5958_MCA Noise v2_4.indd - Institute of Sound and Vibration ...

Code of Practice for Controlling Risks due to Noise on Ships
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7.3.1.1 Types of hearing protectors
7.3.1.1.1 Ear plugs
The simplest form of hearing protection is the ear plug, which works by
fitting into the external ear canal to block noise from reaching the eardrum.
Modern ear plugs are made of soft plastic in a variety of shapes and colours.
Some disposable plugs are made of easily malleable plastic foam, formed
into a cylinder or cone. These are to be compressed by rolling between the
fingers to make a smaller diameter, inserted into the ear canal, and held in
place until they expand to conform to the shape of the canal. When the
expansion is complete after a few seconds, the foam plugs make a good
noise‑tight seal against the skin.
There are drawbacks to such malleable plastic ear plugs. Because the plugs
must be fingered during installation, they can become fouled by dirty
hands. Foam plugs can be washed between insertions, for re‑use a few
times. Alternatively, the plugs be discarded after one use; this will become
expensive after a while. The employer must ensure that sufficient supplies
of disposable plugs are onboard, to last for a voyage.
Other sorts of ear plugs come pre‑moulded in flexible plastic, sometimes
sized for small and large ear canals. These can take fanciful shapes, resembling
a mushroom or a Christmas tree. Such pre‑formed plugs may be washed and
re‑used repeatedly.
It is also possible to acquire individually‑moulded inserts for each employee.
These inserts are moulded to fit the right and left ear canals of each worker;
they cannot be used by anyone else. The taking of ear impressions and the
associated lab work to produce the final protectors make this option very
expensive.
Whatever type of ear plug is chosen, they will usually come in some bright
colour that contrasts with the skin. This is an attempt to make them visible
at a distance, so their use may be monitored.
7.3.1.1.2 Ear muffs
In general, ear muffs provide a more effective form of hearing protection.
They consist of a pair of rigid plastic cups designed to completely envelope
the ears; each cup is fitted with soft‑sealing cushions to fit closely against the
head around the ears. The ear cups are connected by a springy headband (or
neck band) which ensures that the cushions press gently around each ear to
produce a noise‑tight seal. Different types are available and provision should
be made according to the circumstances of use, possibly with other items of
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