Mike Dolt Enterprises
Mike Dolt Enterprises
User: Hobiedog, Location: Upstate, SC
Asked on: Tuesday, April 19, 2011 at 12:29 pm EDT
Answered on: Tuesday, May 14, 2024 at 4:23 am EDT
Question: My client says if they control the H2 concentration such that it's below 30% (by volume) then the area classification drops to Group C. They refer to NFPA but don't cite a particular code number. I cannot find any such written statement in NFPA 497 or 70 (NEC). My 2008 NEC Code book only mentions MESG and MIC levels of which hydrogen falls into that Group regardless of concentration as far as I can see. Could anyone comment or provide a reference to confirm or deny this claim?A Group B rating would greatly limit the types of electrical equipment to be used in this area, so I'm hoping the client is right.Thanks!
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 Section 6.2.
1.1 states that "Hydrogen...shall always be classified as a Group B gas regardless of concentration."NEC 70
500.8(B) Hazardous (Classified) Locations by Division Table 500.8(C) lists hydrogen as a "Group B" gas, without any qualification regarding concentration.
Conclusion:
Neither NFPA 497 nor NEC 70 supports the claim that controlling the hydrogen concentration below 30% (by volume) would result in a downgrade to Group C area classification. Hydrogen is always classified as a Group B gas, regardless of concentration. Flag for review