Past articles in The Expert have described the use of the global positioning system (GPS) in the performance testing of motor vehicles and in the 3-D surveying of bridges. New uses for the versatile technology continue to suggest themselves almost daily. Earlier this year, ATA used its growing inventory of GPS equipment in our most elaborate use of the technology to date.
A program of on-the-water testing was prompted by product liability claims against the retailer of a multi-passenger, inflatable ski tube. The plaintiff alleged that failure of a tow point, where the ski rope attached to the tube, had resulted in the tube's unplanned separation from the powerboat that was pulling it. After separation, it was claimed, the tube had careened into a dock at the shoreline causing undeniably serious injuries to two teenaged girls on the tube.
Separate from the fact that the plaintiff had tied the ski rope to a handhold on the tube rather than to the yoke which was the designated tow point; the plaintiff's description of the tube's trajectory after the alleged separation seemed unlikely. However, given the dearth of published data on the hydrodynamic characteristics of ski tubes, it was impossible to authoritatively reconstruct the tube's behavior solely by mathematical analysis.
To get the data needed to properly assess the plaintiff's claims about the tube's behavior, an exemplar ski boat and tube (the subject tube was discarded after the accident) were acquired, and a test program was planned. The boat and tube were each equipped with a GPS receiver to track their separate movements, and a load cell was employed at the ski rope's attachment to the boat to monitor tension in the rope. In addition, a remotely controlled release was rigged at the tube-end of the ski rope to permit the alleged separation to be triggered at points of interest during the tests.
Tests were conducted in the range of boat speeds described by the plaintiff with the tube weighted to simulate the passenger load at the time of the accident. Turns of various sizes were executed; small radius turns described by the plaintiff and larger radius turns limited by the relatively narrow width of the lake where the accident occurred. Two ski rope lengths were tested; that described by the plaintiff and that recommended by the tube's manufacturer.
The tests confirmed that the plaintiff's description of the accident and her claims about the tube's behavior were at odds with the laws of physics. Separation of the tube from the ski rope was clearly not the proximate cause of the accident. Testing showed that the tube's speed diminished so rapidly after release that, if the tube had struck the dock after a separation, the separation point was necessarily so close by that the tube was already on a path to being towed directly into the dock.
In view of those test results, the plaintiff chose to settle the case without going to trial.
A card game in which the players bet on the top card of the dealers
deck; a game of chance based on guessing and luck. Ironically, FARO
Technologies, Inc., a high tech company in Lake Mary, Florida, has
developed a hybrid measurement tool that gives its users the ability
to record nearly perfect measurements.
Originally designed for assisting surgeons in precision location
of tumors during brain surgery, this highly accurate device uses
analog/digital rotary transducers to measure exact angles and dimensions.
Known as the FARO “arm” because of its appearance, the
device allows for 6 degrees of freedom with a hemispheric measuring
envelope that ranges from 6-12 feet. The FARO arm has developed
to include a wide range of end users. From Boeing, which uses the
arm to measure and inspect jet engines, to General Motors whose
application involves accurately identifying and correcting variations
in their manufacturing procedures.
More recently, FARO has found it’s way into the market of
accident reconstruction with the need to accurately measure crushed
vehicles involved in accidents. Traditionally, vehicle crush measurement
has been a time consuming procedure. Data results generally are
hand written coordinates or measurements generated with tape measures
and documented with photographs. The investigator may leave the
vehicle with an accurate listing of coordinates of the vehicle crush,
but they are only coordinates. Someone now has to take these coordinates
and photographs and create an engineering drawing from them. Depending
on the fidelity of the end product, this could be a long and expensive
task. Using this technique to generate a 3d-surfaced model of a
crushed vehicle simply isn’t practical.
a single point accuracy as low as .0001” and a process that
allows for virtually an endless range, the FARO arm gives the operator
a precise measurement of the entire vehicle in a relatively short
time frame. The procedure consists of:
Setting up the arm next to the vehicle and establishing a coordinate
2. Extending the probe to surface of the object and selecting your
points by pressing a button and,
3. Moving the arm to the next position and starting over again at
step number one.
the data points are selected the computer software builds a surface
between the data points in real time. Points can be taken one at
a time or in a streamline technique that allows for a user set increment.
After taking enough points, you begin to see the 3d-vehicle computer
model beginning to take shape. The investigator walks away with
a highly accurate 3d-computer model of the vehicle. This model can
be used by engineers to measure the amount of crush deformation,
analyzed by biomechanics for passenger biokinematics, and or used
within computer crash simulation or animation of the accident.
Having a computer model of the vehicle preserves it’s current
state and in some instances allows the owner to make repairs and
put the vehicle back into service. Feedback is virtually instantaneous.
Depending on the amount of deformation and if the interior needs
to be captured, most vehicles can be digitized in 2-3 hours.
The application is obviously not limited to just cars. Trucks, tractors,
trailers, boats and just about any component or part that may be
important to a case can be digitized. The unit comes with a very
robust carrying case, which allows for portability of the arm.
Downsides to the FARO arm are minimal but need to be addressed.
Weather can be a factor. The arm cannot be used in the rain. Also,
after setting up the arm, the operator needs to allow approximately
15 minutes for temperature compensation (if there has been a change
in temperature). The probe must touch the surface you are digitizing
to take an accurate point. In some instances, the configuration
of the arm may not allow you to reach an area and hand measurements
may be an alternative.
If you have the money to spend, N Vision in Dallas, Texas makes
a laser attachment to the FARO arm that would allow you to capture
virtually any area of the object. If you do run into a problem,
however, you’ll be glad to know that purchasing a FARO arm
also entitles you to lifetime customer support.
the name suggests, FARO Technologies 6 degrees of freedom digitizer
takes the guesswork out of vehicle crush measurement. If accuracy
is critical to your case, and you need to generate a computer model
of your vehicle or component in a short time frame then you should
consider this reliable and precise FARO arm as an option.
Dynamics Analysis Handbook
Associates is proud to announce the publication of Vehicle Dynamics
Analysis: Handbook of Charts and Tables- with CD-ROM.
The Handbook is a complete reference tool that is a composite of
engineering data expressed in formulas, charts, tables and graphs.
Approximately 80 pages, the Handbook was specifically designed as
a supplement to traditional textbooks. The Handbook covers basic
formulas, acceleration, braking, deceleration, stopping, speed,
maneuvering and curves. It is the ideal resource for those initiated
in the basics of accident reconstruction.
The accompanying CD-ROM contains an application that lets the user
make their own calculations and charts
The Handbook was written for accident reconstructionists, attorneys,
claims adjusters, consulting experts and investigating officers.
While an understanding of physics is helpful in using the Handbook,
it is not absolutely necessary.
variety of expertise contributed to the production of the Handbook.
Authors of the Handbook include Robert Swint, Barry Richard, John
Sweatt and Marvin Larson.
Swint is the CEO and a technical, graphics and animation consultant
at ATA. A former NASA engineer, Mr. Swint has worked in the field
of accident reconstruction for over 20 years. He has lectured in
both the public and private sectors in the capacities of educator,
expert witness and trainer.
Richard is the President of ATA Associates and a Certified Safety
Professional. He teaches graduate courses in safety engineering
and accident investigation at the University of Houston, Clear Lake.
Sweatt is a Technical Associate with ATA and a retired 22 year veteran
of the Houston Police Department. Mr. Sweatt worked extensively
in the Hit and Run Accident Detail and Accident Investigation Division
and is a licensed private investigator in the state of Texas.
Larson, former manager of the production department at ATA, is currently
working as a freelance computer consultant, programmer and web page
designer. Mr. Larson developed the CD-ROM which accompanies the
Handbook is available May 1999. Call Lawyers and Judges Publishing
Company at (800) 209-7109 for more information.
Expands Test Capabilities
sure that most of our long time clients are aware of our test capabilities
and experience. The list includes, for example:
- Boat performance and handling,
- Automobile and truck crashes,
- Automobile and truck braking,
- Trailer under ride guards,
- Automobile braking systems performance,
- Automobile electrical systems,
- Seat belts,
- Seats, and
- Consumer products from power saws to toilets
however, we took a step toward larger scale laboratory testing when
we designed and had constructed two new pieces of equipment to serve
as test beds for our Houston Technology Center.
first is a 10 foot by 5 foot rigid table for conducting structural
tests. The table weighs 3800 pounds and has a top made from a single
sheet of 1 inch steel plate. The table provides a stable base on
which to mount articles to be tested so that variations in data
due to attachment structure flexing are greatly reduced and our
data is more scientifically accurate.
second, and more recent acquisition is a flying bridge lifting frame
designed to allow us to lift a vehicle and put it in unusual positions.
The fixture operating envelope will support positions in 360 degrees
of roll and yaw and plus or minus 35 degrees of longitudinal pitch
. Greater pitch angles up to 55 degrees can be achieved with supplemental
stabilizing devices. This allows us to:
- Test seat belt performance and determine precise lock trip points
for seat belt actuators in a true 3-dimensional environment.
- Determine other vehicle system performance such as fuel system
shut-off switches in adverse situations.
- Study occupant kinematics by performing occupant movement and
position analysis in actual unusual position situations to determine
seat belt support limits and characteristics, body movement and
roof crush clearance in rollover situations.
- Determine vehicle weight and balance within certain parameters
(we are working to refine this.
- Perform more detailed vehicle inspections with vehicles in post
- Improve the quality, accuracy and perspective of photography of
the underside of vehicles.
device is unique to ATA and expands our test capabilities well beyond
what other accident reconstruction firms are doing to test the validity
of accident causation hypotheses.
addition of these two new tools to support our capabilities adds
significantly to the range of services we can provide our clients
and experts and stays with our philosophy of high technology approaches
to the scientific analysis of accidents.
Consumer Safety Associates
evaluating product safety, it is incumbent upon a reasonably prudent
manufacturer, distributor, and retailer to apply the following accepted
principles of safety analysis to insure that the products are reasonably
Establish and observe a written safety policy. This policy should
emphasize commitment to safety. In writing, it will insure all employees
obtain clear guidance on safety issues. The policy should set forth
a method for discussing safety responsibilities.
2. Adequately identify and evaluate product hazards. A hazard is
the inherent capability of a product to do harm. Manufacturers,
distributors, and retailers must review the potential injury-causing
energy and evaluate severity and foreseeability.
3. Perform an adequate design review integrating product hazards,
the environment and foreseeable consumer use. Once hazards are identified,
the reasonably prudent manufacturer/distributor/retailer must consider
the conditions or use under which the injury-causing mechanism (hazard)
can cause harm to the user.
of the environment where the product will foreseeably be used, especially
in light of product promotion, is critical in discerning how the
consumer may foreseeably use the product, even if it is not the
use intended by the manufacturer.
product must be reasonably safe prior to distribution in commerce.
If it is not possible to eliminate the hazard, the reasonably prudent
manufacturer, distributor, and retailer must take steps to guard
against the hazard, to adequately inform users of the danger inherent
in the product, and to motivate them to avoid that danger.
Monitor the safety performance of the product after sale and use
and take corrective action where necessary. Once the product is
distributed to consumers, a responsible manufacturer/distributor/retailer
must determine where injuries can occur, or if a product defect
(including lack of adequate labeling and safety information) could
Consumer Product Safety Commission provides national injury estimates
through the National Electronic Surveillance System, better known
as NEISS, to assist in monitoring safety performance. Where corrective
action is needed to substantially reduce or eliminate injuries,
consumer notification and additional safety measures must be implemented
to insure consumer safety.
Develop adequate warnings and training to motivate consumers to
understand and avoid dangers. A good warning can give consumers
the information they need to protect themselves from injury. Under
the industry developed guidelines established at ANSI Z535.4 standard,
manufacturers and distributors have the information required to
develop a warning that includes a signal word (Danger, Warning,
Caution), a pictorial identifying the hazard, instructions on how
to avoid injury and the consequences for failing to act. While correcting
product defects is the primary goal, warnings are essential in a
reasonable safety program.
key precept of safety analysis concerns products with inherent capability
to do catastrophic harm. In priority order, the duty of a reasonably
prudent manufacturer is to eliminate the hazard, or, if this is
not possible while preserving utility, guard against the hazard.
At a minimum, the manufacturer, distributor, and retailer must properly
inform users of the dangers inherent in the product and motivate
them to avoid it.
Jackson, P.E., CFEI
should ensure that their product is properly designed and properly
manufactured to avoid injury, environmental damage or property damage.
To avoid liability, their products need to be properly engineered
to ensure that they are designed to be safe. If a manufacturer does
not do some sort of safety analysis to identify and hopefully correct
hazards, he will most assuredly be held liable if someone is injured.
The method I use is applying the hierarchy for hazard reduction,
it contains all of the elements that the designer must consider
to reduce or eliminate the hazard.
identify a hazard and determine its relative risk, the probability
and severity of the hazard must be assessed. A high severity hazard
such as being struck by a meteorite from space has such low probability
that you need not concern yourself. Conversely, a low severity risk
such as stubbing your toe on furniture happens quite often but the
severity is not worth taking action. Those hazards with high probability
and high severity need to be addressed immediately.
a manufacturer has identified a hazard with their product they must
work to eliminate it or reduce the severity or probability. Also,
the hazard should be identified and corrected before being placed
on the market. Once the product is in the hands of the populace
it is hard to retrieve it.
hierarchy for hazard reduction is a well known set of circumstances
involving safety and hazardous material and how best to eliminate
or reduce the hazard. Basically the hierarchy tells you to:
1. Implement a fundamental design change or substitution for a less
hazardous design or material.
2. Install an engineered safety feature, an automatic safing device.
3. Install a safety barrier to prevent exposure to the hazard.
4. Provide Warnings for the end user.
5. Provide written policies and procedures on the use of the product.
6. Require or provide Personal Protective Equipment.
or all of these methods can be employed to eliminate or reduce the
hazard, generally the best method is number 1 and they decrease
in effectiveness as you go down the list.
manufacturer should not hide behind the auspices of industry standards
as complying with reasonable design. These are only minimum standards
and they should at least meet them. Some of the standards I have
reviewed are lacking good design and safety practices, although
these standards are better than none.
quality practices, including industry and ISO standards, are required.
These are necessary to ensure the product is produced as it was
designed. Defects in material or workmanship must be avoided in
order to achieve a product free from defects.
manufacturer must maintain records and stay abreast of the current
technology and methods of design, manufacturing and means with which
their product may be used or abused. Determining foreseeable misuse
of their product is necessary and important in steps 4, 5 and 6
of the hierarchy.
the Lab - Models and Mockups
sure that most of our long time clients are aware of our test capabilities
and experience. Keeping that in mind, I thought I would tell you
a little bit about ATA's Model and Mock-up capabilities. Our custom
model making and mock-up capabilities offer a variety of three-dimensional
solutions. From product design, testing and marketing to courtroom
exhibits, models take ideas and concepts beyond words to a visual
it comes to designing and crafting models it is particularly important
to keep your audience in mind. Who will be viewing the display?
For what purpose is it being built? What do you hope to convey?
Detailed pre-proposal interviews eliminate questions regarding scope,
purpose, degree of detail, and material to be used. Size, fidelity
and cost should always be considered before starting any model-making
job. We are dedicated to our customer's needs, so the more information
we gather on the front end the more pleased you will be with the
final product. ATA's modern light manufacturing and testing facility
allows us to work with a wide range of materials including balsa
wood, plastic, steel and aluminum. From low fidelity model repairs
to working scale, high fidelity mock-ups, we are your one stop shop.
Prior to becoming the Laboratory manager at ATA, I was employed
at the McDonnell Douglas/Boeing Space Station Division. At Boeing
I was assigned to an engineering development operations team (E.D.O.)
made up of master modelers from around the country. We built high
fidelity models for everything from a full scale working Space Station
mock-ups to high-speed wind tunnel aircraft models. It is this level
of detail and experience that I proudly bring to ATA.
hope to be able to assist many of you with your projects.
Asked Questions About On - Board Diagnostics
Environmental Protection Agency has regulations in place establishing
requirements for On-Board Diagnostic (OBD) systems on light duty
vehicles, light-duty trucks as well as heavy trucks beginning with
the 1994 model year. The purpose of the OBD system is to assure
proper emission control system operation for the vehicle's lifetime
by monitoring emission-related components and system operation for
deterioration and malfunction.
is an OBD system and how does it work?
engines in today's vehicles are largely electronically controlled.
Sensors and actuators sense the operation of specific components
(e.g., the oxygen sensor, ABS) and actuate others to maintain optimal
engine control. An on-board computer, known sometimes as a "power
train control module" or an "engine control unit,"
controls all of these systems. With proper software, the on-board
computer is capable of monitoring all of the sensors and actuators
to determine whether they are working as intended. It can detect
a malfunction or deterioration of the various sensors and actuators,
usually well before the driver becomes aware of the problem through
a loss in vehicle performance. The sensors and actuators, along
with the diagnostic software in the on-board computer, make up what
is called the On-Board Diagnostic (OBD) system.
the OBD system retain malfunction codes post accident?
and no. Most vehicle manufacturers used the early OBD-1 system,
dated 1985-1996. This early system is not capable of retaining codes
if power has been cut off. Some vehicle manufacturers, however,
have had the second generation of OBD systems in use. This generation
is called OBD-2. With each new year vehicle manufacturers are installing
better faster systems. For example, a 1997 GM with the OBD-2 system
will be limited in the amount of retrievable data compared with
the 1999 GM. The OBD-2 system will retain malfunction codes as long
as they have not been cleared. If, for example, there was a code
41 in the computer and the battery was destroyed during the accident
there is a very good chance the code would be recoverable. If, to
use another example, emergency crews had to cut a main wire harness
(door) the chances of recoverable codes lessens. This information
has to be assessed on a case by case basis.
ATA Associates, we use the Mastertech Global 2 for collecting and
reading OBD data. We are very pleased with the Mastertech's performance
and are excited about using this data in and for accident reconstruction.
GM Recorded Automotive Crash Event Data
Motors (GM) airbag-equipped production cars have, since 1974, recorded
airbag status and crash severity data for impacts that cause a deployment.
The data-recording feature utilizes fuses to indicate when a deployment
command was given and stores the approximate time the vehicle has
been operated with the warning lamp illuminated.
1990, a more complex Diagnostic and Energy Reserve Module (DERM)
was introduced with the added capability to record closure times
for both the arming and discrimination sensors, as well as any fault
codes present at the time of deployment.
the 1994 model year GM vehicles, GM replaced the multiple electromechanical
switches previously used for crash sensing with a combination of
a single solid state analog accelerometer and a computer algorithm
integrated into a Sensing and Diagnostic Module (SDM). The SDM also
computes and stores the change in longitudinal vehicle velocity
?(V) during the impact to provide an estimate of crash severity.
selected 1999 model-year and 2000-year GM vehicles, the capability
to record vehicle systems status data for a few seconds prior to
an impact has been added. Vehicle speed, engine RPM, throttle position,
and brake switch on/off status are recorded for the five seconds
preceding a deployment or near-deployment event. It is reported
that almost all GM vehicles will add that capability over the next
GM uses a proprietary Event Data Retrieval Unit (EDRU) that interfaces
with a standard Tech 1 scan tool to download through the vehicle
diagnostic connector. The data is displayed in a hexadecimal format.
The data is viewed by General Motors as protected and requires their
direct involvement to be analyzed.
make the EDRU data available to interested researchers, GM is developing
software and interfacing cables allowing the data to be downloaded
to commonly used laptop computers. Data useful to researchers (such
as ?V, seatbelt use, pre-impact data, etc.) will be stored and displayed
in a standard format using engineering units, while data requiring
expert knowledge to interpret will continue to be stored in a hexadecimal
format. The kits and software are expected to be available during
the second quarter of 2000.
has purchased the equipment, and is waiting for software to be released.
Call ATA to understand further how this information can be of use
The Technology of Crash Data Retrieval
the mid 1990's the majority of GM vehicles have been equipped with
SDMs (Sensing and Diagnostic Modules). These modules record and
save crash data related to abnormal operating conditions and air
bag deployment. The gathering of this data has become a specialized
field that aids accident investigators and reconstructionists.
first step in any vehicle crash data recovery is looking at the
vehicle to determine:
Did the airbags deploy?
- What systems/computers are on board?
- Where is the SDM or Ford's EDR (Event Data Recorder)?
- Can you recover availab1e data from the vehicle's systems?
this sounds relatively simple, locating and gaining access to the
crash data recorder, event data recorder, ABS computer, or any other
system is about two-thirds of the job.
can I expect to see in the vehicle data?
year vehicle manufacturers have increased their capability to collect
data, and monitor systems. Today, General Motors' products are leading
the way in vehicle crash data systems and in the way it is recovered.
Collecting such items as:
Vehicle speed 5 seconds before impact.
- Engine speed 5 seconds before impact.
- Brake status 5 seconds before impact.
- Throttle position 5 seconds before impact .
- State of driver's seat belt switch (on/off).
- Passenger's airbag enabled/disabled - (on/off).
- SIR warning lamp status- (on/off).
- Time from vehicle impact to time of airbag deploy.
- Ignition cycle count at event time and investigation.
- Max. ?V for near deployment ?V vs. Time for frontal airbag deployment.
- Time from vehicle impact to time of max. ?V.
- Time between near deployment and deployment events if within 5
are three types of files stored in the vehicles' SDM, also known
as, the Black Box. The first file, in most cases, is called the
Near Deployment File. This file opens when the vehicle has a severe
event that "wakes up" the sensing algorithm but not severe
to deploy the air bag(s). It contains pre-crash and crash data.
SDM can store only one near deployment event. This event can be
overwritten by an event that has a greater SDM recorded velocity
change, or after the ignition has been cycled 250 times.
second type of file is a deployment event. It also contains pre-crash
and crash data. The SDM can store up to two different deployment
events, if they occur within a five seconds of one another. The
first will be stored in the deployment file, the event that deployed
the air bag(s), and the second deployment event will be stored in
the near deployment file.
third file in the SDM is called the hexadecimal data. This information
is not shown on a typical download, though contained in the hexadecimal
data, is information concerning times between algorithm enable (wakeup)
and actual deployment of the air bag. This is data can only be interpreted
by manufacturers at this time.
is important to note that deployment events can not be overwritten,
changed, or cleared from the SDM. Once the vehicle's airbag(s) have
deployed, the SDM must be replaced. Note, with Crash Data Recorders,
vehicle battery loss will not affect the recovery of data.
Why-do manufacturers collect this data?
are approximately 18,000 tow-away crashes in the United States everyday.
This is real time free data. With the average cost of a crash test
running between $25K-30K, it makes good business sense to collect
this information when possible. The California Air Resources Board
(CARB) mandated in the early 1980's, that vehicle manufacturers
begin to monitor emissions. With this requirement, the computer
became a valuable tool for monitoring various related systems. With
each passing year, they have gone from the most simple engine controls
to highly sophisticated crash data recording systems, such as General
Motors' SDM and Ford's EDR.
vehicles can tell you a great deal of valuable information, and
in some cases it might be all you have to determine what transpired.
urges investigators and experts to look for valuable scientific
information early in the case process.
Mike Ennor has been in the automotive industry for over twenty (20)
years. He has been trained in Crash Data Retrieval by the Vectronics
Corporation and is among the few certified technicians in the country.
Business of Testing
Associates is a unique organization dedicated to supporting all
types of product testing and evaluation. Although our core business
is accident reconstruction, we have a qualified staff of engineers
and safety experts that can investigate any type of failure analysis
on just about any object. CEO and owner Robert “Bob”
Swint has put together a team of investigators that take pride in
their ability to produce thorough testing protocol.
testing capabilities are endless. We have a fully equipped laboratory
with state-of-the-art microscopic viewing equipment. Also, the technology
center, located in Houston, Texas, is equipped to handle any type
of road vehicle, watercraft, or small aircraft. The video and imaging
equipment used by the ATA staff is professional quality that produces
professional comprehensive reports.
Failure analysis is a crucial part of any type of accident investigation.
Consumer products experience many types of part failures that require
personnel specialized in different types of investigative principles.
ATA has access to some of the most qualified chemists, metallurgists,
and material science experts. We also employ, on staff, aeronautical,
mechanical, and electrical engineers and safety professionals. The
techniques used by our staff and consultants adhere to published
In addition to on site testing, The ATA rapid response team can
be dispatched to any location to perform tests, collect data, and
gather evidence. All testing protocol in the field provides the
same high standards of professionalism that can be achieved in the
most difficult of situations. On-site testing, performed immediately
after an accident, can often be the difference between finding a
cause or not. Crucial evidence and changing environmental conditions
degrade an accident site over time. Quickly introducing qualified
experts into a scene can eliminate costly recreations.
technical nature of quality testing should always be the very first
priority of any investigative team. ATA Associates has assembled
this team and has provided them with the very latest technology
to produce infallible results.
interactive informational CD is available by request. It outlines
the many capabilities of the ATA testing team and describes the
many options available. Please Contact ATA Associates at (281) 480-9847
or visit our website at www.ataassociates.com.
Up – The Brake Analysis
equipped with spring brakes are approximately 98 percent of all
off and on highway trucks. Manually measuring the stroke length
on these brakes can be a time consuming job. There is also the chance
of different interpretations when reading a manual scale in confined
areas. It is now possible to test five (5) pairs of brake stroke
length at once, in a minimal amount of time.
Brake Analyst is a testing device designed to determine slack adjuster
travel on vehicles equipped with S-cam air brakes. It can also determine
if there is excessive wear in the s-cam bushings, broken brake shoe
return springs, broken parking brake chamber springs, and broken
brake chamber return springs.
On a normal class 8 tractor trailer, as seen on today’s highways,
the tractor trailer is equipped with ten separate brakes, one located
at each wheel. The normal adjustment of the slack adjuster is in
the 1 to 1.5 inch range. The re-adjustment point is at 2 inches
for most brakes.
Brake Analyst measures the slack adjuster travel. It accomplishes
this by a purpose built string potentiometer that is attached to
the brake chamber push-rod by a small pair of locking pliers. The
cable from the string potentiometer is magnetically attached to
the face of the brake chamber. A secondary pressure transducer records
air pressure being supplied to the service brake system electrical
cables are routed from the equipment to the control panel. The cables
connect to a laptop computer through a PCM-CIA card. The information
is then fed from the remote sensors into the data acquisition software
that analyzes the information and presents it in a graphical and
tabular form on the computer screen.
Wilma Wagner and Nic Nicodemus
is a very specialized field within the engineering profession. At
the heart of biomechanical analysis is a strong foundation of mechanical
engineering with extensive knowledge of the human body as the system
In the case of an accident where injury has occurred, reconstruction
becomes somewhat of an investigative and analytic matter. For the
biomechanics expert, there are two sides of an equation to develop:
engineering data and physical laws related to detailed injury description
and the medical facts. In most situations, engineering reconstructionists
other than the biomechanicist determine the forces and torque, energy
and time sequencing associated with the vehicles involved. On the
medical side, surgeons, radiologists and other specialists clearly
define the extent of the injury and the prognosis for recovery,
based on experience and knowl edge of the healing process. Medical
experts can discuss the probable cause as it relates to the type
of injury and based on their experience of similar cases.
missing piece supplied by the biomechanics expert directly relates
to the magnitude and directions of forces and energies to the nature
of the tissue damage. For example, bones in the human body differ
in their fracture resistance and manner depending on their shape,
age, function and loading pattern at the time of impact. The physical
properties of bone, muscle and other connective tissue vary greatly
throughout the body. Since they are viscoelastic in nature, they
respond with greater stiffness with a higher rate of loading.
The assigning of causality based on the appearance of similarity
to past experiences may not at all relate to the mechanisms causing
the one currently under examination. What seems obvious as a cause
may not be when a careful dynamic analysis is completed of the accident
as it relates to the victim (not necessarily the vehicle) and its
results applied to the structural properties of the tissue.
is a software program that extracts 2-D and 3-D measurements from
photographs taken in perspective. Using a camera as an input device
and with specific parameters in the photos, PhotoModeler can extract
unknown data. Using several vantage points or camera stations with
common points in each of the photos taken of the scene or object,
the software combines these common points and features into 3 dimensions.
The marked points on the photos become measurable points, lines,
or objects in a single, unified 3-D space.
can create both 2-D drawings or images and 3-D objects and models.
It uses photographs from different angles and unifies them in 3-D
space. To survey or model an object (like a car), as many as five
correctly positioned photos would be required to create the 3-D
model. A front façade of a building may take as little as
three photos. In some cases, when a digital survey has been taken
of an accident scene, PhotoModeler can carry out some operations
on a single photo of the same scene if sufficient control points
has used PhotoModeler to measure distances and create drawings of
accident scenes and vehicles.
PhotoModeler TM is a registered software
program by Eos Sytems.
Recap and Update
GM’s model year 1989, some form of crash data has been recorded
by the vehicle’s onboard computers (EDR - event data recorder).
By March of 2000, private sector consulting reconstructionists were
given access to the vehicle’s computer via a tool called the
Crash Data Retrieval Kit produced by Vetronix Corporation in cooperation
with General Motors and recently Ford Motor Corporation. Generally,
the older the vehicle is, the more limited the crash data available.
Until 1994, the computer that stored crash information would give
delta-v (change in velocity during a crash) postimpact data, but
no pre-impact data. No information regarding braking or throttle
is available for older model cars. As time passes, more and more
information is stored in the computer that is accessed by the CDR.
Today, most GM vehicles offer five seconds of pre-crash information
about speed, throttle position, brake position (on/off), seatbelt
use for both driver and front seat passenger, and about 300 ms of
post crash data which captures delta-v over time in 10 ms increments.
None of the Ford computers capture pre-crash data; however, post-crash
data is more extensive than GM vehicle computers. Like GM, Ford
computers also indicate seatbelt use.
The number of GM and Ford vehicle models available for download
continue to grow. In the not too distant future, accident reconstructionists
can expect to gather such information as seat position, cruise control
status, ABS braking status, Stabilitrak indication, steering angle,
yaw rate, lateral acceleration, tire pressure, traction control,
door locked/unlocked, PDOF (principal direction of force), etc.
Also promised to become available to the public soon is Toyota model
vehicle data. Heavy Trucking Crash Data Like passenger and light
trucks, tractor engines such as Detroit, Cummins, Caterpillar, and
International have data that potentially can be retrieved after
a crash. The accident reconstruction community has access to this
data, but at a much higher cost than the Vetronix kit. There is
no “universal” kit like Vetronix in the heavy truck
world. One must purchase individual decoders from each manufacturer.
The information from heavy trucks is potentially large. I say potentially
due to the fact that the settings for recording the information
may be changed. Also, the data may be erased and the computers may
be re-used, unlike in passenger vehicles. Some of the information
available, depending on the manufacturer of the engine, includes
vehicle speed, engine RPM, throttle position, brake application,
clutch use, cruise control status, and time duration of up to 120
seconds. Other computers may be found on heavy trucks that record
data such as date, time and odometer readings.
Actions - Past, Present & Future
1997, the National Transportation Safety Board (NTSB) and Jet Propulsion
Laboratory (JPL) issued recommendations to NHTSA (National Highway
Transportation Safety Administration) that they should pursue manufacturer
installed sensor data during their crash testing programs. In November
1999, the NTSB issued recommendations for NHTSA to mandate installation
of EDRs (electronic data recorders) on motor coaches and school
buses and gave specific requirements for the data collection and
survivability of the devices. An EDR is an electronic device that
detects a crash and records certain information for several seconds
of time before, during and after a crash. For instance, an EDR may
record pre-crash data, such as impact speed, forces on the vehicle
during the crash, safety belt use and air bag performance and allow
activation of an automatic collision notification to emergency medical
of the approximately 200 million light vehicles in the U.S., NHTSA
estimates that 15 percent of these vehicles are equipped with EDRs
that can be read, and that between 65 and 90 percent of new light
vehicle models will be equipped with EDRs.
1997, NHTSA’s EDR-related effort has been multi faceted. In
2000, NHTSA purchased EDR data retrieval tools for all its investigation
teams, including Special Crash Investigations (SCI), National Automotive
Sampling System - Crashworthiness Data System (NASS-CDS), and Crash
Injury Research and Engineering Network (CIREN). Recently, NHTSA
modified its crash data bases to capture EDR data. As of mid 2002,
NHTSA had investigated about 300 crashes where EDRs were read.
June (2004), NHTSA proposed standard requirements for EDRs that
manufacturers choose to install in light vehicles. The proposed
rule would not require the installation of EDRs.
is proposing, beginning in September 2008, to: (1) require that
the EDRs voluntarily installed in light vehicles record a minimum
set of specified data elements useful for crash investigations;
(2) specify requirements for that data; (3) increase the survivability
of the EDRs and their data by requiring that they function during
and after front, side and rear crash tests; (4) require vehicle
manufacturers to make publicly available information that would
enable crash investigators to retrieve data from the EDR; and (5)
require vehicle manufacturers to include a brief, standardized statement
in the owner’s manual indicating that the vehicle is equipped
with an EDR and describing the purposes of EDRs. NHTSA will accept
comments on this notice of proposed rulemaking for the next 60 days.
Written comments concerning it should be sent to the DOT Docket
Facility, Attn: Docket No. NHTSA 2004-18029, Room PL-401, 400 Seventh
St., S.W., Washington, D.C., 20590-0001, or faxed to (202) 493-2251.
The notice also will be available for viewing on the NHTSA website:
Quick Response Teams have the capability to secure complete, accurate
and prompt collection of site evidence. Our experienced accident
survey teams are ready to travel anywhere in the country within
hours. They know what to look for, what evidence to preserve, and
how to collect and record evidence using photography, video-graphy
and state-of-the-art site mapping technology.
of Quick Response:
Preservation of Scene
Collection of Evidence
Document Key Witness Information
response services include:
Black Box Download
DOT Level V Inspections
Cargo and Loading
Site Survey Measurements
Secure Accident Debris
Tire and Gouge Marks
utilizing Quick Response capabilities is supplied to ATA’s
reconstructionists, case managers and graphics department, providing
clients with seamless, integrated litigation support.
Smart companies, big and small, have a plan that anticipates events
such as accidents. For motor carrier companies, it is especially
important to set policy in order to be prepared for traffic accidents
involving their trucks. Quick Response is an action plan for what
needs to be done both before and after an accident occurs. This
plan would answer questions such as:
When and who does our driver call if he gets into an accident?
• What company personnel should go to the scene?
• What do they need to do when they get there?
• What if the police report is wrong?
• Are our driver qualifications records up to date?
• Have we kept our vehicle maintenance records up to date?
• What is our company’s safety policy? The list goes
accident reconstruction experts, we are interested in the protection
of evidence. Because evidence deteriorates rapidly, it is important
to gather as much information as possible as early as possible.
Accident scene photography and videography is the fastest way to
get the most evidence recorded. Using proper techniques for taking
still photographs ensures that the scene is well documented. Without
a good understanding of the scene evidence, it may be difficult
to properly understand the accident.
Associates’ experienced professionals will take the time to
discuss the issues addressing emergency response planning and evidence
gathering techniques. Just give us a call.
in Accident Reconstruction
from a Detroit Diesel heavy truck engine can be quite extensive.
The complete report is on the order of 40 pages. Of main interests
to accident reconstructionists are the data contained in the “Last
Stop Record,” the two “Hard Brake Records,” and
three diagnostic records. But how is that data related to an accident?
There is no label in the printout that will say, “impact occurred
here” or “the vehicle traveled so many feet prior to
impact,” etc. In fact, the data can be misleading when it
comes to the reported speeds.
In order to relate the data to the accident scene, careful study
of the data and understanding of the anomalies that can occur in
the data must be understood. In the example chart, the time when
impact occurs is not 0:00 seconds as one may think. Time equals
0:00 is when final rest occurs. The system for recording a hard
brake record is usually set at a point, which will typically trigger
when a deceleration rate of 7 mph/sec is achieved. From the chart,
one can determine that impact occurs at -0:07 seconds.
Looking down the vehicle speed column, notice the speed is reported
at 42 mph at minus 14 seconds and 5.0 mph at minus 13 seconds. This
is not physically possible. One of many reasons for this could be
due to the vehicle yawing (the tires are rotating at a different
rate than the vehicle’s overall speed). Another reason for
such an anomaly is the sensor picking up the ABS braking, which
locks the wheel up to two times per second, thereby fooling the
sensor that monitors vehicle speed. Notice the engine speed dropped
from 875 to 117 rpm. This is more likely than not, a correct reading.
Also notice the throttle percentage which drops to zero as the brakes
are applied. One must be aware that in the case of brake application,
a “Yes” is recorded even if the brakes are just lightly
When the above data is examined and understood, vehicle positions
can be plotted on a scale diagram with tire mark evidence, at each
time step in order to build the story of what happened on the road.
ATA Testing Supports Expert Testimony
Rulings by the U.S. Supreme Court in the 1990's raised the standards for expert testimony. Prior to those rulings, anyone with knowledge of a subject greater than that of the average person was usually regarded as an expert on the subject and could testify based upon experience. That changed with the Court's ruling in the case of Daubert v. Merrell Dow Pharmaceuticals, Inc. in 1993.
The Daubert ruling established factors judges were obliged to consider in determining the admissibility of testimony from scientists. Among those factors was whether the testimony was based on theory alone, or if it was also supported by the results of testing that had been conducted using methods accepted by the scientific community. A ruling in Kuhmo Tire v. Carmichael in 1999 extended the applicability of the Daubert standards to the testimony of engineers and other technical experts.
In showing a preference for testimony based on testing over testimony based solely upon theory, the Daubert and Kuhmo rulings effectively made testing a necessary foundation for much expert testimony. Following the Court's lead, ATA Associates, which had always offered testing as part of its services, made testing a principle focus of the company's efforts. In the years since Daubert and Kuhmo, ATA has become well known for providing the personnel, expertise, equipment, and facilities needed to conduct tests in a variety of technical areas. An abbreviated discussion of some of ATA's testing capabilities follows.
ATA's testing experience includes dramatic full-scale re-enactments of automobile collisions and rollovers and numerous recreational boating mishaps resulting from steering system malfunctions. ATA has also tested the stability and braking performance of a variety of motor vehicles using standard government and industry test protocols.
ATA has tested the stability of tow vehicle/travel trailer combinations at highway speeds; the dynamics of roller coaster cars; and heavy truck behavior following a steer axle tire blowout. ATA has measured the inertial loads experienced by riders on energetic amusement park rides and the inertial forces routinely experienced by passengers on public transportation buses and trains.
In less dramatic but equally important testing, ATA has measured the visibility of stationary and moving vehicles under various night-time illumination conditions; the effectiveness of confined space ventilation in mitigating carbon monoxide hazards; the forces exerted by garage door openers in various operating situations; and the normal and anomalous cycling of electric water heater control circuits.
As a part of its services, ATA documents test results through written reports and appropriate electronic data and photos or video recordings. In conducting tests, ATA typically follows previously established testing protocols such as may be found in Federal Motor Vehicle Specifications. However, in unusual circumstances where no established peer-reviewed testing protocol exists, as happened in tests that used sandbags to model passenger ejection from an amusement park ride, ATA will prepare an appropriate written protocol to document the test method in detail, so the test may be repeated independently.
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ATA Conducts Boat Tests in Louisiana
In April and May of 2006, ATA Associates conducted a series of tests to determine the cause of a single-boat accident that occurred in 2003 on Louisiana's Lake Bisteneau. The boat involved was a late model, 17 ft. aluminum fishing boat powered by a 75 HP outboard motor. A passenger was seriously injured when he was ejected from the boat and was struck by the boat's propeller.
In its testing, ATA examined the steering performance of the subject boat involved in the accident. An almost identical exemplar vessel and motor were also tested. After a day of inspection and rigging with electronic test instrumentation, each boat was subjected to a full day of in-water performance testing on the Cypress Bayou Reservoir near Shreveport, Louisiana.
Items of particular interest were: 1) how the outboard motor's mounting location and orientation on the boat influenced its steering performance; and 2) how the motor's trim tab setting influenced steering. The influence of the motor's adjustable trim angle, relative to the transom, was also examined in tests which were conducted over each boat's full range of operating speeds.
The Louisiana tests were just the latest chapter in a long history of boat tests conducted by ATA Associates. With ATA's founder and owner, Robert Swint, at the helm, the subject boat in this case was put through its paces in a series of tests that ranged from benign, low speed maneuvers to higher speed tests which culminated in anticipated, but nevertheless dramatic, losses of control. Though special care was taken to ensure Bob's safety in the latter tests, those tests were still not for the squeamish, nor for the boat operator who wished to stay dry.
While the drama of the loss-of-control tests was reminiscent of the early, glory days of boat testing by Bob Swint, upon which ATA was founded, the Louisiana tests as a whole represented the great strengths of today's ATA. The tests were monitored and recorded by video cameras on shore and by miniature video cameras mounted on-board the boat. In addition, during each test steering wheel input torque, steering wheel rotation angle, boat plane angle, motor trim angle and the forward, lateral and vertical accelerations of the boat at the passenger's seat location were all measured electronically and continuously logged at the rate of 500 samples per second. Boat position and speed, as determined by global positioning system (GPS) equipment, were also recorded, permitting a level of post-test performance analysis that would not have been dreamed of in ATA earliest days of boat testing.
Test results demonstrated and quantified the strong influence of the outboard motor's trim tab setting on boat steering performance. The lesser influences of trim angle and the improper mounting of the motor on the subject boat were also quantified. These observations led to the conclusion that an improper trim tab adjustment, and to a lesser extent an un-centered mounting of the motor, made the subject boat inherently unstable and dangerous if the steering wheel was released, even momentarily.
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Doing it in the Dark! Night Imaging Techniques
Questions arise when accidents occur at night. If the incident is reconstructed for litigation, these questions become vital to the outcome of the case. From what distance can a vehicle be seen? Was a vehicle or object illuminated? Does the subject disappear or become more difficult to see when surrounded by other lights? Does this night scene refute or substantiate witness testimony? The goal of quality night photography is to create an image that reasonably represents the lighting conditions and general luminance of a scene at the time of the incident. This image must represent what an accident reconstruction expert or consultant can see and testify to in a court of law
ATA has developed and refined methods required to create admissible night photographs and video footage for presentation as evidence or visual aids in the litigation process. Professional quality equipment is a key ingredient. Film cameras are preferred over the newer digital formats because film shows more detail and clarity in shadow areas and low light situations. A medium format still camera demonstrates distinct advantages over the smaller 35mm or digital formats and has accessories useful in night photography. The larger film provides better quality enlargements.
One major advantage of a professional quality medium or large format camera is the interchangeable film back. A film back using an instant color film may be used as well as one loaded with standard color print film. Proper exposure of night-time photos involves long shutter speeds�from one second to ten seconds or more, depending on the film used and the physical conditions. The advantage of using an instant film is on-the-spot confirmation of the proper exposure and the lighting situation before exposing the color print film. The case expert can immediately confirm that the instant film exposure faithfully depicts scene illumination at that moment. Once the instant photo is approved, the color negative film is exposed. Immediate confirmation of scene depiction using instant film lessens the necessity for a re-shoot because of improper exposure of the color negative film.
Night photo shoots can be very involved and time consuming. Personnel such as photographers, experts, witnesses, lawyers for both sides, and police for traffic control, may be involved in the shoot. Physical conditions such as the time of the month (moon phase) and weather also may be important factors.
Once on site, the camera (either still or videotape) must be positioned at a viewpoint approved by the case expert. The lighting should be as accurate a re-creation of the original event lighting as possible. The viewpoint may be that of an approaching driver, a witness alongside the road or another person involved in the incident. Additional lights in the scene (street lights, stop lights, business signs, yard or security lights) should be compared to the original event. This information may be available from accident reports, depositions and witness testimony. The resulting color negatives are printed accurately for the approval of the expert who must testify that the resulting photo represents conditions as they were the night it was taken.
These techniques have proven very useful in creating effective photographs and video footage of night lighting situations. They consistently produce accurate visual representations of situational lighting similar to that of the original incident.
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If you're interested, you can find a lively debate on the Internet on whether a front tire blowout or a rear tire blowout is more dangerous when driving your car. There is similar controversy concerning truck tire failures. While the dual rear axles and wheels on heavy trucks provide redundant traction and support in the rear, there is no redundancy with the individual wheels up front. You might think then that a front tire blowout on a truck would be a sure recipe for disaster. However, a study by a major tire manufacturer suggests that power steering can provide a truck driver with sufficient control to overcome the ill effects of a front tire blowout.
Such were the contradictory theories that ATA Associates, Inc. had to consider recently when reconstructing a truck accident involving a blowout. In October 2004, the left front tire of a 62,000-pound mobile drilling rig blew while the rig was traveling on a central Texas highway. Immediately after the blowout, the rig crossed the highway centerline and struck an oncoming car head-on, killing that car's driver. Marks on the road and other evidence at the scene clearly indicated what had happened. What was less evident was whether any practical, alternative reaction by the rig's driver had been possible after the blowout and if that alternate reaction would have changed the outcome. To answer those questions and to address the conflicting theoretical possibilities, ATA re-enacted the blowout portion of the mishap to actually observe and to quantify the post-blowout behavior of both the rig and its driver.
The re-enactment was conducted in November 2006 on a closed course in a fenced-in parking lot. The mobile drilling rig, which had been involved in the subject accident and which had subsequently been repaired, was outfitted with electronic instrumentation to record its inertial responses during the test. Video cameras were also positioned at several locations around the test course and in the rig's cab to visually document the behavior of the rig and its driver as the staged blowout unfolded. In those preparations, the test was similar to many other dynamic vehicle tests that ATA has conducted in recent years, but there was one feature that made this test unique. To initiate a blowout in the rig's left front tire while the rig was underway, the rig was equipped with a black powder mortar that had been specially designed and built for the test by M.E. Prescott, a movie special effects and stunt coordinator and one of many specialized consultants known to ATA. Prescott's mortar was attached to the rig's front axle and aimed to pierce the inboard sidewall of the left tire when the mortar was fired at the driver's command. The driving task in the re-enactment went to Phil Smith, an expert in truck driving and a frequent collaborator with ATA on heavy truck cases.
After carefully coordinated preparations by Prescott, Smith, and the ATA staff, the re-enactment began. The initial test run was aborted when the top-heavy rig tipped precariously during a sharp turn as the driver and vehicle got acquainted. Once that miscue passed without harm, a second run to the 35 mph test speed was made and the mortar was fired. A thunderous boom and big cloud of smoke were unmistakable signs that the mortar had been fired. The tire deflated immediately after the mortar's blast pierced not only the inboard sidewall but also the outboard sidewall of the rig's massive tire which was rated to carry 12,300 lbs. The rig veered to the left as it had in the subject accident with the driver's steering inputs having little effect as it rolled to a stop 450 feet later.
Post-test analysis of the collected electronic data revealed that in the first second after the blowout, the rig's lateral acceleration was erratic but generally to the left despite the fact that initial steering input was to the right. In the next second, a steering wheel rotation of 150 o to the right brought the lateral acceleration to zero, but as soon as the steering wheel was turned back towards the straight-ahead position, the rig again accelerated to the left, reaching a maximum acceleration of 0.3G to the left at 2 seconds after the blowout. Sustained steering inputs to the right, beginning 2.5 seconds after the blowout and continuing thereafter, decreased the acceleration to the left, but a survey of the rig's path after the blowout showed that the steering inputs to the right never arrested the rig's persistent movement to the left. In sum, the test suggested that in the central Texas accident the driver had little control of over his vehicle's path once the front tire blew.
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BP Texas City Explosion: Catalyst for Dramatic Change in Chemical Plant Operation & Safety
A devastating explosion occurred two years ago at BP's Texas City refinery, causing 15 fatalities and over 175 injuries. This well-publicized accident will force changes in refinery and chemical plant operation and safety. Nearly 20 years ago, a similar shock from a string of major chemical accidents in the U.S. and overseas galvanized the process industry to improve safety, and prompted new OSHA and EPA regulations at that time.
BP's tragic explosion was traced to a startup mistake in the refinery's gasoline octane-boosting isomerization unit overfilling a distillation tower and attached blowdown drum with highly-flammable liquid hydrocarbons. The blowdown drum vented through a stack directly to atmosphere without a burning pilot flare, so that the equivalent of a tanker-truck of highly-flammable liquids and vapor spilled back down to the ground. A flammable cloud dispersed rapidly, running beneath temporary trailers with personnel inside planning work on a nearby unit. The vapor cloud was ignited by a running diesel pickup, initiating explosions and fires that swept through the entire area.
The US Chemical Safety Board (CSB) immediately began a careful and exhaustive investigation. Their official findings were just released, and emphasized organizational and safety deficiencies at all levels in the BP Corporation. CSB asserted that cost-cutting, production pressures and failure to invest led to a progressive deterioration in safety at the refinery. Investigators found evidence of infrastructure and equipment in complete decline, fatigued workers, a chronic lack of preventative maintenance and training, and a prevailing culture that accepted cost reductions without challenge. Even more compelling was CSB's rendition of BP's own internal audit findings before the accident detailing widespread non-compliance with basic health, safety and environmental rules, and poor implementation of safety management.
CSB calls for changes. Within refining and chemical companies they expect a new standard of care for corporate boards of directors and CEO's throughout the world with boards examining every detail of safety programs to ensure that no terrible tragedy like this occurs.
OSHA was challenged to step up their inspections and enforcement of Process Safety Management (PSM) standards at refineries and chemical plants. Industry should expect more highly-technical, complex, and lengthy inspections designed to uncover the sorts of systemic shortcomings highlighted in the recent BP investigation.
For assistance in implementing robust process safety programs, or for careful, forensic investigations of process incidents, contact Robert Swint at ATA Associates (Houston).
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ATA Evaluates Dangerous Houston Intersections for KHOU-TV
Bob Swint, ATA CEO and accident reconstruction expert, went with a local KHOU Channel 11 TV reporter to evaluate intersections most prone to automobile wrecks.
After researching five years of data from TXDOT, ten of the most dangerous crossroads in the Houston area were pinpointed. Each spot was visited and Swint pointed out the traffic flow problems and dangers of each intersection. Some of the problems he observed were narrow intersections where heavy truck traffic flows come together along with prolonged times for the clearing of truck traffic; uphill inclines leading to limited sight distances and short distances for traffic to change lanes. Skid marks on approaches to some areas indicated sudden and unexpected traffic problems.
Swint said that at all of the top ten most dangerous intersections, as well as anywhere else, drivers need to beware.
The spot aired on KHOU 11 News on November 11, 2013. Click KHOU TV Dangerous Intersection Reports to view the interview and accompanying transcript.
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Surveillance in Accident Reconstruction
It is no longer uncommon to find accidents that have been captured on surveillance video cameras located at nearby businesses. Bearing this in mind, ATA has placed a heightened focus on the study of surveillance video to help answer reconstruction questions about the speed, time and distance of a subject of interest.
For the purpose of answering the questions above, the usefulness of the video varies greatly on the video system installed. A time stamp is usually embedded within each frame of the video. In order to determine vehicle speed, it is first necessary to know the frame rate (speed at which the video camera is recording the scene).
Video cameras operate at 30 frames per second but that may not be the rate at which the video is recorded to an electronic file. Businesses often have more than one camera at their facility so it is necessary to have a master program to control the cameras.
A software program and a bus (mechanism to communicate between the cameras and software) is in charge of recording. The company may, for example, have camera #1 record to the file at five frames per second while camera #2 is sending its information at 15 frames per second. Perhaps they have camera #3 sending information only when it is triggered to do so (such as when a gate opens or closes).
Complicating that is that the frame rate may not be constant throughout the recording. The reason is that the data from each camera is sent to the controlling computer via a BUS communication system which transfers data between components. Because the information from each camera cannot reach the computer at exactly the same time, there are delays which can cause drops in the frame rate for a particular camera.
Determining speed from wheel base movement and effective frame rate.
Once all of this is understood, frame-by-frame analysis of the objects of interest in the video are carefully examined. Location of fixed objects such as poles or building edges helps with determining distances traveled within a number of frames of video. If no such reference exists, sometimes it is possible, depending on the angle of view, to place an artificial vertical line in the video at the front axle of the vehicle of interest, then count the number of frames until the rear axle crosses that fixed artificial vertical line. Knowing the wheelbase of the vehicle and the frame rate, then the speed of the vehicle can be estimated to a reasonable degree.
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