The future space debris environment will be governed by the production of fragments coming from massive breakups. In order to identify the most relevant parameters influencing the long term evolution of the environment and to assess the criticality of selected space objects in different regions of the circumterrestrial space, a large parametric study was performed. In this framework some indicators were produced to quantify and rank the relevance of selected fragmentations on the long term evolution of the space debris population. Based on the results of the fragmentation studies, a novel analytic index, the Criticality of Spacecraft Index (CSI), aimed at ranking the environmental criticality of abandoned objects in Low Earth Orbit (LEO), was formulated. It takes into account the physical characteristics of a given object, its orbit and the environment where this is located. The results corresponding to a sample of LEO objects in the initial population at the epoch of January 1, 2020 and mass larger than 100 kg are shown.