justification • Statistics • 14% of working population employed in jobs with greater than 90 dBA noise level • 1.7 million US workers affected (have compensable hearing loss) • Cost to industry – greater than $500 million • Note • Hearing loss could be due to aging (presbycusis) – in the high frequency area

12. Justification

13. Common Sound Pressure Level

14. Effects of Noise • Perceived • Negative emotions • Surprise • Frustration • Anger • Fear • Disturb rest or sleep • Interfere sensory and perceptual capability

15. Effects of Noise • Physiological • Temporary threshold shift (TTS) • Ear discomfort • Ear pain • Fatigue • Vertigo, disorientation, nausea • Reduced visual acuity; respiratory changes • Permanent threshold shift

16. Effects of Noise • Other • Performance degradation • Vigilance decrement • Interfere mental work • Hearing overload • Balance impairment • Initially affects 3 – 6kHz freq.

17. Regulations • OSHA (1974) • Maximum exposure to 90 dBA, time weighted average • 8 hours • OSHA (1983) • TWA >85dBA • Action level: Implement hearing protection plan • TWA > 90dBA • Permissible exposure level: Noise reduction

18. Exposure Duration • OSHA Duration (hrs) Noise Level (dBA) 8 90 6 92 4 95 3 97 2 100 1 105 .5 110

19. Formula Em = C1/T1 + C2/T2 + …+ Cn/Tn Em > 1 Exposure exceeds limit Exposure above 115 dBA not permissible for any length of time Exposure to impact noise greater than 140 dBA is not permissible

20. Noise Control - Measurement

21. Noise Control - Measurement

22. Noise Control

23. Noise Control • Engineering • Maintenance • Substitution of machines • Substitution of process • Minimize causes of vibrating surfaces • Reduce forces; minimize rotational speed • Minimize vibrating surfaces

24. Noise Control • Engineering • Minimize radiation of noise from vibrating surfaces • Reduce sound transmission • Reduce sound produced by gas flow • Reduce noise by reducing its transmission through air • Isolate operator

25. Noise Control • Administrative • Production schedules • Job rotation • Split exposure • E.g., 2 x 4hrs/day

26. Noise Control • Personal hearing protection • Hearing protection device • Ear muff • Earplug • Guard against certain frequencies and intensities

27. Industrial Audiometry • Concept • Determining an individual’s hearing ability • Objectives • Obtain baseline audiogram • Provide a record of an employee’s hearing acuity • Evaluate effectiveness of noise control program • Comply with government regulations

28. Industrial Audiometry • Example – Akbar (2007) • Determine hearing ability of people employed in workshops • 10 workers and 10 students (control) • Audiometry on these 20 individuals • Found workers with impaired hearing ability • Baseline greater than 15 dBA at each frequency • Found students with “good” hearing • Conclusion: Jobs might have resulted NIHL

29. Questions • Describe the different parts of the ear. • What is TTS, PTS, and NIHL? • Why NIHL initially affects speech intelligibility? Explain. • What is the difference between dBA and dBC? • In a grinding activity, noise levels (in dBA) and the durations are 100 (1 hr), 80 (3 hrs), 90 (2 hrs), 85 (2 hrs). Evaluate this work condition. What are your recommendations?