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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
Damaged hair cells in ear
Looks like blown over grass After exposure to 120dB for 5 hours
26
Long term hair cell damage
Prolonged, unprotected exposure to noise could cause irreversible damage
27
Characteristics of noise induced hearing loss
Insidious and undetectable Noise intensity below 140dB but above 85dB Physical pain not evident Initially higher frequencies affected (3000 to 6000 Hz)
28
Audiograms
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
Noise in Army aircraft
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
Noise in Army fixed-wing aircraft
Engines and propellers in close proximity to the cockpit Other fixed wing aircraft are beter insulated to attenuate noise levels
31
Rotary-wing aircraft noise
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
Noise protection
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
Ear plugs
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
Ear muffs
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
Headsets
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
Protective helmets
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
Vibration
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
Sources of vibration
Increased air speed Internal and external loading Environmental factors (turbulence) Most intense during transition from hover to cruise and cruise to hover
39
Physical effects of vibration on performance
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
Physical effects of vibration (short term)
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
Long-term effects of vibration
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
Reduction of vibration effects
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
Maintain good physical condition
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
Frequency
Frequency - number of oscillations of any object in a given time. 1 cycle per second (CPS) = 1 Hertz (Hz)
45
Amplitude
Amplitude - the max displacement about a position of rest
46
Duration
Duration - time of exposure
47
Natural Body Resonance
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
Damping
Damping - Loss of mechanical energy in vibrating system; slows vibration (like body tissue)

Aeromed BM (13 decks)

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