Dust Combustibilty Testing - What is the Correct Particle Size

[JoeChem]

Greetings,

We have an existing process where we load a solid into a hopper on top of a batch reactor and charge to a liquid (well below flash point). The solid is granular (roughly 1/16"-1/8" dia) and is free flowing. Closer inspection does reveal the presence of a significant amount of "fines" that are of much smaller particle size - all the way down to "dust".

When this product was introduced to the plant, the process safety professional that participated in the hazard review relied on the suppliers minimum ignition energy data (> 1000 mj) to conclude the solid was not combustible so no major issues.

Now enter in a new safety professional. This individual wants to re-evaluate the solids handling hazard by sending out some of the "fines" out to determine the minimum ignition energy and other properties - essentially a full battery of combustibility tests. As solids handling hazards increase with decreasing particle size I am anticipating some problems.

I do not disagree with this exercise but I am struggling to determine the appropriate particle size to send out for testing. Essentially, we have a complete distribution. I can make the results as safe or as hazardous as I want by choosing to test larger or smaller particle size distributions respectively.

Does anyone know if there are any standards/guidelines/good engineering practices that address this issue? Seems like it is based more on opinion than anything else.
Not finding much in the NFPA documents to help either.

Thanks,

JoeChem

 

[IRstuff]

Is your antipathy possibly clouding your approach? You should be using some sort of representative distribution of what you actually have, not what some random spec says.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[RVAmeche]

From my limited dust knowledge, particle size for the specific material is very important. Like IRStuff mentions, you would ideally take a collective sample from your hopper that includes a representative sample of all sizes. The lab will then conduct their experiments and let you know what the results are. If the safety guy just sent the smallest particles the lab should be made aware of that.

Your comment about "making the results safe or hazardous...by choosing particle size" is kind of moot. You don't just have large or small particles, you have both. NFPA 652 is a good starting point.

 

[Compositepro]

Take a real sample of your worst case. That would be the dust in your dust collector, for example. Ignition energy does not mean anything for 1/8" particles. The original test was probably done on air filled with dust from an agitated sample of your actual material. This is representative of what you would get when adding material to your reactor.