Negative vs positive air pressure in powder manufacturing room

We are debating the correct air flow direction for a new room we are building for manufacturing of powders.  The powders are easily airborne.  The room will be separated from the warehouse and other powder manufacturing areas with swinging double doors, and we are not sure if we should use negative air pressure in the room to keep the dust and occasional allergens inside, or use positive air flow to keep warehouse air out of the room.  During the manufacturing process, the door will be opened frequently, to allow personnel to move in and out of the room, or to move packaging in or packaged finished product out.  Additional info:  Additional construction or installing an additional door to create an airlock are not options.  The warehouse contains finished products and raw materials (including segregated allergens).  Our finished product is a "low risk" for pathogens (< .60 aw). 

Does anyone have knowledge of or experience with this scenario who can recommend the proper air flow direction? 

Many thanks!

Interesting question!

Assuming you have no exposed products in your warehouse, I would still vote positive pressure inside the room. There's no reason to assume that so much dust will leave the room, contaminate secondary packaging in your warehouse, be carried back into a different allergen profile room, and get into the product if you're treating your secondary packaging as non-food contact and removing any dust/debris prior to bringing it into the room. The food safety concerns with keeping your warehouse air out outweigh the potential for cross contamination IMO.

You can still address the issue of things leaving the room by examining your airflow and making sure that nothing is directed in such a way as to promote powders from blowing out of the room. That would be ideal.

FurFarmandFork is right - the area with the most likelihood of contamination (i.e. open product, which is what is occuring inside your rooms) is the area that should be positively pressurized or, at least, neutral.  Having come from a powder processing facility at my last QA job, I can tell you that your best bet is trying to keep the air only slightly positively pressurized...just enough to keep air from flowing in to the room, but not enough that it's clearly noticeable when you open the door to the room.  That way, you reduce your risk of contaminating the open product, but also limit the amount of dust escaping into the warehouse.