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Thread: Ploystyrene Extrusion Die's

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    Ploystyrene Extrusion Die's

    I've worked in extrusion across the globe for over 20 years. I've been told that the extruder die area is "exempt from being a Class 1 Division 1 area. Well now I'm being asked to prove the precedence. Does anyone know of where this exemption started or where I might find it?

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    Quote Originally Posted by WMBELEDES View Post
    I've worked in extrusion across the globe for over 20 years. I've been told that the extruder die area is "exempt from being a Class 1 Division 1 area. Well now I'm being asked to prove the precedence. Does anyone know of where this exemption started or where I might find it?
    I don't think there is one. is the area around it classified? if so it would appear that it would have to be at least D2.

    I have seen only a handful of plastic extrusion machines and I don't recall any were classified as being in a hazardous area. Maybe there is something special about polystyrene.

    as a practical matter maybe it is hot enough that it would not do any good to classify that space.
    Bob

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    Polystyrene Extrusion Dies

    Bob,
    If I were to use the definition of a C1D1 or D2 500.5(1&2) it might fall under D1 due to rare occurrence where an operator could inject a bubble of gas into the extruder that is released. If I read 500.5(2)(2), "Concentrations are prevented by positive mechanical ventilation". The plant has wall fans with ceiling louvers that replace quite a large volume of air, might this drop the Zone from D1 to D2? How might this be decided? Is there a more detailed article for testing to determine a zone? If so, is this a self test or a test of a certified mature?

    Bill

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    Quote Originally Posted by WMBELEDES View Post
    Bob,
    If I were to use the definition of a C1D1 or D2 500.5(1&2) it might fall under D1 due to rare occurrence where an operator could inject a bubble of gas into the extruder that is released. If I read 500.5(2)(2), "Concentrations are prevented by positive mechanical ventilation". The plant has wall fans with ceiling louvers that replace quite a large volume of air, might this drop the Zone from D1 to D2? How might this be decided? Is there a more detailed article for testing to determine a zone? If so, is this a self test or a test of a certified mature?

    Bill
    What kind of gas is it? If it is not flammable it would likely not matter.

    Part of classifying an area involves judgement and experience. It might be that experience has shown the risk is very low so it does not need to be classified.
    Bob

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    Polystyrene Extrusion Dies

    Quote Originally Posted by petersonra View Post
    What kind of gas is it? If it is not flammable it would likely not matter.

    Part of classifying an area involves judgement and experience. It might be that experience has shown the risk is very low so it does not need to be classified.
    Flammable, butane and pentane. Our experience shows risk is low but an inspector want's more than precedent.

    Bill

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    Quote Originally Posted by WMBELEDES View Post
    Flammable, butane and pentane. Our experience shows risk is low but an inspector want's more than precedent.

    Bill
    If you are unable to convince the inspector it might be necessary to hire someone with a PE after his name who has the experience and knowledge to be able to explain why it is that it does not need to be classified.

    It seems to me that the machine manufacturer would be a good place to start. I doubt their product liability insurer would let them sell a product like this that their insurer had not vetted first.
    Bob

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    I've said before and say again, with the exception of installations within the Scopes of Articles 511 to 516, you cannot classify a location from the NEC itself. You must use one of the Referenced Standards in Section 500.4(B), especially Informational Note No.2. In the OP's case none of them speak directly to the mentioned process either. However, NFPA 497 - 2017, Chapter 5 does address the applicable principals and Section 5.6.4 specifically addresses "experience".

    BTW unless the presence of flammable gases or vapors happens under "normal" operating conditions, i.e., when everything is operating as designed, Division 1 is inappropriate per the root definition in Section 500.5(B)(1)(1).
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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    Quote Originally Posted by rbalex View Post
    BTW unless the presence of flammable gases or vapors happens under "normal" operating conditions, i.e., when everything is operating as designed, Division 1 is inappropriate per the root definition in Section 500.5(B)(1)(1).
    In post #3 the OP indicated the gas release is rare but seemed to indicate it did happen as part of the regular operation of the equipment, albeit unintentionally caused by operator error.

    ETA: The other issue I would think needs to be considered is how much flammable gas could be released and would it actually do any damage if it actually ignited.

    Every time someone uses a butane lighter typically a small amount of raw butane is released into the air before the spark ignites the stream of butane. if the amount of butane released is small enough and disperses fast enough there may not be an ignitable concentration of butane.
    Bob

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    I have a direction.

    Quote Originally Posted by rbalex View Post
    I've said before and say again, with the exception of installations within the Scopes of Articles 511 to 516, you cannot classify a location from the NEC itself. You must use one of the Referenced Standards in Section 500.4(B), especially Informational Note No.2. In the OP's case none of them speak directly to the mentioned process either. However, NFPA 497 - 2017, Chapter 5 does address the applicable principals and Section 5.6.4 specifically addresses "experience".

    BTW unless the presence of flammable gases or vapors happens under "normal" operating conditions, i.e., when everything is operating as designed, Division 1 is inappropriate per the root definition in Section 500.5(B)(1)(1).
    Thank you,
    I am consulting our insurer and purchased NFPA 479 for review. This should hopefully resolve the concerns of the inspector.
    Bill

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    Quote Originally Posted by petersonra View Post
    In post #3 the OP indicated the gas release is rare but seemed to indicate it did happen as part of the regular operation of the equipment, albeit unintentionally caused by operator error.

    ETA: The other issue I would think needs to be considered is how much flammable gas could be released and would it actually do any damage if it actually ignited.

    Every time someone uses a butane lighter typically a small amount of raw butane is released into the air before the spark ignites the stream of butane. if the amount of butane released is small enough and disperses fast enough there may not be an ignitable concentration of butane.
    Actually, I did read it and considered mentioning it in my previous post but decided not to because it muddies the issue. However it's more or less addressed in the "further" definition of Division 1, Section 500.5(B)(1)(2) where the releases are from frequent repair or maintenance operations not incidental misoperation which, BTW, still isn't operating "as designed". Some additional training may be warranted, but not classifying the location Division 1.

    I may as well mention Section 500.5(B)(1)(3) too. This is where a faulty operation will cause a simultaneous release and electrical equipment failure which might create an ignition source. This doesn't appear to apply to the OP either.

    Quantity of release is indeed another consideration mentioned in NFPA 497, otherwise the whole world would be at least Division 2 if you apply Section 500.5(B)(2)(1) doggedly. The tendency to over-classify is common when the "classifier" hasn't read Section 500.4(B) IN No.1.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

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