Gas Groups

[GordS]

In Canada, we used to classify hazardous areas where the gas groups were designated A, B, C, D. Even though Gp A was generally felt to represent more dangerous gases than Gp D, it was a Code requirement that the Gp labelled on the equipment had to match the Gp in the area classification (i.e. you could not say a Gp A protection could be used in a Gp D area just because Gp A gases were more dangerous so therefore the protection had to be good enough for Gp D)

The most recent Code classifies gasses in surface installations with designation IIA, IIB, IIC where IIC is now the more dangerous gases and IIA roughly equivalent to the old Gp D. The Code Handbook however implies that in installations where " protection by method" is used, a IIC enclosure CAN be used in a IIB or a IIA classification.

This is in total opposition to the understanding we had prior to the latest Code revision in that a "higher level" of gas group can seemingly be used in an area with a "lower level" of gas.

Am I misunderstanding something here? If not, does anyone know why the difference?

 

[cherryg]

GordS :
The CEC standard & NFPA 70 i.e NEC have been modified to add the Zone concept of area classification adopted from IEC 60079-10. The Gas Groups that you have cited are also derived from IEC. There is a relationship between the US traditional gas groups A,B,C & D ( if you are classifying per the Division method ) and the IEC Gas Groups IIC,IIB & IIA ( if you are classifying per the Zone method ).