How to Reduce Workplace Noise Levels

The first step in reducing workplace noise levels is to carry out a noise survey to determine which machines require noise reduction measures. Usually the aim is to reduce workplace noise below the 85 dBA legal limit set by the Control of Noise at Work regulations. So, the aim of the noise survey is usually to identify which machines generate noise of 85 dBA or more.

The second step is to carry out diagnostic noise tests to identify the main noise sources within each type of machine that requires noise reduction. If this is not done, you are limited to only a few noise reduction options. Identifying the main noise sources opens up additional noise reduction options, most of which cost considerably less than the limited options available otherwise.

Vibratory Bowl Feeders

 

If you don't know what the main noise sources are, your only option is to fit an acoustic enclosure over the whole machine, But if, for example, diagnostic tests show that most of the noise emanates from the exhaust of an extract fan that is fitted to the machine, then the solution could be as simple as fitting a small silencer to the fan exhaust. This would cost considerably less than encasing the whole machine inside an acoustic enclosure. And it avoids the access restrictions of an acoustic enclosure, which can make it difficult for the worker to operate and maintain the machine. Details of low cost noise solutions that don't restrict machine access can be found on best way to reduce noise at work.

Some companies guess which are the main noise sources then install noise reduction measures based on these guesses. This usually results in little or no noise reduction. The reason is that the chances of guessing correctly are usually very low. Companies often spend considerable time and money implementing noise reduction measures based on guesses - all of which is wasted when the treatment provides little or no noise reduction.

How do you diagnose which are the main noise sources? It can be difficult especially when there is a complex machine or a production line with many noise sources. However, there are many machines for which common sense or some simple basic diagnostic methods can easily identify the main noise source(s). We will provide more details on how to diagnose noise sources on this website in due course.

 

6 Ways to Reduce Machine Noise in the Workplace

There are 6 ways to reduce noise from industrial machines in a workplace. The following guide explains the options and provides information about each to help you to choose between them:-

 

1) Reduce Machine Noise at Source

Reducing the machine noise at source is usually the best option in terms of noise reduction and especially cost. It means identifying the main noise sources within a machine or production line, then suppressing them at source.

Sometimes the best noise solution is to fit standard items that can be bought off the shelf, like a silencer for example. Sometimes, the solution needs to be purpose-designed specifically for the application - for example by designing something to reduce the noise by smoothing out the airflow or by cushioning impacts, etc.

See industrial noise control at work for more details of this option.

To see examples which illustrate this noise control at source type of solution,
click machine noise reduction examples.

 

Care is needed in selecting off-the-shelf items like silencers. Many companies fit any standard silencer. But the noise reduction performance of different silencers can vary enormously. So it's important to select the optimum type and size of silencer, otherwise there may be insufficient noise reduction.

The installation cost of this reduce noise at source option can be as low as a few hundred, or sometimes even tens, of pounds. The amount of noise reduction varies enormously, especially as normal practice is to select the solution depending on the noise reduction needed. So, reducing the noise at source can provide around 5 - 8 dBA sound reduction on some machines, or 10 - 15 dBA on other machines, and sometimes as high as 20 - 25 dBA.

 

2) Fit an Acoustic Enclosure around Noisy Machine

Another way to reduce machine noise in an industrial workplace is to fit an acoustic enclosure around each noisy machine. This can provide a high noise reduction, of in the region of 30 dBA, if the acoustic enclosure is well designed and well fitted. However, the noise reduction actually achieved is nearly always considerably less than 30 dBA. One reason is contributions of noise from machines and other equipment that are outside the enclosure. The high cost of acoustic enclosures means that only the noisiest machines are enclosed and lower noise machines and equipment elsewhere in the factory are left outside the enclosure.

For example, if an industrial machine produces 90 dBA and it is encased in an acoustic enclosure that provides 30 dBA noise reduction, the machine noise transmitted outside the enclosure would be 60 dBA. However, it there are other production machines or equipment nearby that produce a noise level of 85 dBA at the outside of the acoustic enclosure, then the total noise just outside the enclosure is 85 dBA (85 dBA plus 60 dBA = 85 dBA). So the acoustic enclosure has reduced the noise by only 5 dBA and the operator of the noisy machine who is located just outside the enclosure only benefits from a 5 dBA sound reduction.

 

The full potential (about 30 dBA) noise reduction of an acoustic enclosure is only achieved if all the machines are enclosed and / or any machines or equipment outside the acoustic enclosure are very quiet - at least 40 dBA quieter than the unenclosed machines. In industrial factories, it is very rare for this to happen. In practice, acoustic enclosures typically achieve noise reductions of about 5 - 10 dBA in common industrial situations. Sometimes acoustic enclosures might provide as much as 15 - 20 dBA noise reduction in a factory if the enclosed machines are very noisy and the background noise outside the enclosures is relatively low.

Workers often have to enter acoustic enclosures to resolve blockages or carry out checks. Where this happens it is very common for workers to leave the enclosure doors or access panels open. Even a small opening allows a lot of noise to escape from an acoustic enclosure. This can result in the acoustic enclosure providing little, or no, noise reduction.

 

Acoustic enclosures are expensive. For example a small enclosure around a vibrating trough and vibratory bowl feeder could cost in the region of £5000 to £6000. An acoustic enclosure around a large industrial press could cost in the region of £10,000 to £12,000. So if there are 20 presses in the factory, the total cost would be about £200,000 to £240,000.

Example: a food manufacturer received a quote for £55,000 per production line for an acoustic enclosure. Each production line included a filler machine, multi-head weigher, laser coder, cartoning machine and shrink wrap machine. All of these would have been inside the acoustic enclosure.

 

3) Fit an Acoustic Hood or Cover over the Noisy Parts of the Machine

An acoustic hood or cover over the noisy parts of a machine is, in effect, a partial acoustic enclosure. So the same comments apply as for acoustic enclosures. The amount of noise reduction depends on how noisy the covered part of the machine is compared with the rest of the machine that is not covered. As a rough guide, an acoustic hood / cover could provide a noise reduction in the region of 3 - 6 dBA in a typical industrial situation.

It is common for workers to leave acoustic covers and hoods open, in which case no noise reduction is achieved.

As a rough guide, the cost of an acoustic hood could be as low as £1,000 for a small hood or £3,000 - £5,000 per machine for larger, more complex hoods.

 

4) Install a Sound Booth for Workers

A sound booth is a quiet room for workers. It means enclosing the workers instead of the machines and can be beneficial where workers do not need to attend the machines often and can work remotely. Commonly, computers are installed in sound booths for workers to monitor the production line machines. Workers then spend most of their time inside the sound booth, only leaving when there is a problem to resolve on the machine / production line, or when taking samples, etc.

A sound booth can reduce the noise by 30 dBA or more, so can be beneficial where it is practicable for workers to spend most of their time inside. Of course, as soon as workers leave the sound booth, they are exposed to high noise levels. The reduction in workers' daily noise exposure depends on how long they spend outside the booth during each shift.

 

For example, if a worker spends a total of 1 hour outside the quiet booth and the remaining 7 hours of the shift inside, the booth would reduce the worker's daily noise exposure by 9 dBA. 2 hours outside the quiet booth (and 6 hours inside) would reduce the daily exposure by 6 dBA. If half the shift is spent inside the quiet booth and half outside, the booth would reduce the daily noise exposure by only 3 dBA. So obviously a quiet booth is only worth considering if workers spend most of their time inside it.

The cost depends on size of the sound booth but might be in the region of £10,000 for a reasonable sized booth and much higher for a large booth.

 

5) Install a Noise Barrier

Noise barriers are not very effective inside factories because sound is reflected off the ceiling then down towards the ground on the opposite side of the barrier. Barriers are more effective outside buildings. Inside a factory their effectiveness depends on the machine layout, ceiling height and location of the noise barrier.

For example, if there are noisy machines at one end of the factory and quiet operations at the other end, a noise barrier could reduce the noise by about 5 - 7 dBA. This noise reduction applies on the quiet side of the sound barrier. On the noisy, machine side, there would be no noise reduction. In fact, the noise can increase on this side unless the barrier incorporates suitable sound absorbent material. This is because the noise reflected from the barrier adds to the noise transmitted from the machine, increasing the total noise level. So a noise barrier would not reduce noise close to machines, which is where workers are normally located. This means a noise barrier would not normally reduce workers' noise exposures.

 

6) Fit Acoustic Absorbent to the Factory Ceiling and / or Walls

Installing acoustic absorbent panels on the ceiling or walls of the factory is very expensive. A typical cost is about £40 to £50 per square metre area covered. So to treat a factory ceiling of 2000 square metres area, the typical cost could be in the region of £80,000 to £100,000.

 

Also, this type of treatment only becomes effective well away from noisy machines. Close to noisy machines, it typically provides 0 - 1 dBA noise reduction. The noise reduction increases with distance from noisy machines and about 5 - 6 dBA reduction can be achieved at around 10 metres or so from noisy machines. The noise reduction can vary considerably depending on the layout of machines and how low the ceiling is. The lower the ceiling the higher the reflected noise, so the larger the potential noise reduction when fitting acoustic absorbent to the ceiling.

Because it only becomes effective well away from noisy machines, this treatment often provides little or no noise reduction for operators who work close to machines. So there are very few situations where it is worth implementing this type of treatment - because operators usually work close to machines. Reducing the noise at source suppresses noise levels close to machines as well as at a distance away, so is usually a better option for reducing noise at work.

 

Guide: How to Choose Between the 6 ways to Reduce Machine Noise at Work

The lowest cost option for reducing noise at work is usually to reduce the noise at source. This reduces the noise close to machines, where operators normally work, as well as further away. This option usually provides a medium to high noise reduction at low cost. For more details of the benefits of reducing the noise at source, click on suppress noise at work.

 

If noise levels are very high - for example 110 dBA or more - an acoustic enclosure may well be the only way to achieve sufficient noise reduction. This assumes the operator can manage with restricted access to the machine (for example if access is only needed occasionally) and does not leave enclosure panels open for ease of access. If there is only one machine, the cost may be affordable but if there are many machines, the cost can be extremely high.

Fitting an acoustic hood may be an option if one part of the machine is particularly noisy, but this may not be practicable if the operator needs frequent access to the noisy part of the machine. If the need for frequent access means the acoustic hood is likely to be left open, there is no point fitting one.

Example of reducing vibrating feeder noise at biscuit factory

 

Noise Solution for Shredder

Enclosing the workers in a quiet sound booth is only worth considering if they can work remotely from machines and do not need to go close to the machines frequently. In most cases, operators work close to machines, for example to feed materials in and take product out the machine, so this option is not feasible.

The other options of a noise barrier and fitting acoustic absorbent to the factory ceiling or walls have only limited application because they do not reduce noise close to machines where operators usually work and only reduce noise some distance away (where no-one might work!). The exception is where there is a low ceiling and workers are not close to the noisiest part of a machine most of the time. In a case like this, fitting acoustic absorbent to the ceiling can provide a substantial reduction in workers' noise, but the cost can be high.

 

How we can help you solve a noise problem

It can be very difficult to find the best noise reduction solution to reduce noise at work. This is particularly true for the option of reducing the noise at source. This is because the diagnostic noise tests to identify the main noise sources can be difficult, especially in complex situations where the main noise source is not obvious. Also, the solution is often not obvious, and there are many different solutions that are not well known and which most companies are unaware of. For the option of reducing the noise at source, there are often several different solutions available. So in order to find the best solution, all these need to be assessed in terms of their noise reduction, cost and ease of installation.

The first stage in our noise reduction projects is to go to the customer's site and carry out detailed diagnostic noise tests on the noisy machines to identify the main noise sources. We then use this information to assess all the noise reduction options so we can determine the best option in terms of noise reduction and cost. We then recommend the option that we consider best for the customer's situation. For details of how we can help you reduce workplace noise levels, ring us on the number below or click help to reduce noise at work.

Dust Extractor Fan Noise Control

 

Important Note on Costs and Noise Reduction

Note: the above costings for the various options to reduce noise at work are very approximate and are only intended to give a rough guide. Costs can vary considerably due to the complexity and size of the machine and noise product. Also, where installed by local contractors, installation costs can vary considerably in different parts of the UK.

Similarly the noise reduction figures given above are only estimates and intended as a rough guide. The noise reduction can vary considerably with different machines, manufacturing processes and products.

Helping to reduce workplace noise levels