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)

Directional

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