Awakening effects of church bell noise: geographical extrapolation of the results of a polysomnographic field study 1.

Based on a previously published exposure-effect model of Electroencephalography (EEG)-awakening reactions (AWR) due to nightly church bell noise events, as well as on geocoded building and population data, we estimated the total number of the church bell noise induced awakenings on the population of the Canton of Zurich, in Switzerland. The calculated mean number of EEG awakenings per person in the studied region, triggered by church bell ringing, varied between 0 and about 5.5 per night. The results suggest that up to 120-150 m distance from churches, on average more than one additional EEG awakening occurs per night per person. An estimated 2.5-3.5 percent of the population in the Canton of Zurich experiences at least one additional awakening per night due to church bell noise. To provide a simple decision support tool for authorities that consider limiting bell ringing in the night in some form, we simulated different scenarios to estimate the effects of different sound attenuation measures at the belfry as well as the effects of different lengths and positions of nocturnal bell ringing suspension periods. The number of awakenings could be reduced by more than 99 percent by, for example, suspending church bell ringing between midnight and 06 h in the morning. A reduction of the number of AWRs of about 75 percent could be achieved by reducing the sound-pressure levels of bells by 5 dB.