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NFPA. The National Fire Protection Association is a voluntary membership organization whose aim is to promote and improve fire protection and prevention. The NFPA publishes 16 volumes of codes known as the National Fire Codes.

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.

NTP. National Toxicology Program. The NTP publishes an Annual Report on carcinogens.

N.O.S. entry (not otherwise specified entry). A collective entry to which substances, mixtures, solutions or articles may be assigned if they:
(a) are not mentioned by name in Table A of Chapter 3.2; and
(b) exhibit chemical, physical and/or dangerous properties corresponding to the Class, classification code, packing group and the name and description of the n.o.s. entry.
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.