During summer the incidence of lightning increases around the world. Its beauty and power are the energetic release of storm clouds, and have forever been an ingredient for mythical tales and stories told by the campfire. In Scandinavian mythology, light-ning was described as the weapon of the god Thor, who was the foe of demons and hurled lightning at his enemies. However, the appeal of lightning vanishes the first time you feel the hair stand up on the back of your neck or sense the buzz of metal objects as the air around you becomes charged. These are nature’s warning signs.

LIGHTNING MORTALITY

While global reporting of non-fatal lightning strikes by victims is postulated to be ra-ther poor, it is estimated that the annual odds of being struck by are 1-in-700,000, with a lifetime risk of 1-in-3,000. The only natural disaster to take more lives each year is flooding. Despite an American review of data since 1900 that predicts lightning mortality and morbidity rates of 30 percent and 70 percent respectively, contemporary mortality and morbidity rates may actually be as low as 5 percent to 10 percent. While previous lightning fatality estimates approximated 24,000 deaths per year (2011), an updated extrapolation tool puts this estimate closer to 6,000 deaths per year, approx-imately 50 of which occur in the United States each year (1). It is believed that despite lightning being a significant cause of weather related mortality, the incidence is on a century-long downward trend. Theories to explain this include greater urbanization away from labor-intensive agriculture, and improved forecasting, education, and med-ical care. However, despite popular beliefs the contrary, lightning strikes are still rela-tively common; for perspective, you are about 264 times more likely to be struck by lightning than to win the lottery in the United States.  

LIGHTNING INCIDENCE AND ANATOMY

There are approximately 25 million cloud to ground flashes per year in the United States, although surprisingly, these account for only about 25 percent of all lightning strikes in the world. Lightning is typically formed by rapid air movement that causes a charge imbalance in the atmosphere. The dissipation of this imbalance is what leads to lightning, which is not dissimilar to rubbing a balloon on your head or walking across a carpeted floor in your socks and then touching a metal object. That spark is lightning on a micro scale. The electrical discharge from a weather front is direct current (dif-ferent than alternating current that is used in your house), nearly 100 million volts, has a temperature as high as 50,000 degrees Celsius, and lasts only milliseconds. The chal-lenge around lightning safety, strike prevention, and forecasting is its unpredictability. If you like to adventure in the outdoors there are very few places to truly be safe. Fur-thermore, common approaches to lightning safety actually do very little to minimize your risk of sequela secondary to a direct strike or exposure via other avenues such as splash or ground current. 

LIGHTNING CASE REVIEW, HANKO FINLAND

The following case review is of a lightning strike emergency in Hanko, Finland in July 2011, when a summer storm with accompanying lightening overtook a military en-campment. Eight military conscripts were injured, three of them critically, after light-ning struck a tree next to their encampment. This review is based on material pro-duced by the Finnish Safety Investigation Authority (SIA) and is publically available.

On the evening of July 1st, eight conscripts arrived at the Hanko Encampment (see be-low) to rest. The small group was involved in a march competition with a group of of-ficer students. The weather was warm and it was not raining when the conscripts ar-rived to setup camp. Earlier in the afternoon there had been a soaking rain leaving the ground saturated in the vicinity of the camp. Although the storm passed quickly a fire was held in the stove so that the conscripts could dry their clothing and gear.

Images 1 and 2: Incident location in the Gulf of Finland
(Source: Ministry of Justice/National Land Survey of Finland) 

Early in the morning hours the precipitating thunder moved into the area as a new line of rain cells began moving across the Baltic Sea from Estonia towards the west coast of Finland. The front was most dramatic between 00:30 A.M. UTC and 02:30 A.M. UTC, and the lightning density was about 11 flashes/100 km2, which is considered abundant but not exceptional. The storm front included a strong, spasmodic wind and hard rain, which are not uncommon to a Finnish summer. At the time of the incident the Finnish Meteorological Institute’s lightning locator system evaluated two powerful flashes near the tent site (see below). The black symbols represent lightning strikes while the colored portions represent intensity of precipitation. Colors (blue-green-yellow-red) correspond to various degrees of rain (drizzle-weak-moderate-heavy rain).

Image 3: Lightning and weather radar view at 02:00 UTC
(Source: Finnish Meteorological Institute) 

The initial lightning strike hit a pine tree, which was approximately 1.5 meters from the effected conscript tent. The track proceeded along the trunk towards the ground (Image 4) and then, about a meter from the surface, it jumped to the metal tent pole (Images 5 and 6). From the pole, the lightning proceeded into the tent, washing over the conscripts causing some typical injury patterns listed below. The seriousness of the situation was worsened by the damp conditions and wet soil underneath and inside the tent. The tent occupants were asleep at the time of the event and most had no recol-lection of the lightning strike.

Image 4: Pine tree with resulting 4 meter long crack from the lightning strike
(Source: SIA case report) 

Images 5 and 6: Melt marks on the tent pole
(Source: SIA case report) 

The medical officer in charge immediately made an emergency call and organized first aid procedures. Initial post strike triage was performed and one of the injured conscripts was found to be lifeless. CPR was initiated immediately. The first EMS unit arrived on scene at 02:22 A.M. UTC, 16 minutes after the initial call for help. A defib-rillator was transported to the scene but there was no possibility for electrical inter-vention secondary to asystole. There was a litany of other injuries, which included sei-zures, chest pain, superficial and partial thickness burns, confusion, numbness in the feet and hands, nerve palsy, and psychological symptoms. The remaining injured con-scripts were transported to a regional hospital by five EMS units. Of those transported, all survived, although some of their injuries were reported to plague them for months after the event.

LIGHTNING INJURIES

Common, less acute injury patterns include linear ruptured tympanic membranes, ocular injury, traumatic injury including blast perpetuated sequela, confusion, and neuro-logic deficits. Burns are often superficial and fan-like in nature, and occur in less than half of strike victims. Current tends to flow across the surface of the skin and may ei-ther directly or indirectly ignite materials close to the skin. Rapid evaporation of moisture from the skin surface can cause explosive kinetics, causing some of the infamous scenarios where clothes are blown from a victim. While direct human strikes are un-common they are often fatal when they do occur. Respiratory and cardiac arrest are the most ominous outcomes, though are potentially responsive to rapid ventilatory support. Respiratory drive may be effected for a protracted period leading to cardiac arrest if dysrhythmia doesn’t already exist. There exists little data to support the adage that prolonged resuscitation efforts actually improve outcomes in the setting of cardio pulmonary arrest in remote settings.

After Action Review, Finnish Defense Forces:
The Tent Site

Because the encampment was near a group of pine trees, it was possible for the tent to be struck by lightning indirectly via splash and/or ground currents originating at the tree. While the Finnish Defense Forces now have a directive for preparing encampments during lightning storms, at the time the regulations did not include safe distances between tent sites and stands of trees. The after-action evaluation of this incident determined that a safe distance of at least 3-5 meters should have been maintained. Further evaluation of the campsite showed that it was situated in a historically very dry pine forest with a peat floor. The hard rain earlier in the day did not absorb fully into the soil, leaving the tents to be pitched in standing water. It was also noted that there was water in the tent and that the conscripts were all wearing damp clothing at the time of the strike. As a result, it is believed that some of the lightning current was probably conducted via the water. Lastly, it was presumed that the uninsulated metal tent poles were likely a very good transmitter of current and may have led to greater conductivity of the sleeping structure. Unfortunately, the Faraday Cage Principle does not apply to structures such as tents as it does to other structures, such as large grounded buildings and automobiles.

Weather Forecasting and Standard Operation Protocols

The Finnish Defense Forces had previously identified the danger of thunder and light-ning and issued a directive in 2008 to improve safety. The directive at that time dealt with the nature of the defense forces' activities, and the related electrical storm threats and general protection measures. It also outlined responsibilities of conscripts, preparations for lighting protection, the measures through exercises and training events, activities of an accident, and an after action review. It provided information about the properties, occurrence, and guidance on protecting against lightning strikes. Unfortunately, in this situation the directive was not followed which led to the en-campment being in a high risk area. When surprised by the storm, the safest option would have been to decentralize troops moving them away from standing water and into a dense region of trees, which would have limited the risk and potential injuries if the site was struck by lightning. Environmental exposure during these events becomes a top priority as elemental exposure quickly becomes a hazard and hypothermia may be a real threat.

Lightning Strike Prevention Strategies

Generally speaking, there is very little that can be done once in a thunderstorm to mit-igate the risk of being exposed to the electrical current from a lightning strike. Steer-ing clear of electrical storms is the best prevention, which means understanding local weather patterns. In most regions you are at greatest risk when exposed on a moun-taintop or ridgeline (truly any relative high spot) between noon and 6 P.M. during the summer months, though thunder and lightning can happen even in the winter. Proper trip planning to include evacuation options are key. Keep in mind the 30 seconds:30 minutes rule (also known as the 30-30 rule) which guides us with some general light-ning safety. If the time between flash and bang of lightning is less than 30 seconds you are too close to a storm to be considered safe; the second 30 dictates you should wait 30 minutes from the last sound of thunder before resuming activity. While this may not be totally feasible in a backcountry setting, it remains a useful principle. Reduce your risk, spread out from fellow travelers, remembering to also stay warm and dry, and adequately hydrated and fed.

In urban settings, the best places to be are either inside a substantial building or a ve-hicle where Faraday Cage Principle will allow the current to travel the path of least resistance along the outside of the structure. The transition away from hardwired tele-phones limits the risk of being struck via those avenues, though the piping that carries your water still might be a viable pathway to meet Thor’s weapon of destruction firsthand.  

References:

1. Cardoso, I., Pinto Jr, O., Pinto, I., Holle, R., A New Approach to Estimate the An-nual Number of Global Lightning Fatalities. 14th International Conference on Atmospheric Electricity, August 8-12, 2011, Rio de Janeiro, Brazil

2. Finnish lightning center. 2015. http://www.flcenter.net/

3. Finnish Meterological Institute. 2015. http://en.ilmatieteenlaitos.fi/

4. Lehtinen, K. & Kokko, K. 2011. Salamanisku varusmiesten telttaan Hangossa 1.7.2011. Onnettomuustutkintakeskus. Finnish Safety Investigation Authority. www.turvallisuustutkinta.fi

5. Ministry of Justice. 2015. http://www.oikeusministerio.fi/en/index.html

6. National Land Survey of Finland. 2015. http://www.maanmittauslaitos.fi/en/kartat