*2.2. RPN Technique*

RPN is a relative potential failure evaluation measure that is primarily used in FMEA, and it prioritizes management and corrective actions. RPN consists of three items: severity (S), occurrence (O), and detection (D). The value of each item is divided into 10 levels from 1 (bad) to 10 (good); the value of RPN is between 1 and 1000 and is obtained by the product of each item [17–20]:

$$\text{RPN} = \text{S} \times \text{O} \times \text{D} \dots$$

Figure 2 shows the meaning of each RPN item. S affects the customer in relation to the process or product when a potential failure occurs. The degree of S of the effect is scored and evaluated, and a reduction in the S class can only be affected through design changes. O refers to the possibility of the cause and mechanism taking place. The O class must be consistent. D indicates whether a potential failure mode and its cause can be discovered or detected.

**Figure 2.** The meaning of each risk priority number (RPN) item.
