Q9 is widely used in industries handling flammable fluids and is central to explosion risk assessment (ERA). Q9 transforms complex flammable clouds from pressurised releases to simple cuboids with uniform stoichiometric concentration, drastically reducing the time and resources needed by ERAs. Q9 is commonly believed in the industry to be conservative but two studies on Q9 gave conflicting conclusions. This efficacy issue is important as impacts of Q9 have real life consequences, such as inadequate engineering design and risk management, risk underestimation, etc. This paper reviews published data and described additional assessment on Q9 using the large-scale experimental dataset from Blast and Fire for Topside Structure joint industry (BFTSS) Phase 3B project which was designed to address this type of scenario. The results in this paper showed that Q9 systematically underpredicts this dataset. Following recognised model evaluation protocol would have avoided confusion and misinterpretation in previous studies. It is recommended that the modelling concept of Equivalent Stoichiometric Cloud behind Q9 should be put on a sound scientific footing. Meanwhile, Q9 should be used with caution; users should take full account of its bias and variance.

The dispersion of vapour of liquefied natural gas (LNG) is generally assumed to be from a liquid spill on the ground in hazard and risk analysis. However, this cold vapour could be discharged at height through cold venting. While there is similarity to the situation where a heavier-than-air gas, e.g., CO2, is discharged through tall vent stacks, LNG vapour is cold and induces phase change of ambient moisture leading to changes in the thermodynamics as the vapour disperses. A recent unplanned cold venting of LNG vapour event due to failure of a pilot, provided valuable data for further analysis. This event was studied using CFD under steady-state conditions and incorporating the effect of thermodynamics due to phase change of atmospheric moisture. As the vast majority of processing plants do not reside on flat planes, the effect of surrounding topography was also investigated. This case study highlighted that integral dispersion model was not applicable as key assumptions used to derive the models were violated and suggested guidance and methodologies appropriate for modelling cold vent and flame out situations for elevated vents.

In two previous papers (Cordeiro et al., 1973a, b ) a methane pressurization process was described by which the solubility of high molecular weight hydrocarbons in a solid phase could be enhanced within a liquid hydrocarbon phase by pressurizing the solid-liquid system with methane gas. This solubility enhancement was demonstrated to occur for two diverse hydrocarbon solids in the following prototype systems : System I: methane (gas) -normal decane (liquid) -normal dotriacontane (solid) System 11: methane (gas) -normal decane (liquid) -phenanthrene (solid) and some speculation was offered concerning the selectivity of aromatic vs. paraffinic solids of similar melting point under methane pressurization with n-decane being the liquid solvent in each case.In this paper, several thermodynamic aspects of the process are considered with respect to the Systems I and I1 and also System 111: methane (gas)-trans decalin (liquid) -normal dotriacontane (solid) the study of which has been recently completed. These experimental results are presented below. EXPERIMENT-SYSTEM IllAn experimental study of the phase equilibria behavior of the ternary system methane-trans decalin-normal dotriacontane was performed. The data was correlated with the Flory-Huggins model (Flory, 1942; Huggins, 1942) solely for the purpose of aiding the later thermodynamic analysis of the system with respect to process behavior. Our previous work (Cordeiro et al. 1973a) presents the equations of this model in detail. The model works as well as with System I, and better than with System 11, using the following partial molar volume and inter- where T is "K. The data are applicable in the range of 323-340°K up to pressures of 70 abn. These data were obtained from the following laboratory experiments, each of which was reproduced at least once.