A Straight Dope Classic from Cecil's Storehouse of Human Knowledge

Do lightning rods really work?

August 24, 2001

Dear Cecil:

Everyone learns about lightning rods in grade school. There is the heavy-duty kind on skyscrapers that takes the brunt of bolts and conducts them safely to ground, and the delicate, sharply pointed ones that protect residences by bleeding off electric charge and preventing strikes. Having been well schooled in skepticism by our beloved Cecil, I tried to find a scientific study showing that rods actually ward off lightning, before plunking down dollars. No luck, except for manufacturers' marketing propaganda. I've seen a scale-model village successfully protected by tiny lightning rods from a "lightning" machine. But models don't always scale up to the real world. Do houses with lightning rods actually get hit less often than houses without?

You're thinking: What a stupid question. Everybody knows lightning rods work. People wouldn't have put them on buildings for more than 250 years (lightning rods were initially proposed by Benjamin Franklin in 1749) if there weren't a sound scientific basis for them, would they?

Well … maybe they would, maybe they wouldn't. We need to have a little talk.

Current U.S. lightning protection standards are embodied in a document published by the National Fire Protection Association known as NFPA 780. First issued in 1904 and updated periodically since, NFPA 780 codifies the traditional lightning rod installation, in which sharpened metal "air terminals" known as Franklin rods are connected to an earth ground by means of heavy conductors. A lightning bolt strikes a Franklin rod and is carried harmlessly to earth by the grounding apparatus, sparing lives and property. Though technically voluntary, NFPA 780 has been adopted by many local jurisdictions and government agencies and is the de facto national code.

Some years ago manufacturers of a new type of lightning rod using what's called early streamer emission (ESE) technology began agitating for a new NFPA code for their product, which supposedly requires fewer air terminals that can be placed farther apart than the traditional Franklin rods. An ESE terminal, described as looking like "a chrome cantaloupe with a chrome Frisbee around it and a little sharp prong on top and mysterious portholes around the sides," uses radioactive material to send a stream of ions aloft. This supposedly provides a path for lightning and guides it harmlessly to ground.

Most research to date shows that ESEs work no better than Franklin rods and fails to justify the claim that fewer terminals can be used. In 1993 the NFPA declined to approve proposed NFPA 781, which would have set ESE standards and presumably given the ESE industry a shot in the arm. ESE makers sued, claiming NFPA 781 had just as much scientific backing as NFPA 780. In a settlement the NFPA agreed to have ESE technology reevaluated by an outside panel.

The panel confirmed that there was no scientific basis for NFPA 781. But guess what, it said. There's no scientific basis for NFPA 780 (traditional lightning rods) either.

NFPA membership voted to approve an updated 780 anyway, but the NFPA standards council overruled them and announced its intention to rescind 780 unless somebody could give them good reason not to. While the NFPA wouldn't come right out and admit it when I called, I suspect the threat of another lawsuit was in the back of everybody's mind.

Proponents of traditional lightning rods freaked. A report from the Federal Interagency Lightning Protection User Group said, in essence, Come on, everybody knows this stuff works — if you rescind NFPA 780 it'll be back to the anything-goes days of the 19th century, when lightning rod con artists abounded. But there was an unmistakable air of desperation to the group's plea. Much of the evidence was from sources like the Iowa state fire marshal's annual report from the 1920s, which talked about barn fires. After 1950 research largely ceased; people just assumed traditional lightning rods worked.

They probably do work, but maybe not as well as was once believed. Critics of 780 point out that lightning remains a largely unpredictable phenomenon and that rods merely improve your chances rather than offering guaranteed protection, as the old code assumes. (Another beef: the committee in charge of 780 includes too many lightning rod manufacturers, who have a vested interest in maintaining the status quo.)

The NFPA standards council deferred a final decision "to give proponents of NFPA 780 an adequate opportunity to set forth the claimed substantiation for traditional lightning protection systems." Comments are currently being accepted; the group will decide what to do next at its October meeting. I'm betting the sparks will fly.

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A Straight Dope Classic by Cecil Adams

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