 For example, a prudent designer will have allowed for foreseeable variations within the process creating a larger design envelope than just the basic requirements and the HAZOP will be looking at ways in which this might not be sufficient.For processes plant, the nodes are chosen so that for each a meaningful "design intent" can be specified and they are commonly indicated on piping and instrumentation diagram (P&IDs) and process flow diagram (PFD).The extent of each node should be appropriate to the complexity of the system and the magnitude of the hazards it might pose.