Risk Analysis Methods

Systematic techniques for hazard identification and risk analysis in medical device development.

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Risk Analysis Methods

Systematic techniques for hazard identification and risk analysis in medical device development.

Table of Contents

Method Selection Guide
FMEA - Failure Mode and Effects Analysis
FTA - Fault Tree Analysis
HAZOP - Hazard and Operability Study
Use Error Analysis
Software Hazard Analysis

Method Selection Guide

Method Application Matrix

Method	Best For	Standard	Complexity
FMEA	Component/process failures	IEC 60812	Medium
FTA	System-level failure analysis	IEC 61025	High
HAZOP	Process deviations	IEC 61882	Medium
PHA	Early hazard screening	-	Low
Use FMEA	Use-related hazards	IEC 62366-1	Medium
STPA	Software/system interactions	-	High

Selection Decision Tree

What is the analysis focus?
        │
        ├── Component failures → FMEA
        │
        ├── System-level failure → FTA
        │
        ├── Process deviations → HAZOP
        │
        ├── User interaction → Use Error Analysis
        │
        └── Software behavior → Software FMEA/STPA

When to Use Each Method

Project Phase	Recommended Methods
Concept	PHA, initial FTA
Design	FMEA, detailed FTA
Development	Use Error Analysis, Software HA
Verification	FMEA review, FTA validation
Production	Process FMEA
Post-Market	Trend analysis, FMEA updates

FMEA - Failure Mode and Effects Analysis

FMEA Overview

Aspect	Description
Purpose	Identify potential failure modes and their effects
Approach	Bottom-up analysis from component to system
Output	Failure mode list with severity, occurrence, detection ratings
Standard	IEC 60812

FMEA Process Workflow

Define scope and system boundaries
Develop functional block diagram
Identify failure modes for each component/function
Determine effects of each failure mode (local, next level, end)
Assign severity rating
Identify potential causes
Assign occurrence rating
Identify current controls (detection)
Assign detection rating
Calculate Risk Priority Number (RPN) or use risk matrix
Determine actions for high-priority items
Validation: All components analyzed; RPNs calculated; actions assigned for high risks

FMEA Worksheet Template

FMEA WORKSHEET

Product: [Device Name]
Subsystem: [Subsystem]
FMEA Lead: [Name]
Date: [Date]

| ID | Item/Function | Failure Mode | Effect (Local) | Effect (End) | S | Cause | O | Controls | D | RPN | Action |
|----|---------------|--------------|----------------|--------------|---|-------|---|----------|---|-----|--------|
| FM-001 | [Item] | [Mode] | [Local Effect] | [End Effect] | [1-10] | [Cause] | [1-10] | [Detection] | [1-10] | [S×O×D] | [Action] |

S = Severity (1=None, 10=Catastrophic)
O = Occurrence (1=Remote, 10=Frequent)
D = Detection (1=Certain, 10=Cannot Detect)
RPN = Risk Priority Number

Severity Rating Scale

Rating	Severity	Criteria
10	Hazardous	Death or regulatory non-compliance
9	Serious	Serious injury, major function loss
8	Major	Significant injury, major inconvenience
7	High	Minor injury, significant inconvenience
6	Moderate	Discomfort, partial function loss
5	Low	Some performance loss
4	Very Low	Minor performance degradation
3	Minor	Noticeable effect, no function loss
2	Very Minor	Negligible effect
1	None	No effect

Occurrence Rating Scale

Rating	Occurrence	Probability
10	Almost Certain	>1 in 2
9	Very High	1 in 3
8	High	1 in 8
7	Moderately High	1 in 20
6	Moderate	1 in 80
5	Low	1 in 400
4	Very Low	1 in 2,000
3	Remote	1 in 15,000
2	Very Remote	1 in 150,000
1	Nearly Impossible	<1 in 1,500,000

Detection Rating Scale

Rating	Detection	Likelihood of Detection
10	Absolute Uncertainty	Cannot detect
9	Very Remote	Very remote chance
8	Remote	Remote chance
7	Very Low	Very low chance
6	Low	Low chance
5	Moderate	Moderate chance
4	Moderately High	Moderately high chance
3	High	High chance
2	Very High	Very high chance
1	Almost Certain	Will detect

RPN Action Thresholds

RPN Range	Priority	Action
>200	Critical	Immediate action required
100-200	High	Action plan required
50-100	Medium	Consider action
<50	Low	Monitor

FTA - Fault Tree Analysis

FTA Overview

Aspect	Description
Purpose	Determine combinations of events leading to top event
Approach	Top-down deductive analysis
Output	Fault tree diagram with cut sets
Standard	IEC 61025

FTA Process Workflow

Define top event (undesired system state)
Identify immediate causes using logic gates
Continue decomposition to basic events
Draw fault tree diagram
Identify cut sets (combinations causing top event)
Calculate probability if quantitative analysis required
Identify single points of failure
Validation: All branches complete; cut sets identified; single points documented

Fault Tree Symbols

Symbol	Name	Meaning
Rectangle	Intermediate Event	Event resulting from other events
Circle	Basic Event	Primary event, no further development
Diamond	Undeveloped Event	Not analyzed further
House	House Event	Event expected to occur (condition)
AND Gate	AND	All inputs required for output
OR Gate	OR	Any input causes output

FTA Worksheet Template

FAULT TREE ANALYSIS

Top Event: [Description of undesired state]
System: [System name]
Analyst: [Name]
Date: [Date]

BASIC EVENTS:
| ID | Event | Description | Probability | Control |
|----|-------|-------------|-------------|---------|
| BE-001 | [Event] | [Description] | [P] | [Control] |

CUT SETS:
| Cut Set | Events | Order | Probability |
|---------|--------|-------|-------------|
| CS-001 | BE-001 | 1 | [P] |
| CS-002 | BE-001, BE-002 | 2 | [P] |

SINGLE POINTS OF FAILURE:
| Event | Risk | Mitigation |
|-------|------|------------|
| [Event] | [Risk assessment] | [Mitigation strategy] |

Cut Set Analysis

Cut Set Order	Meaning	Criticality
First Order	Single event causes top event	Highest - single point of failure
Second Order	Two events required	High
Third Order	Three events required	Moderate
Higher Order	Four+ events required	Lower

HAZOP - Hazard and Operability Study

HAZOP Overview

Aspect	Description
Purpose	Identify deviations from intended operation
Approach	Systematic examination using guide words
Output	Deviation analysis with consequences and safeguards
Standard	IEC 61882

HAZOP Guide Words

Guide Word	Meaning	Example Application
NO/NOT	Complete negation	No flow, no signal
MORE	Quantitative increase	More pressure, more current
LESS	Quantitative decrease	Less flow, less voltage
AS WELL AS	Qualitative increase	Extra component, contamination
PART OF	Qualitative decrease	Missing component
REVERSE	Logical opposite	Reverse flow, reverse polarity
OTHER THAN	Complete substitution	Wrong material, wrong signal
EARLY	Time-related	Early activation
LATE	Time-related	Delayed response

HAZOP Process Workflow

Select study node (process section or component)
Describe design intent for the node
Apply guide words to identify deviations
Determine causes of each deviation
Assess consequences
Identify existing safeguards
Recommend actions if needed
Validation: All nodes analyzed; all guide words applied; actions assigned

HAZOP Worksheet Template

HAZOP WORKSHEET

System: [System Name]
Node: [Node Description]
Design Intent: [What the node is supposed to do]
Team Lead: [Name]
Date: [Date]

| Guide Word | Deviation | Causes | Consequences | Safeguards | Actions |
|------------|-----------|--------|--------------|------------|---------|
| NO | [No + parameter] | [Causes] | [Consequences] | [Existing] | [Recommendations] |
| MORE | [More + parameter] | [Causes] | [Consequences] | [Existing] | [Recommendations] |
| LESS | [Less + parameter] | [Causes] | [Consequences] | [Existing] | [Recommendations] |

Use Error Analysis

Use Error Analysis Overview

Aspect	Description
Purpose	Identify use-related hazards and mitigations
Approach	Task analysis combined with error prediction
Output	Use error list with risk controls
Standard	IEC 62366-1

Use Error Categories

Category	Description	Examples
Perception Error	Failure to perceive information	Missing alarm, unclear display
Cognition Error	Failure to understand	Misinterpretation, wrong decision
Action Error	Incorrect physical action	Wrong button, slip, lapse
Memory Error	Failure to recall	Forgotten step, omission

Use Error Analysis Process

Identify user tasks and subtasks
Identify potential use errors for each task
Determine consequences of each use error
Estimate probability of use error
Identify design features contributing to error
Define risk control measures
Verify control effectiveness
Validation: All critical tasks analyzed; errors identified; controls defined

Use Error Worksheet Template

USE ERROR ANALYSIS

Device: [Device Name]
Task: [Task Description]
User: [User Profile]
Analyst: [Name]
Date: [Date]

| Step | User Action | Potential Use Error | Error Type | Cause | Consequence | S | P | Risk | Control |
|------|-------------|--------------------| -----------|-------|-------------|---|---|------|---------|
| 1 | [Action] | [Error] | [Type] | [Cause] | [Harm] | [S] | [P] | [Level] | [Control] |

Error Types: Perception (P), Cognition (C), Action (A), Memory (M)

Human Factors Risk Controls

Control Type	Examples
Design	Forcing functions, constraints, affordances
Feedback	Visual, auditory, tactile confirmation
Labeling	Clear instructions, warnings, symbols
Training	User education, competency verification
Environment	Adequate lighting, noise reduction

Software Hazard Analysis

Software Hazard Analysis Overview

Aspect	Description
Purpose	Identify software contribution to hazards
Approach	Analysis of software failure modes and behaviors
Output	Software hazard list with safety requirements
Standard	IEC 62304

Software Safety Classification

Class	Contribution to Hazard	Rigor Required
A	No contribution possible	Basic
B	Non-serious injury possible	Moderate
C	Death or serious injury possible	High

Software Hazard Categories

Category	Description	Examples
Omission	Required function not performed	Missing safety check
Commission	Incorrect function performed	Wrong calculation
Timing	Function at wrong time	Delayed alarm
Value	Function with wrong value	Incorrect dose
Sequence	Functions in wrong order	Steps reversed

Software FMEA Worksheet

SOFTWARE FMEA

Software Item: [Module/Function Name]
Safety Class: [A/B/C]
Analyst: [Name]
Date: [Date]

| ID | Function | Failure Mode | Cause | Effect on System | Effect on Patient | S | P | Risk | Mitigation |
|----|----------|--------------|-------|------------------|-------------------|---|---|------|------------|
| SW-001 | [Function] | [Mode] | [Cause] | [System effect] | [Patient effect] | [S] | [P] | [Level] | [Control] |

Failure Mode Types: Omission, Commission, Timing, Value, Sequence

Software Risk Controls

Control Type	Implementation
Defensive Programming	Input validation, range checking
Error Handling	Exception handling, graceful degradation
Redundancy	Dual channels, voting logic
Watchdog	Timeout monitoring, heartbeat
Self-Test	Power-on diagnostics, runtime checks
Separation	Independence of safety functions

Traceability Requirements

From	To	Purpose
Software Hazard	Software Requirement	Hazard addressed
Software Requirement	Architecture	Requirement implemented
Architecture	Code	Design realized
Code	Test	Verification coverage
Test	Hazard	Control verified

---name: risk-analysis-methodsdescription: Systematic techniques for hazard identification and risk analysis in medical device development.---# Risk Analysis MethodsSystematic techniques for hazard identification and risk analysis in medical device development.---## Table of Contents- [Method Selection Guide](#method-selection-guide)- [FMEA - Failure Mode and Effects Analysis](#fmea---failure-mode-and-effects-analysis)- [FTA - Fault Tree Analysis](#fta---fault-tree-analysis)- [HAZOP - Hazard and Operability Study](#hazop---hazard-and-operability-study)- [Use Error Analysis](#use-error-analysis)- [Software Hazard Analysis](#software-hazard-analysis)---## Method Selection Guide### Method Application Matrix| Method | Best For | Standard | Complexity ||--------|----------|----------|------------|| FMEA | Component/process failures | IEC 60812 | Medium || FTA | System-level failure analysis | IEC 61025 | High || HAZOP | Process deviations | IEC 61882 | Medium || PHA | Early hazard screening | - | Low || Use FMEA | Use-related hazards | IEC 62366-1 | Medium || STPA | Software/system interactions | - | High |### Selection Decision Tree```What is the analysis focus? │ ├── Component failures → FMEA │ ├── System-level failure → FTA │ ├── Process deviations → HAZOP │ ├── User interaction → Use Error Analysis │ └── Software behavior → Software FMEA/STPA```### When to Use Each Method| Project Phase | Recommended Methods ||---------------|---------------------|| Concept | PHA, initial FTA || Design | FMEA, detailed FTA || Development | Use Error Analysis, Software HA || Verification | FMEA review, FTA validation || Production | Process FMEA || Post-Market | Trend analysis, FMEA updates |---## FMEA - Failure Mode and Effects Analysis### FMEA Overview| Aspect | Description ||--------|-------------|| Purpose | Identify potential failure modes and their effects || Approach | Bottom-up analysis from component to system || Output | Failure mode list with severity, occurrence, detection ratings || Standard | IEC 60812 |### FMEA Process Workflow1. Define scope and system boundaries2. Develop functional block diagram3. Identify failure modes for each component/function4. Determine effects of each failure mode (local, next level, end)5. Assign severity rating6. Identify potential causes7. Assign occurrence rating8. Identify current controls (detection)9. Assign detection rating10. Calculate Risk Priority Number (RPN) or use risk matrix11. Determine actions for high-priority items12. **Validation:** All components analyzed; RPNs calculated; actions assigned for high risks### FMEA Worksheet Template```FMEA WORKSHEETProduct: [Device Name]Subsystem: [Subsystem]FMEA Lead: [Name]Date: [Date]| ID | Item/Function | Failure Mode | Effect (Local) | Effect (End) | S | Cause | O | Controls | D | RPN | Action ||----|---------------|--------------|----------------|--------------|---|-------|---|----------|---|-----|--------|| FM-001 | [Item] | [Mode] | [Local Effect] | [End Effect] | [1-10] | [Cause] | [1-10] | [Detection] | [1-10] | [S×O×D] | [Action] |S = Severity (1=None, 10=Catastrophic)O = Occurrence (1=Remote, 10=Frequent)D = Detection (1=Certain, 10=Cannot Detect)RPN = Risk Priority Number```### Severity Rating Scale| Rating | Severity | Criteria ||--------|----------|----------|| 10 | Hazardous | Death or regulatory non-compliance || 9 | Serious | Serious injury, major function loss || 8 | Major | Significant injury, major inconvenience || 7 | High | Minor injury, significant inconvenience || 6 | Moderate | Discomfort, partial function loss || 5 | Low | Some performance loss || 4 | Very Low | Minor performance degradation || 3 | Minor | Noticeable effect, no function loss || 2 | Very Minor | Negligible effect || 1 | None | No effect |### Occurrence Rating Scale| Rating | Occurrence | Probability ||--------|------------|-------------|| 10 | Almost Certain | >1 in 2 || 9 | Very High | 1 in 3 || 8 | High | 1 in 8 || 7 | Moderately High | 1 in 20 || 6 | Moderate | 1 in 80 || 5 | Low | 1 in 400 || 4 | Very Low | 1 in 2,000 || 3 | Remote | 1 in 15,000 || 2 | Very Remote | 1 in 150,000 || 1 | Nearly Impossible | <1 in 1,500,000 |### Detection Rating Scale| Rating | Detection | Likelihood of Detection ||--------|-----------|------------------------|| 10 | Absolute Uncertainty | Cannot detect || 9 | Very Remote | Very remote chance || 8 | Remote | Remote chance || 7 | Very Low | Very low chance || 6 | Low | Low chance || 5 | Moderate | Moderate chance || 4 | Moderately High | Moderately high chance || 3 | High | High chance || 2 | Very High | Very high chance || 1 | Almost Certain | Will detect |### RPN Action Thresholds| RPN Range | Priority | Action ||-----------|----------|--------|| >200 | Critical | Immediate action required || 100-200 | High | Action plan required || 50-100 | Medium | Consider action || <50 | Low | Monitor |---## FTA - Fault Tree Analysis### FTA Overview| Aspect | Description ||--------|-------------|| Purpose | Determine combinations of events leading to top event || Approach | Top-down deductive analysis || Output | Fault tree diagram with cut sets || Standard | IEC 61025 |### FTA Process Workflow1. Define top event (undesired system state)2. Identify immediate causes using logic gates3. Continue decomposition to basic events4. Draw fault tree diagram5. Identify cut sets (combinations causing top event)6. Calculate probability if quantitative analysis required7. Identify single points of failure8. **Validation:** All branches complete; cut sets identified; single points documented### Fault Tree Symbols| Symbol | Name | Meaning ||--------|------|---------|| Rectangle | Intermediate Event | Event resulting from other events || Circle | Basic Event | Primary event, no further development || Diamond | Undeveloped Event | Not analyzed further || House | House Event | Event expected to occur (condition) || AND Gate | AND | All inputs required for output || OR Gate | OR | Any input causes output |### FTA Worksheet Template```FAULT TREE ANALYSISTop Event: [Description of undesired state]System: [System name]Analyst: [Name]Date: [Date]BASIC EVENTS:| ID | Event | Description | Probability | Control ||----|-------|-------------|-------------|---------|| BE-001 | [Event] | [Description] | [P] | [Control] |CUT SETS:| Cut Set | Events | Order | Probability ||---------|--------|-------|-------------|| CS-001 | BE-001 | 1 | [P] || CS-002 | BE-001, BE-002 | 2 | [P] |SINGLE POINTS OF FAILURE:| Event | Risk | Mitigation ||-------|------|------------|| [Event] | [Risk assessment] | [Mitigation strategy] |```### Cut Set Analysis| Cut Set Order | Meaning | Criticality ||---------------|---------|-------------|| First Order | Single event causes top event | Highest - single point of failure || Second Order | Two events required | High || Third Order | Three events required | Moderate || Higher Order | Four+ events required | Lower |---## HAZOP - Hazard and Operability Study### HAZOP Overview| Aspect | Description ||--------|-------------|| Purpose | Identify deviations from intended operation || Approach | Systematic examination using guide words || Output | Deviation analysis with consequences and safeguards || Standard | IEC 61882 |### HAZOP Guide Words| Guide Word | Meaning | Example Application ||------------|---------|---------------------|| NO/NOT | Complete negation | No flow, no signal || MORE | Quantitative increase | More pressure, more current || LESS | Quantitative decrease | Less flow, less voltage || AS WELL AS | Qualitative increase | Extra component, contamination || PART OF | Qualitative decrease | Missing component || REVERSE | Logical opposite | Reverse flow, reverse polarity || OTHER THAN | Complete substitution | Wrong material, wrong signal || EARLY | Time-related | Early activation || LATE | Time-related | Delayed response |### HAZOP Process Workflow1. Select study node (process section or component)2. Describe design intent for the node3. Apply guide words to identify deviations4. Determine causes of each deviation5. Assess consequences6. Identify existing safeguards7. Recommend actions if needed8. **Validation:** All nodes analyzed; all guide words applied; actions assigned### HAZOP Worksheet Template```HAZOP WORKSHEETSystem: [System Name]Node: [Node Description]Design Intent: [What the node is supposed to do]Team Lead: [Name]Date: [Date]| Guide Word | Deviation | Causes | Consequences | Safeguards | Actions ||------------|-----------|--------|--------------|------------|---------|| NO | [No + parameter] | [Causes] | [Consequences] | [Existing] | [Recommendations] || MORE | [More + parameter] | [Causes] | [Consequences] | [Existing] | [Recommendations] || LESS | [Less + parameter] | [Causes] | [Consequences] | [Existing] | [Recommendations] |```---## Use Error Analysis### Use Error Analysis Overview| Aspect | Description ||--------|-------------|| Purpose | Identify use-related hazards and mitigations || Approach | Task analysis combined with error prediction || Output | Use error list with risk controls || Standard | IEC 62366-1 |### Use Error Categories| Category | Description | Examples ||----------|-------------|----------|| Perception Error | Failure to perceive information | Missing alarm, unclear display || Cognition Error | Failure to understand | Misinterpretation, wrong decision || Action Error | Incorrect physical action | Wrong button, slip, lapse || Memory Error | Failure to recall | Forgotten step, omission |### Use Error Analysis Process1. Identify user tasks and subtasks2. Identify potential use errors for each task3. Determine consequences of each use error4. Estimate probability of use error5. Identify design features contributing to error6. Define risk control measures7. Verify control effectiveness8. **Validation:** All critical tasks analyzed; errors identified; controls defined### Use Error Worksheet Template```USE ERROR ANALYSISDevice: [Device Name]Task: [Task Description]User: [User Profile]Analyst: [Name]Date: [Date]| Step | User Action | Potential Use Error | Error Type | Cause | Consequence | S | P | Risk | Control ||------|-------------|--------------------| -----------|-------|-------------|---|---|------|---------|| 1 | [Action] | [Error] | [Type] | [Cause] | [Harm] | [S] | [P] | [Level] | [Control] |Error Types: Perception (P), Cognition (C), Action (A), Memory (M)```### Human Factors Risk Controls| Control Type | Examples ||--------------|----------|| Design | Forcing functions, constraints, affordances || Feedback | Visual, auditory, tactile confirmation || Labeling | Clear instructions, warnings, symbols || Training | User education, competency verification || Environment | Adequate lighting, noise reduction |---## Software Hazard Analysis### Software Hazard Analysis Overview| Aspect | Description ||--------|-------------|| Purpose | Identify software contribution to hazards || Approach | Analysis of software failure modes and behaviors || Output | Software hazard list with safety requirements || Standard | IEC 62304 |### Software Safety Classification| Class | Contribution to Hazard | Rigor Required ||-------|------------------------|----------------|| A | No contribution possible | Basic || B | Non-serious injury possible | Moderate || C | Death or serious injury possible | High |### Software Hazard Categories| Category | Description | Examples ||----------|-------------|----------|| Omission | Required function not performed | Missing safety check || Commission | Incorrect function performed | Wrong calculation || Timing | Function at wrong time | Delayed alarm || Value | Function with wrong value | Incorrect dose || Sequence | Functions in wrong order | Steps reversed |### Software FMEA Worksheet```SOFTWARE FMEASoftware Item: [Module/Function Name]Safety Class: [A/B/C]Analyst: [Name]Date: [Date]| ID | Function | Failure Mode | Cause | Effect on System | Effect on Patient | S | P | Risk | Mitigation ||----|----------|--------------|-------|------------------|-------------------|---|---|------|------------|| SW-001 | [Function] | [Mode] | [Cause] | [System effect] | [Patient effect] | [S] | [P] | [Level] | [Control] |Failure Mode Types: Omission, Commission, Timing, Value, Sequence```### Software Risk Controls| Control Type | Implementation ||--------------|----------------|| Defensive Programming | Input validation, range checking || Error Handling | Exception handling, graceful degradation || Redundancy | Dual channels, voting logic || Watchdog | Timeout monitoring, heartbeat || Self-Test | Power-on diagnostics, runtime checks || Separation | Independence of safety functions |### Traceability Requirements| From | To | Purpose ||------|------|---------|| Software Hazard | Software Requirement | Hazard addressed || Software Requirement | Architecture | Requirement implemented || Architecture | Code | Design realized || Code | Test | Verification coverage || Test | Hazard | Control verified |

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