Designing and operating safe chemical reaction processes HSG143

Health and SafetyExecutive176 The technical documentation may also contain many other pieces ofinformation, eg quality specifications, yields, safety data sheets, environmentalassessments, etc.177 The technical documentation is the history of the design process. The intentand reasoning for the process should therefore be clear to someone new to theparticular process.Safe operating instructions178 The safe operating instructions are for use by the plant operators. They needto be clear, simple and unambiguous. They should contain:(a) the substances used in the process, their hazards and the precautions to betaken, eg the personal protective equipment (PPE) that must be used;(b) any critical safety systems on the plant and the action to be taken when theyoperate - relate this to the safe operating envelope and the basis of safety;(c) a step-by-step procedure to carry out the process; and(d) emergency procedures.179 It is a requirement of PSSR 5 that any person operating a pressure system isprovided with adequate and suitable operating instructions.180 Make the safe operating procedures easier to understand by stating thecritical action points. For example, if you require an operator to control the reactorcontents temperature, state in the instructions that the temperature should notexceed, say, 100 o C and that activation of the emergency reactor cooling shouldoccur at 90 o C and that the reactor should be shutdown at 95 o C.181 You can give operators guidance on the magnitude of a specified action toachieve a specified goal. For example, rather than letting the operator guess howmuch to open a valve, suggest opening to a certain amount, then using minoradjustments to get the desired start-up flow. Give guidance on how to lead or lagin changing setpoints; or advise on how long to blow a line to clear it of liquid. Takeout the guesswork.Process changes and modifications182 It is important that you do not modify the chemical reaction process systemuntil you have considered the safety implications. You need a formal managementsystem developed for modifications to plant, procedures and/or process chemistry.183 Changes considered as minor can lead to hazardous conditions developing.For example, a change of catalyst can lead to a significant increase or decreasein the rate of reaction. Decreases in rate can cause accumulation of reactants.Changing the form of a reactant from a pellet to a powder can significantly increasethe reaction rate.A violent decomposition occurred when a reaction normally carried out in astainless steel reactor was changed to a mild steel one. Traces of iron that haddissolved in the reaction mass catalysed the decomposition.Designing and operating safe chemical reaction processes Page 34 of 64