Noise exposure and hearing loss
Sound variables:
| Variable | Unit | Governs |
|---|---|---|
| Frequency | hertz (Hz) | Pitch |
| Intensity | decibels (dB) | Loudness |
| Duration | - | Quality of perception and discrimination |
Frequency ranges:
| Range | Hz |
|---|---|
| Audible | 20 to 20,000 |
| Most sensitive | 500 to 4,000 |
| Normal conversation | 500 to 3,000 |
- Hearing damage depends on intensity and duration together.
- Short loud sound can equal long, less intense one.
Types of noise:
| Type | Duration | Level | Examples |
|---|---|---|---|
| Steady | Continuous, over 1 second | - | Powerplant, propeller, pressurization |
| Impulse/blast | Sudden, under 1 second | Usually over 140 dB | Handgun, firecracker, piston-engine backfire, high-volume radio squelch, sonic boom |
Noise effects: physiologic (ear) or psychologic (pilot).
Physiologic, by level:
| Level | Effect |
|---|---|
| 120 dB | Ear discomfort |
| 130 dB | Ear pain |
| 140 dB | Eardrum rupture |
Physiologic, by exposure (over 90 dB):
| Exposure | Impairment |
|---|---|
| Several hours, unprotected | Temporary, usually gone within hours |
| 8 or more hours a day, for years | Permanent, starts near 4,000 Hz, can go unnoticed |
Psychologic effects:
- Distraction, fatigue, irritability
- Startle responses, headache, nausea
- Impaired concentration and memory
- Masked speech
- More errors in tasks needing vigilance, calculation or time judgment (over 90 dB)
- Loud noise before flight (home, road, party) can harm in-flight performance as much as aircraft noise
Trap: Hz is pitch, dB is loudness; not interchangeable. Early noise-induced loss starts near 4,000 Hz, outside conversation range: speech sounding normal does not mean hearing is intact.
References
- FAA CAMI, Hearing and Noise in Aviation (AM-400-98/3)