FAQs

NO! Lightning rods don’t attract lightning to a structure; they merely provide it a safe path to ground in the event of a strike.

No, just as lightning rods will not attract lightning, they will not prevent a strike either. Nothing can prevent a lightning strike from occurring, but you can handle it safely with a properly installed lightning protection system.

No! Lower roof levels and structures are just as likely to be hit as tall objects. Lightning zigs and zags in the air looking for the lowest resistance path to ground and won’t pick its target until within 150 ft. of where it will strike.

YES! A properly protected building can withstand a multitude of lightning strikes. Major buildings like the Sears Tower or Empire State Building take dozens of strikes a year and they are still standing!

Lightning originates around 15,000 to 25,000 feet above sea level when raindrops are carried upward until some of them convert to ice. For reasons that are not widely agreed upon, a cloud-to-ground lightning flash originates in this mixed water and ice region. The charge then moves downward in 50- yard sections called step leaders. It keeps moving toward the ground in these steps and produces a channel along which charge is deposited. Eventually, it encounters something on the ground that is a good connection. The circuit is complete at that time, and the charge is lowered from cloud to ground. The flow of charge (current) produces a luminosity that is very much brighter than the part that came
down. This entire event usually takes less than half a second.

Lightning comes from a parent cumulonimbus cloud. These thunderstorm clouds are formed wherever there is enough upward motion, instability in the vertical, and moisture to produce a deep cloud that reaches up to levels somewhat colder than freezing. These conditions are most often met in summer. In general, the US mainland has a decreasing amount of lightning toward the northwest. Over the entire year, the highest frequency of cloud-to-ground lightning is in Florida between Tampa and Orlando. This is due to the presence, on many days during the year, of a large moisture content in the atmosphere at low levels (below 5,000 feet), as well as high surface temperatures that produce strong sea breezes along the Florida coasts. The western mountains of the US also produce strong upward motions and contribute to frequent cloud-to-ground lightning. There are also high frequencies along the Gulf of Mexico coast westward to Texas, the Atlantic coast in the southeast US, and inland from the Gulf. Regions along the Pacific west coast have the least cloud-to-ground lightning. Flashes that do not strike the surface are called cloud flashes. They may be inside a cloud, travel from one part of a cloud to another, or from cloud to air.

Since the 1980s, cloud-to-ground lightning flashes have been detected and mapped in real time across the entire US by several networks. In 1994, the networks were combined into one national network consisting of antennas that detect the angle from ground strike points to an antenna (direction-finder antenna), that detect the time it took for them to arrive at an antenna (time-of-arrival method), or a combination of both detection methods. The network is operated by Global Atmospherics, Inc. Flashes have also been detected from space during the past few years by an optical sensor. This experimental satellite covers the earth twice a day in tropical regions. The satellite also detects flashes that do not strike the ground, but cannot tell the difference between ground strikes and cloud flashes.

Over the continental 48 states, an average of 20,000,000 cloud-to-ground flashes have been detected every year since the lightning detection network covered all of the continental US in 1989. In addition, about half of all flashes have more than one ground strike point, so at least 30 million points on the ground are struck on the average each year in the US. Besides cloud-to-ground flashes, there are roughly 5 to 10 times as many cloud flashes as there are to ground.

Cloud-to-ground lightning can kill or injure people by direct or indirect means. The lightning current can branch off to a person from a tree, fence, pole, or other tall object. It is not known if all people are killed who are directly struck by the flash itself. In addition, flashes may conduct their current through the ground to a person after the flash strikes a nearby tree, antenna, or other tall object. The current also may travel through power or telephone lines, or plumbing pipes to a person who is in contact with an electric appliance, telephone, or plumbing fixture. Similarly, objects can be directly struck and this impact may result in an explosion, burn, or total destruction. Or, the damage may be indirect when the current passes through or near it. Sometimes, current may enter a building and transfer through wires or plumbing and damage everything in its path. Similarly, in urban areas, it may strike a pole or tree and the current then travels to several nearby houses and other structures and enter them through wiring or plumbing.

How to stay safe when lightning is around: use the 30-30 Rule! The best defense is to plan ahead and avoid exposure to lightning when a thunderstorm occurs. Know where safe shelter is located and leave enough time to reach safe shelter before your danger level is high. Don’t be an isolated tall object, and don’t be connected to anything that may be an isolated tall object. Use the ‘flash-to-bang’ method to find the distance to lightning. Safe shelter must be reached by the time a flash is within 30 seconds flash-to-bang. In most cases, then, when you can hear thunder you are no longer safe. The best shelter is a substantial building that has plumbing and wiring–in other words, one that is used or lived in by people for a major portion of the day. A very unsafe building for lightning has only a roof and some supports, but no wiring or pipes extending into the ground. A vehicle with a metal roof provides good shelter, and is much better than being in the open or in an ungrounded building, but is not as good as being in a building that is grounded by wires and pipes.

Lightning is a capricious, random and unpredictable event. Its’ physical characteristics include current levels sometimes in excess of 400 kA, temperatures to 50,000 degrees F., and speeds approaching one third the speed of light. Globally, some 2000 on-going thunderstorms cause about 100 lightning strikes to earth each second. USA insurance company information shows one homeowner’s damage claim for every 57 lightning strikes. Data about commercial, government, and industrial lightning-caused losses is not available. Annually in the USA lightning causes more than 26,000 fires with damage to property (NLSI estimates) in excess of $5-6 billion.

The phenomenology of lightning strikes to earth, as presently understood, follows an approximate behavior:

1. The downward Leaders from a thundercloud pulse towards earth seeking out active electrical ground targets.
2. Ground-based objects (fences, trees, blades of grass, corners of buildings, people, lightning rods, etc., etc.) emit varying degrees of electric activity during this event. Upward Streamers are launched from some of these objects. A few tens of meters off the ground, a “collection zone” is established according to the intensified local electrical field.
3. Some Leader(s) likely will connect with some Streamer(s). Then, the “switch” is closed and the current flows. We see lightning.

Lightning effects can be direct and/or indirect. Direct effects are from resistive (ohmic) heating, arcing and burning. Indirect effects are more probable. They include capacitive, inductive and magnetic behavior. Lightning “prevention” or “protection” (in an absolute sense) is impossible. A diminution of its consequences, together with incremental safety improvements, can be obtained by the use of a holistic or systematic hazard mitigation approach, described below in generic terms.

The Need for Lightning Protection:

Lightning can strike anywhere on earth – event the North and South Poles! In any U.S. geographical location, lightning storms occur as few as five times or as many as 100 times per year (see Fig. 1). -The Northeast United States has the most violent thunderstorms in the country because of the area’s extremely high earth resistivity (see Fig. 2). High earth resistivity (the earth’s resistance to conduct current) increases the potential of a lightning strike. If struck, structures in these areas will generally sustain more damage when there is no lightning protection system present.

Each year, thousands of homes and other properties are damaged or destroyed by lightning. It accounts for more than a quarter billion dollars in property damage annually in the United States. Lightning is responsible for more deaths and property loss than tornadoes, hurricanes and floods combined, but of these violent forces of nature, lightning is the only one we call economically afford to protect ourselves against.

Some properties have a higher risk of lightning damage. When considering installation of a lightning protection system, you may want to assess this risk. A risk assessment guide for determining lightning loss for all types of structures can be found in Appendix I of the National Fire Protection Association’s Lightning Protection Code, NFPA 780. This guide takes into consideration the type of structure, type of construction, structure location, topography, occupancy, contents and lightning frequency. Information may be obtained from tile NFPA, I Batterymarch Park, Quincy, MA, 02269, (800) 344-3555.

Lightning is the visible discharge of static electricity within a cloud, between clouds, or between tile earth and a cloud. Scientists still do not fully understand what causes lightning, but most experts believe that different kinds of ice interact in a cloud. Updrafts in the clouds separate charges so that positive charges moves end up at the top of the cloud while negative flow to the bottom. When the negative charge moves down, a “pilot leader” forms. ‘This leader rushes toward the earth in 150-foot discrete steps, ionizing a path in the air. ‘The final breakdown generally occurs to a high object the major part of the lightning discharge current is then carried in the return stroke which flows along the ionized path.

A lighting protection system provides a means by which this discharge may enter or leave earth without passing through and damaging non-conducting parts of a structure, such as those made of wood, brick, tile of- concrete. A lightning protection system does not prevent lightning from striking; it provides a means for controlling it and preventing damage by providing a low resistance path for the discharge of lightning energy.

FIG. 3 Lightning protection system for a dwelling: 1) air terminals spaced 20 feet apart along ridges and within two feet of ridge ends; 2) down conductors; 3) minimum of two groundings at least 10-feet deep; 4) roof projections such as weather vanes connected to system; 5) air terminal located within two feet of outside corners of chimney; 6) dormers protected; 7) antenna mast connected to roof conductor:- 8) connect gutters or other grounded metals as required; 9) surge arrester installed at service panel to protect appliances; 10) transient voltage surge suppressors installed in receptacles to which computers and other electronic equipment are connected.

FIG. 4 Lightning protection system commercial/industrial installation 1) air terminals spaced 20 feet apart around the perimeter of the building; 2) down conductors; 3) ground rods at least 10-feet deep; 4) art handling units bonded to system (may be in need of air terminals mounted on unit); 5) air terminals mounted within two feet of outside corner; 6) mid-roof conductor and air terminals at maximum 50-foot spacing; 7) grounded metal bodies bonded into system; 8) surge arresters installed at main electrical panels; 9) transient voltage surge suppressors installed in receptacles to protect computers and other office equipment.

UL’s Master Label Program for lightning protection involves periodic factory testing and inspection of system Components, along with field inspection components of completed installations. The program requires that all installers comply with UL’s internationally recognized Standards for lightning protection components and systems. UL,’s field representatives countercheck compliance with these Standards.

As a home or building owner, you should make sure that your installed system complies with the UL requirements. Here’s how:

Make certain that your installer is listed by UL and that a Master Label application is submitted to UL for your installation.When You request a Master Label for your system, your installer will ask you to sign the owner’s statement on the Master Label application form. The fourth (yellow) copy of the application is for your records. This should be done before the installer submits the Master Label application to UL for issuance of the Label. Make sure you receive the Master Label from the installer and place it on the protected structure as requested.

Buildings that are changed structurally or provided with additions can be re-examined under UL’s Reconditioned Lightning Protection Program. Under this program, the entire system must comply with the current UL Standards.

Install a UL Master Label Lightning Protection System that complies with current nationally recognized codes. Lightning protection systems consist of air terminals (lightning rods) and associated fittings connected by heavy cables to grounding equipment, providing a path for lightning current to travel safely to ground.

Install UL Listed surge arresters at your service and telephone equipment to prevent surges from entering the home or other buildings oil power or telephone lines. Surges are diverted to ground, and both wiring and appliances are protected.

Install UL Listed transient voltage surge suppressors in receptacles to which computers and other electronic equipment are connected in order to limit the voltage to 11/2 times the normal (maximum for solid state devices).

Look for the UL Mark. Remember, your lightning protection system may be installed using UL,’s requirements, but the system is not a Master Label system unless installed by one of UL’s Listed installers and a Master Label has been sent to you. Always “Look for the Master Label” on your lightning protection installation.