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NACE: National Association of Corrosion Engineers.

NAPPED: The rupturing of the filling yarns to produce a fleecy surface on woven fabrics.

NATURAL FREQUENCY: The frequency at which a component or system resonates.

NEC: National Electrical Code.

NEEDLED FELT: A felt made by the placement of loose fiber in systematic alignment with barbed needles. The needles move up and down, pushing and pulling fibers to form an interlocking of adjacent fibers. It is the most commonly used construction method since it is stronger than pressed felt.

NEDS: National Emission Data System.

NEMA (The National Electrical Manufacturers Association): The trade association establishing standards of dimensions, ratings, enclosures, insulation and other design criteria for electric motors.

NESHAP: National Emissions Standards for Hazardous Air Pollutants.

NEW SOURCE: A stationary source; the construction or reconstruction of which is commenced after the proposal date of the standard. Also NSPS (New Source Performance Standard).

NFPA: National Fire Protection Agency.

NIOSH (NATIONAL INSTITUTE FOR OCCUPATIONAL SAFETY AND HEALTH): Created by the Occupational Safety and Health Act of 1970, NIOSH is part of the Centers for Disease Control under the Department of Health and Human Services. Its mandate includes conducting research in developing criteria and/or recommendations to be used in setting occupational exposure standards, identifying and evaluating workplace hazards, measurement techniques and control technologies, and providing professional education as well as health and safety information.

NOISE CRITERIA: A way for an architect to specify the maximum permissible sound power level in each of the eight octave bands NC curves give. In a graphical form, maximum permissible intensity per octave band.

NON-ATTAINMENT AREA: An area that has not achieved air quality as good as the National Ambient Air Quality Standards as defined by the CAAA.

NON-WOVEN FELT: A felt made by either needling, matting of fibers or compressed with a bonding agent for permanency.

NOX (NITROGEN OXIDES): Chemical compounds containing nitrogen and oxygen. Reacts with volatile organic compounds in the presence of heat and sunlight to form ozone. It is also a major precursor to acid rain. Nationwide, approximately 45% of Nox emissions come from mobile sources, 35% from electric utilities, and 15% from industrial fuel combustion.