of 85 db(a) and for impulse noise (instant events such as bangs or crashes) of 140 db(a). the agency published this recommendation along with its origin, noise measurement devices, hearing loss prevention programs, and research needs in 1972 (later revised june 1998) as an approach in preventing occupational noise-related hearing loss. the occupational safety and health administration (osha) within the department of labor issues enforceable standards to protect workers from occupational noise hazards. the permissible exposure limit (pel) for noise is a twa of 90 db(a) for an eight-hour work day. however, in manufacturing and service industries, if the twa is greater than 85 db(a), employers must implement a hearing conservation program. the federal aviation administration (faa) regulates aircraft noise by specifying the maximum noise level that individual civil aircraft can emit through requiring aircraft to meet certain noise certification standards. these standards designate changes in maximum noise level requirements by "stage" designation. the u.s. noise standards are defined in the code of federal regulations (cfr) title 14 part 36 – noise standards: aircraft type and airworthiness certification (14 cfr part 36). the faa also pursues a program of aircraft noise control in cooperation with the aviation community. the faa has set up a process to report for anyone who may be impacted by aircraft noise. the federal highway administration (fhwa) developed noise regulations to control highway noise as required by the federal-aid highway act of 1970. the regulations requires promulgation of traffic noise-level criteria for various land use activities, and describe procedures for the abatement of highway traffic noise and construction noise. the department of housing and urban development (hud) noise standards as described in 24 cfr part 51, subpart b provides minimum national standards applicable to hud programs to protect citizen against excessive noise in their communities and places of residence. for instance, all sites whose environmental or community noise exposure exceeds the day night average sound level (dnl) of 65 (db) are considered noise-impacted areas, it defines "normally unacceptable" noise zones where community noise levels are between 65 and 75 db, for such locations, noise abatement and noise attenuation features must be implemented. locations where the dnl is above 75 db are considered "unacceptable" and require approval by the assistant secretary for community planning and development. the department of transportation's bureau of transportation statistics has created a to provide access to comprehensive aircraft and road noise data on national and county levels. the map aims to assist city planners, elected officials, scholars, and residents to gain access to up-to-date aviation and interstate highway noise information. states and local governments typically have very specific statutes on building codes, urban planning, and roadway development. noise laws and ordinances vary widely among municipalities and indeed do not even exist in some cities. an ordinance may contain a general prohibition against making noise that is a nuisance, or it may set out specific guidelines for the level of noise allowable at certain times of the day and for certain activities. noise laws classify sound into three categories. first is ambient noise, which refers to sound pressure of all-encompassing noise associated with a given environment. the second is continuous noise, which could be steady or fluctuating, but continues for more than an hour. the third is cyclically varying noise, which could be steady or fluctuating, but occurs repetitively at reasonably uniform intervals of time. new york city instituted the first comprehensive noise code in 1985. the portland noise code includes potential fines of up to $5000 per infraction and is the basis for other major u.s. and canadian city noise ordinances. european region in 1995, the world health organization (who) european region released guidelines on regulating community noise. the who european region subsequently released other versions of the guidelines, with the most recent version circulated in 2018. the guidelines provide the most up-to-date evidence from research conducted in europe and other parts of the world on non-occupational noise exposure and its relationship to physical and mental health outcomes. the guidelines provide recommendations for limits and preventive measures regarding various noise sources (road traffic, railway, aircraft, wind turbine) for day-evening-night average and nighttime average levels. recommendations for leisure noise in 2018 were conditional and based on the equivalent sound pressure level during an average 24-hour period in a year without weights for nighttime noise (laeq, 24 hrs); who set the recommended limit to 70 db(a). 2018 who european regional office environmental noise guidelines noise source recommendation for day-evening-night average level (lden) recommendation for nighttime average noise (lnight) road traffic 53 db(a) 45 db(a) rail 54 db(a) 44 db(a) aircraft 45 db(a) 40 db(a) wind turbine 45 db(a) no recommendation