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Facts, Figures and Frequently Asked Questions about Lightning Protection
Lightning (lît’nĭng) n. The flash of light that accompanies a high-tension natural electric discharge in the atmosphere.
- The United States receives 20 million lightning strikes each year
- Between three and five percent of all commercial insurance claims are lightning related.*
- Total lightning losses in the United States reach approximately $5 billion annually.*
- A bolt of lightning can generate heat in excess of 50,000 degrees F.
- Lightning travels 90,000 miles per second!
- Lightning strikes cause more than 15% of fires in wood shingle roofed buildings.
- Talking on the telephone is the leading cause of lightning injuries inside the home.
- Standing under a tall tree is one of the most dangerous places to take shelter.
- A bolt of lightning can contain a hundred million volts of electricity.
- It is estimated that the earth as a whole is struck by an average of more than a hundred lightning bolts per second.
- Although some victims are struck directly by the main lightning strike, many victims are struck as the current moves in and along the ground.
- Lightning can- and often does- strike in the same place twice.
- The average lightning bolt is 6-8 miles long and can easily travel 25 to 40 miles horizontally prior to turning downward toward the ground.
- The temperature of lightning’s return stroke can reach 55,000 degrees Fahrenheit, more than five times hotter than the surface of the sun.
- The U.S. Department of Agriculture estimates that lightning causes over 80% of all accidental livestock deaths.
- The United States averages over 100,000 thunderstorms each year.
- The metal of an automobile acts as a “Faraday Cage” where it allows the lightning to travel over the surface of the vehicle and down to ground by jumping over the rubber tires from the metal wheels. Rubber tires have nothing to do with protecting you from lightning.
*Source Factory Mutual Insurance Co.
Frequently Asked Questions
- Do people still use lightning rods?
Yes. In fact, more lightning protection systems are installed now than ever before. Today’s lightning protection systems are inconspicuous. Since buildings today are equipped with many sensitive electronic systems, planners tend to include lightning protection systems not only to protect the structure but also to help protect the electronic systems and to keep the buildings up and running.
- Don’t lightning rods attract lightning?
No. This common misconception dates back to Ben Franklin’s day. Lightning rods simply intercept a lightning strike and provide adequate pathways to safely conduct the lightning to the ground. If lightning is zeroed in on a particular location, it will strike that location, whether there is lightning protection in place or not. It is helpful to remember that lightning travels several miles to reach the earth. Tiny objects on the ground have no influence on controlling the path lightning takes through the air.
- What do lightning rods look like?
In most cases unless you are looking for the lightning rods you can’t notice them. Lightning rods are just 12 inches tall and 3/8” in diameter. That’s not much bigger than a pencil. Placed on a roof that is 30 –50 feet high and 18 inches in from the roof edge, the rods are barely visible from ground.
There are a number of measures that can be taken to make lightning protection even less noticeable. There are different materials that can be chosen to blend with the architectural features, style and materials. For instance, tin-plated copper can be chosen to blend with gray stonework or copper blends well with dark materials.
When designed during construction all of the lightning protection system, except the rooftop terminals, can be concealed and run inside the structure. There are also ways to avoid the use of air terminals, such as substituting thick-walled metal railings for the lightning rods. Decorative finials can also be used as air terminals, making the lightning protection an architectural accent.
- If there is a steel frame in a building is it already safe?
The structural steel of a building does conduct lightning, but you need a lightning protection system to provide the necessary interconnections to make sure that the lightning is able to pass harmlessly through the building.
Without the lightning protection system, when a building is struck the lightning attempts to find a path to ground. If there are not enough interconnections providing a continuous path for the lightning to follow, there will be arcing or side-flashing. The lightning will also travel on other mechanical systems in a building such as the electrical or HVAC systems. The lightning current jumping from object to object within a building is dangerous and has been known to cause fires, explosions, etc.
- What are the odds of a building getting hit anyway?
There are satellites that monitor lightning activity all over the world. This activity is charted and provides statistics that tell just how often lightning strikes any given area. At any given moment there are 2000 thunderstorms happening somewhere in the world. The earth experiences 100 lightning flashes per second. The US alone has more than 40 million lightning strikes each year. Any given square mile in the US can expect approximately 40 strikes per year.
Some statistics regarding lightning damage include:
- Between 1992 – 1996, it is estimated by that 1.7 billion dollars were paid out by insurance companies in lightning related commercial claims.
- The Insurance Information Institute reports that approximately 5% of all commercial claims are lightning related.
- In 1996 a Federal judge upheld a judgment levied by OSHA against a Pennsylvania firm for failure to provide adequate lightning protection, after two workers were killed by a lightning caused explosion.
- The US Fire Administration reported in 2002 that it estimates 17,400 structural fires are caused by lightning each year. Dollar losses per lightning fire are nearly twice that of fires started by other means.
- What types of buildings need lightning protection?
Any structure is a good candidate for lightning protection. All buildings are subject to lightning damage. The NFPA 780 Risk Assessment guide is a useful tool in evaluating a structure’s vulnerability to lightning damage. A structures use and contents are as much a consideration as location and construction when determining lightning risk.
It is commonplace for lightning protection systems to be installed on schools, hospitals, health care facilities, airports, shopping centers, office buildings, manufacturing facilities, etc. In some parts of the country there has been a move to mandate the installation of lightning protection on certain types of buildings. For example, in Florida, lightning protection systems are required for installation on schools and health care facilities. Correctional facilities are also required to have lightning protection systems.
- How much does lightning protection cost?
Cost varies greatly depending on the location of the structure, its size, its construction, the complexity of the roof-line and the ground conditions. Costs are lower when the system is designed and installed during construction. Retrofitting a system, is very common, but tends to be slightly more expensive. In comparison with other building systems, such as security or plumbing, the lightning protection is usually less costly.
- Doesn’t the electrician take care of this?
Lightning protection does not fall under the expertise of most electricians. Lightning rods have their own NFPA standard that is separate from the National Electric Code that electricians are trained on. Lightning protection work should be performed by a lightning protection specialty contractor. ECLE recommends using a firm that works full-time on lightning protection; These firms are specialists, that are listed with Underwriters Laboratories, certified by the Lightning Protection Institute and familiar with the NFPA and UL requirements for lightning protection.
- Isn’t the purpose of lightning protection to prevent lightning from striking?
Nothing can prevent lightning from striking. If lightning is zeroed in on a particular object it will strike that object regardless of anything that is on the ground. The purpose of lightning protection is to intercept the lightning strike and carry it to ground. This is accomplished by placing the rods at regular intervals on all of the highest and most exposed parts of a structure. These rods become the most likely point for the lightning streamer to attach, since they represent the shortest path to ground. The rods are connected by a network of highly conductive cables that provide a low-resistance path to ground.
- Do I have to have all those cables running all over the roof?
Some cables are inevitable, but if the system is installed during construction much of the system can be run under the roof, leaving just the air terminals exposed. The structural steel of a building can often be used in lieu of conductors. This also limits the number of roof conductors that you will see.
- Do lightning rods really work?
Yes. The NFPA has maintained a standard for lightning protection for 100 years. The standard is continually updated and edited to incorporate new findings. For example, in the last few years, sharp-tipped lightning rods have been replaced by blunt or round-tipped rods in NFPA requirements. This is the result of field research at New Mexico Tech that has proven that blunt tipped rods are always successful in capturing a lightning discharge in comparison to a sharp tipped rod. The NFPA’s standard is based on the same practices and principles as standards for lightning protection all over the world.
The FAA, NASA, Dept of Energy, and DoD typically do not build any structures without lightning protection systems. In fact, there was a federal report issued in 2004 that reviewed the technical validity of lightning protection and concluded that lightning protection systems are critical to protecting our national infrastructure. The American Meteorological Society issued a similar paper in early 2003.
- Is lightning protection required?
Not always. There are different guidelines in different parts of the country. Some Federal agencies require lightning protection, other agencies have requirements that if lightning protection is to be installed it must comply with NFPA 780. For example, the Veteran’s Administration requires UL Master Label Certification for all lightning protection installations. The Federal Bureau of Prisons requires lightning protection systems. In Florida, the State Building Code requires lightning protection for all health care facilities including, outpatient buildings and extended care homes as well as for schools.
- What do design professionals need to know about lightning protection?
Architects and engineers should be offering lightning protection to their clients and making their clients aware that without lightning protection, their buildings are at risk. The NFPA 780 Risk Assessment guide is a helpful evaluation tool for project planners. Designers can also review lightning protection plans to ensure that the aesthetics of the building are not compromised. For example, architects can recommend the use of railings in lieu of air terminals for a particular parapet wall or the use of tin-plated air terminals to blend with the color of the roof material.
Other things to be aware of when planning for lightning protection might be provisions for chases if conductors are to be run inside concrete walls and the use of compatible adhesives as recommended by roofing manufacturers.