Tackling sound issues when the heat rises
The long-running, scorching hot summer of 2018 provided a new range of considerations for health and safety professionals looking to protect their workforce.Aside from the usual concerns of dehydration, skin protection for workers outdoors and general lethargy, the issue of noise control also came to the fore.
In this article, expert acousticians from the Association of Noise Consultants (ANC), led by author David Garritt, set out some of the main issues that should be considered at this time of year to ensure good acoustic performance is achieved when the temperature rises.
The need for good acoustics
Environmental noise can have negative impacts on the health and wellbeing and is a well-recognised public health risk.The World Health Organization in their latest Environmental Noise Guidance states that exposure to noise presents the second largest health risk to the population of Western Europe, second only to poor air quality.
Impacts on health and wellbeing include cardiovascular disease, annoyance and distractions in activities such as reading and conversation. The workplace is one area where unwanted noise can have a considerable impact – and the warm weather can significantly amplify the issue.his is therefore a very important matter, as good acoustics are a vital element of the workplace environment, yet it is a subject which is often overlooked.
Working in hot conditions
Within the workplace, the most obvious change in noise levels during heat-spells affects people working indoors – typically in offices – as they open their windows during hot weather.
The sound insulation of a closed window is generally around 25-30dBA but this drops to only 10-15 dBA when opened. As offices are by their nature often in town or city centres, they are often subject to significant road traffic sound.While it may be expected that sound levels will increase with the opening of windows and a moderate increase may be tolerated, the resulting indoor sound climate may not be acceptable.Furthermore, simply opening the windows on a hot, calm day may not be enough to achieve the indoor conditions/temperature desired. A large open plan office with many people in may still have issues of temperature control and feeling ‘stuffy’ because of too little air circulation even with windows open.Workers often then reach for the desk fans, which create some air circulation and can feel a little cooler, however, the fans are usually noisy.As a result, the combination of feeling too hot, then having elevated sound levels from outside through open windows, plus the extra sources of many desk fans can lead to a rather unpleasant and inefficient working environment.
In industrial environments, and commercial ones too depending on the nature of the work carried out within, for example, night clubs and other music venues, there is also the potential for noise inside the building to escape and impact on nearby dwellings or other noise sensitive buildings when windows or doors are opened for ventilation.
One solution to control the heat whilst avoiding these issues of excessive noise inside and outside the building is to have an effective air conditioning/ventilation system.This does of course create its own noise issues though, so attention needs to be paid in this area.
The issue of noise, ventilation and overheating is a pressing one, particularly in light of the changing climate patterns and drive towards more energy efficient buildings.The upshot is that maintaining a comfortable acoustic and thermal environment in the workplace during the summer months can be helped with an appropriate ventilation strategy, but it is often not as simple as “sticking an air conditioning unit on the side of the building”.
To ensure good acoustic performance is achieved in harmony with an effective cooling method, it is important to consider the acoustic design of a mechanical ventilation system in a few key areas including the following.
Sound level created in the room via ventilation terminations
Sometimes referred to as ‘job side’ or ‘room side’, – sound level design targets/ requirements must be specified either as overall dBA values or expressed as Noise Rating (NR) values that are frequency (or musical pitch) dependent. Some clients have their own requirements for this when commissioning a new building.
Noise and vibration from ventilation plant items
This can be plant noise which affects other noise sensitive premises or the development they are serving, either because the units are mounted outside or have external inlet and/or outlet terminations (sometimes referred to as ‘atmosphere side’). It can also be sound received in the offices either via outdoor plant sound getting inside through windows etc, or it can be noise and vibration transmitted through the building structure if plant is mounted indoors.
Sound can travel through ducted ventilation systems which connect rooms, effectively bypassing the sound insultation of the wall or floor separating them. Good acoustic design can provide mitigation against crosstalk.
The right specification
As discussed, a properly designed ventilation strategy can help to mitigate noise problems associated with trying to maintain thermal comfort in warm weather.Key to a successful outcome in terms of noise is that acoustic design is considered right at the start and included within the specification.Some ventilation engineers and attenuator suppliers will do the acoustic design as part of their remit – but they will need an appropriate acoustic performance specification to adhere to, both for indoor sound levels and outdoor noise impact and this would normally be provided by an acoustic consultant.
Not all ventilation suppliers do the actual acoustic design though, and sometimes acousticians are asked to undertake this, especially for ventilation systems which serve highly noise sensitive spaces, such as auditoria.
It can be a complex area.
There is some general information in BS 8233: 2014, but detailed ventilation design is beyond the scope of that standard.The other aspect is that new fixed plant, especially outdoor mounted, may require planning permission, or evidence that the proposed units will meet any current planning conditions.Again, this is likely to need the skills of an acoustic consultant. The most common standard for rating sound from fixed plant affecting nearby noise sensitive premises is BS 4142: 2014.
The issues which influence the sound from a ventilation system are wide ranging and all need to be considered adequately, for example:
Vortex noise caused by turbulent airflow across fan blades
Rotational noise caused by the interaction between fan impeller and the surrounding air
All the sound sources in fan motors, bearings and gears
Noise generated within the ductwork itself, where turbulence can generate significant noise, especially where turbulent air hits objects such as dampers and grilles
The sound level received in the room is also affected by every aspect of the system including duct lagging, changes in direction of ducts, branches, changes in duct cross section area, any attenuators in the system, the terminations as well as the acoustic properties of the room being ventilated.
Coping with hearing protection in the heat
Another important consideration in warm conditions is the protection of workers who are already exposed to noise regardless of the weather conditions. The Noise at Work Regulations require companies to reduce the noise levels that employees are exposed to as much as practicable, but it is not possible to provide everyone with a suitably quiet working environment. This not only applies to factories and workshops, but is also inevitable in spaces which are designed to have high noise levels, such as night clubs.
For those members of staff whose job demands hearing protection as a permanent fixture, the situation can present unwelcome discomfort and distraction as temperatures soar.
One of the main complaints heard from workers during Noise Awareness Training in the workplace is that they find ear protection uncomfortable at the best of times. Add perspiration to the mix and people can find them even more of an irritation.Personal comfort is really the main problem with the actual use of hearing protection in the heat, and this can bemitigated to some extent by individuals finding the type of protection they find most comfortable.
It is highly recommended to try as many different sorts of protection as possible to reach the most satisfactory outcome, because our ears are all different and there are a number of options available.Most of the disposable ear protection plugs ones are cheap and so can be tried at will. The ‘in ear’ foam/sponge tyre plugs come in a few shapes, and there are also the ‘in ear’ plugs on string, which look like little Christmas trees.Another type of protection are ear caps on a hard, blue plastic band – and there are even ones moulded to an individual’s ear. Interestingly, some types of ear protection even incorporate active noise control.
Finally, there are also the big over ear defenders. These are my personal “The human ear is an incredible device that can detect an enormous range of sounds. To cope with this range, sound levels are measured using a logarithmic scale – the decibel.
It is actually the Bel scale that is truly logarithmic and was used at first for sound, with the human range being between 0-13 Bels. This is not very descriptive and so each Bel was divided into ten, hence the deci – Bel with a small d and capital B with a typical range of 0-130 dB.This means that a change in sound level of 3 dB is equivalent to a doubling or halving of sound energy. A change of 10 dB represents a change in sound energy by a factor of 10. So for example, 90 dB has twice the sound energy of 87 dB, and 80 dB has just one tenth of the sound energy of 90 dB.
To add further complexity, the human ear has a very unique set of gain controls so that we hear changes in sound level differently to the physical change in energy.
For most people, a change of 3 dBA is significantly noticeable if the two sounds are played consecutively, but it does not sound like the doubling or halving in sound energy that a 3 dBA change actually represents. A change of 10 dBA is often experienced as a doubling or halving of perceived loudness or volume, whereas it is in fact a change in sound energy by ten times or one tenth. The letter ‘A’ that appears after the ‘dB’ in a lot of literature, standards and articles refers to an ‘A’ weighting scale that is applied to measured sound levels to take account of the way our ears respond to frequency, or musical pitch.
Our ears are not as sensitive to low frequency (bass) sound as they are to higher frequency sound, and this A weighting scale seeks to provide a numerical correction for this to enable accurate comparison of sound levels that we may hear in the environment.”method of choice and the ones I prefer to use, but I only need them for relatively short periods and in hot weather they really can make you feel hot and uncomfortable.
This list of types of ear protection is by no means exhaustive and clearly there are a number of options to try.Regardless of the type of hearing protection chosen, it is absolutely vital to bear in mind that the discomfort which might be encountered through wearing hearing protection in the heat still remains a better proposition than sustaining hearing damage.