18 Knowledge Objectives

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Failure Analysis and Analytical

Tools

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Knowledge Objectives

? Describe the methods that are available to assist in the analysis of a fire incident.

? Document information collected during the incident.

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Skills Objectives

? Organize information into a rational and logical format.

? Use models to analyze fire incident data.

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Introduction

? Investigator is often faced with multitude of data and facts

? Needs to organize and analyze the information

? In order to formulate a hypothesis

? Several analytical tools are available.

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Timelines

? Graphic or narrative representation of events related to fire incident

? Arranged in chronological order

? Value of timeline depends on accuracy of information included

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Hard Times (1 of 2)

? Also called actual times ? Incidents that are related to known exact

times ? Used as benchmarks in developing timeline

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Hard Times (2 of 2)

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Soft Times

? Estimated times ? Relative and generally provided by witnesses ? Relative time can be subjective and varies with

witness ? Estimated time is approximation based on

information or calculations

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Benchmark Events

? Particularly valuable as foundation for timeline

? Have significant relation to fire cause, spread, detection, or extinguishment

? Important to synchronize times from different hard time sources

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Multiple Timelines (1 of 2)

? May be required to effectively document sequence of events

? Macro evaluation can cover months or years ? Micro evaluation looks at small segments of

macro timeline in detail

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Multiple Timelines (2 of 2)

? Parallel timelines look at multiple events that occur simultaneously.

? Graphic timelines and approaches involving matrices may be helpful.

? Scaled timelines show time of events and elapsed time between them.

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System Analysis

? An analytical approach ? Takes into account characteristics, behavior,

and performance of various elements

? Including human activities and mechanical features of equipment

? Integrates these to provide as complete a picture of incident as possible

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Fault Trees (1 of 2)

? Also called decision trees ? Illustrate series of events and decisions

necessary to specific outcome ? Sometimes makes solution readily apparent ? Investigator uses deductive reasoning ? Same principle used as for "and" and "or"

gates in computer programming

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Fault Trees (2 of 2)

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Failure Mode and Effects Analysis (FMEA)

? Another graphical method used to determine causes and effects of event leading to fire

? Table used with column headings such as:

? Item or action being analyzed ? Basic fault (failure) or error that created hazard ? Consequence of failure

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Mathematical/Engineering Modeling

(1 of 4)

? Hand calculations to evaluate specific issues ? Computer-aided analysis to examine more

complex fire dynamics and fire progression ? Engineering models are sometimes used that

incorporate:

? Known and approximated properties of materials ? Specific features and components of incident ? Physical property estimates

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Mathematical/Engineering Modeling

(2 of 4)

? Engineering models are sometimes used that incorporate:

? Known and approximated properties of materials and systems

? Specific features and components of incident ? Physical property estimates defined to a stated

degree of certainty

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Mathematical/Engineering Modeling

(3 of 4)

? Fire growth curves are an example of mathematical modeling.

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Mathematical/Engineering Modeling

(4 of 4)

? Caveats include:

? Not the only tools used to test hypothesis ? Do not necessarily provide definitive solution ? Results should be considered in light of all data ? Fire model may be useful in understanding fire

damage or injury ? Services of an expert may be needed

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Limitations of Mathematical Modeling

? Can never be used as sole basis to determine origin and cause

? Uncertainties surround inputs, generic fire science data used in models, and results.

? Investigator should retain original input and output files for other parties to examine

? Some analyses may require advanced training and experience.

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Heat Transfer Analysis

? Heat transfer models

? Allow investigator to determine how heat was transferred from source to target

? Can be used to:

? Test hypotheses of ignition source ? Explain damage to adjacent buildings ? Explain ignition of secondary fuel items ? Follow heat transmission through building

elements

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Flammable Gas Concentrations

? Investigator determines concentration of gas within given space

? Can support or disprove involvement of flammable gas in the incident

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Hydraulic Analysis

? Performed when fire is not controlled by sprinkler system

? Did sprinkler system function as intended? ? Was design adequate? ? Did system and water supply match the hazard

they were protecting?

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Thermodynamic Chemical Equilibrium Analysis (1 of 2)

? For fires/explosions believed caused by chemical reactions

? Useful in evaluating hypothesis about:

? Chemical reactions ? Role of contamination ? Role of ambient conditions ? Potential of overheating ? Other related scenarios

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Thermodynamic Chemical Equilibrium Analysis (2 of 2)

? Computer programs can be used.

? The analysis may show that the reaction of certain chemicals was either thermodynamically favored, or not.

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Structural Analysis

? Can provide clues on why building failed by collapse during fire

? Helps determine when fire had most significant impact on building strength

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Egress Analysis

? Determines reason why a fire victim did not escape from fire

? Causes may be design features, maintenance issues

? Computer-based Consolidated Model of Fire and Smoke Transport (CFAST) can be used

18

Fire Dynamics Analysis (1 of 2)

? Hand calculations ? Computer models

? Zone models ? Field computational fluid dynamics (CFD) models

? Assist investigator in determining fire growth and development

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Fire Dynamics Analysis (2 of 2)

? Uncertainties can influence results:

? Fire load characteristics ? Ventilation openings ? HVAC flow rates ? Heat release rates

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Specialized Fire Dynamics Routines

? Simplified procedures that require minimal data to run a computer model

? Can often answer narrowly focused questions, such as:

? Time to flashover ? Heat release rate ? Flame height

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Computer Fire Models (1 of 2)

? Allow for complex, detailed analysis of fire growth and behavior

? Zone models divide compartment into two zones: hot upper zone and cooler lower zone

? Can be run on personal computers ? Generally well accepted and validated by peer

review

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Computer Fire Models (2 of 2)

? CFD (computational fluid dynamics) models divide compartment into many small cells

? Numerous calculations occur in each cell. ? Activity in one cell affects surrounding cells. ? Require high level of expertise ? Often require large capacity computer

workstations

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Graphic Representations

? Drawings ? Physical models ? Computer animations

? Used to:

? Understand an incident location better ? Assist in interviewing witnesses ? Define and identify better materials and systems and

their involvement

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Fire Testing (1 of 3)

? Can help check data collected or test hypotheses

? Can be conducted in field and/or controlled environment

? Caveats:

? Impossible to re-create all conditions ? Following established practices will help ensure

credibility of results.

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Fire Testing (2 of 3)

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Fire Testing (3 of 3)

Fire testing uses fire endurance testing techniques.

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Data Required for Modeling and Testing

? The "garbage in, garbage out" concept applies.

? Results are only as valid as the data from which they were derived and the care taken to develop them.

? Important information to obtain:

? Structural information ? Materials and contents ? Ventilation information

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Summary (1 of 7)

? Understanding the timeline of any incident is key to creating the failure analysis because it assists the investigator in determining the sequence of events that occurred.

? When developing a timeline, incidents that can be related to a known exact time are generally referred to as hard times.

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Summary (2 of 7)

? Soft time is either estimated or relative and is generally provided by witnesses.

? Benchmark events are particularly valuable as a foundation for the timeline or may have significant relation to the cause, spread, detection, or extinguishment of a fire.

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Summary (3 of 7)

? A scaled timeline will show the time of each event with the spacing between the time events being scaled in a manner that would show the elapsed time between each event.

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Summary (4 of 7)

? Analytical approaches involving systems analysis take into account characteristics, behavior, and performance--including human activities and mechanical features of equipment--and integrate these to provide as complete a picture of events surrounding an incident as possible.

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Summary (5 of 7)

? Models commonly used to analyze fire incidents are generally of two types: mathematical/engineering models and graphic models.

? Mathematical models simulate or predict events using established scientific principles and empirical data.

? Graphic models include drawings of all sorts, physical models, and computer animations.

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Summary (6 of 7)

? Fire testing can help check data collected or test a specific hypothesis. It can be conducted in the field and/or in a controlled environment and may range from bench tests to full-size recreations of the event.

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Summary (7 of 7)

? A meaningful analysis of a fire requires understanding of the heat release rate, the fire growth rate, and total heat released.

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