Serious reduction in alertness, Attention lapses occur, although attention duration is usually not affected.
Temporary hearing loss occurs if no protection is provided in the region 600-1200 Hz. Most
peoples will consider this level unacceptable, and 8 hour is the maximum duration they will accept.
95 Considered to the upper acceptance level for occupied areas where people expect the environment be
noisy. Temporary hearing loss often occurs in the range of 300-1200 Hz. Speech will be extremely
difficult, and people will be required to shout, even through they may be talking directly in to a
listener’s ear.
90 At least half of the people in any given group will judge the environment as being too noisy, even
through they expected a noisy environment. Some temporary hearing loss in the range of 300-1200 Hz
occurs. Skill errors and mental decrements will be frequent. The annoyance factor is high and certain
physiological changes often occur.
85 The upper acceptance level (noise expected) in the range of 150-1200 Hz. Some hearing loss occurs
in the range of 300-1200 Hz. This is considered the upper comfort level, although some cognitive
performance decrement can be expected, especially where decision making is necessary.
80 Conservation is difficult i.e. people have to converse in a loud voice less than 30cm (1ft) apart. It is
difficult to think clearly after about 1 hour. There may be some stomach contraction and an increase in
metabolic rate. Strong complains can be expected from those exposed to this level is confined spaces,
and 8h is the maximum duration acceptable within the frequency range 1200-4800 Hz.
75 To noisy for adequate telephone conservation. A raised voice is required for conversation from 60 cm
(2ft) apart. Most people will still judge the environment as being too noisy.
70 The upper levels for normal conversation, even when conversation are close together (at a distance of
1.83m (6ft) people will have to shout). Although persons such as industrial workers and shipboard
personnel who are used to working in a noisy environment will accept that this noise level, unprotect
telephone conversation will be difficult (upper telephone level is 68dB).
65 The acceptance level when people expect a generally noisy environment. Intermittent personal conversation
is acceptable. About half of the people in a given population will experience difficulty in
sleeping.
60 The upper limit for spaces used for dining, social conversation, and sedentary recreational activities.
Most people will rate the environment as ‘good’ for general daytime living conditions.
55 The upper acceptance level for spaces where quite is expected (150-2400 Hz.). People will have to raise
their voices slightly to converse over distances greater than 2.44 m. (8ft.). This level of noise will
awaken about half of the given population about half of the time. It is still annoying to people who are
especially sensitive to noise.
50 Acceptable to most people where quiet is expected. About 25% will be awakened or delayed in falling
sleep. Normal conversation is possible all distances up to 2.44 m.
40 Very acceptable to all. The recommended upper level for quite living spaces, although a few people
may still have sleeping problems.
30 Necessary for specialized listening tasks (e.g., threshold signal detection).
Below
30
Introduces additional problem, i.e., low-level intermittent sounds become disturbing. Some people have
difficulty getting used to the extreme quite and a few may become physiologically disturbed.