Accidental release source terms are the mathematical equations that quantify the flow rate at which accidental releases of liquid or gaseous pollutants into the ambient environment which can occur at industrial facilities such as petroleum refineries, petrochemical plants, natural gas processing plants, oil and gas transportation pipelines, chemical plants, and many other industrial activities.
Governmental regulations in many countries require that the probability of such accidental releases be analyzed and their quantitative impact upon the environment and human health be determined so that mitigating steps can be planned and implemented.
There are a number of mathematical calculation methods for determining the flow rate at which gaseous and liquid pollutants might be released from various types of accidents.
Such calculational methods are referred to as source terms, and this article on accidental release source terms explains some of the calculation methods used for determining the mass flow rate at which gaseous pollutants may be accidentally released.
Choked velocity, also referred to as sonic velocity, occurs when the ratio of the absolute source pressure to the absolute downstream pressure is equal to or greater than [(k + 1) / 2]k / (k − 1), where k is the specific heat ratio of the discharged gas (sometimes called the isentropic expansion factor and sometimes denoted as
The equations were derived from field tests performed by the U.S. Air Force with pools of liquid hydrazine.
The equations were developed by Warren Stiver and Dennis Mackay of the Chemical Engineering Department at the University of Toronto.
This is known as "adiabatic flashing" and the following equation, derived from a simple heat balance, is used to predict how much of the liquefied gas is vaporized.