Glossary of Terms: N

National Electrical Manufacturers Association (NEMA)
US standards developing organization. NEMA rating of enclosures is similar to the IP rating system.
Natural gas
Fossil fuel formed almost entirely of Methane.
Nature of Injury or Illness
The main physical characteristics of a workplace injury or illness (for example, burn, cut, sprain, dermatitis, hearing loss).
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.
Noise
Any unwanted sound, particularly those that can lead to hearing loss or stress, or interfere with the ability to hear other sounds or to communicate.
Noise Dosimeter
A small instrument that measures personal exposure to noise, usually worn clipped to an employee pocket or hard hat. Calculates TWA and Dose.
Noise floor
The signal magnitude at the bottom of the instrument’s linear range. Input signals below the noise floor cannot be differentiated from the internal noise of the instrument. Measurements must always be at least 5 dB above the Noise Floor to be valid.
NRTLs
Nationally Recognized Testing Laboratories (US).
Nuisance Dust or Particle
Dust that does not cause disease or harmful effects when exposures are kept at reasonable levels. It does not produce significant organic disease or toxic effect when exposures are kept under reasonable control.