Health and Safety Safety Advice

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Health and Safety

Executive

Safety advice for bulk chlorine

installations

This is a free-to-download, web-friendly version of HSG28

(Second edition, published 1999). This version has been adapted for online

use from HSEs current printed version.

Youcanbuythebookatwww.hsebooks.co.ukandmostgoodbookshops.

ISBN 978 0 7176 1645 2

Price 14.00

Thisbookletgivesguidanceonthesafehandlingofchlorineatsiteswhichreceive

bulkdeliveriesofchlorinebyroadorrailtanker.

Itisaimedatthemanagersoftheseinstallations,butitisalsorelevantforplant

supervisors,designandmaintenanceengineersandsafetyprofessionals.

HSE Books


2/91Page2of91

Health and Safety

Executive

Crown copyright 1999

Firstpublished1987

ISBN9780717616452

Allrightsreserved.Nopartofthispublicationmaybereproduced,storedin

aretrievalsystem,ortransmittedinanyformorbyanymeans(electronic,

mechanical,photocopying,recordingorotherwise)withoutthepriorwritten

permissionofthecopyrightowner.

Applicationsforreproductionshouldbemadeinwritingto:

TheOfficeofPublicSectorInformation,InformationPolicyTeam,

Kew,Richmond,SurreyTW94DUore-mail:[email protected]

ThisguidanceisissuedbytheHealthandSafetyExecutive.Followingtheguidance

isnotcompulsoryandyouarefreetotakeotheraction.Butifyoudofollowtheguidanceyouwillnormallybedoingenoughtocomplywiththelaw.Healthand

safetyinspectorsseektosecurecompliancewiththelawandmayrefertothis

guidanceasillustratinggoodpractice.


3/91Safetyadviceforbulkchlorineinstallations Page3of91

Health and Safety

Executive

ContentsForeword 5

Introduction 6

Management of health and safety and risk assessment 7

Riskassessment 8

Design and location of installations 10

Potentialincidents 10

Sitingofinstallations 10

Unloadingarea 12

Design and location 12

Deliveries of liquid chlorine by road tanker or ISO tank container 13

Interlocks 14Deliveries of liquid chlorine by rail tanker 15

Connectionsbetweenthetankerandthefixedlinestothestorageinstallation 16

Types of connection 16

Flexible couplings (semi-rigid loading arms) 16

Flexible hoses 17

Articulated arms 17

Pipeworkforliquidchlorine 17

Permanent pipework at the unloading point 18

Design criteria for pipework transferring liquid chlorine to storage tanks or

from storage to point of use 18

Protection of pipework 19

Marking 20Protectionofliquidchlorinepipeworkagainstoverpressure 20

Provision of relief systems 20

Valves 21

Types of valve 22

Vertical globe valves 22

Conical plug valves (PTFE-sleeved) 22

Ball valves 23

Remotely controlled valves 23

Storagevessels 23

Design criteria 24

Connecting pipework and means for isolation of storage tanks 25

Liquid chlorine inlet 26

Liquid chlorine outlet 26Vent and compressed dry gas lines 28

Relief system 28

Instrumentation and chlorine detector systems 28

Chlorine detectors and alarms 29

Protectionofstoragevesselsagainstoverpressure 30

Relief system 31

Bursting discs 31

Arrangements for relief systems 31

Expansion vessels 33

Pressure alarms 33

Arrangementsforunloadingofliquidchlorinefromroadtankerstostorage 34

Unloading using dry compressed air or dry nitrogen 34Supply of dry padding gas to the system 35

Unloading using chlorine gas pressure 35

Use of re-compressed chlorine vapour 35

Chlorinevaporisers 36



Health and Safety

Executive

Types 36

Regulation of throughput 37

Methods of heating 37

General installation 38

Hazards 38

Routine and emergency isolation 40

Pressure control valve 41

Corrosion 41

Chlorineabsorptionsystem 42

Vent collection system 43

Absorption equipment 43

Instrumentation 43

Disposal of effluent from the chlorine absorption plant 44

Operating and maintenance procedures, training and PPE 45

Operatinginstructions 45

Maintenance,inspectionandinstallation 45General maintenance requirements 45

Maintenance of connections 46

Inspection and commissioning of chlorine tank installations 46

Inspection procedure 47

Testing 48

Modificationofthechlorinesystemandclearanceprocedures 48

Unloadingofliquidchlorinefromroadtankerstostorage 49

UseofISO(demountable)tankcontainers 50

Transferofchlorinetotheconsumingunits 51

Transfer of gaseous chlorine 51

Transfer of liquid chlorine using vapour pressure 51

Transfer of liquid chlorine by padding with dry compressed gas 51Transfer of liquid chlorine using a separate pumping tank 51

Precautions 52

Training 53

Competency and audit 53

PersonalProtectiveEquipment(PPE) 54

Selecting suitable respiratory protective equipment (RPE) 54

Emergency arrangements 57

Emergencyequipment 57

Controlofleakages 58

Releases inside buildings 59

Appendices 601Toxicologicalpropertiesandfirstaid 60

2Characteristicsofchlorine 61

3RelevantlegislationandHSEguidance 64

4Usefulcontactsandstandards 72

5Outsideinstallationsandinsideinstallations 75

6Proceduresfordischargingroadtankersofchlorine 77

7Typesofvaporiser 80

8Emergencyplans 83

References 85

List of acronyms and abbreviations 90

Further information 91



Health and Safety

Executive

ForewordTheaimofthisguidancenoteistohelpthoseresponsibleforthesafeuseof

chlorinefrombulkcontainerstomeettheirobligationsunderhealthandsafetylaw.

Thisguidance,likethedocumentthatprecededit,waspreparedwiththehelpof

thechlorineproducers,users,tradeunions,theWaterServicesAssociation(WSA),

andtheChemicalIndustriesAssociation(CIA).

Wearegratefultothosewhocontributedfortheirassistanceandco-operationin

preparingthisadvice,andtoShawValvesandtoDescoteLtdforpermissiontouse

thephotographslinkedtoparagraph74,toWestonPointStudiosforpermissionto

usethephotographslinkedtoparagraph216andtoZenecaplcforpermissionto

taketheremainingphotographs.

Theguidelinesmaybeappliedtoanybulkchlorineinstallationbuttheyarenotintendedtobeadetaileddesigncode.Someexistinginstallationsmay

notatpresentmeetalltherecommendationsand,insomecases,notallthe

recommendationsmaybeappropriate.Itisfortheoccupier,usuallyinconsultation

withthechlorinesupplierand/orspecialistadvisers,tojudgetheneedforfurther

riskcontrolmeasures,followinganassessmentoftheactualrisks.Ifimprovements

areshowntobeneeded,aresponsibledecisionisrequiredfromtheoperating

companyonthenatureandtimingofchangessothattheycanbemadesafely.

WherereferencetoBritish,Europeanandotherstandardsismadeinthisdocument

equivalentstandardsareequallyacceptablealternatives.

Youmayneedhelpbeyondthatgiveninthisguidance.Ifyoudo,tradeandemployerassociations,suchastheChemicalIndustriesAssociationandEuroChlor,

oryourchlorinesuppliercanofferarangeofadviceandsupport.Theseandother

sourcesofinformationaregiveninAppendix4.



Health and Safety

Executive

Introduction1 Thispublicationgivesguidanceonthesafehandlingofbulkliquidchlorineat

siteswhichreceiveliquidchlorinebyroadorrailtanker,orbyISOtankcontainer.

Theguidanceisaimedprimarilyatmanagersoftheseinstallations,butitisalso

relevantforplantsupervisors,designandmaintenanceengineers,andsafety

professionals.Applicationoftheguidancewillhelptoensurethattheriskstopeople

on-siteandoff-siteareminimisedsofarasisreasonablypracticable.

2 Therisksarisebecausechlorineisahighlytoxic(seeAppendix1)andreactive

substance(seeAppendix2).Itformsflammableandexplosivemixtureswithsome

organicandinorganicsubstances.Whenreleasedfromcontainmentitformsagas

cloudthatisheavierthanairandwhichmaintainscontactwiththegroundasit

disperses,possiblyendangeringpeopleinitspath.

3 Despitetheserioustoxicandreactivehazards,andthepotentialtoharmpeopleoff-site,thechlorineindustryhasestablishedaverygoodsafetyrecord.This

hasbeenachievedthroughthedevelopmentandpracticeofeffectiveprocedures

forhandlingchlorinesafely.Thisguidance,likethedocumentitreplaces,isissued

tohelpmaintainandenhancethatrecord.Guidanceonthesafehandlingofchlorine

suppliedindrumsandcylindersisgivenelsewhere.1

4 TheguidanceisbasedonthecombinedexperienceofthefourUK

manufacturersofchlorine,theircustomers,tradeunionsandassociationsandHSE.

Itcoversthesafetyandhealthrequirementsatallstages,fromthereceiptofthe

liquidchlorinetothepointofuse,includingthelocation,design,testing,operation

andmaintenanceofequipment.Proceduresfordealingwithemergenciesarealso

outlined.



Health and Safety

Executive

Management of health and

safety and risk assessment5 EmployershavealegalresponsibilityunderSections2and3oftheHealth

andSafetyatWorketcAct1974(HSWAct)2toensure,sofarasisreasonably

practicable,thehealthandsafetyoftheiremployeesandotherswhomaybe

affectedbytheiractivities.Otherpeople,suchasdesigners,installersandsuppliers,

alsohavesimilardutiesundertheHSWActwithrespecttoproducts.Since1974

variousregulationshavebeenmaderequiringspecificcontrolsforparticularhazards

(egpressuresystems),oractivities(egmanualhandling).Alistoftheseandother

currenthealthandsafetylegislation,codesofpracticeandguidanceispublished

annually.3Thislistalsocoversamendmentstotheregulations.Referencesinthis

documentaretothebaseregulations.Appendix3givesanoverviewofthemain

legislationandregulationsrelatingtothesafehandlingofchlorine.

6 Youmustobtainplanningpermissionfornewinstallationsintheusualway

fromtheLocalPlanningAuthority,whowill,whenappropriate,refertoHSEfor

advice.Ifyoustore,orplantostore,morethan10tonnesofchlorine,yoursitewill

besubjecttoanumberofspecificregulations.

7 TheNotificationofInstallationsHandlingHazardousSubstancesRegulations

19824requireyoutonotifyyouractivitytoHSEifmorethan10tonnesofchlorine

isliabletobekept.Youmustalsonotifysubsequentchangestoyouractivity.New

installationsover10tonneschlorinecapacity,orproposalstoincreasethenotified

capacitytomorethanthreetimestheoriginalcapacity,mustbenotifiedthree

monthsinadvance.TheformofthenotificationisintheRegulations.

8 TheControlofIndustrialMajorAccidentHazardsRegulations1984(CIMAH)5

alsoapplytositesstoringorprocessingchlorine.Theseregulationsapplyattwo

levels.Thelowerlevelrequirementsapplytositeswhichstore10ormoretonnes.

Theyalsoapplyatsiteswherechlorineisinvolvedinaprocessinanyquantity,

unlesstheprocessoperationisincapableofproducingamajoraccidenthazard.

Youneedtocomplywithtwogeneralrequirements:

(a) todemonstratetoHSE,atanytime,thatmajoraccidenthazardshavebeen

identifiedandadequatelycontrolled;and

(b) toreportanymajoraccidentstoHSE.

Forsiteswhichstore75ormoretonnes,orwhichprocesschlorineandhaveinventoriesof25ormoretonnes,unlesstheprocessoperationisincapableof

producingamajoraccidenthazard,morestringentregulationsapply.Theserequire

thepreparationofasafetyreport,thepreparationofon-siteandoff-siteemergency

plansandtheprovisionofinformationtomembersofthepubliclikelytobeaffected

byamajoraccident.CIMAHwillbereplacedinFebruary1999bytheControlof

MajorAccidentHazardRegulations(COMAH)whichimplementtherequirementsof

theSevesoIIDirective6onthecontrolofmajoraccidenthazards;thethresholdfor

thelowertierrequirementsis10tonnes,and25tonnesforthetoptier.

9 ThePlanning(HazardousSubstances)Regulations19927applytositeswith

10ormoretonnesofchlorine.Undertheseregulationstheconsentofthelocal

HazardousSubstancesAuthority(HSA)isneededforthepresenceofchlorineinsuchquantities.TheHSAmustconsultHSEontheassociatedrisklevels.

Toquantifytheoff-siterisksHSEmayrequesttechnicalinformationaboutthe

installation.8



Health and Safety

Executive

10 Inaddition,anyprocesswhichinvolvesthemanufactureoruseofchlorineor

anyprocesswhichislikelytoresultinthereleaseofchlorineintotheairorwater,

isaprescribedprocessundertheEnvironmentalProtection(PrescribedProcesses

andSubstances)Regulations1991.9Otherprocessesarealsoprescribedinthe

Regulations.UndertheEnvironmentalProtectionAct199010nopersonshallcarry

onaprescribedprocessexceptunderanauthorisationgrantedbytheenforcing

authorityandinaccordancewiththeconditionsintheauthorisation.Applications

fortheauthorisationofaprescribedprocessinEnglandandWalesmustbemade

totheEnvironmentAgency(EA)andinScotlandtotheScottishEnvironmental

ProtectionAgency(SEPA).InadditioninScotlandwheretheAlkaliandWorks

RegulationAct1906,11asamendedbytheHealthandSafety(Emissionsinto

Atmosphere)Regulations1983,12isstillinforce,suchprocessesarelistedas

ScheduledworksandmustberegisteredannuallywithSEPA.

11 Ifyoufillcontainersfromyourbulkinstallationandtransportthemoff-site,

youwillneedtocomplywiththeCarriageofDangerousGoods(Classification,

PackagingandLabelling)andUseofTransportablePressureReceptaclesRegulations1996,13andtheCarriageofDangerousGoodsByRoadRegulations

199614(inthecaseoftransportationbyroad).Therelevantlegislationisoutlined

inanHSEbooklet.15Note:The(legal)termforgascylindersisnowtransportable

pressurereceptacles.

12 Althoughyoumustcomplywithhealthandsafetylegislation,regulatory

controlcannotcompensatefordeficienciesinthewaythatsafetyismanaged.

Effectivehealthandsafetymanagementismainlyaboutmanagement(atalllevels)

takingaproactiveapproachtominimisethechanceofincidentsoccurringrather

thanputtingthingsrightaftertheyhavegonewrong.Guidanceoneffectivehealth

andsafetymanagementisgivenelsewhere16,17whichadvocatesandelaborateson

thefollowinggeneralprinciplesofgoodmanagementpractice:

(a) setyourpolicyanddemonstratecommitmenttoit;

(b) organiseandtrainyourstafftoensureeffectivecommunications,co-operation,

andtheircompetencetocontrolrisks;

(c) planwhatyouneedtodo,setperformancestandards,andestablishsystems

andproceduresforcontrollingrisks;

(d) measureyourperformancetoassesswhethertherisksarebeingadequately

controlled;

(e) conductsafetyauditstoensurethatyoursystemsareworkingasintended;

reviewyourfindingsandtakeanycorrectiveaction.

Ariskassessmentisessentialtothisproactiveapproachtosafetymanagement

andisastatutoryrequirementoftheManagementofHealthandSafetyatWork(MHSW)Regulations1992.18GuidanceontheseRegulationsandriskassessment

iscontainedinanApprovedCodeofPractice.19

RISK ASSESSMENT

13 TheMHSWRegulationsrequireyoutoconductafullriskassessmentto

identifyallthehazardsandassesstheassociatedrisks.Theriskassessmentneeds

toincludeallsourcesofhazards,includingthoseassociatedwithtransportaround

thesite,accesstoplantandsecurity.Theneedforriskassessmentisalsoa

requirementofotherregulations(egTheControlofSubstancesHazardoustoHealth

Regulations1994(COSHH)20andtheFirePrecautions(Workplace)Regulations

1997.21



Health and Safety

Executive

14 Inoutline,ariskassessmentforyourchlorineoperationsrequiresyouto:

(a) lookforthehazardsiepotentialsourcesofchlorinereleases;

(b) decidehowseriouseachoftheseloss-of-containmenteventscouldbe,iewho

couldbeharmedandhowseriously;

(c) decidethelikelyfrequencyofeachofthesehazardousevents;

(d) evaluatetheassociatedrisksandconsiderwhethertheprecautionstoprevent

releasesofchlorineandtomitigatetheireffectsareadequate,orifmore

shouldbedone(thisguidanceandthesourcesofadvicelistedinAppendix4

isrelevanthere;particularlythepublicationsofEuroChlor;22

(e) recordyoursignificantfindings;thisisastatutoryrequirementifyouhavefive

ormoreemployees;and

(f) updateyourriskassessmentatleasteverythreeyears,andbeforemaking

significantmodifications.Checkthatyouroperationalexperienceaccordswith

anysignificantassumptionsyoumadetocarryoutyourriskassessment.

Safetyaudits,aswellasday-to-daymanagementarrangements,should

addresstheneedtocheckassumptions.

15 Eachsitewillhaveitsownspecialfeaturesandyouneedtotaketheseinto

accountwhenconductingyourriskassessment.Aproperriskassessmentwillhelp

youto:

(a) decidewhethertherisksarebeingcontrolledsofarasisreasonably

practicable;and,ifnot,to:

(b) establishadequatecontrolsandsafeworkingproceduresbasedontheadvice

inthisnote.

16 Yourriskassessmentwillneedtoconsiderthemainpotentialcausesof

releasesofchlorine.Forbulkchlorineinstallationstheseare (seeparagraph20):

(a) plantdamagecausedbyexternalsources(vehicles,hoists,flyingdebrisfrom

nearbyaccidents,firesetc);

(b) incorrectoperation;and

(c) inadequateinspectionandmaintenance.

17 Thepeopleconductingyourriskassessmentmusthaverelevantexperience

andknowledge.Ifnecessary,youmust18seekassistancefromexperiencedand

knowledgeablepeople.Yourchlorinesupplierwillbeabletoidentifycompetent

peopleabletoconducttheriskassessmentonyourbehalf,andsupplyinformation

tohelpyoucarryoutyourriskassessmentandtomanagesafety.

18 Theremainingsectionsofthisbookletprovideguidanceonthearrangements

forpreventionandmitigationofchlorineleaksandspillagesthroughgooddesign,

operation(includingemergencyprocedures)andmaintenance.Theguidance

appliesonlytoinstallationsstoringliquidchlorineunderpressureinbulktanksor

tankcontainers.Youshouldthereforepayparticularattentiontotherequirements

ofthePressureSystemandTransportableGasContainerRegulations1989

(PSTGC).23Precautionsforthestorageofliquidchlorineinrefrigeratedtanksatlow

pressureareoutsidethescopeofthisguidance.Additionalsourcesofadviceand

informationarelistedinAppendix4.



Health and Safety

Executive

Design and location of

installations19 Bulkchlorineinstallationsoperateunderpressure.Consequently,thedesign,

installationandoperation(includingperiodicexaminationandmaintenance)of

thesepressuresystemswillneedtomeettherequirementsofPSTGC.23Pipework,

equipmentandprotectivedevicesforliquidchlorinearepartofthesystem.The

regulationsdonotapplytosystemsoperatingatorbelowpressuresof0.5bar

gauge,exceptforsteamsystems.GuidanceonPSTGCiscontainedinanApproved

CodeofPractice24andthepublicationA guide to the Pressure Systems and

Transportable Gas Containers Regulations 1989;25seeAppendix3forbriefdetails.

POTENTIAL INCIDENTS

20 Whendesigningormodifyingyourinstallation,youshouldincludeprovisionsto

preventthefollowingpotentialincidentswhichcouldresultinareleaseofchlorine:

(a) Damagetochlorinelinesfromexternalsourcesegbyhoistsorvehicles-

includingtheroadtankerwhileitismovingtoorfromtheunloadingpoint.

Whenthetankerispositionedforunloadingyouneedtoprovideadequate

clearanceforthevalvedomewhenitisopen.Youalsoneedtomake

allowanceformovementofthedeliveryvehicleduringthetransferoperation,

egthenormalupwardmovementofthetankeronitssuspensioncancause

damageifthereisinadequateflexibilityintheconnection,ormovement

causedbyinadequatebrakingorwheelchockingorcarelessoperationbythe

driver.

(b) Damagetotheliquidchlorinedeliveryvehicle,storagetankorconnecting

pipeworkcausedbyimpactfromothervehicles.

(c) Jointandgasketfailuresduetofailuretotightenjoints,over-tighteningof

joints,incorrectlyfittedortheuseofunsuitablejointrings,ortheuseof

hydrocarbonbasedlubricantswhichmayburnwhenattackedbychlorine(see

Appendix2).

(d) Errorsinoperatingprocedures,includingover-fillingofthestoragetankand

overloadingoftheventscrubber,failuretoclosevalveswhenremoving

containers,orbreakingintothesystemformaintenance.

(e) Plantandequipmentfailureduetoinadequatemaintenance,egpassing

valves,orleakscausedbycorrosionorerosion,oruseofplantandequipment

beyondtherecommendedlife.

(f) Damagecausedbyfireorexplosion.

SITING OF INSTALLATIONS

21 Theguidanceinthissectionrelatestogeneralfeatureswhichaffectthe

locationoftheinstallation.Morespecificfactorsarereviewedinthedetailedsections

dealingwithoff-loading(seeparagraphs134-147)andemergencyprocedures

(seeparagraphs247-263).Whendecidingthelocationofyourinstallationan

importantconsiderationisthepotentialriskstopeopleandtheenvironment.These

risksdecreaseastheseparationdistanceincreases.Thesizeofsuchseparation

distanceswilldependuponanumberoffactors,including:

(a) thenumberandsizeofstoragetanks;

(b) whetherthestorageisindoorsoroutside;

(c) theoperationalconditionsandthetypeofprocess;

(d) thefrequencyofchlorinedeliveries;



Health and Safety

Executive

(e) thedesignoftheinstallation,eglengthanddiameterofliquidandvapourlines;

and

(f) thesize,distribution,andtype(egsensitivegroups)ofthesurrounding

population.

22 Youshouldcarefullyconsiderthesefactorswhendesigninganddeciding

thelocationofyourinstallationandwhenconductingyourriskassessment(see

paragraphs13-17).Youshouldinvolveyourchlorinesupplieratanearlystage.

Considerationshouldbegiventomaximisingthedistancebetweenthesite

boundaryandthechlorineinstallation.Itshouldbeemphasisedthatyourrisk

assessmentandindividualcircumstances(seeparagraph21)willdeterminethe

separationdistances.Thesameconsiderationsalsoapplywhenmakingsignificant

changestoanexistinginstallationwithinasite.

23 Whenchoosingthelocationforyourchlorinearea,youneedtoconsiderthe

locationofotheron-sitebuildingsinrelationtotheprevailingwinddirection.Itis

recommendedthatthechlorineareashouldbelocateddownwindofbuildingsthatareregularlyoccupied.Ventilationintakestooccupiedroomsshouldbeatleast25

mfromthechlorineinstallation,andpreferablyatahighlevel.

24 Youalsoneedtotakeaccountoftheprevailingwinddirectionwhen

decidingthelocationsofemergencyassemblypoints.Twoassemblypointsare

recommended;theseshouldbelocatedsothatatleastonewillbeavailable

regardlessofthewinddirectionwhenareleaseoccurs.Forcomplexsites,indoor

assemblypointsarerecommended;openairassemblypointsmaybesuitablefor

simplesites.

25 Foranewinstallation,fullaccountwillhavetobetakenofanyrequirements

attachedtotheplanningpermissiongrantedbythePlanningAuthority.InadditionthelocalPlanningAuthorityneedstoensurethattheoverallplanwillavoidproblems

arisinginthefuturefromdevelopmentsleadingtoahighdensityofpopulationnear

theinstallation,orfromtheintroductionofotherpotentialhazardsinanadjacent

area(seeAppendix3:Planning(HazardousSubstances)Regulations1992).For

siteswhichmaypresentsuchhazardsHSEmayrecommendthatthehighest

standardsareapplied,beforeconsentcanbegrantedbytheHSA.Insomecases

theconsiderationofoff-siterisklevelsbyHSEmayrequirecontrolmeasuresin

additiontothoserecommendedinthisguidance.

26 Forexistinginstallations,controlofneighbouringpopulationdensitiesisnot

possibleintheshortterm.However,proposeddevelopmentsnearbywhichwould

increasethenumberofpeoplearecontrollableandwouldbepermittedbythelocal

PlanningAuthorityonlyafterdetailedconsideration.SuchconsiderationwillincludetheadvicereceivedfromHSEontherisksfromchlorinereleasestothosewhomay

occupyorusetheproposeddevelopment.

27 Thelocationofanewchlorineinstallationwithinasiteshouldbedecided

followingariskassessment.Inmakingyourdecisionyoushouldtakeintoaccount

possibledamagefromfloodingorsubsidence,andthepossibledamagetothe

installationifneighbouringplantorfactoriessufferacatastrophebyfireorexplosion.

Installationsshouldbesitedatasufficientdistance(25mminimum)frompublic

roadsormainrailwaylinestoreducetheriskofdamagetotheinstallationifthereis

anaccident.Protectivebarriersshouldbeinstalledwherenecessary.

28 Inallcases,suitablefences,togetherwithadequatesecuritysupervision,shouldbeprovidedtominimisethepossibilityofunauthorisedaccess.

29 Hazardsarisingfromaircraftmaynormallyberegardedasminimalwith

probabilitiesbelowthelevelofsignificancerequiredforanyspecialconsideration.



Health and Safety

Executive

However,attentionmaybenecessaryinexceptionalcircumstances,egifthe

installationisattheendofanairportrunwayorclosetoabusyairfield.Insuch

circumstancesliaisonwiththeairfieldoperatoronsuitableriskreductionmeasures

isessential.

30 Theinstallationispreferablylocatedintheopenair;butundersome

circumstancesanindoorinstallationmaybeappropriate.Indecidingthis,itis

importantthatariskassessmentismade,takingintoaccountthefactorslistedin

Appendix5.Youneedtoconsiderthefollowingpossibleriskreductionmeasuresat

anearlystage:

(a) thescopeforreducingthechlorineinventory,egreschedulingofdeliveries;

(b) interlockingarrangements(seealsoparagraphs35,39-41)fortheautomatic

isolationofleaksandtopreventthedeliveryvehiclemovingduringtransfer

operations;

(c) minimisingthelengthanddiameterofpipeworkcarryingliquidchlorineand

ensuringoverpressureprotection;(d) mechanicallyventilatingchlorinebuildingsanddischargethroughafume

scrubbingsystem;theassociatedairinletductsshouldbeatalowlevel;

(e) improvingtheleak-tightnessofanychlorinebuildingagainstmajorleaks;and

(f) restrictingtransfersofchlorinetodaylighthoursornormalworkinghours(8.00

amto5.00pm)astheweatherconditionsarelikelytobemorefavourablefor

thedilutionofchlorineconcentrationsifthereisarelease.

UNLOADING AREA

Design and location

31 Youshouldaimtominimisethepossibilityofchlorineescapeduringthe

transferofliquidchlorinefromthedeliveryvehiclestothestoragetank.Detailed

attentiontothesiting,designandlayoutoftheunloadingequipmentandoperating

procedureisessential.

32 Theunloadingareashouldbeonreasonablylevelgroundwithadequate

surroundingspaceprovidinggoodaccessfromdifferentdirections.Thelocation

shouldminimisetheriskofimpactdamagefromvehicles,mobileequipmentor

fallingobjectsfromliftingequipment.

33 Theunloadingpointshouldbereasonablyclosetothestorageinstallation.To

avoidimpactdamageaprotectivebarrierbetweenthetankerbayandthestorage

installationisrecommended.Theunloadingpointshouldalsobesitedatasafe

distancefromdrains,rivers,drainagecollectionpointsandanyplantorequipmentwhichmightgiverisetofireorexplosion.

34 Satisfactoryaccessshouldbeprovidedtothepermanentpipeworkfor

dischargeofthechlorinetankersandtoensurethatconnectionstothetankers

canbemadesafely.Wherethisinvolvesworkingfromaplaceabovegroundlevel,

apermanentstructureshouldbeprovided.Thisshouldbedesignedsothat,in

caseofemergency,escapeispossiblewithminimumrisk.Youcanachievethis

byinstallingasubstantialandnon-flammable(egsteel)structureandensuringthat

platformsarefreeofobstructionsandhavenon-slipsurfaces,adequatetoe-boards

andguard-rails.Alternativeescapewaysshouldbeprovidedwithstairwaysof

standardslope.Verticalladdersorsteepstairwaysshouldbeavoided.

Ifverticalladdersareunavoidable,ensurethatsafetyhoops,etc,donotimpedeaccessforpeoplewearingbreathingapparatus.Thedesignofmoveableplatforms

givingaccesstothetopofthetankersneedstominimisethepossibilityofaccidents

duetocollisionwiththetankers.Interlocksystemsmaybeusedforthispurpose,

seeparagraphs39-41.



Health and Safety

Executive

Awelldesignedunloadingarea

35 Youneedtoprovideforthesafeisolationofanyleaksthatmayarise,

particularlyfrompipeworkcarryingliquidchlorine.Itisrecommendedthatremotely

orautomaticallycontrolledvalvesshouldbeinstalledonthetransferlinetothe

storagetanks.Whenautomaticisolationisemployed,operatedbychlorinesensorsintheunloadingarea,thedetectorsystemneedstocloseboththestoragetank

isolationvalveandthatonthetanker.Thepossibilityofliquidchlorinebeingtrapped

betweenclosedvalvesandtheneedforpressurerelief(seeparagraphs61-67)

needstobeconsidered.

36 Itisalsogoodpracticetoprovide:

(a) protectionagainsttheweatheronfixedgantriesatunloadingpoints,egby

windbreaksoroverheadcanopies;

(b) storagespaceforconnectorsusedfortransferoperationssothattheycanbe

keptdryandprotectedfromdirtandmoisturegettingin,andpossibleimpact

damage;(c) storagespaceforemergencyequipment(egfilterrespirators,breathing

apparatus,protectiveclothingandspareequipment)inasafelocationsothat

theequipmentisreadilyavailableinanemergency;

(d) adequatelightingandemergencylightingcoveringtheunloadingarea,andall

escaperoutes;

(e) sufficientmanuallyoperatedalarmstationstoenablewarningtobegivenin

theeventofachlorineescape.Furtherdetailsonemergencyproceduresare

giveninparagraphs247-263.

Deliveries of liquid chlorine by road tanker or ISO tank container

37 TheCarriageofDangerousGoods(CDG)byRoadRegulations199614and

theCDG(DriverTraining)Regulations199626apply.ForsafetyreasonsallUKroadtankersarefittedwithair-operatedshut-offvalvesforthepaddingair(see

paragraphs134-141)andthechlorinedeliveryconnections.Itisalsostrongly

recommendedthatthefollowingmeansofminimisingpotentialrisksareadopted

whereverpossible:

(a) Provisionofaseparateandprotectedunloadingareaforthesoleuseof

chlorinetankers(egbyerectingsideprotectionofthemotorway-typecrash

barrier).

(b) Restrictionbysuitablemeansofthespeedoftrafficonadjacentroads.

(c) Unauthorisedaccessofvehiclesandpersonneltotheunloadingareashould

beprevented,egbyplacingwarningbarriers,notices,moveablebarriersor

roadcones,orclosinggateswhenthechlorinetankersareinposition.(d) Provisionofaninterlock(seeparagraphs39-41)systemtopreventcoupling

ofliquidchlorinelinestothetankersandopeningofthedischargevalve

untilthetankerisimmobilised.Inaddition,theair-operatedtankervalves


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Health and Safety

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41 Interlocksmaybeusedtopreventsomereleasesduetooperatorerror.For

exampletoensurethatliquidchlorineisnottransferredtotheventabsorber,in

additiontoaprocedure(step9ofAppendix6)requiringtheclosureofthemanual

ventvalveontheliquidchlorinedeliverylinebeforestartingthetankerdischarge

procedure,theventvalveshouldbeinterlockedwiththedeliverypointorthetanker

off-loadingvalve.

Theairsupplytothetrucksbrakeshastobedisconnectedbeforetheinstrumentair(neededtooperate

thetankerpaddingairandchlorinedischargevalves)canbeconnected

Deliveries of liquid chlorine by rail tanker

42 TheCarriageofDangerousGoodsbyRailRegulations199627apply.Itis

stronglyrecommendedthatyouadoptthefollowingmeansofminimisingpotential

risks.Yourriskassessmentwilldeterminewhetheradditionalmeasuresareneeded.

(a) Closethesidingstoothertrafficduringtransferofchlorinefromtankersto

storage,bylockingthepoints.Alternatively,frictionbuffersorade-railermay

beused.(b) Controlbysuitablemeansthevolumeandspeedofadjacenttraffic.

(c) Closewarningbarriersand/orplacewarningnoticeswhenthechlorinetankers

areinposition.

(d) Provideaninterlock(seeparagraphs39-41)systemtopreventcouplingor

uncouplingoftheliquidchlorinelines,unlessbarriersorwarningnoticesare

inposition.Itisrecommendedthattheinterlocksystemextendstoensure

thatappropriatepointsontherailsidingsarelockedandwheelstopsraised

beforetransferofliquidchlorinecanstart.

(e) Establishasystemofworkwherebyonepersonisresponsibleforthe

wholeoperationofunloading,andasecondiswithincallduringconnection

anddisconnection.Thesecondpersonshouldbeintheareaandavailable

throughoutunloading.

(f) Routechlorinepipelinesintheareatominimisetheriskofdamagefrom

collisionbythetanker,othervehiclesormobileequipment.

Owingtotheverylimiteduseofrailtransport,therestofthisguidancefocuses

onchlorinedeliverybyroadtanker.Whenrailtransportisused,thesamegeneral

principlesforthesafehandlingofbulkdeliveriesofchlorineapply.

Flexiblecouplingstothetankerforliquidchlorineandpaddingair.Noticetheswiveljointandthespring

loadedpipeworksuspensionforthepaddingairandliquidchlorinelines



Health and Safety

Executive

CONNECTIONS BETWEEN THE TANKER AND THE FIXED LINES TOTHE STORAGE INSTALLATION (see also paragraphs 134 -147)

43 Totransferliquidchlorinetostorage,itisnecessarytocoupletheliquid

chlorineoutletlineonthetankertotheinletlinetostorage.Itisalsonecessary

toincreasethetankerpressurebyabout1.7barabovethatinthestoragetank

byconnectingasupplyofdrycompressedair,nitrogenorchlorinevapourtothe

tanker.Theassociatedpipework(seeparagraphs53-79)shouldbeassimpleas

possibletominimisetheriskofpotentialloss-of-containmentaccidents.

44 Connectionsforthetransferofliquidchlorinerequireverycarefulconsideration,

astheyareapotentialsourceofloss-of-containmentleadingtoareleaseofchlorine

totheenvironment.Failureoftheunloadingconnectionscanresultfrominadequate

design,poorweatherprotection,incorrectmaterialsofconstruction,inadequate

pipeworksupport,improperuse,orinadequateinspectionandmaintenance.

Therefore,youneedtoensurethatthedesignstandardsareadequate,thattesting

andinspectionproceduresareregularlycarriedoutandthattheequipmentissatisfactorilymaintained.

Types of connection

45 Threetypesofconnectionareavailable:

(a) Flexiblecouplings(sometimescalledsemi-rigidloadingarms)have:

(i)asolidconnectionpipewithswiveljointstofacilitateconnectiontothe

tanker;and

(ii)adegreeofflexibilitybuiltintothesupportsandhangertoallow

movementwhencoupledup,ieacrankedfreelengthofpipeoracoiled

pipe.(b) Flexiblehoses.

(c) Articulatedarms.

Flexiblecouplingsarenormallyused,butflexiblehosesorarticulatedarmsmaybe

usedbyagreementwith,orrecommendationof,thechlorinesupplier.

Flexible couplings (semi-rigid loading arms)

46 Flexiblecouplingsarenormallyconstructedfromsteelpipe.However,

HastelloyC(notB)pipeisrecommendeduptothefirstisolationvalve.Thisoffers

greaterlifeinsituationswherethepipeisrepeatedlyexposedtoverysmallamounts

ofatmosphericmoisturebytheconnection/disconnectionprocess.Flexibilityis

providedbyacrankedfreelengthofpipe(lessusuallybyacoil)toallowforvertical

movementofthetankerduringdischarge.Screwedconnectionsareusedforthe

connectionstotheroadtanker;screwedconnectionstoBS2128arecommonly

usedateitherendoftheflexiblecoupling.Swiveljointsinthepaddinggaslineand

theliquidchlorinelinefacilitateconnectiontothetanker.Thesejointsaretightened

oncetheconnectionsaremade.Flangedconnectionsareusedforconnectingto

railtankers.

47 Pipinglocaltothetankerberthshouldnotbefixedforthefirst5-7mbut

itneedstobesupported.Thesystemofsupportusedshouldensurethatthe

pipeworkiskeptabovetheheadroomrequiredbythetankerwhenitisbeingputin

position.Thesupportshouldalsoallowthepipeworksufficientverticalmovementto

accommodatethatinthedeliveryvehiclessuspensionsystemduringtheunloadingoperation-typicallyabout150mm.Aminimuminternalpipediameterof25mmis

recommended.


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Health and Safety

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54 Routingofpipeworkforliquidchlorineshouldnormallybeabovegroundand

shouldbesuchastomaximiseprotectionfrommechanicaldamage,corrosion

andfire.Aminimuminternaldiameterof25mm(1in)isrecommendedtoensure

adequatemechanicalstrength.

Permanent pipework at the unloading point

55 Thepermanentpipeworkattheunloadingpointusuallyconsistsofthe

followinglines:

(a) pipeworkforpressurisingthetankerwithdryair,nitrogenorchlorine(see

alsoparagraph134-147);

(b) pipeworkforthetransferofliquidchlorinetostorage;and

(c) pipeworkforinstrumentairlines,egtooperatetheremotelycontrolledvalves

onthetanker.

Thesourceofcompressedpaddingairneedstobeindependentfromthatsupplyingotherservices.Detaileddesignrequirementsforthepipeworkandfittings

aredescribedinparagraphs56-79.Thesystemforoff-loadingofliquidchlorineis

describedinparagraphs134-147.

Design criteria for pipework transferring liquid chlorine to storage tanks or

from storage to point of use

56 Yourpipeworkwillbepartofapressuresystemandsubjecttothe

requirementsofthePSTGCRegulations.23-25Itthereforeneedstobeproperly

designed,fabricated,inspectedandtestedinaccordancewitharecognisedCode,

egANSI/ASMEB31.332,33andshouldbesufficientlyrobustforallforeseeable

conditionsofwork.

(a) Designpressure.Shouldnotbelessthan12bargauge(174psig),

correspondingtoadesigntemperatureof+45oC.Anypartofthesystem

whichmayoperateatahighertemperatureshouldbedesignedtowithstand

thecorrespondingvapourpressure(seeAppendix2,FigureA2.1).

(b) Designtemperature.Shouldbelessthantheminimumatwhichthepipeis

intendedtooperate,orthetemperaturetowhichitwillbecooledifliquid

chlorineboilsoffatatmosphericpressure(-35oC).Thenormaldesignrange

is-35oCto+45oC.Incertainuncommonsituationslowertemperatures

arepossibleduetochlorinecoolingbelowitsboilingpoint,egwhenpurging

systemswithdrygas-locationswhereliquidchlorinehascollectedmay

cooltotemperaturesaslow-50oCduetoevaporativecooling.Yourchlorine suppliershouldbeabletoprovideadviceontheneedtodesignforsuchlow

temperatures.

(c) Materialsofconstruction.Careisneededinselectingsuitablematerials(see

Appendix2).Seamlesscarbonsteeltubingisrecommendedforpipework.

Allcomponentsofpipes,valvesandfittingsshouldberesistanttotheaction

ofchlorinebetweentheextremesofoperatingtemperaturesandpressures.

Originalmaterialcertificatesshouldbekeptthroughouttheplantslife.

(d) Corrosionallowance.1mm.

(e) Radiusofcurvatureofanyformedbends.Threepipediametersminimum

(weldelbowsmustbeusedwheretighterbendsarenecessary).Elbows,tees

andreducingpiecesshouldbeforgedorhot-formedwithoutreductioninwall

thickness.(f) Bolting.ShouldbedesignedtotherequirementsofBS4882.34

(g) Flanges.Thenumberofflangesshouldbelimitedasfaraspossibleand

thoseusedshouldbetotherequirementsofarecogniseddesigncodeeg


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Health and Safety

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71 Itisemphasisedthat,duringmaintenanceoperations,relianceonvalvesof

whatevertypeforisolationisinsufficient.Thedesignofthesystemshouldbesuch

thatcompleteisolationofthesectionconcernedispossible.Suitablemethods

forachievingthisincludetheinstallationofspoolpiecesinthelineswhichcanbe

removedandsubstitutedbyblanks,ortheinsertionofslipplates.46

Types of valve

72 Valvesofthefollowingtypeshavebeendevelopedforusewithliquidchlorine

ordrychlorinegasunderpressure:

(a) verticalglobevalves;

(b) conicalplugvalves;

(c) ballvalves.

73 Valveshavetobedegreasedusingsteamordetergentsandthencompletely

driedbeforeuse.Alltracesofanysolventusedshouldberemovedasitcouldreactwithchlorine(seeparagraph57(b)).Itisrecommendedthatafterthistreatment

thevalvesshouldbestoredinindividualgas-tightplasticbagsreadyforinstallation

whenrequired.

Vertical globe valves

74 Thistypeofvalveispreferredtoothertypesandisusedforisolationofliquid

chlorinestocktanksorforlargeflowsofchlorinegas.Thebillet-globevalveis

recommendedforinstallationontheliquidchlorineoutletlinefromchlorinestorage

tanks(seeparagraph96).Thegassealaroundthevalvespindleinglobevalves

maybeformedbyapackedgland(preferablyusingringsorchevronsofPTFE)or

byabellowsseal.Thebellowsshouldbebackedupbyasecondaryglandseal.Globevalvesmay,withadvantage,befittedwithabackseatingarrangementwhich

isolatestheglandfromlinepressurewhenthevalveisfullyopen.

Glandpackedglobevalve(typical Bellowssealedglobevalve Anglepatternglobevalve

sizesavailable15mmto250mm) withpneumaticactuator.

Hydraulicandelectrical actuatorsarealsoavailable

Conical plug valves (PTFE-sleeved)

75 Conicalplugvalves,PTFE-sleeved,aresatisfactoryforisolationofliquid

chlorinelines,particularlywhenquickisolationmayberequired,buttheprimary

valveonthestoragetankispreferablyaglobevalve.Rapidisolationcancause

pressuresurgesandyouneedtoconsiderthesewhendesigningyourinstallation

(seealsoparagraph79).

76 Conicalplugvalvesforusewithliquidchlorinerequireprovisionforthe

avoidanceofproblemsarisingfromliquidchlorinetrappedintheborewhenthevalveisclosed.Ifthismakesthevalvesuni-directional,theyneedtobemarkedwith

anindicationoftherequireddirectionofliquidflowtoensurecorrectinstallation.

Gas-tightnessisprovidedbyaPTFEsleeveinsertedintothebodyofthevalveand



Health and Safety

Executive

byasupplementarysealalongthelengthofthespindlebetweenthevalvebodyand

head.Careshouldbetakentoavoidtheapplicationofsidethrusttothespindlesof

plugvalves.

Ball valves

77 Thistypeofvalvecanbeusedforisolationinliquidchlorinelinesandshould

incorporatethefollowing:

(a) sphericalturninglimitedtoaquarter-turn;

(b) straight-throughflanging;

(c) PTFEseals.

78 Ballvalvesshouldbeavoidedwhenoperatingconditionsinvolvelargeand

frequenttemperaturechanges.Ifusedwithliquidchlorine,youshouldmake

provisionforavoidingproblemsarisingfromliquidchlorinetrappedinthebore

whenthevalveisclosed.Liquidtrappedintheballshouldbereleaseddownstreamviaasmallholeintheball.Ifthismakesthevalveuni-directionalitneedstobe

markedwithanindicationoftherequireddirectionofliquidflowtoensurecorrect

installation.(Ballvalvesmaynotsealwhenthesealingpressureandthesystem

pressureareinoppositedirections).Theremarksaboutpressuresurgesin

paragraphs75and79alsoapply.

Remotely controlled valves

79 Therateofclosureofanyactuatedvalveshouldnotbesorapidthatit

causesunduepressuresurgesinthesystem.Thestandardrateofclosureshould

besatisfactoryforpipeworkupto50mmdiameter.Longrunsoflargerdiameter

pipeworkmayrequirelowerratesofclosuretopreventliquidhammer.Youshouldseekadvicefromyourvalvesupplier.

STORAGE VESSELS (see also paragraphs 190-229)

80 Tominimisethedangerofover-fillingyourstoragevessel,itscapacityneeds

tobesignificantlygreaterthanthatofthelargestdeliveryvehicle.Thechosen

capacitywilldependontherateofconsumptionandthefrequencyofdeliveries.

Installationofbulkstoragefacilitiesshouldbeconsideredonlyiftheannual

consumptionofchlorineissufficienttojustifybulksuppliesratherthanpurchaseof

liquidchlorineindrumsorISOcontainers(seeparagraphs216-221).Aninstallation

consistingofsmallertankswhichwouldrequiresplitloadsisnotrecommended.

NewsitesshouldinvolveHSEatanearlystage.

81 Inconsideringthenumberofindividualstoragetanksforarequiredtotal

storagecapacity,takethefollowingpointsintoaccount:

(a) Theminimumworkingcapacityofthetankshouldbeadequatetosafely

accommodatetheworkingstockresidueandthemaximumforeseenunit

delivery.

(b) Ifcontinuityofsupplyisessential,atleasttwotankswillberequiredtoallow

timefornecessaryinspectionsandtofacilitatemaintenance.Thisalsoprovides

greaterflexibilityofoperation.

(c) Increasingthenumberofstoragetanksleadstoanincreaseintheancillary

plantandequipmentwithacorrespondingincreaseincomplexityofoperation.

82 Thedistancebetweenadjacentstoragetanksshouldbeadequatetoprovide

goodaccesstothetanksunderallcircumstances.Thisincludesthoseinwhich

bulkyprotectiveequipment(suchasself-containedbreathingapparatus)isbeing

used.



Health and Safety

Executive

Chlorinestoragevesselandbund.Notetheemergencystopbutton(oneofseveral)attheedgeof

thebund.

83 Allchlorinestoragetanksshouldbeinstalledinabundwhichisimperviousto

liquidchlorine.Thebundshouldbecapableoftakingthecontentsofthelargest

storagetankwithadequatefreeboardandasump.Ifthereisasub-divisiontogivea

separatesectionundereachtank,eachsectionshouldhaveaslopingfloorleading

toasump,whichmayservemorethanonetank.Sumpsshouldnotbeconnected

tothedrain.Provisionshouldbeincludedforremovalofrainwateroverthebundwall,notviathedrainorthroughvalvesinthebund.

84 Leaksofliquidchlorinearepotentiallymuchmoredangerousthanleaksof

gaseouschlorine.Yoursystemthereforeneedstobedesignedsothatsources

ofleakageofliquidarereducedtoaminimum,egbyavoidingjointswhichare

continuouslyexposedtoliquidchlorinesuchasbottomoutlets,seeparagraph88.

85 Theseverityofaleakisreducedbyloweringthepressurewithinthesystem

andthereforeitisimportantthatfacilitiesfortransferringgaseouschlorinetoa

consumingprocessortoawaste-chlorineabsorptionplantareavailable.You

shouldalsoconsiderinyourriskassessmenttheneedforarrangementstotransfer

liquidchlorinefromaleakingtanktoanothertankwhichcanbeisolated.

86 Layoutofthechlorineareashouldbeplannedtoprovideallfacilitiesnecessary

forgoodhousekeepingandemergencyresponse.Chlorinestoragetanks

shouldthereforebeerectedabovegroundlevel.Installationindeeppitsisnot

recommendedbecauseitincreasesthedifficultiesoftreatmentanddispersalofa

chlorineescapeandofaccessformaintenanceorrepair.Amplestoragespaceis

neededformaintenanceandsafetyequipment,whichhastobereadilyaccessible

inanemergency.

87 Thermalinsulationofthestoragetanksisnotnormallyrequired.However,if

yourvesselisrelativelyclosetoafirehazardandlaggingisrequired,thematerial

shouldbefire-resistant,chemicallyinerttoliquidorgaseouschlorineandresistant

toatmosphericmoisturegettingin.Periodicinspectionbeneaththelaggingisessentialwhencheckingforcorrosion.

Design criteria

88 Designcriteriafornewliquidchlorinestorageandexpansionvesselsare

outlinedbelow.

(a) Designpressure.12bargauge(174psig)minimum.

(b) Designtemperature.Whenliquidchlorineevaporatesatatmosphericpressure

itstemperaturefallsto-35oCandthereforetheminimumdesigntemperature

shouldnotbeanyhigher,butlowertemperaturesarepossibleifevaporative

coolingofliquidchlorineoccurs,seeparagraph56(b).Thenormaldesign rangeis-35oCto+45oC.



Health and Safety

Executive

(c) Fillingratio.Fillingratiosfortransportableliquidchlorinecontainersare

detailedinBS535547forvarioussizerangesofmobilecontainersandfor

differenttemperatures.Althoughthereisnoequivalentstandardforfixed

tanks,forsimplicityafigureof1.25kgofl iquidchlorine/litrecapacityis

normallyusedtofixthemaximumleveltowhichthetankmaybefilledand

thesettingchosenforthehighlevelalarm.Thisensuresthatthevolume

ofliquidchlorinedoesnotexceed95%ofthetotalvolumeofthevessel,even

foramaximumtemperatureof50oC.

(d) Designcode.NewvesselsshouldbedesignedandmanufacturedtoBS

550048Category1(oranequivalentstandard).

(e) Corrosionallowance.Minimum1mm.

(f) Supportsandloadcells.Thevesselsupportsshouldbedesignedin

accordancewiththedesigncodetopermitthermalexpansionor

contractionoverthedesigntemperaturerange.Specialconsiderationmay

benecessary(checkwithyoursupplier)whereloadcellsareusedfor

determiningthecontentsofthetank,egcertaintypesofweighingdevice

requiresecondarysupports.(g) Branches.Dimensionsshouldbelimitedtotheminimumrequired,particularly

fortheliquidlines.Allbranchesshouldbemounted,wherepossible,onthe

manholecoverorcovers.Manholeaccessshouldbeprovidedontopofthe

vessel.Theopeningshouldpreferablybe600mmdiameter,butinnocase

shoulditbelessthan460mmdiameter.Bottomoutletsshouldnotbe

providedexceptwhererequiredforchlorinetransferbypumping.Any

bottomoutletshouldhaveaninternalvalve,preferablyremotely-operable,

plusaback-upisolatingvalve(seeparagraph97).

(h) Bolting.ShouldmeettherequirementsofBS4882.34

(i) Gaskets.Useofincorrectmaterialsforgasketscanbedangerous,see

paragraph56(h)forsuitablematerials.

(j) Documentation.Regulation5ofPSTGC23-25

requiresdesigners,manufacturers andsuppliersofpressuresystemstoprovidesufficientwritteninformation

concerningthedesign,construction,examination,operationandmaintenance

toenabletheregulationstobecompliedwith.Youmustretainthisinformation

togetherwithanyCertificateofCompliance(egBS550048orsimilar

documentationifotherstandardsarebeingused).

(k) Marking.ThevesselmustbemarkedwiththedetailsspecifiedinSchedule4

ofthePSTGCRegulations.Allvalvesandpipeworkassociatedwithchlorine

storagetanksshouldbelabelledandcolourcoded(seealsoparagraphs59

and60).

89 Paragraph88appliestonewsystemsdesignedandconstructedin

accordancewithacurrentstandard.Whereanexistingtankhasbeenprovidedin

accordancewithadifferentstandard,thesystemsshouldbeassessedaccordingtotherequirementsofthoseoriginalstandards.Inparticular,ifthevesselssafe

workingpressureislessthan12bargauge(174psig),thentheairsystempressure,

reliefdevicesetcallhavetobealteredtosuit,andthedeliverysystemhastobe

arrangedsoastobecapableofworkingwithinthestoragetankconditions.Itis

recommendedthatsuchtanksarereplacedwithtanksmeetingtherequirementsof

paragraph88.Thetimingofthereplacementshouldbeagreedwithyourchlorine

supplierandthecompetentpersonwhoexaminesyourvessels.

Connecting pipework and means for isolation of storage tanks

90 Themainconnectionstothestoragetanksare:

(a) liquidchlorineinlet;

(b) liquidchlorineoutlet;

(c) ventlinesandcompresseddrygaslines;


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Health and Safety

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satisfactorilyachievedonnewplantbyuseofabillet-typeglobevalve,boltedtothe

flangedbranchonthestoragetank,withthedip-pipescrewedintothebottomof

thevalve.

97 Youneedtobackupthemainisolationvalvewithanadditionalvalveto

enableisolationifonevalvefailstoseateffectively.Dependingonthelocalpiping

arrangement,provisionofoneormoreremotelycontrolledvalvesisrecommended

foremergencycontrol.Aremotelyoperatedvalvewhichisdesignedtogivepositive

isolationandwhichissuitablypositionedmayalsoserveasoneofthetwoisolation

valvesrequired.

98 Inaddition,itisstronglyrecommendedthatyouincorporatearestricting

orificeinthelinetotheconsumingplant.Theobjectofthisistoreducethesizeof

areleasefromamajorfailuretoaslowasreasonablypracticable,ieappreciably

lessthanthefull-boreflowthroughthepipe.Thesizeandlocationoftheorifice

needscarefulconsideration.Theorificeshouldnotbesosmallastoleadto

problems,suchaspronenessoftheorificetoblocking,etc.Insomecasesitmaybepracticabletolimittheflowinthelinetothemaximumrequiredbytheprocess.

Theorificeshouldnotbelocatedwithinthedip-pipebecauseoftheproblemof

removingtheliquidchlorinefromthetankintheeventofablockageoftheorifice.In

someplants,theflowrestrictioncanbereplacedbytheremotelyoperableshut-off

valves(seeparagraph111)controlledbyasuitablefloworpressuresensor.Excess

flowvalvesmaybeadvisableforlinesnormallytakingaflowofchlorinemuchless

thantheflowwhichcouldpassthroughinfaultconditions.Theyarenotsuitable

forlinesinwhichthenormalflowrateishigh,andforwhichothermeansoffault

detectionandflowisolationshouldbeused.

WIA

All UK road tankers haveair-operated shut-off valves.Where practicable theseneed to be linked into theautomatic gas detectionand shut down system(para 113 et seq) and /orbe remotely operablefrom the emergencystop points (para 37d)

Expansion vessel, paras 128-133

see para 96

Storage vessel

H

The parts within the dotted line are repeated on every storage vessel

see paras119 -127

H

'B' L

H

H

H

H

One of these valves shouldbe remotely operablefrom emergency stop

points (para 97)

Uilage pipe(paras 107 and 108)

see para 99

Liquid CI to consuming plant(para 98)

2

2

Restricting orificeIf there is any risk of liquidfrom the vent being suckedback this line should include

a preventive device(107, 174)

Vent absorber(para 171-189)

'A'

Dry air or dry Nsupply system atcontrolled pressure(para 134-141)

Valve A or B shouldbe remotely operablefrom emergency stoppoints (para 95)

Figure 2 AnexampleofthearrangementsfromchlorinetankerstoliquidchlorinestoragevesselsNote:

Notallinstallationswillbetothispattern



Health and Safety

Executive

Vent and compressed dry gas lines

99 Ventlinesandcompresseddrygaslinescanbeconnectedtothestorage

tankeitherthroughseparateinletsorthroughacombinedsingleinlet.Ineithercase,

thevalvedirectlyconnectedtothestoragetankshouldbebackedupbyasecond

valve.

100 Thepreventionofsuck-backofaqueousliquorintotheventlinerequires

similarprecautionstothosedescribedforvaporisers(seeparagraph161).The

preventionofback-diffusionofmoistureisdescribedinparagraphs178-181.The

inlettothescrubbingsystemshouldincludealutepipe(barometricleg)toprevent

liquidfromthescrubbingsystementeringthechlorinesystem.

101 Theprocedurefortransferringliquidchlorinetothestoragetanksshould

providefortheventvalvetobeopenedslightlyattheendofdischargeforabout

aminute(seeAppendix6,paragraph17)toconfirmthatthetankhasnotbeen

significantlyover-filled,ieabovetheextra-highlevelalarm(seeparagraph104).Overfillingisindicatedbyfrostingontheventline,inwhichcasepressurereliefmay

benecessary(seeparagraphs102-132).

Relief system

102 Thespecialrequirementsfortheisolationvalvesonthepressurereliefsystem

onthestoragetanksarecoveredinparagraphs123-133.

Instrumentation and chlorine detector systems

103 Controlinstrumentationonstoragetanksandelsewhereintheinstallation

should,whereverpossible,bedesignedtofailsafe.Electricalandelectronicequipment,unlessspeciallyprotectedagainstcorrosion,shouldnotbeplacedin

areaswhereitcouldbeaffectedbygasleaks.

104 Storagetankcontents.Thequantityofliquidchlorineineachstoragetank

ispreferablydeterminedbyinstallingthetankonloadcellsoronaweighbridge.

Loadcellsshouldberecalibratedwheneverthevesselisinspectedandpressure-

testedwithwater.Accuracycheckscanalsobemadeagainsttheweightof

chlorinesuppliedwheneveradeliveryismade,providedtheplantisoff-line.It

isrecommendedthatloadcellsarerecalibratedatintervalsnotexceedingthree

years.Theweightofliquidchlorineineachtankshouldbeindicatedlocallyandmay

berepeatedintheplantcontrolroom.Thecontents-measuringdevicesneedto

operateahigh-contentsalarminthecontrolroom(andoncomplexplants,possibly

anextra-highcontentsalarm)forsafetyreasons.Theextra-highlevelalarmneedstoberunindependentlyofthesystemgivingthehigh-contentsalarm,forreliability

reasons.Whenfitted,itisrecommendedthattheextra-highlevelalarmisusedto

automaticallyclosethetankinletvalveandthetankeroutletvalve,seeparagraph

105.

105 Asanalternativetothemeasurementofthequantityofliquidchlorineby

weight,measurementbyliquidlevelinthetanksisalsoacceptable.However,

selectionofsuitableequipmentisdifficultandyoushoulddiscussitwithyour

chlorinesupplier.Suchdevicesarepreferredasthemeansoftriggeringtheextra-

highlevelalarm.

106 Tolimittheliquidvolumeinthestoragetanktothatpermittedbythefillingratio(seeparagraph88(c)),anullagepipecanbescrewedintothebottomofthevalve

ontheventline.Thelengthofthisullagepipeneedstobeconsistentwiththefilling

ratiosothat,ifliquidchlorinerisesabovethecorrectlevel,itwillflowthroughthe

ullagepipewhentheventvalveisopenedattheendofadelivery(seeAppendix



Health and Safety

Executive

6)orinresponsetoanalarm.Theullagepipeshouldbecheckedwhentheroutine

inspectionofthestorageinstallationismade.Alowtemperatureorotheralarm(see

paragraph107)shouldbefittedontheventlinefromthestoragetankstowarnif

liquidchlorineisenteringtheullagepipeontheventline.

107Onasimpleinstallation,withgoodstaffingandattendanceatthetanks,an

ullagepipe(seeparagraph106)mayserveastheextra-highlevelalarm.Youneed

tobeawarethatthismethodrequirestheventlinetobeleftopen,whichisnot

necessarilythecaseforalternativemethods,seeAppendix6.Ifahighcontents

alarmisignoredduringfillingofthetank,theliquidreachesthebottomoftheullage

pipeandevaporatesinthevent-lineabovetheventcontrolvalve,producingfrosting

ofthepipe.Anullagepipethereforepresentstheriskofliquidchlorinebeingpassed

tothescrubberunlessthelinecontainsaknock-outdevicefittedwithahighlevel

alarm.Aknock-outpotintheventlinewithlevelalarmsisalsorecommendedfor

otherreasons(seeparagraph157).Theminimumprotectionfittedshouldbea

restrictionorificeplate(seeparagraph98)andalowtemperaturealarm.

108 Ullagepipesarenotrecommendedforcontentsindicationonnewinstallations;

insteadanextra-highlevelalarmonthetankshouldbeinstalled,seealsoparagraph

105.

109 Alowcontentsalarmmaybeusefulforoperationalreasonsandmayhave

safetyimplicationsif,egtherecouldbeprocessupsetsonfailureofchlorinesupply

orpassageofpaddingair(seeparagraph226)intoadownstreamvessel.

110 Storagetankpressure.Thepressureinthechlorinestoragetanksisusually

measuredbygaugesspeciallydevelopedforusewithliquidchlorine;thesehave

silverortantalumdiaphragms.Beforeuse,thegaugesneedtobecompletely

degreased(egwithsteamand/oradetergent),driedandalltracesofsolventremoved,andbepressure-testedusingonlyclean,dry,oil-freecompressedair.

Thepressuregaugesmaybefittedwithswitchestogiveanalarmifthepressure

exceeds,orfallsbelow,apre-setvalue.Alternatively,pressureswitchesmaybe

usedtogiveanindependentsignalforthehighandlowpressurealarms.

111 Wherereferenceismadetofloworpressuresensorsoperatingvalves(see

paragraph98)thereisachoicewhethertheoperationisautomaticorviamanual

intervention(seeparagraph62(b)).Attheextremes,operationshouldbeautomatic

inanunstaffedplant,andmaybeindirectinawell-instrumentedplantwitha

continuouslystaffedcontrolroom.

112 Equipmentassociatedwiththeautomaticpressurereliefsystemisdescribedin

paragraphs120and128-133.

Chlorine detectors and alarms

113 Theairinabuildinghousingchlorinestoragetanksshouldbecontinuously

monitoredusingproprietarychlorinedetectorsystemstogivewarningofchlorine

leakage.Detectorsarestronglyrecommendedinbuildingswhicharenot

continuouslystaffedtoprovideearlywarningofleaks,allowingpromptremedial

action.Foroutdoorinstallations,thevalueofdetectorsystemsneedstobe

assessedbyconsideringfactorssuchasthesizeoftheinstallation,thestaffing

levelsandtheresponsetimesachievable.Ondetectingaleak,thedetectorshould:

(a) raiseanaudiblealarminacontinuouslystaffedareaorcontrolcentre;(b) activateaudiblealarmsintheaffectedarea;

(c) operatetheautomaticisolationvalves;and

(d) controlthemechanicalventilation,iffitted.



Health and Safety

Executive

114 Audiblealarmsneedtohaveadistincttone.Inaddition,warninglightsofthe

amberflashingortrafficlighttypemaybefittedoutsideeachchlorinebuilding.

Whereappropriate,egatlarge,remoteorsensitivesites,alarmsshouldbe

connectedtoatelemetrysystemtoprovidewarningatastaffedcontrolpoint.The

controlpointshouldbeabletoisolatethechlorinesupply,preferablyviaaremotely

operablevalvefittedtotheoutletofthetank.

115 Chlorinedetectorsmaybeplacedinstorageandplantareas.The

manufacturerorsupplierofthesystemshouldadviseonthebestlocationforthe

sensors;typicallysensorsaremountedbetween0.3mand0.5maboveground

level,andattheoutletfromfumescrubbers.Forindoorinstallations,sensorsmay

needtobelocatedinorneartheentrancetoductscarryingchlorinepipework,

andtheairintakestoextractorfans.Whereforcedventilationsystemshavebeen

installed,thedetectorshouldbelocatedattheoutletofthesystem;wherethisis

notreasonablypracticablethedetectorshouldbeplacednearthestorageanduse

areas.

116 Detectionsystemsshouldprovideacontinuousmonitoringfunctionwhen

chlorineisinstorageorinuse.Chlorinegassensorsshouldbetestedregularlyin

accordancewiththemanufacturersinstructionstodemonstratethatthedetector

anditsassociatedcircuitsarefunctioningcorrectly.Arecordofsuchtestsis

recommended.Thedetectionsystemshouldoperatethealarmcircuitsintheevent

ofpowerloss,sensorfailure,orlowconditionofthestandbybatteries.Allalarm

relayoperationsshouldbeprotectedbyabatteryback-upfacility.

117 Thedetectorsystemshouldactivatethelowlevelalarmatachlorine

concentrationof1-5ppm.Lowersettingsareliabletoactivatethesystematevery

tank-fillingoperation,unlessadurationrequirementisalsoimposed.Forexample,

somecompaniessetthelowlevelalarmat0.5ppm,butrequirethesensortoregisterthisconcentrationforatleast30seconds,toavoidspurioustripsofthe

alarmsystemduringfillingoperations.Forindoorinstallations,thelowalarmlevel

shouldactivatetheventilationfan,opentheintakelouvers,andactivatelocalaudio

alarmsandanyremotetelemetryalarm.

118 Multi-stagedetectorsystemsaresometimesusedtogiveanindicationofthe

severityofthemalfunctiontopersonneloutsideachlorineroom.Itissuggestedthat

thehighlevelalarmoperatesataboutthreetimesthelevelofthefirst-stagealarm,

ie3-15ppm,dependingonthedurationthatthesensorneedstoregisterthislevel.

However,somecompaniessetthehighlevelalarmat2ppmwitha30second

durationrequirement.

Onactivationofahighlevelalarmtheventilationsystemshouldbeshutoff,theauto-shutdownsystemactivated(wherefitted)andthehighlevelalarmsounded.

Thetoneofthealarmatlowandhighlevelsshouldbedifferentandoperators

trainedtorecognisethedifferenceandhowtorespondineachcase.Localalarms

maybesupplementedbytelemetrylinkstocontrolrooms,whereappropriate.

Theresponsetoalarmsiscoveredinparagraphs247-263.Somesensorscanbe

damagedbyhighchlorineconcentrations;detectorsystemsshouldthereforebe

checkedafteranyhighlevelalarm.

PROTECTION OF STORAGE VESSELS AGAINST OVERPRESSURE

119 Highpressureontheliquidchlorinestoragetankisindicatedbyahigh

pressurealarm(paragraph110).Overpressureintheliquidchlorinestoragetankscanresultfromover-fillingorexcessivepaddingpressure.Over-fillingwithliquid

chlorineisindicatedbyalarmsontheweighsystemusedtodeterminetheliquid

chlorinecontentofthestoragetanks(paragraphs104-109).Overpressureon

thecompressedairornitrogensupplytothestoragetankispreventedbythe



Health and Safety

Executive

installationofareliefvalveonthesupplysourceofthecompressedgas.Thesupply

sourceshouldbewellupstreamofthetankandseparatedfromitbyisolationvalves

(paragraph139).

Relief system

120 Thestoragetanksneedtobeprotectedagainstoverpressurebyasuitable

automaticpressurereliefsystemwhichissettooperateatapressurebelowthe

designvalue.Thepreferredpressurereliefsystemconsistsoftwoburstingdiscs

placedbacktoback.Aburstingdiscfollowedbyareliefvalvemayalsobeused,

butisalwayssubjecttotheriskofcorrosionofthereliefvalve.Protectionofthe

reliefvalvefromcorrosionmustbecarefullyconsiderediftheburstingdiscrelief

valvesystemisused.Theuseofreliefvalvesaloneisnotrecommendedbecauseof

thecorrosionorblockagewhichcouldoccurifareliefvalvewereleftcontinuously

exposedtochlorine.Whicheversystemisused,youshouldprovideapressure

alarm/indicatorbetweenthetwodiscsorbetweenthediscandreliefvalve(see

paragraph133).Inthelatterarrangementitisgoodpracticetoremoveandoverhaulthereliefvalvewhenevertheburstingdiscisreplaced.

121 Thedischargelinefromthepressurereliefsystemnormallyentersaclosed

expansionvessel(exceptinafewspecialisedarrangements).Anypressurein

theexpansionvesselorbetweencomponentsinthereliefsystemreducesthe

protectiongiventothestoragevessel(seeparagraphs85,128-133).Specialrelief

arrangementsareusuallyrequiredwhenthereisasignificantriskofoverpressure

fromcontinuouspressuresourcessuchasradiantheatorbypumpingchlorine.

Underthesecircumstancesreliefintoaclosedexpansionvesselmaybeinadequate.

Reliefarrangementsbasedonreliefvalvesintoanopensystem(egavent

scrubber)maybepreferabletoburstingdiscs,asthevalvesreseatoncethesource

ofoverpressurehasbeenremoved.Thisarrangementisnormallyonlyfoundon

largerinstallations;youshouldconsultyourchlorinesupplier.

Bursting discs

122 Burstingdiscs(whicharedesignedtofailatorbelowthedesignpressure

ofstoragetanks)arecommonlymadeofnickel,althoughtantalum,silverorother

compatiblematerialsmaybeused.Uncoatedgraphiteisnotrecommended.

DiscsshouldcomplywithBS291549(orequivalentstandard)andshouldbe

carefullyselectedfortheoperatingtemperaturerange,astherupturepressureis

temperature-dependent.

Arrangements for relief systems

123 Onsimpleinstallations,suchasthosewithasinglestoragevesseland

associatedexpansionvessel,asingleburstingdiscsystemwithoutanyisolating

valves,installeddirectlyonthestoragevessel,maybeacceptable.Inpractice,

however,itismoreconvenienttoinstallavalvedsystemtoallowreplacementof

discsunderacontrolledsystemofwork,withoutneedingtocompletelyemptyand

purgethesystem.Wheretwoormorestoragevesselsshareanexpansionvessel,

thereliefarrangementsshouldallowpromptreplacementofdiscsandventingofall

excesspressureoutoftheexpansionvessel.

124 ThepreferredarrangementsareshowninFigures3and4andshouldbe

usedonallnewinstallations.Theisolatingvalvesmaybemechanicallyinterlocked

(recommendedfornewinstallations)sothatonepairofdiscsisalwaysoperative,ortheisolatingvalvesmaybeindividuallylocked.Tobeeffectivethebursting

discsneedtobeofthesimpledomedunsupportedtypewiththeconcaveside

facinginthedirectionsshowninFigures3,4,and5.Theidentifyingtagsshould

beleftattachedtoeachdiscsothattheycanbeidentifiedashavingbeeninstalled



Health and Safety

Executive

correctly.ExistingolderinstallationsusingthearrangementshowninFigure

5shouldreplaceitwithapreferredarrangement(Figure3or4)whenmajor

modificationsareinhand.

125 Thevalveswhichremainopenmustpermittheoperationaldevicesto

dischargeattherequiredratetoanexpansionvessel.Pipeworkbeforetheisolating

valvesshouldbeasshortandsimpleaspossibletominimisetheriskofchlorine

leakagefromjointsandpipework;theisolationusingvalvesbeforethebursting

discsshouldpreferablybefitteddirectlyonflangedconnectionsonthemanlidofthe

storagetanks.

Figure 3 Pressurereliefsystem(preferred Figure 4 Pressurereliefsystem.Double

arrangement).Doublestreamwithinterlocked streamwithlocked-openvalves

valves

Figure 5 Pressurereliefsystem.Singlestreamwithlocked-openvalves

126 Yourproceduresfordealingwithafailureofaburstingdiscshouldbeclearly

defined.Basethemontheprinciplethatatnotimeshouldpressuresbeyondthe

designrangebeallowedtodevelop(seealsoparagraph127).

127 Atanyinstallationwherealocked-openisolatingvalveprecedesabursting

disc,asafesystemofworkshouldbedefinedtopreventunacceptablepressures

fromanysourceoccurringinthevesselwhiletheisolatingvalveisclosed.The

proceduresneedtocoverthesaferemovalofthevesselfromnormalservice,

stabilisingthepressure,changingtheburstingdisc,ventingtheexpansiontankand

returningthevesseltonormaluse.Suchsafesystemswillvarywithplantdesignbut

should:

To expansion vessel

Mechanical

interlock

Bursting discs Bursting discs

Pressure alarm gauge Pressure alarm gauge

(Test connections for pressure gauge not shown)

To expansion vessel

Locked open valve

Pressure alarm gauge

Locked open valve

Bursting discs

To expansion vessel

at least one lineneeds to belocked open

Locked valves

Locked valves

Bursting discs Bursting discs

Pressure alarm gauge Pressure alarm gauge

(Test connections for pressure gauge not shown)



Health and Safety

Executive

(a) beinawrittenform,unambiguousandreadilyavailable;

(b) includeapermit-to-worksystem;

(c) beincludedinplantpersonneltrainingprogrammes;

(d) beproperlysupervisedwithresponsibilitiesclearlyallocated;

(e) beregularlyupdatedandperiodicallysubjectedtoHAZOP50review,

particularlywhenplantdesign,operatingproceduresormanagementsystems

aremodified;and

(f) berigidlyadheredto.

Expansion vessels

Expansionvesselmountedinabund

128 Thedesignrequirementsfortheconstructionoftheexpansionvesselare

similartothoseforthestoragetanks;thecapacityoftheexpansionvesselshould

beatleast10%ofthelargeststoragevessel.

129 Theexpansionvesselshouldbecapableofbeingventedmanuallytoan

absorptionsystem;theventvalveisnormallylockedclosed.Controlledventingshouldbethroughasuitableflowrestrictiondevice,eganorificeplatetoprevent

overloadoftheabsorptionsystem.

130 Theexpansionvesselshouldbeprovidedwithapressure-sensingdevice

whichgivesanalarmifpressurebuildsupinthevessel.Thealarmsystemneeds

tobecapableofbeingtestedregularlytoensurethatitisoperable(seeparagraph

133).

131 Arrangethecompressedairornitrogenconnectiontotheexpansionvesselto

avoidthepossibilityofinadvertentlypressurisingthevessel.Thismaybeachieved

byphysicaldisconnection,isolatingblankingplates,orbydoubleblockvalves

supportedbyasafesystemofwork.Ifanexpansionvesselservesmorethanone

storagevessel,makearrangementsforpromptresponsetoapressurealarmsignal

fromit.

132 Whiletheriskoftheexpansionvesselitselfbeingover-pressurisedwith

chlorineisminimalbecauseoftheprecautionsdescribedinparagraphs128-131,

youshouldestablishproceduralormechanicalmeanstoensurethatthiscannot

occur.

Pressure alarms

133 Thereshouldbeahigh-pressurealarmoneverystoragevessel,andan

additionalpressureindicator/alarmateachimportantsafetylocationontherelief

arrangement.Thismeansthatoneadditionalpressurealarmmaysufficeoneachstoragevesselthathasitsownexpansionvessel,andthatalarmmaybeeitherin

thereliefline(ifthereisasingleburstingdisc)orontheexpansionvessel.Whenone

expansionvesselservesseveralstoragevessels,thereshouldbeanadditional


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Health and Safety

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compressorleakingfromshaftglands.Duringoperationofthecompressor,the

shaftglandsshouldbepressurisedwithdry,compressed,inertgas.

145 Ifcoolingofthecompressorbodyisrequired,thisshouldpreferablybe

accomplishedbyaircooling.Ifjacketcoolingisnecessary,thisshouldbeachieved

bycirculationthroughanexternalheatexchangerwithprovisiontodetectleakageof

chlorineintotheheatexchangefluid.Directwatercoolingshouldbeavoided.

146 Thecompressorneedstobefittedwithabypasssothatthechlorinecan

berecycleduntilitstemperatureisraisedsufficientlytopreventliquefactionin

thedeliverylines.Thetemperatureofthechlorineshouldbemonitoredusingan

indicatorwhichisfittedwithanalarm,settosoundifitexceeds90oC.

147 Apressurereliefsystemonthecompressordeliverylineshouldalsobe

providedtopreventthedeliverypressureexceedingapre-setfigure(seeparagraph

139).

CHLORINE VAPORISERS

148 Vaporisers(alsoknownasevaporators)convertliquidchlorineintogas.A

majoruseofchlorinevaporisersisinwatertreatment,tocontrolweedandalgaein

coolingwaterandtosterilisedrinkingwater.Theseunitsarefrequentlysuppliedas

partofapackagewithotherdosingoranalyticalequipment.Vaporisersarealways

requiredwithafixedordemountablebulktank,toobtainaregular,steadysupply

ofgastoprocess.Thedrawingofgasfromthevapourspaceofabulktankis

unsatisfactoryandunsafe.Thereistheriskofprocessliquidspassingbackintothe

tank,irregularityofsupplyandthepossibleaccumulationoflessvolatile,dangerous

impurities,suchasexplosivenitrogentrichlorideinthetank.51Thesafehandlingof

chlorinecontainingnitrogentrichlorideisdiscussedelsewhere.52

Types

149 Therearefourmaintypesofvaporiser(seealsoAppendix7):

(a) Verticaltubebundle.Theseresembleordinaryheatexchangers,usuallywith

thechlorineinthetubes.Alternativeformatsincludethecommonvaporiser

usedinwatertreatment(acylinderwithadip-pipeliquidchlorineinlet

immersedintheheatingbath)orashellandtubeheatexchangerwiththe

chlorineontheshellside.Abayonetvaporiserisverysimilar.

(b) Coil.Thechlorineisevaporatedinacoilofsteeltubingrunninginsideawet

steambathorawaterbathheatedbysteamorelectricity.

(c) Concentrictube.Theheatexchangesurfaceisatube,typicallyfourinchesin diameter,surroundedbyaheatingjacket.

(d) Kettle.Kettleevaporatorsareusedonlargecapacitysystems.Theycontaina

heatersystem(usuallyatubebundleofhotwaterorheatedfluid-notsteam)

passingthroughavesselcontainingliquidchlorine.Kettleevaporatorsdonot

superheatthechlorinevapour,othersystemsdo.

Coilinbathvaporiserheatedbylowpressuresteam


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Health and Safety

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aself-regulatingevaporator,itispossiblefortheoutgoinggastobeinadequately

superheated,orforfloodingtooccur.Floodingresultsincarry-overofliquidchlorine

intothevapourlines,andapotentialhazard(dependingontheprocessandplant

materials).Thesamemayhappenifthelevelofwaterinawaterbathfalls.In

theextreme,ifchlorineisdrawnoffbutnoheatissuppliedtothevaporiser,itis

possibleforicetoformontheheatexchangersurfacesanddamagethemseverely.

Youshouldconsiderinstallingagasflowrateindicator.Thismaybeofvaluetothe

operatorforroutinepurposes,andwillalsoindicateexcessivewithdrawalrates.

157 Youshouldconsiderfittingaknockoutpot(orspraycatcher)toprevent

chlorinedropletsandsprayfrompassingintogaspipeworkwhenliquidchlorine

mightdamagethematerialofthepipes,orcausetheprocesstobecomeunstable.

Inallcaseswherethepossibilityofliquidpassingtoprocessisunacceptable,itis

stronglyrecommendedthatalowtemperaturealarmbefittedneartheknockout

potandarrangedtocutofftheliquidchlorinesupplytothevaporiseror(inself-

regulatingtypesonly)thegaseouschlorineoutletmaybeclosed,drivingtheliquid

chlorinebackintothestoragevessel(s).Adequateinstrumentationandalarmsshouldalwaysbeprovidedtogiveimmediatewarningofthiscondition.Highand

lowbathtemperatureandlevelalarmswithshut-downfacilitiesarerecommended.

Accelerated corrosion and reaction (high temperature)

158 Toavoidrapidcorrosionofthewatersideofheatexchangesurfacesmade

fromgalvanisedsteel,operatingtemperaturesshouldnotexceed70oC.Ifoperation

athighertemperaturesisrequired,vaporisersmadeofnickelornickelalloys(such

asMonel400orInconel)shouldbeused.Insuchcases,thedownstreamchlorine

gaspipeworkmayalsoneedupgradingtoensureadequateresistancetocorrosion

atelevatedtemperatures.

159 Iftheheatingmediumissteam,thetemperaturecanbemonitoredbylow

pressureandhighpressurealarmsonthesteaminlet.Thepressureofsteamshould

normallybelimitedto1bargauge(120oCequivalent)andthesteamhastobe

saturated,notsuperheated.

High pressure

160 Precautionsmust23beinplacetoprotectthesystemagainstover-

pressurisation,egapressurereliefdevice.Pressurereliefdevicesandhighpressure

alarms,wherefitted,shouldbeproperlydesignedandinstalled,maintainedinan

effectiveworkingorder,andtestedregularly.Theymustbeperiodicallyexamined

byacompetentperson.53Atypicalworkingtemperatureforavaporiseris70oC.The

vapourpressureofchlorineat70oCexceeds21bar,(seeFigureA2.1,Appendix2).Itfollowsthatyouneedtotakethefollowingstepsto:

(a) Ensurethatthevaporiserisnotisolatedwhenfullofliquidchlorine.Strict

observanceofwrittenproceduresforshut-downisvital.

(b) Avoidaccidentallyisolatingthevaporiseronbothsides.Careneedstobe

takentoensurethattheclosingarrangementsfortheemergencyvalvestake

thisintoaccount(seeparagraphs162-165).

(c) Designthevaporisershellandpipestowithstandtheworkingpressureand

duty.

(d) Implementoperationalcontrolswhichminimisetheriskoftheworkingpressure

beingexceeded.

Ifyourchlorinevaporiserisnotsuppliedwithapressurereliefdeviceyouwillneedto

adoptprocedures,orfitsuitablepressurerelief,toensurethattheconditionsin(a)

to(d)aremet.



Health and Safety

Executive

Reverse flow

161 Youshouldeliminatethepossibilityofsuck-backintothevaporisersbysuitable

design.Forexample,waterchlorinatingpackagesystemsusuallyincorporate

asetofvalvesinthecontrolsystemtopreventsuck-backorpush-back.The

arrangementsvary,andcareneedstobetakentoensurethatthesystemprovided

doesgiveprotectionintheeventof,eg,aleakattheejectornon-returnvalve.You

shouldalsoconsiderfittingalowpressuregasalarmtotheoutletgasline.This

giveswarningoflossofsupplytotheprocess,andmayindicateaneedtostart

purgingthesystem,usingdryairorothersuitabledrygas(dewpointlessthan

-40oC)topreventsuck-back.Whatevermethodisused,thesystemneedstobe

regularlyinspectedandmaintained,andadequaterecordskept.

Emergencyshutdownpushbuttonatthevaporiser.Alsoshowninoneofsixchlorinedetectorsatthis

installationwhichcanalsoautomaticallyshutdownthechlorineinstallation(seeparagraphs113-118)

Routine and emergency isolation

162 Thevaporiserhastobecapableofbeingisolatedformaintenance,orinan

emergency,suchasafailureofthevaporiseritselfthroughleakageorafailureofthe

gaslinedownstream.Inadditiontoamanualvalveontheliquidinletandonthegas

outlet,remotelyorautomaticallyoperablevalvesarestronglyrecommendedonboth

inletandoutlet.Apressure-reducingorflowcontrolvalvewillalmostalwaysbefitted

ontheoutletanditissometimespossibleforthisvalvetobetheremotelyoperable

shut-offvalve.

163 Yourriskassessmentshouldconsidertheneedforadditionalprotectionin

theeventthatautomaticvalvesfailtooperate(orremotelyoperablevalvesarenot

activated)inanemergency.Forexampleaflowrestrictionintheliquidinlet(typically

ontheexitfromthestoragetank(s)),willlimitthereleasewhichcouldoccurinthe

eventofamajorplantfailure.

164 Thehazardsoftotallyisolatingthevaporiserareconsiderableandwillbemost

severewhentheevaporatorisfull(egifthevalvesclosetogetherinaconditionofmajorgaslinefailure).Ifthereisagasspaceabovetheliquidchlorinewhenthe

vaporiserisisolatedandheated,theinternalpressurewillreachthatofchlorine

attheheatingmediumtemperature.Thevaporiser,linesandvalvesneedtobe

designedtowithstandsuchpressureorincorporatearrangementstorelieveto

asafeplace.Thecontrolofautomaticvalvesneedstobearrangedsothatthe

valvesdonotclosetogetherwhenanalarmisraised(seealsoparagraph160).

Oneapproachistoarrangeforthegascontrolvalvetocloseonalarmsrelated

toimproperworkingofthesystem(eglowgaspressure,downstreamprocess

alarms,lowtemperature)andtheliquidcontrolvalveatthestoragetanktocloseon

chlorinerelease(egdetectorslocaltothevaporiserandstorage,ormanualalarms).

Iftheplantiscontinuallystaffed,manualinterventionmaybeasuitablealternative

toprovidingwhollyautomaticoperationofshut-down.However,proceduresneedtobeestablishedtoensurethatthisdoesnotintroducesignificantdelaysintothe

responsetoanalarm.Analternativeapproachistouseapressurecontrolglobe

valveforremoteisolationoftheoutletlinesothatexcessivepressureswillliftit

slightlyoffitsseat,preventingexcessiveoverpressures.



Health and Safety

Executive

Reliefpressuresandvalvedirectionneedcarefulconsiderationandshouldbe

discussedwiththevalvesupplier.

165 Isolationofthevaporiserisstillpossible,butinterlocksbetweentheinlet

andoutletvalvestopreventtotalisolationarerarelyfitted.Thisisbecauseitis

occasionallynecessarytoclosebothvalvesduringcleaningandoverhaul.Asafe

systemofworkformaintenanceandoperationisthusavitalpartofthesafety

arrangements,andisarequirementunderthePSTGCRegulations.23

Pressure control valve

166 Allvaporiserdesignsincorporateanelementofsuperheatingofthevapour,

eitherinthevaporiseritselforasaseparateunit.Thisisnecessarytoprevent

chlorinereliquefyinginthecontrolvalves,whereitcouldcauseproblemsofirregular

pressureinoperation.Theseproblemsareavoidedbyreducingthegaspressure

attheexitfromthevaporiser.Asuitablepressure-reducingcontrolsystemis

recommended.

Corrosion

167 Corrosionofthevaporisertubesorcoilscouldleadtoaloss-of-containment

accident.Theconsequenceofaminorchlorineleakfromthechlorinesideofa

vaporiserheatingbathcouldbeveryserioussincethemixtureofchlorineand

moisturewillleadtorapidcorrosionoftheevaporatorsurfacesandasubstantial

releaseofchlorine.

168 Youmustarrangeforacompetentpersontoperiodicallyexamineyour

vaporiserandotherpressuresystemsinaccordancewithyourwrittenscheme

ofexamination.54

Acompetentperson53

mustcertifythatthewrittenschemeforexaminationissuitableforthepurposeofpreventingreasonablyforeseeabledanger

topeoplefromtheunintentionalreleaseofstoredenergyfromthesystem.The

writtenschemeofexaminationshoulddescribethenatureandfrequencyofthe

examination.Thisshouldbebasedonriskassessmentandgivedueconsideration

tothedutyandtheconditionofthevaporiserwhenitwaslastinspected.The

competentpersonwilladviseonsuitableexaminationandtestregimes,andwhen

thevaporisershouldbereplaced.Examinationintervalsbetweenoneandfiveyears

aretypical.Coil-in-bathevaporatorsarecommonlygivenarigorousinspection

everytwoyears,andthecoilsarediscardedifseriouslypitted.Somemanufacturers

advisethatthecoilsshouldberenewedeverytwoyears.Followingexamination

theequipmentshouldbethoroughlydriedtoadewpointlessthan-40oCbefore

recommissioning.Moistureleftinthesystemcanleadtoveryrapidcorrosion.The

procedureshouldbecoveredbyawrittenoperatingprocedure.

169 Corrosionoftheheatexchangersurfacesisnotdirectlymonitored.Instead

theevaporatorvesselortubesarefrequentlyprotectedagainstwatercorrosionby

cathodicprotection.Typicallytheanodesshouldbecheckedvisuallyeverythreeto

sixmonths.Thefrequencyshouldbeestablishedbyexperienceoftherateatwhich

theanodesareconsumedandreplaced.Iftheanodesarefoundwhollyconsumed

atinspection,athoroughexaminationofthevaporisershouldbeundertaken.The

waterbathorcondensateoutletshouldbemonitoredforchlorineleaksbyredoxor

conductivitymeasurements.Thisearlywarningofminorleaksishelpfulinallcases,

andisverystronglyrecommendedifcathodicprotectionisnotprovidedornot

maintained.

170 Accumulationofsoliddepositsreducestheeffectivenessofavaporiserand

canalsoenhancecorrosion.Thevaporiserneedstobecleanedanddriedtoa

dewpointlessthan-40oCregularly.Closeattentiontothecleaningprocedurewill

minimisecorrosionbuttypically,thechlorineevaporatorcylinderinahotwaterbath



Health and Safety

Executive

(seeAppendix7,type1csystem)shouldberenewedafterfiveyears.Theoldone

maybesubmittedtoacompetentinspectionbodyforcertificationforfurtheruseif

required.

CHLORINE ABSORPTION SYSTEM

171 Youshouldgivedetailedconsiderationtoensurethatinallchlorine-using

operationschlorinecan,inanemergency,beventedtoanabsorberwithout

emissiontotheenvironment.

172 Controlofchlorineemissionsfromprescribedprocesses(seeparagraph10)

mustbethesubjectofconsultationswiththeEnvironmentAgencyinEnglandand

WalesandSEPAinScotland.

173 Insomeinstallations,thenatureoftheconsumingprocessissuchthat

absorptionofthechlorineispossiblewithoutaspecialabsorptionunit.However,

insuchcircumstancesoperatorsneedtoensurethatduringmaintenanceperiodsadequateabsorptioncapacityisalwayskeptavailabletoaccommodateanychlorine

emissions.Aseparateabsorptionplantmaynotbeessentialin,forexamplecooling-

watertreatmentplantsandbleachliquorproductionplants.

Lutepipe(baromaetricleg)andventforabsorptionsystem

174 Formostbulkstorageinstallations,however,aseparatechlorineabsorption

plantisrequiredanditshouldalwaysbemaintainedinastateofreadiness.The

quantityofreagentsavailableintheabsorptionsystemneedstobeadequateto

dealwithanyforeseeableemergency.Theinlettothescrubbingsystemshould

includealutepipe(barometr

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