>To mitigate lightning hazards, it is helpful to have a basic understanding of how lightning works. Turbulence within storms leads to the formation of positive charges at the top of storm clouds and negative charges at the bottom. The high concentration of negative charges near the base of the clouds induces areas of positive charge on the earth. As the electrical potential between clouds and ground grows, storms send out invisible channels, called stepped leaders, through which electrons from the cloud travel. As a stepped leader gets close to the ground, streamers of positive charge rise from terrain features and objects on the ground toward it. When a positively charged streamer connects to a negatively charged stepped leader, the result is a return stroke, or lightning.
>What is Lightning?
>Some objects and terrain features are more likely to be struck than others. The three factors that determine susceptibility to lightning strike are height, isolation and shape. Tall objects are more likely to be struck than shorter ones, isolated objects are more likely to be struck than those close to other ones, and pointed objects are more likely to be struck than rounded ones. To dispel two common myths, lightning is not attracted to metal — metal is just a good conductor of heat and electricity, and lightning can definitely strike in the same place more than once.
>Lightning causes injuries in several different ways:
>Mechanisms of Injury
- Direct strike. A stepped leader from a cloud connects with a streamer coming from a person, and a bolt of lightning comes from the sky, striking that person directly.
- Direct contact. Lightning strikes an object such as a flagpole or fence, which conducts current into an individual touching it.
- Splash or side flash. Lightning strikes a nearby object such as a tree and arcs over the victim as it seeks the ground.
- Ground current. Where lightning hits the ground, current travels out through the earth in all directions. The current diminishes over distance.
- Blast. A lightning bolt instantly heats surrounding air to temperatures between 18,000°F and 60,000°F. This sudden rise in temperature causes rapid expansion of air, resulting in a blast (and causing thunder).
>It is much safer to be indoors than anywhere outdoors in a thunderstorm. To avoid being caught out in a storm, familiarize yourself with local weather patterns or listen to a forecast. In many areas, thunderstorms are most common in the afternoon, so plan excursions early in the day. Even if there is blue sky overhead, lightning may still be a hazard if storm clouds are in the area. It is not uncommon for lightning to strike several miles away from a storm; in rare cases, "bolts from the blue" have struck the ground as far away as 10 to 15 miles from storm clouds, possibly even farther.
>Assess Your Risk
>The high speed at which light travels means lightning is visible almost instantaneously, no matter how far away it is. Since sound travels at about five seconds per mile, it's easy to estimate the distance to a lightning strike by counting the seconds between a flash and the associated thunder. For every five seconds you count, the storm is one mile away. It's a good idea to take evasive action when a storm comes within six to eight miles or when the delay between a flash of lightning and its associated thunder is 30 to 40 seconds or less. In the commotion of a thunderstorm it may be impossible to determine which flash of lightning is associated with which clap of thunder, so it is safest to take precautions any time there is enough lightning and thunder to cause such confusion.
>The safest place to seek shelter during a thunderstorm is inside a large, permanent structure. If no such building is available, a vehicle with a metal top and the windows rolled up is probably the next best option. Contrary to popular belief, it is not the rubber tires that make cars reasonably safe during lightning storms, but the metal structure. When lightning hits a car, the current is generally able to reach the ground fastest by moving around the sides of the vehicle rather than moving through the inside. Rubber tires could not provide adequate insulation against the 30,000 amps lightning strikes commonly deliver.
>If you're out in the backcountry and cannot get to a building or a vehicle, the safest places to find shelter are among low, rolling hills or in areas of forest where the trees are of roughly equal height. Since lightning is most likely to strike the highest object in a particular area, stay away from open areas to avoid being the tallest object. You don't want to be close to the tallest object either, so keep away from isolated towers or lone trees as ground current and splash are responsible for the vast majority of lightning injuries. High peaks and exposed ridges are bad places to be. Also keep clear of areas where one type of terrain or ground cover borders another such as shorelines and the edges between forests and fields. Finally, avoid long conductors, too; fences, cables, railroad tracks and even wet ropes can conduct current significant distances. Make sure to consider lightning risk when picking a campsite.
>While finding a safe location is the priority when a thunderstorm approaches, there may also be some benefit to getting into a lightning position. Squat down to minimize your height, and limit your contact with the ground to as small an area as possible. A few feet of height reduction can be sufficient to lower your risk of being struck. Minimize your contact with the ground by keeping your feet close together; this can reduce your risk of being injured by ground current. Some sources advise placing your hands over your ears to reduce the risk of ear injury from blasts. Members of a group should separate at least 50 feet apart to reduce the likelihood of multiple victims. Although lightning position can be uncomfortable, it is best to stay in it when outdoors during a thunderstorm that is within six or eight miles.
>On a boat, go below decks or, if possible, into the cabin. Avoid tall objects such as masts, outriggers and antennas; these should be lowered if possible and if there is time to do so safely. Move toward the center of the vessel, as far as possible from electrical equipment, the water and anything metal. Stay off the radio unless there is an emergency; if you're holding the handset, your body may be the shortest path between the antenna and the ground. Some boats, sailboats in particular, are equipped with a lightning protection system designed to act as a conduit for a strike. Such systems reduce the risk of injury to people and damage to the vessel by presenting an unobstructed path from the highest point onboard down through the hull into the water. If a lightning protection system is present, don't touch any of its components.
>Avoid diving or being in the water during a storm. It's hard not to be the tallest object around if you're on the water, and current can travel significant distances over water's surface. Some might think it is a good idea to stay underwater as lightning does not tend to penetrate very deeply into the water column, but this is not practical in most situations. Gas supply, no-decompression limits, body temperature and stamina are all more important considerations. If you surface from a dive in a storm, it might be reasonable to consider continuing to dive at 20 to 30 feet, especially if you surfaced far from the boat or shore and have reason to believe the storm will be short-lived or is quickly losing intensity. However, this approach should be considered only if all safe diving guidelines can be followed; getting out of the water quickly generally is a better option.
>Victims of lightning strike are safe to touch; they do not carry a current. Administer first aid to anyone injured by lightning, and then get them to a doctor. Lightning can cause the following types of injuries:
- Burns. Electrical burns can occur anywhere on the body. Punctate, or point, burns may result where lightning enters or exits the body. Unusual feathering patterns may appear on the skin. Secondary burns from contact with metal or burning material can also occur. Apply copious water to cool burns.
- Cardiopulmonary and neurological emergencies. The cardiovascular and nervous systems are electrical systems, and the brain controls the respiratory drive. The high current of a lightning strike may cause cardiac or respiratory arrest; immediate rescue breathing or cardiopulmonary resuscitation (CPR) is critically important to these individuals. Lightning may also cause nerve and brain injuries, which can result in motor, sensory, cognitive and psychological problems.
- Trauma. The blast from a lightning strike can cause serious traumatic injuries. Strike victims may be thrown significant distances. Standard treatment recommendations for wounds and musculoskeletal injuries apply.
- Eye/ear injuries. In addition to the flash we see on the visible spectrum, lightning emits infrared and ultraviolet (UV) radiation as well. These UV rays can cause eye injury. Blasts may perforate eardrums. Eye or ear injuries require prompt evaluation by a physician.
>© Alert Diver — Summer 2011