Understanding existing environmental conditions, especially noise levels, is a critical component of a pro-active approach to managing the impact of works. Commonly referred to as 'background levels', and 'rating background levels' or RBLs in NSW, they often guide the noise limits for works. Noise Management Levels (NMLs) are then set, based on the RBLs, usually +10dB in the daytime, and +5dB in the evening/night times.
The methodology widely accepted for calculating background levels is the '10th Percentile Method', as determined by the NSW Noise Policy for Industry: Noise Policy for Industry (2017).
The background level is typically assessed for standard daytime (7am to 6pm), evening (6pm to 10pm) and night time (10pm to 7am) periods, or for a very specific time period if an out of hours work permit is sought.
The calculation requires a minimum of 7 day/evening/night periods to provide a valid background level, and that is after weather affected periods have been removed. Weather affected periods include periods where the wind speed was over 5 m/s, and rainfall. The background level is then the median of the 10th percentile of the remaining day/evening/night LA90 results.
SiteHive now fully automates this calculation for you, removing weather affected periods (see how to select your nearest weather station here), and calculating the background levels from the remaining results.
You can now calculate background levels for each monitoring location/device, for all your sites, from the SiteHive Reporting section below the Noise graph (Note: this feature is in preview mode, if you're interested in giving it a go give us a buzz):
Clicking on 'Calculate Background Levels' will bring up a modal, which will allow you to select which time range and devices should go into your calculation. Pressing 'Calculate Background Levels' will then run the analysis and present your results:
We'll be further enhancing this feature in the coming weeks, allowing custom time periods to be analysed, showcasing the number of relevant periods that went into the calculation, and allow the weather thresholds to be changed. Let us know what you think!