For many terrorist organizations, chemical weapons might be considered an ideal choice for a mode of attack, if they are available: they are cheap, relatively accessible, and easy to transport. A skilled chemist can readily synthesize most chemical agents if the precursors are available. Chemical warfare (CW) is different from the use of conventional weapons or nuclear weapons because the destructive effects of chemical weapons are not primarily due to any explosive force. Chemical warfare involves using the toxic properties of chemical substances as weapons. Discovery of nerve agents in Germany led to the availability of a class of compounds at least one order of magnitude more lethal than previously known where death might occur in a matter of minutes instead of hours. Nerve agent refers to two groups of highly toxic chemical compounds that generally are organic esters of substituted phosphoric acid (G-agents, V-agents). The three most active G-agents are tabun, (Chemical Agent Symbol GA), Sarin (GB), CH3POFOCH (CH3); and Soman (GD).The G-agent liquids under ordinary atmospheric conditions have sufficiently high volatility to permit dissemination in vapour form. They are generally colourless, odourless or nearly so, and are readily absorbable through not only the lungs and eyes but also the skin and intestinal tract without producing any irritation or other sensation on the part of the exposed individual. These agents are sufficiently potent so that even a brief exposure may be fatal. Death may occur in 1-10 min, or be delayed for 1-2 h depending on the concentration of the agent. The objective of this paper is to study the best ventilation system with both Under-Floor Displacement and personalized ventilation (PV) with GB injection in the aircraft cabin of the economy section of a Boeing 767 airplane during cruise and passengers protection by air curtain design for both steady and transient states. Computational fluid dynamics (CFD) modelling techniques using the ANSYS FLUENT 15.0 package solved the continuity, momentum, energy, and species transport equations, in addition to k-ε model equations for turbulence closure. Mesh sizes used in the present work exceeded 6,000,000 mesh volumes in one case. GB mole fraction, temperature, velocity Contours are obtained to realize the air curtain performance for the optimum passengers protection. Air curtain is good for preventing spread of GB, but of course increase temperature and decrease thermal comfort inside the aircraft cabin because of the higher velocity, so it is used only for emergency cases until the aircraft landed.
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