1. Detailed Analyses
Chapter 14

2. Results of Analyses How final product will operate
Problems in operation
Malfunctions & failures
Hazardous characteristics
No one analysis method satisfies all requirements

3. Failure Modes & Effects Analysis (FMEA)
Reliability - probability of successful accomplishment within a specific time & under specified conditions
FMEA - evaluates effects (how and how often) of reliability failure

4. Failure Modes & Effects Analysis (FMEA)
Product listed by major assemblies then sub-assemblies & components
Each component studied for malfunctions & effects
Failure rates determined & listed
Establishes overall probability product will operate without failure for specific length of time & operate certain length of time between failures
Best & principle means to determine where components & designs need improvement to increase life of product & frequency of service
See Figure 14-1, page 152

5. Failure Modes & Effects Analysis (FMEA)
Used for safety purposes
Don’t take human error & hazardous conditions into account
Do take environmental effects into consideration
Don’t consider effects from multiple failures

6. Failure Modes & Effects Analysis (FMEA)
Functions:
Systematic review of component failure modes
Determine effects of failures
Determine parts whose failures critically affect operation
Calculate probabilities of failures within multiple component/sub-assembly systems by considering each mode separately
Establish test program requirements

7. Failure Modes & Effects Analysis (FMEA)
Functions:
Provide input data for trade-off studies
Determine how to reduce probabilities of failure
Eliminate or minimize adverse effects of failures
Deficiencies can be eliminated or minimized through multiple avenues
Don’t include effects of human actions on product

8. Conducting a Failure Modes & Effects Analysis (FMEA)
Know & understand:
Mission of equipment
Constraints within which it is to operate
Limits delineating success & failure

9. Conducting a Failure Modes & Effects Analysis (FMEA)
Divide product into assemblies
Review diagrams, schematics & drawings to determine inter-relationships
Prepare component list & function
Establish operational & environmental stresses affecting product
Determine significant failure mechanisms that could affect components
Identify failure modes of all components

10. Conducting a Failure Modes & Effects Analysis (FMEA)
List each condition which affects a component
Indicate hazard category (page 156)
List preventive / corrective measures to eliminate or control hazard
Enter probabilities of occurrence of each component failure
Compute probabilities of failure of sub-assemblies, assemblies & products
Determine criticality of components & effects of failure (optional)

11. Failure Modes & Criticality Analysis (FMECA)
Critical components given special attention & analyzed more fully
Critical component may be inherently hazardous by nature
Effort should be made to safeguard items that could produce injury or damage through single-point failures

12. Single Point Failure
One in which an accident could result from one component loss, human error or other single, untimely & undesirable event
Example: One source of power for both critical & non-critical operation (hospitals)
Eliminate by separating critical circuits or providing standby power supply

13. Criticality of Failure Modes
Category 1: Failure resulting in potential loss of life
Category 2: Failure resulting in potential mission failure
Category 3: Failure resulting in delay or loss of operational ability
Category 4: Failure resulting in excessive unscheduled maintenance

14. Criticality Ranking Items to more extensively study
Items requiring special attention during production
Special requirements included in specifications for suppliers
Acceptance standards to be established for components
When special procedures, safeguards, protective, warning or monitoring devices are needed
When accident prevention efforts could be applied most effectively

15. Simple Method of Criticality Determination
Multiply the probability of failure by the damage that could be generated.
Criticality rankings generally expressed as probabilities
Ranking does not complete a critical component analysis

16. Limitations FMEA & FMECA - single units or single failures
Fault Tree Analysis - logical diagrams showing how data from FMEA could be interrelated to arrive at a specific event
Reverse process now being used - logic analysis establishes events, failures or successful operations contributing to accident. FMEA studies conditions causing those failures, modes & preventive or safety measures to be taken.

17. Limitations
Inadequate attention given to human error problems due to concentration on hardware failures
Significant omission
Greater number of product failures are result of connector problems, not components
Probability of environmental stresses rarely used

18. Fault Hazard Analysis (FHA)
Does not use same logic principles of Fault Tree Analysis
Does not use same quantitative aspects of FMEA
Originally provided tabulated output
Qualitative analysis method
Detailed extension of PHA
See column headings bottom of page 157

19. Circuit Logic Analysis
Design & evaluation of complex electric & electronic circuitry
Determines how a product can be affected by failures of components in a circuit & if circuit can generate damaging output
Operation described in terms of interacting electronic components & mechanical devices
Circuit elements represented by logic symbols (Figure 14-4, Pages )
Logic equation developed to express condition

20. Blocking Elements
Systems that are designed so they will NOT operate until specific events occur involve this concept
Blocking element - device that must be activated or inactivated to change from a safe to an unsafe state
Done by a person’s action or result of electrical or mechanical process
Example: electrical interlocks

21. Logic Analysis
Determine when a system that has blocking elements that must be removed in order to operate will become unsafe
Can show in the progress of an operation when each safety block will be removed

22. Applications of Logic Analysis
Possibilities of inadvertent activation
Failure analysis
Investigation or interlocks for orderly operation
Determination of safeguard & separation needs
Evaluations of occurrences that might make single-point failures possible

23. Interface Analysis
Determine incompatibilities between subassemblies & subsystems that could result in accidents
Relationships to consider:
Physical
Functional
Flow

24. Physical Relationships
Little clearance that leads to damage upon movement
Access to or egress from becomes impossible or restricted due to dimensions or inadequate clearances
Inability to join mate parts that should fit closely together
Example: Filter in tight spot will not be removed/cleaned

25. Functional Relationships
Zero output - output unit fails completely
Degraded output - partial failure occurs
Erratic output - intermittent or unstable operations
Excessive output - high speed, temperature, voltage
Unprogrammed output - inadvertent operation or erroneous output
Undesirable side effects - other outputs that could be damaging

26. Flow Relationships May involve fluid May involve energy
May be unconfined
Part of interface analysis
Most frequent, severe & varied problems involve fluids & energy flowing through confined passages

27. Potential Flow Problem Causes
Faulty connections
Full or partial failure of interconnections. Consider:
Flammability
Toxicity
Corrosiveness
Loss of pressure
Lubricity
Loss of material
Contamination
Moisture & water
Odor

28. Product Subsystems Figure 14-7, Page 166
Products, subsystems, operators & relationship constitute a system
Subsystems can affect each other while operating
Use of checklists (Figure 7-1, page 57)

29. Mapping
Reveals problems due to location & proximity of units, lines & hazards
Distances between fuel lines & ignition sources
Locations of tanks in storage farms
Mapping of fire zones & fire defense routes
Emergency evacuation routes, safety zones & protective structures
Noise level contours & scope of effects
Accidents involving fires
Accidents involving buses / children
Determine extent of potential micrometeorological problems

30. Checklist Reviews
Assist designers ensuring no adverse features are incorporated into a product & that appropriate safeguards are provided
Lead to good engineering practices
Help avoid specifically prohibited or poor practices
Ensure mandatory requirements are satisfied

31. Checklist Reviews
Questions based on specific standard (PSM Compliance Officer’s Directive)
Source of checklist item included in ( ) at end of question/statement
Verification categories:
Analysis
Examination
Demonstration
Test

32. Checklist Reviews Column spaces for remarks regarding compliance
Space for entering mark when item is satisfied or other information
Standard checklists may not be applicable to product analyzed
Arrange questions / statements sequentially
Provide designer with checklist before design is begun