Group B defined as >/=30% hydrogen, what if hydrogen level is less than 30%?

[Hobiedog]

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!

 

[bphgravity]

Try looking in the NFPA 1...

Possible explanation:

1. The client is classifying by ZONE rather than GROUP.

2. The client is referring to the compounds H2S, HCN, or H2SE rather than pure H.

???

 

[Hobiedog]

From what I can find, IE Zones are equivalent to our Divisions but not Groups. IEC Groups are I, IIA, IIB and IIC. Hydrogen is in IEC Group IIC along with Acetylene, so it must be their most 'critical' Group.

Also, when referring to the concentration, they refer to 'pure' H2.

 

[rbalex]

Group B hasn't been defined as a 30% hydrogen mix since the 1999 NEC.

To determine the Group of mixed gasses, see Annex B of NFPA 497.

 

[bobgorno]

API RP 500 (R2002), Section 5.5.5 still refers to the 30% level for H2 in manufactured gases, but it references NEC in its paragraph title.

As Bob A. says it is not in the NEC any longer.

It is the responsibility of the owner to establish the EAC, including group. Don't take that task on yourself. It would be nice if they established Group by testing, but most do not pay for testing.

Where is their mixing point? What about the potential for H2 leaks upstream of that point?

Note: If you were to use NFPA 497, Annex B and were 30% H2 and 70% Nitrogen or 70% Methane, you would probably still be Group C in either case. so, if they tell you Group C, you can probably rest a little easier (from the mixing point, donwstream).

I would consider using H2 monitors wherever H2 could pocket.