The concern caused by the rising population of space debris has increased. One of the recommended mitigation measures is the safe re-entry disposal either in a controlled or uncontrolled manner. Performing a controlled re-entry, where the spacecraft is guided down to impact in a designated zone such as the ocean or a non-populated area, complies with the mitigation standards. However, it has limitations in terms of the cost of developing and ensuring reliability of a system. Therefore, an uncontrolled re-entry can be preferred as a simpler and cheaper alternative for the disposal of space debris. To reduce the casualty area of the surviving fragments, design-for-demise techniques have been proposed. From the point of view of the design-for-demise techniques, it is significant to identify and investigate the critical components that are directly related to the casualty risk. In this paper, re-entry survivability analysis of critical components has been conducted to identify the most critical ones and to understand the effects of uncertainties on casualty risk. The material properties within elements such as the propellant tanks, balance masses and payloads that can be critical components are crucial parameters. The initial conditions, relative sizes, and aerodynamic forces are also significant. In the view of engineering design, either a change of the material or a mass/size reduction is recommended to demise the components. Monte Carlo simulations are performed to evaluate the sensitivity.