The gas utility areas to which this publication applies are those in which flammable gases are produced, manufactured, stored, transmitted and distributed. It is not intended to include plants of a refinery nature, such as natural gas stripping plants or gasoline plants.
In establishing the limits of classified locations, it is assumed that the gases of concern to this publication are materials classified under NFPA70-2005, as Group B or D in Article 500.6 or as Group IIA, IIB or IIC in Article 505.6 (see Appendix A).
Factors such as corrosion, maintenance, equipment standardization, and interchangeability and possible process changes or expansion frequently dictate the use of special enclosures or installations for electrical systems. Such factors are outside the scope of this publication, which is entirely concerned with the proper application of electrical equipment to avoid ignition of flammable vapors and gases. This publication further recognizes that certain environmental aspects of an installation, such as prevailing winds, site topography, proximity of other installations and climatic conditions, may exert sufficient influence to merit a classification other than that which would have been made had these conditions not existed.
All areas and distances indicated herein are guidance for a minimum level of safety and may be exceeded at the discretion of those responsible for the installation design.