A case of industrial plant close to residential buildings: technical problems and possible solutions

Italian laws on environmental noise establish two different limits (outdoors and indoors); the first one must be respected in the environment and has significance from the point of view of the territory management; the second one permits to protect citizens inside their houses, guaranteeing an adequate acoustic climate. Outdoors noise limits depend on the characteristics of the area and on the period (day or night); indoor values, called “differential limits” since they are based on the difference between noise measured with and without the disturbing source, vary only depending on the time period. With these premises, an industrial plant operating close to residential buildings has to respect both the limits imposed by the law. An important industrial plant in Umbria region, continuous cycle operating, respects the area limits but largely exceeds the differential limits referring to both periods; the overcoming reaches 18 dB(A) with opened windows and 13 dB(A) with closed windows. The best technical solutions, proposed by the owner and applicable to the plant, do not permit to reduce the noise levels to respect the limits, so, as requested by the Regional authority that considers this industrial activity too important from the social point of view, a specific study has been carried out by ARPA Umbria and University of Perugia, with the aim of finding out useful and applicable solutions comparing costs and benefits, not only for the industry but also for the community.