DEPARTMENT OF EMPLOYMENT The disaster Report of the Court of Inquiry

London: HerMajesty's StationeryOffice Crown copyright 1975 First Published 1975

ISBN 01 1 361075 0 ii Formal Investigation into Accident on 1st June 1W4 at the Nypro Factory at Flixborough

Appointment of persons to hold investigation The Secretaryof State,in exerciseof his powers under Section 84 of the Factories Act 1961, herebydirects a formalinvestigation to be held under the saidSection 84into the accidentwhich occurredon the 1st June 1974 at the factoryof Nypro (UK) Limited at Flixborough. The Secretaryof State,in further exerciseof his said powers under the saidSection 84, hereby appoints: ROGER JOCELYN PARKER, ESQ, QC, (Chairman) JOSEPH ALBERTPOPE, ESQ, DSc, PhD, WhSch, CEng, FIMechE, (Deputy Chairman) JOHN FRANK DAVIDSON, ESQ, MA, PhD, ScD, FRS, CEng, FIChemE, MIMechE WILLIAM JAMES SIMPSON, ESQ to hold thesaid investigation.

The Secretaryof State further appointsB~NARD MICHAEL O'REILLY, ESQ, FRIC, to be Secretaryof the saidinvestigation.

Michael Foot Secretaryof Statefor Employment 27th June1974 Introduction l Explosion exerting downward forceon 20 inch assemblyand at the same timean upward force Scopeof theinvestigation I on the motorssufficient to blow themup andto the west Site and generalhistory of FlixboroughWorks 2 Vertical emissionfrom 8 inch rupturelasting for Layout of the works 3 shortperiod after themain explosion Organisationof the Company 3 General observationson the &inch hypothesis 29 The Board of Directors Damageconnected with the 8 inch line 30 EssentialManagement Fracturedpipe-hanger, spring and angleiron The EngineeringDepartment Orientationof zinc cracks in the8 inch line Section25A - The process andlayout 4 Deformationof elbow K and 40" pipe twist General descriptionof process Deformationof elbow G Detaileddescription 20-inch and &inch hypotheses compared32

Startup procedures 6 Miscellaneous 32 Eventsfrom 28thMarch to 1stApril 7 (a) Security (b) Safety precautionsgenerally (c) Storageof potentially dangerous substances Eventsfrom 1stApril to 29th May I I Lessonsto be learned 32 Eventsfrom 29hMay to explosion I I Introduction The explosion andaftermath 13 General observation Sourceof Main Explosion Immediate lessons to be learned from the disaster The problemstated 15 Specific lessons 34 Two-stage ruptureof the by-pass 15 Integrity of plant Eye-witness,film and photographicevidence 15 Management operation Evidenceof the laboratorywitnesses Generallessons 35 Witnessessaid to have seen somethingbefore Nitrogen supply the first event whateverthat event may have Nitrate stress corrosion been Zinc embrittlementof stainlesssteel Conclusions oneye-witness evidence Creep cavitationof stainless steel Films and photographs The 20-inchhypothesis examined Miscellaneouslessons 36 Explosionof vapour clouds in theopen air The &inchhypothesis I9 Investigationof the disaster Background The stepsin the hypothesis Mattersto be referredto the special committeeor otherbodies 36 Examination of individual steps in &inch Plant layout and construction hypothesis 22 Siting of plant Loosebolts Planning procedures Leaksand laggingfire Emergencyarrangements Gasket burst Licensingstorage The flame to produce thedesired results Clad mild steel Fire in areaof fins and embrittlementof enclosed pipes Summary 37 Costs 38 Appendix III Procedural history 50 Acknowledgements 39 Appendix IV List of representations52 Appendix I Experimental and otherevidence Appendix V List of witnesses 53 relating to rupture of 20 inch pipe and bel- lows assembly from internal pressure andAppendix V1 Reports 55 temperature 40 1 Reportsgiven in evidence Flixboroughtests by SMRE 2 Reports referred to in evidence Nottinghamtests onbellows 3 Reports madeavailable to the Court Bretby pipe test Dynamic failure of bellows and pipe Appendix II Damageto the 8 inch pipe and related metallurgicalinvestigations 46 Damageto the pipe Damageto pipe hangers,support bracket, gas- Abbreviations kets and pipe lagging AISI AmericanIron andSteel Institute Displacementof separators BS British Standard Metallurgical investigations BTU British Thermal Unit C Column Creep cavitation DSM Dutch StateMines Swelling of the pipe H Hanger HMFI Her Majesty'sFactory Inspectorate Zinc cracking NCB National CoalBoard Sourcesof zinc NRV Non ReturnValve PCT ProcessControl Technician Zinc transferto stainless steel R Reactor Bulge at the 3 inch split S (four fig. number) Separator S Section Pipehanger spring temperature SMRE Safety in Mines Research Pipe hanger rod temperature Establishment standardwire gauge Summary of metallurgical evidence as to Valve temperatures Mixer Works of Nypro (UK) Ltd beforethe explosion.View from the south-east. Works after theexplosion. View from the south-east. Works after theexplosion, seen from the north. The conflagration,seen from the south-west. The fires seenfrom the south-west. Model of section25A kept in the control roomand destroyedin the explosion. Reactor5 showingcrack which ledto its removaland replacement by the by-pass inMarch 1974. Reactors4 and 6 soon after theexplosion. Thejack-knifed 20 inch pipe with attachedflanges and 28 inch stubpipes. Thejack-knifed 20 inch pipe showingtrapped aluminium cladding and charredwood. Squirmedlower bellowsin the SMRE simulation test. Squirmedbellows in the NottinghamRig. Buckled pipe at Bretby. The 50 inch ruptureon the 8 inch pipe. Broken and bent pipehanger rod, and spring. View of the 8 inch pipewhile testingwater spray system during plantacceptance tests (pipe partly lagged). Typical water spraynozzle with air-operated sensorbelow. Photograph taken after theexplosion.

REPRODUCED BY COURTESY OF HMFI, DR K GUGAN, "SUNDAY EXPRESS', "SCUNTHORPE EVENING TELEGRAPH", NYPRO, SMRE, C H WOOD (BFD) LTD AND CREMER & WARNER. vii List of Figures

Simplifiedplan of Flixborough worksof Nypro (UK) Ltd.

Cyclohexaneoxidation plant Section25A. Simplified plan and elevationof part of Section25A.

Arrangementof 20 inch pipescaffolding (as deducedfrom theevidence). Section25A - chartused for recording oxidationsystem pressure. Sketchof pipe and bellows assembly showingshear forceson bellowsand bending momentson pipe. Principleof NottinghamTest Rig.

Sketchof 8 inch lineas viewed from north-west.

View of 8 inch line showingtypical lagging boxaround valves as viewed from the east.

The damaged8 inch pipe. Stepsin the "8-inch pipe" hypothesis. To the Rt Hon Michael Foot, MP, Secretaryof Statefor Employment

Introduction 1 At about 4.53 pm on Saturday1st June 1974the Flixborough Worksof Nypro (UK) Limited (Nypro) were virtually demolishedby an explosionof warlike dimensions.Of thoseworking on the site at the time, 28 were killed and 36 otherssuffered injuries. If the explosionhad occurredon an ordinary working day,many morepeople would havebeen on the site, and the numberof casualties would havebeen much greater. Outside the Worksinjuries and damagewere widespreadbut no-one was killed. Fifty-threepeople were recordedas casualties by the casualty bureauwhich was setup by the police; hundreds moresuffered relatively minor injurieswhich werenot recorded.Property damage extended overa wide area, anda preliminary surveyshowed that 1,821houses and 167 shops and factories hadsuffered to a greateror lesser degree. 2 On 27th June1974 you appointedus underSection 84of the FactoriesAct 1961to hold a formal investigationto establishthe causesand circumstancesof the disaster andto point out any lessons which we might considerwere immediatelyto be learned therefrom. 3 As requiredby Sub-Section3 of Section 84of the Act we held our investigationin open Court. The hearingsoccupied a totalof 70days. They openedat the Wortley Hotel in Scunthorpeon 9th September 1974.After five days, mostly devotedto the takingof eye-witness evidence,the hearings were adjourned to London. In all we heardevidence from 173 witnesses. 4 Prior to our appointment,investigations and an interim report had alreadybeen madeby Her Majesty's Factory Inspectorate(HMFI), and investigationswere beingpursued by many other persons andbodies. Betweenour appointment and the openingof the investigationat Scunthorpe the following stepswere taken: (a)we held a preliminary meetingfor the purposesof giving directions as to representation and procedure; (b) the taskof assembling theevidence for presentationat the hearing was undertakenby the Treasury Solicitor;(c) Messrs Cremer and Warner, Consulting Chemical Engineersof 140 BuckinghamPalace Road, LondonSWlW 9SQ, were appointedat our requestas technical advisers to the Court and instructedto seekand provideto the Treasury Solicitor evidenceas to the causesof the disaster; (d) thework of recovering, identifyingand examining wreck- age,and of conductingrelevant tests,was undertaken by the Safety inMines ResearchEstablishment at Sheffield(SMRE) to whom we wish to pay a specialtribute; (e) further investigationswere pursued by other persons andbodies. 5 During the courseof our investigationsa large numberof scientificreports were submittedto us and circulatedto all parties.A completelist of suchreports appearsin AppendixVI. Many of such reports althoughof greatvalue to the ascertainmentof the causeof the disasterhave no wider applica- tion. Others containscientific information of a more general kindwhich, we believe, wouldbe of value to publish. We havemarked the paperswhich fall into this categorywith an asterisk.

Scope of the investigation 6 The evidencebefore us establishedconclusively at an early stage two basic facts. (a) thatthe cause of the disasterwas the ignition and rapidacceleration of deflagration,possibly to the point of detonation,of a massivevapour cloud formedby the escapeof cyclohexaneunder at leasta pressureof 8.8 kg/cm2and a temperatureof 155°C. (b) that such escapehad emanated froma section of theplant knownas Section 25A. This section was devotedto the productionof cyclohexanoneand cyclohexanolby the oxidationof cyclohexane with air in the presenceof a catalyst. 7 Our detailedinvestigations were, therefore, primarily directedto ascertaining the causeof such escape,and we wereonly concernedin detailwith other sectionsofthe plant to theextent that they were or might havebeen connected withthe operationsof Section25A, theescape therefrom, or the ignition of the vapourcloud resultingfrom theescape. We shall,however, referto the other sectionsof the plant additionallyto the extentthat they formpart of thegeneral background of relevant circumstances or lead us to the conclusionthat we should pointto some lessonor lessons immediatelyto be learned.

8 With regardto lessonsto be learned,we wereat all times consciousthat you desired usto establish the causesand circumstancesof the disaster asspeedily as possible and to point out only immediate lessonsarising therefrom. Thereforewe did not considerthat we shouldinvestigate, or seekto make recommendations upon,such generalmatters as the properpolicy with regardto safety,siting, layout and constructionof plantssuch as that at Flixborough. To havedone so would haveinvolved the takingof an immenseamount of evidenceconcerning the practiceat similar plants throughout theworld andconcerning thesocial, environmental and economic consequencesof possible changesin currentpolicy, practiceor safetyrequirements. Thiswould have delayedthis Reportby many months.We werereinforced in our view asto the limitsof our taskby the factthat, on the27th June1974 when youannounced our appointment,you also announcedthat you would be settingup anexpert committeeto examinethe hazardsof large scaleplants andthe ways in which people workingin themand living nearbycould be safeguarded.The detailed termsof referenceof this committeewere publishedon the 4th November1974 and were: "To identify typesof installationsexcluding nuclear installationswhich havethe potentialto presentmajor hazards toemployees or the public or the environment andto adviseon measures for control appropriateto the natureand degreeof hazardover the establishment,siting, layout, design,operation, maintenance anddevelopment of suchinstallations as well as overall developmentboth industrial and non-industrialin the vicinity of such installations." The membershipof the committeewas publishedon the 9thJanuary 1975 and it beganits work immediatelythereafter. 9 However,it emergedduring the courseof our investigationthat there is urgent need for a re- considerationof certain aspectsof currentpolicy and practice.Notwithstanding thelimited natureof our task,we havetherefore thought it right,in that sectionof this Reportwhich dealswith lessonsto be learned,to recommendurgent review of such aspects.

Site and general history of Flixborough Works 10 The Works(see Plate l) are situatedon flat low lying land on the east bankof the River Trent aboutsix miles to the southof the pointat which that river joins the Humber.They occupyan areaof some60 acres.The nearestvillages are Flixboroughitself and Amcotts on the opposite bankof the river (both abouthalf-a-mile distant) and Burton-upon-Stather (about twomiles distant). The townof Scunthorpeis approximately threemiles away. 11 The immediateneighbourhood of the works consists largelyof farms and has verya low popula- tion density; the perimeterof the works is surroundedby fields. The sitingof the works wasfortunate. Had they beenin a denselypopulated area thereis no doubt thatdeath and serious injurywould have beenon a much greaterscale and that the property damage,even if more localised, would havebeen moreserious. The factsthat 72 out of 79 housesin Flixborough,73 out of 77 housesin Amcotts,644 out of 756 housesin Burton-upon-Statherand 786 housesin Scunthorpewere damagedto a greater or lesserdegree speak for themselves. 12 The sitewas originally occupiedin 1938 by a Companycalled Nitrogen FertilisersLimited, a subsidiaryof FisonsLimited and usedfor the manufactureof ammonium sulphate.In 1964Nypro wasformed, owned jointly by Dutch StateMines (DSM) and FisonsLimited. It acquired the site from Nitrogen FertilisersLimited. Between 1964 and 1967plant was built for the productionof capro- lactam,which is a basic rawmaterial for the productionof Nylon 6, by a process,the first step inwhich wasthe productionof cyclohexanone viathe hydrogenationof phenol.The workswere commissioned and productioncommenced in 1967.They were then and remained untilthe disaster theonly worksin the United Kingdom producing caprolactam. 13 In 1967Nypro was reconstitutedwith DSM owning 45 %, the National Coal Board45 % and Fisons Limited10%. Almostat oncedesign began for additional plantto increasethe capacityof the works from 20,000tons of caprolactam per annumto 70,000tons per annum. This additional plant, referredto asPhase 2, wascompleted at a costof some£15m in 1972.Its distinguishing featurefor presentpurposes is that in it the cyclohexanonenecessary for the production of caprolactamwas producedby the oxidationof cyclohexaneinstead of via the hydrogenationof phenol.In 1972DSM QEPARTMENT OF EMPLOYMENT

Report of the Court of Inquiry

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