Class I Division 1 vs Division 2

[don_resqcapt19]

In reading this EC&M article it appears that the only way to have a Division 2 location inside a building where flammable liquids or vapors are handled would be to have a ventilation or purge system. I know that is not the case for the facilities I work in that have interior Class I, Division 2 locations.
The following is from the EC&M article:

Div. 1 is the more stringent of the two divisions. In a Div. 1 location, the gas or vapor is (or may be) present under these conditions:

1. During normal operation.
2. Frequently due to repair, maintenance, or leakage.
3. During equipment breakdown or faulty operation.

A Div. 2 exists in a Class I location only under the following three conditions [500.5(B)(2)]:

1. The liquids, vapors, or gases are confined within closed containers or systems.
2. Positive mechanical ventilation prevents “critical mass” accumulation.
3. Positive mechanical ventilation prevents spillover from an adjacent Class I, Div. 1 location.

I think there is enough difference between 500.5(B)(1)(3) and 500.5(B)(2)(1) to permit interior Class I, Division 2 locations without a purging or ventilation system.

500.5(B)(1)(3) In which breakdown or faulty operation of equipment or processes might release ignitible concentrations of flammable gases, flammable liquid–produced vapors, or combustible liquid–produced vapors and might also cause simultaneous failure of electrical equipment in such a way as to directly cause the electrical equipment to become a source of ignition.

500.5(B)(2)(1) In which volatile flammable gases, flammable liquid–produced vapors, or combustible liquid–produced vapors are handled, processed, or used, but in which the liquids, vapors, or gases will normally be confined within closed containers or closed systems from which they can escape only in case of accidental rupture or breakdown of such containers or systems or in case of abnormal operation of equipment, or

The article seems to ignore some of the wording in 500.5(B)(1)(1) and 500.5(B)(2)(3).

 

[rbalex]

The article is a good example of, "This Code is not intended as a design specification or an instruction manual for untrained persons." [Section 90.1] I know and have a high regard for the author. He is not trained in classified locations though. As I have said many times before, attempting to classify a location from Article 500 alone is inadequate without using one of the references listed Section 500.4(B) IN No.2. Classifying per Art 511 to 516 will usually be adequate though.

"Division 1" list:

• Points 1 & 2 are essentially the same since "repair and maintenance" are normal activities and "leakage" is either normal or it isn't actually Division 1.(It may be Division 2)
• Point 3 indeed requires a situation that may simultaneously cause a release and a source of ignition. The action must cause both.

NOTE: All three cases are framed in characteristic terms of possibility ("can" or "may") rather than probability.

​

"Division 2" list:

• Locations where flammable materials are confined by either closed containers or piping (systems), are not usually classified. (With or without ventilation) They may be classified in high traffic locations where containment is subject to damage.
• The common operative term is "adequate ventilation"; it may be achieved by either natural or mechanical means. Natural air flows through openings and vents, especially ceiling vents, are often all that is necessary.
• Ventilation alone cannot prevent "spillover"; it takes a physical barrier such as a wall. In open air, there will always be a Division 2 envelope surrounding a Division 1 location.

 

[HSB_007]

Class I Division II junction box clarification

Class I Division II junction box clarification

The article is a good example of, "This Code is not intended as a design specification or an instruction manual for untrained persons." [Section 90.1] I know and have a high regard for the author. He is not trained in classified locations though. As I have said many times before, attempting to classify a location from Article 500 alone is inadequate without using one of the references listed Section 500.4(B) IN No.2. Classifying per Art 511 to 516 will usually be adequate though.

"Division 1" list:

• Points 1 & 2 are essentially the same since "repair and maintenance" are normal activities and "leakage" is either normal or it isn't actually Division 1.(It may be Division 2)
• Point 3 indeed requires a situation that may simultaneously cause a release and a source of ignition. The action must cause both.

NOTE: All three cases are framed in characteristic terms of possibility ("can" or "may") rather than probability.

​

"Division 2" list:

• Locations where flammable materials are confined by either closed containers or piping (systems), are not usually classified. (With or without ventilation) They may be classified in high traffic locations where containment is subject to damage.
• The common operative term is "adequate ventilation"; it may be achieved by either natural or mechanical means. Natural air flows through openings and vents, especially ceiling vents, are often all that is necessary.
• Ventilation alone cannot prevent "spillover"; it takes a physical barrier such as a wall. In open air, there will always be a Division 2 envelope surrounding a Division 1 location.

Good day Gentlemen
I have a quick question for clarification purposes. We do use junction boxes for instrumentation; the junction box is located in a class I division II area, and we only require the box to be only NEMA 4X (weather proof), since the box is only housing passive terminal blocks. Does this sound right to you? Does the box needs to have a certain number of threads (say 5, or 8) so gases could not penetrate? My understanding is that it does NOT have to have a certain number of threads because the box itself is not explosion-proof. Again, there are no active components inside the box. Could you share with me your valuable thoughts? Thank you all.

 

[gadfly56]

Good day Gentlemen
I have a quick question for clarification purposes. We do use junction boxes for instrumentation; the junction box is located in a class I division II area, and we only require the box to be only NEMA 4X (weather proof), since the box is only housing passive terminal blocks. Does this sound right to you? Does the box needs to have a certain number of threads (say 5, or 8) so gases could not penetrate? My understanding is that it does NOT have to have a certain number of threads because the box itself is not explosion-proof. Again, there are no active components inside the box. Could you share with me your valuable thoughts? Thank you all.

I believe that unless all the circuits in your instrumentation box are intrinsically safe, the enclosure should be rated for Class 1 Div II; ie, big ugly hunk of aluminum. Kinda like this:

 

[nhee2]

Good day Gentlemen
I have a quick question for clarification purposes. We do use junction boxes for instrumentation; the junction box is located in a class I division II area, and we only require the box to be only NEMA 4X (weather proof), since the box is only housing passive terminal blocks. Does this sound right to you? Does the box needs to have a certain number of threads (say 5, or 8) so gases could not penetrate? My understanding is that it does NOT have to have a certain number of threads because the box itself is not explosion-proof. Again, there are no active components inside the box. Could you share with me your valuable thoughts? Thank you all.

See 501.15(B)(4) - A NEMA 4X box is fine for Class I Div 2 areas, provided your installation does not meet any of the conditions of the sections referenced by 501.15(B)(4). It sounds like your installation is fine.

 

[HSB_007]

Great clarification

Great clarification

See 501.15(B)(4) - A NEMA 4X box is fine for Class I Div 2 areas, provided your installation does not meet any of the conditions of the sections referenced by 501.15(B)(4). It sounds like your installation is fine.

Thank you.

I have looked at the mentioned code, and I guess if I do meet any of the conditions, then I would have to seal the conduit(s) around that box.

 

[nhee2]

Thank you.

I have looked at the mentioned code, and I guess if I do meet any of the conditions, then I would have to seal the conduit(s) around that box.

Only if the conduits are passing through a classification boundary to a non-classified area, or to a Div. 1 area. 501.15(B)(2) provides the requirements.

 

[HSB_007]

Clear and concise reply

Clear and concise reply

Only if the conduits are passing through a classification boundary to a non-classified area, or to a Div. 1 area. 501.15(B)(2) provides the requirements.

Thank you for the great explanation. I have read the code and I do understand it. Thank you