SAFETY ANALYSIS

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SAFETY ANALYSIS
Analysis Methods 1
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Risk Assessment
MIL-STD-882c states Design for minimum risk.
From the first, design to eliminate hazards. If
an identified hazard cannot be eliminated, reduce
the associated risk to an acceptable level, as
defined by the MA, through design selection.
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Analysis Methods

• FUNCTIONAL HAZARD ASSESSMENT
• DESIGN APPRAISAL
• DEPENDENCE DIAGRAMS
• ZONAL SAFETY ASSESSMENT
• FAILURE MODE AND EFFECT ANALYSIS
• FAULT TREE ANALYSIS

THE ANALYSIS METHODS EMPLOYED ARE DEPENDENT
ON- i) THE SYSTEM COMPLEXITY ii) THE SEVERITY
OF THE FAILURE EFFECTS
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Analysis Methods
FUNCTIONAL HAZARD ASSESSMENT
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Functional Hazard Assessment
Prime Uses

• The prime function of a Hazard Analysis is to
  identify the potential hazards that might exist,
  i.e. it provides a list of failure conditions

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Functional Hazard Assessment
It may also
- Establish System Boundaries, Functions
Interactions - Establish System
Architectures - Assign Hazard Effects
Classifications - Justification Documentation for
Hazard Classification - Assign Probability
Targets - Highlight Critical Safety
Features - Identification of the Analytical Tools
to be used in the Safety Assessment process
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Functional Hazard Assessment

• TECHNIQUES FOR HAZARD IDENTIFICATION
• Review of Previous Accidents And Incident
• Carrying Out A What If Analysis
• Hazop Studies Using Guide Words (Def-Stan 00-58)

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Functional Hazard Assessment
Def-Stan 00-58 HAZOP Guide Words
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Functional Hazard Assessment
Advantages

• Provides A Systematic Approach To The Derivation
  of Critical Failure Conditions And The Initiation
  of The Safety Assessment Process

Disadvantages

• May Be Disproportionately Time Consuming

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Analysis Methods
DESIGN APPRAISAL
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Design Appraisal

• Prime Uses
• MAY BE USED EFFECTIVELY ON ALL SYSTEMS
• What Happens If ?
• Possibility of Maintenance Induced Failures
• Suitability/compatibility of Materials

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Design Appraisal

• Suitability/compatibility of Materials

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Design Appraisal

• Advantages
• Quick. Hence an effective tool at the early
  design stage to identify potential problem areas.
• Disadvantages
• Not a rigorous and systematic method
• Very dependent on the analysts experience

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Analysis Methods
DEPENDENCE DIAGRAMS
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Dependence Diagrams

• PRIME USES
• May Be Used To Illustrate The Failure
  Combinations of A System
• Determination of Failure Probabilities

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Series Dependence Diagrams
A
B
C
D
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Parallel Dependence Diagrams
A
B
C
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Dependence Diagrams
Total Failure Probability A x B x C
Assumptions

• Failures are independent
• Failure probabilities are small

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Example of a Hydraulic System
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Dependence DiagramLoss Of Hydraulic Power To
Elevators
ELEVATOR JACK J
BLUE RESVR. A
BLUE EDP D
ENGINE 1 X
GREEN EDP E
ENGINE 1 X
ELEVATOR JACK K
GREEN RESVR B
GREEN EDP F
ENGINE 2 Y
RED EDP G
ENGINE 2 Y
RED RESVR C
ELEVATOR JACK L
RED RAT H
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Dependence Diagrams

• ADVANTAGES
• EFFECTIVE METHOD OF PRESENTING FAILURE
  COMBINATIONS TO
• Rapidly Identify Critical Failures
• Determine Failure Probabilities
• DISADVANTAGES
• NOT AN EXHAUSTIVE ANALYSIS TOOL

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Analysis Methods
ZONAL SAFETY ANALYSIS
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Zonal Safety Analysis
PRIME USES - Determination of Compliance With
The Installation Rules - Identification of
Potential Cascade Failures Due To System
Interaction - Identification of Potential Areas
For System Maintenance Errors - Identification
of Potential Areas For System Malfunction Due To
Environmental Factors
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Zonal Safety Analysis Procedures
AIRCRAFT
DRAWINGS
MOCK-UP
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Zonal Safety AnalysisExamples Of Installation
Rules
All pipes, ducts, hoses, wires, cables etc. which
are attached to moving parts should be mounted in
such a way as to minimise stress. Dangerous
effects should not result from inverted
installations of nut/bolt assemblies. Hot air
ducts should normally be routed above the
hydraulic pipes and equipment.
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Zonal Safety Analysis
ADVANTAGES - Considers the potential for failure
resulting from the installation. DISADVANTAGES -
If deficiencies are not identified until the
analysis is carried out on the aircraft then
required changes could be expensive.
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Analysis Methods
FAILURE MODE AND EFFECT ANALYSIS
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Spool Valve Principle of Operation
Supply
Return
Return
3-5lbs
10-15 Tons
Maurice James
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Spool Valve Principle of Operation
Supply
Return
Return
3-5lbs
10-15 Tons
Maurice James
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Failure Mode and Effect Analysis
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Spool Valve Principle of Operation
Supply
Return
Return
POINT A
3-5lbs
10-15 Tons
Maurice James
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Spool Valve Principle of Operation
Supply
Return
Return
POINT A
10-15 Tons
Maurice James
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Failure Mode and Effect Analysis
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Failure Mode and Effect Analysis
PRIME USES - Detailed Analysis Of Failures In
Equipment or Simple Systems
ADVANTAGES - Methodical And Detailed Analysis
Method DISADVANTAGES - Normally Considers Only
Single Failures
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Analysis Methods
THE SAFETY ASSESSMENT PROCESS
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Typical Programme Structure for Safety Analysis
of a Complex System
SYSTEM SAFETY ASSESSMENT
FAILURE MODE AND EFFECT ANALYSIS
ZONAL SAFETY ANALYSIS
FAULT TREE ANALYSIS
DEPENDENCE DIAGRAMS
DESIGN APPRAISAL
FUNCTIONAL HAZARD ASSESSMENT
SYSTEM CONCEPT
DESIGN PROCESS
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Useful References and Data Sources
GUIDELINES AND METHODS FOR CONDUCTING THE SAFETY
ASSESSMENT PROCESS ON CIVIL AIRBORNE SYSTEMS AND
EQUIPMENT - ARP 4761 Published by SAE (The
Engineering Society For Advancing Mobility Land
Sea Air and Space) SYSTEMATIC SAFETYE. Lloyd
W. Tye Published by UK Civil Aviation
Authority HAZOP STUDIES ON SYSTEMS CONTAINING
PROGRAMMABLE ELECTRONICS DEF-STAN 00-58
Published by the UK Ministry of Defence