by Timothy A. Melton and David W. Johnson
Abstract
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. For example, this type of information could be used to determine whether a mixture of chemicals stored at a toxic waste incineration site presents a hazard to the public.
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. Commonly available sources of the required chemical properties are the CCPS DIPPR data base, NIOSH, etc.
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.