Combining Task Analysis and Fault Tree Analysis for Accident and Incident Analysis: A Case Study from Bulgaria

(the paper was presented at European ESREL conference, Estoril, Portugal, 2006)

ABSTRACT: Understanding the reasons for incident and accident occurrence is important for an organisa-tion’s safety. Different methods have been developed to achieve this goal. To better understand the human behaviour in incident occurrence we propose a analysis concept that combines Fault Tree Analysis (FTA) and Task Analysis (TA). These methods were complemented with the use of the Human Error Identification in System Tools (HEIST) methodology and the concept of Performance Shaping Factors (PSF) to deepen the in-sight into the error modes of an operator’s behaviour. To show the validity of the approach, a case study at a Bulgarian Hydro power plant was carried out. An incident – the flooding of the plant's basement – was ana-lysed by combining the afore-mentioned methods. With our case study we show that Task Analysis in combi-nation with other methods can be applied successfully to human error analysis, revealing details about errone-ous actions in a realistic situation.

1 INTRODUCTION

Accidents and incidents have occurred since the in-vention of the first machine and the beginning of the industrial revolution. Despite the efforts of mankind to prevent or avoid them, they continue to occur. The reasons for their happening are usually com-plex. An accident may have 10 or more events that can be counted as causes (Seton, 2006). One failure may lead to another and a chain reaction may propa-gate through barriers and time to produce an unde-sired event. The most common reasons for acci-dent/incident occurrence are failure of people, equipment, supplies, or surroundings to behave or react as expected.

Understanding why accidents/incidents occur and how to prevent them is crucial in our modern world. The works of (Hollnagel, 1998), (Johnson, 2003), (Kirwan, 1994) and (Petersen, 1996) are of excep-tional importance in this respect.

Most traditional engineering accident/incident analysis techniques focus on the technical compo-nents of the system that failed. An exception is the HAZOP method (Redmill & Chudleigh & Catmur, 1999), which is focused on human error in the con-text of a technical system and was developed for the process and chemical industry. Today, due to the complexity of the processes operating and the man-machine interface, the share of human error in acci-dents/incidents occurrence has increased. As re-ported by the Federal Aviation Administration (Clemens, 2002) “… more than seventy percent of all crashes of scheduled commercial aircraft are caused directly by �controlled flight’ into terrain.” The same percentage (human error contribution) holds for the chemical industry.

This paper is divided in 7 sections. It presents the reasons for accidents/incidents occurrence in Bulgar-ian industry – an aspiring EU member country. Chapter 3 introduces the basic concepts of acci-dents/incidents analysis. The next chapter sketches the concepts of the proposed analysis approach, fol-lowed by the presentation of a case study carried out at a Bulgarian power plant, where the concept was applied. We close by presenting the results obtained from the application of the analysis approach and give some conclusions.

2. SAFETY IN BULGARIAN INDUSTRY

2.1 Health and Safety Conditions of Work in Bulgar-ian industry

Bulgaria has about 30 big (large) potentially haz-ardous plants on its territory, including power plants (hydro, thermal, and nuclear), refineries, production plants (chemical, metallurgical, machine, etc) and a shipyard (SACP, 2005). The remaining power, met-allurgical and chemical plants on the territory of Bulgaria, smaller in size or capacity in comparison with these 30, should be also considered when ac-counting for the total number of plants with high risk production unit. According to the analysis, made by the Executive Agency (EA) “Labour inspection” (EAGLI, 2004), (EAGLI, 2005a), (EAGLI, 2005b) for provision of health and safety conditions at work (HSCW) in Bulgarian industry, certain progress has been made, and problems have been identified. The results, which we discuss in a short overview here, are presented jointly for the metallurgical, chemical branch of industry and the plants generating thermal and electrical energy.

2.1.1 Achievements

In all enterprises and power plants inspected by the Executive Agency, the main requirements of the Health and Safety (H&S) regulations are fulfilled: a risk assessment of the places of work and the pro-duction process is carried out, employees are pro-vided with services by the Office of “Labour medi-cine” (Office)*, committees or