(Reuters Health) - With school starting and sporting events getting underway, vigilance and proper planning are needed to protect athletes and spectators from deadly lightning strikes, experts say.

"If there is a storm coming up, maybe plan your activity or athletic event for another day. Empower yourself. Check the local weather and stay inside," advised Katie Walsh Flanagan.

Flanagan chaired a committee that wrote a position statement on lightning for the National Athletic Trainers' Association (NATA).

Thunder should be a warning signal for all involved in outdoor activities, Flanagan told Reuters Health, because lightning can strike anyone within earshot.

It is often the youngest athletes who face the most risk, she added, because parents tend to ignore oncoming thunderstorms during little league baseball and soccer games.

"I think people are just a little bit unaware," said Flanagan, a researcher with East Carolina University. "Just because you're not getting wet, that doesn't mean you can't get struck by lightning."

She also hopes to debunk the "fable" that cell phones and other electronics attract it. "Metal has nothing to do with whether or not lightning will strike you," she said. "Holding a metal baseball bat will only increase your likelihood of being struck because now you are taller. It's the height."

Even indoor pools can be dangerous during a storm, Flanagan said. She recommends that swimmers get written proof that their pool is safe from possible electric currents running through the ground.

NATA, a Texas-based nonprofit representing more than 30,000 members, recommends that every athletic venue should have easily accessible "safe locations," such as fully enclosed buildings. If a secure building is not available, an enclosed vehicle can also provide some protection from lightning. The organization released lightning safety guidelines in an effort to help protect athletes and coaches.

John Jesenius, a lightning safety expert with the National Oceanic and Atmospheric Association (NOAA), echoed Flanagan's concerns.

"The most important thing is to have a plan and to go to a safe place when there's lightning. At sporting events, it should involve the officials, the players and the spectators," he told Reuters Health. Jesenius was not involved in developing NATA's recommendations.

Twenty people in the U.S. have died this year from lightning strikes - the U.S. averages some 25 million strikes each year. About half of all lightning-related fatalities are attributable to sports or other recreational activities.

During the development of a thunderstorm, opposite charges build up in the storm cloud and on the ground near the storm. When the difference in charges becomes too great, a channel of charge starts moving from the cloud toward the ground.

"Once it reaches the ground, the channel discharges, creating the brilliant flash that we see as lightning," Jesenius said. "Every strike has the potential to kill someone."

Lightning can even occur during snow storms.

Frank Matrise, the head football coach for Tremper High School in Kenosha, Wisconsin, said his first priority is student safety and that he takes the threat of lightning seriously. During severe weather, his student athletes take shelter in locker rooms.

"In all our practices, our trainer has a lightning meter on him. If it detects anything, we clear the field and go inside immediately," Matrise told Reuters Health. He said Tremper, home of one of the state's highest profile football teams, has never had an incident involving lightning because of their preparations.

NATA's complete position statement is available online at bit.ly/1nYoRxF.