Not-So Magic Carpet Fall: The Rug in the Lobby – A Surveillance Video Analysis Case Study

Engineering Animation

Laurence R. Penn, CFVT, Senior Forensic Animation / Video Specialist 

When video surveillance recorded an individual’s fall in a building lobby, DJS Associates was tasked with analyzing the video to shed light on the circumstances surrounding the fall.

Unfortunately, the building had been renovated since the incident, but this didn’t prevent accurate photogrammetry camera-match analysis to be performed using LIDAR data acquired of the site by the DJS Associates reality capture field crew.

Implementing common features still present in the environment prior to and after the renovation, the position, orientation, and field of view of the camera were established. Several scene photos were also camera-matched successfully with the LIDAR data. Of particular interest to the case, an edge of a rug in close proximity to the plaintiff’s fall was obscured in the surveillance camera. Utilizing multiple angles of the camera-matched scene photos, the obstructed area of the rugs could be established and reconstructed in 3D space. An articulated 3D model mannequin, scaled to the height of the plaintiff, was superimposed and animated over the surveillance footage to match his position and posture in space and time.

Under the guidance of a biomechanical expert, the 3D mannequin animation was refined relative to the video evidence. With an unobstructed view of the reconstructed scene, the analysis revealed the plaintiff’s footing relative to the positioning of the rug’s edge in much more detail than was originally possible from the surveillance video alone.

Tire Failure: A “Worldly” Analysis

Flat Tire

The primary function of any engineer is to solve problems.  Most people do not realize that tires are complex products made with various components and compounds.  The compounds in tires are continuously changing with time.  The engineering analysis of a failed tire in the “forensic world” differs from an analysis conducted by engineers in the “real world” tire manufacturer industry.  In both “worlds,” the first step is to collect and analyze all the facts related to the tire failure.  The next step that is taken in the “real world” is to cut up and take samples from the failed tire to analyze the materials and compounds, and then compare the test results to what would be expected behavior.  However, in the “forensic world,” this step cannot be done since it is a destructive process that would hinder further analysis.  

In the “real world,” the tire engineers and chemists will review the facts surrounding the tire failure with the test results from the samples taken from the tire.  At this point, scenarios can be developed to explain the tire failure.  In the “real-world,” project tires would be built and tested to duplicate the failed tire, a process that cannot be done in the “forensic world,” unless you have a tire manufacturing facility at your disposal.  

In the “forensic world,” experience in tire failure analysis, construction, and compounding is vitally important.  In most cases there are aspects that will support all parties.  Only very few tire cases are either the result of a definite tire failure, such as a missing steel belt, or a tire failure due to a puncture.  The tire failure analyst must be honest and express to the client what the case facts indicate and the strength of the case solely dependent upon the tire failure.

The following is an example of a case where the determination of the role of the tire itself was at issue.

Case Description: A passenger vehicle traveling at 60 miles per hour exits the highway to the right and strikes a concrete culvert. The right front tire is flat, and the wheel has a 6-inch dent in it.  The right front tire does not have run flat damage but has a quarter inch hole in the inside shoulder.

Analysis: Since the right front tire was flat but did not have run flat damage, it means the tire lost air rapidly just prior to leaving the roadway.  In most cases, if a tire has a slow leak and continues to run on the road at 60 miles per hour, it will have severe run flat damage within 1 mile.  The right front tire going flat puts drag on the right front wheel position, causing the vehicle to pull to the right and run off the highway.  Impact damage to a tire wheel assembly is a continuum of damage to the tire and/or wheel.  A flat tire will flex under the impact and transmit the force to the wheel.  The tire will have little damage, but the wheel will be severely damaged, as was the case with this accident.  A fully inflated tire will absorb the impact, protecting the wheel.  Many times, a radial passenger tire will have a split in the liner ply between the radial body ply cords resulting in a sidewall bulge or sidewall blowout, but the wheel will have little or no damage.  Between these two end points, the impact to a tire/wheel assembly can cause damage of varying degree to the tire and wheel.  

In this case, the quarter-inch hole in the inside shoulder of the tire was the cause of the rapid air loss which translated to drag on the right front wheel position, causing the vehicle to pull to the right, exit the roadway, and strike the culvert.  The tire was not at fault, as the cause was a road hazard impact.

Going Out on a Limb: Tree Care as Part of a Safety Program in a Residential Community

Snow Pile

Case Synopsis: A two-year-old was playing in a snow pile with his parents when a limb, approximately 8 inches in diameter and 14 feet long, fell from a nearby White Pine tree due to a heavy snow load on the limb. It struck the boy on the head, causing serious injury. The snow pile was created by the snow removal contractor, and it was located immediately adjacent to a site where children waited for their school bus. There was also a community recycling center at this location. The community had previously commissioned a study of trees in the community, but the White Pines were not included; only smaller trees planted within the past one to three years were examined.

Expert Analysis: This engagement was to review relevant information and discuss issues related to property management standards and practices.  A number of depositions were reviewed, as were proposals for tree assessments, invoices from contractors, management agreements and other written correspondence. Also, critical to the opinion in the report was a site visit, during which it was noticed that the recycling center (immediately adjacent to the incident location) had gutters that exhibited damage from something striking them from above. The only thing above the recycling center was branches from White Pines. Further, a chain link fence which ran along the property line, and immediately behind the recycling center, had several sections showing damage from something significantly heavy falling onto the top pipe, severely bending it and collapsing the fence. On the far side of the fence, lying on the ground, were broken limbs which appeared to have been there for a period of time. Reviewing deposition testimony and the proposal from the contractor performing the tree assessment showed that the contractor was neither a certified arborist, nor did they have anyone on-staff who was familiar with the standards for conducting a tree risk assessment (part of ANSI A-300).

Conclusion: The management failed to recognize a serious hazard on the site, as exhibited by damaged gutters and fencing. Especially of concern was that the hazard was in close proximity to where it was known that children played regularly, and where residents brought their recycling. Further, there was no effort made to include the large White Pine trees along the perimeter of the property when a tree assessment of approximately 500 trees was made. Management should have retained a qualified arborist or, at a minimum, a company familiar with tree care and assessment standards and should have taken immediate action when fencing and building gutters were damaged, apparently from falling tree limbs.

Results: The Case settled.

Crosswalk Vigilante


Recently there have been reports of residents taking it upon themselves to paint their own crosswalks along roadways in cities such as Seattle and Los Angeles.  As an accident reconstructionist with a background in civil engineering, I find this to be a terrible idea.  First and foremost, painted crosswalks are not meant to be placed arbitrarily wherever local residents feel they might be warranted.  The FHWA Manual on Uniform Traffic Control Devices (MUTCD), which sets requirements used by state and local agencies to ensure that their traffic control devices conform to the national standard, explains as much in §3B.18.08:

Crosswalk lines should not be used indiscriminately. An engineering study should be performed before a marked crosswalk is installed at a location away from a traffic control signal or an approach controlled by a STOP or YIELD sign. The engineering study should consider the number of lanes, the presence of a median, the distance from adjacent signalized intersections, the pedestrian volumes and delays, the average daily traffic (ADT), the posted or statutory speed limit or 85th-percentile speed, the geometry of the location, the possible consolidation of multiple crossing points, the availability of street lighting, and other appropriate factors.

By placing crosswalk markings without the involvement of the local or state departments of transportation (DOT), these residents have bypassed a critical stage of the design process: an engineering study to determine if this painted crosswalk is, in fact, warranted.  It should also be noted that actual pavement markings are not always necessary since states will often define “unmarked crosswalks” at certain places within an intersection.  Pedestrians are still afforded the right-of-way at these crosswalk locations, regardless of whether the crosswalk is painted or not.  Though painting a crosswalk does provide a visual cue to operators of potential pedestrians crossing, the paint itself does not stop a vehicle.  It is not a forcefield.  Pedestrians must take care when crossing at any crosswalk, be it marked or unmarked.

In addition to removing the engineering study from the design process, these crosswalks are not being placed under the supervision of appropriate personnel with expertise in the correct materials to be used, the correct design and placement of the paint, and the proper traffic control during the installation.  One can easily imagine the issues with this guerrilla-style operation; a crew of well-intended but untrained individuals using non-retroreflective paint they got at the local store applying a non-compliant crosswalk pattern all while nighttime traffic is diverted by an insufficient, haphazard traffic control setup before the daytime traffic is then exposed to a new traffic control device deployed without any advanced warning.  Instead, traffic control device placement should be left to those who are actually responsible for them: the DOT.

Garage Door Injuries

Garage Door

Garage door mishaps injure an estimated 20,000 people a year.  While there are numerous ways a garage door can cause injury to a person, the three most common are:

  • The door closing or falling onto a person
  • Fingers entrapped between panels 
  • Injuries while attempting to repair a garage door

The above scenarios could be related to a malfunction of the garage door; or could be improper use of such.  In many cases, people are injured when the door unexpectedly moves. Frequently, this is due to either the failure of a component used to balance the weight of the door or improper maintenance of the door. In other cases, injuries occur due to malfunctions of the automatic openers or are improperly adjusted doors. There could also be issues due to a modified or old opener that lacks safety features. 

When a person is injured by a garage door, the root cause of the injury is often not immediately clear. In a situation where the injured party was alone during the event, it is important to gather as many facts as possible about what they were doing just prior to the incident. Were they opening or closing the door at the time?  Was the door moving as it normally does or was something different?  Did they hear anything coming from the door prior to the incident occurring?  In addition to asking the appropriate questions, it is also important to preserve the garage door immediately after the incident occurred to allow your expert to inspect the condition of the door and connected mechanism. If immediate repair of the door is required, the condition prior to the repair should be documented and photographed. If the door is repaired, all removed parts should be identified, along with where they came from, and they should be retained after removal. The contractor providing the repair of the garage door should also submit a detailed bill indicating the work performed and parts replaced. They should document any adjustments or repairs made to automatic garage door openers when applicable. 

There are some steps you can take to prevent garage door related injuries including:

  • Clear people from the area when garage doors are moving
  • Do not duck under a closing garage door
  • Open or close garage doors fully – do not leave them in a partially open position
  • Have garage doors inspected and maintained by a qualified person regularly
  • Test automatic garage door openers as instructed by the manufacturer

Riding The Hook

Tree services and cranes often overlap in day-to-day work. With the use of cranes becoming more common at tree sites, one question continues to arise and is in constant debate: Is it legal for a Qualified Arborist to be hoisted into a tree in order to access it? This recurring question arises with good reason since it is one of the greyest areas when using a crane to remove trees. 

First, let me explain what is being asked. The question is really asking if a trained, experienced tree cutter can directly tie to a crane hoist line and be lifted into a tree by the crane.

Both tree services and crane companies often quote different rules and different interpretations. That’s because prior to June 2021, OSHA did not have regulations regarding this type of work.  Instead, OSHA had exempted tree work in Subpart CC and had a patchwork of standards they used from the OSH ACT. 29 U.S.C.§654(a)(1) (General duty clause) and the OSH ACT sections 5(a)(1).

So back to our question:  Is it legal to hoist a qualified arborist with a crane into a tree to access it? From the crane operator’s point of view, the answer will most likely be and should be NO. They would be citing OSHA (1926.1431(a) Hoisting personnel), which basically prohibits hoisting personnel with a crane if there’s another, safer way such as aerial lifts, bucket trucks, or even ladders. An employer would have to demonstrate there is no safer way to perform the work in order to be hoisted by a crane and, even then, they still would have to be in a certified personnel platform (Man basket).

Tree services will almost always say YES, it is allowed and will reference ANZI Z133.1-2006 in favor of their argument. ANZI Z133.1-2006 states, 

“a qualified arborist may be hoisted into position utilizing a crane if the arborist is tied in with an arborist saddle and secured to a designated anchor point on the boom or line. The following procedures shall be followed when an arborist is to be lifted by a crane…” 

This goes on to 12 subsections that describe the necessary equipment and proper procedures that must be used. 

However, On June 24, 2021, OSHA canceled their August 21, 2008 instruction CPL 02-01-045, The Tree Care Directive, and provided new enforcement guidance for their Compliance safety and Health Officers (CSHO’s). Among these new requirements is OSHA 29 CFR § 1910.180(h)(3)(v). This requirement prohibits hoisting an individual on the crane load or hook. This requirement applies even though the standards for Arboricultural Operations ANSI Z 133-2017, §5.7.11 allows the hoisting of personnel into a tree. It is important to note that an employer’s reliance on ANSI standards alone is not a defense for violating OSHA.  An employer may claim that it is impossible, or not feasible, or simply presents a greater hazard to the employee if they were to comply with OSHA’s new standard. The burden of proof rest with the employer. It would be a lengthy process to prove and if alternative measures for accessing the tree exist, it will be very difficult to validate doing this. 


The answer to the question is it legal for a qualified arborist to be hoisted into a tree in order to access it, is NO. In short, OSHA trumps all other regulations, including ANSI.  Furthermore, you can not use a crane to hoist an arborist, qualified or otherwise, into a tree. Simply stating the tree isn’t safe to climb is no longer a valid reason. Too often, many tree services used this unchecked excuse to speed up the job completion time, putting profit over safety. Rarely is there not enough room to accommodate another piece of equipment that will allow them access to the tree. It is dangerous to lift personnel by a crane, and doing so needs to be done as safely as possible. OSHA has made an attempt to eliminate this hazard, and while every scenario can’t be foreseen, their new directive is pretty straightforward.

Who’s at the Head of Your Bed? Anesthesia Delivery in the United States


You are greeted in the pre-operative area before your surgery by an anesthesia provider.  Is this the same person who will be delivering your anesthesia care during your procedure?  Maybe, but maybe not. There are several care models in the United States: anesthesiologist MD or DO, certified registered nurse anesthetist (CRNA), and anesthesia assistant (AA).  Many anesthetics are delivered in a team model with one anesthesiologist guiding care for up to four anesthetics occurring at the same time, with CRNA’s and AA’s at the head of the bed for a majority of the case.  Who can do what in the anesthesia world is determined by state and national licensing boards, national and state certifications, hospital credentialling, and by-laws.

The terms medically supervised and medically directed are billing terms in the anesthesia world.  Medicare pays for medical direction of CRNA’s and AA’s at a rate of 50% of the reimbursement allowed for the case.  To meet the medical direction requirement of two to four concurrent cases, and receive the other 50% of the reimbursement for each concurrent case, the anesthesiologist must meet the following tax equity and fiscal responsibility act (TEFRA) rules:

  1. Perform the preanesthetic exam and evaluation.
  2. Prescribe the anesthesia plan.
  3. Personally participate in the most demanding procedures in plan.
  4. Ensure procedures that they do not personally perform are performed by a qualified individual.
  5. Monitor the course of the anesthesia frequently.
  6. Remains physically present and available for immediate diagnosis and treatment of emergencies.
  7. Provides indicated post anesthesia care.

“Medically supervised” applies to circumstances where more than four concurrent cases utilizing non-physician providers are occurring.  When this happens, billing can only occur for three base units.  Base units are part of the anesthesia billing calculation determined by the centers for Medicare & Medicaid services annually.

CRNA’s represent more than 80% of the providers in rural counties.  The Cochrane review in 2014 found no difference in care between nurse anesthetists and physician anesthesiologists.  As of 2022, the American Association of Nurse Anesthesia (AANA) has renamed the profession and is now the American Association of Nurse Anesthesiology.  Some states practice acts forbid nurses to present themselves to patients in terminology other than recognized nursing titles. 

It can be very tricky figuring out who is at the head of the bed and when.

Drinking and Darting Don’t Mix

A box truck was double-parked on the right side of a roadway. As a transit bus was passing the box truck, an intoxicated pedestrian stepped out from in front of the box truck and walked directly into the path of the bus. The engineers at DJS were retained by the bus company to reconstruct the collision.

Video from inside the bus captured the events leading up to the impact. According to the video, the pedestrian first became visible approximately 2 seconds prior to contact; however, an analysis indicated there was not sufficient time for the bus operator to perceive, react, and bring the bus to a stop prior to reaching the point of impact. This was an example of a classic “dart-out” case, where the incident was unavoidable for the driver. The pedestrian was crossing mid-block outside a crosswalk (and from an obstructed position), and, as such, the pedestrian was required by law to yield the right-of-way to the bus operator.

No liability expert report was served on the pedestrian’s behalf. The case was set to go to trial at the beginning of January 2022, but settled in mid-December for a minimal amount.

Wi-Fi Network, Forensics, and Yet Another Way to Determine
A User’s Location

When a device is connected to a Wi-Fi network, it typically stores the credentials for future use, allowing it to automatically reconnect to the Wi-Fi network the next time it is in range. Every time the user leaves a saved location with their cell phone, it disconnects from the Wi-Fi network and automatically reconnects when the user gets home. The date and time of the last auto-connect is stored on the device for each set of Wi-Fi network credentials.

Wifi Log
The preceding table displays the Wi-Fi connection history of an iPhone 8 Plus. The “Last Connected” column displays the last time the device was manually connected to a Wi-Fi network. The “Last Auto Connected” column displays the last time the device automatically connected to the Wi-Fi network. The “SSId” column displays a recognizable name for the Wi-Fi network.

Case Study:

Background – A woman that lived alone was murdered in her home one night. Local law enforcement marked her ex-husband as their first suspect. He claimed that he was at home, watching the Sixers game.

Forensic Analysis – Analysis of the ex-husband’s cell phone showed that it auto connected to the Wi-Fi network of his ex-wife’s home 12 minutes before the time the coroners said she died. His ex-wife’s home is the same place that he called home before the divorce. While the locks had been changed, the internet service remained. The ex-husband’s phone held onto the Wi-Fi network’s credentials and connected to the Wi-Fi network when he arrived at the property, placing him at the scene of the crime, and not at home watching the game.