Determination of the Design Load for Structural Safety Assessment against Gas Explosion in Offshore Topside

The possibility of gas explosion accidents always exists at offshore facilities of the oil and gas industry. In the design of those structures, the structural safety assessment against explosion loads is necessary to prevent loss of lives or catastrophic failure of structures. One of the essential parts in the structural assessment is to determine design explosion loads. Nowadays, the explosion loads are calculated by probabilistic approach rather than deterministic approach. In the recommended probabilistic load calculation procedure of the offshore explosion accidents, for instance, the NORSOK standard, the design load shall be established based on the relation between the predicted overpressure and its duration from numerous scenarios, and also, the exceedance frequency of the loads to the risk acceptance criteria. In most offshore projects, however, the conservative approach has been used, which derives only the design overpressure from the probabilistic load scenarios, or considers overpressure and duration independently because there is no efficient application method for the suggested procedure. In this paper, the practical method to determine the design explosion load, especially considering both overpressure and duration, are presented by using the response surface model with the joint probability distribution and compared with the present industrial practices.