Ventilation and Gas Detection

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stickelec

Senior Member
I am confused about the ventilation and Gas Detection requirements for Natural Gas Compressor Buildings. I understand API RP500 is the final authority and section 6.3.2.4.2 makes the reference. I have searched the web for (1) a copy and (2) specific information in regard to that article, with basically no success at either. The best info by far came from this searching this site.

My questions are:

1) If a Compressor Building (>600 psi) is fully enclosed it must have Gas Detection, but what are the minimum requirements? ie: Sensors per sq. ft. for example.

2) Does the same Building require forced ventilation and if so, is the minimum requirement six exchanges per hour?

3) I understand some users only activate the fans when the LEL =/> 20%. Does that meet the requirements for ?forced ventilation?? If so, apparently forced ventilation is not "full time".

4) If forced ventilation is required, and the minimum is 6 ex/hr, then does that mean the control system must respond to a ventilation failure, and if so, with what response?

5) I understand RP500 makes reference to ?adequate and inadequate?, if a Building falls into the inadequate category what are the consequences?

6) Where can I find access to RP500?

Thanks
 

rbalex

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Professional Electrical Engineer
stickelec said:
I am confused about the ventilation and Gas Detection requirements for Natural Gas Compressor Buildings. I understand API RP500 is the final authority and section 6.3.2.4.2 makes the reference. I have searched the web for (1) a copy and (2) specific information in regard to that article, with basically no success at either. The best info by far came from this searching this site.

My questions are:

1) If a Compressor Building (>600 psi) is fully enclosed it must have Gas Detection, but what are the minimum requirements? ie: Sensors per sq. ft. for example.

2) Does the same Building require forced ventilation and if so, is the minimum requirement six exchanges per hour?

3) I understand some users only activate the fans when the LEL =/> 20%. Does that meet the requirements for ?forced ventilation?? If so, apparently forced ventilation is not "full time".

4) If forced ventilation is required, and the minimum is 6 ex/hr, then does that mean the control system must respond to a ventilation failure, and if so, with what response?

5) I understand RP500 makes reference to ?adequate and inadequate?, if a Building falls into the inadequate category what are the consequences?

6) Where can I find access to RP500?

Thanks
Gas detection is never a requirement; it is a permitted protection technique. It is a very limited protection technique at that. See NEC Section 500.7 (K). API RP 500, Section 6.5.1 further describes the applications permitted in NEC Sections 500.7 (K)(1) and (2).

NFPA 30 defines ?adequate ventilation.? API RP 500 describes, but does not mandate, using gas detection as one means of determining adequate ventilation. Six air changes an hour is a presumptive minimum to achieve adequate ventilation by either natural or forced means. It is a full time requirement per NFPA 30. In Item 3 above the users will have a very difficult time defending their practice.

Where adequate ventilation is used as a basis for electrical area classification, loss of adequate ventilation (determined by whatever means) generally requires shutdown of electrical sources in the affected location or the electrical installations remaining energized must be suitable for Division 1.

API RP 500 may be purchased directly from API. It is also downloadable from IHS. It isn?t cheap in either case.
 

KentAT

Senior Member
Location
Northeastern PA
While the NEC and APIRP500 do not require gas detection as Bob stated, if your natural gas compressor station is regulated under federal DOT Title 49, Part 192 "Transportation of Natural and Other Gas by Pipeline" then you are required to have a fixed gas detection and alarm system unless the compressor building is:

192.736 (a):
(1) Constructed so that at least 50 percent of its upright side area is permanently open; or
(2) Located in an unattended field compressor station of 1,000 horsepower
(746 kW) or less.


Even if required by DOT there is no stated minimum as sensors per sq. ft.. Additionally the DOT requirement for fixed gas detection is mostly concerned with alerting personnel inside or about to enter the building that there is gas inside, and not primarily for NEC or API RP500 compliance (although the reg states that :

192.613 (e) Electrical facilities. Electrical equipment and wiring installed in copressor
stations must conform to the National Electrical Code, ANSI/NFPA70, so far as that code is applicable.


I too have questioned my company's use of the "part time" forced ventilation to reduce our previousely Class 1, Div 1 buildings to Div 2.

kent
 

stickelec

Senior Member
Thanks to both of you, your replies really helped clear up a lot of the confusion.

I purchased 497 but have not purchased RP500 yet, but I will soon (it is a bit pricey).

Bob, in regard to your comment: "API RP 500 describes, but does not mandate, using gas detection as one means of determining adequate ventilation."

Please help me understand how "using gas detection" could influence the definitive ventilation requirements of 6 changes/hr or 1 cfm/sqft.

It is clear to me now that Ventilation actually has significant influence regarding the Area Classification of a compressor building.

Thanks again to both of you
 

rbalex

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stickelec said:
I purchased 497 but have not purchased RP500 yet, but I will soon (it is a bit pricey).
At one time, RP 500 represented over 50% of API operating income. I don’t know the current percentage, but I believe it is still their best seller.

stickelec said:
Bob, in regard to your comment: "API RP 500 describes, but does not mandate, using gas detection as one means of determining adequate ventilation."

Please help me understand how "using gas detection" could influence the definitive ventilation requirements of 6 changes/hr or 1 cfm/sqft.



You will want to start with NFPA 30. In Section 7.3.4 (Ventilation) states:
7.3.4.1 Enclosed processing areas handling or using Class I liquids or Class II or Class III liquids, heated to temperatures at or above their flash points, shall be ventilated at a rate sufficient to maintain the concentration of vapors within the area at or below 25 percent of the lower flammable limit. Compliance with 7.3.4.2 through 7.3.4.5 shall be deemed as meeting the requirements of 7.3.4.1.




The referenced Sections 7.3.4.2 through 7.3.4.5 mention things like fugitive emissions calculations, actual sampling of the air at specific locations, the magic 1 cfm/sqft (actually an exception), etc. These Sections also describe specific installation requirements for recycling and/or makeup air.

API RP 500 is essentially saying 6 air changes/hr will always meet or exceed the 1cfm/sqft. RP 500 also recognizes gas detection for monitoring recycled air. Remember RP 500 is primarily an electrical area classification document and reviews various installation “geometries” to determine classifications.

stickelec said:
It is clear to me now that Ventilation actually has significant influence regarding the Area Classification of a compressor building.
Bingo:grin: – this is actually true for all electrical area classification analysis.
 
rbalex said:
At one time, RP 500 represented over 50% of API operating income. I don?t know the current percentage, but I believe it is still their best seller.






You will want to start with NFPA 30. In Section 7.3.4 (Ventilation) states:
7.3.4.1 Enclosed processing areas handling or using Class I liquids or Class II or Class III liquids, heated to temperatures at or above their flash points, shall be ventilated at a rate sufficient to maintain the concentration of vapors within the area at or below 25 percent of the lower flammable limit. Compliance with 7.3.4.2 through 7.3.4.5 shall be deemed as meeting the requirements of 7.3.4.1.





The referenced Sections 7.3.4.2 through 7.3.4.5 mention things like fugitive emissions calculations, actual sampling of the air at specific locations, the magic 1 cfm/sqft (actually an exception), etc. These Sections also describe specific installation requirements for recycling and/or makeup air.

API RP 500 is essentially saying 6 air changes/hr will always meet or exceed the 1cfm/sqft. RP 500 also recognizes gas detection for monitoring recycled air. Remember RP 500 is primarily an electrical area classification document and reviews various installation ?geometries? to determine classifications.

Bingo:grin: ? this is actually true for all electrical area classification analysis.

Thank you all this is a very useful clarification for all to benefit! Kudos!
 

stickelec

Senior Member
I too want to thank both of you again.

I have been reading DOT 192.736, and I ordered RP500 yesterday. I really appreciate the willingness of knowledgable people to share with others on this forum.
 

stickelec

Senior Member
I received my RP500 and now... and the saga continues.

6.3.2.4.4 and 6.3.2.4.8 Recirculation of inside air is permitted if... appears to indicate that recirculation is ok in lieu of Adequate Ventilation because it speaks of an alarm condition "providing exhaust to the outside" at the previously defined 6 ex/hr, etc.

I can see where recirc could be really nice in real cold country. But, it doesn't specify the rate; only that it has to be monitored with Gas Detection.

Am I missing something? I admit I haven't read much of it yet. (Reading while working).

Thanks
 

rbalex

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Before you go much further and begin interpreting Sections out of Context, I suggest reading ALL of RP 500's Chapters 1, 6 and 7. Especially read the document’s scope (Chapter 1) very carefully.
 

stickelec

Senior Member
rbalex said:
Before you go much further and begin interpreting Sections out of Context, I suggest reading ALL of RP 500's Chapters 1, 6 and 7. Especially read the document?s scope (Chapter 1) very carefully.


Bob, I carefully read the chapters but I'm still not clear on Recirculation.

I understand that ventilation must be given serious consideration when determining the Area Classification of a Comp Bldg. Determining Adequate and Inadequate ventilation is also straight forward, but I still don't understand 6.3.2.4.4 and 6.3.2.4.8 Recirculation of inside air is permitted if... it appears to offer Recirculation as an option to full-time Adequate Ventilation.

If a Building was totally Div.1 then no ventilation requirements would be necessary. However, if Div.2 then ventilation enters the equation. With that said how does Recirculation fit in... it appears to replace Adequate Ventilation because it does say that a Gas Detection Alarm would "provide exhaust at the rate of 6 ex/hr, etc". Its as if the exhaust did not exist until the Alarm condition occurred, then it was activated.

Thanks
 

rbalex

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I?m now going to redirect your attention to the NEC for a moment. Which of the ONLY three permissive applications in Section 500.7(K) are API Sections 6.3.2.4.4 and 6.3.2.4.8 addressing?
 

stickelec

Senior Member
rbalex said:
I?m now going to redirect your attention to the NEC for a moment. Which of the ONLY three permissive applications in Section 500.7(K) are API Sections 6.3.2.4.4 and 6.3.2.4.8 addressing?

Combustible Gas Detection shall be permitted as a means of protection... IF the following three application/requirements are observed:

1) Industrial establishments
2) Restricted public access
3) Maintained & supervised by qualified personnel

So, I would deduct that Gas Detection can be a satisfactory means of protection IF - one of the following types of Ventilation is provided:

1) Ventilating by either Natural or Mechanical means (per RP500 spec).
2) Recirculation - PLUS Mechanical Ventilation when LEL =/>25% (per RP500 spec).

Therefore as Kent pointed out, if we fall under DOT Title 49, Part 192 requirements, Gas Detection is required... but thats not the end of the story.

If the choice was to not meet the requirements for Natural Ventilation, then there is going to be some Fans on... either Ventilating or Recirculating.
 

rbalex

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That isn't what I asked. Which of 500.7(K) (1), (2) or (3) is being addressed? Those are the only applications recognized by the NEC for gas detection to be a classified location protection technique. The DOT requirements are for personnel signaling, not electrical area classification.
 

stickelec

Senior Member
rbalex said:
That isn't what I asked. Which of 500.7(K) (1), (2) or (3) is being addressed? Those are the only applications recognized by the NEC for gas detection to be a classified location protection technique. The DOT requirements are for personnel signaling, not electrical area classification.

Sorry I missed the question. I've read 500.7(K) and RP500 6.3 & 6.5 at least 10 times, so here goes:

6.3.2.4.4 & 6.3.2.4.8 are addressing "rooms, buildings, or spaces" therefore in 500.7(K) I would say all three are being addressed: (1) Inadequate Ventilation, (2) Interior of a Building (3) Interior of a Control Panel.
 

rbalex

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OK, you’ve read the Section titles, now explain how the accompanying text applies to YOUR installation.

From NEC Sections 500.7(K)(1), (2) and (3):
(1) Inadequate Ventilation In 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.
(2) Interior of a Building In a building located in, or with an opening into, a Class I, Division 2 location where the interior does not contain a source of flammable gas or vapor, electrical equipment for unclassified locations shall be permitted.
(3) Interior of a Control Panel In the interior of a control panel containing instrumentation utilizing or measuring flammable liquids, gases, or vapors, electrical equipment suitable for Class I, Division 2 locations shall be permitted.
Hints:

500.7(K)(1) If it applies - explain how and what are you actually permitted to do?
500.7(K)(2) Is this a condition "... where the interior [of the location] does not contain a source of flammable gas or vapor..."
500.7(K)(3) How does it apply? - Don't guess.
 
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stickelec

Senior Member
rbalex said:
OK, you?ve read the Section titles, now explain how the accompanying text applies to YOUR installation.

From NEC Sections 500.7(K)(1), (2) and (3):Hints:

500.7(K)(1) If it applies - explain how and what are you actually permitted to do?
500.7(K)(2) Is this a condition "... where the interior [of the location] does not contain a source of flammable gas or vapor..."
500.7(K)(3) How does it apply? - Don't guess.

I've done much more than read the section titles, I've studied the content many times, I'm sorry I've tried your patience. I paid $288 to get RP500 here before the long-weekend to try to get an understanding of how the various codes apply to my question.

500.7(K)(1): If it applies - explain how and what are you actually permitted to do?

If I had a Natural Gas Compressor Building that was classified Div.1 solely because of Inadequate Ventilation, I could use Div.2 equipment IF I had Combustible Gas Detection per RP500 6.5

500.7(K)(1): Is this a condition "... where the interior [of the location] does not contain a source of flammable gas or vapor..."

Well, I suppose it is a condition. I take this to mean a building like an office, shop, storage, etc., can be in a surrounding Div.2 area IF there is no source of gas within the building AND Combustible Gas Monitoring per RP500 6.5 is present.

500.7(K)(1): How does it apply? - Don't guess.

It would apply to a Control Panel that had an Instrument(s) that used Natural Gas. ie: H2S Analyzer, I/P on Instrument-Gas, etc. In that case it would be okay to have Div.2 equipment inside the same Panel. All this is okay IF Combustible Gas Detection is present per RP500 6.5
 

rbalex

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You have not tried my patience. You are obviously trying to learn. I?m just trying to get you to quit attempting to force-fit answers and recognize when something doesn?t apply to a given situation.

Your answer to 500.7(K)(1) is correct as it applies to your original question.

Sections 500.7(K)(2) and (3) simply don?t apply to your question.

It is important to recognize that gas detection DOES NOT change the electrical area classification under Section 500.7(K). It simply permits using different equipment and wiring techniques. Sections 500.7(K)(1) and (3) permit using Division 2 methods in certain specific Division 1 locations and Section 500.7(K)(2) allows using unclassified methods in certain specific Division 2 locations.

In all three cases the application is very specific and NONE of them have anything to do with air recirculation. Therefore, many of the API ?applications? aren?t consistent with the NEC at all. They are however, consistent with certain practices permitted by the US Coast Guard in various marine facilities which are not under NEC jurisdiction.

Note the ?RP? in API RP 500 means ?Recommended Practice.? The document is not a ?Code.?
 

stickelec

Senior Member
rbalex said:
You have not tried my patience. You are obviously trying to learn. I?m just trying to get you to quit attempting to force-fit answers and recognize when something doesn?t apply to a given situation.

Your answer to 500.7(K)(1) is correct as it applies to your original question.

Sections 500.7(K)(2) and (3) simply don?t apply to your question.

It is important to recognize that gas detection DOES NOT change the electrical area classification under Section 500.7(K). It simply permits using different equipment and wiring techniques. Sections 500.7(K)(1) and (3) permit using Division 2 methods in certain specific Division 1 locations and Section 500.7(K)(2) allows using unclassified methods in certain specific Division 2 locations.

In all three cases the application is very specific and NONE of them have anything to do with air recirculation. Therefore, many of the API ?applications? aren?t consistent with the NEC at all. They are however, consistent with certain practices permitted by the US Coast Guard in various marine facilities which are not under NEC jurisdiction.

Note the ?RP? in API RP 500 means ?Recommended Practice.? The document is not a ?Code.?

Excellent, thank you very much! I'm going to do a bit more reading and digest what you have given me.

I was really trying to plug recirculation in there. It sounded like a nice option. :grin:
 

rbalex

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Permit me to offer one other thing to digest. Ignoring Section 500.7(K) for the time being, what electrical area classification does gas detection imply?
 

stickelec

Senior Member
rbalex said:
Permit me to offer one other thing to digest. Ignoring Section 500.7(K) for the time being, what electrical area classification does gas detection imply?

I would think it implies either Div.2 or Unclassified.
 
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