According to the above analysis, the process to determine the improper degree of domino effect is as below:
(1) Evaluate the primary accident risk/ domino risk for every vulnerable facility in the concentration zone, and attach a ranking number for every facility;
(2) Calculate the sum of the distances to other facilities for every facility, and attach a ranking number Ni for every facility;
(3) Bring the i and Ni that calculated by step (1) and step (2) into the equation (3) to get the Improper degree of domino effect.