It’s not just fire. As a general consideration items on common property access areas may be a trip hazard, and if someone did trip/fall and injure themselves the OC could be liable for any injuries, because the items are on common property. Usually you would assess the risk on a case by case basis. For example in our building there is an apartment near the back door with a narrow walkway, and we have told them they are not to put plants and other items in that area.