Assessing Lightning Risk in Vulnerable Outdoor Environments

Despite large improvements in lightning detection technology and safety awareness in recent years, lightning continues to cause injuries and fatalities throughout the United States. Many fatalities occur as a result of individuals enjoying outdoor leisure activities. The assessment of lightning risk allows for the quantification of lightning danger surrounding specific circumstances and is therefore advantageous for the continued advancement of lightning protection. Existing lightning risk analyses vary in procedure, but typically use ground flash density (or isokeraunic level) in combination with variables such as the area and population of a location. One such analysis is within the International Electrotechnical Commission (IEC) Standard 62305, “Protection Against Lightning.” The section on risk management (IEC 62305-2) details an adaptable procedure to evaluate the lightning risk associated with a specified structure. A “total risk value” is calculated and then compared with a designated “tolerable risk value” to determine whether lightning protection measures must be implemented. To address outdoor locations as opposed to structures, concepts from the standard are useful but with further modifications.

For this study, we developed a lightning risk analysis method tailored to calculate a numerical value of risk associated with human safety. Concepts from existing risk assessments such as IEC 62305-2 along with original contributions are compiled and adapted into a unique analysis. The primary application discussed is in an outdoor environment comparable to those where a high proportion of lightning fatalities occur. The sensitivity of the calculation to varying lightning data sources is also examined. While other lightning risk analyses output a stagnant value in terms of annual risk, this research additionally aims to consider shorter time scales and evolving forecast scenarios. For example, the use of real time ground flash density associated with an approaching storm would produce a changing risk value with time that could be monitored with respect to designated tolerance thresholds. Ultimately, insight gained from these risk assessments can provide quantitative underpinning for strategic methods of communicating the dangers associated with lightning, thereby influencing safe human behaviors and organizational action thresholds.