Class I Boundary Seals

[sirdle]

The production area of an oil and gas lease is below grade in a large open pit, perhaps 100'x50'x20'. A new set of area classification drawings shows a combination of Class I, Division 1 and Division 2 areas with everything above the pit as unclassified (and everything inside the pit as at least a Div 2 area).

Conduit seals have been installed at the Div 2/unclassified boundary, but not at the Div 1/Div 2 boundaries. ALL electrical equipment in the Div 2 areas is currently rated for Div 1, and the conduit wiring system is suitable for Div 1.

If the Div 2 area were to be overclassified as Div 1, could the engineer eliminate the Div 2 area altogether? (The purpose of this would be to eliminate the considerable plant downtime which would be required to install Div 1/Div 2 boundary seals.)

 

[petersonra]

Re: Class I Boundary Seals

I always thought there had to be an area surrounding a divison 1 area that is classified as division 2. but I looked in the code and it does not seem to actually say that.

 

[rbalex]

Re: Class I Boundary Seals

Unfortunately you can?t eliminate the Division 2 location:

500.5(B)(2) Class I, Division 2. A Class I, Division 2 location is a
location
?
(3) That is adjacent to a Class I, Division 1 location, and to which ignitible concentrations of gases or vapors might occasionally be communicated unless such communication is prevented by adequate positive-pressure ventilation from a source of clean air and effective safeguards against ventilation failure are provided.

You correctly spotted the real problem: the absence of the Div 1/ Div 2 boundary seals.

If you ?over classified? the location so that it was all Division 1 you only move the Div 2 / Unclassified boundary problem to a new location. Beginning with the 2005 NEC, the Div 2 / Unclassified seals are not required to be explosionproof; nevertheless a seal of some sort must still be present at the boundary.

Side Note: If this were a true IEC ?Zone? system it would not require a Zone 2 transition between Zone 1 and unclassified locations. The NEC however ?force fit? the requirement in 505.5(B)(5)(4) anyway.

[Edit: Completed the full 500.5(B)(2) reference citation]

[ July 01, 2005, 12:41 PM: Message edited by: rbalex ]

 

[rbalex]

Re: Class I Boundary Seals

Originally posted by sirdle:
... A new set of area classification drawings ...

Has the process actually changed? If not, why was the Electrical Area Classification changed?

 

[sirdle]

Re: Class I Boundary Seals

Thanks Bob, that was my thinking also, but I was grasping at straws... trying to help reduce the necessary upgrade costs.

I guess that is one of the advantages of the zone system.

When we arrived at the lease we found a partial set of electrical drawings in a jumbled heap next to a transformer in the electrical room. Apparently this was the best place to take a nap during the night shift. There were no area classification drawings in the bundle. We persuaded the owners to hire an outside engineering firm to produce new drawings based on the P&IDs and site visits.

 

[sirdle]

Re: Class I Boundary Seals

Could the Div 2 area be only 1' wide? Then any of the conduits that pass completely through the Div 2 area without unions, couplings, boxes, or fittings would not need to be sealed at the Div 2/unclassified boundary and a single seal would be required.

One end of the conduit terminates at an unclassified location, the other terminates in the Div 1 area. Or do both ends of the conduit need to terminate in an unclassified location for 501.5(B)(2) Exception No. 1 to apply?

... still grasping at straws.

 

[rbalex]

Re: Class I Boundary Seals

The NEC "Zone" system is just as bad as the "Division" system for this particular issue.

The reason for my last immediately previous post was that it?s possible (I emphasize possible) that the engineer may have already ?overclassified.? Outside Articles 511 to 516 applications, Electrical Area Classification is largely an art as well as a science. A great deal of judgment needs to be applied.

I must confess I?d like to see at least a 10:1 ratio between the longest side and the pit depth before I?d automatically begin to consider the pit as an ?open air? application. On the other hand, aside from lousy documentation, if the facility has been in good repair it may indicate the location can be classified by ?experience.?

From NFPA 497:

3-4.4 When classifymg buildings, careful evaluation of prior experience with the same or similar installations should be made. It is not enough to merely identify a potential source of the combustible material within the building and proceed immediately to defining the extent of either the Class I, Division 1 or Division 2; or Class I, Zone 1 or Zone 2 classified areas. Where experience indicates that a particular design concept is sound, a more hazardous classification for similar installations may not be justified. Furthermore, it is conceivable that an area might be reclassified from either Class I, Division 1 to Division 2, or from Class I, Division 2 to unclassified or from Class I, Zone 1 to Zone 2, or from Class I, Zone 2 to unclassified based on experience.

API RP500 and 505 have similar verbiage.

If the gases in question were lighter than air (not too likely I?ll admit) I wouldn?t hesitate to classify the whole pit Div 2 and not look back.

With heavier than air gases I still might consider a blower/collector vent system; although in that case I typically like to see at least a 10:1 ratio between the side dimensions. A ventilation specialist can help determine the ?dead-air? locations. They become the Division 1 locations. Often you can arrange it so no electrical equipment is in those locations.

[ July 01, 2005, 05:44 PM: Message edited by: rbalex ]

 

[rbalex]

Re: Class I Boundary Seals

Originally posted by sirdle:
Could the Div 2 area be only 1' wide? Then any of the conduits that pass completely through the Div 2 area without unions, couplings, boxes, or fittings would not need to be sealed at the Div 2/unclassified boundary and a single seal would be required.

Typically, in absence of a physical boundary such as a wall or grade, the Division 2 hazard radius from the Division 1 location is at least 5? to 10?.

One end of the conduit terminates at an unclassified location; the other terminates in the Div 1 area. Or do both ends of the conduit need to terminate in an unclassified location for 501.5(B)(2) Exception No. 1 to apply?

Both ends need to be It is an exception to the main rule statement: ? 501.5(B)(2) Class I, Division 2 Boundary. In each conduit run passing from a Class I, Division 2 location into an unclassified location?? In this case, you are describing running from a Division 1 location.

... still grasping at straws.