Noise & Ultrasound
Noise is an inevitable consequence of activities in a workplace but the noise level at work is usually no more than encountered in many other aspects of life, for example groups of people conversing, traffic noise, city ‘bustle’, children playing, etc.
However there some work activities which create noise levels above what most people would describe as comfortable. This “intrusive” noise is if for example you have to raise your voice to hold a conversation beyond a couple of meters or if noisy powered tools are used. Other work activities which might cause extremely loud continuous or sometimes sudden explosive noises include machinery, workshops, manufacturing and laboratory activities – such as hammering, rapidly moving belts, pneumatic impacts, high pressure release, high speed fans etc. Noise levels in such work places need to be assessed and if necessary measures put in place both to prevent noise interfering with communication and making warnings harder to hear and to protect workers – the result of not doing so could be immediate and permanent hearing damage.
People exposed to intrusive noise levels for continuous periods or intermittent periods of at least half an hour regularly during the working day sometimes experience temporary deafness afterwards. Even though their hearing usually recovers within a few hours, this should not be ignored because continued exposure could result in permanent damage.
Anyone with a concern about intrusive noise in their workplace should seek advice from the Health and Safety Department via HealthSafetyHelpdesk at warwick dot ac dot uk as this department is able to measure the sound levels with a special sensitive noise meter, the results will indicate what course of action to take (see section on noise risk assessment and action levels).
Noise is measured in decibels (dB). An ‘A weighting’ sometimes written as ‘dB(A)’, is used to measure average noise levels, and a ‘C weighting’ or ‘dB(C)’, to measure peak, impact or explosive noises. A 3dB change in noise level is actually either a halving or doubling of the sound pressure level and may only just be noticed by the human ear. This is simply due to the way in which our ears work.
Sound pressure level (SPL) - Given in decibels (dB), it is 20 times the logarithm to the base 10 of the ratio of a given sound pressure to the reference sound pressure, which is 20 micropascals (mPa) for airborne sound. The sound pressure is the root mean square value of the instantaneous sound pressure over a given time interval.
dB(A) – Unit of measurement for sound levels, “A” weighted to measure response the same as the human auditory system.
Exposure action value – Levels of noise exposure that must not be exceeded.
Hearing protection – personal protective equipment designed to reduce noise entering the ear.
Competent person – An individual appropriately trained to carry out suitable and sufficient noise risk assessments.
1/3-octave band - The interval between two frequencies whose ratio is 21/3:1. These frequencies define the edges of the band. Normally, the band is referred to by its band centre frequency, which is the geometric mean of the two edge frequencies. For upper sonic and ultrasonic frequencies the bands have been designated as the 10, 12.5, 16, 20, 25, 31.5, 40 and 50 kHz bands.
Ultrasonic - Utilizing, produced by, or relating to, ultrasonic waves or vibrations. For the purposes of this document, ultrasonic waves are acoustic waves having a frequency above 20 kHz.
Upper sonic - Utilizing, produced by or relating to upper sonic waves or vibrations. For the purposes of this document upper sonic waves are acoustic waves in the frequency range between 10 and 20 kHz.
Noise Risk Assessment
The University has a duty to prevent or reduce risks to health and safety from exposure to noise in its workplaces. The Noise Regulations (The Control of Noise at Work Regulations 2005) require that an assessment of the risks from noise at work is made and that (a) legal limits on noise exposure are not exceeded and (b) action is taken if necessary to reduce the noise exposure that produces the risk. Hearing protection (e.g. ear defenders) may have to be provided if the noise exposure cannot be reduced enough by other methods (e.g by putting noisy equipment inside a noise attenuation cabinet). Information, instruction and training must also be provided to workers, and where the risk assessment has identified a risk to health, health surveillance must be provided.
The Noise Regulations require specific action to be taken at certain action values. These relate to:
· the levels of exposure to noise of workers averaged over a working day or week
· the maximum noise (peak sound pressure) to which workers are exposed in a working day.
The values are:
Lower exposure action values:
- daily or weekly exposure of 80 dB;
- peak sound pressure of 135 dB;
Upper exposure action values:
- daily or weekly exposure of 85 dB;
- peak sound pressure of 137 dB.
There are also levels of noise exposure which must not be exceeded:
Exposure limit values:
- daily or weekly exposure of 87 dB;
- peak sound pressure of 140 dB.
These exposure limit values take account of any reduction in exposure provided by hearing protection
Taking Action to Reduce Noise Exposure
Wherever there is noise at work you should be looking for alternative processes, equipment and/or working methods which would make the work quieter or mean people are exposed for shorter times. You should also keep up with what is good practice or the standard for noise-control connected to the associated industry (where the equipment is generally used), eg through a trade association, or machinery or equipment suppliers.
Where it is likely that exposure to noise is at or above the upper exposure action values, you must take action to reduce noise exposure with a planned programme of noise control.
Even where noise exposures are below upper exposure action values, you should take action to reduce the risks, eg reducing exposure further.
Any action you take should be ‘reasonably practicable’ – in proportion to the level of risk. If exposure is below lower action values, the risk is low and it is likely no action is required – but if there are simple, inexpensive practical steps that would reduce risks further, you should consider implementing them.
First think about how to remove the source of noise altogether – for example, housing a noisy machine where it cannot be heard by workers. If that is not possible, investigate:
- using quieter equipment or a different, quieter process - gather information from the supplier on noise levels for the equipment you are interested in before you place your order and make comparisons with other equipment on the market;
- engineering/technical controls to reduce, at source, the noise produced by a machine or process;
- using screens, barriers, enclosures and absorbent materials to reduce the noise on its path to the people exposed;
- designing and laying out the workplace to create quieter work areas;
- improved working techniques to reduce noise levels;
- limiting the time people spend in noisy areas.
Measures that give ongoing or medium- and long-term benefits expected as part of a noise-control programme expected of Departments are:
- ensuring noise is considered prior to purchase of machinery and equipment (low-noise policy);
- proper and regular maintenance of machinery and equipment that takes account of noise.
Guidance to support the management of noise in the workplace is also available for specific sectors. The Music and Entertainment sector has dedicated guidance in this area.
Hearing protection should be issued to persons:
- where extra protection is needed above what has been achieved using noise control;
- as a short-term measure while other methods of controlling noise are being developed.
You should not use hearing protection as an alternative to controlling noise by technical and organisational means. Where there remains a requirement to provide hearing protection, see the accompanying guidance: Providing Hearing Protection
Providing Hearing Protection
The Noise Regulations require you to:
- provide hearing protectors to workers and make sure they use them fully and properly when their noise exposure exceeds the upper exposure action values (at or above 85dB(A));
- provide hearing protectors if workers ask for them, and their noise exposure is between the lower and upper exposure action values (between 80dB and 85dB(A));
- identify hearing protection zones – areas of the workplace where access is restricted, and where wearing hearing protection is compulsory.
To make sure protectors are worn fully (all of the time they are needed) and properly (fitted or inserted correctly) will require you to have systems of supervision and training. Also consider the use of spot checks and audits.
Providing health surveillance
Health surveillance is required for any employees who are likely to be frequently exposed above the upper exposure action values, or are at risk for any reason, eg they already suffer from hearing loss or are particularly sensitive to damage.
Occupational Health can provide advice and information to managers and staff on health matters including health surveillance. Health surveillance needs should have been identified during the risk assessment process.
Approved signage and PPE suppliers can be found via the Procurement webpages
Ultrasound is included under the heading of noise for the reason that, even though it cannot be heard, it is airwave pressure (like audible sound) but with a frequency greater than the upper limit of human hearing (approximately 20 kHz). Ultrasound is used in many different fields, typically to penetrate a medium and measure the reflection signature or supply focused energy. The reflection signature can reveal details about the inner structure of the medium. The most well known application of ultrasound is its use to produce pictures of foetuses in pregnancy but there are many other biomedical, industrial and laboratory applications as well, including
· Ultrasonic testing of testing of metals, plastics, composites, construction materials etc to identify flaws or measure thickness
· Heat transfer in liquids
· Ultrasonic cleaning
· Ultrasonic disintegration and dispersal
· Ultrasonic welding
Health effects can result from exposure to ultrasonic noise such as localised heating from direct contact and potential hearing loss. Anyone whose work involves use of ultrasound should consult the separate section which goes into more detail about carrying out risk assessments and control measures.
This guidance is intended as a supporting document for risk assessors when assessing the risk of workers exposure to hazards when using devices with ultrasonic frequencies.
Research has indicated that ultrasonic noise has little effect on general health unless there is direct body contact with a radiating ultrasonic source. Contact exposure is when there is no air gap between the ultrasonic source and the tissue. This may be direct contact or when transferred through a solid or liquid medium. Contact exposure can in some case transfer nearly 100% of the energy to tissues.
An air gap can reduce the energy transfer significantly. For example, if a person’s finger is in the water bath of an ultrasonic cleaning device the energy transfer to the bone is approximately 65%, but if the finger is just outside of the water the energy transfer is 106 less.
The American Conference of Government Industrial Hygienists (ACGIH) has established permissible ultrasound exposure levels. These recommended limits (set at the middle frequencies of the 1/3 octave bands from 10kHz to 50kHz) are designed to prevent possible hearing loss cause by the sub harmonics of the set frequencies, rather than the ultrasonic sound itself. The HSE have not set any exposure action values or limits for ultrasound, they consider that such effects from exposure to upper audible or ultrasonic frequencies are as yet unproven.
Within the University typical uses for ultrasonic frequencies include; cleaning, dissolving, dissolution, degassing, non-invasive testing and imaging etc. These applications may produce sub harmonic frequencies in the audible region; the noise levels associated with these sub harmonics are significantly below the exposure action values as defined in the Control of Noise at Work Regulations 2005. The risk to an individuals hearing of this type of device is typically not significant, but the sub harmonic noise may cause a “nuisance”. For these instances the position of the ultrasonic device and any shielding will help to reduce the propagated noise.
Ultrasound Risk Assessment
The following is guidance on how to manage the potential risk of health from working with devices that generate ultrasonic frequencies.
- Ensure compliance with Control of Noise at Work Regulations 2005 . Ensure there is no direct contact, or indirect via a solid or liquid medium, with ultrasonic generating devices.
- Manufacturer’s information should include noise levels at 1m from the ultrasonic device when operating under normal conditions. Ensure the measured audible noise levels are below the exposure action values as specified in the control of noise at work regulations.
Use the preliminary noise risk assessment, if required a competent person can carry out monitoring of audible noise (Safety Adviser).
Important information to consider when conducting a risk assessment
- The energy from ultrasonic waves dissipate rapidly in air
- Attenuation for ultrasound is similar to that for audible noise.
o Reduce the energy at source.
o Block the path of the energy
o Protect the worker
- Attenuation for ultrasonic frequencies is simpler and easier than for audible noise energy.
o Ultrasonic frequencies are more readily absorbed and reflected inwards by enclosures.
o Ultrasonic frequencies are less liable to diffraction.
o A barrier of 3mm cardboard reduces SPL by 70dB between 20kHz and 50kHz.
o Attenuation offered by hearing protection is usually referenced up to 8kHz, according to published information it is likely that attenuation in the ultrasonic region will be at least that offered at 8kHz.