Analysis of equipment failures as contributors to chemical process accidents

A database study of chemical process accident cases was carried out. The objective of the study is was to identify the reasons for equipment based accidents. The most frequent accident causing equipment were piping (25%), reactors and storage tanks (both 14%) and process vessels (10% of equipment accidents). The six most accident-prone equipment is process related involve nearly 80% of accidents.78% of equipment accident contributors are technically oriented including design and human/technical interface faults. Purely human and organizational reasons are the most common accident contributors for storage tanks (33%), piping (18%) and heat transfer equipment (16% of causes). For other equipment the technical accident causes are most common.The accident contributors were divided to main and sub-contributors. On average process equipment failures have 2.2 contributors. The contributors, which frequent and act often as main contributors, should be focused. These risky contributors were identified for several equipment types. Also a deeper analysis of the accident causes and their interconnections was made. Based on the analysis a checklist of main risk factors was created for hazard identification on different types of equipment.     

Method for identifying contributors to chemical process accidents

The paper presents a new method for identifying contributors to chemical process accidents by exploiting knowledge on causes of past accident cases. Accident reports from the Failure Knowledge Database were analyzed and utilized for hazard identification. The accident information gathered was used as a basis to develop an accidents ranking and points-to-look-for approach for the safe design and operation of chemical process equipment. In the method, accident contributors including technical, design and operation errors of major process equipment types and piping are identified. The method is applicable throughout the process lifecycle, even for process changes in the early design stages. The Bhopal tragedy is used as a case study to demonstrate and test the method. The proposed method can predict on average up to 85% of accident causes and design and operation errors.     

Design as a contributor to chemical process accidents

The paper discusses the design errors in chemical process industry (CPI) by analyzing major equipment related accident cases from Failure Knowledge Database (FKD). The aim is to recognize the contribution of design to chemical process accidents and to evaluate the time of occurrence of the errors in a plant design project. The analysis of accident cases found out that the contribution of design to accidents is very significant: 79% of accident cases analyzed were contributed by design errors. The most critical design errors were poor layout (17%), insufficient consideration of chemical reactivity and incompatibility (16%) and incorrectly chosen process conditions (16%). The design errors were initiated at basic (32%), detailed (32%) and preliminary (22%) design phases of the project. Errors in fundamental aspects of chemical processes e.g. route selections are more severe (as compared to others errors class) and might creates many similar errors in later phases of design project. Based on the accident information gathered, a straightforward point-to-look list for error detection and elimination was suggested for process lifecycle stages.     

Origin of equipment design and operation errors

The paper discusses the origin of chemical process equipment accidents by analyzing past accident cases available in the Failure Knowledge Database (FKD). The design and operation errors of the process equipment that caused the accidents were analyzed together with their time of occurrence. It was found that design errors contributed to 79% of accidents while the rest were only due to human and organizational errors in the operation stage and external factors. The most common types of errors were related to layout, organizational errors in the operation stage, considerations of reactivity and incompatibility, and wrongly selected process conditions (each approx. 13% of total accident contributors). On average there were about 2 design errors per accident. The timing of the errors was quite evenly distributed between various lifecycle stages. Nearly half (47%) of the errors were made in process design-oriented stages, one fourth (26%) in detailed engineering, and one fifth (20%) in operation. In addition, the most frequent design and operation errors for each equipment type were identified. A points-to-look-for list was created for each equipment type, showing also the typical time of occurrence of the error. The knowledge of type and timing of design errors can be utilized in design to focus the hazard analysis in each stage on the most error-prone features of design.