MYTH: Lightning rods 'discharge' a thunderstorm cloud and prevent a lightning strike.
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By DAN ROBINSON
Storm Highway Editor/Cameraman |
TRUTH: Lightning rods, along with a good lightning
protection system of grounded cable, only serve to divert lightning
current safely to ground, should lightning strike. There is no way to
'discharge' or 'drain' the charge from a storm with lightning rods, or
with anything, for that matter.
Most storms are ten to twenty (or more!) miles wide and many miles high-
simply enormous! A lightning rod is a tiny speck in comparison to the
mighty electrical charge generation inside these mammoth clouds.
Although there can be slight corona discharge off of pointy rods
(sometimes called St. Elmo's fire),
this current 'leak' is simply too small to have any hindering effect on
the
huge rate of charge buildup inside the storm cloud.
Draining a storm cloud of its charge to prevent lightning with a
little (or more than one) lightning rod is impossible. It would be like
trying to keep a reservior from overflowing by drilling a pencil-sized
hole in the dam - while a mighty river keeps filling the reservior up.
Lightning dissipation / elimination myths
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Products called 'lightning elimination' or 'lightning dissipation' devices have arisen as a result of two myths: one, that a thunderstorm's charge can be drained or otherwise affected by objects on the ground, and two, cloud-to-ground lightning discharges begin from the ground. These products, that are still being sold today, claim to be able to prevent a direct lightning strike to any object on which they are installed. The devices have widely varying appearances, but usually are characterized by a metallic frame with hundreds of sharp-pointed bristles, needles or thin rods. The frame designs range from comb-like to umbrella-shaped.
The devices are said to prevent or reduce direct lightning strikes to objects on which they are installed, using corona discharge to perform one or more of the following: 1.) to drain a storm of its charge before lightning can occur, 2.) to create a localized 'space charge' over the protected area that diverts lightning strikes, or 3.) to make initiation of upward leaders from the object more difficult, thereby reducing the chances of a direct stepped leader-ground leader connection.
As we discussed in our article about thunderstorm charge dissipation, the problem with these devices is that while they do create corona discharge, the rate of charge 'leakage' is completely insignificant in comparison to the rate of charge generation in the 10-mile-high, 15 to 25 mile-diameter thunderstorm overhead! No amount of man-made corona discharge on such a small scale has the slightest chance of draining charge faster than a gargantuan thunderstorm cloud is producing it. And although small-scale corona does help prevent the initiation of laboratory-generated sparks (such as from Van de Graaff generators), this cannot be extrapolated to apply to full-sized lightning discharges, which are several thousand times larger than the artifical counterparts (see our article on comparing artificial and natural lightning). Corona discharge from small 'dissipators' is insignificant to a full-sized thunderstorm and will do nothing to alter the occurence or behavior of lightning in its geneeral vicinity.
Cloud-to-ground lightning strokes initiate high in thunderstorms, miles above the surface where ground objects have no effect. Even after initiation of the discharge, the downward-moving stepped leader is 'blind' to objects on the ground until it is very close to the ground, within 50 to 100 feet. At that distance, lightning will strike within the very small area it is already descending in, regardless of any devices nearby that claim to divert or prevent the strike. For example, a photograph exists of a lightning strike to the Merchandise Mart building in downtown Chicago. Merchandise Mart is very close to the 1,700 foot tall Sears Tower, yet not even the Sears Tower influenced the ground connection of this close cloud-to-ground stroke.
In addition to the obvious scientific flaws with the concept of lightning 'dissipation' and 'elimination' devices, they have been proven to be ineffective in real-world installations. Many 'lightning dissipation' devices on towers and buildings have been struck directly. Despite the evidence, they continue to be sold, installed and promoted.
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