BS4142:2014 Method for rating industrial and
commercial sound
Alan Whitfield
Academic Lead Environmental Health
University of Derby
[email protected]
Presentation Outline
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When and when not to use
Definitions
Principles of Use
Measurement Approach
Character Corrections
Background Sound Level
Assessment Outcome
Context
Uncertainty
WHEN TO USE BS 4142
Can be used to assess:
 sound from industrial and manufacturing processes;
 sound from fixed installations with mechanical and
electrical plant and equipment;
 sound from the loading and unloading of goods and
materials
 sound from mobile plant and vehicles that is an intrinsic
part of the overall sound emanating from premises or
processes e.g. forklift trucks, train or ship movements.
What does it do?
 Assessment of outdoor sound levels for likely effects
of sound on people in residential dwellings
Used to:
 investigate complaints (NOT statutory Nuisance!!)
 assessing sound from proposed, new, modified or
additional source(s) of sound; and
 assessing sound at proposed new dwellings or
premises used for residential purposes.
What Doesn’t it Cover?
 Determination of statutory nuisance
 Passage of vehicles on the Highway or Railways
 The derivation of indoor sound levels arising from sound
levels outside, or the assessment of indoor sound
levels.
 Assessment of low frequency noise.
Specific Exclusions
 recreational activities, including all forms of
motorsport;
 music and other entertainment;
 shooting grounds;
 construction and demolition;
 domestic animals;
 people;
 public address systems for speech; and
 other sources falling within the scopes of other
standards or guidance.
DEFINITIONS
 Acoustic environment
 Ambient sound
 Ambient sound level (La=LAeq,T)
 Specific sound source
 Specific sound level (Ls=LAeq,Tr)
 Reference time interval (Tr)
 Residual sound
 Residual sound level (Lr=LAeq,T)
 Background sound level (LA90,T)
 Measurement time interval (Tm)
 Rating level (LAr,Tr)
Assessment Preparation
To understand context conduct an appraisal to identify:
 ALL the sounds that can be heard, and identify their
sources;
 appropriate measurement methods
 potential measurement locations;
 identify the necessary measurement frequencies,
durations and timings; and
 for new development understand the potential impact
GENERAL PRINCIPLES OF BS 4142
 Determine specific sound level
 If specific sound levels vary take necessary
measurements
 Measure residual sound level in absence of specific
noise
 Take away effect of residual sound on specific sound
 Measure background sound level of residual sound
BS 4142 in Practice
Measurement Procedure
The Key aspects are:
 Field calibration check
 Measurement locations
 Precautions against interference
 Weather conditions
Field Calibration Check
 “Field calibration check”, not a calibration
 For attended measurements acceptable drift to
±0.5dB
 Can exceed ±0.5dB for long period monitoring
 If the drift exceeds ±1dB – why?
 Beyond this your data is questionable
Field Calibration Check - Practical Advice for Errors
Dramatically altering the SLM offset at the first
calibration check can result in an unacceptable drift at
the final check
 Check the calibrator coupling
 Allow more time for the pressure inside the coupling
to settle
 Disconnect and reconnect the microphone etc
 Check the batteries in the calibrator
 Consider any changes in the weather conditions
(particularly the atmospheric pressure)
Measurement Location
 Choose representative locations – can be nearest
residential or proposed dwelling location
 Normally ground level
 1.2 to 1.5m above ground
 Minimise influence of reflections – 3.5m from
reflecting surfaces
 For above ground level – 1m from façade with 3dB
facade correction
Precautions against interference
Minimise the risk of:
 Wind induced microphone noise
 Rain noise
 Electrical and EMF
 Temperature
 Don’t wear rustley jacket!
Weather Conditions
 Wind speed (using an anemometer)
 Wind direction
 Cloud cover (percentage cover or oktas)
 Rainfall
 Temperature (beginning and end)
Must be measured at the monitoring location. Not
weather forecasts, or data from other locations.
Weather conditions
 For long-term unattended
measurements use a
logging weather stations
 This needs to be AT the
noise monitoring station
National Park Service 2013
So What Do I Need to Do on Site?
 Determine the Specific Sound Level:
 Measure the ambient sound level
 Measure the residual sound level
 Measure the background sound level
 Undertake a subjective assessment of the Specific
Sound Level:
 Are there any acoustic features
 If yes need to apply a character correction
 Understand the Context
Determining the Specific Sound Level
 Measure the Ambient Sound Level (ASL)
 Distinguish the Specific Sound from the Residual
Sounds
 Minimise influence of Residual Sounds through good
practice
 Measure the Residual Sound Level (RSL)
 Subtract RSL from ASL to give SSL:
𝐿𝑠 =
𝐿𝑎
10log(1010
𝐿𝑟
− 1010 )
Determining the Rating Level (RL)
Need to apply character correction to SSL to obtain RL
There are character corrections for:
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Tonality
Impulsivity
Other sound characteristics
Intermittency
Three ways to obtain:
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b)
c)
subjective method;
objective method for tonality;
reference method.
Tonality
Subjective Method:
 +2 dB for a tone which is just perceptible at the noise
receptor,
 +4 dB where it is clearly perceptible and
 +6 dB where it is highly perceptible.
Tonality
Third Octave Band Method:
 +6 dB correction if the sound pressure level in the
one-third-octave band of interest exceeds sound
pressure levels of both adjacent one-third-octave
bands by:
 15 dB in the low-frequency one-third-octave bands (25
Hz to 125 Hz);
 8 dB in middle-frequency one-third-octave bands (160 Hz
to 400 Hz);
 5 dB in high-frequency one-third-octave bands (500 Hz to
10 000 Hz).
Tonal Correction (25 to 125Hz)
100Hz 1/3 Octave
≥+15dB
Tonal Correction (160 to 400Hz)
250Hz 1/3 Octave
≥+8dB
Tonal Correction (500 to 10,000Hz)
1600Hz 1/3 Octave
≥+5dB
Tonality
Reference Level:
 Based on Joint Nordic Method in ISO 1996-2
 See Annexe D BS4142
Impulsivity
Up to +9dB for sound that is highly impulsive
Subjective Method:
 +3 dB for impulsivity which is just perceptible at the
noise receptor;
 +6 dB where it is clearly perceptible and
 +9 dB where it is highly perceptible.
Impulsivity
Reference Method:
 Onset rate for measuring the prominence of impulsive
sounds
 See annexe E
Other Sound Characteristics
 For specific sound features characteristics
 Neither tonal nor impulsive
 But readily distinctive against the residual acoustic
environment
 Penalty of +3 dB can be applied
Intermittency
 Identifiable on/off conditions and
 Intermittency is readily distinctive against the residual
acoustic environment
 Penalty of +3 dB can be applied.
Notes on Character Correction
 For Impulsive and Tonal corrections these can be
additive
 The SSL + character correction gives the Rating Level
Background Sound Level – LA90,T
Definition:
‘A-weighted sound pressure level that is
exceeded by the residual sound at the assessment
location for 90% of a given time interval, T,
measured using time weighting F and quoted to the
nearest whole number of decibels’
There is NO SINGLE background sound level
What is it?
 ‘…. might in part be an indication of relative quietness at
a given location’
 ‘…. does not reflect the occurrence of transient and/or
higher sound levels … ’
 ‘…. generally governed by continuous or semicontinuous sounds’
Determining LA90,T
 Important to ensure values are:
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reliable
representative
typical of the period concerned
account for the range of levels experienced
 Objective is NOT to obtain the lowest measured level
 Can include industrial and/or commercial sounds
What to measure and assess - LA90,T
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LA90,T (T normally not less than 15 minutes)
Continuous or disaggregated periods
Not a mean average of values
Sound sources that comprise the acoustic
environment (absence of specific noise)
 Meteorological conditions
 describe and report all sources of sound
 > 10 dB above instrument noise floor
Where do I Measure?
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at the assessment location(s); or
alternative, comparable location
justify alternative location(s) – consider uncertainty
values typical of the period concerned
Using statistical analyses
LA90
Terminology for Assessment
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SOAEL
LOAEL
NOEL
- Significant Observed Adverse Effect Level
- Lowest Observed Adverse Effect Level
- No Observed Effect Level
Terminology for Assessment
Increasing Sound Pressure Level
Refer to National Noise Policy Statement for England
SOAEL
LOAEL
NOEL
Assessment of the Impacts
 Initial estimate of impact of specific sound:
 rating level - background sound level
 The greater this difference, the greater the magnitude of
the impact.
 The lower this difference the lesser the impact
 difference of around +10 dB or more indication of a significant
adverse impact
 Difference of around +5 dB indication of an adverse impact
BUT ALL THIS DEPENDS ON THE CONTEXT!!
Pertinent Factors for Context
Absolute sound level:
 Impact is relative to residual sound and background
sound levels
 High residuals may already have significant adverse
effects and so specific source may worsen this
Example of Context – Poultry Rearing Units
Pertinent Factors for Context
 Character of the existing residual sound.
 Is it tonal or impulsive or intermittent
 Do you need to compare tonal spectrums for residual
and specific?
 Sensitivity of receptor
 Do dwellings incorporate design measures to secure
good internal and/or outdoor acoustic conditions:
 facade insulation treatment;
 ventilation and/or cooling that will reduce the need to have
windows open so as to provide rapid or purge ventilation; and
 acoustic screening.
Uncertainty
“Consider the level of uncertainty in the data and
associated calculations. Where the level of uncertainty
could affect the conclusion, take reasonably practicable
steps to reduce the level of uncertainty. Report the level
and potential effects of uncertainty.”
Uncertainty of Measured Values
 Complexity and relationship between specific & residual
sounds
 Locations of measurements, source(s), receiver
 Measurement durations, times, number, conditions –
weather/ operating, …
 Technique/ competence: data recording (rounding,
observations), parameters, …
Some points for consideration
 Standing waves/ interference
 Point/ line/ area sources – near & far field
 Source: configuration, condition, height,
location(s)
 Multiple sources
 Weather: measurement effect, residual variability
 Transmission path: ground effects, barriers/
foliage
 Receiver: representative background, equipment
reliability
 Survey duration, reporting, data storage
Measurement variability
Spatial and temporal variability:
 Select location(s) to control/ understand spatial effects
 Select duration, timing, measurement quantity, conditions
to understand temporal effects
 Highly variable level – greater uncertainty, longer
measurement period
 Steady level – less uncertainty, shorter measurement
period may be appropriate
 Interaction between residual and specific levels
Uncertainty in calculations
Due to several factors:
 Measured levels
 Source variability
 Calculation method
 Modelling
 Calculation error
Effect of Uncertainty on Assessment
 Assessment result is a range, not a single value
 Magnitude of the range can depend on uncertainty
and variability of the residual and specific levels
 Uncertainty may be insignificant for a very clear
assessment outcome, but may significantly affect the
outcome if borderline
INFORMATION TO BE REPORTED 1
 Statement of qualifications, competency, professional
memberships and experience directly relevant to the
application of this British Standard of all personnel
contributing to the assessment.
INFORMATION TO BE REPORTED 2
Source under investigation as follows:
 description of source and of specific noise;
 hours of operation;
 mode of operation (e.g. continuous, twice a day, only in
hot weather);
 operational rates (e.g. load setting, max rate etc
 description of premises in which source is situated (if
applicable);
INFORMATION TO BE REPORTED 3
Subjective impressions, including:
 dominance or audibility of the specific sound;
 main sources contributing to the residual sound; and
 existing context including assessment of sensitivity of
receptor
INFORMATION TO BE REPORTED 4
location of measurement positions
 distance from the specific sound source
 topography of the intervening ground
 include photograph or dimensioned sketch with a north
marker
 include justification for measurement locations
INFORMATION TO BE REPORTED 5
Sound measuring instruments used
 type;
 manufacturer
 serial number;
 date of last verification test
 Operational test:
 calibration levels before and after measurements
 reference level(s) of calibrator,
INFORMATION TO BE REPORTED 6
Weather conditions including:
 wind speed(s) and direction(s);
 presence of conditions likely to lead to temperature
inversion (e.g. calm nights with little cloud cover);
 precipitation;
 fog;
 wet ground;
 frozen ground or snow coverage;
 temperature; and
 cloud cover.
INFORMATION TO BE REPORTED 7
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Date(s) and time(s) of measurements.
Measurement time intervals.
Reference time interval(s).
Specific sound level:
measured sound level(s);
residual sound level(s) and method of determination;
ambient sound level(s) and method of determination;
specific sound level(s) and method of determination;
INFORMATION TO BE REPORTED 8
 justification of methods; and
 details of any corrections applied.
 Background sound level(s) and measurement time
interval(s) and, in the case of measurements taken at an
equivalent location, the reasons for presuming it to be
equivalent.
INFORMATION TO BE REPORTED 9
 Rating level(s):
 specific sound level(s);
 any acoustic features of the specific sound; and
 rating level(s).
 Excess of the rating level(s) over the measured
background sound level(s) and the initial estimate of the
impacts.
 Conclusions of the assessment after taking context into
account.
 The potential impact of uncertainty (see Clause 10).