6.4 Controlling noise and noise exposure

Question 1

Lower
exposure
action
value

Answer 1

80 dB(A) 135 dB(C)

 Provide information and training.
 Make hearing protection available.

Question 2

Upper
exposure
action
value

Answer 2

85 dB(A) 137 dB(C)

  Take reasonably practicable measures 
to reduce noise exposure (engineering 
controls / technical measures). 
  Provide  mandatory  hearing  protection 
pending  engineering  controls  and, 
where  necessary,  after  engineering 
controls.

Question 3

Exposure

limit value

Answer 3

87 dB(A) 140 dB(C)

 Ensure level is not exceeded, taking
hearing protection into account.

Question 4

Noise transmission pathways

Answer 4

Noise energy can be transmitted directly through the air or can be transmitted
through other materials such as structural components. Noise energy also reflects off
solid surfaces.

Question 5

Noise control strategies involve controls at the

Answer 5

source, the pathway and at the

receiver

Question 6

The ability of a material to absorb, reflect and transmit sound can be measured. Two
particular indices are useful when specifying structural materials:

Answer 6

 The sound absorption coefficient indicates how well a material absorbs the
sound energy it receives. The higher the figure the more sound is absorbed. The
coefficient can be determined for sounds at different frequencies. It is calculated
as:

intensity of sound absorbed by material
intensity of sound incident on the same area of material

Sound absorption coefficients for common building materials can be found in
Approved Document E to the Building Regulations.

 The sound reduction index (SRI) or ‘transmission loss’ is a measure of the
attenuation provided by a material. It is the difference in dB between the noise
energy falling onto a material and the level transmitted through it. Real world
measures are unlikely to match the stated index which is determined by
laboratory tests and does not address secondary transmission pathways.

Question 7

Noise control hierarchy

Answer 7

 Eliminate the risks by doing the work in a different way or by eliminating or
minimising exposure to noise.
 Modify the work, process or machine to reduce noise emissions.
 Replace the tools and equipment used with lower noise alternatives.
 Arrange the workplace and workflow to separate people from the noise.
 Controlling the noise on its path from the source to reduce the noise reaching
people.

Question 8

Consider the source of noise:

Answer 8

 Replace the machine with one with lower noise emissions (if cost effective).
 Move the machine to an area with fewer employees (so long as it does not
disrupt production).
 Properly maintain the machine.
 Modify parts of the machine, for example: by replacing components with quieter
ones.

Question 9

Consider how the noise source radiates noise:

Answer 9

 Isolate or dampen any vibrating panels.
 Isolate the machine from the building with isolation mounts or foundations.
 Reduce the noise caused by impacts from falling material by adding damping
material to receiving trays and chutes and/or reducing the distance the material
falls.
 Line machinery guards with sound-absorbing material (taking care not to
compromise ventilation).
 Fit silencers to air and gas inlets and exhausts.
 Fit silencers to compressed air systems, or direct the exhaust away from the
working area.

Question 10

Consider the path of the noise:

Answer 10

 Position the worker away from the source of noise.
 Fit a suitably designed enclosure around a machine (if it does not require ‘hands
on’ operation).
 Position employees in a noise haven if enclosing the whole machine would be
difficult.
 Erect acoustic barriers or screens to separate quiet operations from noisy ones.
 Add absorptive materials to the building to reduce reverberant noise (echoes).
 Use active noise control to counter constant low-frequency tones from fans and
dryers.

Question 11

Technical controls

Answer 11

Screens and barriers - placing an obstacle between the noise
source and the people

Damping - adding material to reduce vibration and noise

Isolation - separate the machine from its surroundings and
supporting structures

Active noise control - electronically-controlled noise-reduction

Question 12

The receiver can be protected from the effects of noise by:

Answer 12

 positioning (distance)
 reduction of the time exposed
 provision of PPE.

Question 13

The following factors should be considered in selecting appropriate hearing
protection: 9

Answer 13

 types of protector, and suitability for the work being carried out
 noise reduction (attenuation) offered by the protector
 compatibility with other safety equipment
 pattern of the noise exposure
 the need to communicate and hear warning sounds
 environmental factors such as heat, humidity, dust and dirt
 cost of maintenance or replacement
 comfort and user preference
 medical condition of the wearer.

Question 14

The risk assessment should consider:

Answer 14

(a) the level, type and duration of exposure, including any exposure to peak sound
pressure
(b) the effects of exposure to noise on employees or groups of employees whose
health is at particular risk from such exposure
(c) so far as is practicable, any effects on the health and safety of employees
resulting from the interaction between noise and the use of ototoxic substances
at work, or between noise and vibration
(d) any indirect effects on the health and safety of employees resulting from the
interaction between noise and audible warning signals or other sounds that need
to be audible in order to reduce risk at work
(e) any information provided by the manufacturers of work equipment
(f) the availability of alternative equipment designed to reduce the emission of noise
(g) any extension of exposure to noise at the workplace beyond normal working
hours, including exposure in rest facilities supervised by the employer
(h) appropriate information obtained following health surveillance, including, where
possible, published information
(i) the availability of personal hearing protectors with adequate attenuation
characteristics.