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Weather Library > Lightning FAQ: If metal doesn't attract lightning, then why do laboratory sparks always hit the metallic objects?

By DAN ROBINSON
Storm Chaser/Photographer
25 Years of Storm Chasing
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A common question regarding the subject of a metal object's ability to attract a lightning bolt arises after observing the behavior of laboratory-generated sparks, such as those from Van De Graaff generators or Tesla coils. Sparks from these machines always seem to prefer the more conductive object. For instance, sparks will always hit an iron pipe rather than a PVC one, when both are brought close to the generator's terminal.

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The key difference, however, between lab-generated sparks and lightning is the scale. A tabletop Van De Graaff generator spark might reach a couple feet at best, while a lightning bolt is miles in length. To accurately represent the true scale of a natural cloud-to-ground lightning bolt and the effects of metal objects, you would need your 'test' objects to be proportionately sized.

As it stands, a six-inch spark being attracted to a 6" metal pipe is roughly equivalent to a natural lightning strike being attracted to a 10,000 foot tall skyscraper. Of course, a huge metal object of that size would get hit by lightning every time if the storm was overhead.

For an example, let's say you wanted to test an umbrella's lightning-drawing power. Let's assume the natural lightning bolt you want to simulate is two miles long (10,560 feet or 126,720 inches). Your six-inch Van De Graaff spark is roughly 21,000 times smaller than the naturally occuring bolt. Therefore, your 'test' umbrella needs to be proportionally smaller, namely microscopic in size! Even tiny items like iron filings and sawdust would be too large.

So yes, metal objects do attract small sparks, but this setup isn't representative of the scale of the full-size lightning discharge.

Mythbusters Episode

A recent 'Mythbusters' episode tested this myth by striking ballistics-gel dummies with large laboratory-generated sparks. They found that the only object that consistently 'attracted' the lightning was a doorknob placed on the head of the dummy. However, the difference between these tests and natural lightning was once again, the scale. The spark-generating terminal was aimed at the dummies at point-blank range, directly above the dummies' heads by only a few feet. In reality, a lightning bolt is starting out at high altitudes, traveling through miles of air before it reaches the ground. If lightning is coming down and happens to end up a few feet over your head like the Mythbusters' test sparks, only then may something metal on your person have some influence. But that is going to be an extremely rare scenario. In reality, lightning is going to be much further away from you during an average storm. It's similar to the difference between firing a gun at a target from a distance of three feet to a shot from a distance of two miles - the target will get hit more often when the gun is fired at close range.

A strike like this, that is, at a distance of less than a few feet, is something most people will never experience. Even if a strike that close does not hit a person directly, they will still be close enough to be injured or even killed by its resultant current flowing through the ground. In the case of the Mythbusters setup, moving the dummies out of 'point blank' range from under the spark terminal by just a few feet would have resulted in fewer or no direct strikes to the test subjects, and would have demonstrated that small metal objects would not infuence even a close lightning strike.

See Also:

Artificial and natural lightning: Practical comparisons
Examining the differences between small man-made sparks and natural lightning.
FAQ: What can the outdoorsperson do to reduce the risk of getting hit by lightning?
MYTH: Small metal objects attract lightning, and I'm safer outside without any metal nearby.
MYTH: Lightning always strikes the tallest object.
MYTH: Lightning only strikes good conductors.

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