Tuesday, June 18, 2013

Pole collapse due to design error

The collapse of a lightning rod pole in Penang recently was probably due to an error in its design.

The pole was fitted with more than a dozen metal discs that served as a ladder for a maintenance technician to reach the lightning rod mounted on top of the pole.

Due to the presence of strong winds at the time of the collapse, the discs offered a much stronger resistance to the wind and this caused the pole to bend in various directions.

The extreme length of the pole resulted in strong physical forces on the brackets that anchored it to the building and this resulted in the pole being ripped off the building, along with whatever that was anchored to it.

This analysis is based on my observation of hundreds of lightning rod poles that were installed in various cities in Japan nearly two decades ago.

Although they are impacted annually by strong typhoon winds that are at least twice as strong as the one reported in Penang, they hardly collapse even after years of exposure to the typhoons.

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The reason is that the Japanese lightning poles do not have any disc shaped ladder mounted on them and hence they offer very little resistance to the strong typhoon winds.

Furthermore, a study by Australian and Singapore lightning experts has shown that a lightning pole mounted on one side of a building offered no protection on the other exposed sides against lightning strikes.

Their findings have been published in an international technical journal and have been included in the international lightning protection standard (IEC62305:2006).

Since 2007, this country has endorsed the international standard as a Malaysian standard (MS-IEC62305).

There could be two flaws in the design of the pole – adding decorations to the pole that render it dangerous in the presence of high winds and not complying with the Malaysian standard on matters of public safety.

Finally, since the building seems to have been fitted with sheet metal facades, no lightning protection system is really necessary but these metal sheets must be bonded properly all the way to a grounding system.

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