Air Carrier Captain reported hazmat pallets were stacked in the cargo compartment. After researching the issue it was determined that the practice of stacking was the result of incorrect and misleading information from the FOM and DG Specialist.

Narrative

During Dangerous Goods inspection it was discovered that the Dangerous Goods load team had loaded a pallet of Corrosives on top of another pallet of Dangerous goods. The top pallet did have netting that secured the Corrosives. I reviewed the FOM Dangerous Goods section and I could not find a specific section that prevented the practice of stacking Pallets on top of another pallet so I did not remove the Dangerous goods container. Our concern as the crew was that there might be a possibility of a load shift with this loading practice. The following day; I contacted the Ramp to investigate if this was a normal practice (Stacking pallets on pallets); and they are in the process of researching. I submitted an Insight on Regarding this Issue. Person A investigated and in his research he received confirmation from Person B that IAW DG Manual; there is a warning 'DO NOT LOAD DANGEROUS GOODS ON PALLET STACKS'. My goal was make sure this was a legal and safe way to pack Dangerous Goods in case this occurs on a future flight. It was neither legal or safe.[The issue was the result of] Incorrect; misleading information from our DG specialist and the lack of guidance in the FOM caused this Event. In the future I will involve the Duty Officer in these type of events.[Highly recommended to] Add the warning 'DO NOT LOAD DANGEROUS GOODS ON PALLET STACKS' to the FOM.