Definition(s)
Class I Material Groups
For the purpose of testing, approval, and area classification, various air mixtures (not oxygen enriched) are subdivided into Groups A, B, C, or D for Class I, Division 1 and Class I, Division 2 locations.
Group A—Atmospheres containing acetylene. Refer to Section 5.5, NEC Article 500.6(A)(1) and NFPA 497:3.3.
Group B—A typical Class I Group B material is hydrogen. Refer to Section 5.5, NEC Article 500.6(A)(2), and NFPA 497:3.3 for a more complete definition.
Group C—A typical Class I Group C material is ethylene. Refer to Section 5.5, NEC Article 500.6(A)(3), and NFPA 497:3.3 for a more complete definition.
Group D—Atmospheres containing butane, gasoline, hexane, methane, natural gas, propane, and many other hydrocarbon gases and vapors encountered in oil and gas production, refining and pipeline operations. Refer to Section 5.5, NEC Article 500.6(A)(4), and NFPA 497:3.3 for a more complete definition.
API RP 500, Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Division 1 and Division 2, Third Edition, December 2012, Global Standards