Unit 7 - Industrial Flashcards
BS4142 outline
BS 4142, Methods for rating and assessing industrial and commercial sound is the method for assessing industrial noise recommended within many planning guidance documents.
BS4142:1997 sets out a methodology for predicting the likelihood of complaints based upon a comparison of the noise level of the industrial source and the prevailing background noise level.
2014 revision re-describes noise as ‘sound’ and adds ‘commercial’ to the industrial sources subject to assessment under the standard.
The standard defines and specifies procedures for measuring ambient, residual background and specific sound levels outside premises likely to be affected by sounds of an industrial and/or commercial nature; and for the assessment of the specific sound levels.
Unaligned local noise policy to updated bs4142:2014 revision
there may be specific local noise policies which may not be aligned to assessments under the 2014 provisions.
The most significant assessment differences are likely to be in the differing approaches to applying character corrections to obtain the ‘Rating Level’
What is BS4142 intended for for
BS 4142: 2014 is intended to be used to assess sound sources of an industrial and/or commercial nature in three situations:
- Complaint investigation
- Assessing impact of proposed new, modified or additional sources
- Assessing the impact of an existing source on proposed dwellings/residential uses
The standard defines and specifies procedures for measuring ambient, residual background and specific sound levels outside premises likely to be affected by sounds of an industrial and/or commercial nature; and for the assessment of the specific sound levels
what do Industrial and commercial sources include in reference to BS4142
Industrial and commercial sources include:
- Industrial and manufacturing processes
- Fixed mechanical and electrical plant and equipment
- Loading/unloading goods and materials
Limitations of BS4142
Limitations to prevent it being misapplied are re-stated and further clarified in that assessments of the following are outside its scope:
- Determination of (statutory or civil) nuisance
- Passing vehicles on public roads and railway systems
- Recreational activities, including motor sport and shooting grounds
- Music and other entertainment
- Construction and demolition
what Additional important factors that have to be considered when making a case for nuisance
- the character of the neighbourhood,
- the absence of a fixed standard for comfort,
- any element of malice in the noise creator,
- the time of day and the duration of the noise,
- the palpable presence of interference with personal use or enjoyment of their land,
- noise levels such that a “reasonable” person would find unacceptable.
BS 4142 does not take all these factors into account it cannot, of itself, be used to assess nuisance
reasons for BS4142 used to assess nuisance and/or used to assess noise sources outside its scope
BS4142 is often used to assess nuisance and/or used to assess noise sources outside its scope. There are two reasons for this:
- It provides a method for rating a noise which is based upon field noise measurements and gives a quantified assessment that can be easily understood by local government officers and magistrates.
- There is a general lack of comparable methods for other noise sources, so it is pressed into service in the absence of alternatives.
BS4142 Measurement and Assessment
Assessment Concept
Assessing the impact of sound from a source is based on a comparison of the ‘rating level’ and‘background sound level’.
The rating level is determined by applying appropriate character corrections to a source ‘specific sound level’ at relevant sensitive receptor locations.
The ‘background sound level’ is the representative LA90 of the ‘residual sound’ at these locations(residual sound - all sources present, excluding the ‘specific’ sound source(s) being assessed).
The greater the rating level exceeds the background sound level, the greater the significance of adverse impact at the assessment location
BS4142 Measurement and Assessment
Preparation and Uncertainty
All relevant sound sources and sensitive receptors should be appraised and understood to
- inform selection of measurement method
- provide contextual information regarding impact of new industrial sources or new sensitive receptors,and
- assist in considering uncertainty and how to minimise it.
- variability of meteorological conditions.
- reliability of any manufacturer sound source information
BS4142 Measurement and Assessment
Instrumentation & Verification
Sound pressure level measurement systems) to conform to Class 1 and be calibrated.
BS4142 Measurement and Assessment
Measurement Procedure
Carry out a field calibration check at the beginning and on completion of each measurement session.
- Measurement results with a calibration drift greater than 0.5 dB should be treated with caution.
- Select outdoor measurement locations which will give results representative of both ‘ambient’ (includes the specific source(s)) and residual sound at the assessment location(s).
- All measurements are at a height between 1.2 – 1.5 m above the ground and at least 3.5 m from reflecting surfaces as necessary to minimise the influence of reflected sound.
- Take all necessary precautions to minimise the influence of wind, rain, temperature and electric and electro-magnetic interference.
- Windshields should be used (generally considered effective up to wind speeds of 5 m/s).
- Record wind speed &direction, precipitation, temperature and a visual estimate of cloud cover
BS4142 Measurement and Assessment
Specific Sound Level of the Source
The specific sound level is measured as an𝐿Aeq,𝑇 with the measurement period ‘T’, chosen so as to give a measurement that is representative of the average sound from the source under investigation
- measurement period will encompass the whole cycle of the source eg the industrial process.
Ideally, the specific noise is measured against a very low level of noise from other sources (the residual noise).
- Residual sound contribution must be corrected to remove this contribution through log subtraction
BS4142 Measurement and Assessment
Rating Level
Subjective
Consider how perceptible, at the assessment location, any specific source acoustic feature is (tonal, impulsive, intermittent or another characteristic).
Tone perceptible: just = +2 dB; clearly = +4 dB; highly = +6 dB
Impulsivity perceptible: just = +3 dB; clearly = +6 dB; highly = +9 dB
Neither tonal nor impulsive: otherwise readily distinctive against the residual sound = +3 dB
Intermittency:readily distinctive on/off against the residual acoustic environment = +3 dB
BS4142 Measurement and Assessment
Rating Level
Objective
To be used if the subjective method results are contested or not considered sufficient to assess the audibility oftones or the prominence of impulsive sounds.
- Tones - one-third octave method, if tone present = +6 dB
- Tones - Reference method, narrow band (preferably FFT) = scale from +0.0-6.0 dB
- Impulsivity - A number of the highest impulsive events, over a half hour time history
- 𝐿𝑝𝐴𝐹, are used to calculate a character adjustment based on the ‘predicted prominence’ of the impulsiveevents.
- Very sudden, loud impulses can yield a maximum adjustment of + 18 dB.
The 1997 Standard corrections - either ‘+5’ (for acoustic features present) or ‘0’ (for none).
BS4142 Measurement and Assessment
Background Sound Level
This should be measured at the assessment location, without the specific sound present, but at a time and under conditions when the specific sound source is (or will be) normally operational.
If the specific sound is continually operational then it can be measured at an equivalent site with a detailed justification for the alternative location being equivalent.
Measurements are made as an 𝐿𝐴90,𝑇 exceedance level. T
- measurement time intervals not less than 15-minute interrvals,
BS4142 process summary
