In this 3 part article, Acoustic Consultant Teli Chinelis discusses environmental noise monitoring and the steps you should take when conducting one.
The third part concludes with what information is required, monitoring locations, meteorology’s effects, and how to conduct the survey. You can catch up on parts one and two here.
- Information required.
Whilst planning the survey the surveyor needs to understand the brief and engage with the instructing parties in order to prepare appropriate survey methods.
Depending on the purpose of the monitoring, various types of information are likely to be required:
– time histories of parameters such as background noise levels, maximum or average levels;
– differentiation of noise climate between day and night-time periods;
– number of exceedances of defined sound levels;
– frequency analysis of sound levels;
– specific analysis of individual noise ‘events’ such as train passings;
– levels within buildings (as well as external levels).
It should be noted that the type of analysis to be undertaken may dictate particular measurements/information: e.g. if using BS4142 (when assessing impacts from industrial premises) it is important to measure background sound levels with specific time samplings which are different for daytime and night-time periods, or if providing an assessment for compliance with Approved Document O, it is important to establish the number of individual maximum noise levels during the night-time.
- Monitoring locations
Ideally, monitoring locations should be at the position of the receptor (e.g. a dwelling) and since we spend most of our time indoors[1], the measurement location ought to be indoors as well. This is clearly not practicable or even desirable (due to the possible interference from internal sound sources).
However, after consideration for the necessary access requirements, security concerns and potential need for a power supply it is understandable to expect most monitoring locations to be located at the site boundary.
With appropriate planning, it may be possible to establish a measurement location near a receptor (e.g. by placing a sound level meter on a lamp post), however, there may be instances when such locations are not useful (e.g. locations where other nearby noise sources may prohibit measurements near the receptor locations).
In any case, since the monitoring locations are rarely 100% representative of the noise climate that is the subject of the assessment, various corrections will need to be applied to the measured sound pressure level readings and this will require great professional care in order to acquire the best representative readings and minimise any challenges from various stakeholders.
- Effects of Meteorology
When undertaking environmental noise monitoring the effects of meteorology must be considered.
It is common to avoid monitoring when:
- the wind speed exceeds 5 m/s;
- unusual temperature conditions are occurring;
- when there is significant precipitation (unless these are the normal conditions for the area).
Care should be taken to ensure that the equipment is capable of operating satisfactorily under the prevailing conditions. The calibration of the equipment should not be compromised under cold or wet conditions.
However, if non-ideal weather conditions cannot be avoided, such periods of poor conditions should be indicated in the data records, and any relevant account taken of their effects in describing the noise climate under review. Detailed weather records are great, but it may not be practicable to set up logging weather stations alongside the sound level meters. Due to the effects of buildings and other structures, wind effects at the microphones may not be readily quantified and sometimes it may be better to make estimates of the likely effects of weather conditions instead of trying to capture accurate weather data. Online resources for monitoring weather information are readily available to assist, however, it should be noted that different conditions may apply to the site compared to the location of the weather station.
If the receptors are located at long distances, it will be crucial to also consider atmospheric effects (e.g. temperature gradient, air absorption) as well as weather effects.
- Conducting the Survey
The survey ought to be conducted in a competent matter and some pertinent points to consider include:
- ensure arrival on-site at the specific time;
- ensure all relevant paperwork is in order;
- ensure adherence to all relevant health and safety requirements;
- review the variables used to derive pre-selected monitoring locations and if new evidence is found, re-select (if possible whilst on site) a new monitoring location;
- understand the location orientation of nearby receptors and assess their significance status;
- leave a good impression on home or business owners if setting up equipment at their premises.
- Competence
As discussed above, noise monitoring is a complex endeavour. As such, if your project requires noise monitoring you need to ensure that this is undertaken only by qualified and experienced practitioners. In the UK, normally these will be qualified acousticians who are corporate members of the Institute of Acoustics. They should be experienced in the measurement and prediction of noise and have a good understanding of the issues involved in the assessment of noise. In addition, if the company undertaking the monitoring is a member of the Association of Noise Consultants then this should provide additional confidence in the competency of the assessors due to the rigorous selection process for member companies.
If you want to discuss anything you have read here please email [email protected].
[1] According to a study (see https://www.ribblecycles.co.uk/ The Not-So Great Outdoors? | Ribble Cycles) Britons spend around 92% of their time indoors.
