Going down under: once or twice?

Status
Not open for further replies.

Dave58er

Senior Member
Location
Dearborn, MI
Guys I am having a difference of opinion with another foreman on an interpretation of the code as it relates to conduit seals and would like your input.

501.15 (B) (2) is the article in question.

Here is the scenario:
We are leaving C1D2 locations by going underground, thus going from C1D2 to unclassified. In some places this is to go under roads or lots and in others it is to go through/under retention dikes.

In all cases these conduits re-emerge from underground directly back into C1D2 areas.

IMHO this is two separate boundaries and requires a seal off where entering the ground and a seal off where leaving the ground.

He is interpreting "the sealing fitting shall be permitted on either side of the boundary" to mean only one seal off is required at either end.

Please help with a second opinion on this.

Also, thanks in advance for any extra details that may help me move beyond basic knowledge and into an area of "understanding" on this subject. In other words, the reasons behind the rules. :)
 

dicklaxt

Senior Member
I would interpret it this way just using common sense,Area Classifications are a judgement call in a lot of different scenarios IMO .

Scenario #1: If a conduit routes around "Aboveground" and stays within an established Div2 area it is not required to be sealed IMO.

Scenario #2: If that conduit in a similar but different routing is routed around within that established Div2 area and had to go "Underground" at a point within that area because of lack of support aboveground and then stubbed up at a support but still within the same established Div2 area,it would not require seals at either end, IMO.

Scenario #3: Now if the conduit were ducking "Underground" in an established Div2 area(lets call this area#1) and was routed underground to a second established Div2 area (lets call this area#2) then a conduit seal would be required at both ends/sides of the unclassifeid underground area,IMO.This being to hinder gas migration from one Div2 area to another.

Scenario #4:A conduit leaving any classified area, and passing into another classified area requires a seal whether "Abovegound" or "Underground" except as listed in some of the Exceptions.

Now if anyone thinks I'm full of " it " just tell me and we all can laugh,but thats the way I see it.

dick
 

Dave58er

Senior Member
Location
Dearborn, MI
Scenario #3......

This is the situation I have. 15-20 separate established C1D2 areas.

Wouldn't one seal off within 18" of the ground prohibit gas migration from one classified area to the other? If that is the reason for the seal off then I can see 1 being sufficient. But I thought the reason for the seal off was to prevent gas from migrating to the unclassified location.

I get that it seems to have nowhere to go underground but I don't see where the code makes a distinction between leaving a classified location by going underground and leaving by going into another room or building or whatever.

As I said I'm hoping for some background info on these rules so I can try to understand why they are there.
 
Last edited:

dicklaxt

Senior Member
I assume they are separated from each other by some real estate and not just area boundaries that denote a new area but having a common boundary.If they are different areas with in an overall plot with common borders then they are just one large Div2 area for sealing requirements.

dick
 

Dave58er

Senior Member
Location
Dearborn, MI
Some are separated by roads, some by parking lots, most are separated by mounded retention dikes made of aggregate. These conduits run from the retention area of one tank, into the 5'-6' high 10' wide dike and come out into a new and completely separate retention area of another tank.

Our site specific engineered drawings show 100% of the areas inside of these dikes as C1D2.
 

dicklaxt

Senior Member
The engineering firm who prepared those Area Classification Drawings was kind of splitting hairs except for the parking lots,maybe the plant owner was behind making the top of diked areas non hazardous> I have been involved in the preparation of many of these scenarios of diked tank farms and it was usually a blanket Div2 all the way with some areas of Div1,the cost of error to the more hazardous side is probably much better than putting a contractor's feet in the fire.It looks like flamable liquids is the case and not explosive gases,just thinking out loud.

dick
 

dicklaxt

Senior Member
That situation brings up the age old question of,,,, is the underground classified.It is normaly not IMO but in this case with it being elevated dikes and or berms ,,,hmmmm what do we have here.Thats not the question is it, sorry for going off on a tangent.

dick
 

Dave58er

Senior Member
Location
Dearborn, MI
The engineering firm who prepared those Area Classification Drawings was kind of splitting hairs except for the parking lots,maybe the plant owner was behind making the top of diked areas non hazardous> I have been involved in the preparation of many of these scenarios of diked tank farms and it was usually a blanket Div2 all the way with some areas of Div1,the cost of error to the more hazardous side is probably much better than putting a contractor's feet in the fire.It looks like flamable liquids is the case and not explosive gases,just thinking out loud.

dick

A blanket Div2 may make it easier but then again the specs on this job require to follow NEC also.
Wherever there is a conflict I must follow the more strict ruling.
Which takes me back to the question of whether a seal off is required per code on both sides of these dikes, parking lots, and public roads.
 

dicklaxt

Senior Member
I say yes,the code says a conduit leaving a classified area to unclassified shall be sealed,it happens twice even tho its the same conduit.If the AHJ will not buy into anything else ,you have no choice but to seal it twice as I see it.
dick
 

erickench

Senior Member
Location
Brooklyn, NY
NEC 500.2 is the definitions section for article 500. The code defines unclassified locations as the following:

Locations determined to be neither Class I, Division 1; Class I, Division 2, Class I, Zone 0; Class I, Zone 1; Class I, Zone 2; Class II, Division 1; Class II, Division 2; Class III, Division 1; Class III, Division 2; Zone 20; Zone 21; Zone 22; or any combination thereof.

Underground does not come under any of these areas. So it's unclassified.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
An interesting interpretation of that definition; especially, in light of Sections like 501.15(A)(4) Exception No. 2 which specifically recognize the potential of a Division 1 boundary below grade. The problem is, outside Articles 511 to 516, the NEC is a terrible source for determining electrical area classifications. Other NFPA Tech Committees that define electrical area classifications within the scope of their own documents have disagreed with CMP 14 and each other. The Tech Committee that controls NFPA 30A is particularly notorious. The overall consensus has improved considerably over the last few years though.

Nevertheless, I agree that underground is rarely classified nor does it need to be. It doesn?t matter though; a boundary is still created and the rules of 501.15(B)(2) apply.

I also agree with that electrical area classification is largely a judgment call ? but an educated one, if done properly. However, once classified and properly documented [500.4(A)] ? determining the seal locations are pretty clear, if one takes the time to study Section 501.15.

So back to the OP ? I don?t necessarily like all the rules, but if there are two boundaries in the same raceway run there are two sets of seals. ONE REASONABLE EXCEPTION: if there is 10? or less raceway between the boundaries then a single seal may serve as both.
 

james_mcquade

Senior Member
Isn't the intent of a seal off to prevent the material in the classified area from getting in the
conduit to prevent the potential of a fire created by the electrical components in the general purpose area?

To carry this further, since this is class 1 area, if no seal offs were used, a fire in one classified area could be spread to the other classified area via the conduits.

regards,
james
 

dicklaxt

Senior Member
A seal off, #1 is intended to contain an explosion from an ignition source and stop the fire ball from traveling thru the conduit ,#2 the escaping hot gases that may escape around the threads in a seal off will cool it sufficiently not to cause a 2nd explosion.If the differential pressure is greater on one side or the chico dam within a poured seal off then gas will migrate thru the chico to the unclassified area where seals are not always required and could cause a subsequent explosion if an ignition source is present..

A compound poured seal as manufactured for a particular sealing fitting manufactured and which is tested and approved for use in a particular atmosphere will stop gas migration but not necessarily contain an explosion.

I believe the above is correct some one holler if I goofed,working from memory here.

dick
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Isn't the intent of a seal off to prevent the material in the classified area from getting in the
conduit to prevent the potential of a fire created by the electrical components in the general purpose area?

To carry this further, since this is class 1 area, if no seal offs were used, a fire in one classified area could be spread to the other classified area via the conduits.

regards,
james
See Section 501.15 FPN No.(s) 1 and 2. (No. 2 should scare the hell out of you if you believe it)
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
...The Tech Committee that controls NFPA 30A is particularly notorious...
I have been severely (and correctly) reminded by a former CMP14 colleague, that it should have read, ?The Tech Committee that controlled NFPA 30A was particularly notorious.?

The Automotive and Marine Service Stations Technical Committee was reformed (in several senses of the term) in 2002 and it began to enter the general consensus of CMP14 and several other TCs. The effect on Article 514 was dramatic as indicated by the subtle but very significant revision of Figure 514.3 [Extracted from NFPA 30A: Figure 8.3.1]

I happen to like the NFPA Staff Liaison for the TC, Bob Benedetti quite a bit; he has helped me several times with extracting the proper citation from the proper NFPA document in my quest for electrical area classification enlightenment. He also served as the NFPA Recording Secretary when I served on CMP14. So, while he is actually a genuine Flammable Liquids expert ? as far as I?m concerned, he?s Electrical. He?s also one of the most gracious men I know ? so he wasn?t have been ?former CMP14 colleague.? I mentioned. :D
 

erickench

Senior Member
Location
Brooklyn, NY
An interesting interpretation of that definition; especially, in light of Sections like 501.15(A)(4) Exception No. 2 which specifically recognize the potential of a Division 1 boundary below grade.

Yes but that exception was meant for a pit that was below ground. It's in one of Mike Holt's books "Understanding the NEC Vol. 2". Look on page 75, Fig. 501-11.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Yes but that exception was meant for a pit that was below ground. It's in one of Mike Holt's books "Understanding the NEC Vol. 2". Look on page 75, Fig. 501-11.
That's even more interesting - I was on the API Subcommittee on Electrical Equipment (SOEE) Task Force on the NEC when we developed that Exception and I don't think any of the 15-20 of us knew that was the application intended.
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
That's even more interesting - I was on the API Subcommittee on Electrical Equipment (SOEE) Task Force on the NEC when we developed that Exception and I don't think any of the 15-20 of us knew that was the application intended.
I hate going senile.

First, let me give credit where credit is due; Fred Hartwell was the originator of the Exception. Second, while it was briefly discussed at the SOEE, my cloudy memory about the discussions occurred when I was a member of CMP14 in 2002.

Nevertheless, none of us was aware of the application as you have suggested.

The original substantiations was:

SUBSTANTIATION: Section 501-5(c)(1) requires seals to be accessible. Since hazardous locations frequently involve flammable gases and vapors heavier than air, generally area classifications require graded locations below a classified location to retain the same area classification. Some Code rules expressly impose this requirement, such as Section 515-6, which mandates a Division 1 classification for below grade conduits. The only way to literally combine these two rules is to go through the burden of installing a handhole within a conduit length of the transition point. This proposal is a reasonable compromise to address this problem. Its principle is reflected in Sec. 514-8, which has allowed this procedure since the 1987 NEC through the verbal sleight of hand of artificially extending the boundary of the classified location. I am submitting a companion proposal to remove that language from Section 514-8, since it won’t be necessary if this general procedure is agreed to. Although this is my own substantiation, the proposal is the final panel action in the ROP on Proposal 14-126 in the previous cycle. It is one of four proposals that the panel accepted in the ROP, forgot about, and in-advertently wiped out through unrelated editorial activity in the comment period.
As I mentioned elsewhere in this thread, many of these issues have been created because underground "philosophy" for electrical area classification is not consistent throughout the various NFPA TCs.

Edit Add: the referrenced Proposal 14-126 from the previous cycle was indeed the API Proposal I remembered.
 
Last edited:
Status
Not open for further replies.
Top