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FMEA, FTA, HAZOP and Other Risk Analysis Methods: Which One to Use

Choosing the wrong risk method creates a lot of paperwork and little insight. This table compares the common methods side by side: does it start from components or from an unwanted event, what is it good at, what does it produce and where is it described.

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Method	Approach	Best used for	Typical output	Related standard or source
DFMEA	Inductive, bottom-up	Finding how product functions could fail in design	Ranked failure chains with design actions	AIAG-VDA FMEA Handbook; SAE J1739; IEC 60812
PFMEA	Inductive, bottom-up	Finding how process steps could fail to deliver requirements	Ranked failure chains, controls and actions	AIAG-VDA FMEA Handbook; SAE J1739; IEC 60812
FMECA	Inductive, bottom-up	FMEA plus criticality ranking, common in defense and aerospace	Criticality matrix or numbers	MIL-STD-1629A (cancelled, still cited); IEC 60812
System FMEA (SFMEA)	Inductive, bottom-up	System-level functions and interfaces	System failure effects and mitigations	AIAG-VDA FMEA Handbook
FMEA-MSR	Inductive, bottom-up	Monitoring and system response in electronic and software-heavy systems	Failure chains with monitoring and response	AIAG-VDA FMEA Handbook
FMEDA	Inductive, bottom-up	Failure rates and diagnostic coverage for safety hardware	Safe, dangerous, detected and undetected failure rates	IEC 61508; ISO 26262
Fault tree analysis (FTA)	Deductive, top-down	Finding combinations of events leading to one unwanted top event	Fault tree and top event probability, minimal cut sets	IEC 61025
Event tree analysis (ETA)	Inductive, forward-looking	Following consequences after an initiating event	Outcome branches with frequencies	IEC 62502
HAZOP	Structured team review with guide words	Process plants and flow systems, deviation from design intent	Deviation, cause, consequence and safeguard table	IEC 61882
LOPA	Semi-quantitative	Deciding if safeguards give enough risk reduction	Scenario frequency against tolerable frequency	CCPS LOPA guidance; IEC 61511
Preliminary hazard analysis (PHA)	Early qualitative	Identifying hazards early in concept	Hazard list with initial risk ranking	SAE ARP4761 (aircraft); ISO 31010
What-if analysis	Brainstorming	Quick review of procedures or small changes	Question and answer list with actions	ISO 31010
Bow-tie analysis	Visual barrier model	Showing threats, barriers and consequences around one hazard	Bow-tie diagram	ISO 31010
5 Whys	Iterative questioning	Simple root cause of a single problem	Cause chain	Lean and 8D practice
Ishikawa (fishbone) diagram	Brainstorming by cause category	Listing possible causes of one problem	Cause categories diagram	ISO 9004 and quality tool literature
Reliability block diagram (RBD)	Quantitative structure model	Availability of series and parallel systems	System reliability or availability	IEC 61078
Reliability-centred maintenance (RCM)	Function-based maintenance analysis	Choosing maintenance tasks for assets	Maintenance strategy per failure mode	SAE JA1011 and JA1012; IEC 60300-3-11
Weibull analysis	Statistical life data	Modelling wear-out or infant mortality from failure data	Shape and scale parameters	IEC 61649
Job safety analysis (JSA)	Task-based hazard review	Hazards in a work task	Step, hazard and control table	OSHA guidance on job hazard analysis
Risk register	Ongoing qualitative scoring	Tracking project and business risks over time	Ranked log with owners and actions	ISO 31000; PMI practice

Standards and handbooks change by edition. Confirm the current edition and your customer's requirements before citing one in a deliverable.

Talk through risk methods for your program

Optional: a short conversation on which analyses suit your product and how to keep them connected to ERP and quality data.

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Bottom-up versus top-down

FMEA works bottom-up: take each item or step, ask how it could fail and trace the effect upward. It is thorough for single failures and ties neatly to controls. Fault tree analysis works top-down: pick one unwanted event and ask which combinations of lower events cause it. It handles combinations and redundancy well, which FMEA does not. Many safety cases use both: FMEA to find single-point failures, then an FTA on the few top events that matter most.

Matching the method to the question

Start with the question, not the template. If the question is how a product or process could fail and what controls exist, use DFMEA or PFMEA. If it is whether two failures together could cause a hazard, use FTA. If it is deviation in a flowing process, HAZOP fits. If you need to prioritise a long project risk list, use a risk register. If you need the cause of a single event that has happened, use 5 Whys or an 8D with a fishbone.

Single failures in design or process: DFMEA or PFMEA
Combinations and redundancy: fault tree analysis
Process plant deviations: HAZOP, then LOPA if needed
Maintenance planning: RCM using FMEA outputs
Past events: 5 Whys, fishbone, 8D

Common mistakes

Teams run FMEA to answer questions it cannot answer, such as the likelihood of two simultaneous failures. They also treat a risk register as a hazard analysis, scoring vague items with no structure. Another trap is using a method because the customer form asks for it, without checking that it suits the risk. Where a customer or regulator specifies a method, follow it, and add a complementary method if it leaves gaps.

Frequently Asked Questions

Is FMEA better than fault tree analysis?

Neither is better; they answer different questions. FMEA is a systematic bottom-up review of single failures. FTA models how several events combine to cause one top event. Safety-critical programs often use both.

What is the difference between FMEA and FMECA?

FMECA adds a criticality analysis to FMEA, ranking failure modes by severity and probability or failure rate. It is common in defense and aerospace programs, historically under MIL-STD-1629A.

When should I use HAZOP instead of FMEA?

HAZOP suits process plants and flow systems where deviations from design intent, such as no flow or high pressure, are the natural way to explore risk. FMEA suits discrete products and manufacturing steps.

Which standard describes FMEA?

IEC 60812 describes FMEA and FMECA generally. For automotive, the AIAG and VDA FMEA Handbook is the reference, and SAE J1739 has been widely used. Your customer may specify which applies.

If your risks and failure data sit across ERP, quality and maintenance systems, Netray can talk through how to bring them into one view without moving the data.

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