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The Risks of Environmental Noise Assessments. Presented by Andrew Bullmore Hoare Lea Acoustics Co-authored by Justin Adcock. To inform the outcome of some decision making process … research strategic planning complaint resolution specification of noise control measures

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slide1

The Risks of Environmental Noise Assessments

Presented by Andrew Bullmore

Hoare Lea AcousticsCo-authored by Justin Adcock

why undertake an environmental noise assessment
To inform the outcome of some decision making process …

research

strategic planning

complaint resolution

specification of noise control measures

specification of building element performance

compliance testing

etc. ……

Why undertake an environmental noise assessment?
slide3

Can noise data help?

  • the decision making process to be informed must have some ‘target’ outcome
  • would a knowledge of noise assist in the outcome of the decision making process?
  • noise may be one of many factors affecting the potential outcome
  • compared with the other controlling factors, is noise a significant factor?
  • do planning requirements necessitate the consideration of noise?
slide4

Specification of building elements

External traffic noise levels– PPG24 NEC assessment?

Internal noise levels– WHO, BS8233, BB93 etc?

slide8

Source

(emission)

Receiver

(immission)

Transmission

(propagation)

Factors affecting received noise levels

  • variations in the source (e.g. traffic flows, wet roads)
  • variations in the propagation path (mainly distance and wind effects)
  • local effects at the receiver (including cumulative effects of all sources)
slide9

LAmax

LA10,t

LAeq,t

LA90,t

LAmin

Accounting for temporal variability- noise measurement indices

slide10

Temporal variability of noise levels

Despite extensive averaging, significant variability in environmental noise levels can still exist from day to day – be warned!

slide11

PPG24 Noise Exposure Categories (NEC) for traffic noise

* N.B. daytime levels LAeq,16hr, night time levels LAeq,8hr

slide12

Measurement versus Calculation

Calculated – constant level

Measured – variable levels

fourteen days

slide13

Assessment methodology – measurement

  • provides an absolute indication of the noise level existing attheprecisetimeandlocation of the measurement
  • provides a measure of the temporal variability of the sound field over the duration of the measurement period
  • does not isolate noise from the specific source under study from other extraneous sources
  • significance of trend changes can be less than natural variability
slide14

Assessment methodology – prediction

  • allows isolation of specific noise from other sources
  • allows trends due to specific source to be positively identified without problems of measurement variability
  • allows generation of results over wide areas
  • output results only as good as the input data
slide15

What is the risk?

What if the ‘wrong’ decision were to be made due to ‘incorrect’ or ‘inadequate’ noise data?

  • money directed towards ineffective strategic .. noise mitigation measures
  • refusal of planning consent
  • over / under design of building performance
  • health implications to the exposed population
  • enforcement action

The design and ‘accuracy’ requirements of any noise assessment should focus on the RISK associated with the outcome

slide16

What defines ‘accuracy’ in the context of environmental noise?

  • ‘accuracy’ should be driven by the need to manage ‘risk’ to the appropriate degree
  • ‘accuracy’ should not be driven by the desire to minimise ‘uncertainty’ at all costs
  • ‘accuracy’ requirements can therefore only be defined within the context of a particular assessment
slide17

Need to differentiate between …

  • variability
  • uncertainty
  • risk
slide18

Variability versus uncertainty

Source (emission)

Receiver (imission)

Propagation

  • overall noise output level
  • noise character (tonal, impulsive)
  • cumulative effects of variable multiple sources
  • meteorological / seasonal changes (e.g wet roads, holiday traffic, etc.)
  • meteorological effects
  • ground effects
  • screening
  • mobile sources
  • cumulative effects of multiple sources in different directions
  • subjective response / reaction
  • measurement device accuracy
  • directional response
  • exposed population at home or work
  • windows opened or closed

variable

variable

variable

slide19

Increased variability does not mean increased uncertainty

…… provided the causes of variability are known and can be quantifiede.g. measurement under light downwind conditions promotes slightly higher, morestable noise levelssupporting non-acoustic data can be as important as noise data ….

slide20

ISO 9613(based on typical downwind propagation conditions)

20m

200m

Calculated noise level, dB

1000m

Harmonoise PE model (based onannual measured meteorological conditions)

Percentage of time below stated noise level, %

Worst case principle adopted by many noise calculation methodologies(downwind propagation)

slide22

Noise measurements – summary

  • 5 x groups of 10 simultaneous measurements
  • groups arranged either side of main roads (major sources of noise)
  • simultaneous measurement of meteorological conditions
slide26

Time of day – 06:00 to 23:00

Scenario 1 – road traffic noise clearly dominates at high level due to proximity of main road

80

75

70

65

60

55

50

45

40

Sound pressure level, dB(A)

slide27

Time of day – 06:00 to 23:00

Scenario 2 – road traffic noise still dominates, but because road more distant noise is at a lower and more variable level

80

75

70

65

60

55

50

45

40

Sound pressure level, dB(A)

slide28

In general, roadtrafficnoise demonstrates a strong inverse relationship between absolute noise level and the variability of measured noise levels (see also Alberola et al Forum Acousticum 2004)

80

75

70

65

60

55

50

45

40

Sound pressure level, dB(A)

0.5 1.5 2.5 3.5 4.5 5.5

Standard deviation, dB(A)

slide29

Time of day – 06:00 to 23:00

Scenario 3 – non- road traffic noise source dominate the overall measured noise levels

80

75

70

65

60

55

50

45

40

Sound pressure level, dB(A)

slide30

Corruption by non-road traffic noise sources can significantly affect the expected trend in variability

80

75

70

65

60

55

50

45

40

Sound pressure level, dB(A)

0.5 1.5 2.5 3.5 4.5 5.5

Standard deviation, dB(A)

slide31

Background Sound Variability

Noise level, dB

Distance from source

slide32

Industry Sound Variability

Noise level, dB

Distance from source

slide33

Uncertainty and Potential Risk

critical region = risk

Noise level, dB

Distance from source

measurement design approach

1. Investigate requirement

2. Design

Review strategy & potential risk

3. Execute

4. Analyse & Report

Measurement Design Approach

increasing site knowledge

slide35

Guidance….

Investigate requirement

Design Survey

Survey and Analyse

investigate measurement requirement
Investigate Measurement Requirement
  • understand the nature of the decision to be made
  • consider significance of noise in the context of the decision to be informed
  • understand the nature of the noise value to be derived
  • review availability of any existing data
  • review utility of noise measurements as part of a decision making tool
design measurement strategy
Design Measurement Strategy
  • systematically review all potential sources of temporal or spatial variablity – are they significant?
  • establish acoustic and non-acoustic information requirements & select appropriate survey method
  • liaise with commissioning body over potential risks
  • review requirements against available resources (time/cost/access/equipment/personel/ etc.)
post measurement analysis
Post Measurement Analysis
  • analyse according to assessment methodology and selected survey strategy
  • establish if uncertainty equates to risk
  • review requirement for further studies
conclusions summary
Conclusions & Summary
  • always consider the relationship between uncertainty and risk BEFORE attempting any assessment
  • understand as far as possible the relationship between variability, uncertainty and risk
  • understanding and quantifying the causes of variability reduces uncertainty
  • tailor assessment strategies to address risk totheappropriatelevel (i.e. the ‘criticality’ of the outcome) and NOT to minimise uncertainty at all costs