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Lightning and Fires

June 24-30, 2012 is Lightning Safety Awareness Week. To promote lightning safety awareness, the NOAA has introduced a new website providing lightning safety information where you can "learn more about lightning risks and how to protect yourself, your loved ones and your belongings." This site has tips, handouts, brochures, toolkits for communities, links, and more. Check it out at: http://www.lightningsafety.noaa.gov/.

We hope you will also find the following information useful.

From Air To Ground: The Fire Potential of an Electric Sky

Hundreds of lightning strikes occur annually in southern Oregon and northern California. Some of them ignite fuel loads. There is no way to predict just when and where this will happen.



(Photo section from a photo by Bill Ostrander, ODF
Source: ODF's Oregon Forests Report 1997, Page 18)


The association of lightning with fire is well established, in both folklore and history.

Lightning was recognized as preferring to strike certain species. Numerous rituals involving oaks reflect this belief. So does the proverb:

"Beware the oak.
It draws the stroke.
Avoid the ash,
It courts the flash.
Crawl under the thorn,
T'will save from harm."

Modern candidates include wire fences, clotheslines, overhead wires, railroad tracks, isolated buildings, pools, ponds, lakes, open fields, high areas, and trees.

What causes the lightning in a thunderstorm?

Lightning strikes before thunder.

Thunder results from the air disturbance caused by the sudden heating and expansion of air during the electrical discharge; an occurrence of lightning without thunder is not recorded as a thunderstorm.

Lightning strokes occur between clouds, or between clouds and the earth.

There are many forms of lightning, such as sheet, streak, beaded, ribbon, forked, heat and globular or ball lightning.

The most typical is streak lightning; ribbon, beaded, forked, and heat lightning are variants of streak lightning.

Heat lightning is the name often applied to streak lightning far enough away so that no thunder is heard.

One of the more beneficial consequences of lightning is that it helps to fix atmospheric nitrogen into an organic form that rain can bring to earth. A less recognized function is that lightning restores electrical equilibrium to the earth.

It was calculated as early as 1887 that the earth would lose almost all of its electrical charge in less than an hour, unless the supply was replenished.

And this is exactly what happens: each hour, on a global scale, lightning discharges a fresh supply of electricity to the earth equal in quantity to the earth's entire charge.

Because air is a poor non-conductor, some electricity constantly leaks to the atmosphere, creating an electrical potential. When the potential is great enough, electricity moves back toward earth according to the gradient of the potential.

During a thunderstorm, the gradient becomes very steep, and the electrical potential discharges as lightning.

In other words, charges of opposite polarity are generated in the cloud, while the charge in the ground below the cloud is induced by the lower cloud charge. The result is effectively a giant capacitor. When the charge builds up enough, discharge occurs.

The charged cloud produces a "downward leader" which heads towards the earth in progressive steps, each step being "about 50 micro-seconds apart." Each step changes direction, resulting in the zig-zag characteristics of lightning.

The "pilot streamer" or leader ionizes a path in the air, beginning at speeds of 100 miles per second, and reaching as much as 20,000 miles per second by the main stroke that breaks down the remaining air gap, or the "striking distance," to the ground.

Maximum electrical currents of 270,000 amperes have been recorded, with electrical potentials produced by the initial current reaching an estimated 15 million volts.

It is estimated that the earth experiences some 1,800 storms per hour, or 44,000 per day. Collectively, these storms produce 100 cloud-to-ground discharges per second, or better than 8 million per day globally.

 

Myth: Lightning never strikes in the same place twice.

Fact: As it turns out, lightning is more likely than not to strike twice in the same location. Lightning favors the path of least resistance.

 

Lightning-Caused Fires:

Lightning must interact with other environmental conditions before fires can result. Ignition depends upon sufficient heat production from the lightning, weather, and fuel conditions to ignite combustible materials.

The most effective fire starters are "dry" lightning storms -- thunderheads from which little precipitation reaches the ground and which commonly occur after droughts or dry seasons. Dry lightning is especially likely when the earth's surface moisture dries out.

The lightning strokes they generate are responsible for over 10% of the total number of fires per year in the United States alone. By contrast, lightning fires account for about 20% of burned wildfire acreage.

Lightning is the leading cause of fire in the Pacific Northwest, with major dry lightning storms occurring several times each decade.

In Oregon, although lightning accounts for less than one-quarter of the total number of fires each season, lightning fires are responsible for burning about one-third more total acreage than human-caused fires are.

The following chart is an example of these statistics:

2000 Statistical Fire Summary

Cause

Number of Fires

Acres Burned

Lightning
162
3,319
Human
757
9,928
Total
919
13,247

(Source: ODF's Oregon Forests Report 2001, page 30)


Major episodes are rare, but proportionately greater change results from these larger eruptions than from the cumulative effects of minor events. Lightning fires are randomly distributed, and remote fires, of whatever size, escalate suppression costs rapidly.

Many of the most stubborn and costly fires of recent years have been the result of lightning, often of multiple lightning fires in remote areas that burned together. An example of this is the 1987 conflagration in southern Oregon, which resulted from nearly 400 lightning strikes during one afternoon.

Fuel loads have significantly increased over the last thirty years, partly due to drought-killed timber, and insect-killed timber stands that have been weakened by drought.

Prescribed burning, a normal forest management practice intended to reduce forest fuel loads, has remained minimal, resulting from fewer 'safe burning' days, which depend on factors such as air quality and wind.

Lower levels of precipitation over the last decade have further increased the forests' vulnerability to lightning. A long period of hot, dry weather combined with large amounts of dry fuels is a stage set for a lightning fire disaster.

 

Myth: Lightning that comes with rain is less likely to start a forest fire.

Fact: Any air-to-ground strike can cause fire. Often, a lightning hit is not visible immediately, due to the combustibility of the fuel base involved. Larger, greener fuels may smolder for several days before breaking out and spreading, as can thick ground duff. Rain may only limit or delay the spread of a lightning fire.

 

During the 2002 fire season, lightning from thunderstorms on July 13th alone caused over 500,000 acres to burn in southern Oregon and northern California. During the remainder of that season, over 75,000 additional acres ignited by lightning burned in this region.

SOURCES: Fire Protection Handbook, 16th ed., section 12, pub. National Fire Protection Assn.; Fire In America: A Cultural History of Wildland & Rural Fire. Stephen J. Pyne. Princeton UP, 1982; & Encyclopaedia Britannica, and the Medford Mail Tribune.


Personal and Structural Lightning Hazards

While the human skin acts as insulating material, the flesh underneath does not, and acts as an electrical conductor.

The result to a person from being struck by lightning is usually electric shock or burns or both, necessitating artificial respiration and other first aid measures.

A lightning strike can be fatal, however. Lightning kills over 200 Americans each year, and injures another 1,500.

Nearly 90 per cent of these accidents occur in rural areas.

Lightning hazard is greater in the open country, in contrast with closely built-up towns and cities. Rural farm barns are most frequently hit, because of their isolation and prominence relative to the surrounding landscape.

In hilly or mountainous areas, a building located upon high ground is usually subject to greater hazard than one in a valley or otherwise sheltered area.

Trees nearby structures have been thought by some to offer lightning protection. However, in general they represent a hazard, because the tree, if struck, would probably side-flash to the structure, since trees are not good electrical conductors. (A properly grounded lightning rod in the tree would give protection.)

Substantial damage from lightning can occur, without resulting in fire. Dry wood beams in houses struck by lightning are often severely splintered, and windows are blown outward. Such damage primarily results from pressure generated by the expanding lightning channel.

Indirect damage is also possible, such as when lightning strikes overhead wires, which can then conduct electricity to buildings. Lightning arrestors are often used to minimize such damage.

Contrary to popular belief, lightning rods do not act to prevent lightning strokes, but rather exert a local influence to direct strokes to the air terminals and then safely to earth.

Lightning rod protection (originally developed by Benjamin Franklin) consists of pointed air terminals mounted on the ridge of gable roofs or around the edge of flat roofs, on chimneys, and other elevated places likely to be struck. These are then connected together and grounded so that lightning contacting these terminals will be safely conducted to the earth without damage to the structure.

Similarly, people are usually safe within grounded steel structures and inside of vehicles with metal tops, which conduct electricity safely to the earth. The minimum thickness of metal necessary to ensure that lightning will not puncture it is 3/16 of an inch.

 

Myth: Rubber vehicle tires, rubber-soled shoes, and other rubber materials act as insulating protection against lightning.

Fact: Lightning cannot be stopped by just a few centimeters of rubber, after charging thousands of miles per second through the air to the ground.

It is the conductivity of vehicles' metal that effectively carries a lightning charge to the ground. It has to be a "closed circuit," i.e., not an open top vehicle or one made of fiberglass material, to carry lightning to ground.

The key to personal safety, if you take shelter in a vehicle, is to not touch any of the interior electrical or metal components (radio, CB, window handles, door, floor, or dashboard metal, ignition key, etc.). The motor should be turned off.

 

PERSONAL SAFETY: The National Fire Protection Association Handbook gives the following information and personal safety guidelines:

The probability of injury to an individual is in general very small, except under certain circumstances of exposure outdoors.

Within buildings of considerable size and modern construction, cases of injury are relatively rare. They are more frequent within small, isolated, and unprotected (ungrounded) older buildings, which may present a considerable hazard during thunderstorms.

During a thunderstorm, DO NOT:

Do not go out of doors or remain out during thunderstorms unless it is necessary. Seek shelter inside buildings that are protected against lightning; large metal or metal-framed buildings; underground shelters; enclosed vehicles with metal tops and bodies; or other structures or locations that offer protection from lightning.

If possible, avoid the following places, which offer little or no protection from lightning: small, unprotected (ungrounded) buildings, barns, sheds, etc.; tents and unprotected temporary shelters; vehicles with non-metal tops or open tops; recreational vehicles (non-metal or open).

Avoid use of, or contact with, electrical appliances, telephones (land lines), and plumbing fixtures (hoses, faucets, etc.). Cell phones are not affected.

Certain locations are extremely hazardous during thunderstorms and should be avoided if at all possible.

Approaching thunderstorms should be anticipated and the following locations avoided when storms are in the immediate vicinity: open fields; other open areas: parking lots, etc.; swimming pools, lakes, ponds, streams, or other bodies of water, or near edges or shores of water; near wire fences, clotheslines, overhead wires, or railroad tracks; or under isolated trees.

In the above locations, it is especially hazardous to be riding in or on any of the following during lightning: open tractors and other farm machinery operated in open fields; motorcycles, bicycles, scooters, ATV's, etc.; open boats and autos, or non-metal top autos.

If caught outdoors during a thunderstorm:

It may not always be possible to choose an outdoor location that offers good protection from lightning. In that case, follow these rules when there is a choice in selecting locations: seek depressed areas; avoid hilltops and high places. Seek dense woods; avoid isolated trees. Seek buildings, tents, and shelters in low areas; avoid unprotected buildings and shelters in high areas.

If you are hopelessly isolated in an exposed area and you feel your hair stand on end, indicating that lightning is about to strike, drop to your knees and bend forward, putting your hands on your knees. Do not lie flat on the ground or place your hands on the ground.

If you are with others, spread out 10 to 15 feet apart, so that if one person is hit by lightning, the others will not be, and can assist afterwards.

Those hit by lightning may experience disorientation, and/or may need immediate first aid, CPR, or defibrillation (heart arrhythmias and cardiac arrest are not uncommon).

Victims of lightning hits are not themselves electrically charged, and can be safely touched. Although moving accident victims is not usually advised, a lightning strike victim may need to be moved to a safer location, if it is possible to do so without jeopardizing others.

Lightning strikes can hit from miles away, with clear blue sky overhead. If you can see lightning, it's time to find shelter indoors.

Lightning can kill - why take this risk, and possibly endanger those who attempt to come to your assistance? Best advice: play it safe.

 

More Lightning Safety Information Links:


The National Lightning Safety Institute has a number of informative pages on lightning:

 

COMMON MISCONCEPTIONS AND MYTHS:

  1. Lightning never strikes twice… it strikes the Empire State Building in NYC some 22-25 times per year!

  2. Rubber tires or a foam pad will insulate me from lightning… it takes about 10,000 volts to create a one inch spark. Lightning has millions of volts and easily can jump 10-20 feet !

  3. Lightning rods will protect my ropes course…lightning rods are "preferential attachment points" for lightning. You do not want to "draw" lightning to any area with people nearby.

  4. We should get off the water when boating, canoeing or sailing…tall trees and rocky outcrops along shore and on nearby land may be a more dangerous place.

  5. A cave is a safe place in a thunderstorm…if it is shallow cave, or an old mine with metallics nearby, it can be a deadly location during lightning.

 

LIGHTNING SAFETY TIPS:

AVOID: Avoid water. Avoid all metallic objects. Avoid the high ground. Avoid solitary tall trees. Avoid close contact with others - spread out 15-20 ft. apart. Avoid contact with dissimilar objects (water & land; boat & land; rock & ground; tree & ground). Avoid open spaces.
SEEK: Seek clumps of shrubs or trees of uniform height. Seek ditches, trenches or the low ground. Seek a low, crouching position with feet together with hands on ears to minimize acoujstic shock from thunder.
KEEP: Keep a high level of safety awareness for thirty minutes after the last observed lightning or thunder.

MYTH: Cars are safe because the rubber tires insulate them from the ground.
TRUTH: Cars are safe because of their metal shell.

 

About your computer during lightning storms: (this info from Starband ISP:)

"Lightning storms can cause power surges and damage electrical devices plugged into electrical outlets. When lightning strikes on or near a power line, whether underground, in a building or running along poles, harmful power surges can be introduced on the power lines servicing your home or office.

"This causes an extremely large power surge to be presented to equipment connected to the outlets. When this happens, it's not uncommon that we hear from customers whose modems are no longer working.

"The best protection for your ... satellite modem against these surges is to unplug your modem during the storms.

"Unplugging the satellite modem may not always be possible, in which case a good backup strategy is to install a surge protector.

"You can find a great deal of advice on what you should look for when selecting a surge protector by searching the Internet. Surfing to www.howstuffworks.com and reading "How Surge Protectors Work" is a good start. This site has links to other informative resources.

"We would also like to remind people that damage to your satellite modem caused by “Acts of Nature” is not covered under warranty. Unplugging your ... modem, PC and other electronics during electrical storms and installing surge protection can help guard against expensive replacement costs."

 

More General Links:


NASA's well-written summary, "Lightning Detection From Space: A Lightning Primer."

The Center to Protect Worker's Rights has an article, "Lightning Protection: Hazard Alert." (Note: This requires Acrobat PDF software to read it.)

NASA's Space Science News article, "Human Voltage: What Happens When People and Lightning Converge."

Golf Coast Products has an informative lightning summary section.

The National Weather Service's National Severe Storms Laboratory home page and sublinks on lightning research (more links) and Questions & Answers about Lightning

The National Weather Service's Lightning Safety article, "Lightning Kills, Play It Safe."

The NWS's link to the National Oceanic & Atmospheric Administration (NOAA) National Severe Storms Laboratory's List of Links for Lightning Safety

The NWS's link to the National Oceanic & Atmospheric Administration (NOAA) National Severe Storms Laboratory's Lightning Safety: NCAA Guideline 1D

The following is excerpted from this site: "Avoid using the telephone, except in emergency situations. People have been struck by lightning while using a land-line telephone. A cellular phone or a portable remote phone is a safe alternative to land-line phones, if the person and the antenna are located within a safe structure or location, and if all other precautions are followed."

The American Meteorological Society, based in Massachusetts, has information on Lightning Protection Systems.

More general info: The Lightning Protection Institute, based in Illinois.

Bob Vila's Tip Library has a comment on installing a home lightning protection system. The following is an excerpt from Bob Vila's site:

"Lightning Protection: Installing a lightning protection system is not a do-it-yourself project, but it is very important in protecting your home from the massive damage lightning can cause. Systems vary, but they all consist of an air terminal on the roof that is connected by a copper or aluminum conductor to a 10' grounding rod driven into the ground. Have it installed and inspected by a certified specialist."

The Minneapolis Star Tribune Fixit Editor, Karen Youso, has more Home Lightning Protection info.

David O. Stilling's site, Lightning Stalker - basic lightning facts and more links.

University of Florida's Extension Agent Mary E. Crisp's article, "When Lightning Strikes," a good general overview of lightning safety.

 

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