The use of probits is essential for the study of domino effect in chemical process industries, to enable the assessment of the probability of escalation of accidents. This paper reports a more comprehensive and reliable method for formulating the probits than has been accomplished by the earlier reported methods. It is based on a larger data set, a finer level of classification of the equipment and a different method of linking the qualitative description of the damage to the quantitative probability. The probits thus obtained have significantly higher coefficients of determination (R-2) than those obtained by the previous authors, indicating a much better interpretation of the past data for calculating the probits. In most cases, the R-2 was greater than 0.9. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.