Presentation on theme: "Flare and Overhead Systems"— Presentation transcript:
1 Flare and Overhead Systems Safety Talk Objectives1) Understand the risks associated with flare and overhead systems.Hardware design aspects, and possible equipment problems.Process design envelope, and possible excursions outside design limits.2) Know the controls.Hardware controls.Good operating, maintenance and inspection practices.Procedural controls / critical tasks.3) Review incidents that have happened in the past and learn the lessons.Meeting attendees should have confidence that they understand the risks and can apply the appropriate controls. They should know where to go for help or further information.This handout also contains some specific / technical considerations.Meeting preparationSupervisors are encouraged to review the BP Oil Key Safety Topic entitled ‘Successful Group Meetings’ before delivering this safety talk.Note: The controls described in this Safety Talk are generic guidance, and may not cover the precise risks or circumstances at your site. Local procedures and practices will be needed.Safety Talk 17
2 Why discuss flare and overhead systems ? Flares and overhead systems present many and varied hazards. Accidents continue to happen to experienced people, who repeat previous mistakes, and fail to learn the lessons. It is often in common systems like the flare where problems occur. Ownership and extra vigilance are neededWorkplace safety depends on people !Discussions like this are essential:To maintain awarenessTo learn the lessons from past accidentsTo hear your local knowledge and experiencesWhy discuss ? (slide 2)Flares and overhead systems present many and varied hazards. Accidents continue to happen to experienced people, who repeat previous mistakes, and fail to learn the lessons. It is often in common / utility systems that problems occur, sometimes over long periods eg. build-up of deposits. Extra vigilance, rather than (more usually) less attention, is needed in these areas.Workplace safety depends on peopleDiscussions like this are essential to maintain awareness, to learn the lessons from past accidents, and to hear your local knowledge and experiences.Function of a flare systemThe function of a flare system is to safely dispose of vented material during normal operations, start ups, shut downs and emergencies. Material may be liquid or vapour, hot or cold, and may be vented automatically (unexpectedly) eg. by a relief valve lifting, or manually.Function of overhead systemsOverhead systems handle gases and vapours from the tops of columns and other vessels, often condensing vapours to form overhead liquid, some of which is returned as reflux. Water is often present leading to acidity and risk of corrosion.
3 What are the risks ?Fire and explosion – air ingress, ignition sourcesToxic – hydrogen sulphide, asphyxiation, pyrophoric and chemical depositsEnvironmental – smoke, glare, noise, smellLeakage / rupture – corrosion, embrittlement, vibration / hammer – overpressure, restriction or blockageCritical equipment or locations – flare area, incinerators, working at heightCritical tasks – draining liquid, lighting pilots, hot workThe unexpected – unexpected physical and / or chemical combinations1. UNDERSTAND THE RISKS ASSOCIATED WITH FLARES AND OVERHEAD SYSTEMSWhat are the risks ? (slide 3)Fire and explosion; air ingress, ignition sourcesToxic; Hydrogen sulphide, asphyxiation, pyrophoric materials which ignite on contact with air, and chemical deposits, which block pipework and process equipment.Environmental; Smoke, glare, noise, smellLeakage / rupture; Corrosion, embrittlement, vibration / hammerOverpressure, restriction or blockageCritical equipment or locations; Flare area, incinerators, working at heightCritical tasks; Draining low flash point, liquid, lighting pilots, hot workThe unexpected – flare systems present hazards of unexpected physical and /or chemical combinations
4 Managing the risks Plan and think through the work in advance Identify and assess the risks – what are the risks ? – what can go wrong ? – how likely ? – what consequences ?Apply the appropriate controls to the extent warranted by the risks – use a safer method, time or location – reduce the risk – procedural controls, work permits – training, including contractors
5 risks Risks – air ingress leading to explosion Vacuum systems Pump suctionsDraughtDrawn in through water seals, blanketting systemsDuring workPurging air to flareWhere else can air be pulled in ?
6 Risks – Fire and explosion Hydrocarbon leaks and spills – failures due to corrosion, vibration – liquid carryover, blowdown – flare puking, grass and ditch fires – cold work, breaking containmentIgnition sources – flare tip / flashback, incinerators, furnaces / stacks – pyrophoric scale – hot workExplosion – liquid carryover to incinerator, stack, sulphur plant – hot oil in contact with water eg. in K.O. / Blowdown drumsFire and explosion (slide 6)Air ingressVacuum systems eg. vacuum distillation, amine regenerators.Start-up / commissioning of equipment where air is purged with steam or nitrogen.Pump suctions where suction head is low.Maintenance or repair work involving opening up flare lines.Low flow and / or low density (eg. hydrogen rich) flare gas allowing air to enter flare stack by diffusion.Via blown water seals.Drawn in through blanketting systems.Ignition sourcesFlare tip, burnback.Pyrophoric scale from corrosion of mild steel by wet sour gas.Hot work (including external).Note: That external hot work on an overheads line caused an internal fire leading to 2 fatalities inside the column – see Safety Talk 9 Preparation for overhauls.Flare flame-outExplosion in incinerator.
7 Risks – ToxicHazardous substances – hydrogen sulphide, other flare / overhead gases – benzene, PCAHs – acids, alkalis, injections eg. ammonia – additional substances from physical changes or chemical reactions – solid deposits, sludgeCritical tasks – draining, venting, sampling, gas testing – cold work, breaking containment eg. spade swingingCritical locations – K.O. and blowdown drums, sumps, hotwellsToxic (slide 7)Flare systems receive materials from a wide variety of sources depending on the complexity of the refinery, and design / segregation of the system.Other flare / overhead gases.Benzene, PCAHs (Poly Cyclic Aromatic Hydrocarbons)Chemical deposits, sludge.Physical changes or reactions can produce additional substances.Critical tasks eg. liquid draining.Cold work; spade swinging, breaking containment.Acids, alkalis, injections.Hydrogen sulphide.ConcentrationParts per million Effect10 Threshold limit valueSmell distinctly disturbing and may be irritant to the eyesLoss of sense of smell. Slight symptoms after one to several hours exposureMaximum concentrations that can be inhaled for one hour without serious consequencesDangerous after 30 minutes>700 ppm Risk of death within 30 minutes1,000 ppm. Immediate loss of consciousness and fatal within a few minutes (0.1% volume)Note how dangerous H2S is at concentrations of 0.1% volume
8 Risks – Overloading or restriction Overloading – inadequate design, modifications or additions – simultaneous relieving eg. during power failure – unit upsetRestriction (or complete blockage) – closed valves or broken fittings – blockage of flame arrestors or molecular seals – ice hydrate, heavy oils / wax, hydrates – liquid accumulationOverloading or restriction (slide 8)Inadequate design or modifications / additions.Simultaneous relieving eg. during power failure.Restriction or blockage; Even a restriction is very serious as it reduces the relieving capacity of the system.Examples of material restricting flare / overhead systems; ice and hydrate, heavy oils / wax, hydrates, high freezing point components eg. benzene and cyclohexane (C6), blockage of flame arrestors / molecular seals with dirt, rust and iron sulphide, refractory debris.Liquid accumulation, slugging, poor draining / pump out facilities, heavy and light material, disposal for light material (separator caught fire – flashed off the flare at Antwerp).Hot oil; blowdown from heaters, heavy oils (contact with water).
9 Risks – Leakage or rupture Corrosion – water is often present in flare and overheads systems – the aqueous phase is usually acidic – chemical injections eg. ammoniaMetal embrittlement – low temperature eg. during depressuringVibration – liquid slugging (and solids eg. ice) – water / steam hammer – RV chatterWater injection – local corrosion / erosionLeakage or rupture (slide 9)Corrosion; water is often present in overheads systems, coming from water in the feed and stripping steam. The aqueous phase is usually acidic, as a result of sulphur compounds present, and may need neutralising eg. with ammonia.Overhead condensers – leaks both ways.Vibration; RV chatter, liquid slugging.Water hammer; water is often present in overhead systems, and can create a water hammer effect if it is allowed to build up and is refluxed back to the tower. This is most likely during start ups and shutdowns and during upset unit conditions. The hammer effect may be caused by slugs of liquid or by pressure surges resulting from water flashing to steam.Low temperature embrittlement eg. during depressuring.The noise and escape of vapours can hamper efforts to control the situation.Unless properly designed and installed, operation of water injection points installed to reduce fouling caused by deposition of soluble salts can result in severe local corrosion and / or erosion of the pipe wall. It was the recommissioning of a water injection to an FCCU Depropaniser overheads system which caused failure of the piping leading to a major explosion which destroyed most of the unit.
10 Risks – Environmental Glare, radiation Smoke Noise Smell Puking Community perceptionsEnvironmental (slide 10)Glare, radiation; open location, wide visibility.Smoke; acid rain, smuts, angry housewives.Noise; roaring, pulsating, steam purge.Smell; sour gas flare.Puking, overflowing knockout drum or seal pot.Unsightly sterile area, water contamination, grass fires.Community perceptions; flare associated with danger, bad smell, dirty washing etc.These can all have ‘licence to operate’ implications.
11 Risks – Critical tasks, equipment, locations Critical tasks – draining liquid (toxic and flammable) – lighting flareCritical equipment – incinerators, explosionsCritical locations – flare area, radiation (flare and sun), several hundred feet long – work at height eg. from platform, on flare stackCritical tasks, equipment and locations (slide 11)Critical tasksDraining liquid (toxic and flammable), lighting flare.Critical equipmentSour gas is often burnt in an incinerator rather than routing it to flare. Explosions have occurred where hydrocarbon liquid has been carried forward into an incinerator.Overhead condensers, leaks (both ways).Critical locationsFlare area, radiation (flare and sun), several hundred feet long, liquid, solid – coke and ice have been ejected from flare stacks.Working at height eg. from platformWorking on flare tip exposed to discharges from elsewhere eg. other flares and stacks. Fumes can be carried by the wind, and provision of emergency escape breathing apparatus and safety basket may be necessary – these prevented a serious incident in one refinery.
12 Risks – The unexpected Change is one of the greatest risks If you are surprised, you and / or the plant are at riskUnblocked drainUnexpected substanceUnusual pressure, temperature, level, flowUnusual operating mode eg. plant floating on flareInternal heat exchanger leaksAny other surprises ?The unexpected (slide 12)Change is one of the greatest risks.If you are surprised, you and / or the plant are at risk.• Unblocked drain• Unexpected substance• Unusual pressure, temperature, level, flow• Unusual operating mode eg. plant floating on flare during shutdown can introduce H2S into plant and equipment unexpectedly.• Internal heat exchanger leaksAny other surprises ?
13 Controls – Air ingressPrevent air ingress using molecular seals, purge gas, water seals (check)Address the hazards of air in start up and shutdown procedures eg. break vacuums with adequate gas or nitrogenMonitor oxygen content at strategic locations2) KNOW THE CONTROLSFire and explosionAir ingress (slide 13)Prevent air ingress using molecular seals and water seals (check). However water seals may freeze, tend to cause surge or uninterrupted flow at high flowrates.A minimum flow of purge gas is maintained up the flare stack to prevent air being drawn in.Against flashback; flame arrestor, water seals, molecular seals.Address the hazards of air in start up and shutdown procedures eg. break vacuums with adequate gas or nitrogen.Monitor oxygen content at strategic locations. Where process units handle air or oxygen eg. cat cracker, monitor oxygen content on the flare disposal from the unit involved, or on the flare main itself.
14 Controls – Fire & explosion Ignition sources – beware adjacent ignition sources including pilots and adjacent flares – remove and / or wet down pyrophorics – use the hot work permit systemFlare area – keep flare areas clean, free from vegetation, and under observation (by TV)Ignition sources (slide 14)Ignition sourcesBeware adjacent ignition sources including pilots and adjacent flares.Remove and / or wet down pyrophorics.Use the hot work permit system.Flare areaKeep flare areas clean, free from vegetation, and under observation (by TV).
15 Controls – Breaking containment Use work permits for all work on flare systems – assume all valves will pass – use positive pressure face mask BA – drain liquid at all low points – assume H2S and pyrophorics will be presentDetailed planning and procedures, and senior staff authorisation for high risk workCarry out work when refinery is steady, and allow no process changes during workBreaking containment (slide 15)Use work permits for all work on flare systems.Assume all valves will pass.Use positive pressure face mask BA.Drain liquid at all low points.Assume H2S and pyrophorics will be present.Detailed planning and procedures, and senior staff authorisation for high risk work.Carry out work when refinery is steady, and allow no process changes during work.Note: Most activities carried out on flare systems will be at height necessitating scaffolding for access. Allowances need to be made for workers to escape quickly wearing breathing apparatus if things go wrong.
16 Controls – Toxic Consider what may be present, and assess the risks Can the risk be reduced ?Prepare procedures for critical tasksPPE must be worn to provide adequate protectionWhen exposure to flare gas is possible, use positive pressure face mask BAIdentify equipment containing H2S (>0.5%) with yellow bandsToxics (slide 16)Consider what may be present, and assess the risks.Flares collect material from all over the refinery.New substances can form by physical and chemical changes.Can the risk be reduced eg. by purging, flushing, steaming ?Prepare procedures for critical tasks.PPE must be worn to provide adequate protection against toxic gas, vapour or spray, caustic and acidic liquid, (ejected) solid, sludge.When exposure to flare gas is possible, use positive pressure face mask BA.draining, venting, sampling, gas testing, breaking a flange.Identify equipment containing H2S (>0.5%) with yellow bands.Work permits and task procedures for critical tasks involving hydrogen sulphide or flare / overhead systems.
17 Controls – Overloading or restriction Overloading – clear responsibility for the flare system – carry out Hazops – prepare contingency plans – flare system alarms to be handled independently of the DCS – trips to reduce amount flared – trips to prevent liquid disposal to flare – venting directly to atmosphereRestriction – block valves must be locked open – drain liquid regularly – tackle root causes of restrictions & blockagesOverloading or restriction (slide 17)Contingency plans eg. loadshedding, alternative routings.HAZOPS of flare and incineration systems should consider unusual routings /circumstances where plants are shut down or equipment is being repaired. BP Oil has carried out flare and relief studies at all of its refineries worldwide. The results are contained in a ‘Register of Safety Related Devices’.Liquid handling; ability to handle all material eg. light ends, heavy / waxy material, water ?Drain liquid regularly, with extra attention in winter.Overpressure; trips to reduce amount flared, venting directly to atmosphere (but environment).High integrity trips to prevent vessels overfilling and disposing liquid to flare.Critical alarms to be handled independently of the DCS.High maintenance priority for the flare system (flare needs ownership).Block valves aroung RVs and on the flare main must be locked open. Locks and chains must be attached to the block valves to prevent unauthorised operation. Interlocks or special locking devices such as the Castell interlock system can be used.
18 Controls – Leakage or rupture Corrosion – monitoring and inspection – pH control, chemical injectionEmbrittlement – segregation of wet and dry (cold) streams – material selection eg. stainless steelLiquid slugging – liquid knockout eg. on units – grading and low point drainsWater hammer – dewatering eg. reflux drums, pumpsInspection and maintenance priority for the flare systemLeakage or rupture (slide 18)Corrosion; Monitoring and inspection, pH control, chemical injection.Embrittlement; Segregation of wet and dry (cold) streams, material selection eg. stainless steel.Liquid slugging; liquid knockout eg. on units, grading and low point drains.Water hammer; Dewatering eg. reflux drums, pumps.A high inspection and maintenance priority for the flare system.
19 Controls – Environmental Low level (ground) flare for normal / low flows (but safety implications)Height of stack to dilute / disperse emissionsTip design and maintenanceSteam injection for clean burningLiquid knockoutCommunity relations programmeEnvironmental initiatives eg. landscaping, tree plantingEnvironmental (slide 19)Low level flare for normal / low flows (but there are safety implications if the flare goes out and gas forms a flammable cloud at ground level and is then ignited).Height of stack to dilute / disperse emissions.Tip design and maintenance is essential to ensure reliability and total combustion.Steam injection for clean burning.Liquid knockout.Community relations programme.Environmental initiatives eg. landscaping, tree planting.
20 Controls – Critical tasks, equipment, locations Critical tasks – work permits, procedures and training – PPE, including positive pressure BA – standby / rescue personnelCritical equipment – operating instructions and technical guidance – inspection and maintenance schedules for critical equipment – relief valve removal needs proper technical approval – high priority must be given to completing work and re-installingFlare area – restrictions on entry to flare area, for what tasks, length of time, precautions needed etc.Critical tasks, equipment and locations (slide 20)Critical tasksWork permits, procedures and training.PPE, including positive pressure BA.Standby / rescue personnel .Critical equipmentOperating instructions and technical guidance.Inspection and maintenance schedules for critical equipment.Relief valve removal needs proper technical approval.High priority must be given to completing work and re-installing. (In one case reported the valves were off site for more than eight months).Flare areaRadiation; defining acceptable levels (flare / sun), extent of sterilisation zone etc.Restrictions on entry to flare area, for what tasks, length of time, precautions needed etc.For work on flare lines and elsewhere where gas may be present, breathing apparatus must be worn at all times. Also, a person must be available to effect rescue if required. These work practices must be reinforced by training.
21 Fire due to liquid carryover A fire occurred when hydrocarbons were carried over into a crude unit stack. The acid gas KO pot was designed for water but not hydrocarbon.3. REVIEW PAST INCIDENTS AND LEARN THE LESSONSFire due to liquid carryover (slide 21)A fire occurred when hydrocarbons were carried over into a crude unit stack. The acid gas KO pot was designed for water but not hydrocarbon. The liquid disposal route to the incinerator was blinded off and removed after the incident.There is a common but false assumption that an incinerator is designed to handle all disposal problems. Liquid knockout must be provided, and protective instrumentation eg. on flame failure may be warranted.Disposal of liquid to sulphur plant incinerators has caused explosions and fire in stacks, made worse where the stack is common.In another incident, carry over of light gas oil from the overheads of a VDU column ultimately led to an explosion in the waste gas incinerator.
22 Explosion at flarestack Beware ignition sources including pilots, pyrophorics, adjacent flaresDuring decommissioning of a flare, a steam purge was replaced with nitrogen. As a spectacle blind was being removed there was an explosion which blew a worker to the ground killing him.Explosion at flarestack when air sucked in (slide 22)During decommissioning of a flare, a steam purge was replaced with nitrogen. As a spectacle blind was being removed there was a rumble followed by an emission of gas and soot from the open joint. A second rumble followed by an explosion blew one of the workmen to the ground killing him. The nitrogen purge flow was inadequate to prevent air being sucked in as steam condensed, and hydrocarbon sludge remained in the knockout pot. Source of ignition was the flare pilot. Lessons learned include using only nitrogen purging, and using water to seal the knockout vessel.Air sucked in by flare draught / chimney effect.Another incident occurred when air was sucked in by the chimney effect of the flare stack while a damper plate was being inserted with the system under low (seal) pressure. No purging was used.Remove hydrocarbons by filling with water and skimming the surface.Nitrogen purge the system, testing for hydrocarbons.Presence of pyrophoric iron sulphide must be allowed for.Breathing apparatus, fire resistant clothing, and fire extinguishing equipment will be needed at critical stages of the work eg. when opening flanges for insertion of blinds.Closed valves in flare systems are not likely to be leak tight, due to deposits interfering with closure.Beware of possible ignition to flare under purge from adjacent flare flame pilots.
23 Fire during flare valve removal A flare main valve was being removed by contractors working on a temporary platform. There was a release of hydrocarbon liquid, which vaporised and ignited. 2 men died and 2 suffered serious burns.Fire during valve removal (slides 23 and 24)A flare main valve located some 20ft above ground level was being removed by contractors working on a temporary platform. The section of the flare main had been valve isolated. As the flanged joints were being broken there was a substantial release of hydrocarbon liquid, which vaporised to form a gas cloud. This ignited and in the subsequent fierce fire two of the men died and a further two suffered serious burns. The fire continued to burn for some 40 hours and was only extinguished by shutting down all the process units and injecting nitrogen into the flare system.The liquid had passed through closed valves. The flare line sloped away from the flare KO drum to the job-site, and the test to check for liquid in the line was not carried out at a low point.The source of ignition was probably a mobile air compressor, whose exhaust spark arrestor was missing. (The compressor was originally sited close to the job-site, but the Plant Supervisor had it moved some 35ft (11 metres) away).All the block valves were passing, partly due to sludge preventing the gates sealing properly. Installing valves ‘upside-down’ would help avoid this problem. Tell-tale devices to be fitted to all major flare valves to give indication of valve closure.More senior members of the Refinery Staff should have been involved and a written procedure prepared. High risk work on flare systems will be done only when refinery operation is steady and flare status is satisfactory. No unit changes will be made whilst flare work is in progressVenting points have been provided to allow inert gas to be injected into the flare main. Consideration will be given to necessity for nitrogen purging of pipework and wetting of work area surfaces.Survey of flare line slopes (topography) will be made.Work site to be spaded off prior to commencement of work.Initial breaking of joints should take place at points near drain valves.Refinery will investigate the use of hydraulic devices for splitting flanges from a remote location.
24 Flare valve removal Install flare valves ‘upside-down’ Survey flare line topography for low pointsInitial break near drain valvesSpade isolationInvestigate use of hydraulic devices to split flanges remotelyVenting points to inject inert gasNitrogen purging and wetting of work surfacesLocation and protection of machineryMore senior staff involvement / written procedureCarry out work only when refinery is steady, and allow no process changes during workFire during valve removal (slides 23 and 24)A flare main valve located some 20ft above ground level was being removed by contractors working on a temporary platform. The section of the flare main had been valve isolated. As the flanged joints were being broken there was a substantial release of hydrocarbon liquid, which vaporised to form a gas cloud. This ignited and in the subsequent fierce fire two of the men died and a further two suffered serious burns. The fire continued to burn for some 40 hours and was only extinguished by shutting down all the process units and injecting nitrogen into the flare system.The liquid had passed through closed valves. The flare line sloped away from the flare KO drum to the job-site, and the test to check for liquid in the line was not carried out at a low point.The source of ignition was probably a mobile air compressor, whose exhaust spark arrestor was missing. (The compressor was originally sited close to the job-site, but the Plant Supervisor had it moved some 35ft (11 metres) away).All the block valves were passing, partly due to sludge preventing the gates sealing properly. Installing valves ‘upside-down’ would help avoid this problem. Tell-tale devices to be fitted to all major flare valves to give indication of valve closure.More senior members of the Refinery Staff should have been involved and a written procedure prepared. High risk work on flare systems will be done only when refinery operation is steady and flare status is satisfactory. No unit changes will be made whilst flare work is in progressVenting points have been provided to allow inert gas to be injected into the flare main. Consideration will be given to necessity for nitrogen purging of pipework and wetting of work area surfaces.Survey of flare line slopes (topography) will be made.Work site to be spaded off prior to commencement of work.Initial breaking of joints should take place at points near drain valves.Refinery will investigate the use of hydraulic devices for splitting flanges from a remote location.
25 Ditch fire near flarestack During clean-up of drainage ditches, burning liquid fell from the flare tip and ignited oil in the ditchThe fire spread quickly beneath crude and propane pipelinesDitch fire near flarestack (slide 25)A fire in a flare stack area threatened crude oil and propane pipelines. On the day of the fire contractors were removing accumulated oil residues from the drainage ditches in the vicinity of the flare stack. Burning liquid fell from the flare tip and ignited oil residues in the ditches and the fire spread quickly to involve parts of the flare stack plant and adjacent crude and propane pipelines.Avoidance measures include:• Vegetation in the sterile area to be kept down• Oil spillages to be cleaned up promptly• Liquid in flare systems to be drained on a routine basis with special attention in winter• Access of personnel to the sterile area must be restricted and rigorously controlled• Flare tip maintenance schedules need to be held to• Process operators should monitor flare condition closely, TV monitoring is helpful in this respect• Remember that ditches can be very extensive and can spread fire quickly
26 Fatal gassing while replacing RV No work permit was in forceThe fitters began their work without informing anyoneThe plant flare was not isolated from the refinery flare main because other equipment within the plant was ‘live’The Refinery Fire Service were notified 13 minutes after the Medical CentreA fitter replacing a RV on a plant flare main was killed when a large emission of gas containing H2S occurred. He was wearing a ‘demand’ BA set – where the pressure inside the face mask drops below atmospheric. A second fitter and 2 rescuers (without BA) also collapsed.Gassing while replacing RV (slides 26 and 27)2 fitters were replacing a relief valve when a large emission of gas occurred from the open side connection of the relief valve. Although self contained breathing apparatus was being worn by both fitters, one of them felt unwell and collapsed. He was later found to have been fatally affected by the gas at some time during the incident when his breathing apparatus was not properly in position.2 rescuers began helping to move the victim but they also collapsed. Other men working nearby were alerted and began to assist in rescue work. The surviving fitter managed to make his own way down the east ladder before collapsing at the bottom.The Nurse administered first aid to the rescuers and the second fitter. The Refinery fire service were notified 13 minutes after the medical centre.The relief valve had previously been removed, reinstalled and re-removed using cold work permits. No permit was in force at the time of the incident.The flare main inside the plant was not isolated from the refinery flare main because other equipment within the plant was ‘live’ to it at the time.The fitters began their work without informing anyone.The BA used was a ‘demand’ set ie. air is supplied to the wearer as he inspires and so for a short period of time the pressure inside the face mask drops to sub-atmospheric.At the time of the accident, it is almost certain that the Refinery flare main contained hydrogen sulphide.The deceased had recently received refresher BA training.
27 Fatal gassingWork on a live flare system requires detailed risk assessment, preparation and precautions, with authorisation by senior managementTechnical guidance should be availableWork permit systems need regular reinforcement and auditingBA should have a positive pressure face mask with no in-leakageGassing while replacing RV (slides 26 and 27)Work on a live flare system requires detailed preparation and safeguards, and authorisation by senior management. Detailed technical guidance should be available.Breakdown in the control of the work prior to the incident as a result of poor communication and a failure to observe laid-down refinery procedures and practices.SCBA should be positive pressure type with no in-leakageFirst action is to raise the alarm and call for the appropriate emergency services.Only fully trained and equipped rescuers can attempt rescueWork Permit System needs upgrading, reinforcing and regular auditing.First action in an emergency is to raise the alarm and call for the appropriate emergency servicesOnly fully trained and equipped personnel may attempt rescue
28 Flare gas backs into unit 7 people were overcome by flare gas entering via a pressure control valve during spade swinging on a Cat. Cracker start-up.A fire was prolonged by flare gas entering via a RV bypass following an emergency depressurisation. A fire occurred on an ESV bonnet that had not been isolated from flare.Flare gas backs into unit (several incidents) (slide 28)The incident occurred during commissioning operations on the Cat. Cracker Unit when the spade isolating the regenerator and reactor systems from the main fractionator was being removed. Work had progressed to the point where the flanges had been jacked open and the spade removed. 3 of the men engaged on the job were affected by gas, the fourth apparently suffered no ill effects. Breathing apparatus was not being worn. The other 4 men affected were those who went to the scene on hearing cries for assistance. 1 worker lost three work days.The spade was completely removed with lifting gear when a rigger collapsed. The alarm was raised and the refinery ambulance called. Then a pipefitter and a second rigger collapsed, and personnel answered the call for assistance. Only one person wore breathing apparatus but the mask was not fitted correctly. Other rescuers either did not have breathing apparatus with them or just carried it. This resulted in further casualties. The emergency service and refinery nurse arrived to administer first aid and removed casualties to medical centre.The fractionator pressure control valve was open to the refinery flare system allowing flare gas containing H2S to flow back into the unit. The gas could have emerged through the open vent on the main fractionator overhead condensers or emerged from the column side spade flange.Main recommendation was positive isolation from the flare to be defined in operating procedures.Flare gas backs into unit via RV bypass: Following an emergency depressurisation during a fire, the fire is thought to have been prolonged by flare gas backing into the unit via the vent line- in this case a relief valve bypass.Fire on ESV bonnet: In this particular case the normal operating pressure of the flare header is mbar (1.3 psig) since a flare gas recovery compressor is installed. Thus, it is even more important than usual to isolate the ESV from the flare header by means of the block valve.Remember that the flare can be a source of gas when equipment is depressuredPositive isolation from the flare must be defined in operating procedures
29 Unexpected outcome ?A fitter received chemical burns during the swinging of a spade in a flare line. He was off work for 1 day.Unexpected outcome (slide 29)A fitter was off work for 1 days when he received chemical burns during the swinging of a blank in the flare line. Although warned about and protected against any possibility of gas, he disregarded liquid which ran out of the flange This was a mixture of steam condensate, caustic soda and amine.If you think work through and ask “what if?” you should never be surprised - and you will be much safer
30 Mis-use of flare system Clay treaters on a MEROX plant were being water washed via the RV bypass, using the flare K.O. drum as a pump out vessel. An undetected valving error routed kerosene into the flare for 8 hours. The flare stack water seal overflowed, contaminating ground water and the river.Mis-use of flare system (slide 30)Clay treaters on a MEROX plant were being water washed via the relief valve bypass, using the flare knockout drum as a pump out vessel. Inadvertently the clay treater outlet valve was left open allowing kerosene to back into the flare system for about 8 hours. This was discovered when the water seal at the flare stack base started to overflow, spilling kerosene into the river and contaminating ground and ground water.A basic cause was the inappropriate use of the flare system for flushing and pumping out – it was recognised that with large parts of the flare system filled with liquid it would not have been able to cope if a major relief situation had developed. There was poor visibility in the level glass of the flare knockout drum, and no independent high level alarm.Lessons learned include critical task procedures, check lists for verifying isolation, inspection and testing of alarm systems and communication between shifts.
31 Overhead vent failureA 2 inch vent located on the top of a horizontal 10 inch line completely failed, releasing a large vapour cloud which fortunately did not ignite.Overhead vent failure (slide 31)A vent on an overhead line completely failed, releasing a large vapour cloud which fortunately did not ignite. The vent was located on the top of a horizontal 10” line and consisted of a reducer, a valve and a blind flange. It failed when a relief valve lifted and began to chatter, vibrating the overhead line.The vent system was a modification with unknown installation date.Investigation revealed fatigue and indicated that the crack had propagated over a long period of time. The failure occurred in the heat affected zone of the reducer to flange weld, immediately below the valve. The design configuration was inadequate with a large valve supported on a 2 inch connection with no reinforcement pad or gusset.Inspections should include critical items such as small connections to main pipelines where failure could lead to significant release.
32 Disastrous accumulation of liquid During a lightening storm a RV lifted and disposed liquid to flare. A second RV lifted 5 hours later, and 2-phase flow created mechanical shocks leading to a 30 inch corroded elbow failing. The resulting explosion and fire injured 24 people, damaged 2 units, and caused structural damage to buildings 2 miles away.Disastrous accumulation of liquid (slide 32)Following a major upset caused by lightening storms a relief valve lifted and filled a flare drum with liquid. A large compressor subsequently (5 hours later) tripped relieving a large gas flow to flare. The 2-phase flow created mechanical shocks in the flare leading to a 30” corroded elbow failing. The release of gas and liquid ignited from a process heater and resulted in an explosion and fire, injuring 24 people, damaging 2 units, and causing structural damage to buildings 2 miles away.A critical cause was the liquid remaining in the knockout drum – a review of K.O. drum pump-out times is needed, including the ability to pump out light material containing LPG.High integrity trips to prevent vessels overfilling and disposing liquid to flare.In a refinery wide shutdown, the DCS may be lost and critical alarms may need to be independently handled.Two phase flow is possible where unit KO drums are not provided.Maintenance priority accorded to the flare system was not as great as that given to process units.The failure was due to vibration which was two pipe diameters at the time of failure due to the combined effects of surge and liquid carry over. Retiral limits of pipework were also an issue.Spill from flare KO drum which was full for 17 hoursDue to a defective level controller light gasoline entered the flare system, and the flare KO drum was full of liquid for about 17 hours, the high level alarm being overlooked because many other alarms were on during start up. Spillage resulting in soil contamination occurred at the flare, but the most serious potential was clearly the risk of high pressure build up if a large release had occurred from a relief valve.Light gasoline spilled into the oily water system and the flare trap pump failed to start because of the low density of light gasoline in the trap, which was calibrated for water.Lessons learned included increasing flare KO drum capacity, installing automatic start up pumps and flare pumps, segregating important alarms onto a separate monitor.Emergency depressuring hits 30 cubic metres of liquid and dislodges 100m. of flare line from supportsDuring an emergency depressuring operation gas was diverted into a flare line and hit a 30 cubic metre slug of liquid. The vibration dislodged about 100 metres of the flare line which fell 10 metres to the ground and buckled. A leak at this point could have caused a major disaster.The flare sump and drain line were blocked by scale and discarded welding rods from 4 years earlier.Blockage and corrosion is most likely at low point drains.Detecting extent of problems is not easy, pipeline radiography being used with some success.Selective cleaning of sections such as bends, cross overs and expansion loops. Use of higher grade steels, and purging at dead legs of the flare system are methods used at some sites.
33 Blocked flareDuring an upset, a cat. reformer relieved into a 42 inch flare stack that was blocked by ice. Temperature was about °C, which was normal. Fortunately the crude unit was cracked open to flare, and this allowed the crude column to act as a pressure buffer.Blocked main flare (slide 33)A 250 ft, 42” flare stack containing a molecular seal located 30 ft below the tipwas blocked by ice. The flare tip has a top steam ring and a centre steam injection nozzle approximately 8 feet from the top to lift the flame off the tip and prevent overheating. The centre steam flow rate is held constant but the steam flow to the outer ring is controlled to minimise smoking. Night temperatures were – 18°C which was normal.The refinery concluded that the molecular seal had been slowly plugging over a number of days due to a blocked drain at the bottom of its seal caused by small pieces of refractory from the flare tip. Steam from the centre nozzle was condensing and running down the stack.The centre-steam injection point will be shut down during cold weather.The molecular seal drain will be modified so that it can be checked free of blockages at regular intervals.Fortunately at the time of the incident a small quantity of gas from the crude unit was being flared and this allowed the gas released from the cat. reformer during the upset to back-up into the crude column which acted as a pressure buffer/damper.Several other flare blockages have been reported.Flare blockage is a major risk – do we adequately cover it ?Blocked H2S flare: Sour stripper gas was routed to an H2S flare system that was blocked with severe salt sediments. The system was not insulated and condensation salts had built up in the flare gas compressor lines.HAZOPS of flare and incineration systems should consider unusual routings /circumstances where plants are shut down or equipment is being repaired.It is often in these peripheral utility systems that problems occur, sometimes over long periods. Extra vigilance, rather than (more usually) less attention, is needed in these areas.
34 Optional quiz1. Name 5 general risk areas associated with flare systems2. How can air find its way into the flare ? (5 ways)3. List 5 ignition sources found in flare and / or overhead systems4. List hazardous substances found in the flare (5)5. What precautions should be taken when draining flare drums / pots ? (4)6. Which of your critical tasks are associated with flare / overhead systems (5)7. What specific precautions should be taken when breaking into a flare line ?8. What can cause blockages in flare / overhead systems (5)9. Give 5 examples from this Safety Talk of incidents involving flare systems (5)10. Give 2 more examples from your experience.(4)ReferencesAPI RP 520 / 1BP Oil Cleveland, USA, has put together further sets of analyses of incidents additional to those listed in previous QSBs – a complete listing of analyses is found below. The information extracted from reports includes parts of the units, or plant, where the inci- dent or failure occurred; the task or operation in progress; hazards which were present at the onset of, or developed during the incident; consequence or loss; and, in some case, identification of causes considered to have contributed to the incident.These analyses have been prepared on behalf of the US Refineries to facilitate incident reviews during Project Safety Reviews and Process Hazard Analyses.Information can be obtained from Marsha Mezenski, BP OUS, Cleveland. She can be reached by way of , telephone ( ), or fax ( ).
35 Safety Talk 17 Attendance roster Name Date Safety Talk 17
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