Page 1 of 2 12 LastLast
Results 1 to 10 of 14

Thread: New Chemical

  1. #1
    Join Date
    Apr 2008
    Posts
    370

    New Chemical

    We are adding a new chemical in our process that will expand the HAC bubble to about 25 ft 3ft off the floor. Existing today I have several PLC panels & other equipment that will be inside the bubble. Looking for ways to reduce the bubble if possible (ventilation) or other means. Trying to avoid the expense of moving cabinets or purge systems. Any help would be greatly appreciate.

  2. #2
    Join Date
    Apr 2004
    Location
    Mission Viejo, CA
    Posts
    4,971
    Sadly, if your premise is correct, you have pretty much identified your only reasonable alternative - purged/pressurized enclosures. You will also need to review boundary seals and the suitability of existing wiring methods in the new envelope. Ventilation alone wouldn't make a difference.

    That is - if your premise is correct. I'm curious what "chemical" alone would cause the envelope to expand. Other process conditions such as an increased pressure may but, assuming the "chemical" is otherwise compatible with the existing process and materials, it is difficult to see where the envelope would need to be increased - unless you started with an unclassified location to begin with.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  3. #3
    Join Date
    Jul 2015
    Location
    Soldotna, AK, USA
    Posts
    88
    Quote Originally Posted by cornbread View Post
    We are adding a new chemical in our process that will expand the HAC bubble to about 25 ft 3ft off the floor. Existing today I have several PLC panels & other equipment that will be inside the bubble. Looking for ways to reduce the bubble if possible (ventilation) or other means. Trying to avoid the expense of moving cabinets or purge systems. Any help would be greatly appreciate.
    Rack up the OT and update... Cost of doing business

  4. #4
    Join Date
    Apr 2008
    Posts
    370
    Don't know all the history but I suspect early on the area was standard and has been evolving. Luckily the process engineer engaged our HAC team to look at the introduction of the new chemical. Just need to figure out the most cost effective way to implement the change. Was hoping there might be some back door methods of constant monitoring that may give us some relief. We are currently looing at the area and making a list of changes that we need to make the area compliant. Appreciate the replies!

  5. #5
    Join Date
    Apr 2004
    Location
    Mission Viejo, CA
    Posts
    4,971
    Quote Originally Posted by cornbread View Post
    Don't know all the history but I suspect early on the area was standard and has been evolving. Luckily the process engineer engaged our HAC team to look at the introduction of the new chemical. Just need to figure out the most cost effective way to implement the change. Was hoping there might be some back door methods of constant monitoring that may give us some relief. We are currently looing at the area and making a list of changes that we need to make the area compliant. Appreciate the replies!
    Other than pressurizing, you may (only may) have a Combustible Gas Detection System (CGDS) option [Section 500.7(K)]. I say, "may", because the various acceptable CGDS applications are highly restrictive with lots of maintenance and alarm requirements AND you will still have a Division 2 location as a minimum. Pressurizing actually alters the internal electrical area classification; CDGS only permits using "lower" protective wiring methods and you still have to deal with boundary seals, although they aren't usually required to be explosionproof. Personally, I don't see any of the permissible CDGS applications as suitable for your installation as you have described it, but I'm not there.
    Last edited by rbalex; 01-15-18 at 09:59 AM.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  6. #6
    Join Date
    Dec 2014
    Location
    NM
    Posts
    33
    What did you add for the area to increase like that?

  7. #7
    Join Date
    Aug 2004
    Location
    Northern illinois
    Posts
    15,821
    Quote Originally Posted by MrJLH View Post
    What did you add for the area to increase like that?
    I have to admit I was curious too but figured he didn't want to tell us for some reason.
    Bob

  8. #8
    Join Date
    Apr 2008
    Posts
    370
    Unfortunately the company restrict us from any specifics.... probably on the edge for asking the question. I do appreciate the replies. I have reached out to several other resources and one interesting discussion was the process being batch or continuous. Several opinions that NFPA was primarily addresses continuous processes. We are making progress and the replies on this board are greatly appreciated.

  9. #9
    Join Date
    Apr 2004
    Location
    Mission Viejo, CA
    Posts
    4,971
    OK, I can say this - batch or continuous makes no difference. Remember, the basic Article 500 definitions are based on possibility not probability. Read them carefully and note the various Section 500.5 root definitions are characterized by "can" or "may". This is a subtle difference between the NEC and IEC. The IEC definitions are characterized by "will" or "usually". NOTE: The Article 505 (Zone) definitions are an attempt to "force fit" the IEC definitions into the NEC philosophy.
    "Bob"
    Robert B. Alexander, P.E.
    Answers based on 2014 NEC unless otherwise noted.

  10. #10
    Join Date
    Apr 2008
    Posts
    370
    The conversation was around NFPA 497. I kind of see where batch versus continuous could be argued based on volume.

    Sect 5.5.6 5.5.6
    The volume of combustible material released is of extreme importance in determining the extent of a hazardous
    (classified) location, and it is this consideration that necessitates the greatest application of sound engineering judgment.
    However, one cannot lose sight of the purpose of this judgment; the area is classified solely for the installation of electrical
    equipment.

    I can see where the conversation was leading, if you have a small volume (small batch) and use sound engineering judgment the generic figures in 497 may not apply to the application.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •