Improvement of Dynamic Quantitative Risk Assessment Method: Moving Boundary Conditions.

Improvement of dynamic quantitative risk assessment methodology: moving boundary condition

Wonje Lee, Ph.D. candidate

Seoul National University

 To ensure the safety of a process system, engineers use various methods to identify the potential hazards of a system. One of the most popular methods is quantitative risk assessment (QRA) and it can quantifies the risk of a particular process activity. But one of disadvantages of QRA is its isolation and lack of integration with the process operation. A conventional QRA methodology is unable to update risk during the life of process and reflect risk according to the process change because it uses a statistical accident occurrence probability. This was identified as one of the main causes of the BP Texas refinery accident. For this reason, a methodology which is able to calculate the accident occurrence probability dynamically should be studied. Recently, a dynamic QRA methodology which calculate the accident occurrence probability using the remaining time is suggested. The remaining time is calculated by measuring the change amount of a process key variable to upper bound or lower bound. But this methodology has two problems. First, the existing methodology make accident occurrence probability zero when a variable has no change in a dangerous level. If a variable has no change currently but is near boundary condition, it should have a reasonable accident occurrence probability. Second, the existing methodology is unable to calculate the probability proper to the oscillation of a variable. For example, a variable which vibrate with sine function close to upper bound has high probability when it is increasing but when it is decreasing, it has very low probability because of long distance to lower bound. It cannot classify difference between the oscillation and the control of a variable dynamically.

 In this study, improved dynamic QRA methodology is suggested being able to consider the current state of a key variable as well as the change amount of it. A imaginary boundary condition is calculated and updated dynamically which has the same distance from current value of a variable to nearer boundary condition and opposite direction. The more a variable is near one of the original boundary condition, the more distance between updated imaginary boundary condition and original boundary condition become narrow. So, it can calculate reasonable probability about small change amount of a variable in dangerous level. This methodology is applied to dynamic simulation data of single compressor system which has recycle line and is verified by comparison to the result of existing methodology.

Session : Sustainable engineering forum – environmental health & safety and sustainability