This document presents an audit of acceptable outdoor and indoor noise levels. It includes the objectives of ensuring outdoor noise levels conform to CPCB standards and indoor levels meet NBC 2005 guidelines. Outdoor standards designate acceptable noise levels for different area categories like industrial, commercial and residential zones. Indoor guidelines provide recommended noise levels for various room types. The audit methodology, use of sound level meters, and strategies to control indoor and outdoor noise are also summarized.

1. ACCEPTABLE OUTDOOR AND
INDOOR NOISE LEVELS AUDIT
Presented by :
K.S.S.N. Prakash
Chiranjeeb Mohan
07/09/2017
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2. Contents
1. What is an Audit ?
2. Flowchart of an Audit.
3. Acceptable outdoor and indoor noise levels (Audit objectives).
4. Noise ambient standards (for outdoor noise levels).
5. Indoor noise levels acceptable values.
6. Sound Audit format.
7. Audit Methodology.
8. Sound Level Meters.
9. Estimating average noise levels from sound level meter readings.
10.Noise Level Control Strategies .
11.Strategies to control outdoor noise levels.
12.Strategies to control indoor noise levels.
13.References.
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3. What is an Audit ?
Audit is the examination or inspection of various parameters and factors (related
to books of accounts, energy, noise levels, etc.) by an auditor followed by
physical checking of inventory to make sure that all departments are following
the prescribed documented system.
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4. There are four main steps in the auditing process :-
• The first one is to define the auditor’s role and the terms of engagement which
is usually in the form of a letter which is duly signed by the client.
• The second step is to plan the audit which would include details of deadlines
and the departments the auditor would cover.
• The next important step is compiling the information from the audit.
• The last and most important element of an audit is reporting the result. The
results are documented in the auditor’s report.
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5. Flowchart of an Audit
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6. Acceptable outdoor and indoor noise levels
(Audit objectives) :-
• To use appropriate noise controls for providing acceptable levels of outdoor
and indoor noise levels to enhance comfort.
• To ensure that the outdoor noise level conforms to the CPCB-Environmental
Standards-Noise (ambient standards).
• To ensure that the indoor noise levels conform to the levels described in NBC
2005 (BIS 2005a).
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7. Noise ambient standards (for outdoor noise levels):-
Area code Area category Limit in dB (A) Leq
(equivalent sound level)
Day time Night time
A Industrial area 75 70
B Commercial area 65 55
C Residential area 55 45
D Silence zone 50 40
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8. Indoor noise levels acceptable values :-
Location Noise level dB (A)
Auditoria and concert halls 20-25
Radio and television studios 20-25
Music rooms 25-30
Hospitals and cinema theatres 35-40
Apartments, hostels and homes 35-40
Conference rooms, small offices and libraries 35-40
Court rooms and class rooms 40-45
Large public offices, banks and stores 45-50
Restaurants 50-55
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9. Sound Audit format
Outdoor noise levels
Facade Measured
sound level
dB(A)
Recommended sound level as set in CPCB-
Environmental Standards-Noise (ambient standards) dB
(A)
Note : Sound level should be measured outside each façade of the building
Indoor noise levels
Room Location Measured sound
level dB (A)
Recommended
sound level as set in
CPCB-
Environmental
Standards-Noise
(ambient standards)
dB (A)
Note : In case of more than one building on site conduct outdoor and indoor
sound level audit for all buildings separately. 07/09/2017
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10. Audit Methodology :-
In order to ensure that the indoor and outdoor noise levels are acceptable and
meet the CPCB standards, the ambient noise levels on site should be reported by
a competent agency. Following is an example where the noise levels on site
have been reported.
Date of Sampling : 18.06.2007
Type of Sample : Noise Level Monitoring
Report No. : 0706/1857
Serial No. Location Noise Level [ In decibel (A) ]
1
2
3
Near D.G. Set
Near Site Office
Near Mixer
71.5
65.0
68.2
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11. Sound Level Meters
• A sound level meter measures noise at any
particular moment.
• They are good for spot checking and
determining loudness of equipment.
• They are useful for noise audits.
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12. Estimating average noise levels from sound level meter readings
If someone is exposed to several different noise levels, we can estimate average
noise level with the following formula:
D = 100(C1/T1 + C2/T2…Cn/Tn)
where C = time at specific noise level
T = reference duration
If D is greater than 50, then average noise level exposure of that employee is
over 85 decibels.
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13. Noise Level Control Strategies
• While doing acoustical planning the following two key material properties are
analyzed.
1. Noise Reduction Coefficient (NRC) : NRC reflects the ability of a material to
absorb sound.
2. Sound Transmission Class (STC) : STC reflects the barrier effect of a
material/assembly.
• The following are two fundamental ways in which noise can be controlled.
1. Keeping the noise source away from the occupant/building user.
2. Screening/blocking excess noise.
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14. Strategies to control outdoor noise levels
1. Control noise at source.
2. Increase the length of the path.
3. Block the length of the path :-
a) Position of the barrier.
b) Height of the barrier.
c) Continuity.
d) Barrier length.
e) Material of the barrier.
f) Texture of the barrier.
g) Vegetation and earth berms.
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15. Strategies to control indoor noise levels
For reducing indoor noise levels, the following steps should be implemented.
• Reduce the hard paved surfaces around the building in order to minimize
ground reflections of sound. Develop maximum area around the building as
softscape or covered in plantations.
• Buildings should be located at a distance of at least 30 m from a road with
heavy traffic (80-90 dB) (NBC 2005).
• Walls or partitions should have a Sound Reduction Index of 40 dB or higher
(NBC 2005).
• In general offices, the reverberation time should not exceed 1 sec (NBC
2005).
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16. References
• GRIHA Manual Volume 1, 4 and 5 by TERI.
• Noise Audit by Division of Occupational Safety and Health.
• Executive Summary : The Evaluation on Noise Environmental Impact
Management – A Case Study.
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17. THANK YOU
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