Intrinsic barrier necessary for this Class I, Div 2 application?

[FAZERS]

I am trying to determine whether or not an equipment upgrade we are planning to implement to our existing equipment will necessitate the use of an intrinsic barrier device. We are adding a bank of 3 or 4 connectors to the side of the equipment in order to electrically connect to some remote boxes (each up to 100 feet away) that will be attached via cable to the box's internal gas flow meters. While the meters each provide 4-20mA back, they are flexible configuration devices and as such require a 3-wire connection that uses vsup (24V) and gnd.

This mobile (immobile during energization/use) natural gas field service equipment currently has 2 LEL detection devices, one inside the equipment enclosure with other electronic devices per 500.7(K)(4), and the other located outside the enclosure, but on the chassis of the equipment that, presumably, can sometimes achieve Inadequate Ventilation (500.7(K)(2)) due to its potential to be in a semi-enclosed configuration whereby the doors come down and surround most of the piping which the NG is routed through before we individually meter it.

Before I spend $80 to buy C22.2 #213-17 and decide if there's verbiage that grants me something nonincendive, does the exterior LEL sound like its alarming capabilities could permit me to not use a barrier? I say the exterior one instead of the interior one because I am assuming its exposure to gas would occur first.

Also, the flow meters are 18-30Vdc, <100mA each. Each "box" is comprised of 4 meters. In an ideal world, maybe it would be nonincendive somehow already, because we sure are running out of space inside these equipment enclosures, and I am already having to allocate a large chunk of what little remaining DIN we have left to accommodate the AI for this upgrade.

Thanks for any opinions on the matter!

 

[rbalex]

• Any legitimate application of gas detection [Section 500.7(K)] will automatically be a Division 2 location. It may permit altered wiring methods, but the classification does not change.
• Intrinsic Safety (IS) is not itself required in Division 2. Section 501.10(B)(3) permits unclassified [nonincentive (NI)] wiring methods with a properly applied and identified control drawing.

Those are my opinions. I cannot detail design your installation.

 

[FAZERS]

I'll back up a little bit here.

We are working under the assumption that the classification is Division 2. I also acknowledge IS is not a hard requirement in D2. However, in IEC 60079-11, the "ignition limit curves" for hazardous gases still seem to be applied beyond just Division 1. Our concern is that a cable getting damaged or severed -- internally shorting VSUP and GND -- in the segment extending from the equipment to as far as 15 feet out, could permit too much energy release beyond this ignition limit curve.

Our confusion largely thus seems to be fully understanding the definition of "nonincendive." Looking into it a little further, my interpretation of the word seems to be shared with this graphic, credited to John Vu of Automation.com:



...In my mind, the "energy-limited" portion in Installation Approaches isn't much different than IS, but that if we could develop a non-arcing approach, it would be sufficient. Though we do require the flexibility to be able to plug and unplug new sensor boxes in during a live job without shutting down the system, I do feel like we could still potentially use a "non-arcing, not energy limited (similarly nA)" approach. On our system, we do already utilize an interlocked protection box for an optional 120VAC extension cord socket. The box must be opened which in turn opens a limit switch and prevents energization during mating. I think this same approach could be used for this system without requiring the use of intrinsic barriers.

That's about as far as I've gotten with it.

 

[FAZERS]

One obvious thing I left out is the severing issue. The above works for makes/breaks, but not severing. However we've already been using the interlocked power box, which is also accompanied by our SOP stating to keep all employees out of the designated C1D2 radius as well as cone off the perimeter.

 

[rbalex]

Unless you are designing an IEC project, citing any IEC 60079 series document is meaningless in a US domestic application. Very few AHJs have any idea what they would be looking at.

For more on IS or NI installations see ANSI/ISA RP 12.06.01 or ANSI/UL 12.12.01.

A little HAZLOC philosophy:

• The fire triangle requires air, a source of ignition, and a source of fuel. Remove one of them, and the fire or explosion cannot occur.
• Air is usually always available. We aren’t discussing protection techniques at the moment, we are discussing ignitions.
• A source of fuel may or may not be available in “normal” operating conditions BUT it can be available under some conditions in classified locations. See the definitions in Section 500.5. Note they are defined in terms of possibility rather than probability.
• Sources of Ignition may be normal, that is doing what they are supposed to do or abnormal, that is created by accident or malfunction.

Now we can talk about probability.

• In Division 2, fuel is usually absent in normal operations and we tend to worry only about “normal” sources of ignition; arcs, sparks, and high temperatures (ASH).
• In Division 1, you can’t count on fuel being absent in normal operations, so any and all sources of ignition are considered.

In your case, unless “severing” is a common occurrence, it would not be usually be considered.

 

[don_resqcapt19]

....
Our confusion largely thus seems to be fully understanding the definition of "nonincendive." Looking into it a little further, my interpretation of the word seems to be shared with this graphic, credited to John Vu of Automation.com:
...

If you are talking about nonincendive in an NEC application, the only definitions that count are the ones in the NEC.

Nonincendive Circuit.
A circuit, other than field wiring, in which any arc or thermal effect produced under intended operating conditions of the equipment, is not capable, under specified test conditions, of igniting the flammable gas–air, vapor–air, or dust–air mixture. (CMP-14)
Nonincendive Component.
A component having contacts for making or breaking an incendive circuit and the contacting mechanism is constructed so that the component is incapable of igniting the specified flammable gas–air or vapor–air mixture. The housing of such a component is not intended to exclude the flammable atmosphere or contain an explosion. (CMP-14)
Nonincendive Equipment.
Equipment having electrical/electronic circuitry that is incapable, under normal operating conditions, of causing ignition of a specified flammable gas–air, vapor–air, or dust–air mixture due to arcing or thermal means. (CMP-14)
Nonincendive Field Wiring.
Wiring that enters or leaves an equipment enclosure and, under normal operating conditions of the equipment, is not capable, due to arcing or thermal effects, of igniting the flammable gas–air, vapor–air, or dust–air mixture. Normal operation includes opening, shorting, or grounding the field wiring. (CMP-14)
Nonincendive Field Wiring Apparatus.
Apparatus intended to be connected to nonincendive field wiring. (CMP-14)

 

[rbalex]

Unless you are designing an IEC project, citing any IEC 60079 series document is meaningless in a US domestic application. Very few AHJs have any idea what they would be looking at.

I must correct myself. Protection by Electrical Resistance Trace Heating “60079-30-1" is Section 500.8(P). It ‘s my understanding citing a Standard in other than Informative Notes (IN) is a violation of the NFPA/NEC Manual of Style (MOS). See Section 90.5(C).
It’s not too surprising though. The ISA has been ramming through European standards for a long time.
Nevertheless, 60079-30-1 doesn’t apply to the OP and the rest of the previous reply is accurate.