Scott Davis, PhD., P.E., CFEI
\nTom DeBold, P.E., CFEI
\nand
\nJohn Pagliaro, Ph.D.
\nGexcon US, USA<\/p>\n
Presented at the International Symposium on Fire Investigation Science and Technology, 2018<\/p>\n
ABSTRACT<\/p>\n
When investigating a flash fire or explosion, it is common to test and evaluate the integrity of a fuel gas\u00a0system \u2013 such as LPG systems. One common technique is to use a pressurized inert gas, such as nitrogen, to not\u00a0only identify possible holes for propane to leak through but also quantify the flow rate of the leak. However, if the\u00a0leak is located under the liquid level of the propane cylinder, there is a common misconception that the mass flow\u00a0rate for a liquid propane release must be approximately 270 times larger than a vapor release through the same hole\u00a0size. In a recent case, an investigator concluded that a small hole identified during a leak test using nitrogen gas\u00a0would be more than sufficient to cause a large flash fire because the hole would have been below the liquid propane\u00a0level and thus would be 270 times larger than a vapor propane leak through the same hole. This misconception\u00a0regarding the magnitude of liquid propane leaks stemmed from the fact that liquid propane has a density that is\u00a0approximately 270 times larger than the density of gaseous propane at atmospheric pressure and temperature.\u00a0Under practical conditions, the mass flow rates of liquid propane will actually be much closer to those of vapor\u00a0releases given identical hole sizes. In fact, the difference will be only approximately 6-8 times larger if both liquid\u00a0and gaseous propane are stored at ambient temperatures of 20\u00b0C. This near 30-fold reduction in liquid flow is due to\u00a0how propane is stored and the physics governing a compressible vapor release compared to an incompressible liquid\u00a0release. More specifically, for propane at 20\u00b0C the vapor will exit a small hole at the speed of sound and due to the\u00a0high storage pressure (e.g., approximately 105 psig at 20\u00b0C) the density of the vapor leaking will be much higher\u00a0than atmospheric conditions. Conversely, an incompressible liquid will be limited by the pressure difference\u00a0upstream and downstream of the hole.\u00a0The present study demonstrates the differences in liquid and vapor propane release rates and shows that liquid\u00a0releases are not 270 larger than vapor releases. This is accomplished by: (1) providing an overview of the\u00a0theoretical orifice flow equations for pressurized vapor and liquid releases; (2) presenting results from actual\u00a0releases of liquid and vapor propane from a 120-gallon water capacity tank and a 20 lb cylinder; and (3) presenting\u00a0CFD results that highlight the importance of accurate estimates of leak rates when it comes to formulating origin\u00a0and cause hypotheses.<\/p>\n
Download Complete Paper Here<\/a><\/p>\n","protected":false},"excerpt":{"rendered":" Scott Davis, PhD., P.E., CFEI Tom DeBold, P.E., CFEI and John Pagliaro, Ph.D. Gexcon US, USA Presented at the International Symposium on Fire Investigation Science and Technology, 2018 ABSTRACT When investigating a flash fire or explosion, it is common to test and evaluate the integrity of a fuel gas\u00a0system \u2013 such as LPG systems. One … Continue reading Are Liquid Propane Leaks Really 270 Times Larger Than Gas? Case Study Regarding The Physics Of Liquid And Gas Propane Leaks<\/span>