NBR 10151 Noise Std

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ABNT STANDARD NBR 10151

ACOUSTIC

EVALUATION OF NOISE LEVELS IN LIVING

AREAS FOR COMFORT OF COMMUNITY

Procedure

1.

Objective1.1This standard establishes the conditions for the acceptance of noise levels in communities,

regardless the existence of complaints.

1.2This standard specifies a noise level measurement method, the correct application of theverified levels with special characteristics, and a comparison of corrected noise levels using acriterion based in multiple factors.

1.3The evaluation method is based on the measurement of the levels of equivalent soundpressure (LAeq) in decibels A or dB(A), except for the provisions of item 5.4.2.

2. ReferencesThe regulations and standards listed below contain provisions that, once mentioned in this text,

shall be taken into consideration. The editions indicated below were in force at the time of thepublication of this regulation. As any standard is subject to revision, it is recommended that any

agreement based on this regulation shall verify the convenience of using an updated issue of

such regulations. ABNT has information about the regulations in a given moment.

IEC-60651:1979 Sound level meters

IEC-60804:1985 Integrated averaging sound level meters

IEC-60942:1988 Sound calibrators

3. Definitions3.1Equivalent continuous sound pressure level (LAeq), in decibels A (dB(A)): level obtained

from the mean value of sound pressure during the period of time being measured.

3.2Impulsive sound: sound containing pulses that are peaks of acoustic energy with duration ofless than 1 sec. and with a repetition pattern greater than 1 sec. (for instance: hammering,

jack-hammer, gunshots, explosions)

3.3Noise with tone components: noise containing pure tones, as the noise from a whistle.3.4Background noise level (Lra): Level of equivalent sound pressure at the place and time

considered, in the absence of noise generated by the noise source in question.

4. Measuring equipment4.1Sound meter

The sound meter or sound metering system shall comply with specification IEC 60651 fortype 0, type 1 or type 2.

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It is recommended that the equipment is suitable to measure equivalent continuous sound

pressure level (LAeq) as per IEC 60804.

4.2Sound calibratorsSound calibrators shall comply with specification IEC 60942 and shall be Class 2 or better.

4.3Calibration and adjust of instrumentsThe sound meter the sound calibrator shall have a calibration certificate fromRede Brasileira

de Calibrao (RBC)or from theInstituto Nacional de Metrologia, Normalizao e

Qualidade Industrial (INMETRO), renewed every 2 years at least.

A verification and eventual adjustment of the sound meter or the sound metering system shallbe performed by the equipment operator using the sound calibrator, immediately before and

after each measurement or group of measurements related to the same event.

5. Measuring procedure5.1General

Noise levels shall be measured externally to the property limits where the noise level islocated, in accordance with 5.2.1.

In case of complaints, measurement shall be taken in the place and conditions indicated by

the complainer, according to 5.2.2 and 5.3, provided all other general dispositions are

complied with.

In order to have a better evaluation of the community discomfort, it might be necessary tocorrect the metered sound level in case the noise presents special characteristics. The

application of this correction shall be according to 5.4 and is used to obtain the corrected

level (Lc).

All values of noise level shall be corrected to the nearest entire unit.

Measurements shall not be taken in case of audible interference caused by nature (thunder,heavy rain, etc.)

Reading time shall be defined to allow the collection of the noise in question. Measurementmay present a sole sample or a sequence of samples.

5.2Measurement outside buildings.Wind effect on microphone shall be prevented by using a protection as instructed by the

manufacturer.

5.2.1 Measurement taken outside buildings with noise source shall be done in pointslocated approximately 1.2 meters from the floor and at least 2 meters from theproperty limit and from any other reflective surface such as walls, fences, etc. If it is

not possible to follow this recommendation, the measurement conditions shall be

described in the report.

5.2.2 Outside the complainers house, the measurement shall be taken in points locatedapproximately 1.2 meters from the floor and at least 2 meters from any other

reflecting surface such as walls, fences, etc.


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If the complainer indicates any point that differs from the provisions of item 5.2.1 and

5.2.2, the value measured at this point shall also be part of the report.

5.3Measurements inside buildingsMeasurement taken at interior spaces shall be done at a distance of at least 1 meter from anysurface such as walls, ceiling, floor, furniture, etc.

Sound levels at interior areas shall be the mean value measured at a minimum of 3 different

positions away from each other at least 0.5 meters.

If the complainer indicates any point that differs from the above condition, the mean value at

this point shall be also included on the report.

Readings shall be taken at normal using conditions of the ambient, i.e., with open or closed

windows according to the instructions of the complainer.

5.4Correction for noise with special characteristics5.4.1 The corrected level Lc for noise without pulse pattern and without tone components

shall be determined by the equivalent continuous level (LAeq).If the meter does not automatically give the L Aeq, the procedure of Annex A shall beused.

5.4.2 The corrected level Lc for noise with pulse characteristics or impact characteristics isdetermined by the maximum value measured with the sound meter set to fast and

adding 5 dB(A).

Note: Brazilian Regulations for evaluation of the discomfort caused by noise shall be

applied when published.

5.4.3 The corrected level Lc for noise with tone components shall be determined by LAeqplus 5 dB(A).

5.4.4 The corrected level Lc for noise with both characteristics (pulse and tone) shall bedetermined by using procedures of items 5.4.2 and 5.4.3, assuming the greater value.

6. Noise evaluation6.1General

The method for evaluating the noise level is based in the comparison between the correctednoise level Lc and the criteria of level evaluation NCA according to the table 1.

6.2Criteria of level evaluation (NCA) definition6.2.1 The criterion of level evaluation for external areas is shown on table 1.6.2.2 Daytime and nighttime according to the table 1 shall be defined by the authorities

based on the local habits. However, the nighttime shall not begin after 10 PM andshall not end before 7 AM of the next day. If next day is a Sunday or a holiday, the

period shall not end before 9 AM.


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6.2.3 The criteria for level evaluation NCA for internal spaces shall be considered as thelevels of table 1 with a correction of 10 dB(A) for open window and 15 dB(A) forclosed window.

6.2.4 If the background noise level Lrais above the values of table 1 for the area and time,Lrawill be taken as NCA.

Table 1

Criteria for level evaluation NCA for external areas in dB(A)

Type of area Day time Night time

Farms and ranches 40 35

Urban areas - strictly residential, hospitals or schools 50 45

Mixed area, mainly residential 55 50

Mixed area, mainly commercial and administrative 60 55

Mixed area, recreational 65 55

Industrial area 70 60

7. Test reportThe report shall present the following information:

a) manufacturer, type or class and serial number of all equipment used for measuring soundlevels;

b) date and number of last calibration certificate for each piece of equipment;c) schematic drawing or detailed description of the measuring points;d) time and duration of the measurement;e) corrected noise level Lc, informing the corrections applied;f) ambient noise level;g) value of criteria for level evaluation (NCA) used for the area and time of measurement;h) reference to this regulation.


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Annex A

Alternative method to determine LAeq

This Annex A presents an alternative method for the calculation of the equivalent sound pressure

level LAeq, if the sound meter does not have this feature. In this case, the equivalent soundpressure level LAeqin dB(A) shall be calculate by the expression:

n

LAeq = 10 log 10Li

10

i=1

1

n

where:

Li = level of sound pressure in dBA(A), with the instrument in fast mode (every 5 sec)during the reading time.

n = total number of readings.

NBR 10151 Noise Std

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