the principles of noise measurement · details of the hearing conservation survey overview of the...

THE PRINCIPLES OFNOISE MEASUREMENT

James JeromeSr Occupational Audiologist

Tom LloydNoise Control Engineer

The Principles of Noise Measurement

� Acoustical instrumentation� Types of noise surveys� Noise exposure criteria� Details of the hearing conservation survey� Overview of the principles of noise control

Agenda topics

Federal Regulations

� Occupational Safety & Health Act (OSHA)-29 CFR 1910.95 (effective March 8, 1983)

� Mine Safety & Health Act (MSHA)-30 CFR Part 62 (effective September 13, 2000)

� Federal Railroad Administration (FRA)-49 CFR 227 & 229 (effective February 26, 2007)

Acoustical InstrumentationThe basic tools for noise measurement include the sound level meter, personal noise dosimeter, and acoustical calibrator.

Sound Level MetersThe sound level meter (SLM) measures sound pressure level (SPL).

SLM ComponentsRegulations require use of the following microphone

types:

� Type 2 (±2dB accuracy)� General survey measurements� Lower cost than precision SLM� May be used with octave-band filters

� Type 1 (±1dB accuracy)� Diagnostic measurements� Commonly used with octave-band filters

Frequency Analysis

Serial-band filters divide the audible frequency range into separate bands.� Octave-Band (1/1): nine filter bands cover the

audible range

� Third-Octave Band 1/3): each octave is split into three narrow bands for more resolution

Real-Time Analyzer (RTA) or Octave Band Analyzer (OBA)

Acoustical Calibrators

An acoustical calibrator is a device that produces a fixed SPL at a fixed frequency.

Instrument Settings

Measurement parameters must be set to match the process and survey objectives.� Range: measured signal is near the middle of

range limits� Integration: average signal over time; set by

user with run/stop key

Instrument SettingsWeighting

Three weighting networks are commonly used for industrial surveys:

� Linear: used for octave-band analyzers (OBAs)

� A-weighting: used for regulatory compliance, employee exposure, and noise control evaluation

� C-weighting: used for quick evaluation of low-frequency noise without full spectrum

Instrument Settings

WeightingAs per the federal regulations, the A-weighted level must be used when conducting a sound survey for hearing conservation purposes.

� The A-weighted sound level provides a single number rating that correlates reasonably well with human perception of the loudness of sound and hearing-damage risk due to exposure to continuous sound.

� The results are expressed in dBA.

� Used world-wide.

A-weighted Sound Level

A-weighted Correction Factors

Instrument Settings

ResponseFour settings are typically available:

� Slow: 1-second time constant

� Fast: 1/8th-second time constant

� Peak: measures instantaneous peak level

� Impulse: for special conditions

Instrument Settings

ResponseAs per the federal regulations, the Slowresponse setting must be used when conducting a sound survey for hearing conservation purposes.

Using the Sound Level Meter

Several factors affect the measurement results:

� Instrument position

� Environmental variables

� Human factors

Instrument position

� Microphone orientation:� Hold at 70-degrees for pressure microphone

(random incidence)� Point SLM at source for free-field microphone

� Windscreen:� Use outdoors when wind speed above 10mph� Use indoors to protect mic from bumps and

moisture

� Vibration:� Never set SLM on vibrating surface

Using the SLM

Environmental variables

� Wind speed and direction:� Sound level increases downwind from source

� Barometric pressure and temperature:� Small effect on sound level readings� Calibrate SLM at site elevation

� Humidity:�Water can damage microphone diaphragm

Using the SLM

Human Factors

� Body reflections:� Hold SLM away from body� Position body perpendicular to noise source

� Reflecting surfaces:� Choose test location away from walls or large

machine panels.

� Background noise:� Does background add to machine noise?

Using the SLM

Human Factors

Study machine/source function:Match instrument settings to machine process

Use Leq to average over fluctuating work cycleUse Lmax to identify compressed-air burstUse Lpeak to measure peak levels due events such

as gun fire

Identify cyclical operations to capture loudest parts of total work cycle

Using the SLM

Perform these tasks for each survey period:

� Understand settings of SLM� Check batteries; replace if necessary� Inspect SLM for damage� Pre-survey calibration� Verify instrument settings for survey� Take written notes of machine operation� Post-survey calibration check

Using the SLM

Personal Noise DosimetersA noise dosimeter is basically an SLM designed to measures a worker’s noise exposure over the entire work shift, and it is worn by the worker. Almost all dosimeters are Type 2 instruments.

Personal Noise Dosimeters

� Miniature microphone positioned at the employee's mid-shoulder with a wire running to a microprocessor unit, which, in turn, is clipped to the wearer's belt or placed in a pocket.

� Newer units are one piece "badges" that are placed mid-shoulder. Very compact and easy to wear.

� Continuously measure and process A-weighted sound levels obtained from person's "hearing zone". Then produces a dBA TWA or equivalent per cent dose based on the length of the sampling period.

Types of Noise Surveys

� Preliminary� General Purpose� Noise Control


Preliminary� Basic needs assessment.� Involves a walk through of each plant area, using a

sound level meter to identify areas at or above 80 dBA, which would then be identified for follow-up under the General Purpose - Hearing Conservation Survey.

� Quite often the Preliminary survey is bypassed and a General Purpose survey is conducted in all areas.

� Include a memo in the “noise file” of all low-noise areas (<80 dBA).


General Purpose� This is the Hearing Conservation Survey� The objectives are:

� Determine employee daily noise exposures� Measure and document the sound levels

throughout an area� Identify equipment for potential noise control

evaluation

The Hearing Conservation Survey

� Who typically does this service?� Industrial Hygienists, Safety Professionals, and

Audiologists trained in noise measurement

� What does it cost?� Roughly $500-$1500 per day - depending on the

scope

The Hearing Conservation Survey

� When should a survey be conducted?� After the initial survey, repeat surveys are required

when changes in production or equipment occur that may affect the noise exposures. Recommend updated surveys every 2-3 years.

� Where should a survey be conducted?� In all areas where sound levels are 80 dBA or above

The OSHA Regulatory Criteria are:� Inclusion in the HCP when the daily-

average noise exposure equals or exceeds 85 dBA, or an equivalent 50% dose. This is termed the Action Level.

�The Permissible Exposure Limit (PEL) is a daily-average noise exposure of 90 dBA, or an equivalent 100% dose.

Hearing Conservation Requirements

Action Level

� Point at which an effective hearing conservation program must be implemented (≥85 dBA 8-hr TWA).

� At minimum, program consists of:� Conducting annual hearing testing

� Conducting annual hearing conservation training

� Making hearing protection available (mandatory when TWA is >90 dBA or if worker has an STS when working between 85-89 dBA of noise)

The OSHA Regulatory Criteria are:� Engineering noise controls are required to be

investigated when worker noise exposures exceed the PEL of 90 dBA (100% dose)

� Noise controls must be implemented when determined to be feasible

� The feasibility assessment must take into account both technical and economic factors


� The OSHA Regulatory Criteria are:� Hearing protection must be made available for all

workers with a daily-average noise exposure equal to or above 85 dBA (≥50% dose),

� Use of hearing protection is mandatory for all workers exposed above 90 dBA (≥100% dose), unless they have a standard-threshold shift (STS) in hearing at which point mandatory protection is required for exposures at or above of 85 dBA.


Best-Practice Criteria:The hearing conservation program action level (inclusion), permissible noise exposure limit, mandatory hearing protection, and noise control assessment are recommended when the daily-average noise exposures equal or exceed 85 dBA.


Determining Worker Noise Exposure

� One objective of the hearing conservation survey is to determine the average daily noise exposure of workers.

� To complete this objective the federal regulations first require determination of the workers’ Noise Dose.

Noise Dose is a percentage (%) of the maximum allowable noise that a worker may be exposed per day.


Noise Dose (%) is calculated using the following variables:

� Criterion Level (CL) = 90 dBA

� Threshold Level (TL) = 80 dBA and 90 dBA

� Exchange Rate (q) = 5 dBA


Criterion Level (CL) is set to 90 dBA and represents the daily limit of accumulated sound energy a person may be exposed to in an 8-hour period. So a Noise Dose of 100% would be equal to 90 dBA.

Note: for shorter or longer work shifts, the Noise Dose calculation should be normalized to 8 hours, which allows comparison of the results to the regulation criteria.


� The Threshold Level (TL) is the cutoff level below which no sound energy is added into the dose calculation.

� The federal regulations require the use of two separate cutoff or threshold levels, which are 80 dBA and 90 dBA.


What is the purpose of two threshold levels?

� LTL = 80 dBA; referred to as the “low” threshold level and is used to determine whether or not worker noise exposures warrant inclusion in the hearing conservation program.

� HTL = 90 dBA; referred to as the “high” threshold level and is used to determine compliance with the PEL of 90 dBA.


The Exchange Rate (q) is the trade-off relationship between an increase (or decrease) in sound level and the corresponding change in allowable exposure time.

(see Table in next slide)


TABLE G-16a (OSHA) orTABLE 62-1 (MSHA)

Reference duration, T (hours)Sound level, dBA3280

27.98124.38221.18318.4841685

13.98612.18710.6889.289890

7.0916.1925.3934.694495

3.5963.0972.6982.3992100

1.7101Table continues for higher sound levels

q = 5 dBATime isdoubled orhalved

As the sound level increases by 5 dBA, the allowable reference duration one is permitted to be exposed to that level is cut in half. Conversely, as the sound level decreases by 5 dBA, the allowable time of exposure to that level doubles.

Regulatory

ACGIH – as the sound level increases by 3 dBA, the allowable reference duration one is permitted to be exposed to at that level is cut in half. Conversely, as the sound level decreases by 3 dBA, the allowable time of exposure to that level doubles.

Table 1. TLVs for Noise (ACGIH)Reference Duration, T (hours)Sound Level, dBA

248020.2811682

12.78310.184

8856.3586

587488

3.2892.590291

1.6921.393194

0.8950.63960.5970.4980.3990.251000.2101

-Table continues for higher sound levels-

q = 3 dBATime isdoubled orhalved

Best Practice

02468

10121416

85 90 95 100 105 110 115

Noise Level, dBA

Allo

wab

le T

ime,

Hrs

NIOSH OSHA

0

2

4

6

8

10

12

14

16

85 90 95 100 105 110 115

Noise Level, dBA

Allo

wab

le T

ime,

Hrs

NIOSH OSHA

HLPP Inclusion Criteria

OSHA = 5 dB exchange rate; NIOSH = 3 dB exchange rate

Slide courtesy of Rick Neitzel

Calculation of Noise Dose (D),%:

D = 100 (C1/T1 + C2/T2 + ... + Cn/Tn)

Cn = Total time of exposure at a certain noise level,

Tn = Reference duration for that level, as given by in the appropriate federal regulations


As you can see in the previous equation, Noise Dose is a function of the noise level and duration of exposure to each level a worker experiences throughout the workday.


� Noise Dose (D), %

� Action Level (AL) is a dose of 50% or more,

� Permissible Exposure Limit (PEL) is 100%

� Time-weighted average (TWA), dBA

� AL is a TWA of 85 dBA,

� PEL is a TWA of 90 dBA.


Time-Weighted Average (TWA), dBA

The average noise level a worker is exposed to throughout the day normalized to an 8-hour period. Once the TWA is determined it may be compared to the regulation criteria for compliance with the PEL and inclusion in a hearing conservation program.


Time-Weighted Average (TWA), dBA

TWA = 16.61 Log(D/100) + 90

If you know the dose (D), the TWA can be found by looking in Table A-1 of the OSHA standard or Table 62-2 of the MSHA regulation. (See Example in next slide)


Example:

During a typical 8-hour shift, an employee spends:

4 hours at 87 dBA

3 hours at 92 dBA

30 minutes at 95 dBA

30 minutes at 84 dBA.

What is this employee’s TWA?


TABLE G-16a (OSHA) orTABLE 62-1 (MSHA)

Reference duration, T (hours)Sound level, dBA3280

27.98124.38221.18318.4841685

13.98612.18710.6889.289890

7.0916.1925.3934.694495

3.5963.0972.6982.3992100

1.7101Table continues for higher sound levels

Example:

L1 = 87 dBA C1 = 4 hours T1 = 12.1 hours

L2 = 92 dBA C2 = 3 hours T2 = 6.1 hours

L3 = 95 dBA C3 = 30 min. T3 = 4 hours

L4 = 84 dBA C4 = 30 min. T4 = 18.4 hours


Example:

D = 100 (C1/T1 + C2/T2 + ... + Cn/Tn)

D = 100 x (4/12.1 + 3/6.1 + 0.5/4 + 0.5/18.4)

D = 100 x (0.975)

D = 97.5%

TWA = 89.8 dBA (from formula or table)


Who Needs to be Monitored?

� Determining who to monitor needs to be carefully planned.

� The goal is to determine the daily-average noise exposure per worker. But the level of accuracy needs to be decided upon:� Are you just trying to identify the potential for a

worker to be exposed at or above 85 dBA?� Or, do you prefer more precise exposure results?

Who Needs to be Monitored?

� If the survey objective is to identify the potential for a worker to be exposed at or above 85 dBA, then considerably less sampling is required than a precise exposure determination. In the former situation, it is a “go” or “no go” decision as far as inclusion in the HCP.

� If you prefer more precise exposure results, then it is very likely significantly more sampling is required to establish a more accurate and representative exposure level for each worker.

Measuring Equipment and Area Sound Levels

The second objective for the hearing conservation survey is to measure and document equipment and/or area sound levels.

� This survey is conducted with at least a Type 2 sound level meter (±2 dB), as per ANSI requirements.

� Typically, the A-weighted sound level is measured approximately 3 feet or one meter away from each piece of equipment in the area of concern.


� These data may be documented in a separate table report, as a point measurement on a floor plan or equipment layout, or be used to generate a series of noise contour maps.

� An example of a noise contour is shown in the next slide.


Noise contour maps may be used to illustrate to workers the degree of noise hazard in their work areas, as an easy-to-understand educational tool, to illustrate hearing protection required areas, or to identify dominant noise sources that may be further investigated for potential noise control measures.



Noise Control SurveyThe objectives are:� Identify and prioritize dominant noise sources,� Determine source contributors to excessive

worker noise exposure, and� Obtain frequency data for the selection of the

appropriate control measures and/or acoustical materials.

Hierarchy of Noise Reduction

Elimination

Substitution

Engineering Controls

Administrative Controls

Personal Protective

Equipment (PPE)

Safe

Workplace

Safe

Worker

Engineering Controls

Can be accomplished by:

� Reduction at source: mufflers, enclosures

� Interrupt noise path: barriers, curtains, sound absorbing materials

� Reduction at receiver: enclosures

Comparison of HC Regulations

“The Modern Evolution of HearingConservation Regulations”

Theresa Schulz, PhD

http://www.cdc.gov/niosh/mining/userfiles/works/pdfs/tmeoh.pdf

Issue OSHA 29 CFR 1910.95

MSHA 30 CFR Part 62

FRA 49 CFR 227 & 229

Exposure limit PEL = 90 dBA TWA. Similar to OSHA, except integration range is explicit in regulation (62.101), and is for all sounds from 90 to at least 140 dBA.

Same as OSHA

Action level 85 dBA TWA. Similar to OSHA, except integration is for all sounds from 80 to at least 130 dBA.

Same as OSHA

Exchange rate 5 dB Same as OSHA. Same as OSHA

Impulse noise Should not exceed 140 dB peak SPL; to be integrated with measurements of all other noises

Integrate with measurements of all other noise.

Same as OSHA


MSHA 30 CFR Part 62

FRA 49 CFR 227 & 229

Ceiling No exposures > 115 dBA, interpreted as no unprotected exposures; give credit for HCP, HPDs and engineering controls.

No exposures > 115 dBA; no adjustment for use of hearing protection; “P” code issued where the miner is still over-exposed even though feasible engineering and administrative controls are in place.

No exposures > 115 dBA, except continuous > 115 dBA and < 120 dBA are permissible, provided total daily exposures < 5 seconds.

Monitoring noise exposure

Once to determine risk and HCP inclusion; then as conditions change resulting in more potential exposure.

Mine operator must establish system to evaluate each miner’s exposure sufficiently to determine continuing compliance with rule.

Same as OSHA; measurement artifacts may be removed.


MSHA 30 CFR Part 62

FRA 49 CFR 227 & 229

Noise control Feasible controls required where TWA > 90 dBA, compliance policy (OSHA can change/revoke any time) permits proven effective HCP in lieu of engineering where TWA < 100 dBA.

Feasible engineering and administrative controls required for TWA > 90 dBA; even if controls do not reduce exposure to PEL, they are required if feasible (i.e. > 3-dBA reduction); administrative controls must be provided to the miner in writing and posted.

FRA describes the specific actions that railroads and manufacturers must take when designing, building, and maintaining locomotives (instead of engineering controls); “noise operational controls” (administrative controls); hearing protection (same); “FRA has no hierarchy of noise controls.”

Administrative controls / noise operational controls

Feasible administrative controls required where TWA > 90 dBA

Administrative controls must be provided to miner in writing and posted.

FRA does not require the use of noise operational controls but makes them operational.

The Principles of Noise Control

� Identify sources of noise and their relative importance.� List noise control options as they apply to the source,

path and receiver.� Identify contributions from direct and reflected sound.� Distinguish between sound absorption and sound

isolation materials.� Identify and evaluate significance of flanking paths.� Identify and evaluate significance of structure-borne

noise.

The Principles of Noise Measurement

Questions/Discussion?

the principles of noise measurement · details of the hearing conservation survey overview of the...

Documents