風險管理是職業安全衛生管理系統設計和運作的主軸，而風險評估則是職安衛風險管理關鍵作業。風險評估方法約可分為定性、半定量和定量三類，但是大部分的風險評估方法都存在著過於主觀、結果不具說服力、不易被現場人員接受等問題。風險矩陣因為容易了解、使用簡單，是常見的風險評估方法，但是因為可能性和後果嚴重性表達的方式並無一致的標準，評估的結果因人而異。此外，風險等級如可接受或可容忍的判定，多半採用經驗法則，無法發揮後續風險控制機制選擇或風險控制有效性評估的功能。情境分析可幫助了解由危害導致事故發生的事件序列，包含危害、原因、偏離、事故、影響等情境因子和考量預防、控制、保護、消減等安全屏障，並可根據情境分析結果，作為後果嚴重度與可能性等級的分類依據，和評估後果嚴重度、可能性等級。因此，本研究是以工作場所作業個人傷害風險為基礎，發展情境分析架構，利用情境分析結果和合理可行概念結合風險矩陣，並以衝擊事件為後果探討風險等級的判定基準，彌補風險矩陣無法判定評估結果可接受度的缺失，降低風險評估的不確定性，提昇評估結果的可信度及可用度。本研究為針對工作場所中的作業人員進行個人傷害風險評估，因此對於風險可容忍度的判定標準提出較為嚴格的要求，並以局限空間作業和矽甲烷換鋼作業為案例，驗證本研究所建立之風險評估方法的可行性。利用特定作業的標準作業程序建立可信的事故情境以評估風險，並假設風險控制策略可降低30%的情境發生率和一等級的後果嚴重度，評估實施風險控制策略後的殘餘風險。研究結果顯示本研究所建立的風險評估方法可有效的評估職業安全衛生風險和判定風險可接受度，達到合理可行的降低風險和預防事故發生的雙重效益。

Risk management is an integral part of most occupational health and safety management system standards. It serves to identify and assess the risks associated with the hazards in a workplace. Risk assessment provides organizations with an insight in health and safety risks and the opportunity to prioritize risk management strategies. Despite its importance and increasing applications, two outstanding issues remain in the risk assessment process. The first is subjectivity since there is always uncertainty, the need for judgment, differences in human perception of risk, and reliability of the data used. The second issue arises from the varying criterion for risk acceptability and tolerability.
This study aims to provide practical solutions to the dilemmas encountered in occupational health and safety risk assessment. Because of its ease of use and popularity, risk matrix is chosen as the risk assessment tool in this study. Instead of using qualitative descriptors for likelihood and consequence, semi-quantitative scales are adopted. To minimize bias of the risk assessors, a protection layer-based scenario development technique is proposed in this study. Four categories of safety barriers with specific functions for prevention, control, protection and mitigation of accidents are used in developing the most credible accident scenarios and estimating the likelihood and consequence of each scenario. The issue of acceptability and tolerability is addressed by applying the fundamental principles of as low as reasonably practicable.
Validity of the proposed scenario development technique and the combined use of as low as reasonably practicable and risk matrix is tested with two case studies. The first case involves hazard identification and risk assessment of tasks performed in a confined space environment. The second case attempts to assess the risks associated with silane cylinder change. The results illustrate that credible accident scenarios can indeed be derived from the standard operating procedures of a specified task and more reliable estimations of the consequence and likelihood of each scenario can be achieved. Acceptability and the effectiveness of risk control mechanism can be clearly demonstrated in the risk matrix. The scenario-based risk assessment technique may provide the much needed solutions in alleviating the inherent dilemmas of subjectivity, bias and uncertainty of risk assessment.

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