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IAQ Glossary N


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N.C.: Normally closed contacts of a relay. Contacts are close-circuited when the relay is de-energized.

NEPHROTOXIN: A chemical which has a primary toxic effect on the kidneys.

NEUROTOXIN: A chemical which has a primary toxic effect on the central nervous system. Styrene, mercury, carbon disulfide.

N.O.: Normally open contacts of a relay. Contacts are open-circuited when relay is de-energized.

NATURAL VENTILATION: The movement of air into and out of a space through intentionally provided openings, such as windows and doors, or through nonpowered ventilators or by infiltration.

NIOSH: The National Institute for Occupational Safety and Health is a federal agency. It conducts research on health and safety concerns, tests and certifies respirators, and trains occupational health and safety professionals.

NOISE CRITERIA CURVES (NC CURVES): Curves that define the limits which the octave band spectrum of a noise source must not exceed if a certain level of occupant acceptance is to be achieved.

NOISE REDUCTION (NR): The difference between the average sound pressure levels of two spaces. Usually these two spaces are two adjacent rooms called, respectively, the source room and the receiving room.

NORMALLY OPEN (OR NORMALLY CLOSED): The position of a valve, damper, relay contacts, or switch when external power or pressure is not being applied to the device. Valves and dampers usually are returned to a "normal" position by a spring.

NOSOCOMIAL INFECTIONS: The type of infections that are acquired in hospitals.

NUISANCE DUST: Have a long history of little adverse effect on the lungs and do not produce significant organic disease or toxic effect when exposures are kept under reasonable control.

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