Failure Mode Effect and Criticality Analysis Adam Adgar School of Computing and Technology

FMECA ► Failure Mode Effect and Criticality Analysis Detailed study of a system to determine which parts are most critical to operation under various failure modes ► Developed in USA in 1950’s ► Objective is to prevent failures ► Can be used at design stage or process stage ► Different Industries have different standards but all are very similar in philosophy and procedures

What is FMECA ► A set of systemized group activities intended to: recognize and evaluate the potential failure of a product or process and its effects identify and prioritize actions which could eliminate or reduce the chance of the failure occurring document the process ► It involves: Brainstorming to identify “all” potential failure causes Assigning numerical priorities to all modes Tracking and documenting corrective actions

Definitions ► Failure Mode Analysis Incorrect behavior of a subsystem or component due to a physical or procedural malfunction ► Failure Effect Analysis Incorrect behavior of the system caused by a failure ► Failure Criticality Analysis The combined impact of  The probability that a failure will occur  The severity of its effect

FMECA Stages ► Stage 1 Identify all components, assemblies etc of the system under consideration ► Stage 2 Make an exhaustive list of all possible FMs of each component ► Stage 3 Establish the effects that each FM would have on the overall system or process ► Stage 4 Make a list of all possible causes of each FM ► Stage 5 Assign a numerical value to each occurrence for each of the following FM criteria  P = Probability of FM  S = Seriousness/Criticality of FM  D = Difficulty of detecting FM ► Stage 6 Determine criticality index or risk priority number (P  S  D) for each FM ► Stage 7 Determine corrective action needed to avoid FM ► Stage 8 Rank the RPN for the whole system so action may be taken using resources available

Example CI / RPN ► Automobile hydraulic braking system ► Criticality Index / Risk Priority Number = 2 x 9 x 5 = 90 ► Criteria sometimes ranked on a scale of 1 – 4. (4 = worst) ► Each level may have detailed verbal description harder to misrepresent a threat minimizes impact of “judgment” on numerical value Value PX SX DX

Sample FMECA Data Sheet

Summary of FMECA ► Is a formalized group-based problem solving method Similar to design review standards in many industries Uses brainstorming to try to identify “all” risks ► Has become an industry-standard approach Is revised and improved based on experience Attempts to define a general “best known method” ► Tries to accomplish the following: Identify risks Prioritize them Define and track corrective actions and their effects Document the entire decision process

Example: Pressure Cooker ► OPERATOR: 1. loads cooker 2. closes/seals lid 3. connects power 4. observes pressure 5. times cooking at prescribed pressure 6. offloads dinner. ► SYSTEM DESCRIPTION: Electric coil heats cooker. Thermostat controls temperature  Switch opens >120 °C. Spring-loaded Safety Valve opens on overpressure. Pressure Gauge red zone indicates overpressure. High temperature/pressure cooks/sterilizes food — tenderizes and protects against botulin toxin. ► Prepare an FMEA at component level for cooking (after loading/ closing/ sealing). ► Targets are personnel (P), product (R), and the pressure cooker itself (E). Ignore facility/kitchen and energy consumption. Food is for private use.