Read Chapter 6, Basic Flight Physiology

Most common expression of noise - decibels

Spectrum of sound - 20 Hz - 20,000 Hz

Truly useful range is 600Hz - 6,000Hz

Speech spectrum = 500Hz - 3000Hz

Non - auditory effects of noise

At normal decibels it may pose nothing

more than an annoyance.

At high decibels it may cause nausea,

vomiting or disorientation!

General fatigue is the usual symptom

When listening to speech, many factors are at play

1. Noise intensity

2. Communication intensity

3. Noise intermittency

4. Listener familiarity

Face to face communication is best because you can see lip movement and gestures

Noise interference results in auditory masking

Masking occurs when two sounds are present in the same place

Above 85 -95 decibels, ear protection will improve speech understanding

If 115db is exceeded for prolonged periods, permanent loss will occur --------

-----Loss is slow and insidious as a result of repeated exposure

Speech interference level

ambient Db person to person comm.

1. 30 - 40 Normal voice OK 6 -30ft

Telephone use OK

2. 40 - 50 Normal voice OK 3 - 6 ft

Raised Voice OK 6 - 12 ft

Telephone use Marginal OK

3. 50 - 60 Normal voice OK 1-2 ft

Raised voice OK 3 - 6 ft

Telephone slightly Difficult

4. 60 - 70 Raised voice OK 1 - 2 ft

Raised voice difficult 3-6 ft

Telephone use difficult

Hearing Protection aids Comm.

5. 70 - 80 Shouting slightly difficult

Tele. very difficult

6. 80 -85 Shouting difficult

No telephone capability

Temporary Threshold Shift (TTS)

Felt as fullness in the ears and a dullness in hearing

May have a ringing in ears

Recovery is different for different folks

If you get it - you have over exposed yourself and you should not repeatedly have the same exposure.

Permanent Threshold Shift (PTS)

May occur in some people at the same db level as stated during TTS.

No way to know individual tolerance until damage occurs!!!!

Don't gamble ---- Use ear protection!!!

Narrow bands of pure noise is more dangerous

That is the same as the sound of an idling jet engine

Impulse noise such as gunfire can reach 170db and can have immediate damaging effects

Anytime speech is difficult you can assume that you are being over-exposed to noise

Helicopters and props create noise primarily in the low frequency range - less likely to damage hearing

Turbo-props and jets create noise in the mid to high frequency range and can be more damaging to hearing

Ground support equipment = High potential for damage

91 -122db range

Several factors may effect flight line noise

1. Distance from noise - 6db for each 200ft

2. Angle of source - 40 -45 degrees from exhaust is the worst

3. Noise source location

4. Other flight-line noise

Protection from noise

Engineer it out

Ear protection

1. Ear plugs

2. Ear muffs

3. Headsets

4. Combinations

Reducing exposure to noise is another option

Vibration and its effects

Has physical implications on body

Skull vibrates and the neck trys to stabilize

The eyes also vibrate and make instrument flight difficult

Harmful symptoms

Loss of appetite

Perspiration

Salivation

Nausea

Headache

Vomiting

Pains in joints may occur and also chronic stiffness

Aircraft manufacturers have taken great strides to engineer vibrations out

A 20 year Helicopter pilot may develop cervical osteoarthritus

Bottom line ----- Once hear is lost you will NEVER get it back.

Those nerve cells for that specific frequency is gone forever if damaged. They DO NOT regenerate

WEAR EAR PLUGS AND HEADSETS

IT'S WORTH A FEW HUNDRED BUCKS TO KEEP YOUR LIFE AND CAREER HAPPINESS INTACT.