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Human Voltage What happens when people and lightning
One of a series of stories covering the quadrennial International Conference on Atmospheric Electricity, June 7-11, 1999, in Guntersville, Ala.
According to a study entitled "Demographics of U.S. Lightning Casualties and Damages from 1959 - 1994," by Ronald L. Holle and Raúl E. López of the National Severe Storms Laboratory and E. Brian Curran of the National Weather Service, males account for 84% of lightning fatalities and 82% of injuries.
Men can take comfort in the fact that the actual number of deaths and injuries from lightning strikes has decreased in the past 35 years. Holle's team attributes 30 percent of the decrease in lightning deaths to improved forecasts and warnings, better lightning awareness, more substantial buildings, and socioeconomic changes. They attribute an additional 40 percent to improved medical care and communications.
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Says Gourbière, "The pathology of lightning, or keraunopathy, is known only to a few specialists."
Most doctors are more familiar with electrical shocks, such as those received by industrial workers when they have an accidental run-in with high-voltage equipment. But lightning injuries are not the same as electrical shocks. For one thing, the contact voltage of a typical industrial electrical shock is 20 to 63 kilovolts, while a lightning strike delivers about 300 kilovolts.
Industrial shocks rarely last longer than half a second (500 milliseconds) because a circuit breaker opens or the person is thrown far from the live conductor. Lightning strikes have an even shorter duration, only lasting up to a few milliseconds. Most of the current from a lightning strike passes over the surface of the body in a process called "external flashover."
Both industrial shocks and lightning strikes result in deep burns at point of contact - for industry the points of contact are usually on the upper limbs, hands and wrists, while for lightning they are mostly on the head, neck and shoulders. Industrial shock victims sometimes exhibit deep tissue destruction along the entire current path, while lightning victims burns seem to center at the entry and exit points. Both industrial shock and lightning victims may be injured from falling down or being thrown, and the leading cause of immediate death for both is cardiac or cardiopulmonary arrest.
If you survive a shock, you still have to deal with the consequences
of the electrical burns. Industrial shock burns can lead to kidney
failure, infection, muscle and tissue damage, or amputation.
Lightning burns are exceptionally life threatening (see box at
the end of this story).
Right: High voltage electrical equipment can cause severe shocks and burns slightly similar to those from lightning strikes.
Gourbière says that 70 percent of lightning survivors experience residual effects, most commonly affecting the brain (neuropsychiatric, vision and hearing). These effects can develop slowly, only becoming apparent much later.
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Feel the Burn
If you'd like to experience a lightning strike, go golfing one Sunday in July around 4 p.m. If you're really determined, be sure you do it in Florida.
Florida has twice as many lightning casualties (deaths and injuries combined) as any other state. Most lightning casualties occur in the afternoon - two-thirds between noon and 4 p.m. local standard time with a casualties maximum at 4. Sunday has 24% more deaths than other days, followed by Wednesday. Lightning reports reach their peak in July.
Many lightning victims had been walking in an open field or swimming before they were struck. Other lightning victims had been holding metal objects such as golf clubs, fishing rods, hay forks, or umbrellas. But even those not holding metal objects are as likely to be struck by lightning as a bronze statue of the same size.
When you hear thunder, you are already within the range where the next ground flash may occur. N. Kitagawa of Central Lightning Protection, Inc. and A. Sugita and S. Takahashi of Franklin Japan determined the average intervals between lightning strikes in order to estimate how much time someone has to seek shelter. Their news is far from encouraging.
"It is concluded that there exists no safe time interval during which a human is free from direct strikes," they wrote.
In an area with a radius of 500 meters (1,640 ft), most of
the intervals between lightning strikes range from 0 to 600 seconds,
with a maximum frequency of 40 seconds.
Right: The top ten states in number of lightning casualties (deaths and injuries combined). Florida leads the list, with twice as many casualties as any other state. Other states represented are Georgia, Tennessee, North Carolina, New York, Pennsylvania, Ohio, Michigan, Colorado and Texas.
To avoid being struck by lightning, you should seek shelter when you hear even the faintest thunder. Some of the best places to take refuge are enclosed buildings, or cars and buses (but don't touch the metal!). In case there are no safe spaces nearby, bend into a crouching position until there is a break in the storm.
NASA's Global Hydrology and Climatology Center - Lightning and atmospheric electricity research.
The mechanism for how towers attract lightning is not really understood. But scientists have known for a long time that towers attract more lightning than the undisturbed ground nearby.
The tale of a family in North Carolina clearly illustrates
how towers can concentrate lightning strikes. In 1998, a 42 meter
(138 ft) tall water tower was erected near Murfreesboro, NC. This tower was about 45 meters away from a farmhouse
that was situated on a one acre plot in a large open area of
farmland. The family had lived in the farmhouse for the past
10 years, and they had never experienced any lightning damage.
After the tower was erected, 5 separate discharges near the house
occurred over a period of 5 months, causing the deaths of 2 trees,
a fire in electrical equipment, complete destruction of all phone
wiring, and damage to electrical fixtures.
Right: Lightning flirts with a 335-ft tall radio tower. Credit: Jeffrey K. Herzer/Missouri State Highway Patrol Communications Division.
Lightning damages have been on the increase in the past 35 years. Holle's team attributes most of this increase to population growth. Storm Data recorded 19,814 property-damage reports due to lightning in the United States from 1959-1994. Pennsylvania has the largest number of damage reports, while the highest rates of damage reports weighted by population are on the plains from North Dakota and Oklahoma.
According to Richard Kithil of the National Lightning Safety Institute, most reports of the economic impact of lightning are contradictory and underreported. The National Weather Service Storm Data figures place the most recent yearly losses at $35 million, but the process by which this figure is tabulated is open to error. Storm Data collects much of its severe weather information from newspaper reports. If an incident is not reported in the paper or is overlooked by the Storm Data reviewer, it may not get into the publication'sstatistical base.
Kithil conducted his own study based on insurance reports and other sources that keep track of weather damages, and he came up with a much larger figure for the annual cost of lightning strikes.
"It seems reasonable to estimate that there may be $4 to 5 billion in lightning costs and losses each year in the US," said Kithil.
There are currently several different methods used to keep track of lightning strikes, but none of them can be considered perfect. Medical reports, for instance, sometimes report "burns" as the primary cause of death, with lightning listed as a secondary effect. Despite such instances of underreporting, the methods used in the United States to track lightning strikes are considered to be the best available.
"We work with people from other countries who wish they had what we have," said Holle.
Humans versus Lightning
To stand against the deep dread-bolted thunder?
In the most terrible and nimble stroke
Of quick, cross lightning?
(Wm. Shakespeare, "King Lear", Act 4, Scene 7)
Right: Photo Credit: Australian Severe Weather/Michael Bath
In the contest between people and lightning, lightning wins. Although lightning rarely strikes more than one person at a time, over the course of a year the damages, deaths and injuries add up to make lightning a serious threat. By studying the outcome of human-lightning encounters, scientists hope to find more ways to prevent such meetings from occurring in the first place.
|Most Typical Disorders Associated with Lightning Strikes|
(from "Lightning Injuries to Humans in France" by
Dr. Elisabeth Gourbière of the Electricité de France,
Service des Etudes Médicales)
Lightning deaths (~20%)
-Inhibition of brainstem respiratory centers
-Multi-system failure (delayed death)
-Arrhythmias - Arterial pressure changes
-Myocardial damages (infarction)
-Pulmonary edema - Respiratory distress syndrome
-Loss of consciousness/coma
-Numbness/Weakness in limbs/Partial or complete (but temporary) paralysis
-Spinal cord injury/Parkinsonism
-Sleep and memory disorders/Concentration
disturbances/Irritability/Depression/Various other disturbances such as headaches, tiring easily, lightning storm phobia, etc.
-Post traumatic Stress Disorder
Burns and Cutaneous marking
-Small, deep entry/exit points (typical)
-Contact, metal chain heating (typical)
-Lichtenberg figures (arborescent, fern-like markings):pathognomonic(on trunk, arms, shoulders)
-Exploded off, torn off, shredded, singed
Blunt traumas (explosion)
-Contusion, internal hemorrhage (brain, lungs, liver, intestine )
-(rarely) Fractures (skull, cervical spinal column, extremities )
Auditory and ocular injuries
-Tympanic membrane ruptured (typical)
-Transient blindness/Photophobia-Conjunctivitis - Corneal damage
-Retinal abnormalities (macular hole) - optic neuritis
"Lightning injuries are varied and take many different forms. The most dangerous (and possibly fatal) immediate complications are cardiovascular and neurologic. It must be kept in mind that only immediate and effective cardiorespiratory resuscitation (started by rescuers), followed as soon as possible by emergency medical treatment, can save victims who are in cardiopulmonary arrest, or avert the serious consequences of cerebral hypoxia. Some victims remain in a coma despite intensive resuscitation and die of secondary causes including hemorrhages and multiple lesions (encephalic, cardiac, pulmonary, intra-abdominal)."
Voltage (June 18,1999)
What happens when lightning meets people
News shorts from Atmospheric Electricity Conference (June 16,1999) Poster papers on hurricanes and tornadoes summarized.
Soaking in atmospheric electricity (June 15, 1999) 'Fair weather' measurements important to understanding thunderstorms.
Lightning position in storm may circle strongest updrafts (June 11, 1999) New finding could help in predicting hail, tornadoes
Lightning follows the Sun (June 10, 1999) Space imaging team discovers unexpected preferences
Spirits of another sort (June 10, 1999) Thunderstorms generate elusive and mysterious sprites.
Getting a solid view of lightning (June 9, 1999): New Mexico team develops system to depict lightning in three dimensions.
Learning how to diagnose bad flying weather (June 8, 1999): Scientists discuss what they know about lightning's effects on spacecraft and aircraft.
Three bolts from the blue (June 8, 1999): Fundamental questions about atmospheric electricity posed at conference this week.
Lightning Leaders Converge in Alabama (May 24, 1999): Preview of the 11th International Conference on Atmospheric Electricity.
What Comes Out of the Top of a Thunderstorm? (May 26, 1999): Gamma-rays (sometimes).
Lightning research at NASA/Marshall and the Global Hydrology and Climate Center.
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