• 품질경영학회지
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• 제47권3호
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• pp.571-582
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• 2019

Purpose: To develop a risk metric for failure cause that can help determine the action priority of each failure cause in FMEA considering time sequence of cause- failure- detection. Methods: Assuming a quadratic loss function the unfulfilled mission period, a risk metric is obtained by deriving the failure time distribution. Results: The proposed risk metric has some reasonable properties for evaluating risk accompanied with a failure cause. Conclusion: The study may be applied to determining action priorities among all the failure causes in the FMEA sheet, requiring further studies for general situation of failure process.

• 대한임상독성학회지
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• 제18권2호
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• pp.116-122
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• 2020

Acute respiratory failure is an important risk factor for mortality in patients with acute pesticide poisoning. Therefore, it is necessary to investigate the risk factors to predict respiratory failure in these patients. This study retrospectively investigated the clinical features of respiratory failure among patients with acute pesticide poisoning requiring mechanical ventilation. This study included patients who were admitted with intentional poisoning by pesticide ingestion from January 2017 to December 2019. Paraquat intoxication was excluded. Among 469 patients with acute pesticide poisoning, 398 patients were enrolled in this study. The respiratory failure rate was 30.4%. The rate of respiratory failure according to the type of pesticide was carbamate (75.0%), organophosphate (52.6%), glufosinate (52.1%), glyphosate (23%), pyrethroid (8.9%), and others (17%). The mortality was 25.6% in the respiratory failure group. The risk factors for respiratory failure were old age, low body mass index, and ingestion of more than 300 mL. In conclusion, respiratory failure is a risk factor for mortality in pesticide poisoning. Old age, low body mass index, and ingestion of more than 300 mL are the risk factors for predicting respiratory failure.

• 한국안전학회지
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• 제31권2호
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• pp.10-17
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• 2016

The purpose of this paper is to deduct components that are in the group of highest risk(top 10%). the group is conducted for classification into groups by values according to risk priority through risk priority number(RPN) of FMEA(Failure modes and effects analysis) sheet. Top 10% of failure mode among total potential failure modes(72 failure modes) of ESS included 5 BMS(battery included) failure modes, 1 invert failure mode, and 1 cable connectors failure mode in which BMS was highest. This is because ESS is connected to module, try, and lack in the battery part as an assembly of electronic information communication and is managed. BMS is mainly composed of the battery module and communication module. There is a junction box and numerous connectors that connect these two in which failure occurs most in the connector part and module itself. Finally, this paper proposes RPN by each step from the starting step of ESS design to installation and operation. Blackouts and electrical disasters can be prevented beforehand by managing and removing the deducted risk factors in prior.

• 한국안전학회지
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• 제26권6호
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• pp.104-110
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• 2011

In FMEA, the risk priority number(RPN) is used for risk evaluation on each failure mode. It is obtained by multiplying three components, i.e., severity, occurrence, and detectability of the corresponding failure mode. Each of the three components are usually determined on the basis of the past experience and technical knowledge. But this approach is not strictly objective in evaluating risk of a given failure mode and thus provide somewhat less scientific measure of risk. Assuming a homogeneous Poisson process for occurrence of the failures and causes, we propose a more scientific approach to evaluation of risk in FMEA. To quantify severity of each failure mode, the mission period is taken into consideration for the system. If the system faces no failure during its mission period, there are no losses. If any failure occurs during its mission period, the losses corresponding to the failure mode incurs. A longer remaining mission period is assumed to incur a larger loss. Detectability of each failure mode is then incorporated into the model assuming an exponential probability law for detection time of each failure cause. Based on the proposed model, an illustrative example and numerical analyses are provided.

• 한국안전학회지
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• 제33권3호
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• pp.83-91
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• 2018

This paper suggests a weibull time delay model to evaluate failure risks in FMEA(failure modes and effects analysis). Assuming three types of loss functions for delayed time in failure cause detection, the risk of each failure cause is evaluated as its occurring frequency and expected loss. Since the closed form solution of the risk metric cannot be obtained, a statistical computer software R program is used for numerical calculation. When the occurrence and detection times have a common shape parameter, though, some simple results of mathematical derivation are also available. As an enormous quantity of field data becomes available under recent progress of data acquisition system, the proposed risk metric will provide a more practical and reasonable tool for evaluating the risks of failure causes in FMEA.

• 한국안전학회지
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• 제31권4호
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• pp.136-142
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• 2016

The FMEA is a widely used technique to pre-evaluate and avoid risks due to potential failures for developing an improved design. The conventional FMEA does not consider the possible time gap between occurrence and detection of failure cause. When a failure cause is detected and corrected before the failure itself occurs, there will be no other effect except the correction cost. But, if its cause is detected after the failure actually occurs, its effects will become more severe depending on the duration of the uncorrected failure. Taking this situation into account, a risk metric is developed as an alternative to the RPN of the conventional FMEA. The severity of a failure effect is first modeled as linear and quadratic severity functions of undetected failure time duration. Assuming exponential probability distribution for occurrence and detection time of failures and causes, the expected severity is derived for each failure cause. A new risk metric REM is defined as the product of a failure cause occurrence rate and the expected severity of its corresponding failure. A numerical example and some discussions are provided for illustration.

• 한국지반신소재학회논문집
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• 제17권4호
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• pp.53-64
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• 2018

본 연구에서는 안정성과 위험도 평가의 중요성이 증대되고 있는 DCM(Deep Cement Mixing, 이하 DCM) 보강 지반상의 항만 구조물에 대하여 위험도 평가를 위한 파괴확률을 산정하였다. DCM 개량 지반의 위험도에 영향을 미치는 확률변수로 개량체의 설계기준강도와 시공중첩, 원지반의 강도 및 내부마찰각, 개량지반의 단위중량을 선정하고 관련 통계치를 산정하여 적용하였다. 또한, 상시 조건과 지진시 조건에서의 전체 시스템에 대한 파괴확률을 분석하였다. 본 연구를 통해 DCM 개량지반의 위험도 평가를 위한 확률변수에서 변동계수가 가장 큰 것은 설계기준강도이나 안전율의 변동성 즉, 시스템의 위험도에는 큰 영향을 미치지는 않는 것을 알 수 있었다. DCM 보강 지반에 대한 시스템의 파괴확률 영향인자 즉, 주된 위험요소는 상시 및 지진시 모두 외적안정의 경우 수평활동, 내적안정의 경우 압축파괴인 것으로 평가되었다. 또한, 수평활동에 대해서는 상시 파괴확률이 지진시 파괴확률보다 높고 압축파괴에 대해서는 상시 파괴확률이 지진시 파괴확률보다 낮은 것으로 나타났다. 전체 시스템의 상시 파괴확률과 지진시 파괴확률은 유사하지만, 본 사례의 경우 지진시 위험도가 다소 높은 것으로 나타났다.

• 품질경영학회지
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• 제44권2호
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• pp.373-388
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• 2016

Purpose: This paper suggests a hierarchical time delay model to evaluate failure risks in FMEA(failure modes and effects analysis). In place of the conventional RPN(risk priority number), a more reasonable and objective risk metric is proposed under hierarchical failure cause structure considering time delay between a failure mode and its causes. Methods: The structure of failure modes and their corresponding causes are analyzed together with the time gaps between occurrences of causes and failures. Assuming the severity of a failure depends on the length of the delayed time for corrective action, a severity model is developed. Using the expected severity, a risk priority metric is defined. Results: For linear and quadratic types of severity, nice forms of expected severity are derived and a meaningful metric for risk evaluation is defined. Conclusion: The suggested REM(risk evaluation metric) provides a more reasonable and objective risk measure than the conventional RPN for FMEA.

• Earthquakes and Structures
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• 제19권6호
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• pp.471-484
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• 2020

Previous earthquakes show that, structural safety evaluations should include the evaluation of nonstructural components. Failure of nonstructural components can affect the operational capacity of critical facilities, such as hospitals and fire stations, which can cause an increase in number of deaths. Additionally, failure of nonstructural components may result in economic, architectural, and historical losses of community. Accelerations and random vibrations must be under the predefined limitations in structures with high technological equipment, data centers in this case. Failure of server equipment and anchored server racks are investigated in this study. A probabilistic study is completed for a low-rise rigid sample structure. The structure is investigated in two versions, (i) conventional fixed-based structure and (ii) with a base isolation system. Seismic hazard assessment is completed for the selected site. Monte Carlo simulations are generated with selected parameters. Uncertainties in both structural parameters and mechanical properties of isolation system are included in simulations. Anchorage failure and vibration failures are investigated. Different methods to generate fragility curves are used. The site-specific annual hazard curve is used to generate risk curves for two different structures. A risk matrix is proposed for the design of data centers. Results show that base isolation systems reduce the failure probability significantly in higher floors. It was also understood that, base isolation systems are highly sensitive to earthquake characteristics rather than variability in structural and mechanical properties, in terms of accelerations. Another outcome is that code-provided anchorage failure limitations are more vulnerable than the random vibration failure limitations of server equipment.

• 한국안전학회지
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• 제31권6호
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• pp.58-66
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• 2016

This study aims to estimate the failure probability of concrete gravity dams for their risk analysis under flood situation. To the end, failure modes of concrete gravity dams and their limit state functions are proposed based on numerous review of domestic and international literatures on the dam failure cases and design standards. Three failure modes are proposed: overturning, sliding, and overstress. Based on the failure modes the limit state functions, the failure probability is assessed for a weir section and a non-weir section of a dam in Korea. As water level is rising from operational condition to extreme flood condition, the failure probability is found to be raised up to the warning condition, especially for overturning mode at the non-weir section. The result can be used to reduce the risk of the dam by random environmental variables under possible flood situation.