Risk assessment hazards

Risk analysis of accidents serves a dual purpose. It estimates tlie probability tliat an accident will occur and also assesses the severity of the consequences of an accident. Consequences may include damage to tlie surrounding environment, financial loss, injury to life and/or deatli. This Part of the book (Part IV) is primarily concerned witli tlie metliods used to identify liazards and causes and consequences of accidents. Issues dealing with healtli risks have been explored in tlie previous Part (III). Risk assessment of accidents provides an effective way to help ensure eitlier tliat a inisliap will not occur or reduces tlie likelihood of an accident. Tlie result of tlie risk assessment also allows concerned parties to take precautions to prevent an accident before it liappens. 

As with Healtli Risk Assessment (HRA), tliere are four key steps involved in a liazard risk assessment (HZRA). Hiese are detailed below (see figure) if tlie system in question is a chemical plant 

The event or series of events tliat will initiate an accident has to be identified. An event could be a failure to follow correct safety procedures, improperly repaired equipment, or failure of a safety mechanism. 

Tlie probability that an accident will occur has to be determined. For e. ainple. if a chemical plant has a given life, wliat is tlie probability tliat tlie temperature in a reactor will e.xceed the specified temperature range The probability can be ranked qualitatively from low to high. A low probability means tliat it is unlikely for tlie event to occur in tlie life of the plant. A medium probability suggests that tliere is a probability that tlie event will occur. A liigh probability means that the event will probably occur during the life of the plant. 

Tlie severity of the consequences of the accident must be determined. Tliis will be described later in detail. 

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To chanicterize potential disasters by tjpe and extent, a survey of hazards or foreseeable tlireats in die community must be performed and evaluated. Widiout such information, an appropriate plan cannot be developed. An inventory of the community protection assets, liazard sources, and risks must be done before die actual plan is written. The procedures followed here is similar to diat provided in Part IV of this book - Hazard Risk Assessment. 

Chronic. Continuous exposure occurs over long periods of time, generally several mondis to years. Concentradons of inlialed (toxic) contaminants are usually reladvely low. This subject area falls in die general domain of healdi risk assessment (HRA) and it is diis subject tliat is addressed in die next five chapters. Thus, in contrast to the acute (short-term) exposures dial predominate in hazard risk assessments, cliroiiic (loiig-temi) exposures are the major concern in health risk assessments. 

This cliapter serves to introduce tlie general subject of hazard risk assessment and analysis, including cause-consequence risk evaluation. The cause-consequence aspect of this topic is perliaps tlie key to understanding hazard risk. As such, it is treated in a separate section later in diis cliapter. 

This book is divided into five parts the problem, accidents, health risk, hazard risk, and hazard risk analysis. Part 1, an introduction to HS AM, presents legal considerations, emergency planning, and emergency response. This Part basically ser es as an oveiwiew to the more teclmical topics covered in the remainder of the book. Part 11 treats the broad subject of accidents, discussing fires, explosions and other accidents. The chapters in Parts 111 and Part IV provide introductory material to health and hazard risk assessment, respectively. Pai1 V examines hazaid risk analysis in significant detail. The thiee chapters in this final part include material on fundamentals of applicable statistics theory, and the applications and calculations of risk analysis for real systems. 

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