PPE - Can You Have Too Much of a Good Thing?

Dee, S., Exponent
Cox, B. L., Exponent, Inc.
Ogle, R., Exponent, Inc.
Garner, S. W., Exponent, Inc.
During the last decades, there has been a growing concern in the chemical and petrochemical industry regarding losses of storage materials caused by natural phenomena. These events have the potential to cause significant damage, especially in areas where large quantities of hazardous substances are stored. The release of these substances may lead to fires, explosions, or the emission of toxic clouds into the atmosphere; and might have a significant impact on the population located in neighbor urban areas and on the environment. When industrial accidents are triggered by natural events such as earthquakes, floods and storms, or any other natural event, these chemical accidents are known as Natech events (Natural Hazard Triggering Technological Accidents). This paper will focus on the assessing of risk present in vertical storage tanks once they have been affected by different natural phenomena such as extreme winds, floods, earthquakes or MultiHazard such as Hurricanes and tsunamis. In addition, a computational tool is proposed which contains a method for the quantitative assessment of the risk in storage tanks that works at near atmospheric conditions. This method allows to establish possible accidental scenarios, as well as the estimation of different failure or loss probabilities due to shell buckling, roof detachment, tank overturning or sliding, among others. It is a tool that takes the interaction of both the mentioned natural phenomena and the physical and mechanical characteristics of storage tanks into account, besides the characteristics of the substance stored (hazardous materials, hazmat). Furthermore, the tool allows to perform an evaluation of different types of loss or failure of the storage tank through fragility, vulnerability and normalized probit curves, which take into account the uncertainty of the involved variables. In addition, the method allows calculating the losses of different hazmat once the storage tank has failed, estimates the consequences of the loss of containment to finally assess the associated risk. This model can be used as a verification and validation tool for existing risk-assessment models of both new and existing tanks; also, it provides insight on the necessary operating conditions and design practices for risk mitigation upon different types of natural phenomena.