[redJ85]

 I was hoping you could please help me or orient me in the right direction to find an answer to my problem. The company I work for produces brass alloys in a furnace and one of our byproducts is zinc oxide dust. We sell this zinc oxide to other manufacturers. The last shipment we sent on a truck combusted, it burned out of the plastic bag, burned the wooden pallet it was on and it burned a hole in the wooden bed on the truck. This has only happened twice in the 30 yr span of the company. We keep our zinc oxide for two weeks before we sell it, to make sure it has cooled down, we also use two plastic bags, closed off with tape to avoid contact with moisture. Based on a past profile done on our material, some of the other elements found in our zinc oxide dust are: H2O 1.92%, Cd 0.13%, Cu 0.66%, Fe 0.17%, Pb 7.43%, Mn 0.01%, K 0.36%, Na 1.18%, Ca 0.06%, Mg 0.01%, Al 0.02% Do you have any idea what could have caused this reaction? Can you please suggest a source I can look into for more information and answers? We don’t want to risk shipping this substance if there is a chance it will combust and put people in danger.

Thank you very much!

[discodermolide]

Sorry to hear about your problem.
It seems to me that you have a problem with grounding the transport containers before during and after filling. Also you need to keep the dust formation during filling of said container low.
Otherwise you will get a static discharge and a dust explosion, which is what probably happened in the case you describe.Flushing your containers with nitrogen before sealing may also help.

[Borek]

I think dust explosion requires a combustible material, which ZnO definitely is not.

[discodermolide]

Well dust explosions are well established for baking flour, talcum powder and the like.
I can't see any other explanation for this.

[DrCMS]

Well dust explosions are well established for baking flour, talcum powder and the like.

Those materials are combustible. 

Also you do not get a dust explosion 2 weeks after filling the bags.

[Arkcon]

I'd never heard of ZnO autoheating with moisture, and I don't see how it could react with oxygen further, it should be done.  Unless your ZnO contains finely divided pure metals, but I don't see how you would get that from a furnace.  A nitrogen flush may work, but we're no closer to the cause of the problem than we ever were.

[redJ85]

Thank you for your insight!

By doing the nitrogen flush, we would eliminate most oxygen from the bag and thus taking out one of the necessary elements for the fire. Is that right? I think that is definitely worth a shot.

Do you believe that leaving the outer plastic bag unsealed during transport and only closing the porous bag would eliminate the pressure build up and prevent an explosion? Or would we be making things worse by exposing the zinc oxide to even more oxygen?

Also, how would we go about grounding the material?

Thank you!

[Enthalpy]

Could the zinc oxide possibly have leaked and catalyzed the ignition of an other material?

https://sites.google.com/a/queensburyschool.org/what-s-in-this/zinc-oxide
"A slow application of zinc oxide on linseed oil varnish generates heat, and may ignite"
This must be known from the use as a white pigment in oil paint.

Linseed oil is known to react with air by its double bonds and harden, hence the use as a paint base and varnish. Maybe some other material reacts in a similar way and was present. For instance turpentine, natural rubber, polybutadiene have double bonds.