A Technical Look at BS 4142 Noise Assessments for Kitchen Extraction Systems
The sizzle of steaks and the clatter of pots might be the soundtrack of a busy kitchen, but unwanted noise from extraction systems can disrupt the peace for nearby residents and noise-sensitive receptors if not properly considered. Here's where BS 4142:2014, a British Standard, comes in. This document provides a framework for assessing the noise impact of commercial and industrial noise sources such as a proposed kitchen extract system. The guidance specifically provides a methodology for assessing noise impact on nearby noise-sensitive premises (dwellings, offices, etc.). This blog delves into the technical aspects of undertaking a BS 4142 noise assessment for kitchen extraction systems.
Do Commercial Kitchen Extraction Systems Make Noise?
The short answer to this is yes, commercial kitchen extraction systems can create a lot of noise and are considered to be one of the most frequent causes of noise complaints across the country. Due to this most councils and planning authorities have specific guidance and policies surrounding the control of noise and odour from such systems. An example of this type of guidance can be found on the City of Westminster website
How Do I Calculate the Noise from A Commercial Kitchen Extraction Fan?
The noise from any given system can be calculated before it is installed to ensure that the proposed new system will not adversely impact the amenities of any nearby residents. In order to do this the specific noise from the fan must be calculated and then assessed via a BS4142 assessment. The specific extraction system noise can be calculated from the manufacturer's sound power data which can usually be easily obtained from the system retailer. All calculations should be undertaken in each octave band frequency. Using the manufacturer's sound power levels in each octave band frequency corrections are then applied for the size of the ductwork, end refection, any bends that may occur in the ductwork between the fan and ductwork terminus and any noise attenuators that may be required on the system. An example of a kitchen extraction system calculation can be found in the image below however if you are not experienced with such calculations it is always better to contact an acoustic consultant to do this for you.
Once the specific noise level from the system has been calculated appropriate acoustic feature penalties can be applied in accordance with BS4142:2014 to establish a rating noise level and then a full BS4142 assessment can be undertaken to assess the potential for noise impact.
What is BS4142?
BS 4142 is a British standard which outlines a method for assessing commercial and industrial noise sources such as the noise produced by commercial kitchen extraction systems. The assessment compares the existing background noise level of any given area (LA90,T) to the predicted rating level (LAr,Tr) of the proposed extraction system. The difference between these values indicates the potential for noise impact. Here's a breakdown:
Background Noise Level (LA90,T): This represents the underlying noise in the area, typically measured over a period (T) and expressed in decibels (dB). The LA90 statistic refers to the sound level exceeded for 90% of the time.
Rating Level (LAr,Tr): This considers the specific characteristics of the proposed extraction system, including its sound power level and tonal content (presence of prominent frequencies). It's adjusted for the time period (T) and any penalties for tonality.
The BS4142 Assessment Process:
Site Visit and Information Gathering:
Identify noise-sensitive receptors (buildings with residential units or offices).
Gather details on the proposed extraction system (fan type, power output, location).
Background Noise Survey:
Measure the existing background noise level at representative locations near the receptors.
Consider different times of day (daytime, evening) to capture variations. For example, for a late-night take away the background noise level used in the assessment would be taken from the late-night period. For a daytime café, this may need to be taken from the daytime period.
Noise Prediction:
Acoustic modelling processes and calculations along with manufacturers' data are utilised to establish the specific sound pressure level from the extraction system at the receptors.
Factors like distance, reflections, and barriers all need to be accounted for.
Assessment and Recommendations:
The predicted rating level (LAr,Tr) is then compared with the background noise level (LA90,T).
BS 4142 offers guidance in relation to the potential noise impact based on the difference between background sound level and rating noise level:
Rating noise levels falling below the background sound level suggests low-impact
A difference of +5 dB or more suggests an adverse impact.
A difference of +10 dB or more indicates a potential significant adverse impact.
If the potential for adverse impact is predicted, mitigation measures can be provided to ensure any noise impact is minimised This can include:
Silencers to reduce sound pressure level.
Acoustic enclosures for the fan unit.
Adjusting operation times to avoid sensitive periods.
Additional Considerations:
Local Authority Requirements: While BS 4142 provides a framework, local authorities might have specific noise emission limits. It's crucial to consult them before finalizing the assessment.
Expertise is Key: Acoustic consultancies possess the necessary equipment, software, and expertise to conduct accurate measurements, undertake predictions, and create a comprehensive report compliant with BS 4142.
Conclusion:
By following a BS 4142 noise assessment methodology and implementing good technical design of the extraction system you can ensure your proposed kitchen extraction system operates within acceptable noise limits, minimizing disruption to the surrounding community whilst also avoiding potential planning application hurdles. For further information on BS4142 Assessment of Kitchen Extraction Systems or planning noise assessments in general contact us now.
References
Guidance - Method implementation document (MID) for BS 4142 - https://www.gov.uk/government/publications/method-implementation-document-mid-for-bs-4142/method-implementation-document-mid-for-bs-4142
ANC Guidance - https://www.association-of-noise-consultants.co.uk/wp-content/uploads/2020/07/ANC-BS-4142-Guide-March-2020.pdf