Noise Calculations assignment

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9.3ERHS350Online_Noise_FA2020NOAUDIO.pptx

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Ear Anatomy and Physiology & Noise Monitoring

ERHS 350 Online

Module 9

Section 3

Objectives

When you have completed this module, you should be able to:

Define noise

Calculate a variety of noise parameters given equations

Define and calculate sound power and sound pressure level

Define and calculate octave bands

Objectives

Continued

Add decibels given a list of noise source levels

Describe the types of noise

Define the types of sensorineural hearing loss

Define exchange rates

Describe weighting filters

Important Equations for Homework

Types of Noise

Broadband

SPL distribution has no dominant peaks across the frequency spectrum

Discrete

SPL is prominent at one or more frequencies

Continuous

Continual noise source (no breaks >1 second)

Types of Noise

Impact

Characterized by a rapid rise and a rapid fall in peak sound

Less than 1 second and is high intensity

Impulse

Does not decrease as rapidly as impact noise and is caused by rapid gas expansion

Types of Noise

Noise Measurement

Purpose

Assess damage risk to hearing

Develop and implement controls if necessary

Assess nuisance properties

Evaluate effectiveness of controls

Measurement

Noise may be measured using

Sound level meter

Octave band analyzer

Dosimeter

Measurement

Sound Level Meter

Measures the overall sound pressure level

Octave Band Analyzer

An OBA will measure the noise SPLs for each octave band

SLMs may include an OBA

A noise dosimeter is used to assess personal exposure (dose) versus an environmental exposure measured with the basic SLM

Dosimeters are attached to the worker to measure and integrate SPL over time to get an equivalent SPL (steady state) for a full or partial shift

Measurement

There are different filters in an SLM that will discriminate against specific frequencies

A weighting

C weighting

Flat (no) weighting

Measurement

The A-weighting curve approximates the equal loudness perception for humans for pure tones relative to a reference of 40 dB SPL at 1 kHz

SPL measurements taken with A-weighting correlate most closely with the risk of hearing loss

The A-weighting discriminates against low frequency noises

Weighting Networks

Octave Bands

Industrial Noise Sources

Are typically widely distributed over the noise spectrum

That is, a source will span many frequencies

Different frequencies will encompass larger or smaller magnitudes of the total acoustical energy

Therefore, it is necessary to categorize frequencies into groups or “bands” of frequencies

Octave Bands

Noise control principles are based on controlling a range or “band” of noise

Frequencies are categorized into “octave bands”

A frequency is an octave-band wide when the upper band edge is twice the lower band edge

Where,

f2 = Upper band edge

f1 = Lower band edge

Octave Bands

Center-Band Frequency (fc)

The geometric mean of the upper and lower band-edge frequencies

Octave Bands

If controls need to more precisely pinpoint the acoustical energy of a source

1/3 octave bands may be used

The upper band frequency is the cube root of two times the lower band frequency

There are three 1/3 octave bands in each octave band

Octave Bands

Total SPL

The total SPL of a noise source is equal to the sum of the SPLs of each octave band

The total SPL of different noise sources is equal to the sum of the SPLs for each noise source

BUT, decibels are not directly additive

90dB + 90dB ≠180dB

90dB + 90dB = 93dB

Adding Decibels

Two methods

First

Noise sources of: 82, 84, 85, 83dB

Adding Decibels

Second Method

dB Difference Between Sources	Add to the Higher dB Level
0.0-0.6	3
0.7-1.6	2.5
1.7-3.1	2.0
3.2-4.7	1.5
4.8-7.2	1.0
7.3-13.9	0.5
>13.9	0

dB Difference Between Sources	Add to the Higher dB Level
0	3
1-3	2
4-7	1
>7	0

Adding Decibels

If 4 machines produce 82, 84, 85 and 83dB

Note: using the more precise table yields 89.5dB≈90dB

+2dB = 86dB

+2dB = 88dB

+1dB = 89dB

dB Difference	Add to the Higher
0	3
1-3	2
4-7	1
>7	0

Terminology

Threshold level –minimum sound pressure level an instrument can ‘hear’ (80 dBA)

Criterion level – the sound pressure level that would result in a 100% dose in 8 hours

(90 OSHA; 85 ACGIH)

Exchange rate – the change in sound pressure level that will require a halving/doubling of exposure time

(5 OSHA, 3 ACGIH)

Exchange Rate

The relationship between the increase (or decrease) in decibels and the time allowed at a specific decibel level

All of these result in 100% dose of noise!

Duration of Exposure	Sound Level (dBA)
24	80
16	82
8	85
4	88
2	91
1	94

Duration of Exposure	Sound Level (dBA)
8	90
4	95
2	100
1	105
0.5	110
0.25	115
0	>115

ACGIH

OSHA

Terminology

Dose – exposure to a sound pressure level in relation to the maximum allowed exposure for an 8 hour day.

8 hours at 90 dBA = 100% (OSHA); now notice exchange rate in the following example

16 hours at 85 dBA = 100%; now use concept of exchange rate to figure

1 hour at 110 dBA =

200%

Determining Dose

Loudness

Sound pressure level in decibels

Time

Exchange rate

Frequency

Weighting networks

Physiology

Response times

Noise Dose

The equivalent steady-state SPL is calculated by:

Where

CL = Noise OEL (e.g., OSHA PEL of 90dBA).

T = time in hours;

D% = percent dose of noise;

q = 16.61 for an exchange rate of 5 OR

10 for a 3 dB exchange rate

For example, a 90dBA exposure for 8 hours is a dose of 100%

Noise Dose

To what equivalent SPL is a worker exposed if she/he receives a 100% dose in two hours (use an exchange rate of 5 dB)?

Noise Dose

Can be calculated by:

Where,

D=Noise dose in percent

CN=Exposure duration

TN=Allowed duration

Noise Dose

For Example

A worker is exposed to the following:

95dB for 2 hours

90dB for 3 hours

100dB for 1 hour

75d dB for 2 hours

Noise Dose

Duration of Exposure	Sound Level (dBA)
8	90
4	95
2	100
1	105
0.5	110
0.25	115
0	>115

OSHA

95dB for 2 hours

90dB for 3 hours

100dB for 1 hour

75dB for 2 hours

Allowable Stay Time

To determine how long an employee may stay in a work area given a measured SPL, use:

Where,

SPL=Measured sound pressure level

CL=Criterion level (90 for OSHA, 85 for ACGIH)

ER=Exchange rate (5 for OSHA, 3 for ACGIH)

Allowable Stay Time

Also…

This equation is used to calculate the “allowable” time when calculating dose

If the allowable time of exposure is not on the exchange rate table

Allowable Stay Time

How long may a worker stay in a room that has a sound pressure level of 99dBA?

Calculate for OSHA and ACGIH

End of Session 3

Application of concepts: Homework 9

log

SPL

SWL

SPL

log

SPL

log

SPL

log

PWL

SWL

log

Chart1

31.5	31.5
63	63
125	125
250	250
500	500
1K	1K
2K	2K
4k	4k
8k	8k
16k	16k

Broadband

Discrete

Frequency

SPL

100

105

100

102

110

100

Sheet1

	31.5	63	125	250	500	1K	2K	4k	8k	16k
Broadband	95	100	105	100	97	102	96	100	95	100
Discrete	75	80	78	80	75	110	80	77	82	78

Chart1

1	1
1.5	1.5
2	2
2.5	2.5
3	3
3.5	3.5
4	4
4.5	4.5
5	5
6	6
7	7
8	8
9	9
10	10

Continuous

Impact/Impulse

Seconds

Sheet1

	1	1.5	2	2.5	3	3.5	4	4.5	5	6	7	8	9	10
Continuous	60	60	65	70	70	65	65	70	75	70	65	70	65	60
Impact/Impulse	60	90	60				60	95	80	65	60			70

Chart1

31.5
63
125
250
500
1000
2000
4000
8000
16000

Frequency

Sheet1

	31.5	63	125	250	500	1000	2000	4000	8000	16000
	57	58	60	76	81	73	84	70	81	66

log

SPLi

log

)

log

(

Leq

)

log

(

100

dBA

Leq

log

dBA

Leq

dBA

Leq

100

percent

100

...

percent

100

(

)

137

100

375

CLSPL

)(

min480

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