Pyrophoric classification

[base729]

Alright, I think I have a good question here. I apologize, but I don't have the NEC book in front of me, so I'm going from memory here. I have been asked to install a motor inside a "glove-box" which is similar to an incubator. The glove-box contains the following:

1. 99.99% Nitrogen atmosphere
2. Pyrophoric material (ignites w/ oxygen)
3. Acetone slurry which will evaporate into Nitrogen atmosphere.

The code has a clause that if pyrophoric material is present, it differs classification. Does that mean you don't need special precautions? Also, if means are meant to suppress ignition (in this case Nitrogen), a spark or combustion is impossible unless the Nitrogen system fails. I remember something in the code book referring to this event as well. Any help in clearing this up would be greatly appreciated. I'm going to get an explosion proof motor just to be on the safe side, but the question comes in with reference to the conduit, sealing compound, flexible conduit etc. Even if the electronics are disconnected, failure of the nitrogen system will cause ignition, and with the nitrogen system working, ignition is impossible. To sum it up, what would this area be classified as?

Thanks,

Joe Caulfield
BASE729, Inc.
Deleted email address; respond through PM if necessary.

[ June 06, 2005, 09:59 AM: Message edited by: rbalex ]

 

[ryan_618]

Re: Pyrophoric classification

500.5 Classifications of Locations.
(A) Classifications of Locations. Locations shall be classified depending on the properties of the flammable vapors, liquids, or gases, or combustible dusts or fibers that may be present, and the likelihood that a flammable or combustible concentration or quantity is present. Where pyrophoric materials are the only materials used or handled, these locations shall not be classified. Each room, section, or area shall be considered individually in determining its classification.

 

[rbalex]

Re: Pyrophoric classification

Ryan has cited the relevant Code section for pyrophoric material; however from your description pyrophoric materials are NOT ?? the only materials used or handled?? since acetone is also a flammable material. It is typically a Group D material. Check the relevant Material Safety Data Sheet (MSDS).

A nitrogen blanket is a recognized protection technique. See 500.7(D) and the reference to ?Purged and Pressurized? in 500.2 which further references NFPA 496.

The area classification and protection techniques should be determined [and documented - see 500.4(A)] by someone qualified to do so. It CANNOT be done as an exercise on this forum.

 

[base729]

Re: Pyrophoric classification

Originally posted by rbalex:
... pyrophoric materials are NOT ?? the only materials used or handled?? since acetone is also a flammable material....

I guess my question is more a which came first, the chicken or the egg type question. In a purged and pressurized system, the acetone cannot ignite. Should the purged and pressurized system fail, the pyrophoric material will ignite. The primary source of ignition is the pyrophiric material which WILL ignite with oxygen. Another engieer at the plant made the anology that the motor could be running with sparks shooting out of it. Because if the nitrogen system fails, the box is going up anyway (due to pyrophoric material). Probably not the best design, but it poses the question of each item being classified individually, or as a combined system. There is not the possibility of acetone and not pyrophoric material. I guess my root question is will each item need to be classified individually, when one of them trumps the other?

 

[rbalex]

Re: Pyrophoric classification

It?s certainly a legitimate question, but one that someone intimately familiar with the process must answer. Area classification is an art as well as a science and many judgment calls must be made. That?s why NFPA 497 and API RP 500 are ?Recommended Practices? rather than ?Codes? themselves. Combined there are over 250 pages of analyzing techniques to consider.

You must have someone who both knows what they are doing AND what the process is all about to get a final answer. There are literally scores of considerations.

 

[petersonra]

Re: Pyrophoric classification

I have seen similar systems installed with automatic fire extinguishing equipment added. I always wondered why the halon system was needed.