Expert Witness Blog

In Analysis and Testing In Accident Reconstruction, accident reconstruction expert witnesses at Technology Associates explain the nature of engineering analysis:

Straightforward as the above reasoning is (see 7/16/09 blog entry), it nevertheless constitutes a valid (though simple) example of engineering analysis. Now let us consider what it would take to demonstrate the defect of the steps by testing rather than by analysis. To do this, there must first be devised a suitable test procedure, and this can be arrived at only by further analysis-which is another word for organized and systematic thinking with relevant technical considerations taken into account. From this analysis, there emerged the following requirements:

1. The tests must be done with different subjects, who must not know they are being tested and must not observe each other performing the descent of the stairs-else their performance will be affected, and so will not represent “normal” descent of the stairs by an unwarned person.

Ladders and scaffolds expert witnesses at Technology Associates write on stepladder instability:
Three-leg contact can develop under a number of situations such as set-up on an uneven surface or when climbing, sliding, pivoting or “walking” a flexible ladder along the ground as the user’s work progresses. Dr. John Morse has cited a subtle type of unperceived three-leg stepladder contact named “Type-II racking”, which occurs during climbing as follows.

After the climber has one foot on the floor with his other foot on the first step, and one or both hands on the front rails at chest height, he pulls himself upward with one arm and attempts to keep his body straight. This imposes a torque about a vertical axis to the ladder. This torque, combined with the climber’s pulling force (which is necessary to raise his weight to the next step), tends to unload the rear legs. With these legs offloaded, and while this torque is still applied, the ladder twists or “racks” in the direction of the applied torque. When the climber’s foot then leaves the floor and reaches the first step, weight is shifted back onto the rear legs of the racked (slightly twisted) ladder. When this occurs, only one of the ladder’s rear legs can contact the ground. If this goes undetected, the climber has unknowingly created a three-legged ladder and the potential for instability, should center of gravity diagonal-crossover occur later after subsequent climbing or use.

Seat belt and airbag expert witnesses at Technology Associates describe “whiplash” injuries:

Unfortunately, the effects of whiplash are often downplayed, and its sufferer thought to be malingering, on the grounds that injury isn’t visible. In addition, experiments have shown that the forces to the neck during whiplash are not much greater then those occurring during normal activities (e.g. “plopping down into a seat”, “hopping onto a step”, and even “sneezing”). However, unlike whiplash, normal events do not take a person by surprise, so one can instinctively brace the neck muscles in anticipation, and control the force transmitted to the cervical soft tissues. With whiplash, the force to the neck is violent and sudden, and is not filtered through the neck musculature. Hence, those with thinner or weakened necks (i.e. women and those who have had prior neck injury) are more prone to the effects of whiplash, which can occur from an impact to the car as low as 3G’s.

A problem facing investigators of a whiplash case is that the impact velocity of the striking (rear) car is typically not known with certainty, and this value is needed for determining resulting forces. A conservative estimate of the speed can be surmised by using the damage threshold of the cars’ bumpers (because whiplash injury is caused by low speed impacts involving no (or minimal) damage to the bumpers; hence most of the shock is transmitted to the passengers’ necks). Testing has shown the damage threshold of bumpers of many cars to be about 5 mph; thus lash forces to the neck based on a maximum 5 mph impact velocity to the struck car. However, most crash testing involves the car impacting a rigid barrier, which does not yield in any way, rather than a relatively flexible bumper of another car. Hence, the crash testing can be more severe than an actual impact with another car, and can, in fact, be equivalent to the car’s being struck with another car at up to twice the velocity used for the barrier test.

In Analysis and Testing In Accident Reconstruction, accident reconstruction expert witnesses at Technology Associates explain the nature of engineering analysis:

Persons with no training in engineering are generally unaware of the nature of engineering analysis, and so tend to assume that testing, as a means of determining the causation of accidents, is a dominant tool of the engineer. In the following examples, we shall undertake to explain the nature of engineering analysis, and to show that it is more basic than testing because testing without analysis is meaningless. Further, while analysis is always necessary in accident reconstruction, testing is only sometimes necessary.

Consider, for example, a flight of steps in which the tread of each step (the horizontal surface) is only 6 Inches deep (in the direction from front to back). Since the shoes of most persons are considerably greater than 6 Inches in length, the toes of a descending adult will tend to overhang the tread by a substantial amount, especially since It Is not to be expected that the heel will always be placed as far back as possible, thereby increasing the overhang all the more. The result will be that the footing will not be as secure as If the tread were, say, 10 inches deep. Thus, if a person has fallen while descending the 6-Inch-deep steps, the fall may be ascribed to the inadequate depth with reasonable probability (providing of course that there is no other contributing reason for the fall).

Ladders and scaffolds expert witnesses at Technology Associates write on stepladder instability:

According to Consumer Product Safety Commission (CPSC) accident estimates, tens of thousands of stepladder accidents requiring emergency room treatment occurred annually in the United States. Approximately 85-90% of these accidents involve the user falling from the ladder and 8-9% of these injuries are serious enough to require that the victim be admitted to a hospital. In addition to posing a severe health concern, these accidents have significant loss-of-wages and high medical expense implications.

Having investigated numerous stepladder falls over the years, we have found it very common to learn that ladder accident victims are unaware of the cause of their falls and it is typical for them to respond to questions regarding causation with answers such as: “The ladder just gave way”, or “It was sudden, I don’t know what happened”, or equivalent statements. One possible cause of such accidents is associated with use of the common four legged A-shaped stepladder, which can easily be accidentally positioned such that only three of its legs are contacting the ground. This situation can also go unperceived until it is too late to avoid an accident.

Seat belt and airbag expert witnesses at Technology Associates describe “whiplash”:

What is the syndrome called “whiplash”? Here is a brief description. A stopped car is struck by another vehicle from behind; the struck car and torsos of its passengers are thrown forward. However, the heads of the passengers lag behind for a fraction of a second, causing their necks to be hyper-extended (unduly strained as the torso flies forward while the head stays behind). As their torsos rebound against the seat backs, their heads now move forward, but are snapped back again, by their necks, and overshoot the torso, again causing the neck to be hyper-extended. This effect is most severe if the headrests are too low and set too far back, as they are in many cars. The whole occurrence takes less then a second.

Although the person experiencing this situation does not have overt signs of injury, the possible occurrence of soft tissue damage to the overstretched ligaments of the neck has been well documented. This damage may be permanent, causing chronic pain and limitation in neck movement, the full extent of which may not be apparent until about a day after the accident.