Investigating the current and potential distribution of lightning on a building to determine adequate protective measures

Abstract

Lightning is one of the most powerful and spectacular natural phenomena that mankind has ever encountered. Approximately 3 billion lightning flashes occur around the world every year. In South Africa, lightning is responsible for millions of deaths, which is significantly more than the global average. In particular, Bloemfontein is classified as having a high susceptibility to direct lightning strikes, making it a focal point for imposing lightning education and protection measures, owing to the city's rapid population growth. The challenge exists when people are not educated in lightning protection measures and is considered last when constructing new structures, thus leaving a blank space when it comes to budgeting. There is a widespread misconception that people are immune to the effects of lightning because they are protected by structures and believe that lightning will never come into direct contact with them or have any impact on their daily life. This research’s first objective is to identify appropriate buildings that would clearly distinguish the type of impact that lightning would have on a building, considering various structural and environmental factors. The second objective is to propose a lightning protection system (LPS) for each building based on the outcomes of the lightning risk analysis. The third objective is to conduct a lightning analysis on the pre-defined buildings to outline the types of buildings that are highly susceptible to lightning side effects. The fourth objective is to evaluate the proposed LPS in terms of mitigation to demonstrate the economic impact that lightning would have on a building and focus on the various ways it could interact with people, causing injuries and fatalities. To address each objective of the study, simulations were performed with appropriate computer-based software. A lightning risk analysis was performed using the DEHNsupport Toolbox software to determine the occurrence of lightning strikes, the source of damage and identify the lightning-related risk components for buildings that will be occupied by people. This analysis was performed in accordance with the methods outlined in the lightning standard SANS 62305. The analysis focused on three specific buildings: Boet Troskie Hall, the Free State Provincial Government and Loch Logan Park. After establishing the lightning sources and risk components, a proposed LPS was implemented on the buildings using architectural software, SketchUp, which was the subject of the lightning simulation study. The lightning study was carried out with an earthing and lightning simulation software, XGSLab, focusing on the frequency and time domains and considering a first negative lightning impulse of 50 kA to visualise the engineering aspects of the current and potential distribution across the LPS. It was concluded that each building considered for the analysis showed differing results. First, the ground potential rise (GPR) is highly dependent on the earthing resistance by altering the number of conductive materials buried in the soil surface and the magnitude of impulse injected into the LPS. Secondly, the quantity and length of a down-conductor had a significant impact on the current distribution and potential difference simulated at selective points over the LPS. The separation distance that needs to be maintained to prevent dangerous sparking of any metallic elements, resulting in unsafe conditions for people, electrical and electronic equipment, depends on the length of the down-conductors. Thirdly, the current distribution measured over each down-conductor in the LPS for each building did not exhibit any significant variation from the current injection point and the conductors further away. However, as demonstrated on three buildings, adjusting the length and quantity of the down-conductor produced varying results. Communities should acknowledge the impact of lightning strikes and the extent of damage that could be inflicted on a structure and the consequences that can result from a lightning event. This implementation of an adequate, compliant LPS should be paid attention to by adhering to the appropriate standards. It is recommended not to be designed or implemented with a lack of knowledge, as the effects of lightning may outweigh the benefits, considering the expense of the system.