Risk-Based Approach – Domino Effect and Escalation Triggered by Explosions

This paper proposes a risk-based approach for identifying process equipment impacted by explosions with potential for escalation. The procedure is based on: (1) taking advantage of efforts conducted during the development of a risk-based quantitative assessment, (2) combination of exceedance curve with elasto-plastic Single Degree Of Freedom (SDOF) and pressure-impulse diagrams. The main purpose is to estimate the equipment damage level; i.e., ductility ratio. Once the damage level is characterized, appropriate decision-making process for the equipment affected can be conducted. This paper includes pressure-impulse diagrams.

Introduction

Three concepts should be clearly understood when assessing a domino accident: (1) primary event, (2) secondary target and (3) secondary scenario. A primary event is defined as the accident scenario of concern and its final outcomes are expressed in Secterms of physical effect such as thermal radiation or overpressure. Secondary targets are equipment items that may be damaged by the primary event and, if damaged, the associated secondary scenarios have the potential to cause final outcomes escalating the primary event.

Fire assessments addressing escalation can be performed by following two different approaches: (1) a consequence-based approach that only considers the worst credible event, or (2) a risk-based approach that considers both the consequence and the frequency values that characterize the associated risk level [1]. Detailed information on risk-based quantitative assessment development can be found in references [1], [2], [3], [4], [5] and [6].

After the risk-based assessment is conducted, the results for thermal radiation are used to construct Heat Flux Exceedance Curves (HFECs) at a target location, which properly identify equipment impacted with a high thermal radiation at a cumulative frequency [6]. Based on the HFECs, the heat flux at certain cumulative frequency threshold is determined. If the heat flux impacting the target location is greater than a certain selected value for escalation, an advanced Dynamic Thermal Stress Analysis (DTSA) is conducted to calculate the Time to Failure (TTF) of the equipment. The TTF is the time between the fire start and the rupture of the vessel due to the fire.

Despite the large number of possible fire events, few categories of industrial fires are relevant for escalation leading to domino effect, such as jet fires and pool fires. Further explanation on the types of fires and damage criteria can be found in references [4] and [7].

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