Metal Grindings

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sevlander

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new jersey
A welding school has a grinding cutting classroom. Does this area need to be classified as a class 2 area? You would have to assume aluminum is a metal that will be ground here at times. Each student has a booth with ventilating hood. If classified, where are the boundaries? (i.e. is above the drop ceiling in the zone?). Who can make this determination?
 

dicklaxt

Senior Member
Aluminum fines and flakes are ClassII,Group E............... and is or could be either Div 1 or 2(I think) depending on the dust cloud/layer concentrations.There are many aluminum alloys that must be considered,ignition temps vary between 464 and 806 degrees (f) See 500.6(B)(1)

IMO the Area Class drawing responcibility lies with the engr co or the client.

dick
 

rbalex

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Mission Viejo, CA
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Professional Electrical Engineer
Class II, Group E is always Division 1 - if it exists at all. [500.5(C)(1)(3)]

Obviously, I don't know what particulates will be generated by the grinding process but ?flakes? are not a Group E source material; ?fines? may be if they are actually a dust. Dust is not currently defined in the NEC but it will be in the 2011 edition. It will be the same as NFPA 499 has been using for years:

Combustible Dust. Any finely divided solid material that is 420 microns (0.017 in.) or smaller in diameter (material passing a U.S. No. 40 Standard Sieve) and presents a fire or explosion hazard when dispersed and ignited in air.
 

dicklaxt

Senior Member
I am looking at a 2008 Code Review pamphlet published by Appleton Electric and they list Aluminum flakes as a Group E metal but only dusts are considered electrically continuous for classification purposes.I stand corrected if flakes are not used for classifications.It would make sense to me that if either dust or flakes were present then the other would be as well so where do you draw the line,,,,,,,,,,,,I would think that in the presense of both they would be considered unless all dust was extracted somehow,,,,,,,,,hey I'm just talking/discussing not being argumentative.

BTW my temps above are whacky (I looked at the wrong column) it should be 608 to 1526 degrees (f)

dick
 

dicklaxt

Senior Member
Robert,I don't see where Class II,Div 2 is not one of the prescribed limits in a dust atmosphere, can you explain your reasoning that it doesn't exist, see 500.5 (C)(2)##or#

thanks

dick
 

rbalex

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In order to be a "dust" is must be "... 20 microns (0.017 in.) or smaller in diameter (material passing a U.S. No. 40 Standard Sieve) and presents a fire or explosion hazard when dispersed and ignited in air." "Flakes" are generally much larger. Actually, the and I underlined is pretty significant too.

With regard to Class II, Division 2, Group E - it simply doesn't exist, by definition.
500.5 Classifications of Locations.

(C) Class II Locations. Class II locations are those that are hazardous because of the presence of combustible dust. Class II locations shall include those specified in 500.5(C)(1) and (C)(2).

(1) Class II, Division 1. A Class II, Division 1 location is a location

(3) In which Group E combustible dusts may be present in quantities sufficient to be hazardous.
In other words, if it's "sufficient to be hazardous" it's Division 1; otherwise it's not classified at all. Note the "(3)" is a subpart of 500.5(C)(1)
 
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dicklaxt

Senior Member
I hear what you are saying but,,,,,,,,,,,, 500.5 (C)(2)(1,2 & 3) in my eyes says it is there under such and such conditions then it is Class II,Div 2,what am I missing?

dick
 

rbalex

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Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
I hear what you are saying but,,,,,,,,,,,, 500.5 (C)(2)(1,2 & 3) in my eyes says it is there under such and such conditions then it is Class II,Div 2,what am I missing?


dick
With respect to Group E:
  1. A location is either "sufficient to be hazardous" or not.
  2. If it is "sufficient to be hazardous," it's Division 1.[500.5(C)(1)(3)]
  3. If it's not "sufficient to be hazardous," it isn't.
  4. If one of the conditions in 500.5 (C)(2)(1),(2) or (3) exists, it would still be Division 1 for Group E (See item #2 above), but Division 2 for Groups F or G.
 

rbalex

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Location
Mission Viejo, CA
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Professional Electrical Engineer
Sounds like I am going to have to ask the AHJ directly on this one since interpertations seem to vary greatly in this category. Thanks
There's certainly nothing wrong with having the AHJ's blessing, but I'd inquire about their familiarity with NFPA 499; especially Chapters 4 and 5. Usually, I recommend the facility's insurance company do the review.

I've also attached a short citation from NFPA 499 below. You might want to share it with the AHJ.
 
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