National Electric Code
Codes of practice in the USA & Canada, which have differed largely from the unified IEC standards, define the permitted use of electrical equipment and approved wiring methods in industry.
The standard reference document for electrical installation is the National Electric Code (NEC) in USA and the Canadian Electric Code (CEC) in Canada. Electrical Equipment used in Ordinary, Wet and Hazardous (or Classified) Locations must be ‘listed’ by an accredited approval agency for use in the intended location.
In USA the NFPA (National Fire Prevention Association) is the body that establishes codes of practice for safe working operations in Hazardous Locations.
Typical reference documents are :-
NFPA 497 - Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas.
NFPA 499 - Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas
The hazardous locations include areas in which flammable, combustible or ignitable substances may occur in hazardous amounts.