Lightning rod might have staved off ruin

The Baltimore Sun

A properly installed lightning protection system could have shielded the First Mount Olive Free Will Baptist Church from Tuesday's lightning strike, according to one of the nation's top experts in the field.

"Thirty percent of all fires in church buildings are caused by lightning. And guess why? Steeples," said Martin A. Uman, co-director of the Lightning Research Laboratory at the University of Florida in Gainesville.

And that's why most church buildings have protection.

Witnesses said Tuesday's bolt ignited a blaze in the wooden spire that rose above First Mount Olive's stone bell tower. The spire eventually toppled onto the church roof, and the resulting five-alarm fire destroyed the church. The 140-year-old structure was declared a total loss.

Lightning protection is an 18th-century technology. It was invented in the 1750s almost simultaneously by Benjamin Franklin, working in the British colony of Pennsylvania, and Vaclav Prokop Divis, in Bohemia (now the Czech Republic).

Franklin's early experiments with electricity led him to believe that the electric "fire" in atmospheric lightning could be drawn to a pointy iron rod mounted on a chimney or rooftop, and "diverted" safely to the ground through conductive metal.

His idea worked, and soon "Franklin" lightning rods (also called "attractors," "protectors," "finials" and "air terminals") were turning up on buildings throughout the Colonies.

The largest one installed during Franklin's lifetime was atop Maryland's State House dome. The 28-foot-tall, painted wrought-iron rod is still there, rising 18 feet above the "acorn" and pedestal, according to Mimi Calver, director of exhibits at the Maryland State Archives.

The dome has sustained lightning damage only once in the 219 years the rod has been there, according to the archives' Web site.

Contrary to common perception, lightning rods do not "attract" lightning. Nor do they work by dissipating static charges in the area to ward off a strike.

"The function of a lightning rod ... is to provide something preferential to strike, so it can carry [the current] harmlessly into the ground," Uman said.

Lightning rods work so well that some state and local governments require them on government buildings and certain other structures, Uman said. But the requirements vary from place to place. And while there are industry standards for what constitutes an adequate lightning protection system, its use is largely up to engineers and property owners.

"On houses nowadays, you generally don't find them. On wood barns you always find them because insurance companies require it," Uman said. "And a lot of people who have had fires and lightning damage install protection systems."

Modern lightning protection systems are more than adequate to handle any size bolt, he added.

"Lightning looks awful, and it will blow an insulator [any object that does not easily conduct electricity] like trees to smithereens. But it is easily controllable," he said. "You can run a whole lightning bolt through a copper wire a quarter inch in diameter without appreciable heating."

Specifications for lightning-protection systems are spelled out by the National Fire Protection Association. On a structure like a large church, Uman said, a proper lightning protection system would consist of a copper lightning rod a quarter- to a half-inch in diameter, rising 10 to 12 inches above the church spire.

The rod can even be incorporated into a cross or a weather vane.

The rod is connected to a copper wire a quarter-inch in diameter, or a flexible, braided alloy of equivalent diameter that runs as directly as possible to the ground.

"Any wire will handle 80 percent of all lightning," Uman said. "The chance that you will get hit with a bigger one is pretty small. The chance you will get hit at all is pretty small."

The wires can run outside the building or inside, Uman said. "The danger is when you do something wrong, and you've got it in the roof, and it arcs, jumps and starts a fire. You've got to do the job right."

A building the size of a church should have additional lightning rods every 30 feet or so along its roofline, all connected to wires leading to conductive stakes driven into the ground, Uman said.

A large building should have at least four paths for lightning to follow to the ground. A house should have two. And each needs to be well-grounded.

Where the soil is a poor conductor, Uman said, the goal is to install more metal in the ground -- enough to dissipate the current safely.

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