Designing and operating safe chemical reaction processes HSG143

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Health and SafetyExecutiveAppendix three:Other hazards in chemicalprocessingFire and explosion hazards1 Flammable materials may be:(a) gases or vapours;(b) liquids;(c) mists or aerosols; and(d) solids (including dusts).2 In all cases, for a fire or explosion to occur a flammable atmosphere and asource of ignition must be present at the same time.3 Examples of incidents that can occur during the operation of a reactor are:(a) vapour or dust explosions during the charging of reactants;(b) vapour or gas explosions in the reactor, eg ignited by a pyrophoric catalyst orwhen the hatches are opened, air enters and the contents are above theirautoignition temperature;(c) explosion of a vapour or dust cloud issuing from a vessel, ignited by an externalsource; and(d) autoignition of product when run-off at too high a temperature.4 There are five general principles for ensuring that the risks of fire and explosionfrom the use of flammable materials can be controlled and minimised. The acronym‘VICES’ will help you to remember them. The acronym implies no order of priorityof the principles.Designing and operating safe chemical reaction processes Page 48 of 64
Health and SafetyExecutiveV VentilationIs there plenty of fresh air where the materials are used? Good ventilationmeans rapid dispersion of vapours given off from a spill, leak or release.IIgnitionHave all ignition sources been removed from the area? Ignition sourcescan vary widely. They include sparks from electrical equipment or weldingand cutting tools, hot surfaces, smoking, open flames from heatingequipment and electrostatic discharges from plant, process operators ormaterials being processed.C ContainmentAre your flammable liquids contained adequately? Will a spillage becontained and prevented from spreading to other parts? Means ofcontrolling spillage could be an impervious sill or low bund. An alternativeis to drain the area to a safe place, such as a remote sump or a separator.E ExchangeCan you exchange a flammable liquid for a less flammable one? This isa basic question you should always ask. Can you eliminate the use offlammable materials from your operation altogether?S SeparationAre flammable materials stored and used well away from other processesand general storage areas? Can they be separated by a physicalbarrier, wall or partition?Health hazards5 Toxic substances vary widely in the hazards they create. Acute hazards arisingfrom short-term exposure are more likely to arise than chronic effects from lowlevellong-term exposure.6 Exposure to a chemical substance through inhalation, ingestion or skinabsorption can lead to poisoning or other ill health. Of these routes of exposure,inhalation is generally the most serious as the probability of exposure to vapoursduring routine operations and incidents involving spills is much greater than fromskin exposure or ingestion.7 The Personal Protective Equipment Regulations 1992 54 require employers toprovide suitable PPE to employees who may be exposed to a risk to their health orsafety while at work unless the risk has been adequately controlled by other meansthat are equally or more effective.8 The COSHH Regulations 7 require employers to prevent or control exposure toharmful substances. Guidance on these Regulations is contained in the ApprovedCodes of Practice (ACOPs) entitled Control of substances hazardous to health (Fifthedition). The Control of Substances Hazardous to Health Regulations 2002 (asamended). Approved Code of Practice and guidance. 58Designing and operating safe chemical reaction processes Page 49 of 64
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