Re: NEC Hazardous Atmospheres Categories
To: cfd399, I have been waiting to see if you would get an answer to your question, before I responded.
No.1 I am going to assume that you understand the difference in Class 1, Division 1, and Class 1, Division 2. If you do not understand this, then you need to do some research.
No. 2, Your question was,as I understand it was as follows: "how, and why do they classify the grouping of materials in A, B, C, D, in the Class 1 Division".
No. 3, The NFPA does the classifying of all of the materials, and you can find them in NFPA 325M.
No. 4, How The Groupings Are Determined.
Prior to publication of the 1971 editon of the NEC,the determination of the proper group classification in Class 1 locations was based on three criteria:
1. Maximum experimental safe gap (MESG),
2. Explosion pressure, and
3. Ignition temperature.
You can see cfd399, that it takes a great deal of research, to come up with putting the materials in the proper grouping.
I hope that this may help you in your understanding of "grouping". If not, you may call me at this number, and I would be glad to discuss it with you. BoB Friebel (856)678-9003
