Watch for lightning as summer, rainy season approaches

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Photo by Bill Purtyman, Emergency Management and Response (S-8).

Lightning is one of the most under-rated severe weather hazards, according to the National Weather Service. In the United States every year, lightning kills more people than hurricanes or tornadoes.

One ground lightning strike can heat its path five times hotter than the surface of the sun and generates between 100 million and 1 billion volts of electricity.

Lightning depends on the vertical development of clouds. During summer months, precipitation comes primarily from clouds that have vertical development caused by convection. Ice is a key element in the development of lightning. In a storm, the ice particles vary in size from small ice crystals to large hailstones. In the rising and sinking motions within the storm there are many collisions between these particles. This causes a separation of electrical charges between the upper end and lower region of the clouds. The negatively charged electrons collect at the cloud base.

A moving thunderstorm induces a positive charge along the ground. As the positive charge builds up, it moves up taller objects such as trees, houses, telephone poles and even people. The negatively charged area in the storm sends out an invisible charge toward the ground called a stepped leader. When the leader gets close to the ground, it is attracted by all the positively charged objects and a channel develops. The electric transfer occurs through this channel as lightning.

There have been four employees struck by lightning within the last 15 years on Laboratory property -- one on a telephone, one on a crane, two inside a building that was struck by lightning and three bicyclists who were struck by lightning while standing under a tree.

The Laboratory has a lightning stroke counter at Technical Area 6 that responds to cloud-to-cloud or cloud-to-ground strokes within a 30-mile radius depending on atmospheric conditions. A lightning flash may contain between one and 30 strokes with an average of four strokes per flash. The stroke counter measures, on average, more than 25,000 lightning strokes per year, 97 percent of which occur between May and September. Eighty to 90 percent of summertime lightning activity occurs between noon and 9 p.m.

When the threat of thunderstorms develops, the following precautions should be taken, according to the National Weather Service:

• if your hair stands on end or you feel a tingling sensation, lightning may be about to strike. If no shelter is available squat down with feet together and place hands over ears to minimize hearing damage from thunder. This also reduces your chances of being struck or becoming a conductor for nearby lightning strikes;
• remember the "30/30" rule. If lightning is sighted and its accompanying thunder arrives in less than 30 seconds, the lightning is within six miles and shelter should be taken. Remain in that shelter for 30 minutes after the last clap of thunder;
• avoid projecting above the surrounding terrain as you would if standing in an open field or on a mountain top;
• stay away from open water;
• if indoors, avoid water and stay away from doors and windows. Don't use telephones with cords and take off headsets. If possible, turn off appliances;
• computers, power tools and televisions because an exterior lightning strike of electric or telephone lines can induce shocks to indoor equipment;
• stay off motorcycles and bicycles, tractors and other metal farm or construction equipment;
• put down golf clubs and take shelter. Metal-spiked golf shoes increase the probability of being struck;
• don't stand under natural lightning rods such as tall, isolated trees;
• avoid taking shelter in small structures that are isolated in an open area;
• if in a forest, seek shelter in a low area under a thick growth of small trees; if in an open area, seek a low place such as a ravine or valley but stay alert for possible flash flooding.

Laboratory employees and subcontract personnel who work outdoors should be especially alert to the possibility of being struck by lightning. Heavy equipment vehicles and cranes serve as grounding paths for lightning because of their metal construction and girth.

Ninety percent of lightning victims survive the lightning strike. Individuals struck by lightning do not carry a charge, and it is safe to touch them to provide medical treatment. Providing first aid to the ones who look dead may revive them. This would involve cardiopulmonary resuscitation because the lightning may cause his or her heart and lungs to stop functioning.

To read a LIG on lightning safety, click here.

--Kathy DeLucas and Steve Sandoval