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Mr R W Fearn in his report refers to the need to keep sound levels
below a rating of N85 which is 85 decibels. Some normal levels
found in this country are
Countryside 25 decibels
Quiet bedroom 35 decibels
Road noise 40 to 79 decibels
Conversation 60 decibels
Busy general office 65 decibels
Back seat of car at 40 mph 75 decibels
Unmuffled road drill at 50 ft 85 decibels
Alarm clock (at 3 ft) 88 decibels
Heavy diesel lorry (at 20 ft) 88 decibels
Lathe 86-95 decibels
Mechanical saw 100-110 decibels
Sand blasting . 118 decibels
Rivetting 130 decibels
Jet aircraft (taking off at
25 yds) 140 decibels
A decibel is a unit on a logarithmic ratio of measurement based on
a reference level which is the threshold of hearing. Thus a
zero decibel level is the quietest sound which can be heard by the
normal human ear and an increase of three decibels is the minimum
change which is likely to be distinguished without the
opportunity of direct comparison. Similarly, because it is a
logarithmic scale a change of ten decibels represents a doubling
of the loudness in subjective terms. Measurement of noise is a
complex and difficult problem.
In assessing the potential danger of noise, the intensity, the
varieties of pitch and the duration of exposure all need to be
taken into account. In industry, levels of exposure which should
not be exceeded, are laid down as guidelines. Unfortunately,
there are individuals whose hearing may be damaged more easily.
In general, however, exposure to levels above 130 decibels can be
considered as hazardous to hearing irrespective of the duration of
exposure or of the composition of the noise. Mr Fearn's readings
gave maximum levels of 115 decibels and at this level for the
non-sensitive person it is necessary to assess the composition of
the noise, the duration of exposure and the frequency of exposure.
A small number of well documented studies have failed to show any
definite damage to hearing of rock and roll or pop musicians.
This may be due to:-
(a) the breaks in the noise during the session,
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