Cirrus Research plc

10-Year Noise nuisance mystery finally wrapped up - Case study

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Courtesy of Cirrus Research plc

The Solution
As a result, and coupled with an investigation into the numerous noise sources from the factory, a number of recommendations were made and implemented. To test their efficacy a second BS41421997 assessment was carried out seven months later. The second report concluded that the impact had reduced noise to a level below 'marginal significance' and they didn't envisage any further complaints.

Unfortunately, local residents didn't agree and the complaints continued leaving the factory managers baffled as to the mysterious source or the specific circumstances that were causing the noise nuisance.

The factory itself produces film for food products and residential properties are only 300-400 meters from the perimeter. Further investigations helped to narrow down the issue somewhat and the problem seemed more prevalent depending on weather conditions and wind direction.

Several years after the first complaint was lodged against the factory, Wirral Council's EHO Toby Zorn, was given the project with a view to finally closing the hefty case file once and for all.

He opted to use two Cirrus Trojan2 portable noise nuisance recorders to help carry out a full BS4142 assessment - adding this one to the ever-growing list of noise investigations on the beleaguered site.

The data obtained from the instruments was used to complete a detailed report that was given to the company to analyse and aid their decision making regarding a final remedy.

'Because of the complex history to this site and the complaints we obviously needed to carry out more in-depth analysis, looking at further work and the frequencies of the noise involved. Said Toby.

'The Trojan2 was very easy to set up: plug in, calibrate and press play, you're not messing about with multiple settings but can then take it back to the office, manipulate and look at the frequency analysis later. It is very visual, and you can see the specific frequencies, putting them into 3D charts which was great'

'After some analysis we were able to identify one noise source - a large resin pellet vacuum conveyor system. The company determined that the system was getting to the end of its life and required renewal. There were also multiple vent ducts - more than 20 - and we identified these as another noise source,' he added.

'These were all fitted with brand new acoustic attenuators; the owners even did some vents which we didn't feel necessary, but the problem had been going on for so long they just wanted to put it to bed once and for all.'

Following the remedial work, which was completed by the end of 2016, there have been no further noise complaints from local residents.
This was a great result for all concerned, but you needed to gather and have that body of evidence to work with. It wouldn't have been possible without the Trojan2.' said Toby.

'It was a win/win for all concerned: the local residents, the site owners, ourselves and the local councillors who had been fielding the years of complaints. There was a real spirit of co-operation on this case which was very effective.'

The Solution

  1. As the Trojan2 and NoiseTooIs™ allowed post processing of .wav files 1:12 (FFT) along with octave band analysis - identification of problematic pure tones and their source was possible.
  2. Completed an appraisal to identify all sounds that could be heard in the vicinity: the appropriate measurement methods, identify where the potential measurement locations and the number of measurements/durations/timings.
  3. All measurements taken in accordance with BS7445-1:2003 - Description and measurement of environmental noise.
  4. Take appropriate measurements at source and receiver locations:
  5. Create a representative 5-minute high-quality audio recordings of sound measurements for FFT analysis. Audio recordings taken close to various factory noise sources and at receiver location.
  6. Measurements were taken at night and during day as factory production was a 24-hour operation.
  7. Measurements for multiple wind directions.
  8. Field calibration of the Sound Level Meters carried out before and after each measurement period.
  9. Analysis of sound level data and audio recordings through NoiseTools™ and Audacity software packages.
  10. Record of field measurements and conditions noted to be kept in hand written log book.

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