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
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