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Aeromed BM > Noise And Vibration > Flashcards

Noise And Vibration Flashcards

1
Q

The nature of sound

A

Sound is a mechanical radiant ENERGY that is transmitted by longitudinal pressure waves in a material medium (such as air) and is the objective cause of hearing

*Sound is ENERGY

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2
Q

Sound

A

Produced when an object or surface vibrates rapidly

Transmitted through any elastic substance such as air, water, or bone

Density of the substance determines the speed at which the sound and pressure waves will travel

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3
Q

Perception of sound

A

Sound energy wave enters ear flap (gives direction, intensifies), into ear canal, to the eardrum and middle ear, finally to inner ear and converted to nerve impulses to brain.

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4
Q

Cochlea

A

Inside inner ear

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5
Q

Receptors of sound

A

Detect fluid movement in cochlea

Transmit electrical impulses to the brain where sound is interpreted

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6
Q

Noise

A

Sound that is - loud (perception of listener); unpleasant, unwanted

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7
Q

Effects of noise in aviation enviornment

A

Annoyance and fatigue

Speech interference

Hearing loss

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8
Q

Measurable characteristics of noise

A

Frequency

Intensity

Duration

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9
Q

Frequency

A

Gives sound pitch

Number of times per second air pressure oscillates

CPS = Hertz (HZ)

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10
Q

Intensity

A

Measure that correlates sound pressure to loudness

Measured in decibels (dB)

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11
Q

Decibel levels

A 
0dB - hearing threshold
65dB - average human conversation
**85dB - damage-risk noise limit**
120dB - threshold for discomfort
140dB - threshold of pain
160dB - ear drum rupture
*190dB - death
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12
Q

Duration

A

How long you are exposed to noise - steady noise vs. impulse

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13
Q

Steady noise

A

Continuous noise at high intensity

Wide range of frequencies

Most encountered in Army AV

Engines, drive shafts, transmissions, rotors and propellers

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14
Q

Impulse noise

A

Explosive noise
High intensity with low duration
Measured in milliseconds with less than 1 second in duration

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15
Q

Army noise criteria

A

The Surgeon General has established 85dB as max level of continuous unprotected exposure to steady-state noise for 8 hours

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16
Q

Army noise exposure criteria (chart)

A 
8hrs - 85dB
4hrs - 90dB
2hrs - 95dB
1hr - 100dB
1/2hr - 105dB

Every 5 decibel increase, time exposure allowed cut in half

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17
Q

Types of hearing loss

A

*Conductive hearing loss - CAN be treated/fixed

Sensorineural hearing loss

Mixed

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18
Q

Conductive hearing loss

A

Defect or impediment in the external or middle ear

Impede with the mechanical transmission of sound to the inner ear

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19
Q

Sensorineural loss

A

When cochlea is damaged

Most frequently produced by noise

Occurs in the higher frequencies first

Could be associated with aging

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20
Q

Acoustic trauma

A

Sudden and could cause hearing loss

In excess of 140dB

From impulse noise (blast, gunfire)

Usually predictable and preventable

21
Q

Mixed hearing loss

A

Combination of conductive and/or sensorineural loss

Example) crew-member with middle ear infection (conductive) and a high frequency hearing loss (sensorineural). One is treatable (conductive), one is not.

22
Q

Noise induced hearing loss

A

Temporary Threshold Shift (TTS)

Permanent Threshold Shift (PTS)

23
Q

TTS

A

Temporary Threshold Shift:

Single exposure to high level noise
May last for few minutes/hours
Depends upon frequency, intensity, and duration of the noise
Recovery when noise is removed, usually complete

24
Q

PTS

A

Permanent Threshold Shift:

If continued for 15 hours, eventually permanent loss induced
No recovery when exposure is terminated
TTS could become permanent (cannot be predicted)

25
Q

Damaged hair cells in ear

A

Looks like blown over grass

After exposure to 120dB for 5 hours

26
Q

Long term hair cell damage

A

Prolonged, unprotected exposure to noise could cause irreversible damage

27
Q

Characteristics of noise induced hearing loss

A

Insidious and undetectable

Noise intensity below 140dB but above 85dB

Physical pain not evident

Initially higher frequencies affected (3000 to 6000 Hz)

28
Q

Audiograms

A

Used to determine hearing loss

First one is a “reference audiogram”

Considered normal if hearing thresholds are 20dB or less for all frequencies tested

29
Q

Noise in Army aircraft

A

Overall noise levels are equal to or exceed 100dB’s

Most intense noise below 300Hz

Low frequency noise will produce high frequency hearing loss

MUST USE HEARING PROTECTION

30
Q

Noise in Army fixed-wing aircraft

A

Engines and propellers in close proximity to the cockpit

Other fixed wing aircraft are beter insulated to attenuate noise levels

31
Q

Rotary-wing aircraft noise

A

Noise levels equal or exceed 100dB

Originates from engines, rotor systems and transmissions

Observation helicopters (100-103dB)

Attack helicopters (104dB); increased during missions with weapon systems firing

Utility and cargo helicopters (108-112dB)

32
Q

Noise protection

A

Aircraft design, silent operation or noise suppression

Isolate, distance or enclose source (isolate)

**Personal Protective Equipment ([PPE or PPD] most economical/practical protection). Max attenuation is about 50dB from dB level of device/event.

33
Q

Ear plugs

A

Foam, single flange, and triple flange (foam is best)

Inexpensive, easy to carry

Attenuates 18-45dB across frequency band

Effective when worn with HGU-56, and IHADSS flight helmets

34
Q

Ear muffs

A

10-41dB attenuation across the frequency band

Comfortable to wear

Ground personnel can lose their hearing too

Good control measure to ensure crew wear it - visible

35
Q

Headsets

A

Hearing protection as well as radio comm

Attenuation could decrease due to damaged ear seals (put in bag!)

Commonly worn on VIP aircraft

Lack crash-worthiness of flight helmet

36
Q

Protective helmets

A

Provide crash and noise protection

Great protection against higher frequencies

Low frequency is the concern in the AV environment

Must fit properly

Ear cups must be soft, unwrinkled, tear free

Noise attenuation will bring noise exposure within confines of damage risk criteria for every Army air raft EXCEPT THE UH-60 and CH-47 (wear extra protection for those… COMBINED HEARING PROTECTION)

37
Q

Vibration

A

The motion of an object relative to a reference position (object at rest) involves series of oscillations resulting in the displacement and acceleration of the object

38
Q

Sources of vibration

A

Increased air speed

Internal and external loading

Environmental factors (turbulence)

Most intense during transition from hover to cruise and cruise to hover

39
Q

Physical effects of vibration on performance

A

Manual coordination - coordination and control “touch” degraded, aircrew member may over-control during turbulence/transition from hover to level flight (pilot induced oscillation)

Vision - instrument panel may be difficult to read, helmet mounts start to vibrate at 4-12Hz

Speech - can be distorted during oscillations of 4-12Hz, above 12Hz speech becomes increasingly difficult to interpret

40
Q

Physical effects of vibration (short term)

A

Fatigue - vibration causes muscles to contract, pressure receptors must constantly measure angular position - causes muscles to contract for balance

Respiratory effects - hyperventilation is caused when diaphragm vibrates at 4-8Hz

Circulatory effects - body interprets vibrations, therefore muscular tension of bracing causes pulse rate and blood pressure to increase

Spatial disorientation - vibration affects the semi-circular canals and otolith organs

Pain - pre-existing injuries aggravated by vibration (stress fractures, back pain, degenerative disc disease)

41
Q

Long-term effects of vibration

A

Raynaud’s disease - (white finger) prolonged exposure to vibration. Trauma to nerve endings in extremities

Back ache/pain - may result at earlier age than normal, spine subject to higher pressure while sitting, vibration can cause premature degradation

Kidney/lung damage - is under study, blood in urine or lung damage is a sign of over-exposure

42
Q

Reduction of vibration effects

A

Good posture

Restraint systems used correctly (protect against high vibration at turbulence)

Aircraft maintenance

Isolate crew-members, passengers, and patients from aircraft structures

Limit exposure time (short flights/frequent breaks)

Let the aircraft do the work

43
Q

Maintain good physical condition

A

Fat multiplies vibration, muscles dampen them

Decreases the effects of fatigue

Maintain sufficient hydration! Dehydration with vibration can cause fatigue twice as fast and increase recovery time.

44
Q

Frequency

A

Frequency - number of oscillations of any object in a given time. 1 cycle per second (CPS) = 1 Hertz (Hz)

45
Q

Amplitude

A

Amplitude - the max displacement about a position of rest

46
Q

Duration

A

Duration - time of exposure

47
Q

Natural Body Resonance

A

Natural body resonance - mechanical amplification of vibration by the body occurring at specific frequencies (whole body: 4-8Hz; shoulder girdle: same; head: 25Hz; Eyes: 30-90Hz)

48
Q

Damping

A

Damping - Loss of mechanical energy in vibrating system; slows vibration (like body tissue)

Aeromed BM (13 decks)

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