While traversing through obstacles in the Flash Powder Factory you may come across fallen rubble. Searching these may yield pieces of rogue armour (1/5,000 chance for each piece), flash powder, catalytic powder or sets of apparatus. It is also possible to find nothing at all. Sometimes one set of rubble can be searched multiple times. Wearing a factory mask or rogue mask when searching rubble reduces the chance to find nothing by 15%, while increasing the odds to find a piece of armour to 1/500.
The fallen rubble only appears in the rooms with the Mixer Machine and the rooms with the Reagent Machine (A), as marked in the map below.