Environmental Engineering Reference
In-Depth Information
recorded electrophysiologically. This showed that the lengths of sleep stages were
similar to matched age and sex normal values quoted in the sleep research literature
(eg Hume et al, 1998). However, finer analysis of the data (Hume et al, 2000) showed
that there were clear but small effects within the subjects, with increased shifts to stage
1 (drowsy) sleep, wake and minor perturbations in association with aircraft noise
events. Again, the health consequences of these minor perturbations of the ongoing
sleep process due to aircraft noise are unknown.
Subsequent studies in the US (Fidell, 1995) using behavioural criteria in which
subjects had to press a button to indicate awakening corroborated the UK study, indi-
cating that, unlike laboratory studies, awakening in the home due to aircraft noise,
except in the noisiest locations, is a rare event and only weakly correlated with the noise.
It should not be forgotten that mean values tend to obscure the considerable indi-
vidual differences in noise sensitivity and sleep fragility. There was a large variation in
the degree of sleep disturbance (2.5 times) between the least and most sensitive third
of subjects who had EEG recorded (Hume et al, 2000; Van et al, 1993) in the Oller-
head et al (1992) study.
The threshold for noise-induced awakening is usually quoted at about 55-
60dB(A), but sleep stage changes and minor arousals without perceived awakening
can occur at much lower noise levels (HCN, 1997; Berglund and Lindvall, 1995;
Hume et al, 2000). It is also thought that intermittent noise is more disturbing to
sleep than continuous noise, and leads to decreased time in slow-wave sleep (Carter,
1996). These findings corroborate Ohrstrom and Rylander (1982), who concluded
that intermittent noise leads to poor performance and mood the following day.
Fidell et al (1995) also found that individual noise intrusions were much more closely
related to annoyance/awakenings than long-term noise exposure.
Porter et al (2000) reviewed the potential adverse effects of night-time aircraft noise
as part of a continuing research effort by the UK government. Despite concluding that
there was no hard scientific evidence of clinically significant health impairment, the
possible existence of cause-effect relationships could not be rejected. A model of objec-
tive and subjective outcomes with linked chains of potential cause and effect was
elaborated, which included:
•
immediate physiological responses due to noise events that could lead to acute
annoyance;
•
total night effects as a sum of the immediate responses (eg sleep reduction and
fragmentation);
•
next-day effects, including increased sleepiness and reduced performance, caus-
ing perceived sleep disturbance, increased tiredness and annoyance;
•
chronic effects that may be a deterioration of physical and mental health, with
accompanying chronic annoyance and reduced quality of life.
The authors noted the potential confounding influence of modifying factors, such
as attitude to the noise source, which could strongly influence the cause-and-effect
chain within the model.
Everyday experience strongly suggests that a 'good' night's sleep is important for
one's well-being. The evidence from field studies indicates that the level of sleep dis-
turbance for most individuals is minor and, as such (given the strong homeostatic
