Accidents analysis

Organizations can use a variety of processes to analyze accident causal factors. Hazard evaluations and accident trend analysis can help improve the effectiveness of established hazard controls. Routine analysis efforts can also enable organizations to develop and implement appropriate controls in work procedures, hazardous processes, and unsafe operations. Analysis processes rely on information collected from hazard surveys, inspections, hazard reports, and accident investigations. This analysis process can provide a snapshot of hazard information. Effective analysis can then take the snapshots and create viable pictures of hazards and accident causal factors. 

RCA processes can help connect the dots of accident causation by painting a pictiire that includes beneath the surface causes. Organizations many times fail to use effective and systanatic techniques to identily and correct system root causes. Best guess corrective actions do not address the real causes of accidents. Ineffective quick fix schemes don t change processes to prevent future 

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D. A. Kuemmel and R. M. H2csPo-, Accident Analysis of Ice Control Operations, presented at the Third International Symposium on Snow Removal and Ice Control Technology, Minneapolis, Minn., 1992. 

State intervention in man s activities to protect the health of the inhabitants goes back to prehistory. The motivation may not have been altogether altruistic the king acted to protect his subjects because he regarded them as his property. Public health protection began for disease control. With industrialization, came the need for control of even more hazardous forces and substances. This extended protection became technological in accident analysis and response. Present efforts in controlling risk, such as from nuclear power, are a continuation of this development. 

We previously encountered failure modes and effects (FMEA) and failure modes effects and criticality analysis (FMECA) as qualitative methods for accident analysis. These tabular methods for reliability analysis may be made quantitative by associating failure rates with the parts in a systems model to estimate the system reliability. FMEA/FMECA may be applied in design or operational phases (ANSI/IEEE Std 352-1975, MIL-STD-1543 and MIL-STD-1629A). Typical headings in the F.Mld. A identify the system and component under analysis, failure modes, the ef fect i>f failure, an estimale of how critical apart is, the estimated probability of the failure, mitigaturs and IHissihiy die support systems. The style and contents of a FMEA are flexible and depend upon the. ilitcLiives of the analyst. 

Chen ifi-.il. iiaJ S clear Accident Analysis Methods... 

Two studies resolved the Unresolved Safety Issue A-44, "Station Blackout." The first siudy, The Reliability of Emergency AC Power Systems in Nuclear Power Plants," when combined uh die lelevant loss-oToffsite-power frequency, provides estimates of station-blackout frequencies lor 18 nuclear power plants and 10 generic designs. The study also identified the design and operational features most important to the reliability of AC power systems. The second study, "Station Blackout Accident Analysis" (NUREG/CR-3226), focused on the relative importance to risk of laiion blackout events and the plant design and operational features that would reduce this risk. 

The severe accident research program improved public risk assessment, reduced uncertainties, and the reliance on subjective expert opinion. To close two severe accident issues in NRC s Severe Accident Research Plan (NUREG-1365) Mark I Liner Attack and Direct Containment Heating (DCH) were addressed with a new approach using the Risk Oriented Accident Analysis Method (ROAAM) (Theofanous, 1994, 1989). The resolution of the Mark-I Liner Attack issue constitutes the first full demonstration of ROAAM. It emphasizes the determinism and provides a basis for synergistic collaboration among experts through a common communication frame. 

FSAR - Final Safety Analysis Report (Chapter 15 is the accident analysis section in the FSAR standard format). 

ROAAM - Risk Oriented Accident Analysis Method. 

Nichols, B. D. et al., Fire-Accident Analysis Code (FIRAC) Verification, LA-UR-86-2860, LANL, 19th >OE/NRC Nuclear Air Cleaning Conference. 

Fabiano, B., Pastormo, R., and Solisio, C. 1999. Explosion at an Acetylene Plant A Methodological Approach to Accident Analysis. IChemE Loss Prevention Bnlle-tin. Issue 145 (February 1999). 

The analysis of accidents and disasters in real systems makes it clear that it is not sufficient to consider error and its effects purely from the perspective of individual human failures. Major accidents are almost always the result of multiple errors or combinations of single errors with preexisting vulnerable conditions (Wagenaar et al., 1990). Another perspective from which to define errors is in terms of when in the system life cycle they occur. In the following discussion of the definitions of human error, the initial focus will be from the engineering and the accident analysis perspective. More detailed consideration of the definitions of error will be deferred to later sections in this chapter where the various error models will be described in detail (see Sections 5 and 6). 

Error analysis techniques can be used in accident analysis to identify the events and contributory factors that led to an accident, to represent this information in a clear and simple manner and to suggest suitable error reduction strategies. This is achieved in practice by identification of the causal event sequence that led to the accident and the analysis of this sequence to identify the root causes of the system malfunction. A discussion of accident analysis techniques is included in Chapter 6. 

In the following sections, a number of methodologies for accident analysis will be presented. These focus primarily on the sequence and structure of an accident and the external causal factors involved. These methods provide valuable information for the interpretation process and the development of remedial measures. Because most of these techniques include a procedure for delineating the structure of an incident, and are therefore likely to be time consuming, they will usually be applied in the root cause analysis of incidents with severe consequences. 

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