Some sound advice

Hearing protection equipment should always be the last
resort when managing noise in the workplace but once it is
deemed necessary there are a number of points to consider
in the selection process, explains Sarah Broadbent

The Control of Noise Regulations
details two noise action values
and one exposure limit value for
noise exposure. If the lower action value
of 80dB(A) or 135dB(C) is exceeded,
employers must offer HPE upon request.

Where exposure exceeds 85dB(A) or
137dB(C), employers must provide HPE if
noise cannot be reduced by other means.

The limit values of 87dB(A) or
140dB(C) must not be exceeded under
any circumstances.

Ensuring levels are not exceeded
requires accurate assessment of the noise
type. Specialist equipment is available for
use by in-house safety managers to
measure noise levels, while external
consultancies provide the same service.

Too much protection can be as
bad as too little
British Standard EN458 suggests an
exposure level between 75 and 80dB(A) as
ideal, with 70-75dB(A) and 80-85dB(A)
as acceptable. Anything above 85dB(A) is
deemed excessive noise likely to cause
hearing damage. Conversely, wearing
HPE which reduces noise below 70dB(A)
can cause other problems, as the
employee may experience difficulties in
communication or hearing warning
signals and become isolated from their
environment.

Attenuation can vary greatly with noise
frequency – a product’s overall
effectiveness depends on the frequency
content of incident noise.

Three main methods are used to
calculate sound pressure levels at the ear
when wearing HPE.

The most accurate is octave band
analysis, based on octave band
measurements of the noise’s sound
pressure level.

The High, Medium, Low (H, M, L)
method requires measurement of the Aweighted
(LA) and C-weighted (LC)
sound pressure levels. The H, M, L values
supplied by the manufacturer can be used
to estimate protection required.

The third is the Single Number Rating
(SNR) method requiring measurement of
the C-weighted (LC) sound pressure level.

The SNR value (taken from the
manufacturer’s data) minus the LC value
allows calculation of the effective Aweighted
sound pressure level.

Not everyone will achieve identical
attenuation with an identical item – if
HPE is incorrectly fitted, lower protection
will be achieved. Protection will also
suffer if HPE is dirty or poorly
maintained, or if there are compatibility
issues with other personal protective
equipment (PPE).

“Real world” attenuation
For these reasons, the HSE’s “Controlling
Noise at Work” document suggests a “real
world” factor of 4dB be applied, meaning
when calculating the actual protection
level, 4dB should be deducted from the
manufacturer’s predicted figure.

Another method is to add 4dB to the
calculated sound pressure level (LA) at
the ear under the HPE worn.

With the required attenuation level
calculated, including the 4dB “real world”
allowance, several other selection factors
must be considered.

Key factors affecting
specification
Products must be suitable for the work
undertaken – durable enough and not
needing regular adjustment. HPE must be
compatible with other PPE worn – for
example, an operative wearing a welding
shield will be unlikely to be able to wear
ear muffs underneath. In this instance, ear
plugs or banded ear plugs siting under the
chin or behind the neck may be more
appropriate.

HPE must also account for noise
exposure patterns – for example,
continuous noise or intermittent loud
bangs – and allow for communication if
required. Some HPE offers built-in
communication radios or level-dependent
ear muffs which electronically analyse
sound before transmitting to the ear.

Bluetooth can also be built in, offering
communication and radio capabilities.

The environment where HPE will be
used is a key consideration when choosing
between disposable and reusable HPE –
products used in dirty or dusty
environments are likely to require
frequent cleaning and daily visual
inspections for wear and damage.

However, for all HPE to remain effective,
it is good practice to establish a care and
maintenance policy with employees
undertaking the simple checks required.

Comfort and user acceptance are vital.

Any usage level under 100 per cent in the
exposed area can significantly reduce the
HPE’s effectiveness. Not wearing HPE for
30 minutes during eight hours’ exposure
will reduce attenuation to near zero.

The process should also establish
whether users have any medical disorder
influencing selection, such as earache, ear
canal irritation or hearing loss. In this
instance, the employer should seek
medical advice on the suitability of
hearing protection.

Once the decision on HPE is made,
training and information must be provided
how to fit it, when to put it on, and how to
care and maintain it. A health surveillance
programme should also be established.

Sarah Broadbent is a technical engineer for
occupational health & environmental safety
at 3M. See 3M on Sta