What is the key difference between RPN (Risk Priority Number) and Action Priority (AP) -FMEA?

There is a difference between being alive and living: Gabrielle Zevin

Introduction

As per Newton’s 3^rd Law, ‘every action has an equal and opposite reaction’. In other words, ‘what we sow, so shall we reap’. When we give priority to a particular thing like health, it improves. Similarly, when a Doctor diagnosis the problem accurately, the possibility of curing the disease enhances.     

Objective

The purpose of an FMEA process is to continuously improve the process to reduce risks. The FMEA is of course a living document and will be re-evaluated many times during its lifecycle, and each new revision will show changes in the risk analysis. But how do you determine which risks demand immediate action?

The Risk Priority Number (RPN) or Action Priority (AP) is the most common way to assign the criticality. The key objective of the Action Priority (AP) or Risk Priority Number (RPN) is to prioritize the failure so that suitable actions can be planned, productivity can be improved and customer satisfaction can be enhanced. The first focus is on Severity, followed by Occurrence and Detection.

Definitions

Action Priority: The key objective of ‘Action Priority’ is to choose, how to best prioritize the efforts to reduce the risk. It offers High, Medium and Low priority for action

Detailed Information

FMEA (Failure Mode & Effect Analysis) is a team-oriented, systematic, qualitative and analytical method to identify, analyse and mitigate the technical risks related to the ‘product and manufacturing process design.

The FMEA is the ‘Before the Event’ and not the ‘After the Event’ exercise.

Failure Chain:

• Failure Modes (FM): It means the ways, or modes, in which something might fail.
• Failure Effect (FE): It refers to studying the consequences of those failures’ mode.
• Failure Cause (FC): A indication of why failure mode could occur

Risk Analysis:

• Severity (S): Severity of the Failure Effect (FE)
• Occurrence (O): Occurrence of the Failure Cause (FC)
• Detection (D): Detection of the Failure Cause (FE) and/or Mode (FM)

Prevention: Eliminate (prevent) the Failure Cause (FC) or the Failure Mode (FM) from occurring or reduce its rate of occurrence.

Detection: Identify (detect) the Failure Cause (FC) or the Failure Mode (FM) leading to the development of associated corrective actions.

RPN (Risk Priority Number):

            RPN= Severity (S) X Occurrence (O) X Detection (D)

• The value can range from 1 to 1000
• The RPN gives equal weightage to S, O, and D
• The RPN value is not a threshold for determining the actions (like- More than 100!)
• The key focus is on the failure mode having severity ranking 9 and 10
• Severity ranking can be reduced by considering existing design control or recommended action
• When the severity ranking is 8 or below, the focus shifts to occurrence and detection ranking

Action Priority (AP)

The key objective of ‘Action Priority’ is to choose, how to best prioritize the efforts to reduce the risk.

The focus is not the prioritization of High, Medium or Low risk but the prioritization of the need for the action to reduce risk.

• It accounts for all the possible 1000 combinations of Severity (S), Occurrence (O) and Detection (D)
• The first focus is on Severity, followed by Occurrence and Detection
• The logic is Failure Prevention
• The AP table offers High, Medium and Low priority for action
• The risk matrix represents a combination of S & O, S & D and O & D.
• The Action Priority table is similar for DFMEA and PFMEA but differs for FMEA-MSR (Monitoring and System Response)
• Recommended that severity 9 and 10 with AP High and Medium should be reviewed by the management including any recommended action.

Priority High (H):

• Highest priority for review and action.
• Either identify an appropriate action to improve prevention and/or detection
• Or justify and document why current controls are adequate

  Priority Medium (M):

• Medium priority for review and action.
• Either identify an appropriate action to improve prevention and/or detection
• Or at the discretion of the organization, justify and document why controls are adequate

  Priority Low (L):

• Low priority for review and action.
• Could identify actions to improve prevention or detection controls

Example:

Situation 1: S=8 O=5 D=9 RPN= 360

Situation 2: S=10 O=6 D=6 RPN= 360

Situation 3: S=6 O=6 D=10 RPN= 360

Present Challenges

• How often are the criteria for giving a rating to Severity, occurrence and detection is the real status and not the targeted value!
• Why does the organization feel the pressure of identifying the Action Priority as High?

References:

IATF 16949: 2016

FMEA Handbook (AIAG-VDA 1^st Edition June 2019)

Industry Experts

This is the 123^rd article of this Quality Management series. Every weekend, you will find useful information that will make your Management System journey Productive. Please share it with your colleagues too.

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