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FRIDAY, Aug. 13 (HealthDayNews) -- With the summer thunderstorm season reaching its peak, it's wise to be aware of how not to become a lightning rod.

Lightning is the No. 2 weather-related source of fatalities in the United States, according to the National Lightning Safety Institute. And, the National Weather Service reports, 400 people are struck and approximately 67 are killed each year by the bolts. That's more than succumb to hurricanes or tornadoes. Only floods are more deadly.

Almost three-quarters of those who survive a lightning strike suffer lifelong, severe complications and disabilities. Lightning also causes about $5 billion of economic loss each year in the United States.

All of which leads to your need to take quick precautions as soon as you hear thunder.

"The smartest thing to do during a thunderstorm is stay indoors or in an all-metal automobile," said Martin Uman, director of the Lightning Research Center at the University of Florida in Gainesville. "Definitely avoid wide open spaces and don't take temporary shelter under a large tree or in an open structure that offers limited protection from the elements."

Danger from lightning begins sooner and lasts longer than many people realize, Uman added.

"Too often people continue pursuing whatever outdoor activities they're engaged in -- such as golf, agricultural work, construction, boating or swimming -- until it starts raining," Uman said. "The same folks rush to resume the activity as soon as the rain ends. What they don't realize is that lightning can strike when thunderstorms are in the area, but the sky above them is clear."

He added, "As a rule of thumb, the danger of being hit by lightning begins when the first clap of thunder is audible and continues a full half hour after the last thunder clap or lightning bolt occurs. Often lightning is much closer that it seems. In fact, many casualties from lightning occur from the initial strike."

Lightning expert John Drengenberg has a simple method by which you can judge how far away the lightning is: Estimate the seconds between seeing a flash or bolt of lightning and hearing its accompanying clap of thunder by counting by thousands.

The method may lack sophistication, but it's precise enough to provide you with a margin of safety when seconds count, said Drengenberg, manager of consumer affairs at Underwriter's Laboratories in Northbrook, Ill.

"Every five-second pause between seeing a lightning flash and hearing the thunder translates into about five miles of distance from a storm," Drengenberg explained. "If a storm is fast-moving, it can travel one mile very rapidly and be on top of you before you know it. So don't be lulled into a false sense of security just because the pause between flash and boom stretches to 10 or 15 seconds."

Drengenberg also cautioned that you should avoid many inside activities during thunderstorms.

"Don't use any electrical appliances, including corded phones, washing machines or dishwashers during electrical storms, because if lightning strikes the house, the powerful electrical charge a lightning strike packs can travel through the household wires and into appliances and anyone using the appliances," he said. "Avoid bathtubs, showers and kitchen sinks because metal pipes and even the water in plastic pipes are also good conductors of current. And, don't recline on concrete floors. They conduct electricity as well."

He also noted that simply turning off sensitive electronic equipment won't protect it if lightning strikes the building.

"There's no on-off switch, no surge protector made that would even slightly slow the electrical current generated by one bolt of lightning," he said. "The only way to make sure computers and other audio-video devices are safe is to disconnect them -- unplug them completely."

And standing by an open window or door to admire the brilliant flashes of lightning accompanying summer storms is also unwise.

"When house windows are opened, the warm air from inside the house travels upwards and into the thunder clouds above," Drengenberg explained. "A lighting bolt can travel right back down that shaft of air, into through the window, and strike anyone in its path."

Although scientists are learning more each year about lightning and the more than 1 billion volts of power each bolt packs, Drengenberg said many of the behaviors of the celestial phenomenon remain unknown or poorly understood, even by those who have spent their lives studying it.

For example, he said, scientists have just recently learned that electrical currents often flow from the ground to the atmosphere during electrical storms.

"Thunderclouds are seeking the best conductor of electricity to discharge their electricity," Drengenberg said. "The ground-to-sky currents seem to provide a 'read' about whether objects on the ground are good or poor conductors of electricity. Unfortunately for us, humans, because of the high mineral content of our blood , are generally good conductors. That is the primary reason that we are struck by lightning."

"Even when humans are not the tallest object in a landscape, they're are the best conductor of electricity on the scene," he added.

The National Weather Service, which calls lightning a random, chaotic and dangerous fact of nature, says U.S. lightning detection systems monitor an average of 25 million strokes of lightning from the cloud to ground every year.

Which, if you're counting, gives you about 25 million reasons to prepare in advance for thunderclouds approaching your neighborhood.

More information

You can get additional insight into lightning safety moves from the National Lightning Safety Institute.

(SOURCES: Martin Uman, Ph.D., professor, department of electrical and computer engineering, and director, Lightning Research Center, University of Florida, Gainsville; John Drengenberg, manager, consumer affairs, Underwriter's Laboratories, Northbrook, Ill.; National Lightning Safety Institute, Louisville, Col. )

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