FORENSIC
ENGINEERING
INVESTIGATION
©2001 CRC Press LLC
FORENSIC
ENGINEERING
INVESTIGATION
Randall K. Noon
CRC Press
Boca Raton London New York Washington, D.C.
©2001 CRC Press LLC
Library of Congress Cataloging-in-Publication Data
Noon, Randall
Forensic engineering investigation / Randall Noon.
p. cm.
Includes bibliographical references and index.
ISBN 0-8493-0911-5 (alk. paper)
1. Forensic engineering. I. Title.
TA219 .N64 2000
620—dc21 00-044457
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©2001 CRC Press LLC
Preface
Forensic engineering is the application of engineering principles, knowledge,
skills, and methodologies to answer questions of fact that may have legal
ramifications. Forensic engineers typically are called upon to analyze car
accidents, building collapses, fires, explosions, industrial accidents, and var-
ious calamities involving injuries or significant property losses. Fundamen-
tally, the job of a forensic engineer is to answer the question, what caused
this to happen?
A forensic engineer is not a specialist in any one science or engineering
discipline. The solution of “real-world” forensic engineering problems often
requires the simultaneous or sequential application of several scientific dis-
ciplines. Information gleaned from the application of one discipline may
provide the basis for another to be applied, which in turn may provide the
basis for still another to be applied. The logical relationships developed
among these various lines of investigation usually form the basis for the
solution of what caused the event to occur. Because of this, skilled forensic
engineers are usually excellent engineering generalists.
A forensic engineering assignment is perhaps akin to solving a picture
puzzle. Initially, there are dozens, or perhaps even hundreds, of seemingly
disjointed pieces piled in a heap. When examined individually, each piece
may not provide much information. Methodically, the various pieces are
sorted and patiently fitted together in a logical context. Slowly, an overall
picture emerges. When a significant portion of the puzzle has been solved,
it then becomes easier to see where the remaining pieces fit.
As the title indicates, the following text is about the analyses and methods
used in the practice of forensic engineering. It is intended for practicing
forensic engineers, loss prevention professionals, and interested students who
are familiar with basic undergraduate science, mathematics, and engineering.
The emphasis is how to apply subject matter with which the reader already
has some familiarity. As noted by Samuel Johnson, “We need more to be
reminded than instructed!”
As would be expected in a compendium, the intention is to provide a
succinct, instructional text rather than a strictly academic one. For this rea-
son, there are only a handful of footnotes. While a number of useful references
©2001 CRC Press LLC
are provided at the end of each chapter, they are not intended to represent
an exhaustive, scholarly bibliography. They are, however, a good starting
point for the interested reader. Usually, I have listed references commonly
used in “the business” that are available in most libraries or through inter-
library loans. In a few cases I have listed some hard-to-get items that are
noteworthy because they contain some informational gems relevant to the
business or represent fundamental references for the subject.
The subjects selected for inclusion in this text were chosen on the basis
of frequency. They are some of the more common types of failures, cata-
strophic events, and losses a general practicing forensic engineer may be
called upon to assess. However, they are not necessarily, the most common
types of failures or property losses that occur. Forensic engineers are not
usually called upon to figure out the “easy ones.” If it was an easy problem
to figure out, the services of a forensic engineer would not be needed.
In general, the topics include fires, explosions, vehicular accidents,
industrial accidents, wind and hail damage to structures, lightning damage,
and construction blasting effects on structures. While the analysis in each
chapter is directed toward the usual questions posed in such cases, the
principles and methodologies employed usually have broader applications
than the topic at hand.
It is the intention that each chapter can be read individually as the need
for that type of information arises. Because of that, some topics or principles
may be repeated in slightly different versions here and there in the text, and
the same references are sometimes repeated in several chapters. Of course,
some of the subjects in the various chapters naturally go together or lead
into one another. In that regard, I have tried to arrange related chapters so
that they may be read as a group, if so desired.
I have many people to thank for directly or indirectly helping me with
this project. I am in debted to my wife Leslie, who encouraged me to under-
take the writing of this book despite my initial reluctance. I also thank the
people at CRC Press, both present and past, who have been especially sup-
portive in developing the professional literature associated with forensic sci-
ence and engineering. And of course, here’s to the engineers, techs,
investigators, and support staff who have worked with me over the years and
have been so helpful. I’ll see you all on St. Paddy’s at the usual place.
R. N.
©2001 CRC Press LLC
About the Author
Mr. Noon has written three previous texts in the area of forensic engineering:
Introduction to Forensic Engineering, Engineering Analysis of Fires and Explo-
sions, and Engineering Analysis of Vehicular Accidents. All three are available
through CRC Press, Boca Raton, FL.
©2001 CRC Press LLC
For
Nub and Donna,
Pete and Dickie,
Fanny, Ethel, Althea, and Marcus,
Jeanette, Leo Audel, Emery, and Paul,
Bob and Ruby,
Violet, Sheila, and Vera Mae,
Helen, Ernest, Darwin, Billy, and Thomas E.,
Leo, Leroy, Everet, and Gerald Marcus,
and
Tommy Ray.
Remember me when I am gone away,
Gone far away into the silent land;
When you can no more hold me by the hand,
Nor I half turn to go, yet turning stay.
Remember me when no more, day by day,
You tell me of our future that you planned;
Only remember me; you understand
It will be late to counsel then or pray.
Yet, if you should forget me for a while
And afterwards remember, do not grieve;
For if the darkness and corruption leave
A vestige of the thought that once I had,
Better by far that you should forget and smile
Than that you should remember and be sad.
—Christina Rossetti 1830–1894
©2001 CRC Press LLC
Table of Contents
1 Introduction
1.1 Definition of Forensic Engineering
1.2 Investigation Pyramid
1.3 Eyewitness Information
1.4 Role in the Legal System
1.5 The Scientific Method
1.6 Applying the Scientific Method to Forensic Engineering
1.7 The Scientific Method and the Legal System
1.8 A Priori Biases
1.9 The Engineer as Expert Witness
1.10 Reporting the Results of a Forensic Engineering
Investigation
Further Information and References
2 Wind Damage to Residential Structures
2.1 Code Requirements for Wind Resistance
2.2 Some Basics about Wind
2.3 Variation of Wind Speed with Height
2.4 Estimating Wind Speed from Localized Damages
2.5 Additional Remarks
Further Information and References
3 Lightning Damage to Well Pumps
3.1 Correlation is Not Causation
3.2 Converse of Coincidence Argument
3.3 Underlying Reasons for Presuming Cause and Effect
3.4 A Little about Well Pumps
3.5 Lightning Access to a Well Pump
3.6 Well Pump Failures
3.7 Failure Due to Lightning
Further Information and References
©2001 CRC Press LLC
4 Evaluating Blasting Damage
4.1 Pre-Blast and Post-Blast Surveys
4.2 Effective Surveys
4.3 Types of Damages Caused by Blasting
4.4 Flyrock Damage
4.5 Surface Blast Craters
4.6 Air Concussion Damage
4.7 Air Shock Wave Damage
4.8 Ground Vibrations
4.9 Blast Monitoring with Seismographs
4.10 Blasting Study by U.S. Bureau of Mines, Bulletin 442
4.11 Blasting Study by U.S. Bureau of Mines, Bulletin 656
4.12 Safe Blasting Formula from Bulletin 656
4.13 OSM Modifications of the Safe Blasting Formula in
Bulletin 656
4.14 Human Perception of Blasting Noise and Vibrations
4.15 Damages Typical of Blasting
4.16 Types of Damage Often Mistakenly Attributed to
Blasting
4.17 Continuity
Further Information and References
5 Building Collapse Due to Roof Leakage
5.1 Typical Commercial Buildings 1877–1917
5.2 Lime Mortar
5.3 Roof Leaks
5.4 Deferred Maintenance Business Strategy
5.5 Structural Damage Due to Roof Leaks
5.6 Structural Considerations
5.7 Restoration Efforts
Further Information and References
6 Putting Machines and People Together
6.1 Some Background
6.2 Vision
6.3 Sound
6.4 Sequencing
6.5 The Audi 5000 Example
6.6 Guarding
6.7 Employer’s Responsibilities
©2001 CRC Press LLC
6.8 Manufacturer’s Responsibilities
6.9 New Ergonomic Challenges
Further Information and References
7 Determining the Point of Origin of a Fire
7.1 General
7.2 Burning Velocities and “V” Patterns
7.3 Burning Velocities and Flame Velocities
7.4 Flame Spread Ratings of Materials
7.5 A Little Heat Transfer Theory: Conduction and
Convection
7.6 Radiation
7.7 Initial Reconnoiter of the Fire Scene
7.8 Centroid Method
7.9 Ignition Sources
7.10 The Warehouse or Box Method
7.11 Weighted Centroid Method
7.12 Fire Spread Indicators — Sequential Analysis
7.13 Combination of Methods
Further Information and References
8 Electrical Shorting
8.1 General
8.2 Thermodynamics of a “Simple Resistive” Circuit
8.3 Parallel Short Circuits
8.4 Series Short Circuits
8.5 Beading
8.6 Fuses, Breakers, and Overcurrent Protection
8.7 Example Situation Involving Overcurrent Protection
8.8 Ground Fault Circuit Interrupters
8.9 “Grandfathering” of GFCIs
8.10 Other Devices
8.11 Lightning Type Surges
8.12 Common Places Where Shorting Occurs
Further Information and References
9 Explosions
9.1 General
9.2 High Pressure Gas Expansion Explosions
9.3 Deflagrations and Detonations
©2001 CRC Press LLC
9.4 Some Basic Parameters
9.5 Overpressure Front
Further Information and References
10 Determining the Point of Ignition of an
Explosion
10.1 General
10.2 Diffusion and Fick’s Law
10.3 Flame Fronts and Fire Vectors
10.4 Pressure Vectors
10.5 The Epicenter
10.6 Energy Considerations
Further Information and References
11 Arson and Incendiary Fires
11.1 General
11.2 Arsonist Profile
11.3 Basic Problems of Committing an Arson for Profit
11.4 The Prisoner’s Dilemma
11.5 Typical Characteristics of an Arson or Incendiary Fire
11.6 Daisy Chains and Other Arson Precursors
11.7 Arson Reporting Immunity Laws
11.8 Liquid Accelerant Pour Patterns
11.9 Spalling
11.10 Detecting Accelerants after a Fire
Further Information and References
12 Simple Skids
12.1 General
12.2 Basic Equations
12.3 Simple Skids
12.4 Tire Friction
12.5 Multiple Surfaces
12.6 Calculation of Skid Deceleration
12.7 Speed Reduction by Skidding
12.8 Some Considerations of Data Error
12.9 Curved Skids
12.10 Brake Failures
12.11 Changes in Elevation
12.12 Load Shift
©2001 CRC Press LLC
12.13 Antilock Brake Systems (ABS)
Further Information and References
13 Simple Vehicular Falls
13.1 General
13.2 Basic Equations
13.3 Ramp Effects
13.4 Air Resistance
Further Information and References
14 Vehicle Performance
14.1 General
14.2 Engine Limitations
14.3 Deviations from Theoretical Model
14.4 Example Vehicle Analysis
14.5 Braking
14.6 Stuck Accelerators
14.7 Brakes vs. the Engine
14.8 Power Brakes
14.9 Linkage Problems
14.10 Cruise Control
14.11 Transmission Problems
14.12 Miscellaneous Problems
14.13 NHTSA Study
14.14 Maximum Climb
14.15 Estimating Transmission Efficiency
14.16 Estimating Engine Thermal Efficiency
14.17 Peel-Out
14.18 Lateral Tire Friction
14.19 Bootlegger’s Turn
Further Information and References
15 Momentum Methods
15.1 General
15.2 Basic Momentum Equations
15.3 Properties of an Elastic Collision
15.4 Coefficient of Restitution
15.5 Properties of a Plastic Collision
15.6 Analysis of Forces during a Fixed Barrier Impact
15.7 Energy Losses and “ε”
©2001 CRC Press LLC
15.8 Center of Gravity
15.9 Moment of Inertia
15.10 Torque
15.11 Angular Momentum Equations
15.12 Solution of Velocities Using the Coefficient
of Restitution
15.13 Estimation of a Collision Coefficient of Restitution
from Fixed Barrier Data
15.14 Discussion of Coefficient of Restitution Methods
Further Information and References
16 Energy Methods
16.1 General
16.2 Some Theoretical Underpinnings
16.3 General Types of Irreversible Work
16.4 Rollovers
16.5 Flips
16.6 Modeling Vehicular Crush
16.7 Post-Buckling Behavior of Columns
16.8 Going from Soda Cans to the Old ‘Can You Drive?’
16.9 Evaluation of Actual Crash Data
16.10 Low Velocity Impacts — Accounting for the Elastic
Component
16.11 Representative Stiffness Coefficients
16.12 Some Additional Comments
Further Information and References
17 Curves and Turns
17.1 Transverse Sliding on a Curve
17.2 Turnovers
17.3 Load Shifting
17.4 Side vs. Longitudinal Friction
17.5 Cornering and Side Slip
17.6 Turning Resistance
17.7 Turning Radius
17.8 Measuring Roadway Curvature
17.9 Motorcycle Turns
Further Information and References
18 Visual Perception and Motorcycle Accidents
18.1 General
©2001 CRC Press LLC
18.2 Background Information
18.3 Headlight Perception
18.4 Daylight Perception
18.5 Review of the Factors in Common
18.6 Difficulty Finding a Solution
Further Information and References
19 Interpreting Lamp Filament Damages
19.1 General
19.2 Filaments
19.3 Oxidation of Tungsten
19.4 Brittleness in Tungsten
19.5 Ductility in Tungsten
19.6 Turn Signals
19.7 Other Applications
19.8 Melted Glass
19.9 Sources of Error
Further Information and References
20 Automotive Fires
20.1 General
20.2 Vehicle Arson and Incendiary Fires
20.3 Fuel-Related Fires
20.4 Other Fire Loads under the Hood
20.5 Electrical Fires
20.6 Mechanical and Other Causes
Further Information and References
21 Hail Damage
21.1 General
21.2 Hail Size
21.3 Hail Frequency
21.4 Hail Damage Fundamentals
21.5 Size Threshold for Hail Damage to Roofs
21.6 Assessing Hail Damage
21.7 Cosmetic Hail Damage — Burnish Marks
21.8 The Haig Report
21.9 Damage to the Sheet Metal of Automobiles and
Buildings
21.10 Foam Roofing Systems
Further Information and References
©2001 CRC Press LLC
22 Blaming Brick Freeze-Thaw Deterioration
on Hail
22.1 Some General Information about Bricks
22.2 Brick Grades
22.3 Basic Problem
22.4 Experiment
Further Information and References
23 Management’s Role in Accidents and
Catastrophic Events
23.1 General
23.2 Human Error vs. Working Conditions
23.3 Job Abilities vs. Job Demands
23.4 Management’s Role in the Causation of Accidents
and Catastrophic Events
23.5 Example to Consider
Further Information and References
Further Information and References
©2001 CRC Press LLC
Introduction
1
Every man has a right to his opinion, but no man has a right to be wrong in
his facts.
— Bernard Baruch, 1870–1965
A great many people think they are thinking when they are merely rearranging
their prejudices.
— William James, 1842–1910
1.1 Definition of Forensic Engineering
Forensic engineering is the application of engineering principles and meth-
odologies to answer questions of fact. These questions of fact are usually
associated with accidents, crimes, catastrophic events, degradation of prop-
erty, and various types of failures.
Initially, only the end result is known. This might be a burned-out house,
damaged machinery, collapsed structure, or wrecked vehicle. From this start-
ing point, the forensic engineer gathers evidence to “reverse engineer” how
the failure occurred. Like a good journalist, a forensic engineer endeavors to
determine who, what, where, when, why, and how. When a particular failure
has been explained, it is said that the failure has been “reconstructed.” Because
of this, forensic engineers are also sometimes called reconstruction experts.
Forensic engineering is similar to failure analysis and root cause analysis
with respect to the science and engineering methodologies employed. Often
the terms are used interchangeably. However, there are sometimes implied
differences in emphasis among the three descriptors.
“Failure analysis” usually connotes the determination of how a specific
part or component has failed. It is usually concerned with material selection,
design, product usage, methods of production, and the mechanics of the
failure within the part itself.
“Root cause analysis” on the other hand, places more emphasis on the
managerial aspects of failures. The term is often associated with the analysis
of system failures rather than the failure of a specific part, and how procedures
and managerial techniques can be improved to prevent the problem from
reoccurring. Root cause analysis is often used in association with large sys-
©2001 CRC Press LLC
tems, like power plants, construction projects, and manufacturing facilities,
where there is a heavy emphasis on safety and quality assurance through
formalized procedures.
The modifier “forensic” in forensic engineering typically connotes that
something about the investigation of how the event came about will relate to
the law, courts, adversarial debate or public debate, and disclosure. Forensic
engineering can be either specific in scope, like failure analysis, or general in
scope, like root cause analysis. It all depends upon the nature of the dispute.
To establish a sound basis for analysis, a forensic engineer relies mostly
upon the actual physical evidence found at the scene, verifiable facts related
to the matter, and well-proven scientific principles. The forensic engineer
then applies accepted scientific methodologies and principles to interpret the
physical evidence and facts. Often, the analysis requires the simultaneous
application of several scientific disciplines. In this respect, the practice of
forensic engineering is highly interdisciplinary.
A familiarity with codes, standards, and usual work practices is also
required. This includes building codes, mechanical equipment codes, fire
safety codes, electrical codes, material storage specifications, product codes
and specifications, installation methodologies, and various safety rules, work
rules, laws, regulations, and company policies. There are even guidelines
promulgated by various organizations that recommend how some types of
forensic investigations are to be conducted. Sometimes the various codes
have conflicting requirements.
In essence, a forensic engineer:
• assesses what was there before the event, and the condition it was in
prior to the event.
• assesses what is present after the event, and in what condition it is in.
• hypothesizes plausible ways in which the pre-event conditions can
become the post-event conditions.
• searches for evidence that either denies or supports the various
hypotheses.
• applies engineering knowledge and skill to relate the various facts and
evidence into a cohesive scenario of how the event may have occurred.
Implicit in the above list of what a forensic engineer does is the applica-
tion of logic. Logic provides order and coherence to all the facts, principles,
and methodologies affecting a particular case.
In the beginning of a case, the available facts and information are like
pieces of a puzzle found scattered about the floor: a piece here, a piece there,
and perhaps one that has mysteriously slid under the refrigerator. At first,
the pieces are simply collected, gathered up, and placed in a heap on the
©2001 CRC Press LLC
table. Then, each piece is fitted to all the other pieces until a few pieces match
up with one another. When several pieces match up, a part of the picture
begins to emerge. Eventually, when all the pieces are fitted together, the puzzle
is solved and the picture is plain to see.
1.2 Investigation Pyramid
It is for this reason that the scientific investigation and analysis of an accident,
crime, catastrophic event, or failure is structured like a pyramid (Figure 1.1).
There should be a large foundation of verifiable facts and evidence at the
bottom. These facts then form the basis for analysis according to proven
scientific principles. The facts and analysis, taken together, support a small
number of conclusions that form the apex of the pyramid.
Conclusions should be directly based on the facts and analysis, and not
on other conclusions or hypotheses. If the facts are arranged logically and
systematically, the conclusions should be almost self-evident. Conclusions
based on other conclusions or hypotheses, that in turn are only based upon
a few selected facts and very generalized principles, are a house of cards.
When one point is proven wrong, the logical construct collapses.
Consider the following example. It is true that propane gas systems are
involved in some explosions and fires. A particular house that was equipped
with a propane system sustained an explosion and subsequent fire. The focus
of the explosion, the point of greatest explosive pressure, was located in a
basement room that contained a propane furnace. From this information,
the investigator concludes that the explosion and fire were caused by the
propane system, and in particular, the furnace.
CONCLUSIONS
ANALYSIS
FACTS AND
PHYSICAL EVIDENCE
Figure 1.1 Investigation pyramid.
©2001 CRC Press LLC
The investigator’s conclusion, however, is based upon faulty logic. There
is not sufficient information to firmly conclude that the propane system was
the cause of the explosion, despite the fact that the basic facts and the
generalized principle upon which the conclusion is based are all true.
Consider again the given facts and principles in the example, rearranged
in the following way.
Principle: Some propane systems cause explosions and fires.
Fact: This house had a propane system.
Fact: This house sustained a fire and explosion.
Fact: The explosion originated in the same room as a piece of
equipment that used propane, the furnace.
Conclusion: The explosion and fire were caused by the propane system.
The principle upon which the whole conclusion depends asserts only
that some propane systems cause explosions, not all of them. In point of fact,
the majority of propane systems are reliable and work fine without causing
an explosion or fire for the lifetime of the house. Arguing from a statistical
standpoint, it is more likely that a given propane system will not cause an
explosion and fire.
In our example, the investigator has not yet actually checked to see if this
propane system was one of the “some” that work fine or one of the “some”
that cause explosions and fires. Thus, a direct connection between the general
premise and the specific case at hand has not been made. It has only been
assumed. A verification step in the logic has been deleted.
Of course, not all explosions and fires are caused by propane systems.
Propane systems have not cornered the market in this category. There is a
distinct possibility that the explosion may have been caused by some factor
not related to the propane system, which is unknown to the investigator at
this point. The fact that the explosion originated in the same room as the
furnace may simply be a coincidence.
Using the same generalized principle and available facts, it can equally
be concluded by the investigator (albeit also incorrectly) that the propane
system did not cause the explosion. Why? Because, it is equally true that some
propane systems never cause explosions and fires. Since this house has a
propane system, it could be concluded in the same manner that this propane
system could not have been the cause of the explosion and fire.
As is plain, our impasse in the example is due to the application of a
generalized principle for which there is insufficient information to properly
deduce a unique, logical conclusion. The conclusion that the propane system
caused the explosion and fire is based implicitly on the conclusion that the
location of the explosion focus and propane furnace is no coincidence. It is
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