Two-dimensional Optical Observation of Striking Distance of Lightning Flashes to Two Buildings in Guangzhou

Abstract

Lightning can strike directly on buildings, lightning protection devices or the lateral surface of buildings, endangering buildings on the ground. Effective lightning protection measures can avoid lightning damage to buildings and prevent possible fire, explosion or other hazards. Striking distance is an important reference index in lightning protection design of buildings, which is widely used in various common lightning protection design methods, such as rolling ball method, collecting volume method, etc. With the development of social economy, there are more and more tall-object in modern cities. It becomes more challenging to accurately estimate the striking distance of buildings with different heights and to formulate more effective lightning protection schemes. Up to now, lots of researches on the attachment process of natural lightning are conducted, especially by means of optical observation, which mainly benefits from the intuition of optical data. Although a large number of observations have been made on the lightning attachment process, reports on the striking distance are still rare.Based on optical data of 21 lightning discharges on two steeple buildings, the Canton Tower (600 m, 12 cases) and the Guangsheng International Building (360 m, 9 cases) from 2012 to 2018, and data of return stroke peak current provided by Guangdong Power Grid Lightning Location System, influences of building height and return stroke peak current intensity on the striking distance are analyzed. Results show that the striking distance on higher buildings is longer, and the median lightning strike distance of the Canton Tower is about 2 times of that of the Guangsheng International Building. For buildings with a certain height, the striking distance tends to increase with the peak current increasing. Moreover, the higher the building is, the stronger the peak current of the corresponding return stroke is. The peak current of return stroke on the Canton Tower is obviously stronger than (about 1.7 times) that on the Guangsheng International Building. In the attachment process, the two-diensional average speed ratio of the downward leader and the upward leader is less than 4 at 0.1 ms before the return stroke. The number of cases with a ratio of 0 to 1 is the largest, accounting for about 65% of the total number of cases.

Keywords

• tall-object
• striking distance
• optical observation
• return stroke peak current