Computer based control systems have been widely used in chemical processes with significant productivity improvements. However, the use of a computer introduces hazards as well as benefits. A hazard analysis framework for computer controlled processes is presented in this paper. The framework involves representation of the process, verification of the control logic, identification of safety critical events, and application of questions derived from industrial incident records. A computer tool is developed to support the hazard analysis framework. A novel modelling representation termed a Process Control Event Diagram (PCED) is described and used to express the control logic and its effect on the process. The control logic is verified by qualitative simulation based on the PCED. The whole procedure of applying the framework using the computer tool is illustrated by a case study.