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Thread: Ventilation In Class I Div 2

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    Ventilation In Class I Div 2

    Can equipment where it could be reasonable for an AHJ to determine that leaks are frequent enough to meet 500.5(B)(1)(2) definition for Class I Div 1, be provided with positive mechanical ventilation to make it Class I Div 2 per 500.5(B)(2)(2)? Is that the point of 500.5(B)(2)(2)?

    If so, what are the standards pertaining implementing the positive ventilation system?
    Time is of the essence, and I am low on essence. ~ Graham Hill

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    Quote Originally Posted by fifty60 View Post
    ... Is that the point of 500.5(B)(2)(2)?
    ...
    Not quite - See Informational Note No. 1

    Quote Originally Posted by fifty60 View Post
    If so, what are the standards pertaining implementing the positive ventilation system?
    See Section 500.4(B) Informational Note No.4
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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    API RP-500

    Quote Originally Posted by fifty60 View Post
    Can equipment where it could be reasonable for an AHJ to determine that leaks are frequent enough to meet 500.5(B)(1)(2) definition for Class I Div 1, be provided with positive mechanical ventilation to make it Class I Div 2 per 500.5(B)(2)(2)? Is that the point of 500.5(B)(2)(2)?

    If so, what are the standards pertaining implementing the positive ventilation system?
    The API RP-500 includes a lot of discussion regarding ventilation and classification choices. It also leaves a lot up to interpretation. Combined with the NEC, it has given me an increased level of confidence when selecting classification for an area.

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    personally, i have always been suspicious of the idea of reducing the classification of an area solely on the basis of having some kind of mechanical ventilation. it is too easy for the fan to fail or get turned off and no one notice.
    Bob

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    Quote Originally Posted by petersonra View Post
    personally, i have always been suspicious of the idea of reducing the classification of an area solely on the basis of having some kind of mechanical ventilation. it is too easy for the fan to fail or get turned off and no one notice.
    For most of our analyzer buildings/rooms we utilize LEL gas detection, in conjunction with a fail safe control system that will start the exhaust fan, activate the alarm strobe lights, and send a signal to the plant PLC in the event of a 20% ppm detection. We believe this satisfies the intent of the NEC and RP-500 and allows us to reduce the classification to CID2. The gas chromatographs and other analyzers work best if the room remains warm in order for the sample/calibration gases or liquids to remain 30* above the dew point. Most of our sample and calibration lines are heat traced tubing bundles anyway, but natural or constant mechanical ventilation in many environments would cool the room excessively. When our customers don't want to deal with the required quarterly calibration of the LEL detectors, we just classify the rooms as CID1 without any ventilation.

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    Quote Originally Posted by Jim1959 View Post
    For most of our analyzer buildings/rooms we utilize LEL gas detection, in conjunction with a fail safe control system that will start the exhaust fan, activate the alarm strobe lights, and send a signal to the plant PLC in the event of a 20% ppm detection. We believe this satisfies the intent of the NEC and RP-500 and allows us to reduce the classification to CID2. The gas chromatographs and other analyzers work best if the room remains warm in order for the sample/calibration gases or liquids to remain 30* above the dew point. Most of our sample and calibration lines are heat traced tubing bundles anyway, but natural or constant mechanical ventilation in many environments would cool the room excessively. When our customers don't want to deal with the required quarterly calibration of the LEL detectors, we just classify the rooms as CID1 without any ventilation.
    I don't see how this is a safe means of dealing with the problem. If the gas detectors see gas levels rising, it seems to me like it has become a C1D1 area. What prevents an explosion at that point since leaks tend to cause gas levels to go up very quickly, quite possibly before someone can respond. But then I have never really understood how the gas detection protection method is supposed to work since I have not had to use it in the past, so never looked at it real closely.
    Bob

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    Quote Originally Posted by petersonra View Post
    I don't see how this is a safe means of dealing with the problem. If the gas detectors see gas levels rising, it seems to me like it has become a C1D1 area. What prevents an explosion at that point since leaks tend to cause gas levels to go up very quickly, quite possibly before someone can respond. But then I have never really understood how the gas detection protection method is supposed to work since I have not had to use it in the past, so never looked at it real closely.
    I don't agree that classifications change with conditions. An area classification is selected and that is that. Yes, a CID2 area can have dangerous levels of liquid or gas in the event of a malfunction, but not under normal circumstances. That is why the requirements for heat and arc producing equipment is basically the same for D1 & D2. The LEL detectors we have worked with, mainly General Monitors and Detcon are very high quality instruments. Some of our customers have us install solenoids to shut down the sample supply and bypass upon 20% LEL detection as well but I don't understand this to be a requirement.

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    Quote Originally Posted by Jim1959 View Post
    I don't agree that classifications change with conditions. An area classification is selected and that is that. Yes, a CID2 area can have dangerous levels of liquid or gas in the event of a malfunction, but not under normal circumstances. That is why the requirements for heat and arc producing equipment is basically the same for D1 & D2. The LEL detectors we have worked with, mainly General Monitors and Detcon are very high quality instruments. Some of our customers have us install solenoids to shut down the sample supply and bypass upon 20% LEL detection as well but I don't understand this to be a requirement.
    my point was that if ventilation failed that would create a hazardous condition, that perhaps it should have been classified as C1D1 in the first place. I realize what I wrote did not say that in a clear way and could have easily been taken for meaning the area classification changed because of the leak.

    like I said, I do not know all that much about this method of protection so maybe what was done was OK. presumably someone who actually knows what he or she is doing classified the area. presumably when he/she made that decision a tome was created that described how it came to be determined. might be interesting to read that tome. do you have a copy of it that could be posted?
    Bob

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    Quote Originally Posted by Jim1959 View Post
    I don't agree that classifications change with conditions. An area classification is selected and that is that. Yes, a CID2 area can have dangerous levels of liquid or gas in the event of a malfunction, but not under normal circumstances. That is why the requirements for heat and arc producing equipment is basically the same for D1 & D2. The LEL detectors we have worked with, mainly General Monitors and Detcon are very high quality instruments. Some of our customers have us install solenoids to shut down the sample supply and bypass upon 20% LEL detection as well but I don't understand this to be a requirement.
    General Monitors and Detronics. I know that didn't seem quite right.

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    Quote Originally Posted by Jim1959 View Post
    For most of our analyzer buildings/rooms we utilize LEL gas detection, in conjunction with a fail safe control system that will start the exhaust fan, activate the alarm strobe lights, and send a signal to the plant PLC in the event of a 20% ppm detection. We believe this satisfies the intent of the NEC and RP-500 and allows us to reduce the classification to CID2. The gas chromatographs and other analyzers work best if the room remains warm in order for the sample/calibration gases or liquids to remain 30* above the dew point. Most of our sample and calibration lines are heat traced tubing bundles anyway, but natural or constant mechanical ventilation in many environments would cool the room excessively. When our customers don't want to deal with the required quarterly calibration of the LEL detectors, we just classify the rooms as CID1 without any ventilation.
    Just curious which Subsection of 500.7(K) [(K)(l), (K)(2), or (K)(3)] do you believe your design "... satisfies the intent of the NEC and RP-500 ...". Note those are the only acceptable NEC designs.

    To satisfy petersonra's angst (): for a short time, a Class I, Division 2 installation is fine in an environmentally stable Division 1 location. That is, the environment itself does not actively attack the installation. Essentially that is what a "Type Y Purge/Pressurize" is - minus a few alarm bells and whistles. It is also why (in my opinion) IEC Zone 1 is more of a glorified NEC Division 2.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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