Designing and operating safe chemical reaction processes HSG143

Health and SafetyExecutiveRate of reaction: The rate at which conversion of reactants takes place.Reactants: Chemicals that are converted into products during the reactionprocess.Reaction: The process in which chemicals (reactants) are converted into otherchemicals (products).Reaction calorimeter: A laboratory test apparatus for measuring thermal effectsof chemical reactions or processes. For the purpose of this guidance, types ofreaction calorimeters include isothermal, isoperibolic and adiabatic systems.Reactive systems screening tool (RSST TM ): A type of pseudo-adiabaticcalorimeter.Reasonably practicable: The degree of risk in a particular job or workplaceneeds to be balanced against the sacrifice in time, trouble, cost and physicaldifficulty of taking measures to avoid or reduce the risk. Measures must be takento eliminate or control the risks unless it is clear that the sacrifice incurred in doingso is grossly disproportionate to the level of the risk. However, the ability to payfor additional control measures is not a deciding factor as to whether they arenecessary.Reflux: A system condition in which a component in the reaction system(usually a solvent) is continually boiled off, condensed in a nearby condenser andsubsequently returned to the reaction system.Relief system sizing: the sizing of an emergency relief vent.Relief system: All parts of the pressure-relief flow path from the protected vesselto atmosphere or containment within a disposal system. This includes reliefdevice(s), piping and any containment and disposal system.Risk: The chance of something adverse happening where ‘something’ refers toa particular consequence of the manifestation of a hazard. Risk reflects both thelikelihood that harm will occur and its severity in relation to the number of peoplewho might be affected, and the consequences to them.Risk assessment: The process of identifying the hazards present in anyundertaking (whether arising from work activities or other factors) and those likelyto be affected by them, and of evaluating the extent of the risks involved, bearing inmind whatever precautions are already being taken.RSST: see reactive systems screening tool.Runaway: A reaction that is out of control because the rate of heat generation byan exothermic chemical reaction exceeds the rate of cooling available.Semi-batch: An operation in which some materials are added to the reactor at thestart, with one or more other reactants added in a controlled manner during thereaction. See also semi-batch reactor.Semi-batch reactor: A type of reactor that is characterised by the supply, in acontrolled manner, of one or more key reactants during the reaction. Productsare only taken from the reactor upon conclusion of the reaction process.Designing and operating safe chemical reaction processes Page 63 of 64