area classification- gas tank 20 ft aboveground

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MIEngineer

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Hello All,

I was hoping for some clarification. I currently have a gasoline dispensing tank that is approximately 15 feet above grade. My understanding is that according to Table 514.3(B)(1) my class 1 division 2 area is 18 in. above grade level within 20 ft horizontally of any edge of enclosure. Also 18 in. from any edge extending horizontally. Class 1 division 1 area is directly below the tank down to grade.

1) I am understanding this as meaning that the conduits down the pole next to the tank are fine (I believe they are RMC) as long as there are no unions in them as they pass through the class 1 division 2 area (501.15(B)(2) exception No. 2).

2) Also I thought I was required to install an emergency stop button does anyone have a code reference to this.

3) Is there any reason I would have to move either the pole or the tank if it is more than 18 inches away?

4) How does the dispensing nozzle play into all of this? Is my class 1 division 2 area anywhere above grade that the dispensing nozzle can reach?

Thank you in advance for any assistance.
 

rbalex

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Professional Electrical Engineer
MIEngineer said:
Hello All,

I was hoping for some clarification. I currently have a gasoline dispensing tank that is approximately 15 feet above grade. My understanding is that according to Table 514.3(B)(1) my class 1 division 2 area is 18 in. above grade level within 20 ft horizontally of any edge of enclosure. Also 18 in. from any edge extending horizontally. Class 1 division 1 area is directly below the tank down to grade.

1) I am understanding this as meaning that the conduits down the pole next to the tank are fine (I believe they are RMC) as long as there are no unions in them as they pass through the class 1 division 2 area (501.15(B)(2) exception No. 2).

2) Also I thought I was required to install an emergency stop button does anyone have a code reference to this.

3) Is there any reason I would have to move either the pole or the tank if it is more than 18 inches away?

4) How does the dispensing nozzle play into all of this? Is my class 1 division 2 area anywhere above grade that the dispensing nozzle can reach?

Thank you in advance for any assistance.
To be honest, I wasn’t familiar with the current NFPA 30A(2008.) Table 514.3 (B) (1) and Figure 514.3 in the NEC-2008 are extracted from NFPA 30A-2005. The Figure has remained essentially the same but the Table has been revised substantially. Typically, the NEC-2011 will reflect the newer (2008) NFPA 30A. Unfortunately, while Figure 514.3 is authoritative, it isn’t exhaustive and there is quite a bit more to consider.

One thing that affects the OP is that aboveground tanks are not currently addressed in Article 514 nor were they in NFPA 30A 2005. Technically, that threw the tank installation into Article 515. Aboveground tanks are now addressed in NFPA 30A-2008.

Basically, the ONLY Division 1 in the installation should be a 5’ sphere around the relief vent’s exhaust port. The rest of the installation is Division 2. Previously, the area within the dike would also have been Division 1. The 18” high - 20’ radius around the dispenser is still in effect.

1) Make sure the raceways are suitable for Division 2. (Section 501.10(B)) I believe you are actually citing Exception No.1. Unions are not the only devices prohibited.
2) See Section 515.11
3) I don’t understand your question.
4) Nozzles have always been a bit problematic since their position is transient. The general concept is that the vapor recovery required on modern systems and the fact that emissions are actually small doesn’t generally require special attention beyond what is already required in the installation.
 

MIEngineer

Member
Location
Michigan
rbalex said:
3) I don?t understand your question.
QUOTE]

Thank you for the reply. For my question 3 I was incorrectly referencing the 18" boundary around a dispenser as shown in figure 514.3. As you indicated I actually have a bulk storage tank.

Just a couple of more question:
1) I also notice in Table 515.3 that the there is a Class 1 div. 2 boundary 10' from any shell of the tank. Am i correct in applying this boundary to this situation.
2) What is the equipment referenced in the table as "Outdoor equipment of the type covered in Section 5.3 ..." I am unable to find a section 5.3 in NFPA 30.

Thank you again
 

rbalex

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Location
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1) Yes
2) I have no idea. NFPA 30A was originally itself extracted from NFPA 30. This may be an artifact of that old relationship. It happens occasionally. Give Bob Benedetti at the NFPA a call.
 

rbalex

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rbalex said:
...
2) I have no idea. NFPA 30A was originally itself extracted from NFPA 30. This may be an artifact of that old relationship. It happens occasionally. Give Bob Benedetti at the NFPA a call.
It appears that some editorial work is necessary.

It appears you are using the 2008 NEC. The FPN to the Article title references NFPA 30-2008. Table 515.3 references NFPA 30, Section 5.3, which doesn’t exist.

The appendages and foot notes to Section 515.3 and Table 515.3 indicate the source of the Table is NFPA 30-2008, Table 8.2.2, which also doesn’t exist.

What DOES exist and is the apparent source of NEC-2008, Table 515.3 is NFPA 30-2008, Table 7.3.3. That Table refers to NFPA 30-2008 Section 7.3 as what should be the “Outdoor equipment of the type covered in Section 7.3 [rather than 5.3] of NFPA 30 where flammable vapor–air mixtures may exist under normal operation.”
 

MIEngineer

Member
Location
Michigan
Thanks for the information.

I am surprised that this one NEC Article has this many discontinuities, starting with the fact that NFPA 30 calls them chapters and not sections. In reading through 7.3 I still see no explanation of how "Outdoor equipment of the type covered in Section 7.3 where flammable vapor?air mixtures can exist under normal operation" differs from a "tank -aboveground, fixed roof"

Once the distances are in place I can work on getting the required E-stop included in the system.
 

rbalex

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What it looks like to me is that the NEC-2008 and NFPA 30-2008 were revised too close in time to get completely coordinated by thier publishing date. It also seems NFPA 30-2008 is a major rewrite from the 2003 Edition.

The ?Outdoor equipment of the type covered in Section 7.3 where flammable vapor?air mixtures can exist under normal operation? seems to be a catch-all statement to cover anything not specifically mentioned elsewhere in the Table.
 
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