Vent Requirements

[XELR8]

Do dust collectors located outside of buildings require vent protection per NFPA 68? If so, what paragraph in the NFPA 68 Standard references this requirement? Thank you!

 

[psafety]

My understanding IF the AHJ is willing to accept the risks and the loss of the equipment in the event of an explosion, so be it.

 

[XELR8]

Hi psafety,

Thanks for your response. I have the same understanding from the NFPA Standard.

Does the owner accept the risk or the AHJ? It seems to me that the AHJ would never accept any risk for loss of equipment or any possible safety risk.

Do you have any feel for industry standards on explosion venting (such as Kst or Pmax values) on dust collectors or material separators located outdoors?

Would silo's having combustible dust fall under this risk option also?

Thanks for any help.

 

[JLSeagull]

What materials? Also refer to EPA emission requirements.

 

[psafety]

Yes silos must be considered if you can have dust in suspension in its combustible range.

I've vented silos, and the more elongation the worse it becomes. I've also proven to maintain less than the LEL, proven and the owner accept the risk.

All conditions and dust/particle size differ. There is no cut and dry.

Combustible dust is getting a LOT of attention currently, and I would NOT cut corners.

 

[XELR8]

I agree that Silos indoors need to be vented per NFPA 68 2007 but do the Silos outdoors away from personnel need to be vented as well?

NFPA says, all combustible dust enclosures should be located outdoors. If they are indoors they should have vent protection as per the standard. It "NFPA" does not say combustible dust enclosures outdoors need venting as well.

The materials can vary but the ranges for Kst are between 100 and 210 bar m/sec.

Is the required venting area equation and calculation in NFPA 68 2007 different then the required area for venting that may have been made by the previous NFPA 68 edition?

Good point on the EPA requirements. I have them covered.

 

[psafety]

Dracula, outdoor installation - you, the owner, the insurance carrier decide. The company I support is 100% self-insured. Taking chances, is much, much harder after their insurance decision.

You will most likely take the complete roof as in a API 650 application of "frangible roof seam", but with your much smaller diameter angle rings/welds must be reduced in size.

There was a very good study, write-up, and computer application written by a group from a Oklahoma University on frangible roofs of tanks less than 50-feet in diameter out on the 'net. I think it was called "saferoof".

I've also taken the upper portion of the cylindrical shell and placed multiple vents around the circumference above the maximum level. This was when I had excess weight on top.

 

[psafety]

About the calculation - much different than previous methods. It took me quite a time to develop my spreadsheet and the iterations required.

 

[XELR8]

About the calculation, if the methods for determineing required vent area have changed from the new NFPA 68 2007 edition is it realistic to say that the old calculation is no longer valid?

Would it be fair to compare the new calcualted vent area vs an existing vent area that may have been installed many years ago?

Thanks!

 

[psafety]

2007 is current. New work should use the current code.

You are NOT required to resize the vent on older installations until an equipment change, process or explosivity change requires it (I think I am correct here, because the older methods were more conservative). There are required changes in documentation, procedures, etc.

The client I work for has 30+ explosion vented collectors, bins, etc. Its been decided to bring them all up to current standards as the old documentation is sketchy and with the growing emphasis on dust, we want all our ducks in a row.

 

[XELR8]

I am in agreement with your statements about older installations and vent calculations are documented that way in NFPA 68 2007 also.

Good chat and I appreciate the help.