- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Why would you need gas detection in an otherwise unclassified location?
Ventilation and Gas Detection
- Thread starter stickelec
- Start date
- Status
rbalex said:
I was thinking of 500.7(K)(2). The interior of the building is using unclassified equipment... yet it resides in the midst of a Div.2 area. However, after looking much closer the Gas Detection is probably outside in the classified area, not in the unclassified building.
I hope I don't undo everything we've discussed but if I could bring it up here, I am still unclear on something.
RP500 6.51 "Provided the conditions of 6.5.2 are met, the installation of combustible gas detection equipment can be a basis for the following:
a. An inadequately ventilated area containing equipment that could release flammable gas or vapor can be designated Division 2."
It looks like we could have an inadequately ventilated Building, and still be Div.2, if gas detection is present per 6.5.2. I'm really struggling to tie it back into NFPA 70 500.7 Protection Techniques
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Think about it this way, in the world of Documents API RP 500 is neither a Code nor Standard. It is a Recommended Practice. It does have benefit of ANSI sanction which will generally give it a sound footing when used as a design basis. However, if there is an interpretive conflict between NEC Section 500.7(K) (1) which says you are permitted to use Division 2 methods in a Division 1 location and API RP 500 Section 6.5.1 which says you can actually reclassify it as Division 2 ? which do you think would win in a court?
I was on CMP 14 when gas detection became a permitted protection technique. I wasn?t so much opposed to it as simply saying the guidelines weren?t sufficient. This was my ?affirmative? comment on the Panel Action:
No matter what the publication date, RP 500 has not been updated since November 1997. In fact, I happened to be on that technical committee too from 1990 to 2002.
Now a rephrase of my earlier question: Why would you have a gas detector if you didn?t expect there to be a possibility of gas to detect? If there is a possibility of gas, what does it imply about the electrical area classification. Hint: See Section 500.5(B)
Edit: Added the API Section number in the opening paragraph
I was on CMP 14 when gas detection became a permitted protection technique. I wasn?t so much opposed to it as simply saying the guidelines weren?t sufficient. This was my ?affirmative? comment on the Panel Action:
NFPA 70 ? May 2001 ROC Comment 14-51 (Log #2326) Page 415
COMMENT ON AFFIRMATIVE:
ALEXANDER: This affirmative comment is being attached to the
initial ballot in order to permit my Code-Making Panel 14 colleagues
to respond to it, as they feel appropriate. I am documenting some
items here for design and enforcement reference. Hopefully, they
will also appear in the 2002 NEC Handbook.
During the discussion on Comments 14-51 and 14-155, it was the
consensus of Code-Making Panel 14 that a "Combustible Gas
Detection System" does not actually alter the area classification - it
simply permits using reduced installation/protection methods under
certain very specific conditions.
Code-Making Panel 14 also agreed that, while gas detection systems
have been used successfully in those specific conditions, they were not
currently a specifically recognized protection method in either
Section 500-7 or 505-8 and Code-Making Panel 14 wanted to validate
those installations that are consistent with the new text of section 500-
7(k) or 505-8(i).
The new definitions in Sections 500-2 and 505-2 are not in conflict
with the above, but I do not believe that it is immediately apparent
that the electrical area classification is not actually altered.
Since the protection technique will be limited to the specific
conditions noted in Sections 500-7(k) or 505-8(i), I do not believe
that this is a problem at the moment; however, Comments 14-51 and
14-155 actually desired a more generalized permitted use of gas
detection systems. While Code-Making Panel 14 was open to the
concept, we felt that the guidance proposed was insufficient.
I suggested that the submitter might wish to contact the NFPA and
propose a committee project to develop a standard for gas detection
systems similar to NFPA 496.
The only contrary comment came from the API representative. Since I happen to know that his company used gas detection far beyond what is/was currently recognized in the NEC Section 500.7(K), that isn?t surprising. COMMENT ON AFFIRMATIVE:
ALEXANDER: This affirmative comment is being attached to the
initial ballot in order to permit my Code-Making Panel 14 colleagues
to respond to it, as they feel appropriate. I am documenting some
items here for design and enforcement reference. Hopefully, they
will also appear in the 2002 NEC Handbook.
During the discussion on Comments 14-51 and 14-155, it was the
consensus of Code-Making Panel 14 that a "Combustible Gas
Detection System" does not actually alter the area classification - it
simply permits using reduced installation/protection methods under
certain very specific conditions.
Code-Making Panel 14 also agreed that, while gas detection systems
have been used successfully in those specific conditions, they were not
currently a specifically recognized protection method in either
Section 500-7 or 505-8 and Code-Making Panel 14 wanted to validate
those installations that are consistent with the new text of section 500-
7(k) or 505-8(i).
The new definitions in Sections 500-2 and 505-2 are not in conflict
with the above, but I do not believe that it is immediately apparent
that the electrical area classification is not actually altered.
Since the protection technique will be limited to the specific
conditions noted in Sections 500-7(k) or 505-8(i), I do not believe
that this is a problem at the moment; however, Comments 14-51 and
14-155 actually desired a more generalized permitted use of gas
detection systems. While Code-Making Panel 14 was open to the
concept, we felt that the guidance proposed was insufficient.
I suggested that the submitter might wish to contact the NFPA and
propose a committee project to develop a standard for gas detection
systems similar to NFPA 496.
No matter what the publication date, RP 500 has not been updated since November 1997. In fact, I happened to be on that technical committee too from 1990 to 2002.
Now a rephrase of my earlier question: Why would you have a gas detector if you didn?t expect there to be a possibility of gas to detect? If there is a possibility of gas, what does it imply about the electrical area classification. Hint: See Section 500.5(B)
Edit: Added the API Section number in the opening paragraph
Last edited:
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Because it doesn't always conform to the NEC, although it intends to. As I said earlier, some of the non-conforming applications are accepted by the US Coast Guard. Then it's the NEC that doesn't apply.stickelec said:
Almost got it - it implies a Class I location. It may be either Division 1 or 2. (Assuming it is detecting an ignitible gas, of course. E.g., it could be an oxygen or nitrogen detector. They each have their own safety issues, they just don't cause Classified locations.)stickelec said:
rbalex said:
Wow... I can see why the the process of Classification (including Gas Detection and Ventilation) is so subjective.
I don't know how I could argue for or against either if I don't have a soild basis to support NEC 500 Classification requirements. I'm even trying to see how NFPA 497 fits into the scheme of things, and what "authority" it has considering it is also a Recommended Practice.
How can I say "parts" of RP500 are applicable but others are not? Please help me get a grasp how this really fits togther.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
I wouldn?t call educated judgment ?subjective.?
The NEC isn?t ??a design specification or an instruction manual for untrained persons.? (Section 90.1(C)) The key is becoming familiar enough with the subject matter to recognize what material does and doesn?t apply and when and where it applies.
As ?Recommended Practices? API RP 500 and NFPA 497 essentially ARE design manuals, but they DON?T necessarily apply in every case and they are still not for ?untrained persons? either. You must recognize when they apply. That is where experience comes in.
One of the problems with RP 500 is that it hasn't been updated since the NEC recognized a limited use of gas detection. I also wish the gas detector industry (the originators of the Proposal/Comment that was accepted) would have taken the advice to develop more comprehensive guidance. If you read their original Proposal they wanted gas detection to be a general purpose solution. After reading the "acceptable" applications in RP 500, I?m sure you know they aren't general purpose solutions. Some gas detector manufactures are still marketing their products that that way though. So caveat emptor.
I?m the one that pointed out to the CMP, "gas detector" automatically means "Class I location." Even my API colleague accepted that.
As we have noted, the NEC doesn?t apply everywhere either ? but it probably applies to your installation. Since it does, except for the very limited application of Section 500.7(K)(1), gas detection doesn?t change the electrical area classification but ?n a Class I, Division 1 location that is so classified due to inadequate ventilation, electrical equipment suitable for Class I, Division 2 locations shall be permitted.? That isn?t subjective at all.
The NEC isn?t ??a design specification or an instruction manual for untrained persons.? (Section 90.1(C)) The key is becoming familiar enough with the subject matter to recognize what material does and doesn?t apply and when and where it applies.
As ?Recommended Practices? API RP 500 and NFPA 497 essentially ARE design manuals, but they DON?T necessarily apply in every case and they are still not for ?untrained persons? either. You must recognize when they apply. That is where experience comes in.
One of the problems with RP 500 is that it hasn't been updated since the NEC recognized a limited use of gas detection. I also wish the gas detector industry (the originators of the Proposal/Comment that was accepted) would have taken the advice to develop more comprehensive guidance. If you read their original Proposal they wanted gas detection to be a general purpose solution. After reading the "acceptable" applications in RP 500, I?m sure you know they aren't general purpose solutions. Some gas detector manufactures are still marketing their products that that way though. So caveat emptor.
I?m the one that pointed out to the CMP, "gas detector" automatically means "Class I location." Even my API colleague accepted that.
As we have noted, the NEC doesn?t apply everywhere either ? but it probably applies to your installation. Since it does, except for the very limited application of Section 500.7(K)(1), gas detection doesn?t change the electrical area classification but ?n a Class I, Division 1 location that is so classified due to inadequate ventilation, electrical equipment suitable for Class I, Division 2 locations shall be permitted.? That isn?t subjective at all.
I wasn't going to pursue this any further but this one bothered me all night, so if I could please...
Per 500.7(K)(1) I can have the following:
a) Compressor Building classified Div.1 due to Inadequate Ventilation.
b) Combustible Gas Detection present.
c) Equipment and Wiring Methods consistant with Div.2 requirements.
Why do I have a Div.1 building, nothing inside is to Div.1 specification?
It looks like an easy out to just classify Div.1 and not go to the trouble to meet the requirements for Adequate Ventilation. As was mentioned earlier, DOT mandates Gas Detection anyway (in our application).
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Please clarify the question if I?m not interpreting it correctly.stickelec said:
To begin with, from the OP I believe we are talking about methane, a lighter than air flammable gas. Since you have RP 500 available now, we start with two basic options ? see Section 9.2.2.2 with its accompanying figures 25 and 26, both on page 35. From what I have understood so far, Figure 26 is the more applicable. Therefore, with no other information and forgetting gas detection and DOT for the time being the interior of the building would be Class I, Division 1.
I believe that answers your direct question.
Now let?s add the DOT requirements ? they are irrelevant for the classification analysis. They are provided for personnel warning and the electrical area classification doesn?t change. The installation still needs to be suitable for Division 1.
Next let?s add gas detection that conforms to API RP 500 Section 6.5.1a. We must also recognize that Section 6.5.1b is not applicable because the location under discussion DOES ??contain a source of flammable gas or vapor?? The rest of Section 6.5.1b is irrelevant for the discussion.
Section 6.5.1a then leads us Section 6.5.2. If you then follow all the instructions in Section 6.5.2, Section 6.5.1a says you may treat the location as Division 2. NEC Section 500.7(K)(1) says you are permitted to use Division 2 methods. For most practical cases it is the same thing
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
That?s interesting ? I had the impression that the compressor building was totally enclosed. If it is more like Figure 25, why are you worrying about ventilation? After you install the DOT required gas detectors the only real concern would be lighting and possibly an overhead crane; neither of which could economically justify additional gas detection.
rbalex said:
I guess I am misinterpreting what 25 is showing. It says "Inadequately Ventilated Compressor Shelter With Lighter-Than-Air Gas Or Vapor Source". It looks like an enclosed building with a 10' (Div.2) perimiter.
Anyway, by building(s) is totally enclosed with multiple Natural Gas Compressors discharging at approx. 1000psi.
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Figure 26 applies. Figure 25 is a "shelter" - open bottom, enclosed (inadequately ventilated) top. You didn't notice it was Division 2 around the "source?"
rbalex said:
Ok my bad. I just wasn't expecting an enclosed Compressor Building (Shelter) with enclosed top, sides, and bottom that doesn't have the "source" inside.
Point is, if we add either Ventilation or Gas Detection inside the Div.1 enclosed area we could use Div.2 equipment.
weressl
Esteemed Member
stickelec said:
Hm......
Open bottom compressor shelters are usually constructed with a top venting ridge that will allow lighter-than-air gases to escape. That COULD constitute adequate ventillation. That construction style was developed just for that reason.
KentAT
Senior Member
- Location
- Northeastern PA
Stickelec - Is your compressor building part of a natural gas pipeline facility?
If YES, then section 14 in the API-RP500 would apply to your installation, and Figure 106 would be for inadequately ventilated compressor buildings.
Bob and stickelec - as you might recall from my prior questions on the subject, our company has taken the position that classifying our compressor buildings as Div 1 has been too conservative (and thus too costly) due to the definition of Div 1, and has reclassified many buildings as Div 2 either because the Div 1 criteria are not met or because ventilation and gas detection are used to reduce it to a Div 2.
However, I now see that the use of ventilation and gas detection just allows Div 2 rated equipment to be used, and the classification is not actually reduced, it remains unchanged. (This, to me, is a major point!)
From API-RP500:
3.2.10.2 Class I, Division 1 location: A location in
which ignitible concentrations of flammable gases or vapors
are expected to exist under normal operating conditions or in
which faulty operation of equipment or processes might simultaneously
release flammable gases or vapors and also cause
failure of electrical equipment.
From 2005 NEC:
(1) Class I, Division 1. A Class I, Division 1 location is a location
(1) In which ignitible concentrations of flammable gases or vapors can exist under normal operating conditions, or
(2) In which ignitible concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or because of leakage, or
(3) In which breakdown or faulty operation of equipment or processes might release ignitible concentrations of flammable gases or 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.
The basis of their explanation is that this is because:
for "normal operating conditions": there is no venting of gas inside the buildings under normal conditions. This is accomplished by prohibiting using any instrument, control, or equipment that uses natural gas as the control medium and vents inside the building. Examples are by using controls that use instrument air instead of gas, piping the vents or bleeds of gas-operated pilots on regulators and relief valves to outside of the buildings. I agree. (But I wonder about the multitude of valve packing glands - I guess if they are leaking this is not normal as the packing should be tightened)
for simultaneous gas release & electrical failure/risk of ignition: No explanation. I have not yet seen any explanation or discussion as how sound engineering judgement can accomplish stating that there is/is not this possibility in an installation, or to examine and quantify the risk therof. I have to believe in the absence of such study, this cannot be eliminated as a condition which requires a Div 1 classification. Does anyone have examples of this?
for "frequenty" existing gas concentrations due to repair, maintenance, or leakage: No explanation. What is considered "frequent"? Without a definition or guiding principle, one cannot say that gas concentrations are frequent, and the "sound engineering judgement" tends to lean towards gas concentrations not being frequent enough.
Kent
If YES, then section 14 in the API-RP500 would apply to your installation, and Figure 106 would be for inadequately ventilated compressor buildings.
Bob and stickelec - as you might recall from my prior questions on the subject, our company has taken the position that classifying our compressor buildings as Div 1 has been too conservative (and thus too costly) due to the definition of Div 1, and has reclassified many buildings as Div 2 either because the Div 1 criteria are not met or because ventilation and gas detection are used to reduce it to a Div 2.
However, I now see that the use of ventilation and gas detection just allows Div 2 rated equipment to be used, and the classification is not actually reduced, it remains unchanged. (This, to me, is a major point!)
From API-RP500:
3.2.10.2 Class I, Division 1 location: A location in
which ignitible concentrations of flammable gases or vapors
are expected to exist under normal operating conditions or in
which faulty operation of equipment or processes might simultaneously
release flammable gases or vapors and also cause
failure of electrical equipment.
From 2005 NEC:
(1) Class I, Division 1. A Class I, Division 1 location is a location
(1) In which ignitible concentrations of flammable gases or vapors can exist under normal operating conditions, or
(2) In which ignitible concentrations of such gases or vapors may exist frequently because of repair or maintenance operations or because of leakage, or
(3) In which breakdown or faulty operation of equipment or processes might release ignitible concentrations of flammable gases or 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.
The basis of their explanation is that this is because:
for "normal operating conditions": there is no venting of gas inside the buildings under normal conditions. This is accomplished by prohibiting using any instrument, control, or equipment that uses natural gas as the control medium and vents inside the building. Examples are by using controls that use instrument air instead of gas, piping the vents or bleeds of gas-operated pilots on regulators and relief valves to outside of the buildings. I agree. (But I wonder about the multitude of valve packing glands - I guess if they are leaking this is not normal as the packing should be tightened)
for simultaneous gas release & electrical failure/risk of ignition: No explanation. I have not yet seen any explanation or discussion as how sound engineering judgement can accomplish stating that there is/is not this possibility in an installation, or to examine and quantify the risk therof. I have to believe in the absence of such study, this cannot be eliminated as a condition which requires a Div 1 classification. Does anyone have examples of this?
for "frequenty" existing gas concentrations due to repair, maintenance, or leakage: No explanation. What is considered "frequent"? Without a definition or guiding principle, one cannot say that gas concentrations are frequent, and the "sound engineering judgement" tends to lean towards gas concentrations not being frequent enough.
Kent
- Location
- Mission Viejo, CA
- Occupation
- Professional Electrical Engineer
Where did they find the definition of normal? "Normal" and "common" are not the same thing.
One of the subtle, and often overlooked, concepts with the US domestic definitions of Class I, Divisions and Zones, is they are defined in terms of ?possibility,? not ?probability.?
One of the subtle, and often overlooked, concepts with the US domestic definitions of Class I, Divisions and Zones, is they are defined in terms of ?possibility,? not ?probability.?
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