Lightning and Lightning Safety by Gareth Stevens

CANOE NEWS Summer 2010 Vol 43/2

Special Feature from Canoe News: Lightning and Lightning Safety by Glen Green From Canoe News, Summer

Vol 43 Issue 2

CANOE NEWS

The magazine for marathon competition paddlers throughout North America

Feature Article:

Lightning and Lightning Safety

What causes lightning? Strong updrafts in thunderclouds carry water droplets upward, supercooling them. When they collide with ice crystals a slight . . . . . . . . . . . . . . . . . . . . . . Glen Green positive charge is transferred to the ice USCA Safety Committee Chairman crystals which causes the upper part of ightning is a capricious and random the cloud to become positively charged. event. It cannot be predicted with Some of the ice crystals melt with these water droplets which gravity pulls down any accuracy. It cannot be prevented. Advanced planning is the best defense. through the Earth’s natural electric field, electrically polarizing them with a Immediate evasive action could save negative charge where they accumulate a life. 25% of strike victims die, and in the lower portion of the cloud. 70% of survivors suffer serious longterm after effects. As a cumulonimbus thundercloud moves over the surface of the Earth, an Of all weather phenomena, lightning electric charge equal to but opposite the is second only behind flooding as charge of the base of the thundercloud is the leading cause of weather deaths. Lightning kills about 100 people in the induced in the ground below the cloud. The induced ground charge follows United States every year. At any given moment there are approximately 2,000 the movement of the cloud, remaining underneath it. When a multimillion-volt thunderstorms on the planet earth. Lightning strikes the Earth’s surface 100 potential develops, electrons from the cloud begin zigzagging downward in a times per second. Generally speaking, lightning activity increases with altitude forked pattern called a “stepped leader”. As the negatively charged stepped leader and as you get closer to the equator. There is no lightning at the North Pole nears the ground, it draws a positively charged streamer (hundredfoot spark) or in Antarctica. upward from the ground. As the leader and streamer come together, a powerful electric current begins flowing with an intense wave of positive charge traveling upward about 60,000 miles per second, following a charge channel about a centimeter (0.4 inch) wide. This return stroke is the most luminous and noticeable part of the lightning discharge.

This woman was reportedly injured by lightning shortly after photo taken. Being struck by lightning is often preceded by a sensation of all your hair standing on end, along your arms and the back of your neck. If you have this feeling, and you are in (or near) a thunderstorm, the chances are you have sent up a “positive streamer”. If this sudden charge connects with the electrons pooling beneath the clouds, lightning will strike. If you feel this sensation, either run as fast as you can for an inside shelter, or crouch close to the ground in the stance described later in this article. By making yourself smaller, lightning may strike another object. If the bolt does strike you, there’s a much better chance that it will pass through your body without causing as bad an injury.

75% of lightning is cloud-to-cloud lightning where there is either discharge between the positively charged upper area of a thundercloud and The return stroke is an unidirectional the negatively charged lower part of (DC) current flow with a voltage the cloud (intra-cloud), or between Lightning strike frequency map: you potential of up to 1,000 million volts clouds (inter-cloud). Also, recently can study the full color enlargement and a current of up to 200,000 amperes cameras on board the Space Shuttle on the inside back cover of this issue. that vaporizes its path with 30,000 have photographed “red sprites” and degree plasma, lasting a duration from “blue jets” – huge colorful emissions one microsecond to one second. The If you can see it, flee it; if you can hear associated with upward-moving main portion of the lightning bolt it, get clear of it. lightning coming from the tops of penetrates the earth down to the water massive thunderstorms and reaching the If you can hear thunder, lightning is table while spurs find far-reaching paths ionosphere 50 miles above the Earth. close enough that it could strike your along the surface. This is “cloud-toLightning can also occur within the ash location at any moment. Go to a safe ground lightning”. clouds from volcanic eruptions or can shelter immediately. If you wait until you see lightning, it may be already too A much rarer ground-to-cloud lighting be caused by violent forest fires which late to take action. Most people struck occurs when negatively charged ions in generate sufficient dust to create a static by lightning are not in the rain. 14% of a stepped leader rise up from the ground charge. and meet the positively charged ions in So-called “heat lightning” is just lightning casualties occur during water the cloud. activities. lightning in the distance where the Map copyright © 2009 by Vaisala; photo copyright © unknown or public dominion Article copyright © 2010 by Glen Green

Canoe News 43/2–Summer

thunder sound waves dissipate before they reach the observer. Lightning occurring during a winter snow storm is called “thundersnow”. The air near a lightning strike is heated to 50,000 degrees, which is hotter than the surface of the sun. The rapid heating and cooling of air near the lightning channel causes a shock wave which results in thunder. The electric field is strongest on groundconnected objects whose tops are closest to the base of the thundercloud, such as trees and tall buildings. Lightning rods are often attached to the highest points of objects like to the top of the Empire State Building and the Washington Monument, and even to the tops of trees in botanical gardens. Lightning rods do not attract lightning, but are mounted where there is a higher possibility of a strike. Lightning rods work as they provide a lightning strike the shortest and easiest route to the ground by offering the path of least resistance. Lightning travels on the surface of the lightning rods down through a connected heavy-gage braided copper cable to a copper ground rod that has been driven down to the water table. Recent scientific research has shown that blunt lightning rods are much more effective than pointed ones. If you are outside, upon the approach of a thunderstorm follow the 30/30 Rule: if “Flash to Bang” is 30 seconds or less – seek shelter. The safest place to go is inside a lightning-protected building. The next best choice is going into the interior of any large building, or getting into a metal-bodied car, bus, or truck. Rubber tires on a vehicle offer no protection since in a strong electric field, rubber tires actually become more conductive than insulating. It is the metal enclosure around the vehicle that provides lightning the path of least resistance to the ground. Convertibles with canvas tops, cars with fiberglass bodies, motorcycles, and bicycles offer no lightning protection. When in a vehicle during a lightning storm, close the windows and keep your hands in your lap. Wait 30 minutes after hearing the last thunder before leaving shelter, because lightning can still come

Canoe News 43/2–Summer

Lightning and Lightning Safety from cumulonimbus clouds as the storm pulls away. 5% of lightning occurs without visible clouds in the sky. Lightning can travel sideways for up to 10 miles, so it is possible for a “bolt from the blue” on the edge of a storm to strike you. This is called positive lightning and unlike the more common negative lightning, the positive charge is carried by the top of the clouds (generally anvil clouds) rather than the ground. The leader forms in the sky traveling horizontally for several miles before veering down to meet the negatively charged streamer rising from below. Because of the much greater distance they must travel before discharging, positive lightning strikes typically carry six to ten times the charge and voltage difference of a negative bolt and last around ten times longer. As a result of their greater power, as well as lack of warning, positive lightning strikes are considerably more dangerous. If you are in a canoe or kayak on a river, lake, bay, or the ocean, you are usually the tallest object around, and if you hear or see lightning, head immediately for shore and take shelter. Keep moving. Don’t stop. The chances of being struck decrease the more you move. If there are no buildings (do not go to picnic shelters) on shore to take shelter in, then find a low spot under short brush or among a more-or-less uniform stand of smaller trees. Stay at least six feet away from

any tree trunk to minimize a side strike. NEVER take shelter under an isolated tree. Other options include crouching in a low area, ditch, depression, ravine, or the foot of a hill. If once on shore you find you are out in the open, squat low to the ground on the balls of your feet. Have your heels touch. Place your hands over your ears, head bowed and mouth open (to help prevent a burst eardrum). Eyes closed to prevent sight damage. If the hair on your arm stands on end which would indicate an immediate close strike, hold your breath to prevent breathing in superheated air that surrounds a lightning bolt. Avoid close proximity of other people – no closer than 15ft. DO NOT LIE FLAT ON THE GROUND.

Although lying flat on the ground gets you as low as possible, it increases your chance of being hit by a ground current. If you can see that on shore there are apparently no buildings, no brush, no stand of small trees, or no low areas in which to take shelter, or the banks of the river are too muddy, too steep, or too rocky to get out on, then you might be better off to stay in your watercraft in the river and continue paddling until you reach a bridge or even a high tension line crossing the river overhead. You can stay in your boat sitting on your foam filled PFD under the bridge or high tension lines (electrical towers usually have lightning protection

Lightning and Lightning Safety

Although lightning cones of protection have been used for over 100 years, and are currently promoted by some, much confusion still remains as to their effectiveness, particularly as applied to personal protection. Other organizations like the United States Power Squadrons say that lighting rods on a tall object like a grounded metal mast on a sail boat or a grounded metal whip on a powerboat protects areas within its cone: • 60 degree cone is 99% effective • 45 degree cone is 99.9% effective MYTH: Lightning hits the highest point or tallest object. Crouch position for lightning safety. installed) and wait out the storm. There REALITY: Hundreds of incidents have been recorded involving lightning is no guarantee that lightning will not hitting the trees instead of the tower bypass striking the bridge or electrical that dwarfs them, hitting ground mere towers, and strike you instead, but at least the odds of some protection are in feet away from telephone poles, and hitting ground in the parking lot of four your favor. story buildings. Diving into the water is not a good idea, The way the concept of “cone of because if lightning were to strike the water or an object close to the water, the protection” can be applied to a canoe or kayak on a river during a thunderstorm, ground current could go through your is that if a river has bluffs higher than body while it is dispersing. you are, or if there is a stand of tall trees There is a “cone of protection” concept or woods growing along the bank, then (“protected zone concept”) that an arguably you have less of a chance of imaginary cone is formed from the tip being struck by lightning if you are in of a tall isolated object to the ground the cone of protection that is formed by around that object, and the chances the trees on the bank, than if you are in are greater that lighting will strike the the river outside this cone of protection. tall isolated object rather than striking The cone of protection is located about an object within the cone. However, half as far from the trees as the trees some organizations like the National are tall (45 degree angle). It should be Lightning Safety Institute say that the repeated that a lighting bolt could still so-called cone of protection” from come down and strike you even if you lightning afforded by a nearby tall are within this cone of protection. object is fallacious, and that in reality lightning can easily strike inside the so- When a tree acts as a natural lightning rod, due to skin effect, most of the called “cone of protection”, and even if lightning does strike the tall object, you lightning currents flow through the skin of the tree and the sap wood. As a are still in danger as it dissipates along result, the bark gets burnt and may even the ground or side flash.

peel off. The moisture in the skin and the sap wood evaporates instantaneously and may get split. Stay as far away from the river bank as you can while still being in the cone of protection in order to avoid a split tree from falling on you, and to minimize the chances of any electricity that can spread out at the tree base, travel through the topsoil, through the water and shock you. Lightning is dangerous and unpredictable. Experts and “standards” bodies have not reached consensus on the subject. You however, have the power to increase your personal safety before and during a thunderstorm by avoiding large bodies of water, great open fields and areas such as golf courses, small shelters such as bus stops and dugouts, towers, flag poles, light poles, and by avoiding using electrical appliances and equipment, telephones, computers, sinks, tubs, and showers, and anything else that has conductive surfaces and conductive power. Technology can help provide an early warning system; there are pager sized lightning detectors currently on the market for under $80 which can be clipped to your lifejacket ad which will sound an audible alarm if there’s a strike with a corresponding LED light which illuminates accordingly at lightning distances of 20-40 miles, 12-24 miles, 6-12 miles and within 6 miles. During an electrical storm, we had best observe Bre’r Fox’s advice closely: “Lay low, an’ don’t say nuffin.” The pocket-sized StrikeAlert personal lightning detector.

The “cone of proctection” concept.

Canoe News 43/2–Summer

Lightning Frequency Distribution Map See Glen Green’s article on pages 41-43. The above map shows the frequency of cloud-to-ground strikes in the continental US over a ten-year period. As the dramatic photo to the left shows – and as USCA member Craig Creighton and his partner Kris Archibald can attest (article in the Fall 2008 issue of Canoe News, Volume 41, Issue 3, p7) – lightning can strike over water, too. Map copyright © 2010 by Vaisala Photo copyright © 2010 by F. Schaefer