CN Tower struck by lightning more frequently than rest of Toronto
November 23, 2006
Source: Ryerson University
Professor Ali Hussein recently authored a study examining lightning strikes to the CN Tower over a 15-year period.
If you're looking for a spectacular lightning show, there's no better seat than finding a safe spot near the CN Tower during a thunderstorm. The tallest freestanding structure in the world is struck by lightning more frequently than any other structure in Toronto, finds a study by university researchers.
In the most extensive and longest study of lightning hitting a tall structure below its top, Ryerson University and University of Toronto researchers found that the tower is hit by lightning at least 40 to 50 times annually compared to other places in Toronto which is struck, on average, two times per square kilometre every year.
"The importance of studying the characteristics and location of lightning strikes to tall structures can't be understated," says Ali Hussein, lead author of a study published online in the November issue of the Journal of Electrostatics and a Ryerson University professor in the Department of Electrical and Computer Engineering. "Tall structures naturally attract lightning so engineers and lightning protection experts need to understand the behaviour of lightning to design better protection for such structures."
Hussein, who is also an adjunct professor at the University of Toronto, and other researchers, analysed images captured by video cameras, which recorded the location and the characteristics of lightning flashes striking the 553-metre tower from 1991 to 2005. They examined the duration and frequency of the strikes. They also observed the number of intense electrical currents, called strokes, emitted during each flash as well as the time intervals between successive strokes.
The researchers recorded 404 flashes over a 15-year period, 16 of which struck the building five to 70 metres below its tip. "It's good to know the probability of the tower being struck beneath the tip and how far below," says the professor. In May 1976, the tower was struck once by lightning 13 metres below its tip causing $25,000 in damages but there has been no lightning damage to the structure since its official opening almost two months later.
The study was funded, in part, by the Natural Sciences and Engineering Research Council of Canada.
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