The role of control room operator's in many complex, highly-automated plants is predominately on process monitoring and supervision. The performance of the plant operator under critical situation is significantly affected by poor HMI (Human Machine Interface), high alarm rates, fatigue, stress, high workload and harsh environments. Lately, there are significant developments in HMI design leading to a user friendly display in the control room; however, less attention is paid towards understanding the cognitive behavior and attention level of the plant operators which could be used in development of HMI. The cognitive abilities of the human are limited and therefore, it is necessary to understand the mental state of the operator. Negligence to realize the operator capability and attention could result in a workload bombardment and probably lead to accidents like Esso Longford & Texas City refinery explosion. © Copyright American Institute of Chemical Engineers. All rights reserved.