Post on 15-Jan-2016
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Noise and VibrationChapter 21
Noise - History
• 100 Years – Noise Exposure results in permanent hearing Loss!
• 1918 – Vibration causes permanent damage to hands and fingers.
Sound Wave
Physics of Sound
• C = Speed of propagation
• λ = c/f• C = speed • f = frequency • λ = wavelength
Physics
• Frequency = 1000 cycles per second
• C = 1128.6 feet/sec (344 meters/sec)
• Λ = 1128.6/125 hz
• =9.02 feet
Physics
• Sound is pressure
• 1 P = 1 Newton/m2
• P = Pascal
• L = 10Log(P/Pref)2
• Pref = 20 µPa
Physics
• Sound Pressure = 0.2 Pascals What is• Sound level?
• L = 10Log(0.2/20 µPa)2
• L = 80 dB
• dB = decibels (deci = 1/10)
Sound
• dBA vrs dBC weighting
• A = close to human hearing
• C = Flat
Noise Control
• Barriers
• Distance
• Isolation
Limits
• 84 dBA 8 hours AF/DOD (4 dB)
• 90 dBA 8 hours OSHA (5dB)• 85 dBA 8 hours TLV (3dB exhange)
See Chapter 21, page 445See TLV booklet page 117.
Limits
• 90 dBA for 8 hours• 95 dBA for 4 hours• 100 dBA for 2 hours
What is the limit for 30 minutes?
5 dBA exchange Rate
Distance
• If a noise source is 96 dBA at 10 feet
• What is the intensity at 20 feet?
Distance• Answer: 90 dBA
• Calc:L =L- 20 Log(D2/D1)
L = L -20 Log (20/10)
L = L- 20 Log (2)
L = L-20 (0.301)
L = 96dbA - 6.01 dB = 90dBA
Rule of Thumb: Double distance, drop 6 dB
Noise Calc - Activity
• A noise source is 102 dBA (Measured) at
• 25 feet. What will the noise level be at 60 feet?
Activity
• L = 20 Log(D2/D1)
• L = 20 Log (60/25)• L =20 Log(2.4)
• L = 20 (0.38)• 7.6 dB
• 102 dBA – 7.6 dBA = 94.4 dBA
Controls
• Turn the Noise Source
• Place Barriers (Frequency dependant)
• Isolation/Absorption materials
Plywood 125 250 500 1000 2000 4000 8000
1/32nd
1/64th
22
19
24
20
29
24
33
27
40
33
43
39
49
43
General Notes
• Lower Frequencies more difficult
• Specialized materials
Hearing Exposure Effects:
• Tinnitus – Ringing, buzzing, whistle – Indicator of damaging noise exposure
• Acoustic Trauma – loss due to a sudden intense noise (Explosion)
• Threshold Shift – change in the response of hearing in certain frequencies
Noise Induced Hearing Loss
Hearing Loss, Sources
Hearing Loss – Noise Induced Hearing Loss (NIHL
Rules of Thumb
• Shout at 3 Feet
• Loud Voice at 1 foot
• It’s Hazardous Noise!
Speech Interference Level
• SpIL = Limit to 55 dBA background
• Difficulty using phones, communicating
Noise Measurement
•Hand-held•Octave Band Analysis•Graphic Level Instruments
Moving the Source
• rotation
Medical Examinations
• Baseline
• Periodic– Annual– 48 hours noise free– Threshold shifts
Medical Examinations
• Threshold shift determination is– Frequency Dependant– Age factors– smoking
Noise Control
• Hearing Protection
19-23 dbA
18-23 dBA
27 dBA
Noise Control
27 –33 dBA reduction
Noise Control
Noise Control
• Noise Source: 117 dBA, 2 hours
• V51Rs
• Noise Exposure:?
Noise Exposure
• 117-27 dbA = 90 dBA
• Adequate?
• In some cases, have to use plugs and muffs!
Vibration
• Human exposure divided into:
• Whole Body
• Hand-arm vibration
Vibration
• Causes:– Vibration induced White Finger (VWF) or– Raynauld’s syndrone
Vibration
• Exposure: (Book)– 8 Million workers
Vibration
- Charts
Vibration
4 Hrs < 8 hrs 4 0.40 g
2 hrs < 4 hrs 6 0.61
1 hr < 2 hrs 8 0.81
< 1 hr 12 1.22
Duration m/s2 gDelta
> 16 hz may need special consideration!
G = 9.81 m/sec
Variations:
• UK 2.8 m/sec 8 hours
• Canada Same.
Average Vibration
• Average Vibration: 9.0 m/sec2 -
Jackhammer (Time Limit?)
Average Vibration
• After Training/Techniques:
• 5.5 m/sec2
ELV = Exposure Limit Value EAV = Exposure Action Value
Hand Direction
Stage Assessment Table
Table 4 Average latent periods for vibration-induced
diseases in different occupations
Occupation Stage of VWF Latency (years)
Foundry worker Tingling Numbness Blanching
1.8 2.2 2.0
Shipyard worker Tingling Numbness Blanching
9.1 12.0 16.8
Chain saw operator Numbness 4
Grinder Blanching 13.7
Table 2. Workers Potentially Exposed to Hand-Arm Vibration
No. of Workers Industry Type of Tool
500,000 Construction Handtools
200,000 Farming Gasoline chain saws
14,000 Metal working Handtools
54,000 Steel Furnace cleaning using powered handtools
30,000 Lumber and wood Gasoline chain saws
34,000 Furniture manufacturing Handtools
100,000 Mining Pneumatic drills
250,000 Truck and auto manufacturing
Handtools
64,000 Foundries Handtools
Total 1,246,000
Controls• Anti-vibration tools
• anti-vibration gloves
• Proper work practices– Keep hands warm
• Medical Surveillance
Break