Lightning – A Force to be Reckoned With!
We all like to watch the fireworks that a summer lightning storm can provide. A lightning strike is also a potentially dangerous event.
A Few Lightning Facts:
• Lightning is a giant discharge of electricity accompanied by a brilliant flash of light and a loud crack of thunder. The spark can reach over five miles (eight kilometers) in length, raise the temperature of the air by as much as 50,000 degrees Fahrenheit (27,700 degrees Celsius), and contain 100,000,000 electrical volts1.
• Lightning detection systems in the United States monitor an average of 25 million strikes of lightning from clouds to ground during some 100,000 thunderstorms every year. It is estimated that the Earth, as a whole, is struck by an average of more than a hundred lightning bolts every second.
• The odds of becoming a lightning victim in the U.S. in any one year are 1 in 700,000. The odds of being struck in your lifetime are 1 in 10,0003.
• Lightning can kill people (over 3,696 deaths were recorded in the U.S. between 1959 and 2003) or cause cardiac arrest. Injuries resulting from being struck by lightning range from severe burns and permanent brain damage to memory loss and personality change. About 10 percent of lightning-strike victims are killed, and 70 percent suffer serious long-term effects. About 400 people survive lightning strikes in the U.S. each year1.
• Lightning is not confined to thunderstorms. It’s been seen in connection with volcanic eruptions, extremely intense forest fires, surface nuclear detonations, heavy snowstormsand in large hurricanes.
• Lightning is the leading cause of farm fires.
Lightning can cause a great deal of damage in a farm environment. A lightning strike can start fires in buildings, damage electrical equipment and electrocute humans and livestock. Losses from lightning can be very costly. Replacing buildings, equipment or livestock incurs considerable expense and time. Farm operations are likely to be severely disrupted. Human life cannot be replaced. Fortunately, most losses caused by lightning strikes can be prevented by installing proper lightning protection systems.
Per the National Agriculture Safety Database, lightning can enter a building in one of four ways:
1. It can strike a metal object on the roof;
2. It can strike a building directly (called a direct strike);
3. It can strike a tree or silo near the building and jump to the building. This occurs when the building provides an easier path to ground; or
4. It can strike a power line or a wire fence and follow the line or fence to the building. 2
A lightning protection system can help protect your property by directing the lightning into the ground and dispelling electrical charges away from your property. Consider connecting silos to your lightning protection system as well to help prevent jumps in the current to other property. It is also possible to extend protection to trees (think of the lone tree in the pasture, under which livestock gather).
Understand Lightning Protection Systems
There is nothing complicated or unusual about a lightning protection system and there are many companies which can offer assistance in choosing and installing a system which will work best for your property. Lightning protection systems consist of five parts:
1) Air Terminals: Air terminals are rods or tubes of metal that are installed at every projecting high point of a building, such as roof peaks, chimneys, dormers, ventilators, gables, flagpoles, towers and water tanks. To be effective they must not be spaced too widely apart;
2) Conductors: Conductors connect air terminals with the ground. Conductors are copper or aluminum cables. Galvanic action will occur between aluminum and copper; therefore, only one metal should be used for the system;
3) Ground Connections: These connections provide contact with the earth for dissipation of the lightning charge. Usually, at least two ground connections are needed for any building, more for large or complex structures. They should be apart from building foundations and extend deeply enough to reach moist subsurface earth no matter how dry the weather.
4) Bonding: Bonding is the interconnecting of metal parts to prevent “side flash”.
5) Arrestors: Lightning arrestors guard against damage that might occur by way of the electric power lines. Properly designed lightning arrestors should be placed between the power circuit and the ground where the circuit enters the building. Large trees need protection from lightning. In addition, trees that are taller than, or within 10 feet of a building, need protection to prevent flashover. Lightning may also cause a tree to fall on a building.
Wire Fencing & Lightning
According to the National Ag Safety Database, wire fencing surrounding livestock pastures presents a significant hazard to livestock and humans if struck by lightning. An ungrounded wire fence can transmit current from a lightning strike a distance of almost two miles. Wire fences supported by wooden or steel posts in concrete are not grounded. The best method for grounding wire fences is to drive ½ to ¾ inch steel rods or pipes next to a fence post at least 5 feet into the ground. Once driven into the ground, the fence wiring should be securely fastened to the rod. This process should be repeated every 150 feet to be most effective. Using a galvanized steel fence post every 150 feet will also provide the same protection. See Diagram 2.
IMPORTANT: Electrified wire fences should not be grounded in the manner described above because they already include a “path to ground” in their circuitry.
Protecting humans from injury or death during a lightning storm is also important factor to which you should attend. Here are a few safety tips for you and your employees to remember when lightning starts to crack:
- Stay away from water faucets, telephones, or electrical appliances and lamps. All of these items conduct electricity from outdoor conductors and can transmit electricity from a strike.
- Stay away from chimneys, fireplaces and stovepipes. Lightning will often strike chimneys which can then funnel the bolt to inside the home or building.
- If you are in a car during a storm with lightning, try to remain there until the storm passes.
- If you are caught outside and no shelter is available, seek a low place away from lone trees and fences and lie down.
Find The Right Resources
Does your farm have adequate lightning protection? It is never too late to evaluate your needs and the available protection. Proper lightning protection is not a “do-it-yourself” job. A safe and effective system should be designed and installed by professionals. Here is a list of resources that provide useful information on codes and standards that a lightning protection system should follow:
LPI-175: The lightning protection code, published by the Lightning Protection Institute.
NFPA 78: National Fire Protection Association Lightning Protection Code.
ASAE EP381: American Society of Agricultural Engineers, Engineering Practice.
96AUL: Requirements for Master Label for Lightning Protection, developed by Underwriters’ Laboratories.
Lightning is a dangerous force that should be given serious consideration. You can take several simple steps to protect your family, employees, buildings and livestock. Ground your building high points and (non-electrified) wire fences. A small investment can protect your farm from a lightning disaster.
Have you or anybody you know been affected by a lightning strike?
1 National Geographic News http://news.nationalgeographic.com/news/2004/06/0623_040623_lightningfacts.html
2National Ag Safety Database http://nasdonline.org/document/1892/d001825/lightning-protection-for-farms.html
3National Weather Service http://www.lightningsafety.noaa.gov/medical.htm
Acadia is pleased to share this material with its customers. Please note, however, that nothing in this document should be construed as legal advice or the provision of professional consulting services. This material is for general informational purposes only, and while reasonable care has been utilized in compiling this information, no warranty or representation is made as to accuracy or completeness. Distribution of this information does not constitute an assumption by us of your obligations to provide a safe workplace. Maintaining a safe workplace in accordance with all laws is your responsibility. We make no representation or warranty that our activities or recommendations will place you in compliance with law, relieve you of potential liability or ensure your premises or operations are safe. We exercise no control over your premises or operations and have no responsibility or authority to implement loss prevention practices or procedures.