Environmental Factors

Environmental Factors Industrial Noise Hardianto Iridiastadi, Ph.D.

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

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

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)

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

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

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

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)

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”

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

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

Justification

Common Sound Pressure Level

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

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

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

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

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

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

Noise Control - Measurement

Noise Control

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

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

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

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

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

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

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?

Environmental Factors