Noise and Vibration

Question 1

Sound

Answer 1

A transfer of energy via pressure waves through a physical medium from a source to cause the sensation of hearing

Question 2

Properties of Sound

Answer 2

Frequency: rate of vibration (pitch or tone)
Wavelength: low frequency sounds (low pitched, long wave length); high frequency (high pitched, short wavelength)
Amplitude: determine sound
Speed: 340 m/s in air
Intensity: average amount of energy passing through a unit

Question 3

Decible Weighings

Answer 3

Weightings of available of various purposes:

• A: standard for occupational management
• C: peak noise
• Z: mining

Question 4

Basic Rules

Answer 4

Noise levels = decibels (dB)
Logarithmic ; can't be added or subtracted arithmetically
- 2x sound energy = 3dB(A) increase
- 10x sound energy = 10dB(A) increase
- 100x sound energy = 20dB(A) increase

Question 5

Effects of Noise on Hearing

Answer 5

Acoustic trauma: immediate physical damage from unprotected exposure
Temporary threshold shift (TTS): exposure to high noise levels, normal hearing returns after rest

Question 6

Exposure Standards

Answer 6

L(Aeq,8h) of 85 dB(A)
Peak sound pressure level of:
- 140 dB(lin): Resource safety
- 140 dB(C): worksafe

Question 7

Equivalent Continuous Sound Level (Leq)

Answer 7

The steady sound pressure level, over a period of time has the same energy content and same hearing damage as actual fluctuating noise

L(Aeq,t)
8hr = 85
4hr = 88
2hr = 91
1hr = 94
15 min = 100
3 min = 106

Question 8

Noise Control

Answer 8

Controls may be applied at the:

• source
• path
• receiver

Question 9

Source Treatments

Answer 9

Radiated noise
Vibration dampening
Vibration isolation
Silencers
Source substitution

Question 10

Controlling the Path

Answer 10

Sound absorption materials
Sound transmission loss
- block or attenuate noise propagating through a structure
Control booth or machine enclosure
Barriers
Lagging

Question 11

Administrative Controls

Answer 11

Scheduling shifts
Noisy tasks in controlled areas
Noise refuge areas
Maintenance and servicing schedules
Planning layout

Question 12

Controls are Reciever

Answer 12

HPD includes:

• ear plugs
• ear-canal caps
• ear muffs
• helmets

Question 13

Other Controls

Answer 13

Regular maintenance

‘Buy quiet’

Question 14

Vibration

Answer 14

Mechanical oscillations of an object around an equilibrium point
2 measurable quantities:
- frequency: no. of cycles of vibrating objects complete in one second (Hz)
- amplitude: distance from stationary position

Question 15

Vibration Exposure

Answer 15

Vibration can influence peripheral vascular structure and consequently blood flow:

• segmental vibration
• whole body vibration
• hand-arm vibration