Off shore platform classified area

[dmkemp]

I am putting a control cabinet in a Class 1 Div 2 area on an offshore platform, but one requirement is no purging of the panel. Is there any way to build this panel in a NEMA 4X by using 24VDC if all the instruments are either hermetically sealed or approved for C1D2 area use. I have controllers, relays, pushbutton switches, and a Fireye burner management unit.

 

[rbalex]

I am putting a control cabinet in a Class 1 Div 2 area on an offshore platform, but one requirement is no purging of the panel. Is there any way to build this panel in a NEMA 4X by using 24VDC if all the instruments are either hermetically sealed or approved for C1D2 area use. I have controllers, relays, pushbutton switches, and a Fireye burner management unit.

You have asked a very broad question. Without knowing the specifics of the components, it is difficult to offer specific advice. Your general description (? all the instruments are either hermetically sealed or approved for C1D2 area use) is generally acceptable. Read all of 501.105(B) carefully.

 

[weressl]

You have asked a very broad question. Without knowing the specifics of the components, it is difficult to offer specific advice. Your general description (? all the instruments are either hermetically sealed or approved for C1D2 area use) is generally acceptable. Read all of 501.105(B) carefully.

I alwas had a problem with this issue, because even if all the components and wiring method is either suitable or approved for Class I, DIvision 2, specific Group and T rating, how can we classify a plain, unvented space as Division 2? If that would be a larger enclosure, say control room, would the same approach still stand, or would you need to classify it. If the control room has unpierced walls, but has a door that regularly opens into the process area and it has no positive pressure ventilation? If the control enclosure has a breather drain?

Seem to me that the Code and 496 does omit this stipulation. Or am I just mmissing it?

 

[rbalex]

I alwas had a problem with this issue, because even if all the components and wiring method is either suitable or approved for Class I, DIvision 2, specific Group and T rating, how can we classify a plain, unvented space as Division 2? If that would be a larger enclosure, say control room, would the same approach still stand, or would you need to classify it. If the control room has unpierced walls, but has a door that regularly opens into the process area and it has no positive pressure ventilation? If the control enclosure has a breather drain?

Seem to me that the Code and 496 does omit this stipulation. Or am I just mmissing it?

The OP simply stated the box was in a Division 2 location. It didn?t state the location itself was unventilated. Offshore facilities do have a fairly large number of Division 1 locations, but not all are.

Making (the possibly wild) assumption that the box had no immediate internal source of ignitable materials, the box?s own direct ventilation is basically irrelevant. The internal wiring methods/components would simply need to be suitable for Division 2 ? just as a simple terminal box in a Division 2 needs no special ventilation.

 

[weressl]

The OP simply stated the box was in a Division 2 location. It didn’t state the location itself was unventilated. Offshore facilities do have a fairly large number of Division 1 locations, but not all are.

Making (the possibly wild) assumption that the box had no immediate internal source of ignitable materials, the box’s own direct ventilation is basically irrelevant. The internal wiring methods/components would simply need to be suitable for Division 2 – just as a simple terminal box in a Division 2 needs no special ventilation.

The control room has no internal source of combustion either.

The missing piece - in my mind - that there is no clear guidance on at what physical dimensions should we start to geting concerned that explosive mixture MAY infiltrate the enclosed space; if and where it does not have "solid, unpierced" boundary between it and the Div 2. area? That is why I bought up the question of breather/drain.

I don't disagree with your evaluation, just trying to point to a gap. Be it wild assumption or not.:roll:

 

[rbalex]

The control room has no internal source of combustion either.

The missing piece - in my mind - that there is no clear guidance on at what physical dimensions should we start to geting concerned that explosive mixture MAY infiltrate the enclosed space; if and where it does not have "solid, unpierced" boundary between it and the Div 2. area? That is why I bought up the question of breather/drain.

I don't disagree with your evaluation, just trying to point to a gap. Be it wild assumption or not.

Just to be clear, when we apply NFPA 496, it is assumed that there is source of ignition inside the control room or any other enclosed space for that matter. Presumably there is also oxygen. For the most part, it is the ?fuel? part of the fire triangle that we are actually addressing.

From NFPA 496:

3.3.8 Pressurization. The process of supplying an enclosure with a protective gas with or without continuous flow at sufficient pressure to prevent the entrance of a flammable gas or vapor, a combustible dust, or an ignitable fiber?

3.3.14 Purging. The process of supplying an enclosure with a protective gas at a sufficient flow and positive pressure to reduce the concentration of any flammable gas or vapor initially present to an acceptable level.

Pressurizing is simply one method of keeping the fuel out of the enclosed space. Purging basically assumes the fuel may already be inside and dilutes it. Theoretically, the volume of the enclosed space is irrelevant with either method although there are some practical limitations with purging large volumes.

A not necessarily obvious assumption is we are dealing with an enclosed space in the first place and physical boundaries may or may not also create electrical area classification boundaries. Pressurization can work with some fairly large volumes or it may not be necessary at all with adequate ventilation. ?Adequate ventilation? is a different subject and not germane to the OP.

In the case of the OP, we can assume that the explosive mixture, should it exist, WILL infiltrate the enclosed space. Since it is Division 2, it is relatively unlikely, but possible. So ? the internals need to be suitable for Division 2 and Section 501.105(B) outlines the precautions that need to be taken.

 

[petersonra]

I did a fair amount of work for offshore stuff. Almost all of it was either zone 2 or div 2.

Most of them required pressurization but not for area classification purposes. It was just to keep the innards of the panels cleaner.

The last panel I worked on was zone 2, was pressurized with d/p switch on it, and an explosion proof electric heater inside. I gather it gets real cold off the coast of China at certain times of the year. The heater was supposed to melt the ice off the cabinet so the inside was accessible all the time. I did not see anyway a small heater like what was used would do that, but I was only software this time.

 

[dmkemp]

Sorry guys had to leave for a time.
The box is a 36x36x18 box and the equipment inside is for burner management. I have found hermetically sealed relays and sealed contact blocks for the operators but one thing I worry about is the Fireye unit is only Nema 1 box. Do I have to put this into a Nema 7 box by itself or is there some other way? Customer gave us no purging option.

 

[rbalex]

What does the flame detector labeling say? If it is provided by the burner management supplier, what do their instructions say? While we are at it, why is the location Division 2 if there is a burner present?

 

[petersonra]

What does the flame detector labeling say? If it is provided by the burner management supplier, what do their instructions say? While we are at it, why is the location Division 2 if there is a burner present?

I have run across a couple places where they had some strange classification schemes around ovens and furnaces. Mostly not classified at all, but once I saw Div2 at grade level around the tunnel openings apparently due to the fear that unburned gas would escape from the furnace if there was some kind of failure. I always thought that would be the worst of their troubles if raw gas started coming out the ends of the tunnel. I think their insurance underwriter did the classification.