PII uses it's qualified experts in human errors, procedural errors, process failures, and equipment failures to perform an IVA. The IVA starts with the definition of disasters based on the significance level of abnormal events. Once the potential disasters are defined, existing design barriers that confine the consequences are examined. Then, various scenarios with multiple human errors, procedural errors, process failures, and equipment failures that can penetrate the barriers are examined. The errors and failures that can easily induce disasters are identified and corrected. Also, improvement in design barriers and consequence mitigation will be recommended.