Saturday, September 17, 2005

A story about a man carrying over 30,000 (sometimes reported as 40,000) volts of static electricity in his body, allegedly generated by a wool sweater and nylon jacket combination, is circulating through major news outlets. The story, carried first by the Warrnambool Standard, says that the man, Frank Clewer, a 58-year old cleaner from Dennington, involuntarily created a scene by causing fire departments to evacuate three buildings where he had left his mark, before he realized he was causing the burn marks on carpets and allowed the fire department to help him.

The story has been picked up by The Register, Guardian, BBC, USA Today, Reuters, local agencies of ABC, the San Francisco Chronicle, and other news outlets.

Several unanswered objections mark the story as a possible hoax:

• Clewer enters and exits his car several times in the story — if he opened the car by touching its presumably metal lock, he would surely release some electricity into the car through his hand; everyone has at some point experienced the painful shock of touching a door handle or car keys to a lock. Though the car might not be grounded, it would still be at a lower potential and thus energy would be transferred. This would be noticeable; the story does not comment that Clewer understood what was happening to him.
• Firefighters supposedly “used a device to check static electricity on him and his belongings.” While firefighters would be likely to carry a high-voltage multimeter around to measure the current and voltage ratings of downed power lines, it is unlikely that the same device could measure such a large voltage resulting from a very small amount of static energy without de-electrifying it.
• For such a large voltage to be stored, humidity would have to have been extremely low on that day for the air around him not to ionize and source current, removing the static energy.
• If he was carrying such a large voltage, his hair would probably have stood on end, as this is a notable effect when one touches a Van de Graaf generator. Note: It is uncertain at what voltage this effect begins, and since Van de Graaf machines routinely exceed Megavolts of electric potential, this may not be a verifiable objection.
• This statement: “Firefighters took possession of Clewer’s jacket and stored it in the courtyard of the fire station, where it continued to give off a strong electrical current.” (Reuters UK) First, there is no reason they would need to take possession of the jacket — the static electricity could be dealt with by simply dumping water on it. Second, the jacket could not “give off” an electric current without some continuous source of energy, which, in storage, is impossible. It is possible that the jacket could hold a voltage, but the effects of this would not be visible — if they were, they would be short-lived as the jacket would lose its static energy. In any event, the current would be miniscule.
• The amount of energy stored on Clewer’s person and possessions could not have been more than a few Joules; this is unlikely to have burned carpet.

The equation for stored energy in capacitors is:

Where U = energy, C = capacitance, and V = voltage. A human body by itself typically has a capacitance of around 250 pF, which would mean a voltage of 30,000 V would produce energy of 0.11 joules. Even if Clewer’s possessions resulted in a parallel capacitance of 1 microfarad, this would still only result in an energy storage of 450 J. This amount of energy would be insufficient to burn carpet or char plastic, although a spark could ignite flammable vapor or gas.