Consider a process that includes a heat exchanger in a duct carrying hot gas. Water flows through the coil in order to cool the gas. The water flow into the heat exchanger would be one of the study nodes. The parameters at this node would include flow, temperature, and pressure. The design intent at this node might be to provide water at a specified flow rate, temperature, and pressure. A set of guide words would be applied successively to the parameters. To illustrate, consider the guide words “NO FLOW.” The cause of “NO FLOW” could be a closed valve, a broken pipe, a clogged filter, or the failure of the municipal water supply. Each of these causes is realistic, so the deviation could occur and the consequences of the deviation must be examined. The possible consequences could include vaporizing the water in the heat exchanger coil, thus producing dangerously high pressure, or allowing the temperature of the gases to rise, yielding dangerously high rates of reaction elsewhere in the process. Both of these consequences are serious and warrant attention. The other parameters at the node—temperature and pressure—would also be studied. All other nodes in the process would be studied in a similar manner.