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Attachment 3 2 5 Environmental Sound Page 14 Nafiona] Standard The use of DNL, for land-use planning has been standardized in a national standard, ANSI S 12.9 Part 5 Sound LevelI)escriptors for DeterminationofCompatible Land Use, Note thatthis is forplanningthe use of land with an existing noise exposwe, rather than for evaluating impact of a new noise on existing development. An appendix to this standazd (which is notstrictly apart ofthe standaid) gives examples of compatible day-night levels for vazious land uses, It indicates that single-family homes with extensive outdoor use are compatible with day-night levels of 55 dBA and less, and marginally compatible in the range of 55 to 65 dBA, International Guidelines The World Health Organization (WHO)has guidelines indicating that "serious annoyance" should be expected in residential areas ifthe average sound levelexceeds 55 dBA in the daytime or45 dBA at night, with "moderate annoyance" for levels 5 dB lower, The WHO also suggests a limit of 60 dBA on the maximum event level at night to protect from sleep disruption. The World Bank Group has guidelines to inswe that their projects in developing countries do not create problems. They require that financed industrial projects not exceed average levels of 55 dBA in the daytime and 45 dBA at night at residential locations. These recommendations are supported by the IntemationalOrganizationforEconomic Co-operation and Development, which further recommends levels 5 dB lower in rural azeas, ><rocal Noise Ordinances The firstknown local noise ordinance containing specific measured noise limits was adopted by Chicago around 1955. It followed an extensive survey of existing city sounds. The limits were expressed iri octave-bands. These were inning regulations aimed primarily at industry. Initially, they applied to steady sounds only and were the same day and night, The equivalent A-weighted levels were 61 dBA for sound entering other business areas; and 54 dBA for sound entering residential areas.. The survey showed that only one percent of the industry in the city would need to act to meet the limits. Ordinances m ay be wring performance standards for new sources, or general ordinances enforced against any source, Zoning perforrriance standards will more commonly include octave band limits and can be more stringent than general ordinances to limit the growth of noise. General ordinances usually aze kept simple and based on measurements over periods typically less than an hour, They cannot be a full assessment of the long-tens noise environment, The limits in them should be appropriate for the measwement method and length of measwement specified. Thus, for a short measurement period, limits should be set a little higher so as not to restrictunduly a sound that only lasts a short period, The limits also