Lightning

This article was last modified Jan 30th 2010 by Jel Coward

What are the chances?

How bad would it be......

How can I avoid it?

What can I do if I can't avoid it?

What are the chances?

Well, higher than you might expect perhaps. Worldwide there are about 100 cloud to ground flashes per second!

 Figures from Colorado are that about 45% of strikes involving people, injure more than one person.  The maximum number of people recorded injured in one strike there was 12. (Ref 1)

There are four ways that lighting can strike a victim.

• Direct strike - a direct hit
• Contact with an object - being in contact with something that is struck
  
• Side splash - lighting hits somewhere near and 'splashes' sideways to hit the person
  
• Ground current - lightning strikes the ground and runs through it, hitting the person on its' way.
  

 Injury can also happen from the blast or blunt trauma as victims are thrown or objects strike them.

It is useful to think about death from lighting strike and survival from lightning strike.

Regarding deaths

Lightning kills more people than other natural disasters such as floods, hurricanes and tornadoes (the figures vary in individual years of course).  It does so one person at a time and so does not tend to make international or national news.  Between 1993 and 2004 in the Transkei Region of South Africa, lightning accounted for 1.4% (151) of 'unnatural' deaths. That's about 14 a year or just over one a month.

the authors identified 38 deaths in a 3 year period in the South African Highveld (an area with 6-9 air to ground lightning flashes/km/year!).

A US report 'Struck-by-lightning deaths in the United States'

J Environ Health. 2005 May;67(9):45-50, 58

identifies 374 deaths from 1995-2000 which is a rate of 0.23 per million people.  Most of which were in the South and Midwest.

Regarding survived lightning strike.

Only about 10-30% of lightning strike victims are killed and most sources say it is closer to 10%. 

According to the American Meteorological Society, there are about 100 deaths a year in the US from lightning strike, which means that we can assume that, conservatively there are about 400 people a year struck. 

Further mathematics suggest we have a 1 in 3000 chance of being struck by lightning in our lifetime.  But of course, this is mathematics and not reality - risks are higher in high strike areas, agricultural and outdoor workers etc so the average couch (insert vegetable of choice) has a lower risk.

Much is about where in the world you are, and if you are in a high risk area you should be much more vigilant.

This map

http://wwlln.net/TOGA_network_global_maps.htm

shows real time lightning strikes around the world.

And here

 is a world map showing density of lightning strikes.

Lightning safety - and other lightning information.can be found at

How bad would it be?

Only somewhere between 10 and 30% of lightning strike victims are killed.  But 25% of survivors suffer long term, often debilitating symptoms.  You can minimise the risk of being struck/close to a strike and of its repercussions.

Lightning is four times hotter than the sun, lasts 0.01-0.0001 of a second, can be over 50,000 amps and occurs in a number of rapid 'strokes' - it is remarkable that it does not kill every person it strikes.

Electricity follows the path of least resistance.

As it hits the body it will flow where it can flow easiest and this can be predicted as nerves/blood/mucous membranes/muscle, dry skin and then tendon and bone - in that order.  

Lightning is of an extremely brief duration and thus although the energy is huge, it tends not to cause much in the way of burns or gross tissue destruction.  It does cause neurological disruption and cardiac arrhythmias.

Frequently seen outcomes are cardiac arrest (usually asystole but sometimes ventricular fibrillation), respiratory arrest and long term autonomic nervous system disruption (often labile blood pressure and vascular spasm).   The asystole and respiratory arrest phenomena are important in decision making when treating victims of lightning strike (see below).

Lightning strike involves a massive release of energy.  Hence victims and objects can be thrown some distance with great force.  There is potential for more usual trauma.  Anyone struck by lighting should be assessed for blunt trauma.

Long bone fractures from muscle contraction are quite common.  Similarly, posterior shoulder dislocation is not infrequently seen. (NB most shoulder dislocations ie. not in lightning strike victims,  are anterior, lightning/electrocution and seizures are two circumstances that tend to produce the more unusual posterior shoulder dislocations).

Perforated tympanic membranes are common, which is why the protective lightning strike position involves covering the ears with the palms of the hands.  It is not known if this, in reality,  provides protection of the tympanic membranes.

Keraunoparalysis is intense vasospasm (constriction of blood vessel walls) and will produce a mottled, pulseless limb which lacks sensation. This is thought to be due to hyperactivity of the sympathetic part of the autonomic nervous system and is known to resolve spontaneously.  Keraunoparalysis affects about 2/3rds of directly struck victims.

Asystole is the commonest cause of cardiac arrest following lightning strike.  It often resolves spontaneously.  Therefore cardiopulmonary resuscitation should be started promptly and continued for longer than might usually be the case in cardiac arrest in the back country.  Return of spontaneous circulation (ROSC) may occur before respiration recommences, so ventilation may need to be continued.  Because of this likelihood of recovery from asystole, the concept of 'reverse triage' is applied, whereby the victim who is apparently in full cardio-pulmonary arrest is treated aggressively, perhaps before someone who is less injured (which is not the usual way that triage is applied).

Ventricular fibrillation can also occur but is less common than asystole.  Like asystole it can spontaneously resolve in the presence of good CPR.  This is notably different than asystole and ventricular fibrillation in other settings.

Distinguishing between asystole and ventricular fibrillation in the field is unlikely to be possible. However, the treatment is the same for both (in the absence of a defibrillator) and that is early, effective CPR.

Respiratory arrest can occur and as for asystole (cardiac arrest) the focus should be on early resuscitation whenever possible - these are the commonest cause of death.  Ventilation should be provided and may need to be prolonged.   The key is to assume that cardiac and respiratory arrest will often resolve so long as we provide early, effective CPR to prevent the lack of circulation or ventilation from causing brain injury.

Burns are less usual than is often thought.  Victims can have their clothing blown off by super-heating of water vapour on the skin but often there is very little burning.  Thermal burns can occur at sites of jewellery contact.  Small punctate burns may be seen and may occur grouped together. 

Lichtenberg figures (fern like appearance on the skin) are often incorrectly said to be burns.  They are not burns and the exact mechanism by which they are produced is not understood.  They can persist from a few hours to 24 hours or so post strike. 

AL Mahajan et al  in J Plast Reconstr Aesthet Surg. 2008;61(1):111-3. Epub 2007 Jul 30 give the following Case Report.

"Lichtenberg figures are reddish, fern-like patterns that appear on the skin when a patient is struck by lightning. These appear to be a result of an inflammatory response as current spreads out causing ionisation and heat effects and damage to the small subcutaneous capillaries. CASE REPORT: A 30-year-old lady was brought to the accident and emergency department with a history of momentary loss of consciousness. All that the patient could recollect was that she had been on the phone when she heard a loud bang following which she 'blacked out'. On examination, she had characteristic cutaneous Lichtenberg figures."

Neurological injury is common.  Brief loss of consciousness occurs in about 3/4s of victims.  This is often followed by a period of confusion and anterograde amnesia (loss of memory for events following the strike).  Seizures can occur.  Cerebral infarction, hypoxia and intracerebral bleeds are frequently seen.  Brain injury also occurs from hypoxia secondarly to either respiratory or cardiac arrest.

Massive electrical injury often produces myoglobinuria (release of myoglobin from damaged muscle that then passes to the kidneys and can cause kidney failure).  It is worth noting that in comparison, this is rare in lightning strike.

Long term consequences of lightning strike are common.  Frequently victims have dysfunction of their autonomic nervous systems. Such a person may have trouble with regulation of blood pressure with episodes of hyper or hypo tension (high or low blood pressure). This can lead to symptoms such as fainting.  Psychological effects can also occur eg. mood disorders and anxiety.

Recognising the lightning strike victim. 

The victim may be unconscious, confused, have obvious injury, have their clothes blown off or have entry/exit marks.  The presence of a storm in the area is usually known but lightning may strike up to 12 miles from a storm, so it may not be apparent.

How can I avoid it?

Timing is everything.

• About 75% of those stuck by lightning are struck in the afternoon.
• Most people are stuck in summer time (although lightning can occur in winter). 

Being alert to changes in the weather and watching the clouds is probably the most useful way to anticipate storms.  Knowing local weather patterns will also help with this.

The 'flash-bang' time gives a good indication of the distance an observer is from a strike.  Light travels at 300,000 km or 186,000 miles per second and thus the lightning flash will be seen just fractionally after it happens.  Sound travels much slower (343 meters or 1,125 ft per second, in air) - this is about 1/5th of a mile per second.  So, working in miles, we can calculate the distance from the strike by dividing the flash-bang time in seconds by 5.

30-30 rule - if there is less than 30 seconds between flash and thunder, then seek shelter for 30 minutes.  This equates to 'if a lightning strike has occurred within 6 miles then seek shelter for 30 minutes'.  (30 seconds, divided by 5 = 6miles).

The 30-30 rule is useful but it would be foolhardy to use it as our only tool.  Watching the weather and predicting a storm is the important first line of defence.

In some areas of the world a useful rule of thumb is 'on by noon off by two' ie. that when summiting it is good to be down by 2pm.

Ridge lines and mountain summits are high risk areas.

Trees and other high objects.  Being close to or under an object that is higher than its surroundings increases the risk of being struck by lightning.  Being in a forest is relatively safe, but under a lone tree is relatively risky.

There is a myth that there is some sort of 'cone of protection' under lone high objects.  This is a incorrect and leads to increased risk.

Open water is a high risk location.  Being on the water in a boat makes us higher than our surroundings.  Some boats are equipped with lightning conductors to take any strike to ground.

Cave mouths are also dangerous because a strike on the ground nearby can result in current arc'ing across the cave mouth.  Being deeper in the care is generally considered a safe location.

Abseiling (rappelling) carries increased risk with ropes and gear spread out over the rock.

Mobile telephone use is not known to increase risk, but using a wired telephone inside a house does increase the risk.

Vehicles are usually a safe location, not because of their rubber tyres but because they form a Faraday cage.

Getting to low ground or a hollow in the ground affords some level of protection

Lightning detectors are available in different forms.  Some are as small as pagers.  They can warn when lightning is in the vicinity.

Groups in the outdoors should have a 'lighting plan' if there is any chance of lightning locally or within a 25 mile radius.  This should detail safe refuges, the 30-30 rule and how to behave if a strike might be imminent (see below).

http://answers.google.com/answers/threadview/id/248659.html has some descriptions of St Elmo's fire in the mountains.  It is worth reading - we don't think you will ever doubt what it is if you experience it.

What can I do if I can't avoid it?

Safe lighting position - get to a safe location if possible.  If not then crouch down with your feet connecting with the ground together and protect your ears with your hands. 

Spread out - so that if someone is struck, the others can resuscitate them.  Remembering that aggressive resuscitation efforts are indicated post lightning strike (reverse triage).

Prepare mentally for the care of lightning strike victims.

Further reading

http://www.lightning-strike.org/DesktopDefault.aspx

http://answers.google.com/answers/threadview/id/248659.html

http://www.lightningsafety.com

http://www.lightningsafety.com/nlsi_info/lightningmaps/worldlightning.html

http://wwlln.net/TOGA_network_global_maps.htm

References

O'Keefe Gatewood and Zane, Emerg Med Clin N America 22 (2004) 369-403