Contents lists available at ScienceDirect Engineering Failure Analysis journal homepage: www.elsevier.com/locate/engfailanal Consequences of an incorrect assessment of a structure damaged by explosion Janusz Krentowski ⁎ , Kamil Ziminski Department of Structural Mechanics, Faculty of Civil and Environmental Engineering, Bialystok University of Technology, Wiejska St. 45e, 15-351 Bialystok, Poland ARTICLE INFO Keywords: RC fermentation chamber Biogas explosion Failure condition Durability Concept of strengthening ABSTRACT The authors indicate the consequences of an incorrect assessment of the condition of a structure that has been damaged as a result of a disaster or failure. The presented thesis is illustrated by progressive degradation processes of fermentation chambers in a digestive sewage tank. The degradation originated from biogas explosion, which in turn, led to unidentified damage to the reinforced concrete structure, thus the tank was not excluded from further service. The justifi- cation for allowing the faulty structure to be put into operation were errors in the assessment of the stress function resulting from using inadequate data concerning the cross-section of the concrete reinforcement and concrete strength undertaken by the user. The changes in the tank's static structure as a consequence of the biogas explosion were not taken into account. As a result, the leaks were observed immediately after beginning of the water test. Consequently, the state of the effort of the tank's structure both at its design stage and during its instantaneous pressure load caused by explosion had to be analyzed again. The impact of the cracks found in the tank's reinforced concrete walls on the safe operation of the facility for collecting liquid medium has been also considered. It was shown that the tank's walls in their central part failed to meet the conditions of ultimate limit state and serviceability of the re- inforced concrete ring cross-section subjected to an exceptional load. Conditions for safe op- eration of the repaired facility, taking into account the change of the static scheme of the structure have been reconsidered. The paper is concluded with a presentation of the concept of restoring the correct durability of the structure to ensure safe resumption of the technological process. Additionally, recommendations were made concerning assessments of structures da- maged as a result of a breakdown or building disaster. 1. Introduction Engineering structures used in technological processes of sewage treatment are designed as buildings with durability no less than several dozen years. In the technological process of sewage treatment plants using closed tanks, biogas is produced, which is a natural effect of chemical fermentation processes. Biogas is an effective energy medium, but in inappropriate conditions of use it can cause a threat to human life and destruction of engineering structures, which is related to its susceptibility to explosion [1]. The operation of specialized structures exposed to the risk of explosion in an aggressive environment of municipal sewage implies the need for periodic inspections. Performing detailed investigations makes it possible to verify the fulfilment of the standard https://doi.org/10.1016/j.engfailanal.2019.03.009 Received 23 October 2018; Accepted 17 March 2019 ⁎ Corresponding author at: Department of Geotechnics and Structural Mechanics, Faculty of Civil and Environmental Engineering, Bialystok University of Technology, Wiejska St. 45e, 15-351 Bialystok, Poland. E-mail address: janusz@delta-av.com.pl (J. Krentowski). Engineering Failure Analysis 101 (2019) 135–144 Available online 20 March 2019 1350-6307/ © 2019 Elsevier Ltd. All rights reserved. T