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, 2008 ed. (Recmm Prac: Class of Flamm Liqd, Gas or Vpr and of Haz (Class) Locations for Elctr Instll in Chem Procss Areas - Amer) {323 NFC}