Designing and operating safe chemical reaction processes HSG143

Health and SafetyExecutiveSupercritical processing: Processing using supercritical fluids. In a gas-liquidequilibrium there is a certain temperature and pressure below which a gas and aliquid can co-exist but above which only a single phase (known as a supercriticalfluid) can form.Thermal runaway: see runaway.Two-phase: Any system in which two phases exist.Untempered: see untempered system.Untempered system: A reacting system in which the temperature cannot be heldconstant at constant pressure, because there is insufficient vapour pressure tocause sufficient cooling by removal of latent heat.Vapour: The gaseous phase released by evaporation from a material at normaltemperatures and pressure.Vapour pressure system: A system type in which pressure is due to the vapourpressure of the reacting system. Tempering will occur with pressure relief via anadequately sized relief.Venting: Emergency flow of vessel contents out of the vessel through an openingprovided. The pressure is reduced by venting, thus avoiding a rupture of the vesselby overpressurisation. The vent flow can be single phase or multiphase, each ofwhich results in different flow and pressure characteristics.Vent Sizing Package (VSP TM ): A type of adiabatic calorimeter.VSP TM : see vent sizing package.Published by HSE 09/09 Page 64 of 64