New Chemical

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cornbread

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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.
 
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.
 
cornbread said:
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.
Click to expand...

Rack up the OT and update... Cost of doing business
 
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!
 
cornbread said:
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!
Click to expand...
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.
 
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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.
 
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.
 
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.
 
It is important to remember that NFPA 497 is a Recommended Practice. (Read the title) So is API RP 500. I value both of them highly and, as ANSI Standards, FedOSHA holds them both in high reqard as well; however, a locally adopted Code like the NEC trumps an RP in any court.

I am assuming from the Part you cited (5.5.6) you are referring to an to an outdated edition of NFPA 497. The 2017 edition is the latest and I will be referring to it later. Part 5.6.6 [2017] contains the same material you cited. You may find the last sentence of Part 5.5.4 of the edition you are using interesting as well - assuming you have the requisite "experience", of course.

Technically, the NFPA 497 Figures are only a recommendation. Of course you do have to “draw the line somewhere” and they represent the consensus judgement of history. However, you should also refer to NFPA 497 [2017 edition] Parts 5.8, 5.9, and 5.10. You will note none of the Parts mention “batches” as part of the underlying analysis.

As I said earlier, "I'm not there" so whatever you (and your insurer) are happy with is fine with me.
 
No room for an isolation wall. Our HAC committee is taking matter under its control and they are using this thread couple with other feed back obtained to determine the area classification bubble. Once that's established then the fun work of bringing anything in that bubble up to code.
 
If you have it available, API RP 500, Annex D provides a sound alternate analysis to the Figures. It can be tedious, but it still isn't "rocket science". What is "rocket science" is Annex B; just kidding, but it is far more analytic and you would probably discover it didn't make any difference in your case.
 
I agree that the best alternative would appear to be getting away from NFPA 497 and using an alternative standard.

IEC 60079-10 is quite analytical, but can sometimes result in reduced area classifications. Also API RP 500, as Bob said.

Also, adding supplementary ventilation and/or cranking up local ventilation may help - some.
 
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