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

• OSHADuration (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 > 1Exposure exceeds limit

Exposure above 115 dBA not permissible for any length of timeExposure to impact noise greater than 140 dBA is not permissible

Noise Control - Measurement

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?