Determining Group (B vs C&D) for flammable gas in vacuum pump service

[thomasfrotten]

I am specifying a vacuum pump for a process

The process is all enclosed, and the flammable is pure, so way above the UEL in the piping. The piping is leak checked to 10-6 cc/s with a He leak detector every cycle.

The room has 15 ACH, and calculations show the lel will never be reached even if a line breaks and there is no restrictions other than the end of the pipe (choke flow).

T
From what I've read. the difference between group b and c or d is based only on MESG and or the MIC. The levels are clear. It also said these are determied experimentally.

1st: is there a place to find these values? The MSDS's are not showing them.

2nd: I am saying the room is class I div II because the gas is contained and there is adequate vetilation to prevent explosive atompspehere from ever buidling, and internal to the process, it is leak tight and should never have any chance of going below UEL.

Given that, the process is pumped through a rotary vacuum pump,

I have to buy a pump, that of course has a motor

if the feedstock to this process is lets say H2, this means Im automatically group B for the motor?

This difference is $500 for a group c or d motor, and $15,000 for a group B motor.

what the pump will see is a mixture of gasses, never pure hydrogen. I cannot find an MIC or MESG for the other type of gas. is there a way to estimate based on other physical properties, or similar gasses?

 

[rbalex]

The test criteria are listed in NFPA 497, Annex B. There are also methods for determining the Group of mixed gases.

Pure Hydrogen is definitely Group B. In fact, that used to basically be the definition of Group B.

If you believe the location is Division 2, then the motor will probably not need to be specifically certified for Group B though. See NEC [2005] Section 501.125 (B).