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Thread: use NFPA and NEC to reduce bldg from CID1 to CID2?

  1. #11
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    > The building has been designated simply as “Hazardous Materials Building” but no one is sure what exactly the materials will be housed
    > within – one must assume both lighter than air as well as heavier than air hazardous vapors could be installed.

    Interesting scenario. I guess it's unspecified flammable liquids in unsealed tanks, and not cylinders of gas, LPG, or the like? (You didn't say.)

    Based on what we know, I pretty much concur with everyone else - adequate ventilation would be the way to go. Since you mentioned ventilation alone is not acceptable, I assume ventilation must be possible. That would (hopefully) get you Div 2 without the need to worry about validity.

    If the client "doesn't trust ventilation alone", and wants combustible gas detection on top, that's fine. But the gas detection would (ideally) have nothing to do with the area classification or the allowable equipment since it would not be needed as a protection method.

    Having built gas detectors for some decades, I would not trust gas detection as a protection method unless I had at least some idea of the substances it's supposed to be detecting. Plus the sensitivity for heavy hydrocarbons is often poor, and T90 times are often long. But if it's only supplementary, gas detection would devolve from critical to merely important, lowering the burden of proof.

    In a practical sense you'd still have to worry about how to detect the heavier hydrocarbons effectively. Plus, if you're expecting both lighter- and heavier-than-air, you'd probably have to have some detectors near the roofline and some near grade, increasing costs. Maybe even different calibrations / correction factors for the upper and lower detectors.

    > Well, reasonable assumptions are made all the time in this business.

    Doesn't make it right.

  2. #12
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    Quote Originally Posted by IntrinsicSafety View Post
    > The building has been designated simply as “Hazardous Materials Building” but no one is sure what exactly the materials will be housed
    > within – one must assume both lighter than air as well as heavier than air hazardous vapors could be installed.

    Interesting scenario. I guess it's unspecified flammable liquids in unsealed tanks, and not cylinders of gas, LPG, or the like? (You didn't say.)

    Based on what we know, I pretty much concur with everyone else - adequate ventilation would be the way to go. Since you mentioned ventilation alone is not acceptable, I assume ventilation must be possible. That would (hopefully) get you Div 2 without the need to worry about validity.

    If the client "doesn't trust ventilation alone", and wants combustible gas detection on top, that's fine. But the gas detection would (ideally) have nothing to do with the area classification or the allowable equipment since it would not be needed as a protection method.

    Having built gas detectors for some decades, I would not trust gas detection as a protection method unless I had at least some idea of the substances it's supposed to be detecting. Plus the sensitivity for heavy hydrocarbons is often poor, and T90 times are often long. But if it's only supplementary, gas detection would devolve from critical to merely important, lowering the burden of proof.

    In a practical sense you'd still have to worry about how to detect the heavier hydrocarbons effectively. Plus, if you're expecting both lighter- and heavier-than-air, you'd probably have to have some detectors near the roofline and some near grade, increasing costs. Maybe even different calibrations / correction factors for the upper and lower detectors.

    > Well, reasonable assumptions are made all the time in this business.

    Doesn't make it right.
    Lots of great input on this string...thanks to all of you.

    Consider the following excerpt from NFPA 497:
    “When classifyingbuildings, careful evaluation of prior experience with the same or similarinstallations should be made.
    It is not enough toidentify only a potential source of the combustible material within thebuilding and proceed immediately to defining the extent of the Class I,Division 1 or the Division 2; or Class I, Zone 1 or Zone 2 classified areas. Whereexperience indicates that a particular design concept is sound, a morehazardous classification for similar installations may not be justified.Furthermore, it is conceivable that any area be reclassified form either ClassI, Division 1 to Class I Division 2, or from Class I, Division 2 tounclassified, or from Class I, Zone 1 to Class I, Zone 2, or from Class I, Zone2 to unclassified, based on experience.”

    If the building is well protected against hazardous vapors with ventilation,gas detectors, alarms etc and the equipment/wiring can therefore be ratedDivision 2, it seems borderline absurd to insist the Building is still Division1, other than to avoid some sort of litigation.

    So how is this accurately communicated on an Area Classification drawing? Do I show the building as Division 1 with a note stating its really Division 2?



  3. #13
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    Quote Originally Posted by Dale001289 View Post
    So how is this accurately communicated on an Area Classification drawing? Do I show the building as Division 1 with a note stating its really Division 2?
    You can do it however your professional liability insurer says you can. When you put your PE seal on the drawing they are the ones holding the bag if you are wrong.
    Bob

  4. #14
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    Quote Originally Posted by Dale001289 View Post
    it seems borderline absurd to insist the Building is still Division1, other than to avoid some sort of litigation.
    It's impossible to argue since you're the only one who knows what we're talking about. The rest of us are flying blind.

    However, the conclusion should be scientifically and legally defensible. If you don't think you're on solid enough ground to convince an expert in the field, it's probably incorrect.

    If the situation really is that absurd, you should have no difficulty listing 6-12 specific reasons why you think the area isn't Div 1. Or Div 2. Or whatever.

    This phrase:

    > Where experience indicates that a particular design concept is sound, a more hazardous classification for similar installations may not be justified.

    This would be more defensible if the "experience" cited:

    - Included specific experience with the actual design concept(s), construction, or other elements that make up this particular area; and
    - Included experiments, measurements, or other empirical data; and
    - The ventilation systems necessary for the area classification were redundant, alarmed, or otherwise failsafe; and
    - Spanned a very long period of time; and
    - so on and so on.

    There are limits to experience as well. For example, it would be possible to take 10 years of gas detection measurements across a number of sites, plus a full review of the site records, and conclude the area(s) should be declassified from Div 2 to non-hazardous because there had never been a leak. And then go on to apply this to other similar sites.

    But there still could be a leak in the future, making both the initial conclusion and the subsequent application to other sites incorrect. Meaning experience doesn't trump basic area classification principles.


    The moral of the story is that you do have to work the worst-case situation. It's not just what should happen, nor what's intended to happen. It's what may happen. I'm not getting the right vibe in that respect, hence my concern.

    In this context, what may happen is unusually broad. Pressurized pipelines are considered subject to leaks; containment systems are presumed to fail; ventilation systems could break down; malfunctions do occur; spillage and leakage during transfers does occur; mistakes and accidents are presumed to happen. Usually, none of these items are expected, routine, or intended, and we actively work to prevent them, but they must be taken into consideration nevertheless.

    I would highly recommend you scour the various area classification standards for something that is more defensible than simply a gut feeling that it "feels borderline absurd".


    Quote Originally Posted by Dale001289 View Post
    So how is this accurately communicated on an Area Classification drawing? Do I show the building as Division 1 with a note stating its really Division 2?
    Area classification drawings show conclusions, not explanations. You would classify it as Div 2.
    Last edited by IntrinsicSafety; 04-06-18 at 01:09 PM.

  5. #15
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    Quote Originally Posted by Dale001289 View Post
    ,,,
    If the building is well protected against hazardous vapors with ventilation,gas detectors, alarms etc and the equipment/wiring can therefore be ratedDivision 2, it seems borderline absurd to insist the Building is still Division1, other than to avoid some sort of litigation.

    So how is this accurately communicated on an Area Classification drawing? Do I show the building as Division 1 with a note stating its really Division 2?
    It's interesting you should cite NFPA 497 as you have. (You even kept my underlines) The obvious question is, "Do you have the experience to justify your evaluation?"

    As we have already mentioned, if you are properly ventilated, it is already Division 2 and the CGDS is a waste of money when you consider the all documentation/maintenance required. Many CGDS often require retests every 3 - 6 months and recertification every 2 - 5 years. They really aren't all that cost effective to begin with. There will come a time someone in upper management will decide the documentation and maintenance isn't worth it (usually around the first recertification) and it will be abandoned.

    If in fact you still choose to rely on the CGDS, it is still Division 1, You would note on your required documentation [Section 500.4(A)] that it Division 1 and you are using Section 500.7(K)(1) as one of your protection techniques.

    Of course, you could use a redundant ventilation system with flow monitoring and all the alarms your heart could desire.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  6. #16
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    Quote Originally Posted by rbalex View Post
    It's interesting you should cite NFPA 497 as you have. (You even kept my underlines) The obvious question is, "Do you have the experience to justify your evaluation?"

    As we have already mentioned, if you are properly ventilated, it is already Division 2 and the CGDS is a waste of money when you consider the all documentation/maintenance required. Many CGDS often require retests every 3 - 6 months and recertification every 2 - 5 years. They really aren't all that cost effective to begin with. There will come a time someone in upper management will decide the documentation and maintenance isn't worth it (usually around the first recertification) and it will be abandoned.

    If in fact you still choose to rely on the CGDS, it is still Division 1, You would note on your required documentation [Section 500.4(A)] that it Division 1 and you are using Section 500.7(K)(1) as one of your protection techniques.

    Of course, you could use a redundant ventilation system with flow monitoring and all the alarms your heart could desire.
    Just curious, if it is already ventilated adequately so it is a division 2 area, and you add gas detectors, are you saying that changes it back to a division 1 area? That seems counterintuitive to me.
    Bob

  7. #17
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    Quote Originally Posted by petersonra View Post
    Just curious, if it is already ventilated adequately so it is a division 2 area, and you add gas detectors, are you saying that changes it back to a division 1 area? That seems counterintuitive to me.
    No, I said if that is what they are going to rely on. Technically, Section 500.7(K)(1) couldn't apply otherwise.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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