Industrial Noise & Vibration Centre

+44 1753 698 800

Technical Notes

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  • chiller fan
  • compressor

Chiller noise control

Chiller unit noise control

Sound file: typical chiller low-frequency noise reduction,

The noise from chillers, air conditioning plant, condensing units, HVAC, heat exchangers, dry coolers etc provides a host of opportunities to waste resources on inappropriate noise control measures that either don't work or that reduce efficiency - or both. In our experience, a substantial proportion of the noise reduction measures used on these units (acoustic enclosures, silencers and barriers) are simply ineffective as they address the wrong problem.

There are only 3 types of noise generated by these systems: broadband air noise, compressor tones and low-frequency fan hum. The hum, for example, cannot be addressed using silencers and barriers, and yet these are often mistakenly fitted at great capital and running cost (reduced efficiency).

10 minutes with a smartphone is all it takes to avoid costly mistakes by determining which sources require treatment and what is the best noise control option for the particular problem. Anyone can do this.

This approach not only dramatically reduces typical noise reduction project costs, but it can even substantially improve system efficiency (by 23% on one data centre application). Find out how best to reduce the noise from chiller, condensing, cooler and related units here >

  • cooling tower

Cooling tower noise attenuation

Cooling tower noise reduction - gearbox

The key to effective cooling tower noise reduction is accurate diagnosis. Far too often, noise control measures are selected without a clear understanding of -

  • the type of noise problem: is it simply the overall dB(A) level or is there tonal character such as a low-frequency hum?
  • the source of the noise: fan (broadband or tonal); falling water; pumps (often tonal) and/or gearbox noise (tonal)

As a result, far too many noise control projects end in costly failure or go through a number of iterations before the problem is solved. Accurate diagnosis is not rocket science. Forward a few photographs and a smartphone video clip to us by email and we can provide a precise and accurate remote noise control diagnosis plus the optimum costed noise control options within an hour. At no cost.

There is also new low-cost aerodynamic technology that cuts the noise from cooling tower fans whilst often improving efficiency (unlike silencers and barriers that reduce efficiency).

Find out details of the best options to control the noise from cooling towers here >

Our technology is saving megawatts per day

environmental noise control

Across the world, organisations using our aerodynamic fan noise control technology are currently saving megawatts of power as a result of the efficiency gains they have realised, compared with both conventional noise reduction technologies and in some cases, compared with unmodified fans.

Coupled with our remote control of noise services that do not require site visits in order to diagnose and implement best practice in noise control (avoiding flight and other transport carbon costs), a key objective is to use our innovative technologies to help clients to reduce their carbon footprints and thereby to render INVC a carbon-negative consultancy.

  • noise control
  • noise analysis
  • environmental noise
  • EHO
  • environment agency
  • environmental vibration
  • remote control

EHO and EA - faster, simpler problem solving

noise in the environment

We provide extensive specialist technical support, information and training on noise and vibration to both regulators (Local Authorities and Environment Agencies) and to industry. As we regularly deal with the same noise and vibration problems encountered, we have probably solved your problem already.

Our acclaimed range of EHO / EA specific noise workshops can help transfer time saving best practice techniques and technology in-house. This approach typically reduces the time to resolve noise complaint and other problems from months or years down to weeks - or even as little as days in some cases... This dramatically reduces the resources spent (freeing them up for other work) and also the time that local residents spend suffering unnecessary stress from unacceptable environmental noise.

We provide a worldwide service via the internet and smartphone technology. Make use of our Remote Control of noise service for a free 2nd opinion and evaluation of best practice - or contact us for advice.

Best Practicable Means / Best Available Technology evaluation service

Complaints or noise nuisance: how do you determine what constitutes “best practicable means” to mitigate. Companies employ consultants to generate reports claiming the cost of mitigation is too high to be practicable. In most cases, the suggested noise reduction technology is not best practice. Our definitions of low-cost BPM are game changers for regulators as problems can usually be resolved within weeks, saving time, resources and money.

We are quite happy to provide definitive definitions of what constitutes BPM/BAT with complete technical justifications, in court if necessary.

Noise and vibration training workshops

We provide very effective training for EHOs and Environment Agencies, from workshops to full CIEH environmental noise competency (some councils have profited from hosting in-house versions by inviting other authorities). These include:-

  • BPM / BAT noise workshop
  • Fan noise control masterclass
  • Venue noise assessment workshop
  • Noise recording and analysis workshop

The Delegate View: “one of the most relevant and informative courses in a long time..” .. “I’d hate to come up against you in court! .. the best value seminar we’ve ever been on” – “standard of presentation was excellent .. humorous and entertaining .. highly recommended”

Digital Noise Assessment (DNA) – automate noise reporting

ppe sign ticked

The Digital Noise Assessment (DNA) provides benchmark report templates covering all the requirements of the noise regulations – including the plan of action. Used either in-house or by consultants as standard format for all updates, it makes noise data easily accessible so that you can find and use the information fast. It features:-

  • DNA report “best practice” template: cut-and-paste from the customisable template Word document
  • Action Plan summary: editable managers’ action plan summary to track implementation of risk management
  • Technical Notes: up-to-date technical notes on regulations, PPE, dose calculations, health surveillance, Buy Quiet, noise control, training
  • Example Report: completed pdf report example including factory plan noise levels
  • Noise Control Audit: if you don’t have the technical background for this mandatory regulatory requirement to make a cost / benefit analysis of the noise control options, we can provide this as an add-on service. Contact us to discuss.

Separating HAVS fact from fiction and mis-information

The depressing evidence is that many HAV assessments are seriously flawed and that industry is storing up future problems despite the best of intentions. There is a minefield of opportunities for vibration risk management mistakes based on mis-information and myth. The most common areas for errors are:-

HAV mis-measurement – monitors measuring vibration to no standards whatsoever…

Misunderstanding HAV measurement and monitoring marketing material can put hands and safety policies at risk. Caveat emptor. Some claims made by some suppliers of the latest “HAV monitors”, “HAV dosimeters”, “vibration monitoring gloves” etc are disingenuous, misleading end-users as to the limitations inherent in these vibration monitors. None of these alternative HAV measurement techniques provide values that can be used for a reliable assessment of the vibration exposure of operators as required by BS EN ISO 5349-1 2001. Read the full details of why hand-arm vibration dosimeters, hand, glove or wrist-mounted transducer vibration measurement systems do not provide vibration values to the standard.

Manufacturers’ Hand-Arm Vibration Data – it’s data, but not necessarily assessment data

HAV traffic light

Manufacturers’ updated declared values (to BS EN ISO 8662; EN 60745; EN ISO 20643 - which they have to provide under the Supply of Machinery (Safety) Regulations 2008) are often used as the basis for "traffic light" risk ranking by hire companies. However, whilst useful as an initial estimate, you cannot use these figures for accurate risk assessment unless you can show that they are representative of your real-use tool vibration. Be particularly careful where the operator dose may be close to action or limit values as there can be serious consequences. Quoting the HSE guidance – “…you will still need to check with the manufacturer that the vibration emission declared in the equipment’s handbook is representative of your normal use of the equipment.” Consider the commercial pressure on suppliers not to go out of their way to publicise the higher vibration values often associated with real field use.

HAVBase can be used to aid optimum tool selection as part of a "Buy/Hire Smooth" policy to minimise HAVS risk.

Hand-Arm Vibration Measurement Accuracy – don’t measure unless you have to…

Accurate HAV measurement is time-consuming and expensive – and often unnecessary. In fact, you may never need to measure vibration again by heeding the HSE guidance that recommends using accurate published field vibration data wherever possible (e.g. HAV-Base). Incorrect transducer mounting and other technical mistakes have led to inaccurate field vibration measurements that can under-estimate vibration risk by factors of x2 to x20. We do measure, often, but take great care to ensure the data is valid.

Repeated Monitoring – and also repeated monitoring

Save your time and money. Once you have good data for your tools and operations, you never have to repeat the process unless you change tools or your operating procedures. Many companies spend a fortune on unnecessary repeat measurements, costly monitoring systems and procedures when it would better be spent on new, low vibration tools and other measures that actually reduce the risk.

Hand-Arm Vibration PPE – an oxymoron

There is no generally effective PPE for HAV, despite claims by some AV glove suppliers. In fact, it is often likely that so called “AV” gloves may actually increase the risk due to their effect on ergonomics.

HAVS programme element guide

The following is a step-by-step check list of the components of any effective HAV risk management programme that should be included in any risk assessment report. Contact us for more on any of the element(s) for which you need more information.

  1. Create a vibrating tool/plant register: always takes much longer and turns up many more tools than expected. Ensure there is sufficient information to define a tool and operation (“blue drill” is not sufficient!). At least make, model, accessory, the operation for which it is used and the material (metal, plastic, grass, scrub etc). Download and fill in our open-source HAV tool register and email to us to evaluate the assessment options for you (see below). Click here to download the free template HAV tool register.
  2. HAV risk assess – don’t measure unless you absolutely must. Surely everyone has already done this? The key HSE message is: “Don’t measure vibration unless you absolutely must”. Get a fast, very low-cost virtual assessment by email and use your resources to reduce risk instead.
  3. Implement an effective HAV risk management programme: include operational factors, working conditions, behaviour, ergonomics, symptom reporting systems etc. It does not include PPE as there is none.
  4. Reduce vibration via tool maintenance and vibration control measures: use HAVBase stats to evaluate which tools pose an increased risk as they wear to prioritise maintenance schedules. Increases in tool vibration from range from completely unaffected to very sensitive to tool condition. Retro-fit engineering modifications can substantially reduce vibration in some cases.
  5. Hire / Buy low vibration tools: base decisions on operational, productivity and ergonomic factors as well as levels of hand-arm vibration. Note: the common HAV traffic light system is based on manufacturers’ data that will often seriously underestimate risk.
  6. Training: as operator risk is very dependent on behaviour, training is an important risk management element – toolbox talks, management briefings and full HAV competency training as appropriate.
  7. Health Surveillance: introduce a programme for all workers likely to be exposed above the Exposure Action Value (A(8) of 2.5 m/s^2). This includes education, reporting system, health checks and communication.
  8. Audit the programme: check you are implementing best practice for all the elements above, in practice, not just on paper. We often find the audit will show disconnects between theory and practice and risk management can be improved in parallel with significant cost savings.

Never measure vibration again?

no vibration measurement needed

Avoid the costs (time, training, instrumentation) and hassles associated with field HAV assessment by using our Virtual Assessment service based on our hand arm vibration database. Download our open source template tool register, fill it in, email it to our office and we can then provide you with a low cost vibration risk assessment from our HAVBase HAV database that complies with the HSE guidance recommending the use of accurate published vibration data wherever possible to avoid wasting resources on measurement.

The data can also be combined with additional on-site field vibration measurements if required to reduce assessment costs by around 70-80% and the time (and hassle of getting all the plant together) involved by up to 95%.

Hire Company HAV Data Traffic Lights - hirer beware!

HAV traffic light

This is an important element of “best practice” in HAV risk management. The commonly used hire tool company HAV risk “traffic light” system is supposed to provide information to users about the relative risks from tools. Unfortunately, it can be dangerously misleading as it is based on manufacturers’ declared values that should not be used for risk assessment. Despite this fact, some hire company literature implies the data can be used for assessment. Relying on this data could leave employers open to claims as tools can be much higher risk than the colour coding suggests.

HAVBase aids selection of the best tools to buy or hire to minimise risk. It also provides you with the tools and information you need to implement “best practice” in risk management (statistics, combinations of tools, finger-on-trigger calculations, automatic risk recalculation to meet the regulations …) plus high quality, automated reporting and graphical representations of the data.

How to focus maintenance on the right tools


The costs of managing Hand-Arm Vibration risks can be reduced very substantially by introducing an effective "likely condition based" maintenance programme. We have used field vibration values for thousands of tools to generate statistics showing maintenance affects vibration. Standard breakers or rivet guns, for example, show little difference between the vibration from “as new” tools and that from old, worn tools. In contrast, poorly maintained angle grinders or leaf blowers generate several times the vibration of well maintained units (see graphic of the statistical spread of vibration levels).

This information can be used to improve your tool maintenance programme by concentrating resources only on those tools that pose the greatest risk if they are not well maintained to reduce the risk of HAVS.

HSE - PPE is an unreliable risk reduction option

PPE hearing protection performance

Research by the Health and Safety Laboratory (report RR720) shows that the common assumption that PPE is a reliable “solution” to hearing damage risk problems is simply untrue, leaving many personnel still at risk and many companies open to claims. Some of the key findings of the research are:-

  • PPE in 25% of the companies visited was so ineffective that it was likely to result in negligible or no protection for most
  • Even in companies with effective PPE use, 14% of workers did not wear protectors when and where required
  • 40% of the workers who should have been wearing protectors got no protection at all

The inadequacy of PPE performance in many real-world situations is also born out by the continuing tidal wave of hearing damage claims (£400 million in one year (2014), despite (or even because of) the over-reliance on PPE without understanding the performance limitations away from the lab. This also brings into sharp focus the need to reduce noise levels to reduce risk, even when the levels cannot be reduced to below 85dB(A).

As a rule of thumb, provided effective (and time-consuming) management systems are in place, most good quality PPE can be made to work up to noise levels of around 95dB(A). Above this level, it becomes increasingly difficult to guarantee sufficient protection and above c 100dB(A) it becomes virtually impossible. However, if you can use very low-cost engineering noise control measures to cut the noise, the risk can be reduced dramatically so that PPE works. For example, reducing noise by 3dB from 97dB(A) down to 94dB(A) halves the risk (and PPE is more effective). By 6dB and the risk falls by 75%.

There is more on the topic of self-financing noise control, including a White paper here.

Download a detailed article on poor real-world PPE performance >

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