Top of pageWritten by Bob Davis
© 2002, ISVR University
of Southampton. All rights reserved.
1 Noise and Vibration - basic questions
and answers
2 Noise from forges and foundries
3 Reducing Noise - the principles
4 Noise Reduction in Practice
5 Pilot Projects
Annex 1 The Black Country Forging and Foundry
Project
Annex 2 Explanation of various terms -- noise
and vibration
Annex 3 Sources of information
This handbook has been prepared as part of an EU-funded project
centred on forges and foundries in the Black Country area of the UK
West Midlands. The Black Country is a traditional centre for
metalworking industries, and in many cases forges and foundries are
situated close to housing. These industries are inherently noisy,
and in recent years problems of noise affecting neighbours have
become more frequent. In some cases, this has meant that foundries
and forges have had to restrict their operations to such an extent
that their viability has been threatened. The Black Country Project
was designed to find out the main causes of noise problems from
these industries and to identify and demonstrate practical
solutions.
There is further information about the Project in Annex 1.
It gives practical advice on how to avoid or resolve noise and
vibration problems affecting people living near forges and
foundries. Although some of the information relates specifically to
these industries, the same principles apply to most other
industries. It is directed towards forge and foundry owners and
managers, although it may also be useful to Environmental Health
Officers, to others involved in noise assessment and control, and
to residents who are bothered by noise from a forge or foundry. The
Project, and this handbook, concentrate on community noise - noise
escaping from industrial sites and affecting neighbours - rather
than noise in the workplace, although often these go
hand-in-hand.
This handbook gives basic explanations about noise and vibration -
causes, methods of measurement and assessment, and principles of
reduction. The emphasis is on practical methods of reducing noise.
A number of noise control projects in forges and foundries are
illustrated with information on costs and effectiveness. Noise and
noise control can be complex mathematical and engineering subjects.
This handbook can provide only general guidance.
Sources of further information and support are listed in Annex 3.
Noise is unwanted sound. Sound is a form of energy which is
transmitted through the air and is detected by the ear as rapid
changes in pressure. The air is set into motion by the source of
the sound, which is most often a vibrating surface or a turbulent
flow of air. The loudness and character of a steady sound are
determined by its frequency (measured in Hertz or Hz) and its level
(measured in decibels or dB). In this handbook, noise levels will
be stated in dB(A) - this is the noise
level measured by a meter which simulates the response of the human
ear to sounds of different frequencies. Noise levels in dB(A) are
almost universally used for the assessment of noise in the
community and in the workplace.
Depending on the level of noise and the duration of exposure,
noise can cause varying degrees of annoyance or difficulties in
communication. It can disturb relaxation or sleep, or can have
adverse health effects including damage to the hearing. This
handbook is about noise affecting people living near industry. In
this situation, the noise levels experienced are such that the
worst adverse effects of noise are annoyance and sleep disturbance.
Some noise may cause only minor and temporary irritation, but in
other cases noise can cause such a strong reaction that an
individual's ability to relax or concentrate is severely
affected.
Peoples' response to noise, particularly to noise from outside
their own home, is highly variable. Some people are far more or
less tolerant than others, for a variety of reasons, many of them
psychological. There are obvious factors such as 'lifestyle' - a
person who is at work during the day is obviously less likely to
complain about daytime noise than is the shift-worker next door who
has to sleep during the day. However, an important factor is the
attitude of the individual towards the source of noise - people are
far less tolerant of noise if they think that the noise-maker is
inconsiderate or unreasonable.
Noise and vibration are inseparable - noise is generated by a
vibrating surface or body of air or gas. However, vibration itself
is a potential cause of problems. Some heavy engineering processes,
particularly the operation of forging hammers, can result in
significant energy being transmitted to the ground through machine
foundations. This can be transmitted to nearby houses and can
sometimes be felt as actual motion, because the human body is a
very sensitive vibration detector.
High levels of vibration can cause physical personal injury or
damage to buildings. However, vibration from industry affecting
nearby houses is never so intense that there is any conceivable
risk of any health effects, and building damage from any source of
ground-borne vibration is extremely rare. However, vibration can be
annoying and disturbing.
Apart from causing detectable (although in fact very slight) motion
in nearby houses, ground-borne vibration from industry can also
cause noise problems in these houses. This is because the internal
surfaces of houses (walls, floors and ceilings) can be caused to
vibrate by vibrations transmitted from the ground through the
foundations and building structure. These surfaces can then radiate
low-frequency noise ('thumps' and 'rumbles') rather in the manner
of large loudspeakers. People living near factories containing
equipment such as forging hammers, large presses or guillotines can
sometimes hear the resulting 'thumps' inside their houses, although
the vibration itself - the actual motion of the structure- is too
slight to be felt. Ground-borne vibration can also be detected in
other ways - objects such as slightly loose central heating
radiators, and glasses or china in light contact, may squeak or
rattle.
Residents who can feel vibration, or hear the 'thumps' and
'rattles' it sometimes causes, are often more concerned about the
possibility of damage to their houses (which is most unlikely to be
caused) than they are annoyed by the actual disturbance to
themselves.
Problems arising from ground-borne vibration are relatively rare,
although drop-hammers can cause detectable ground vibration up to
around 100 metres away, and sometimes at greater distances in some
ground conditions. This handbook concentrates on the far more
widespread situation where houses near forges and foundries are
affected by airborne noise. However, the possibility of a 'noise'
problem being a vibration' problem should be borne in mind - noises
caused by ground-borne vibration must be distinguished from the
effects of noise which is transmitted through the air (airborne
noise) since different control methods are required and incorrect
diagnosis can lead to costly wasted work. Further information about
noise and vibration will be found in Annex 2.
This section explains briefly the Standards and Regulations
which apply to noise from industry in England. There may be minor
differences and exceptions in Wales. Scotland and Northern Ireland.
Different standards and Regulations will apply elsewhere.
Where planning consent is required for a new site, new buildings
or a change of use, this consent often includes conditions to limit
noise emission. These conditions might include restrictions on
hours of use or methods of working, or they may specify maximum
noise levels which are not to be exceeded at specified times of the
day or night. These Conditions are enforced by the Local Authority.
A breach of a planning condition can lead to an Enforcement Notice
and prosecution. If noise affecting other premises amounts to a
nuisance, a Local Authority can also use its powers under the
Environmental Protection Act (the 'EPA' - see below) to abate the
nuisance.
Many industrial sites do not have a formal planning consent,
because a current use which has been carried on for more than ten
years can be considered lawful. Many forges and foundries fall into
this category. In these cases, if noise causes a nuisance to
neighbours a Local Authority would use its powers under Section 80
of the EPA. If the Local Authority is satisfied that noise amounts
to a nuisance, it has to serve an Abatement Notice. The company can
appeal against a Notice within a specified period. Non-compliance
with a Notice can lead to prosecution. If a company can show that
it has applied the best practicable means of reducing noise (often
termed 'Best Available Techniques' or 'BAT') this can provide a
ground for an Appeal against the Notice or for defence against
prosecution.
Where noise is causing a nuisance, private individuals can take
action against an industrial site under Section 82 of the EPA, or
under common law, even when the Local Authority choose not to do
so. Such actions are rare, however.
Noise is a nuisance when it materially affects people's amenity.
There are no fixed limits for industrial noise affecting houses -
what is or is not considered acceptable or a nuisance depends on
local circumstances. However, the following table illustrates the
general range of unacceptable and acceptable noise levels from
industry in a 'typical' built-up environment of mixed residential
and industrial areas.
| Acceptable | Complaints expected |
Unacceptable | |
| Day (7 am - 7 pm) | 50 - 55 | 55 - 60 | 60+ |
| Evening (7 pm - 11 pm) | 45 - 50 | 50 - 55 | 55+ |
| Night (11 pm - 7 am) | 40 - 45 | 45 - 50 | 50+ |
|
Table 1: Range of noise levels in dB(A) from industry - as measured outside nearby houses. Levels are average (Leq) levels - see Annex 2. |
These are 'broad brush' values and must not be taken as specific
guidance for any particular site or situation. Higher noise levels
might be acceptable in areas exposed to high levels of road traffic
noise from trunk roads or motorways. Lower noise levels might be
needed in quieter areas. An important factor is the character of
the industrial noise. Noise which contains bangs and crashes is far
more annoying and disturbing than steady noise of the same average
level. The regular 'banging' caused by forging hammers is a
particularly distinctive and potentially disturbing noise. For
these types of noise, the noise levels in the Table should be
reduced by at least 5 dB(A).
There is a British Standard (BS 4142 - reference 1) which sets
out a method of predicting whether noise from an industrial site is
likely to provoke complaints. This standard is based on comparing
the noise (measured or predicted) from the premises, as received at
any house, with the background noise level at the same position
when the industrial operation is stopped. The method includes a
means of allowing for the 'character' of the noise, by penalising
noise which contains bangs, crashes, whines or hums.
Evidence based on the use of BS 4142 is generally accepted in the
Courts to demonstrate (or to dispute) the existence of a noise
nuisance. Noise limits in Planning Conditions are usually based on
consideration of BS 4142. The Standard is widely used (and often
misused) and will inevitably be quoted whenever an industrial noise
problem arises. However, proper application of the Standard
requires expertise and judgement and a good understanding of its
limitations.
Some companies operate voluntary environmental policies and
procedures which include the assessment of noise emitted to their
locality. These procedures might include, for example, regular
noise monitoring at key locations and a method of assessing the
extent of any change in noise emission likely to result from
changes in plant or operating methods. Some companies formally
accredit these policies under ISO 14001 (ref 2). In some sectors of
industry, ISO 14001 accreditation is a customer requirement.
The introduction of Integrated Pollution Prevention and Control
(IPPC) is likely to have a significant impact on the way noise from
foundries and forges is controlled. IPPC will broaden the scope of
existing pollution controls , which currently apply to certain
industrial processes (including ferrous foundries and but excluding
forges) to include noise and vibration. One objective of IPPC will
be to encourage good practice (BAT).
This handbook is not concerned directly with noise in the
workplace, although reducing noise 'at source' by quietening a
process or operation can often result in benefits both in the
workplace and in the neighbouring area.
Noise levels in the workplace are covered in the UK by the Noise at
Work Regulations 1989 (ref 3). An HSE document (ref.4) explains the
Regulations and gives further guidance. New regulations on noise at
work will appear in a revised EU Physical Agents Directive,
currently being discussed. These changes will work through into UK
regulations.
Regulations and enforcement procedures relating to environmental
matters. including management of noise, are constantly changing. As
far as possible. keep up to date by extracting information from
trade journals and government circulars Trade Associations are a
major source of such information.
Noise (or sound) is generated in two ways:
Most industrial processes involve the use of machinery, the
movement of materials, and the movement of air for ventilation,
heating and cooling. All of these generate noise which can affect
neighbours. The following lists show the sources most likely to
cause people living near forges and foundries to complain about
noise and vibration:
Forges
Foundries
Sources common to both industries
These noises can be grouped under three headings:
There is no 'standard' method of reducing noise from forges and
foundries. Each site and its surroundings is different, and each
will have different 'main' noise sources. This handbook offers
examples of noise reduction solutions which have worked on some
sites, and also explains the basic principles which lead to these
solutions. The basic principles first
Noise travels through the air as a pressure disturbance. Moving
further away from the source, the noise level generally decreases
because the sound energy is distributed over a larger area. In a
simple case, the sound level reduces by 6 dB each time the distance
from the source is doubled (the 'inverse square law'). This rule
does not always apply: for example, close to a large noise source
such as the wall of a factory the noise level does not start to
fall off with distance until you are some way from the wall.
This means that if a factory produces a noise level of 55 dB(A) at
a house 200 metres away, the noise from the factory will be reduced
to about 49 dB(A) at 400 metres. This is not a very dramatic
reduction, even over quite a large distance. Relocating equipment
or operations on a site to move them further away from houses
(unless they are then screened by an intermediate building) may not
be a very effective measure.
If a source of sound is enclosed within a solid 'box', the sound
energy emitted is reduced because a solid material has the property
of sound insulation - only part of the noise energy striking one
side is radiated from the other side. The heavier the material, the
greater the sound insulation. Materials made up in the form of
multiple layers (an example is double glazing) provide more sound
insulation than a single layer of the same total mass. Values of
sound insulation, like sound levels, are stated in dB or dB(A).
Typical values of sound insulation are shown on Table 1
(overleaf).
Note that because decibels are logarithmic units (see Annex 2) the
normal arithmetic rules of addition and subtraction do not apply. A
noise reduction of 10 dB means that the original sound energy has
been reduced by a factor of 10, a reduction of 20 dB means a
reduction in sound energy by a factor of 100, 30 dB means a
reduction by a factor of 1000 (that is to 0.1% of the original
energy).
| Single Panels |
Weight |
Sound |
| 10 mm plywood / chipboard | 5 | 15 dB |
| 12 mm plasterboard / 1.2 mm steel / 4 mm glass | 10 | 20 dB |
| 3 mm lead | 35 | 35 dB |
| 100 mm lightweight concrete | 100 | 40 dB |
| 115 mm brick | 200 | 45 dB |
| 200 mm concrete | 400 | 50 dB |
| Double Skin Panels | ||
| 0.9 + 0.55 mm steel. 150mm spacing. mineral wool infill | 20 | 35dB |
| Double glazed window, 6 mm glass. 100 mm airspace | 30 | 40 dB |
*figures are approximate average values for sound at mid-frequencies (250 - 1000Hz)
Table 2: Typical values of sound insulation - different
materials
An enclosure can only provide good sound insulation if it is
reasonably airtight. Noise will escape through any direct air path.
An enclosure with holes amounting to 10% of its surface area will
provide only 10 dB of sound insulation, however heavy the material
the solid parts are made of. To provide 30 dB sound insulation, as
well as being built of a suitably heavy material the total area of
air gaps in an enclosure has to be less than 0.1% of the total area
- a tall order.
Sound is reflected from hard surfaces such as walls and roadways in much the same way as rays of light are reflected from a mirror. Some materials and surfaces - grassland and undergrowth, porous materials such as glass fibre blankets - absorb some sound and reflect only some of the sound striking them, as a dark surface reflects only some of the incident light. However, it can be misleading to compare the behaviour of sound with that of light. One significant difference is that sound is refracted round obstacles such as fences and buildings - it 'travels round corners'. It is a common observation that things (voices, cars etc) can be clearly heard even when they are not visible. There is some 'noise shadow' effect when a source of noise is hidden from view, but it is a limited effect. This is why attempts to reduce noise by building a wall or fence to hide a source of noise often produce disappointing results. For the same reason, noise radiated from the roof of a factory cannot be ignored even if the roof cannot be seen from a particular nearby house. Roofs are usually the largest part of a building, in terms of surface area. and are often the weakest in terms of sound insulation because the sheeting is light in weight and usually has openings for ventilation.
Noise levels in casting and finishing areas in mechanised
foundries are generally around 85 - 90 dB(A). Shakeout machines
(unless enclosed) can give higher levels, depending on the sizes of
castings and core boxes.
Levels in forges where hammers are used are generally 95 - 100
dB(A). Because of the highly impulsive nature of hammer noise, this
is the major problem facing forge operators.
How do these noise levels relate to levels outside the foundry or
forge? Table 2 shows what noise levels might be expected at
different distances from a typical building (with a floor area of
1000 m2) with average internal noise levels of 85 or 95
dB(A). The building is assumed to provide 15 dB(A) sound insulation
this is a typical figure for a building with lightweight
single-skin cladding and open doorways and ventilators.
| Noise levels inside | Noise level at distance outside | ||
| 100 metres | 200 metres | 400 metres | |
| 85 dB(A) | 52 dB(A) | 46 dB(A) | 40 dB(A) |
| 95 dB(A) | 62 dB(A) | 56 dB(A) | 50 dB(A) |
Table 3: Noise radiated from a lightweight building.
If these numbers are compared with the rough 'guideline' values
on Table 1, it is clear that forges in particular present a major
difficulty. Even 400 metres away, a forge in a lightweight building
will give rise to a noise level 10 dB(A) above what might be judged
reasonable in the early morning or late evening, and at distances
of 100 metres or less is likely to produce unacceptable levels of
noise during the day. Larger buildings will produce rather higher
levels.
Noise levels in the range 50 - 65 dB(A) are commonplace in
residential areas close to working foundries and forges.
The most effective way of reducing noise is usually to avoid
making noise in the first place - to use a quieter machine or
process. Unfortunately this is often not practicable. For example
it would, in theory, be possible to design a 'quieter' forging
hammer. Forging presses are less noisy than hammers (although by no
means quiet). However, most forges and foundries will be using
existing machinery and processes for the foreseeable future.
However, there is some scope for noise reduction at source, even in
an existing forge or foundry. When new ancillary equipment such as
an air compressors or a ventilation system is installed, there is
often a choice between noisy and quiet equipment to do the same
job. It is not unusual for a company to buy new equipment without
consideration of noise levels and create a 'new' noise problem.
Always obtain information on noise levels when buying new machinery
or tools. This is particularly important for equipment to be
located outside or in a plant room which is directly ventilated to
outside through louvres, such as dust collectors, heat exchangers
or compressors. Suppliers are legally obliged to provide such
information. You may need to take specialist advice to interpret
the information, and on whether you should specify a maximum noise
limit for new machines, and what this limit should be. A visit to
see and hear the same machine working on another site is often a
good way to assess the likely noise levels.
Equipment is usually noisier if it is defective. Worn fan motor
bearings, or a badly-maintained clutch on a drop hammer, can
produce distinctive noise which might not seem like a problem on
the working site, but might be very annoying to neighbours.
Many noises in forges and foundries arise from hard
metal-to-metal impacts. The main problem is the noise caused by
small forgings or castings falling into hoppers. on to chutes and
tables, or into bins ('stillages). The resulting 'crashes are
frequent causes of complaint from neighbours.
These noises can often be reduced by low-cost methods. For
example:
Reducing the number of transfer operations. In most forges and
foundries, pieces are tipped from stillage to hopper or bin and
returned to stillage several times between production and the end
of finishing operations. A review of working methods and re-design
of fixtures can often reduce these operations.
Reducing the height from which pieces fall on to hard surfaces.
Sometimes this is difficult to control - a crane driver moving
scrap metal using a magnetic crane has considerable freedom.
However, some measures are effective: for example, raising
stillages at fettling stations or at the discharge of shot-blast
machines, using a simple fixture to reduce the drop distance, can
be effective.
The main problem with steel stillages, hoppers, chutes and benches
is that they 'ring' when struck by a metal object. This 'ringing'
can be reduced by reducing the impact force using a resilient
surface covering, by 'deadening' or 'damping' the response of the
structure being hit, or by making it a less efficient radiator of
noise. Examples of these techniques are illustrated in the case
studies in Section 5.
There is no great problem in producing a 'quiet' stillage, which
does not 'ring' when metal pieces are thrown or tipped into it.
However, there are thousands of stillages in use, which circulate
between final customers, forges and foundries, heat treatment and
machining companies. The universal introduction of quiet stillages
(which would invariably cost more than the standard steel stillage)
is therefore an unrealistic aim. However, a company might find it
practicable to have a number of 'quiet' stillages dedicated to a
particular task or area, to resolve a particular problem For
example, it might be possible to use a small number of 'quiet'
stillages to take scrap from an external stockyard to the
furnaces.
Always be on the lookout for ways to reduce noise.
Never buy a new machine or tool without considering its likely
noise levels.
Noise reduction should be a key element in process engineering -
quieter methods can often be introduced in conjunction with changes
designed to improve efficiency or quality.
Where you have houses near your site. especially if noise has
caused problems in the past. make a regular 'patrol of the site
boundary to identify new noises and possible defective
equipment.
Identify operations where there are frequent metal-to-metal
impacts. Eliminate unnecessary material transfers. Reduce impact
forces by reducing drop heights. 'cushion 'impacts using resilient
linings, make stillages, chutes, and tables less effective noise
radiators.
Noise emitted from machines and operations can be reduced by
enclosing them. Enclosures present some problems - they may
obstruct access, they take up floor space, and if personnel have to
work inside they may present a hazard. However, sometimes
enclosures are effective solutions to noise problems. To be
effective. enclosures intended to reduce noise must have good sound
insulation properties. To provide a high degree of sound
insulation, as explained in para. 3.2, enclosures must be
reasonably heavy and well-sealed to eliminate direct air paths.
However, lightweight enclosures, with some openings, often provide
useful attenuation. For example, an enclosure made from overlapping
PVC strip curtains can provide a noise reduction of around 10
dB(A). Such enclosures have been used with some success around
foundry shake-out stations, to control dust as well as noise. They
have the advantages of providing ready access and reasonable
vision, although they are not very durable and obviously cannot
withstand contact with hot castings.
For noise reductions greater than about 10 dB(A), careful design is
needed to deal with features such as access doors and openings for
materials. There are numerous specialist suppliers of 'acoustic'
enclosures. Proprietary enclosures are built up using modular sheet
steel panels with an internal lining of mineral wool faced with
perforated steel sheet. This sound absorbent lining reduces noise
reflections within the enclosure, which would otherwise lead to a
'build-up' of noise inside and resulting inferior performance.
Effective enclosures can also be built (at a lower cost) using
brick or concrete blocks, timber, plasterboard or materials such as
wood-wool cement slabs, although without specialist advice results
may be disappointing.
Forges and foundries can be tough environments. Enclosures round
machines need to be well-engineered and robust to withstand assault
from fork lift trucks, for example. If buying an enclosure from a
specialist supplier, find a supplier with specific experience in
these industries.
Examples of acoustic enclosures fitted to shot-blast machines are
described in the case studies in Section 5.
Enclosing individual machines or processes to reduce noise can
be effective. but the drawbacks (access. space. creation of
workplace hazards) should be carefully considered.
The effectiveness of an enclosure in reducing noise depends on the
detailed design. Seek specialist advice.
Enclosures in forges and foundries must be robust. A
badly-engineered enclosure of unsuitable materials will require
regular repair during a limited life.
The buildings which house a forge or foundry can be thought of
as a large acoustic enclosure - the sound insulation provided by
the building determines how much noise escapes to annoy neighbours.
Most forge buildings are of lightweight construction, with many
openings for ventilation. The noise reduction afforded by such a
building is poor, usually no better than 10 - 15 dB(A). (Foundry
buildings tend to be rather better than forges in this respect,
because more stringent environmental controls have led to the
widespread introduction of mechanical ventilation, with cleaning
systems to remove dust and fumes. There is therefore less reliance
on natural ventilation and fewer openings in the buildings to
provide escape paths for noise).
Inside an enclosed space with solid surfaces the level of noise
builds up because of the repeated reflections of sound from the
walls, floor and roof - this effect is termed 'reverberation'.
Treating the internal surfaces with sound-absorbent (less
reflective) materials will reduce the reverberant noise. Reducing
the noise level inside a building reduces the level outside by the
same amount. However, the installation of internal sound-absorbent
treatment does not have a dramatic effect -- a reduction of around
5 dB(A) in average noise levels might be achieved by lining the
inside of the roof. The most widely used material is semi-rigid
boards of mineral wool, 50mm thick, which can have a woven cloth or
very thin plastic facing to resist dust contamination. For new
buildings (or re-sheeting) some proprietary double-skin steel
sheeting systems have a perforated inner skin which exposes the
mineral wool between the skins and provides sound absorption,
although the actual sound insulation of these systems (the
resistance to sound passing through) is inferior to that of two
solid skins.
The obvious way of reducing noise from a building which contains
numerous noise sources (for example, a forge with a number of drop
hammers) is to improve the sound insulation of the building itself,
to keep the noise in. This is rarely a simple task. Improving the
sound insulation of the actual cladding of the building (often
single-skin metal sheeting) means adding considerable weight, which
may not be possible without strengthening the structure. More
fundamental is the need to limit the escape of noise through
openings, which have to be closed off or greatly reduced in area.
This immediately presents a problem with ventilation: high air
change rates are needed to maintain reasonable working
temperatures, particularly during hot weather. Access to and from
the building is required, and an open doorway will provide a large
noise escape path. Doors must therefore be kept open for a minimum
time, and when closed must provide sound insulation to match that
of the rest of the building. At an existing forge or foundry it is
unlikely to be possible to suspend operations whilst major building
works are carried out. which further limits the scope of
practicable works.
It is tempting to believe that treating only part of a building,
perhaps just the wall facing nearby houses - will reduce noise
significantly. As explained in 3.3, noise 'goes round corners'. The
noise which reaches neighbours is coming from all parts of the
building, including the parts which cannot be seen. The roof of a
building is usually of much greater total area than the walls, and
is often of lighter construction. Improving the sound insulation of
the walls of a building, without treating the roof, is almost
always ineffective. An acoustics specialist with experience of
industrial buildings can identify the contribution of each part of
the building to the noise level at any point outside, and design a
suitable 'balanced' package of insulation works.
One of the pilot projects involved extensive modifications to a
forge building. involving the installation of a second external
'skin', easily-operated acoustic doors. and a system of mechanical
ventilation which allowed other ventilation openings to be closed
off. Adding a second skin outside the existing sheeting has several
advantages - the building can be made more weatherproof, appearance
can be improved, and the work can often be carried out without
disrupting production. This project is described in para. 5.2.
If a building contains many sources of noise, improving the
sound insulation of the building could to be the only practicable
means of reducing noise escaping to outside.
It will usually be necessary to treat large areas of the building -
at least 3 walls and the roof - to achieve a significant noise
reduction.
Holes and openings must usually be closed off. and a mechanical
ventilation system installed.
Assistance from an acoustics specialist, structural engineer and
heating/ventilating engineer is generally essential. Planning
consent may be required.
Building modifications are expensive. However, a scheme has been
demonstrated in the course of this project which has proved to be
effective and practicable. and was installed without disrupting
normal production to any appreciable degree.
It is often assumed that hiding a source of noise
from view will reduce or eliminate the noise. Because sound goes
round corners (unlike light) the effect of placing a physical
barrier ( a wall or fence) between a source of noise and a listener
is quite limited. This is particularly true for low-frequency noise
(such as a dull rumble) which passes round a barrier very readily,
whereas high-frequency noise (such a high-pitched whistle) behaves
more like light and can be screened more effectively.
Screens can be effective in reducing noise from a small source
(such as a cooling tower or an open doorway, for example) escaping
in a particular direction. A screen is most effective if placed
near the source or the receiver (see diagram), because the noise
reduction is higher if the angle 'a' is greater. For the same
reason, a large screen is more effective than a small one, even
though both may hide the noise source from view.
Fig 1: Acoustic barrier - (close to source or
receiver and as high as possible to increase angle 'a' for more
noise reduction.)
Because the noise reduction provided by a screen is
limited by the noise which passes over the top and round the edges,
the screen does not need to provide very high resistance to noise
passing through it. As a screen, a close-boarded fence will provide
the same noise reduction as a brick wall or earth mound of the same
height and width. However, on a factory premises a robust form of
screen is needed. Timber sleepers slotted into vertical steel
columns can serve as a useful and durable screen, and can also form
(for example) material bays in a foundry stockyard.
In practice, a screen is unlikely to provide a noise reduction of
more than 5 - 10 dB(A). A screen may have a psychological benefit
as well as an acoustic one: for example, a screen which conceals a
lighted doorway at night, or which prevents local residents
observing truck movements in a factory yard, may satisfy complaints
even though the actual noise reduction is quite modest.
Screens can be expensive and are rarely a cost-effective solution
to a noise problem. Proprietary 'acoustic screens', primarily
intended to be used as noise barriers alongside trunk roads and
motorways, are widely promoted by the manufacturers for more
general use but in many applications are no more effective than a
simple close-boarded timber fence (although they are constructed to
a higher specification and would be more durable). Specialist
advice should always be obtained before erecting a screen in an
attempt to reduce noise - there is often a better way of achieving
the same effect.
A barrier or screen in the form of a wall or fence can provide a
modest noise reduction, and may be useful in concealing a noise
source from view.
The noise reduction provided by a screen depends mainly on the
width and height. Cheap forms of construction - timber fencing or
reclaimed timber sleepers - are usually adequate. Expensive
'acoustic screens' often provide little or no advantage.
Obtain specialist advice before erecting a screen as a noise
reduction measure -the results are often disappointing, and there
may be a better solution.
Ventilation and dust-extraction equipment are regular causes of
noise problems. The main noise source is the fan powering the
system. Ventilation openings such as louvres to compressor houses
can also transmit noise to outside. Any passage. duct or opening
which permits the flow of air will also transmit noise. Note that
the transmission of noise along an air passage or duct is not
affected by the direction of air flow - it is a common
misconception that noise travels 'with the flow', so that no noise
escapes from an air inlet opening such as a fan intake. The reason
is simple - sound travels at about 330 metres per second in air,
and it is hardly impeded by the flow of air in a ventilation duct
which would rarely exceed 20 m/s.
Noise emitted from fan intakes or exhausts, or from exhaust stacks
and louvres, can be reduced using silencers. These are of various
types, but they generally contain passages lined with porous
sound-absorbent material, which 'take out noise whilst permitting
air to flow through. Silencers almost always restrict the airflow
and may reduce the performance of a system - this has to be taken
into account.
The positioning of a silencer can also be important. A silencer too
close to a fan can disturb the air flow and make the fan noisier. A
silencer too far from a fan, connected by a duct, may allow noise
to 'break out' through the duct before it reaches the silencer.
Selection of silencers, and choosing where to put them, is a
specialist job.
Beware of making fans and equipment containing fans (such as
cooling towers) too quiet. A continuously running fan, as long as
the noise it makes is 'smooth' in character, may actually be useful
in masking intermittent noises from other sources. There have been
many cases where factories have spent a great deal of money and
effort in reducing noise from fans and have provoked more
complaints because bangs and crashes, previously masked by fan
noise, became audible. (Some neighbourhood noise problems have
actually been solved by introducing continuous noise - and hence
actually raising average noise levels -to conceal intermittent
impact noises, although this is not a recommended approach in most
circumstances).
Noise travels against as well as with the direction of air
flow
Silencers reduce noise travelling along a duct or through an
opening whilst permitting the flow of air. Specifying silencers and
where to put them is a specialist job. Incorrectly sized or
wrongly-positioned silencers may be ineffective and can seriously
reduce air flow.
Before reducing noise from a fan, make sure that it is not doing a
useful job by masking other more intrusive noises - noise control
does not always mean noise reduction.
Some industrial sites are laid out in a way which almost invites complaints from neighbours, with the noisiest (and most visually intrusive) areas and buildings close to a boundary shared with a residential area. This is often historical ("the factory was here before the houses ) and major reorganisation of a site is not often feasible. When designing a new site, the major sources of noise and visual impact can be identified and located away from a sensitive boundary, perhaps using 'quieter' buildings such as a warehouse or office block as a 'buffer'. This is usually a matter of common sense, not acoustics.
Even on existing sites, some changes in layout may be possible.
One Black Country foundry had a long-standing problem caused by
noise from the stockyard which faced houses across a residential
road. Deliveries of scrap iron and coke, and movements of the crane
and trucks in the yard, were regular causes of complaint. As part
of a programme of general improvements to the site the stockyard
was relocated to land previously used as the employees' car park,
further from the houses, and screened from view with a barrier of
timber sleepers. This has successfully reduced the problem of
stockyard noise.
Even without a change in processes or site layout, noise problems
can sometimes be resolved by relatively minor changes in the way an
industrial site is operated and managed. Such 'non technical'
measures might include:
The need for such measures can only be established by carrying
out regular assessments of noise from the site, as experienced by
neighbours. Some problems do not need the services of an acoustics
specialist to find a solution - an employee with a good knowledge
of the site operations can sometimes define the problem and
identify the solution better than the 'expert'.
People living close to forges and foundries in the Black Country
are generally extremely tolerant of noise from these premises, at
least during reasonable daytime working hours. Residents are most
likely to complain if they experience some noise which they believe
to be unnecessary - a door to a noisy shop left open, shouting and
revving of a truck engine in the yard, or a radio being played
loudly. These problems can be avoided by adequate management
control and the development of greater 'noise awareness' amongst
employees.
Last, but by no means least, any company should have a proper
method of dealing with complaints from local residents. Experience
shows that if a company deals with complaints in a courteous and
organised way and makes efforts to reduce 'avoidable' noise, then
residents are far more tolerant of other noise (for example, from
drop hammers) which they appreciate is difficult for the company to
reduce whilst staying in business.
On many sites with noise problems. some benefit could be
obtained by relatively minor changes to the layout of the site.
Such changes should always be considered before embarking on
'acoustic' remedies.
Consider how noise can be reduced by management measures. Avoid
unnecessary noise, make employees 'noise aware'.
Develop good relationships with neighbours. Respond quickly to
complaints.
Noise from an industrial site often arises from a number of
separate sources. There are many ways of controlling noise, but
each noise problem is different. Many attempts at reducing noise
from industrial sites have failed because the problem was not
properly identified, and inappropriate control measures were
carried out. Before attempting to reduce noise affecting
neighbours, it is essential to develop a strategy to address the
following key points:
What are the noise levels at the houses affected? What noise levels would be acceptable?
What are the noise sources which contribute to the problem?
Sometimes this is obvious. However, often it is necessary to make
detailed measurements, perhaps with equipment operated individually
or in groups, to find out how much each source contributes to the
overall noise. Remember that noise measurements do not tell the
whole story - some noises cause far more annoyance than might be
expected from the actual measured noise levels they produce. A
visit to a complainant's house to listen to the noise from your
site can be most instructive, and sometimes reveals an obvious
solution to a problem.
Some sources of noise will be more important than others - they will not all need the same degree of reduction. However, the difficulty and cost of reducing noise from each source must also be considered. As an extreme example, if there are ten equal sources of noise, a reduction of 10 dB(A) could be achieved by reducing the noise of each source by 10 dB(A). Alternatively, you could reduce the level of nine of the sources by 30 dB(A) and leave the 'difficult' source unchanged, to achieve the same effect. The objective is to develop the most effective and economical package of works to achieve the overall result.
Solving noise and vibration problems often needs specialist
assistance, from a consultant or noise control equipment
supplier. Trade Associations can usually help to locate a
source of advice. However, do not rely on an outside
specialist to arrive at the bets strategy. He/she will not be fully
conversant with your operations, and noise control equipment
suppliers may be inclined to concentrate on solutions which use
their products. The close involvement of company employees
(perhaps the Works Engineer or one of his staff) is essential to
reaching a practicable solution to any industrial problem.
Three pilot projects were part-funded within the overall Project. Other projects were proposed but were not taken up by the companies concerned, because of financial or other constraints.
The projects were intended to demonstrate specific principles, and to assess the effectiveness of remedial measures which in some cases have not been systematically applied and evaluated elsewhere. They were not necessarily expected to provide a complete solution to a noise problem, and it was anticipated that some would reveal practical drawbacks which would limit their usefulness.
This is a foundry close to a residential area. The nearest houses share a common boundary with the yard area, beyond which is the finishing building, where castings are fettled and inspected. This building is of part-brick construction, with steel sheeting to upper walls and roof. There are three doors giving access to the yard. The finishing building also serves as a despatch area: castings in bins or on pallets are loaded on to vehicles in the yard by forklift truck, using one of the doors. The general layout is shown below.
Fig 2: Chamberlin and Hill - Site layout
An initial inspection revealed a number of noise sources, audible in the yard. All were intermittent in nature and most were caused by metal-on-metal impacts:
Average noise levels in the yard area, close to the boundary, were sometimes as high as 70 dB(A) when doors were open, and 60-62 dB(A) with doors closed. The noise was distinctive, with repeated impact noises (crashes and rumbles).
A package of works was carried out to demonstrate the effects of various noise reduction measures. The main objective was to reduce the number of metal-to-metal impacts involved in the various materials handling operations, and to apply treatments to reduce impact noise at source or by locally enclosing particular operations. Some means of limiting the time for which doors were left open was also considered essential: the existing doors were manually-operated and tended to be left open for long periods when forklift trucks were loading a vehicle in the yard.
The rapid-action doors have proved to be particularly effective and practicable, reducing door open times to a minimum. The finishing area does not generate significant heat, and there is local air extract from fettling benches, and no adverse effects on building ventilation have been observed.
The lining treatment to hoppers and inspection chutes reduces maximum noise levels (Lmax) from component impacts by 10 - 15 dB(A). The material is extremely durable and has reasonable low-friction properties, although castings sometimes have to be 'assisted' down the chutes from the inspection benches. The main drawback is cost, around £100 per square metre.
Noise from wheelabrator loading and unloading operations has been reduced by 57 dB(A) Lmax.
The bin-lifter device was effective in eliminating a tipping operation but lack of floor space precluded the widespread use of these devices, without major changes to layout.
Overall, average noise levels at the boundary have been reduced by around 5 dB(A), and the noise 'peaks' associated with the various impact sources are subjectively far less apparent. The major remaining source is impact noise from loading the hoppers at the fettling benches. Further work is in progress to construct a partial wall between the fettling and inspection areas to limit the spread of noise from this area into the inspection area, and to outside.
The various measures, although intended to demonstrate reductions in external noise, have also significantly reduced work-area noise.
| Cost: | Approximately £25k |
| Contractors/suppliers: | Clark Door Limited |
| The Noise Control Centre | |
| Polyurethane Products Ltd. |
This is a large site with two forge shops. The larger shop houses 6 hydraulic and gravity forging hammers and 3 forging presses. Billet heating is mainly by electric induction. There are two bar cropping machines in an adjoining shop. There is a history of complaints from residents who live 60 - 100 metres away from the large forge, mainly concerning noise in the early morning.
The forge building is mainly of corrugated sheeting on a steel frame, with some lower walls of brick. The roof sheeting incorporates translucent sheeting, to provide some natural light, and has open roof shutters and full-length ridge openings for ventilation. Access is through roller shutter doors. The layout is shown on the sketch below.
Fig 3: Clydesdale Forge Company - Site Layout
The main noise sources were identified as follows:
Previous noise surveys revealed average (Leq) typical noise levels of 60 - 62 dB(A) at the nearest houses. The impulsive character of the noise was clearly a major feature. Noise levels inside the main forge are 94 - 102 dB(A).
The high external noise levels result from the high noise levels inside the main forge and the poor sound insulation provided by the building. The feasibility of enclosing individual forging units, to reduce noise within the forge, was assessed. This approach was judged impracticable because of problems of access for production and maintenance. There was no prospect of reducing noise from the hammers and presses at source. The more obvious but potentially the most costly approach was to improve the sound insulation of the building.
Following preliminary costing exercises, this was the course of action adopted.
The building modifications (cladding and doors) were carried out successfully with little or no disruption to production.
Installation of the forge ventilation system involved some out-of-hours and weekend working for access to install high-level ductwork. It became apparent the ventilation was inadequate to maintain reasonable working temperatures close to the forging units during warm weather. This problem could not be overcome by local 'man-cooler' fans or portable evaporative cooler units. It was resolved by the addition of a powered extract system, together with uprating the supply fan, to provide an air change rate of 10 changes per hour. The retention of adequate ventilation to control internal temperatures is clearly a major concern, since to obtain significant improvements in sound insulation it is necessary to close off any unsilenced openings in the building.
Measurements after completion of works demonstrated that with doors closed, noise emitted from the forge building and cropper bay had been reduced to less than 48 dB(A) at the nearest houses, a reduction of about 14 dB(A). Actual noise levels remained above 50 dB(A), because of the steady noise from the heat exchanger fans. However, with these fans running the impact noise from the forging units cannot generally be distinguished, and the 'masking' noise they create is probably beneficial.
Compressor noise is not generally detectable beyond the site boundary.
| Costs: | Approximately £200k |
| Contractors/suppliers: | UK Industrial Roofing Ltd. Fumac Ltd. Clark Door Ltd. Amber Doors Ltd |
.
This is a foundry with housing in close proximity on two sides. There is a history of noise complaints, most of which have been resolved by major works - installing a new cupola, improving buildings, and re-locating the stockyard. Some problems remain, including noise from the two shot-blast machines in the finishing shop, which is a lightweight building close to the boundary. It is sometimes necessary to work these machines during the evening, and the loud crashes during loading and unloading can be audible in residential areas (although it may be masked by noise from passing traffic). Within the finishing areas, short-term average noise levels during loading and unloading the shot blast machines are around 100 dB(A). There is also a more general problem of noise from materials being dropped into stillages, particularly in open areas.
|
|
 1.
Two skins of 1.6 mm x 25 mm strips, close butted |
 3.
Woven 1.6 mm x 25 mm strips, 20 mm square openings |
 2.
Two skins 2.0 mm x 1.2 mm randomly spot welded |
 4
3.2 mm, 40% perforated |
The shot blast machine enclosures reduced noise levels from these machines, during loading and unloading, by 10-12 dB(A). However, maintaining this reduction has proved difficult because the enclosures, particularly the doors, suffer regular impact damage from forklift trucks. This is to some extent the result of limited access round the machines. made even more limited by the enclosures. More robust enclosures and local barriers would alleviate this problem, but probably not resolve it (and barriers round the enclosure would further restrict access).
The quiet stillages reduced maximum impact nose levels, when dropping a single casting, by up to 15 dB(A) Lmax. Average noise levels Leq,10s when dropping a load of scrap into the stillages were reduced by 7 - l0 dB(A). The quiet stillages are also noticeably quieter when carried on a forklift truck, unloaded - the characteristic metallic rattle at the stillage bounces on the forks is noticeably dulled. There is clearly scope for further development, and for consideration of adoption of a 'quiet' design as standard. The most practicable alternative to the standard single-skin construction is the double-skin spot-welded type. This would seem to have no significant disadvantages (apart from first cost) compared with the standard stillage. Other types are likely to be less robust. The 'woven' type, although very effective, appears more liable to damage and to components becoming 'hooked' into the mesh.
The double-skin technique can also be used effectively on chutes and tables which are subject to metallic impact. This form of construction is unlikely to be as effective as a resilient lining in reducing impact noises, but it has the advantage of being suitable for dealing with hot components.
| Costs (typical) | Shot blast machine enclosures: £20k |
| Quiet stillages (each) £200 - £300 |
|
| Contractors/suppliers: | The Noise Control Centre |
The CD or video tape which accompanies this handbook gives further information about these projects.
This project was conceived in 1996 by forging and foundry industry groups, the Black Country local authorities (the Boroughs of Dudley, Sandwell, Walsall and Wolverhampton) and the GMB Union. It was perceived that companies in these industry sectors were experiencing a growing number of complaints from local residents concerning the environmental impact of their operations, from smoke, dust, fumes, odour, vibration and noise. These problems were to a large extent due to the location of the forges and foundries in the Black Country. These traditional industries are often based on sites which are within or close to residential areas.
There was a general concern that the profitability and even viability of some companies might be seriously compromised by adverse community reaction to their operations, with consequent effects on the local economy and on employment. The extent of the perceived problem was investigated by questionnaire, which was sent to approximately 170 forges and foundries during October and November 1996. The company list was compiled by the GMB Union from information provided by the Confederation of British Forgers (CBF), the British Foundry Association (BFA), local authorities and other sources. From this survey, it was concluded that a significant number of companies, accounting for perhaps 3000 jobs (out of a total of 10,000 in this industry sector in the Black Country) were receiving complaints about environmental problems which they thought might adversely affect their ability to maintain or expand their businesses.
Noise was clearly identified as the most widespread cause of unresolved problems.
As a result of this preliminary survey, a project proposal to investigate environmental noise and vibration in the forging and foundry industries was developed jointly by industry, local authorities (led by Dudley MBC) and the GMB Union. This proposal was submitted by Dudley MBC to the Government Office for the West Midlands, and was accepted for grant assistance under the Regional Development Fund in November 1997.
The overall objectives of the project were:
To make contact with (as far as possible) all forges and foundries in the Black Country area and to identify companies interested in participating in the project.
To collate the experience of these companies and to identify the principal causes of environmental noise and vibration problems in these industries.
To carry out a review of published research into noise and vibration in these and related industries.
To identify the techniques and solutions currently available to deal with the most widespread noise and vibration problems experienced by forges and foundries, and to identify where innovative solutions might be required.
To carry out, if appropriate, theoretical and experimental research into novel methods of noise and vibration control, suitable for the specific conditions in these industries.
Reports on the Research phase of the project can be seen on-line on the CMB website (see cover page for contact details)
To set up, within forges and foundries, pilot projects to demonstrate and further develop cost-effective and practicable methods of noise and vibration control. To implement the pilot projects.
To disseminate the project outcome throughout the industries through organised visits to completed pilot projects, journal articles, presentations and other media.
The progress and direction of the work was supervised by a Steering Committee comprising:
| N Powell | Dudley MBC |
| R Winzer | Dudley MBC |
| J Mundell | Woodcote Industries Limited (CBF) |
| J Wood | Caparo Engineering Limited (CBF/BFA) |
| J Young | Henley Foundries Limited (BFA) |
| B Johnson/C Humphries | GMB Union |
| B Parkin/G Field | CBM (Confederation of British Metalforming) |
| J Parker | CMF (Cast Metals Federation) |
Some meetings were also attended by G Johnston (representing S Murphy MEP). Contracts for technical work were placed with the following consultants:
ISVR Consulting, University of Southampton
(Acoustics Consultants)
Paul Mantle Partnership, Halesowen
(Building Consultants and Quantity Surveyors)
Engineering Design Partnership, Alcester
(Building Services Consultants)
Structural Design Services Ltd., Stourbridge
(Consulting Civil & Structural Engineers)
Tunnicliffe Wall Associates, West Bromwich
(Building Services Consultants)
Contracts for video/CD production were placed with:
LBV Television, Northorpe, Lincolnshire.
Frequency (or pitch) is measured in hertz (Hz) or cycles per second. The normal human ear can detect frequencies between about 20 Hz and 15,000 Hz, although it is most sensitive to sound in the range of frequencies between 500 Hz and 5,000 Hz.
Sound at a single frequency of (say) 100 Hz might be described as a low-pitched 'drone' or 'hum'. Sound at a frequency above 1,000 Hz might be described as a 'whine' or 'whistle;. Most industrial noise arises from a large number of machines and processes and contains a range of frequencies.
The magnitude of the changes in air pressure are used to determine the sound (or noise) level. The human ear is very sensitive and can detect very small repeated changes in air pressure, as low as around 20 micropascals (2x10-5 Pa). Repeated changes in pressure greater than about 200 pascals are perceived as painfully loud noise and can damage the hearing instantaneously. Even this is a very small change in pressure compared with the mean steady atmospheric pressure of 100,000 (105 Pa). For a number of reasons which we do not need to explain here, noise levels (or sound pressure levels) are almost always measured in decibels (dB). In decibels, the range of sound pressures between 20 microPa and 200 Pa is represented by a scale from 0 dB to 140 dB. Most commonplace sounds have levels between about 20 and 100 dB. The decibel scale is logarithmic - each increase of 10 dB means that the sound energy has increased by 10 times, so that (for example) if a machine produces a noise level of 70 dB, ten machines of the same type would produce 80 dB and 100 machines would produce 90 dB. It follows that decibel levels cannot be added in the normal way - two machines each giving 70 dB would give 73 dB, not 70 + 70 =140 dB (which would be the noise level produced by 10 million of these machines!)
Noise levels are most often measured using a sound level meter. This is a hand-held instrument using a microphone connected to an amplifier and signal processing circuitry to provide a direct indication, usually on a digital display, of the noise level in dB.
As pointed out above, the human ear is not equally sensitive to all frequencies of sound. This means that a simple statement of a noise level in decibels does not describe the apparent loudness of the noise. This has been overcome to some extent by the use of electronic filters or 'weighting' networks in sound level meters to simulate the frequency response of the ear. For most purposes, the weighting network called 'A' is used. Noise levels measured using a sound level meter using the 'A' weighting network are expressed in dB(A).
Many sound level meters, except the simplest, can also provide information about the frequency content of the measured noise as well as giving an overall dB(A) level. This extra information is often vital for identifying a particular source of noise or for devising methods of noise control. The most basic form of frequency analysis is so-called octave band analysis, where the noise can be 'split' by electronic filters into frequency bands which are identified by their centre frequency. The standard octave band centre frequencies are 63, 125, 250, 500, 1000, 2000, 4000 and 8000 Hz. More sophisticated meters and specialist frequency analysers can analyse noise in more detail using filters of narrower bandwidth.
The level of a steady noise can be described by a single measurement in dB(A). However, noise levels are rarely steady. Noise may fluctuate slowly, or may change rapidly from second to second. Noise caused by impacts, such as the operation of a forging hammer or castings being dropped into a steel bin, or by explosions such as gunshots, is termed 'impulsive'. Additional units of measurements are needed to describe non-steady and impulsive noises. Three commonly-used measurement units (there are many others) are:
The equivalent continuous level or Leq,T This is a time-average level over time T. For example, if a noise level is stated as being 60 dB(A) Leq,5min this means that the time average level over a period of 5 minutes was 60 dB(A). The time average level gives no information about the range of noise levels actually occurring during the measurement period.
The maximum noise level Lmax. Lmax is the highest noise level during the measurement period. For impulsive noises, the value of Lmax depends on the response time of the sound level meter. Most meters have two response time settings termed 'fast' or 'F' and 'slow' (S), which are defined by international standards. A measurement of Lmax using the 'fast' setting would be expressed as (for example) 70 dB(A) Lmax(F).
The noise level exceeded for a given percentage of the time, LN. The L90 noise level is often used to describe the noise level during the quietest periods of a measurement. L90 is the noise level exceeded for 90% of the time - for example, 45 dB(A) L90.
The meaning of these noise measurement units is further illustrated on the figure below, which shows the values of Leq, L90 and Lmax for a measurement period during which the noise varies in level with time and includes some impulsive sounds (the sharp 'peaks' on the graph).
Fig 5: Different noise measurement units
Measurement and assessment of vibration is outside the scope of this handbook, and it is likely to be beyond the scope of most manufacturing companies. Measurements generally involve the use of transducers called accelerometers, which are fixed to the surface (the ground or part of a building) to be measured. Vibration intensity or level is commonly expressed in terms of the peak particle velocity (p.p.v.) in millimetres per second (mm/s), although other units are widely used.
Standards for assessing the response of people and structures to vibration are given in refs 5 and 6.
The following provide a useful introduction to the principles and practice of noise control.
(i) Noise Control in Industry. Sound Research Laboratories Limited. Pub. E & F N Spon.
(ii) Woods Practical Guide to Noise Control. Pub. Woods of Colchester Limited.
(iii) *Sound Solutions. Techniques to reduce noise at work. HSE Books. HMSO (1995).
*Note: HSE Publications on noise are directed primarily towards reducing noise in the workplace. However, many of the principles are equally applicable to the reduction of neighbourhood noise. Some HSE reports and notes are specifically about reducing noise in forges and foundries.
The following organisations can provide general information on how to approach noise problems, and can give assistance in locating specialist advice:
Confederation of British Metalforming
Cast Metals Federation
Both at:
Association of Noise Consultants
6 Trap Road
Cast Metals Federation Tel: (0121) 601 6390 Confederation of British Metalforming Tel: (0121) 601 6350
Both at:
National Metalforming Centre
