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Lightning – An Act of God

Andrew Rudin -- Interfaith Coalition on Energy -- September 1992

A quick-moving storm passed over northeast Philadelphia in August 1991.  When lighting struck the Episcopal Church of the Resurrection, no one was in the building.  A malfunctioning alarm system was the initial symptom that something was wrong.  The church security system had automatically dialed a list of numbers to say that the power was off.


Along with some members of the congregation, the police and fire personnel arrived at the church.  Nothing seemed out of place on the outside of the building, so the police and fire personnel departed.  Then a parishioner looked up at the cross, the highest part of the building, to see that it was no longer standing upright.

Lightning had hit the concrete covering of the cross, traveled down the steel rods reinforcing its center, zapped through the lead lines in a large stained glass window, and loosened every pane, and then spread out through the building's electrical system to blow out not only the alarm system but a television set in the basement at the far end of the basement.  The force was so great that pieces of plaster from the wall were found at the other end of the sanctuary, over 100 feet from where the lightning struck.

Eight months later, the congregation received a check from their insurance company for $22,500.  Payment was much slower than the lightning.

Lightning is electricity

While each of us sees its force only occasionally, lightning actually strikes somewhere on the earth 100 times per second.  For the United States, that averages 13 ground strikes per square mile annually.  The average stroke is 25,000 amps and 30,000,000 volts.  Compare that to our mere 15 amp circuits with 110 volts inside our building, which can also kill us.

We are slowly learning how to avoid getting killed by lightning.  In 1989, sixty-seven Americans died from lightning while 149 died in 1965 and 340 died in 1940.  Lightning kills one woman for every seven men.

But lightning creates other problems.  It creates strong electro-magnetic fields which can charge nearby utility wires, and fry microprocessors.  Inside our buildings, these jolts ruin expensive electronic, air conditioning and audio-visual equipment.

Lightning and religion

Myths of lightning abound.  Egyptian and Greek gods, Buddha, and the Norse god Thor all were identified with lightning.  Thursday is named after "Thor's Day," in reference to Thor creating lightning by striking his hammer as he rode his thunderous chariot across the skies.  Some native tribes in both North America and Africa believed that lighting came from a "thunderbird."

Lightning has been also associated with churches through the ages.  An 18th century German book describes how, over just 33 years, lighting killed 103 bell ringers while they were at work.

The temple in Jerusalem, built by Solomon, survived 1,000 years of lightning because its metal dome and connecting metal rain spouts provided safe paths to ground for the energy from lightning.

One part, or three

Lightning seems instantaneous, but it actually happens in three steps.  First, a stream of electrons flows toward the earth at about 60 miles per second.   Secondly, a "stepped leader" of barely visible, negatively-charged air molecules strips away electrons near the earth.  This creates a positively-charged "streamer" currents which reach up toward the leader.   Finally, a branch of the leader comes in contact with one of these streamers, and bang!  A massive positive return spark rises through a channel at one half to one tenth the speed of light.  If we could capture the electricity, it would run one common light bulb for several months.

The diameter of a current-carrying core is one to two centimeters.  Its temperature is about 50,000F degrees.  The flash lasts for an average of two-tenths of a second, but the intense heat rapidly expands the air, creating thunder.

Thunder is rarely heard over 15 miles from lighting.  The clap of the thunder is from the lighting strike.  The rumble after the clap is from the air expanding from the upward channel of lightning.

Lightning protection

Houses of worship ask for trouble when they build ungrounded spires into the sky.  The National Fire Protection Association (NFPA) rates risk of damage from lightning.  They point out that steeples and spires that are 50 feet higher than the surrounding buildings, on a high location, with historic contents, and covered by a wood roof over wood frame, as having the highest risk of expensive damage from lightning bolts.  Over 30% of all destructive fires in houses of worship resulted from lighting.  Lightning also can ruin expensive electronic, air conditioning and audiovisual equipment.

Ben Franklin flew his kite in a thunderstorm in 1752 to prove that steps can be taken to prevent harm from lighting.  Lightning rods to this day are still often referred to as "Franklin Rods" and remain the best way to protect a building.

The more formal name for a lighting rod is an "air terminal."  A "grounded electrode" is a thick copper-clad rod that brings the charge to earth.  "Interconnecting conductors" connect one rod to another, which are usually spaced 20- to 25 feet apart.  This grid is connected to the ground electrode by a "down conductor."

The area protected was thought to lie within a circle whose radius is the height of the rod.  Recent research has redefined the definition of a protected zone as the area under an arc having a radius of 150 feet and is tangent to the earth while touching an air terminal.

What to ask for

When purchasing a lightning system, ask that it conform to NFPA 78, the Lightning Protection Code.  Underwriters Laboratories UL96A specifies a Master Label Code.  A third code was written by the Lightning Protection Institute, which now appears to be out of business.

To limit damage to electronic equipment, you may wish to purchase surge suppressors.  Some people say that surge suppressors save energy while protecting equipment.  They don't.  Surge suppressors should be approved by Underwriters Laboratory following UL Safety Standard 1149, which covers both performance and safety guidelines.  Surge suppressors are available for both telephone and electric outlets.  Personal computers are often damaged by electric surges through connected modems.

Personal safety

If you are in a lightning storm, the Church Mutual Insurance Company recommends the following precautions:

Inside a building:

  • Stay clear of open doors and windows
  • Stay away from large appliances
  • Don't use the telephone

Outside a building:

  • Seek protection inside a protected shelter
  • Don't touch metal fences
  • Don't stand under lone or tallest trees
  • Get out of pools, lakes or the ocean
  • Stay away from railroad tracks


Summary

"I am of the opinion that houses, ships and even towers, and churches may be effectively secured from the strokes of lightning by their means; for if, instead of the round balls of wood or metal which are commonly placed on the tops of weathercocks, vanes, or spindles of churches, spires or masts, these should be a rod of iron eight or ten feet in length, sharpened gradually to a point like a needle and gilt to prevent rusting, or divided into a number of points, which would be better, the electrical fire, would, I think, be drawn out of a cloud silently, before it could come near enough to strike."

                                         -- Benjamin Franklin - 1749

Our thanks to Dr. Richard E. Orville of Texas A&M University, Patrick M.  Moreland of Church Mutual Insurance Company, and Dave Goodwin of the Philadelphia Electric Company for help in preparing this article.