High sensitivity must be shown during the transportation of chemical cargoes due to their flammability, toxicity, purity and incompatibility with each other. Therefore, one of the most crucial procedures in chemical tankers is cleaning the tanks of cargo residues and getting them ready for loading the cargo. Inspection of the tank's suitability for the loading is first performed by a wall wash test (WWT). Evaluation of the errors made during WWT application is essential to prevent cargo contamination with costly consequences. In this study, the risks associated with the application of WWT are analyzed using the Bayes technique in a fuzzy environment. The Bayesian network is used to detect hazards and calculate the probabilities of contributing sub-causes, while fuzzy logic is utilized to quantify the uncertainty in risk assessment. The paper provides practical contributions to all maritime stakeholders in assessing and preventing risks in WWT to the contamination problem, which is one of the most critical problems of chemical tanker transport.