As far back as 1909, lightning-to-thunder distance calculations were used to determine if a distant lightning strike presented a clear danger. Today, some call this the flash-to-bang lightning warning method or what is commonly known as the 30-30 Rule for lightning safety.
It is helpful to examine the history of the data challenging these old detection practices and exactly how lightning prediction technology has dramatically changed the statistics relating to lightning tragedies. We will also consider how prediction-based education has made people more aware of lightning's true nature than at any time in history. The objective is to differentiate the true data-based safety methodologies and technology from those tried-and-failed practices of years gone by.
History of Lightning Detection Technology and Associated Safety Practices
All lightning detection systems simply react to the occurrence of an actual lightning strike. Detection technology accomplishes this task by monitoring the Earth's electromagnetic atmosphere and reacting to disturbances usually caused by a lightning discharge. Some companies use light/flash detectors that see the lightning flash then wait until the algorithm determines the distance from ground zero, or the sensor location. Many companies install networks of sensors throughout the country and detect lightning, then use triangulation algorithms to locate a strike on a map and measure its amperage. All of these technologies are considered after-the-strike indicators because they can only react to a strike that has already occurred.
Single, on-site detection systems are faster in reporting than networked detection products because the sensor is right there and is not waiting for a collective sample and triangulation of multiple sensor data to report back to the customer's location via the internet. The true value such systems bring to a specific location is that it can react to lightning beyond a human's perception. If, however, an individual is outdoors on a typical ball field or park, a lightning strike within five to six miles will be immediately seen, faster than they would be notified by any detection system manufactured today. After a strike is visible, the thunder would be heard, and the distance to the lightning could then be calculated immediately. However, standing in an open field counting after seeing any lightning strike is a potentially dangerous decision.
The 30/30 Rule of Lightning Safety
Typical lightning safety guidelines trace back to the flash-to-bang warning practices, which were later re-defined as the 30/30 Rule for lightning safety. Initially, the first part of the 30 Rule (thirty seconds divided by five equals six miles) was about calculating a safe distance from a strike. Detection systems from the early 1990's to the early 2000's all used this distance as a safe warning parameter. However, the six-mile rule was far too dangerous to adhere to, so most modern lightning detection systems today use an eight-mile or ten-mile strike distance for warning purposes.
After a study in 1998 for The Severe Storms Laboratory by Ron Holle and R.E. Lopez, it was concluded that six miles was a new recommended safe minimum because lightning can easily travel more than six miles from a thunderstorm. Also determined was that 80 percent of all lightning injuries and deaths occurred away from the storm's rain shaft. This study revealed the inherent weakness in lightning detection protocols for small area warning.
The second part of the 30/30 Rule is concerning because it requires a mandatory thirty-minute wait or time out period after the last strike occurs in your overall detection range. The thirty-minute wait is not based on local data measurements of any kind, but rather a "feel good" wait period that some guess is a safe period of time to assume there is no energy left behind in the area which could attract a strike back from the storm that has passed. Historically, this practice is no better than the front-end count and perhaps even more dangerous. It also creates long waiting periods before activities can continue for no logical reason.
Lightning Prediction as the Alternative
A true lightning prediction system senses and measures the Earth's electrostatic atmosphere in the immediate area of a sensor. The Earth's atmospheric electricity that is generated before and after a storm actually creates lightning. The beginning and build-up of an impending lightning strike can be measured and quantified. Prediction systems are not based on distance to a strike (detection) but rather the time required for a strike to fully develop.
Prediction systems read the energy prior to a strike, so they do not require a live lightning strike to occur in order to provide an accurate warning of an impending lightning strike. Prediction systems also detect discharges in the atmosphere but, because they are measured from an initial energy build-up to collapse, there are very few false signals and no filtering of incoming signals is required.
Prediction systems work like intelligent, large voltmeters. As a storm builds in the distance, energy voltage is moved around the Earth's surface. The prediction system measures changes in the voltage, measures the polarity and specific movement and size of the electric fields and draws conclusions based on that local electrical data. If the local energy is growing and is attracted to a developing or an active storm in the distance, then an alert will be given 8 to 20 minutes prior to a strike hitting your immediate area. If the storm is paralleling your facility six to fifteen miles away, and there is no concentrated energy in your area, you would get no notice to discontinue play. Obviously, a detection system set to an eight-mile or ten-mile range would force one to call all outside activities.
Another possibility is that a storm is brewing twelve to twenty miles from you. If the storm decides to fire a strike from that far away at your facility, the energy required to allow that strike to occur will take time to grow and develop. Once a critical level of electricity and conductivity is achieved, a prediction system will force a suspension of play. Again, a detection system set to twelve miles misses this strike because they have no means to quantify a measurable data point at your site.
After a Storm Seems to Have Passed - The Second Half of the 30/30 Rule
As a lightning producing storm passes through your immediate area, it has discharged its electrical field (lightning) multiple times. Please keep in mind that lightning is a way for a storm with active electrical energy to return to a neutral state. Clouds with no lightning are normal and, therefore, neutral. On occasion, the storm leaves behind unused energy fields that were not neutralized by the storm.
Quite often these electric fields accumulate on flagpoles, light poles, steel structures and large trees. As the storm moves away and the standing electrical fields remain strong, they may connect with a leader from the distant storm and create a back strike. These are dangerous and often kill because they are totally unexpected. This is a predictable event because there is a measurable local data point (energy field) and the prediction system is designed to see such abnormalities. You could wait an hour after the last strike six, eight or ten miles away and still be caught off guard.
If you can't measure the local energy correctly, you can't provide an accurate All Clear. Admittedly, return strikes are not as normal as your typical localized lightning strike coming from an active overhead lightning storm. Let us step back and look at the same facility where we could have been the target of a back strike from a storm. What about the 30 minute rule on waiting after a storm passes and there is no lingering electric field left behind?
Imagine you are at the stadium and the game has been delayed for an hour. It appears to all the fans that the storm has passed though there may still be visible lightning five or more miles away. With a prediction system measuring the local electrical data points, if the energy drops below the threshold capable of producing a return strike, then it will issue an All Clear. Often, this call is forty-five minutes or more prior to a detection system employing a thirty minute wait. In the end, it all comes down to utilizing a hard data-based calculation or a feel-good time out of thirty minutes.
is President of Thor Guard, Inc., and began with the company in 1988. Bob grew up in Albany, NY, and Pittsfield, Ma. Bob graduated from the College of the Holy Cross in 1975 and now resides in Marco Island, FL. For more information, email Bob at bdugan@ thorguard.com or call 954-835-0900.