Exemplars & Urban Legends

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Exemplars & Urban Legends

On the Scene E-Newsletter, Edition 116, May 26, 2010

You are at the gas station, standing next to your car, filling up your tank, when your cell phone rings. Should you answer it?  Because you have heard that a cell phone can create a large enough spark which could ignite gas fumes and cause a huge explosion. But wait…is that true or just an urban legend?

Solving puzzles like this one is often similar to what forensic engineers do; with one major exception. While a television show like “Mythbusters” gets to solve these problems on the front end (for fun or before anything bad happens), forensic engineers usually get called in on the back end (after something bad has happened).  This calls for a different approach as often the original situation the incident occurred in has been altered in some way by the incident itself.

For example, there has been an explosion at a gas pump and a cell phone manufacturer finds itself in litigation.  The plaintiff’s attorney alleges that the cell phone was dangerous and defective in that when their client answered a call, a spark was created by the phone which ignited the gas fumes near the pump.  The forensic engineers involved scurry off to prove this can or cannot happen.  Since this specific situation cannot be recreated very well using a burnt car and melted cell phone, any test would need to be conducted with a similar vehicle and cell phone. These substitutes worthy of imitating the original pieces of equipment are called exemplars.

There are many advantages to using exemplars.

· No spoliation of evidence.  Even if the original equipment may be available for testing, often times testing will result in the alteration or destruction of the original equipment, which can be an undesirable affect on evidence that needs to be preserved.

· Theory versus Scientific Fact.  The more science an expert can put behind his or her opinion, the stronger that opinion is.  Drawing conclusions from calculations made from measurements and descriptions can be valid, however seeing results in a practically applied situation that back up what those calculations indicate certainly adds strength to any conclusion.

· Demonstrative Evidence.  A three dimensional, physical, real time, credible demonstration creates a much more powerful impression than a two dimensional paper report.  A jury can instantly visually grasp points made with exemplars, the result of which often aligns their perception with the expert’s opinion.  If a picture is worth a thousand words, an exemplar is certainly worth more.

So, cell phone at the pump…urban legend?  Yes!  According to the show Mythbusters, “A properly-working cell phone poses almost no danger of igniting gasoline, even when surrounded by gasoline vapor with the optimum fuel-air mix for ignition. The actual risk comes from an electrostatic discharge between a charged driver and the car, often a result of continually getting into and out of the vehicle.