Before explaining how lightning can injure or kill you, it would be helpful to see just how lightning attaches to the ground. The video below shows lightning striking a tall television tower in Rapid City, South Dakota. It was filmed at 7,200 images per second. A negatively charged leader descends from the cloud toward the ground. The negative charge results from a surplus of electrons near the tips of the leader due to the strong electric field that drives the ionization of the air. The high conductivity of the ionized plasma channel allows relatively free travel of electrons, and they shift downward along the channel through induction and more are liberated from the ambient air at the tips of the leaders through further ionization. As the negative leader approaches the ground, objects on ground and the ground itself have electrons travel away due to the strong repelling electric field. Therefore, the ground and objects become positively charged due to a deficit of electrons. When the electric field gets strong enough due to the approaching negative leader (50 – 100 m), ionization of the ambient air results in positively charged leaders initiating from the taller objects and these upward propagating leaders travel toward the descending negative leader. When a connection is made by one of the positive leaders, a bright return stroke results due to a sudden decrease in resistance along the channel path. A zone of rapidly accelerating electrons travels both upward and downward from the leaders’ connection point at 1/3rd the speed of light brightening and heating the channel to near 30,000ºC. This is the return stroke, and current along zone of electron acceleration typically reach 30 kiloamps for a few microseconds.
Once the zone of acceleration reaches the upper extent of the leader network that formed prior to the return stroke, the brightness and current decreases, but will continue at a lower value if the upper end of the leader network grows following the return stroke. This results in continuing current along the leader network, and the second high-speed video shows return strokes expanding through the leader networks followed by continued growth of the network after the return stroke. Unlike the previous example, these flashes have positive leaders (with a deficit of electrons) descending toward ground. The return stroke causes and acceleration of electrons upward along the connected channel in these examples, whereas electrons accelerate downward in first example.
With the better understanding how lightning attaches to objects on the ground and how current can continue to flow into the ground following the return stroke, the following video presentation discusses the different ways lightning can injure of kill you and what steps you can take to reduce your exposure to lightning hazards.
The 5 Ways Lightning Can Injure or Kill You
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