Concurrent events risk assessment generic models with enhanced reliability using Fault tree analysis and expanded rotational fuzzy sets

•Generic risk assessment models to estimate combined influence of concurrent risks.•Generic & inclusive risk breakdown structure to avoid overseeing influential risks.•Logic gates to avoid accumulating of dependent, redundant, & non-concurrent risks.•Effectiveness of safety measures are accounted for to produce residual risk value.•Enhanced gradation of fuzzy truth values to reduces rounding and misrepresentation. Knowledge limitations, ambiguities, and indecisiveness at the modeling stage of a risk assessment model can tend to induce structural errors in the model. Operational logic misuse and fuzzy values misrepresentation are a major source of structural error that can overestimate or underestimate the overall risk assessment values. This paper proposes generic risk assessment models to overcome reliability limitations in risk assessment of concurrent events. An enhanced rotational fuzzy model for quantifying possible subjective risk values is proposed to be used along with Fuzzy Fault Tree Analysis (FFTA) model for risk assessment. A fault tree is built upon a generic but inclusive risk breakdown structure, which can help avoid assessment underestimation by providing a structure for deducting influential events from the top risk event under assessment. Adequate operational logic gates are suggested to avoid assessment overestimation related to accumulating the effect of dependent, redundant, and non-concurrent risks, and ignoring the effectiveness of the existing safety precautions and measures that may reduce or eliminate risks. The proposed FFTA model can be used as a prognostic risk assessment tool to combine the influence of concurrent risks from basic events at the bottom of the tree to the top risk event defined by risk assessor. The FFTA risk assessment model is applied to five different sample cases, with a case of graphical and numerical details, to illustrate the general applicability on diverse domains, namely, truss failure during placement risk, slipping risk, frozen pipe burst risk, virus spread risk, and project completion delay risk.