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Focus: exposure to noise in schools
Excessive noise levels in schools represents a genuine problem which affects pupils, teachers and other people working there. Various measurements have been taken which have highlighted acceptable levels in classrooms, but excessive levels in sport halls, refectories and other multi-purpose rooms. Solutions are available and offer genuine improvement if they are implemented correctly. In the case of new buildings, taking acoustics into account right from the start of the project can avoid potential extra costs at a later stage.
A public health issue
Besides their effects on pupils' hearing, noise can cause tiredness, stress, behavioural issues (aggression, hyperactivity), a reduction in concentration and an impaired capacity to carry out cognitive tasks (learning, complex tasks, problem solving). In addition to the noise encountered in school, some children and adolescents are subject to an intensive use of portable music players and/or music use or practice (concerts, parties, instruments, etc.) at noise levels which are often excessive, leading to an overexposure to noise. The danger of the exposure to the noise depends on the noise level and the duration of the exposure. By regularly exceeding tolerable doses of noise, pupils progressively wear out their hearing.
With regards to teachers and other people working in schools, apart from causing stress and tiredness, excessive noise obliges them to raise their voices in order to be heard. If this becomes habitual, there is a risk of often irreversible damage to the voice.
The reduction of noise pollution in schools is therefore a priority, for which the stakes involved are enabling more fruitful exchanges, better concentration, an improvement in listening quality and above all, the preservation of everyone's health.
This issue is all the more important given that the Brussels-Capital Region will be confronted with considerable demographic expansion in the years to come. The most recent forecasts anticipate growth of between 1 and 1.5% per year, or an increase of 170,000 inhabitants by 2020 (BISA, May 2010). In view of the steady increase of the Brussels population, the Brussels Institute for Statistical Analysis (BISA) predicts an increase of 42,500 school pupils between 2010 and 2020 (BISA, June 2010).
Brussels will therefore be confronted by growing demand for school places. Whether this will be receiving pupils in existing schools, or building new schools, it is crucial to make sure schools are well thought through from an acoustics perspective, to ensure that students have an acoustic environment which is conducive to learning.
Noise levels recorded in schools
Source: Brussels Environment, Noise data department, 2012
Notes: 1. A relaxation room, 2. Whispering voice, 3. A library, 4. A speaker, 5. A classroom, 6. A refectory, 7. A sports hall, 8. Shouting voice and 9. The pain threshold
Objective: assess exposure to noise in schools
In recent years, Brussels Environment has conducted fifteen noise measuring campaigns in schools. Different types of measurements were taken in various locations (classrooms, refectories, school yards, sports halls or other multi-purpose halls) in order to take stock of the noise situation at schools in the Brussels-Capital Region. The reverberation time and the ambient noise were measured in almost every case.
Reverberation times: satisfactory in classrooms but unsatisfactory in other types of location
The reverberation time is the time (expressed in seconds) required for the noise level to decay 60 dB from its initial level after the source of the noise has stopped. It characterises the acoustic comfort of a location: the longer the reverberation time, the more an echo phenomenon is observed, and the greater the impression that the location is "loud". The reverberation time depends on the volume of the hall as well as the absorption properties of the materials used in the location. The Belgian standard NBN S01-400-2 :2012 defines the acoustic criteria for school buildings which will be constructed, or for parts of school buildings in need of renovation for which planning permission is required. The requirements are defined according to the type of room. The reverberation times measured in classrooms are generally good since they are lower than the recommendations given by the standard. On the other hand, this is not the case in nursery classes. However, this last observation can be qualified by the fact that for nursery classes, the standard recommends a reverberation time which does not depend on the volume of the location (less than or equal to 0.6s) whereas for other types of classrooms, the reverberation time does depend on the volume of the location (around 0.8s for the classes studied). In fact the measurements give comparable results whether they are taken in nursery classes or other classes. Unlike the good results achieved in classrooms, the reverberation times measured are almost systematically higher than the recommended values in school yards, refectories and multi-purpose halls. This observation is not surprising, given that these locations generally have a large volume with little in the way of absorbing material.
Ambient noise: acceptable in classrooms but excessive in other locations
There are no reference values for ambient noise in schools. It is generally considered (see the chart above) that the noise level of a conversation in an assembly is around 60 to 65 dB(A) and for an address to be clearly heard, the elocution level of the speaker must at least exceed the background noise level by 10 dB(A). On the basis of these observations, the level of background noise in a classroom should ideally remain below 50 dB(A) in order for the teacher to talk without raising his or her voice.
It is also considered that in order to ensure effective understanding of the teacher and keep the attention of pupils, the ambient noise (all sources of noise combined: pupils, teachers, external noises, etc.) in a classroom should ideally remain below 65 dB(A) during lesson times. Likewise, the ambient noise in a refectory should remain below 75 dB(A), during mealtimes, so that pupils can have conversations without raising their voices excessively.
The chart below shows pupils' exposure to noise during a typical day at school. These are average levels, calculated using the measurements taken in several Brussels primary schools.
Measurements of noise levels to which pupils are subjected during the day in primary school
Source: Brussels Environment, Noise Department, levels calculated using the measurements taken by Brussels Environment in 6 primary schools in 2011
Remarks: break time took place in a closed school yard, a setting conducive to high levels of noise.
The red line represents the equivalent level (= "average" noise level) for each period.
Although the ambient noise levels recorded in classrooms remained below or equivalent to the optimum values calculated by Brussels Environment above, the levels of ambient noise are particularly high in the refectories and closed yards of the schools.
Solutions are available, both for renovations and new constructions.
In two schools, measurements were taken before and after the works which were intended to improve the acoustics in a refectory on the one hand, and in a sports hall on the other. These comparative studies have shown that when a prior acoustic study is carried out and the work is undertaken with care, the implementation of solutions makes it possible to achieve very clear improvements. In both cases, shown below, the reverberation times measured after the work were in compliance with the standard.
Reverberation time measurements before and after the fitting of absorbing panels
Source: Brussels Environment, Noise Department
In order to improve the noise situation, it is not always necessary to undertake costly works. Other solutions exist such as space planning, the organisation of several services so as to reduce the number of pupils present in a refectory, adjustments to the furnishings (rubber pads underneath chairs, the layout of tables, tablecloths to absorb the impact of crockery, etc.), choosing equipment which is not very loud and the maintenance of this equipment, or even awareness-raising among the occupants, pupils and teachers.
In the case of new buildings, particular attention should be given to the acoustics in the location, right from the initial phases. In order to ensure an optimum result, the acoustic comfort performance, with regard both to internal and external noises, should be included in the building specifications. And to the extent possible, new schools should be built in calm environments.
The solutions should be adapted on a case by case basis, given that the objectives to be achieved for a renovation are not the same as those for new constructions, and that in any case they depend on the type of education (technical workshops, nursery classes, etc.), as well as on the budget, location and the environment. It is important to reiterate however the preventive consideration of the acoustics issue would result in additional costs of less than 5%. However, when interventions are necessary to correct poorly designed situations, this generally entails additional costs of between 15 to 30% of the budget allocated for the work carried out.
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