Declassifying a Class1 Div2 location by using ventillation?

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cgoulette

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Hi.

Newbie here.

I'm currently working on installation design details for an area that's classified as Class1, Div2.

The owner is asking that I look into declassifying the area by using mechanical ventilation, understandably, he'd like to avoid the additional expense. I found information on this page: http://www.safteng.net/index.php?op...=49:chemical-process-safety-psmrmp&Itemid=294 which suggests that declassifying an area using mechanical ventilation is not an option based on multiple codes, but when I was looking on this forum, I came across some posts that suggested that it may in fact be an option.

Can anyone clarify if I can in fact declassify a Class1, Div2 area by designing a set number of air exchanges per hour with mechanical ventilation. If so, what is the number of air exchanges required, and can you please point me to the location within NEC code that would allow that?

I'd like to be able to bring an answer back to my customer as to whether or not this is allowed, with the evidence to back up the assertion.

Thanks, I appreciate any guidance offered.
 
I don't know which posts you're referring to but you need to realize purging, pressurizing and ventilation each have different purposes and effects.

If you were using conventional IEC Zones (not NEC Zones) ventilation may significantly reduce (but not entirely eliminate) some Zone 2 location's hazard radii.

Purging/pressurizing can reduce Division 2 to unclassified but it's difficult to achieve for any significantly large spaces/volumes. There are some significant requirements for monitoring. See NFPA 497 for typical applications.

You may want to review gas detection schemes. See Section 500.7 (K). Again, there are application and equipment restrictions.
 
You make no mention of the type of area/facility. We are not sure if we are commenting on an area that is correctly classified as Div 2, or incorrectly classified as Div 2. If it was correctly classified as Div 2, which we can only assume, you are not likely to come up with the answer he is looking for. We can't classify for you, but may be able to direct you to appropriate codes and standards based on the facility type.
BobG
 
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