Quantitative assessment of loss of containment induced by lightning impact

Lightning is a frequent cause of accidents in the chemical and process industry. Fires, mainly affecting storage farms and involving atmospheric storage tanks, are the most frequent final scenario associated to such events. A recent survey of industrial accidents databases evidenced that lightning is the more frequent cause of NaTech accidents (Natural events triggering technological disasters). In spite of these protection codes, lightning strikes that hit equipment and storage or process vessels containing flammable materials caused devastating accidents at refineries, bulk plants, processing sites and other facilities. Scarce attention is dedicated in the technical literature to the quantitative assessment of the contribution that accident scenarios triggered by lightning may cause to the industrial risk. The present study is aimed at the development of a framework for the quantitative assessment of these events. Past accident data were revised to identify the equipment categories that are mainly involved in this type of accident. The development of a specific quantitative methodology for the assessment of the risk due to major accidents triggered by lightning was addressed. The methodology takes advantage of the relevant progress made in recent years in the assessment of the expected frequency. The methodology was developed within a common framework for the quantitative assessment of risk due to external hazard factors in chemical and process plants. The starting point of the methodology is the assessment of the frequency and severity of the lightning event. The standard parameter for the frequency is the isokeraunic number given by meteorological studies. The lightning severity was quantified by two parameters: current intensity and strokes number given by detection systems. Distribution functions for lightning intensity were used to assess the frequency and severity of lightning. A specific attention was given to damage models. In particular, criteria to assess expected damage intensity and consequent intensity of loss of containment were developed. Quantitative data relating the lightning energy and the damage intensity were developed. Thus, different damage states were defined, and damage probability functions were derived. Standard models for consequence analysis allowed the assessment of the physical effects of the final scenarios. Individual and societal risk figures were calculated using the conventional risk recomposition procedure made it possible to calculate.