One task carried out by process safety experts that has received increasing attention in recent years is the building siting study. These studies strive to locate buildings in proximity to petrochemical facilities in places where the risk of occupant injury or building damage is acceptable. Although the studies evaluate potential toxic gas impacts and fire impacts, the most important hazard is often vapor cloud explosion (VCE) overpressures. Simple models, such as Multi-Energy and Baker-Strehlow-Tang, are the most common methods used to estimate overpressures for the purpose of locating buildings in relation to process units. These models suffer from a common problem: the user is required to pick the “strength” of the explosion using one or more simple parameters. This paper presents a systematic approach to empirical explosion overpressure modeling that allows consideration of a wider set of variables important to VCEs. This approach provides the user with a method of describing a VCE that is more detailed than current models, and establishes a more refined system for predicting the overpressures generated.

The Baker-Strehlow-Tang (BST) vapor cloud explosion model is one of the most common methods used to estimate overpressures for the purpose of locating buildings in relation to process units. This model suffers from a problem common to all simplified explosion models: the user is required to pick the “strength” of the explosion using one or more simple parameters. In the BST model, the fuel reactivity, flame expansion, and obstacle density parameters are used to select a flame speed from a limited matrix of possible values. This paper presents the Quest Model for Estimation of Flame Speeds (QMEFS), a systematic approach to estimating flame speed that does not rely on the BST categories. It provides for a continuous range of flame speeds that can then be used with the existing BST blast curves to calculate the characteristics of the vapor cloud explosion (VCE). The QMEFS approach provides the user with a method for describing a VCE that is more detailed than the BST model, and establishes a more refined system for predicting the consequences of vapor cloud explosions.

Although spills of low volatility toxic liquids do not receive the public attention given to releases of high volatility or flammable liquids, releases of low volatility toxic chemicals may present a hazard to facility personnel and the public. The purpose of this paper is to develop a method of ranking and evaluating the hazard presented to the public by a low volatility toxic chemical or a low volatility mixture of toxic chemicals. The ranking system, named LOVRS (LOw Volatility hazards Ranking System), can be used to determine if currently stored chemicals present a hazard to the public, or to screen the list of chemicals that might be stored at a proposed facility.

LOVRS employs readily available chemical properties, such as vapor pressure, molecular weight, Short Term Exposure Limit (STEL), Time Weighted Average (TWA), or other selected measure of toxicity, to compute a numerical value that is related to the hazard potential of each chemical.

This paper presents ten toxic chemicals which were ranked using LOVRS and compares the results with other ranking methods. Extension of the pure-component ranking equations to multi-component mixtures of hazardous chemicals is developed. Evaporation rate and dispersion calculations were made for the ten chemicals ranked using LOVRS. The results of the calculations for worst-case conditions (Pasquill F stability, 1.5 m/s wind speed) with an assumed distance of 16,500 ft (5,030 m) to an area of concern are presented. Using the computed results, a relationship is shown to exist between the LOVRS Toxic Index value and the maximum mole fraction of a component that can be present in the released mixture. This relationship can be used to determine the maximum mole fraction at which a toxic chemical can be stored in a low volatility mixture without presenting a hazard to the public.