A streak of lightning can be as thin as a ruler, carry the heat of the sun and kill in a flash.While fatal strikes remain rare, they are happening at a surprisingly higher rate this lightning season.As of Monday, 17 people have died across the United States — with Florida and Alabama tied for first with three deaths each. That number is nearly twice the average for the same time period over the past five years and twice as high as last year. The dead include anglers, hikers, campers and farm workers. Most were men and most just steps away from shelter, said John Jensenius, a lightning safety specialist with the National Oceanic and Atmospheric Administration."People are not reacting soon enough to the threat,'' he said. "They're not getting inside, which has always been a problem," Jensenius said.In Florida, three men have been killed since mid May, according to NOAA's records. Two were working on roofs in Port Orange and Bonita Springs. A third was walking near his home in Largo.Fatal strikes occur most often while people are outside for fun. Anglers, not golfers, get hit more than others, both historically and this year. A little more than half the deaths so far this year happened while people were fishing, camping or walking outside. A 12-year-old girl playing volleyball on an Alabama beach over July 4 weekend was the latest to die.What's causing the rise is not clear, Jensenius said. More leisure time could be contributing, he said, or less caution. The number of lightning strikes — about 25 million a year in the U.S. — does not seem to be a factor, he said, though researchers predict the number could go up if temperatures rise according to climate-change models.In the past seven decades, the number of deaths had dropped dramatically as scientists gained a better understanding of how lightning works and how to avoid being hit, Jensenius said. In the 1940s, an average of 319 people died each year. That number started falling in the 1950s, and by 2000 was less than 50 every year. In the past decade, the number averaged 32.While Texas claims the title of the state with the most lightning strikes, due to its size, Florida ranks first in density, fueled by the humidity and sea breezes that can stir up the atmosphere during a longer lightning season over hot months."In some places, it's over 33 lightning strikes per mile in a typical year," Jensenius said.Ground current, not direct strikes, kills most people. So running for shelter — not crouching in place — is the best plan. And seeking shelter out at the first sound of thunder is better than waiting for lightning to appear, since thunder can be heard 10 miles from a storm and lightning can easily travel that distance. If you're in a boat and can't outrun the storm, avoid metal and water. Also, rising hair is not an opportunity for goofy pictures — that means your body is carrying a positive charge trying to connect with a storm cloud's negative charge, an obvious sign danger is near.Once inside, avoid anything plugged in or connected to plumbing — as in computers or showers — that could carry current.NOAA calculates the average person has a 1-in-3,000 chance of being struck, much higher than a plane crash. But most strikes are avoidable."If you can hear even a rumble of thunder," Jensenius said, "you're in danger."Not everything about lightning is bad. Aside from its sheer beauty, lightning also helps keep the earth's electrical balance in check. Another cool fact: When it strikes the ground, lightning can fuse dirt and clay to make a hollow glass tube shaped by the path of the current, creating an archeological record of lighting across the eons.