Lecture 10
- 1. Safety and loss prevention (Lecture 10) •LLF0916 •1
- 2. Contact Hours •8/15/2016 •LLF0916 •2 Lecture Tutorial Self – Study Library Search Assignment Exam Total Student Learning Time (hours) 2 2 4 4 2 NIL 14
- 3. Learning Outcomes •To identify potential hazards that associated with chemical processes •To identify measurement that helps to control and prevent hazardous deviation •To introduce basic principles and procedure to develop Hazard and Operability Study (HAZOP) •8/15/2016 •LLF0916 •3
- 4. Introduction •8/15/2016 •LLF0916 •4 • Legal and moral obligation to safeguard the health and welfare of its employees and the general public. • Safety is good business as good management practices are needed to ensure safe operation and this will ensure efficient operation. • Loss prevention an insurance term LOSS •Financial loss - damaged equipment, plant, claim - Lost production and sales •Reputation loss •Human assets loss
- 5. Introduction •8/15/2016 •LLF0916 •5 Safety and loss prevention in process design Identification and assessment of hazards Control of the hazards: eg: containment of flammable and toxic materials Control of the process: Prevention of hazardous deviations in process variables( pressure, temperature, flow) by provision of automatic control systems, interlocks, alarms, trips etc) Limitation of the loss: The damage and injury caused if an incident occurs: pressure relief, plant layout, provision of fire fighting equipment
- 6. Introduction •8/15/2016 •LLF0916 •6 Intrinsic Safety Extrinsic Safety which safe operation is inherent in the nature of the process, a process which causes no danger, or negligible danger under all foreseeable circumstances. ?
- 7. Introduction •8/15/2016 •LLF0916 •7 Extrinsic Safety • the safety has to be engineered in • chemical manufacturing processes are generally inherently unsafe and dangerous situations can develop if the process conditions deviate from the design values • The safe operation of such processes depends on the design and provision of engineered safety devices and on good operating practices • Provision in the design of control systems, alarms, trips, pressure relief devices, automatic shut-down systems, duplication of key equipment services, fire fighting equipment, sprinkler system, blast walls etc • Examples, PSH, PSHH, LSH, LSHH, PSV, PCV, LCV
- 8. hazard •8/15/2016 •LLF0916 •8 • Ionising radiation • Pressure • Temperature deviation • Noise • Toxicity • Flammability • Explosion • Source of ignition
- 9. Hazard – toxicity •8/15/2016 •LLF0916 •9 • The potential health hazard to an individual by a material used in any chemical or process plant is a function of the inherent toxicity of the material and the frequency and duration of exposure. • Have to distinguish between the short term effects (acute) and long term effects (chronic) of the material • Highly toxic material that causes immediate injury such as chlorine or phosgene would be classified as a safety hazard • A material whose effect is apparent only after long exposure at low concentrations, eg vinyl chloride, would be classified as industrial health and hygiene hazards
- 10. Hazard – toxicity •8/15/2016 •LLF0916 •10 • Both the permissible limits and the precautions to be taken to ensure that such limits are not exceeded are quite different for these two classes of toxic materials. • Inherent toxicity is measured by tests on animals. It is expressed as the lethal dose at which 50% of the animals do not survive and this is known as LD50 value. Test on rats
- 11. Hazard – toxicity •8/15/2016 •LLF0916 •11 • The permissible exposure limit (PEL) of concentration for the long term exposure of humans to toxic materials is set by the threshold limit value (TLV)- upper permissible concentration limit that is safe to humans with exposure of 8hrs/day, 5 days/week over a period of many years • Most significant source of workplace exposure to toxicity is inhalation. Hence an understanding of the sources of contaminants to which workers are exposed is important for the recognition, evaluation and control of occupational health hazards
- 12. Hazard – toxicity •8/15/2016 •LLF0916 •12 • Recommended TLVs are published by OSHA (Occupational Safety and Health Administration) • Handbook prepared by Sax and Lewis provides a comprehensive source of data as well as guidance on the interpretation and use of the data • Prepare a Material Supply Data Sheet (MSDS) for the materials used
- 13. Hazard – toxicity •8/15/2016 •LLF0916 •13 • Preventative aspects of the use of hazardous substances are: - substitution: processes using less hazardous material - containment: sound design of equipment and piping, avoid leaks - ventilation: use open structures or adequate ventilation - disposal: effective vent stacks - emergency equipment: escape routes, rescue equipment, respirators, safety showers and eye baths
- 14. Hazard – flammability •8/15/2016 •LLF0916 •14 • Flammable – materials that will burn • Hazards caused by flammable material depends on: • Flash point of material- a measure of the ease of ignition of liquid. It is the lowest temperature at which the material will ignite from an open flame. • Autoignition temperature-temperature at which a substance will ignite spontaneously in air, without any external source of ignition. Indication of the maximum temperature to which a material can be heated in air
- 15. Hazard – flammability •8/15/2016 •LLF0916 •15 • Flammability limits- the lowest and highest concentration in air, at normal pressure and temperature, at which a flame will propagate through the mixture. Range of concentration over which the material will burn in air if ignited.
- 16. Hazard – flammability •8/15/2016 •LLF0916 •16 • For a fire to occur, there must be a fuel, an oxidiser and an ignition source. In addition, the combustion must be self sustaining. • Air is the oxidiser, a minimum concentration of fuel is necessary for the flame to be ignited. Minimum concentration required depends on the temperature of the mixture and to a lesser extent on the pressure, greatest interest is focused on the ignition conditions necessary at ambient temperature.
- 17. Hazard – flammability •8/15/2016 •LLF0916 •17 • Flame traps - fitted in the vent lines of equipment that contains flammable material - prevent the propagation of flame through the vents - providing a heat sink, usually expanded metal grids or plates to dissipate the heat of the flame - installed in the plant ditches to prevent the spread of flame
- 18. Hazard – explosion •8/15/2016 •LLF0916 •18 • Explosion is the sudden, catastrophic release of energy, causing a pressure wave. An explosion can occur without fire, such as the failure through over-pressure of a steam boiler or an air receiver. • Different types of explosions: 1. Confined vapour cloud explosions(CVCE) 2. Unconfined vapour cloud explosions(UCVCE) 3. Boiling liquid expanding vapour explosions (BLEVE) 4. Dust explosions
- 19. Hazard – source of ignition •8/15/2016 •LLF0916 •19 • Electrical equipment Source of ignition - sparkling of electrical equipment - electrically operated instruments, controllers and computer system Hazardous area – explosive gas-air mixtures are present Zone 0: explosive gas-air mixtures present continuously for long periods; intrinsically safe equipment to be used Zone 1: explosive gas-air mixtures likely to occur in normal operation; intrinsically safe equipment, or flame proof enclosures to be used Zone 3: explosive gas-air mixtures not likely to occur during normal operation, but could occur for short periods; intrinsically safe equipment, or total enclosure or non-sparkling apparatus to be used. Hence the standards have to consulted for full specification before selecting equipment for the designated zones
- 20. Hazard – source of ignition •8/15/2016 •LLF0916 •20 • Static electricity – movement of any non-conducting material, powder, liquid or gas can generate static electricity, producing sparks. Have to ensure that all piping is properly earthed (grounded) and that electrical continuity is maintained around flanges. - Escaping steam, other vapors or gases can generate a static charge. Gases escaping from a ruptured vessel can self-ignite • Process flames – flames from process furnaces and incinerators are obvious sources of ignition and these equipment have to be located well away from plant containing flammable materials • Miscellaneous source - control entry of obvious source of ignition, matches, cigarettes - used of portable electrical equipment, welding, spark producing tools and movement of petrol-driven vehicles - exhaust gases from diesel engines
- 21. Hazard – ionizing radiation •8/15/2016 •LLF0916 •21 • Radiation emitted by radioactive materials is harmful to living matter. • Small quantities of radioactive isotopes are used in the process industry for various purposes e.g in level and density measuring instruments and for the non-destructive testing of equipment.. • Use of radioactive isotopes covered by government legislation
- 22. Hazard – pressure •8/15/2016 •LLF0916 •22 • Over-pressure (pressure exceeding the system design pressure) is one of the most serious hazards in chemical plant operation. Failure of a vessel or the associated piping can result in a sequence of events that can culminate in a disaster. • Pressure vessels are fitted with pressure relief devices set at the design pressure so that potential over-pressure is relieved in a controlled manner. •
- 23. Hazard – pressure •8/15/2016 •LLF0916 •23 • Three different types of relief devices commonly used are: -Directly actuated valves-spring loaded valves that open at a predetermined pressure and which close after the pressure has been relieved. The system pressure provides motive power to operate the valve -Indirectly actuated valves- pneumatically or electrically operated valves which are activated by pressure sensing instruments -Bursting discs- thin discs of material that are designed to fail at a predetermined pressure, giving a full-bore opening for flow • Relief valves are normally used to regulate minor excursions of pressure and bursting discs as safety devices to relieve major over-pressure. • Relief valves and bursting discs are proprietary items and vendors are consulted prior selection • API 520 and 521 for sizing of relief valves and overpressure
- 24. Hazard – pressure •8/15/2016 •LLF0916 •24
- 25. Hazard – pressure •8/15/2016 •LLF0916 •25 • Vent piping -Relief systems have to ensure that flammable or toxic gases are vented to a safe location -Vent to a safe height to ensure the gases are dispersed without creating a hazard. -For toxic materials necessary to provide a scrubber. HP Flare Scrubber, LP Flare Scrubber etc •-Rate of venting will be determined by the design of the complete venting system, the relief device and the associated piping. Maximum venting rate will be limited by the critical sonic velocity. •-Vessels also have to be protected against external fire so the relief valve has to be sized for fire etc
- 26. Hazard – pressure •8/15/2016 •LLF0916 •26 Vent piping Flare
- 27. Hazard – pressure •8/15/2016 •LLF0916 •27 • Under-pressure (vacuum) - Unless designed to withstand external pressure, a vessel has to be protected against the hazard of under-pressure, as well as over- pressure - Under-pressure normally means vacuum on the inside with atmospheric pressure on the outside. A slight drop in pressure below atmospheric pressure will result in the tank collapsing - Not uncommon for a storage tank to be sucked in (collapsed) by the suction pulled by the discharge pump, due to the tank vents having become blocked. - Vacuum breakers should be fitted in such cases
- 28. Hazard – pressure •8/15/2016 •LLF0916 •28
- 29. Hazard – temperature deviation •8/15/2016 •LLF0916 •29 • Excessively high temps, over & above the design temperature can cause structural failure & initiate a disaster • High temperatures can result from loss of control of reactors and heaters, from open fires • Protection against high temperatures to be provided for processes where high temperatures are a hazard - High Temp alarms & interlocks to shutdown reactor feeds or heating systems -Provision of emergency cooling systems -Structural design of eqpt to withstand worst possible temp excursion -Selection of intrinsically safe heating systems for hazardous material
- 30. Hazard – temperature deviation •8/15/2016 •LLF0916 •30 •Steam and other vapour heating systems are intrinsically safe as the temperature cannot exceed the saturation temperature at the supply pressure •Electrical heating systems are particularly hazardous • Fire protection - To protect against structural failure water-deluge systems are usually installed to keep vessels and structural steelwork cool in a fire. - Lower sections of structural steel columns are often lagged with concrete or other suitable material
- 31. Hazard – noise •8/15/2016 •LLF0916 •31 • Excessive noise is a hazard to health and safety. Long exposure to high noise levels can cause permanent damage to hearing. At lower levels, noise is a distraction and causes fatigue • Sound is measured in decibels • Permanent damage to hearing can be caused at sound levels above 90db
- 32. Hazard – noise •8/15/2016 •LLF0916 •32 • Normal practice to provide ear protection in areas where noise is above 80db • Noise pollution from factories causes complaints from residents • Compressors, fans, burners and steam relief valves cause excessive noise-consider in plant layout
- 33. Hazard – noise •8/15/2016 •LLF0916 •33
- 34. Dow fire and explosion index •8/15/2016 •LLF0916 •34 • Hazard classification guide developed by DOW Chemical Company gives a method of evaluating the potential risk from a process and assessing the potential loss • A numerical “Fire & Explosion Index” is calculated. • The larger the value of the F&EI, the more hazardous the process.
- 35. Dow fire and explosion index •8/15/2016 •LLF0916 •35 • The potential hazard of a new plant can be calculated after the P&IDs and equipment layout diagrams have been prepared. • Indicate alternative, less hazardous process routes should be considered.
- 36. Safety study •8/15/2016 •LLF0916 •36 • HAZID - Hazard Identification • HAZOP - Hazard & Operability Study • FERA - Fire & Explosion Risk Analysis • QRA - Quantitative Risk Assessment • SGIA - Smoke & Gas Ingress Analysis • EERA - Escape, Evacuation & Rescue Analysis • ESSA - Emergency System Survival Analysis • TRIA - Temporary Refuge Impairment Analysis • HFE - Human Factor Engineering • HRA - Health Risk Assessment • ERP - Emergency Risk Assessment
- 37. Hazard and operability study (hazop) •8/15/2016 •37 • HAZOP - systematic technique for identifying all plant or equipment hazards and operability problems. When applied to a process design or an operating plant, it indicates potential hazards that may arise from deviations from the intended design conditions. • In this technique, each segment (pipeline, piece of equipment, instrument etc) is carefully examined and all possible deviations are identified. This is accomplished by fully defining the intent of each segment and then applying the guide words to each segment. • Seven guide words for carrying out HAZOP
- 38. More – quantitative increase eg: higher temperature Hazard and operability study (hazop) •8/15/2016 •38 7 guide words No or not – no part of the intent is achieved and nothing else occurs eg: no flow Less – quantitative decrease eg: lower pressure As well as – Something in addition to the design intention eg: impurities, side reaction Reverse – Reverse of or opposite to the design intention eg: reverse flow Part of – Something missing, only part of the intention is realized, such as change in the composition of a stream or a missing component Other than– No part of the intention is achieved, something completely different occurs. Covers all conceivable situations other than intended such as start up, shutdown, maintenance
- 39. Hazard and operability study (hazop) •8/15/2016 •39 • These guide words are applied to flow, temperature, pressure, liquid level, composition and any other variables affecting the process. • Normally carried out by Specialists eg HAZOP Leader and HAZOP Scribe. Include all the main disciplines but mostly Process Engineers, Instrument and Piping • Require Flow Sheets (PFDs, UFDs), P&IDs, Plant Layout • HAZOP Study Report-Close out the findings
- 40. Hazard analysis •8/15/2016 •40 • HAZOP identifies the hazards but gives no indication on the likelihood of an incident occurring or the loss suffered. The sequence of events that leads to a hazardous incident can be shown as a fault tree (logic tree) • Fault tree analysis (FTA)- means of analysing hazardous events after they have been identified. Used to estimate the likelihood of an accident by breaking it down into its contributing sequences. Use of the fault tree provides a graphical representation between certain possible events and undesired consequences. • Sequence of events forms pathways on the fault tree with AND and OR gates.
- 42. Safety audits •8/15/2016 •42 • Safety audits carried out to verify the adequacy of safety equipment and safety rules. • Safety equipment includes eqpt for fire protection, personnel protection and on-site emergency responses • Explicit safety rules for new process will be identified • Safety Checklist for identifying process hazards • Critical assessment of the checklist will identify the major hazards in the proposed new facility or existing facility • This should be done in the early stages of the design
- 43. Environmental protection •8/15/2016 •43 • All individuals and companies have a duty to care for the neighbours and to the environment • Agencies to monitor this include: -OSHA: Occupational Safety and Health Administration -NIOSH: National Institute for Occupational Safety and Health -EPA: Environment Protection Agency • EIA-Environment Impact Assessment gives a full disclosure statement of project parameters that have a +ve environmental impact, -ve environmental impact or no impact at all