Large storage tank areas are easily involved into severe accidents because of event-chains. According to the accidental escalation's law of tank accidents

the quantitative risk assessment method based on event-chains is developed. In the method

the individual risk (IR) and societal risk (SR) are calculated based on the practical accident scenarios that may occur because of event-chains. Moreover

the principals of individual risk are introduced to determine the effective scenarios

and thus many practical scenarios will be cut down. In the paper

the lightning event chain of tank areas is taken as an example. From the result

it can conclude that some common scenarios that have obvious effects are neglected and the calculated results are conservative by using the traditional method. Moreover

the planning areas enlarge obviously as the event chains are considered. Therefore

it is essential to consider the event chain especially for big tank areas.