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Health and Safety Executive

Compressed air safety

This is a free-to-download, web-friendly version of HSG39 (Second edition, published 1998). This version has been adapted for online use from HSE’s current printed version.

Youcanbuythebookatwww.hsebooks.co.ukandmostgoodbookshops.

ISBN 978 0 7176 1531 5 Price £7.50

Thisbookaimstopromotethesafeuseofcompressedairanddescribesthemanywaysinwhichcompressedaircanbedangerousaswellashowtominimisetheriskofsuchdangersoccurring.

Itisaimedatdesigners,manufacturers,installers,usersandothersconcernedwithorresponsibleforhealthandsafetyatwork.

HSE Books

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© Crown copyright 1998

Firstpublished1990

ISBN9780717615315

Allrightsreserved.Nopartofthispublicationmaybereproduced,storedinaretrievalsystem,ortransmittedinanyformorbyanymeans(electronic,mechanical,photocopying,recordingorotherwise)withoutthepriorwrittenpermissionofthecopyrightowner.

Applicationsforreproductionshouldbemadeinwritingto:TheOfficeofPublicSectorInformation,InformationPolicyTeam,Kew,Richmond,SurreyTW94DUore-mail:[email protected]

ThisguidanceisissuedbytheHealthandSafetyExecutive.Followingtheguidanceisnotcompulsoryandyouarefreetotakeotheraction.Butifyoudofollowtheguidanceyouwillnormallybedoingenoughtocomplywiththelaw.Healthandsafetyinspectorsseektosecurecompliancewiththelawandmayrefertothisguidanceasillustratinggoodpractice.

Compressedairsafety Page3of50


ContentsINTRODUCTION 5

COMPRESSOR PLANT 6Groups of compressors 6Hazards 6General information and advice 6Precautions 7Safetyvalves 7Pressureindication 7Thermalprotection 7 Coolantprotection 8 Lubricantprotection 8 Explosionprotection 8Airinlet/outletmonitoring 8 Otherinstrumentation 8Airinlet/outletcontrol 9

AIR RECEIVERS 11Statutory requirements 11Hazards 12General information and advice 12Precautions 12

COOLERS 13Hazards 13General information and advice 13Precautions 13

AIR DRYERS 14Hazards 14General information and advice 14Refrigerant 14Dessicant 14Precautions 14

INSTALLATION OF COMPRESSORS 16Precautions 16Smallcompressors 16Mediumandlargecompressors 16Noise 16

MAIN LINE SYSTEMS 18Hazards 18General information and advice 18Precautions 18Pipe-runs 18Filters,traps,separatorsandlubricators 21Pressureregulators 22

PORTABLE PNEUMATIC EQUIPMENT 23Statutory requirements 23Hazards 23General information and advice 23Precautions 24Flexiblehoses 24



Blowguns 24Portabletools 25

PNEUMATIC POWERED MACHINERY 26Hazards 26General information and advice 26Precautions 26

ACTUATORS 28Hazards 28General information and advice 28Precautions 28

INTERLOCKING METHODS AND CIRCUIT DESIGN 31General information and advice 31Interlocking systems 31Singlecontrolsysteminterlocking 31Dual control system interlocking 32Power interlocking 40Circuit design 41Pistonarrest 41Pistonarrestandhold 41Overridinglockedposition 41Predeterminedposition 41

INSPECTION AND MAINTENANCE 42Statutory requirements 42Hazards 42General information and advice 42Maintenance of compressors and ancillary plant 42Supervisionandprocedures 42Daily 43Checks mainly directed to reciprocating compressors 43Weekly 43600hours 43Six-monthly 432000hrsorannually 44Precautions 44Maintenance of air powered equipment 44Supervisionandprocedures 44Daily 44Weekly 45Monthly 45Threemonthly 45Sixmonthly 45Precautions 45

TRAINING 46Statutory requirements 46Hazards 46Precautions 46Further information 46British standards 47Health & Safety Executive publications 48Legal requirements 49

FURTHER INFORMATION 50



Introduction1 Thisguidancebookletaimstopromotethesafeuseofcompressedair

bygivingadvicetodesigners,manufacturers,installers,usersandothersconcernedwithorresponsibleforhealthandsafetyatwork.Itwasoriginallyproducedin1990duringarapidlychangingsituationinEuropearisingfromthepreparationforthesinglemarketandwasfurtherrevisedunderthe‘ReviewofRegulationsandGuidance’undertakenbytheHealthandSafetyExecutive(HSE)in1996.

2 Therearemanywaysinwhichcompressedaircanbedangerous,forexample:

(a) itcanenterbodyorificessuchasthemouth,earsandanus,causing severeandoftenfatalinjuries;

(b) athighpressureitcanpenetratetheskin; (c) particlesoroilcarriedinanairjetcandamagetheeyes; (d) oil-cokedepositsinasystemcanspontaneouslyigniteandcausean

explosion; (e) vesselscontainingcompressedair,evenatcomparativelylowpressure,

canexplodeviolentlyoncetheirintegrityislost;and (f) dirtyor‘wet’aircanleadtocorrosionandblockedvalveswhichmay

makethesystemunsafe.

3 Thisbookletexplainshowtominimisethelikelihoodofsuchproblems,butitdoesnotgivespecificadviceonairseparationplant,thepneumatictransportationofmaterialsthroughpipelinesorthesupplyofrespirableair.Referenceinthisguidancebooklettoaparticularstandarddoesnotprecludeusinganequallyeffectivealternativestandard.



Compressor plant Groups of compressors

4 Forthepurposesofthisbookletcompressorsaredividedintothreegroups:small,mediumandlarge.

5 Asmallcompressordeliversupto40litrespersecondoffreeairand/orhasapowerinputofnomorethan15kW.Suchcompressorsmaybemobileorfixedandmaybesuppliedaspackagedunits.Atypicalonewouldcompriseareciprocatingcompressordrivenbyanelectricmotorontopoforalongsideanairreceiver.

6 Amediumcompressordeliversbetween40and300litrespersecondoffreeairand/orhasapowerinputofbetween15and100kW.

7 Alargecompressordeliversmorethan300litrespersecondoffreeairand/orhasapowerinputofmorethan100kW.

8 Manymediumandlargecompressorsaresuppliedaspackagedunits.Atypicalonewouldcompriseacompressor,airintakefilter,motorandaircooler,allonacommonbedframewithfactory-connectedpipingandfactory-installedelectricalcontrolsandwiring.Itcouldbeenclosedinasheetmetalhousingtreatedwithsoundproofingmaterialtoreducenoiselevels.

9 Usingapackagedunithasanumberofadvantages;itsimplifiesfoundationwork,reducesinstallationtimeandprovidesaproperlyengineeredandadequatelyguardedassemblyofcomponentsinacompactspace.However,theuserisstillresponsibleforsitingthesystemsothatincomingairisasdryandfreefromcontaminantsassiteconditionsallow.Boththeairenteringthecompressorplantandthedeliveredairmustbeasdry,cleanandcoolaspossible.Adviceonsitingisgiveninparagraphs60to67.

Hazards

10 Themajorhazardassociatedwithcompressorsisoverpressurisation,whichmayarisefrom:

(a) ablockedoutletorsomeotherrestrictiontoflow; (b) failureofautomaticcontrolscombinedwithlowairconsumption; (c) compressormalfunction,egoverspeeding; (d) anexternalfirenearthepressuresystem;and (e) overheatingandthebuild-upofcarbonaceousdeposits,bothofwhich

canleadtofiresorexplosions.Althoughtheyarerare,firesand explosionscanalsooccurasaresultofoiloroilvapourbeingignitedin thepressuresystem.

11 Dirtyor‘wet’aircancauseasystemtofailegbycausingfineparticlesofdebristoagglomerate,blockingsafetyrelatedvalves.

General information and advice

12 Standardsforthesafedesign,construction,installationandoperationofmanytypesofstationarycompressoraresetoutinBS6244Code of practice



for stationary air compressors.Itspecifiesrequirementstohelpminimisecompressoraccidentsanddefinesgeneralsafetypractices.BSEN1012Parts1&2coverCompressors and vacuum pump safety requirements.

NOTE: It is important that records are amended following modifications to plant and pipework.

Precautions

13 Transmissionmachineryeg‘V’belts,pulleysandotherdangerousparts,shouldbeguardedtopreventaccess,seeBS5304Code of Practice for Safety of machinery.

Safety valves14 Onallmediumorlargemulti-stagepositivedisplacementcompressorsa

safetyvalveshouldbefittedbetweeneachstageand,whereappropriate,intheinteroraftercoolercircuit.

15 Whereanisolatingvalveisinstalledinthedischargepipeworkbetweenthecompressorandreceiver,thepipeworkonthecompressorsideofthevalveshouldbeprotectedbyasuitablesafetyvalvethatcomplieswithBS6759,Part2Specification for safety valves for compressed air or inert gasesandisinstalledtoBS6244,clause21,unlessthesystemhasbeendesignedtowithstandthemaximumpressurethatcanbegenerated.(Thisvalveisinadditiontotheairreceiversafetyvalve.)Onsmallfixedandsmallandmediumtransportablecompressorunits,wheretheoutletofthecompressorisdirectlyconnectedwithoutshut-offornon-returnvalvestoanairreceivertowhichnoothersourceofpressureisattached,onesafetyvalveontheairreceiverissufficient.

Pressure indication16 Anaccuratelycalibratedairpressuregaugewithareadilyvisibleappropriate

scale-readingshouldbeprovidedaftereachstageofcompression.However,onsmalltwo-stagecompressorsthisisnotrequiredafterthefirststageofcompression,butasuitabletappingtoenableatestdevicetobefittedshouldbeprovided.GaugesshouldbeconstructedtocomplywithBSEN837-1Part1-Bourdon tube pressure gauges- Dimensions, metrology, requirements and testing andinstalledtocomplywithBSEN837-1Part2 Selection and installation recommendations for pressure gauges.

17 Onmediumandlargereciprocatingcompressorswithforcedfeedlubricationsystemsitisimportantthatagaugeisprovidedintheappropriatepositiontoindicateoilpressure.

Thermal protection18 Tominimisetheriskofoverheating,largecompressorsshouldbeprovided

withasuitablethermalprotectivedeviceasnearaspracticabletothelaststagedischargevalveor,wherethereismorethanonevalve,atacommonpointofdischargewhichwouldautomaticallyshutdownthecompressorwhenapredeterminedtemperatureisexceeded.Note - where automatic compressor shut-down may adversely affect the safety of pressure-dependent systems, additional high temperature warning devices may be required so that action can be taken prior to automatic shut-down.

19 Onlargetwo-stagecompressorsathermalprotectivedeviceshouldalsobeprovidedasnearaspossibletothefirst-stagedischargevalve.Largecompressorswiththreeormorestageswouldrequireaseparatedeviceforeachstage.



20 Formediumandlargeair-cooledcompressorsprotectivedevicesshouldbeprovidedtomonitorgeneralcompressoroverheatingwhichmaybecausedbycooling-fanfailureorthefoulingofcoolingsurfaces.

21 Oil-floodedrotarycompressorsshouldhaveanautomaticshut-downdevicetopreventthetemperatureofthecompressedairfromexceedingasafelimit.

Coolant protection22 Ifthecompressoriswatercooled,athermostatshouldbeprovidedtothe

coolingwateroutletorwaterreturntotheradiatorheadertanktoshutdownthecompressorwhenthewatertemperatureexceedsthemanufacturer’srecommendedmaximum.Wherethethermostatdevicedoesnotgive‘nowater’or‘noflow’protection,awaterflowdetectiondeviceshouldalsobeprovided.Sufficientgoodqualitycoolingwaterisrequiredtocoolallpartsofthesystemandinhibitblockagesandcorrosion.Thesupplymayrequireprotectionagainstfreezinginlowtemperatures.

Lubricant protection 23 Onmediumandlargecompressorsapressure-sensingdeviceshouldbe

providedtoshutdownthecompressorandactivatevisibleandaudiblealarmsifthelubricatingoilpressuredropsbelowthemanufacturer’srecommendedminimum.Gravity-feedlubricationsystemsshouldbefittedwithalevelsensingdevice.Athermalsensingdeviceshouldbefittedtosetoffanalarmandshutdownthecompressoriftheoilinthecrankcase,sumporscavengesystemsexceedsthetemperaturespecifiedbythelubricantmanufacturer.Therecanbesafetyadvantagestousingsyntheticester-basedoilsforlubricatingcompressors.

Explosion protection24 Ifcomponentsrunhot,oroilcokedepositsspontaneouslyignite,theremay

beanexplosion.BS6244describesthechemistryofsuchconditionsandexplainshowoilcokedepositscanbeprevented.Toreducetheexplosionriskonmediumandlargecompressors,afusibleplugcanbefittedontheundersideofthepipebetweenthecompressorandthereceiverascloseasispracticabletothecompressor.Whenorderingsuchaplug,userswillneedtoprovidethefollowinginformationforthemanufacturer:

(a) maximumdesignworkingpressure; (b) makerandgrade,orclosedflashpointoftheoilusedforcylinder

lubrication; (c) maximumdesignoutlettemperatureofair;and (d) boreofoutletpipefromcompressor.

25 Fusibleplugsaregenerallyavailableforpressureupto340bar(5000psi).Asanadditionalprecautionregularinspectionsofthecompressorshouldbecarriedout(seeparagraphs142to170).

Air inlet/outlet monitoring26 Awatermanometerorotherpressure-indicatingdeviceshouldbefittedto

eachinletairfilteronlargecompressors.Thedevicemeasuresthepressuredropacrossthefilter,indicatinghowcleanitis.Itisrecommended,whereitisreasonablypracticabletodoso,thatsuchdevicesbefittedtosmallandmediumcompressors.

Other instrumentation27 Onmediumandlargecompressorsconsiderationshouldbegiventofitting

temperaturereadingorrecordinginstrumentstoindicate:



(a) airtemperatureat: (i) theinlettothecompressor; (ii) theoutletfromthefirststageofcompression,neartothedischarge

valve; (iii) theinlettothelaststageofcompression; (iv) theoutletfromthelaststageofcompression,neartothedischarge

valve;and (v) theoutletfromtheaftercooler (b) oiltemperatureat: (i) thecrankcase;or (ii) withforcedfeedandscavengelubricationsystem,thepointwhere

theoilleavesthecrankcase; (c) watertemperatureat: (i) theinlettoeachcoolingcircuit(exceptonradiator-cooledsets);and (ii) theoutletfromeachcoolingcircuit.

Itisimportantthattheuserandmanufacturerdiscusswhethersuchinstrumentsareneeded.

Air inlet/outlet control28 Theinletvalvecaneitherbedesignedsothatitcannotbeusedinapartially

openposition,orbefittedwithvisibleandaudiblewarningsthatindicatewhetherthevalveisfullyopenorclosedduringplantoperation.Thevalveoperationisnormallyautomaticexceptwhenrequiredforstartingupthecompressor.Oil-floodedrotarycompressorshavebuilt-inself-regulatinginletthrottles.Constantspeedcompressorsshouldbeprovidedwithsuitablecontrolgearsothattheamountofairdeliveredcanbecontrolledtosuitdemand.

29 Figure1showsanillustrationofalargecompressorinstallationandthepositionsatwhichsafeguardsarerequiredorrecommended.Itisunlikelythatanyinstallationwillrequireallthesafeguardsindicated.Thefinalrequirementwilldependonrelevantstatutoryrequirements,thedegreeofsupervisiontheinstallationwillreceiveandthelocalenvironment.



Figure 1 Illustrationofalargecompressorinstallationshowingthepositionatwhichsafeguardsare

requiredorrecommended

Thermal protective device to monitor air-cooled

compressor general overheating

Stopvalve

Receiveridentification

Cooling water feed

Compressor Aftercooler

Intercooler

Lowpressurecylinder

Highpressurecylinder

Air inletfilter

Totalclosure

unloader

Cooling water discharge

Receiver

Manhole

AR1SWP

Oil pressure protective device Manometer

Thermometer Safety valves or relief valves Non return valves Drain

GHI

L

JK

ABCDEF

Fusible plug Thermal protective device Water flow protective device Oil level protective device Oil pressure gauge Air pressure gauge

It is unlikely that any installation will require all the safeguards indicated. However, a combination of these should be fitted, taking into account the statutory requirements and the degree of supervision the installation will receive.

Instruments will normally be mounted on a common panel

NOTEKEY

Water or air flowI

I J F

II L

B F I

I

J K J F I

A

I L

F

J

A

I

L

I

B C I

IBDEGI

IBI

H

B



Air receivers Statutory requirements

30 Bothmanufacturersandusersshouldbefamiliarwiththestatutoryrequirementsapplyingtocompressedairsystemsandairreceivers.TheseareprincipallycontainedinthePressureSystemsandTransportableGasContainersRegulations1989.AdditionalrecommendationsaregivenintheApprovedCodeofPracticeSafety of pressure systems.

31 Inpremiseswheretheairreceiversmustbecleanedandexaminedatregularintervalsandforairreceiverswithavalueofpressuretimesvolumegreaterthan250barlitres,thenatureandfrequencyoftheexaminationmustbecontainedinawrittenschemeofexamination.Thewrittenschemeofexaminationdrawnuporcertifiedbyacompetentpersonwillnormallyspecifyaperiodbetweenexaminationsof24to48months.

32 Whenconnectedtoanaircompressingplantareceivershouldeitherbeconstructedtowithstandthecompressor’smaximumpressuresafely,orbefittedwithasafetyvalveandapressure-reducingvalvetopreventthereceiver’ssafeworkingpressurefrombeingexceeded.Whenprovidingasafetyvalveandpressuregaugeforasetofairreceiversthatareinterconnectedandcollectivelysuppliedthroughasinglepipe,theymaybetreatedasonereceiver,providedthat:

(a)anyreducingvalveorothersuitableapplianceisprovidedinthesingle supplypipe;and

(b)thereisnomeansofisolatinganyinterconnectingpipework.

33 ThereceivershouldbefittedwithasuitablesafetyvalvecomplyingwithBS6759,Part2orsimilarequivalentstandardandadjustedsothatairisallowedtoescapeassoonasthesafeworkingpressurehasbeenexceeded.Itisessentialthatthevalveiscapableofdischargingmoreairthanthesystemcansupplytothereceiver.

34 ThereceivershouldbefittedwithacorrectpressuregaugecomplyingwithBS1780orsimilarequivalentstandardandwhichindicatespressureinbar,lbf/sqin,orothersuitableunits.

35 Thereshouldbeasuitableappliance,eithermanualorautomatic,fordrainingthereceiver.Itisrecommendedthatmanualdrainvalvesshouldbefullboreandstraightthrough,tominimiseanybuild-upofdebriswhichcouldpreventtightshutoff.Automaticdrainvalvesshouldhaveadequatecapacityforliquiddischarge,bedesignedtominimisedebrisbuild-upandhaveamanualoverridetocheckperformance.Astrainerpositionedimmediatelyupstreamofthevalvewillhelppreventdebrisbuild-up.Protectionagainstfreezingofvalveswillberequiredininlowtemperatureconditions.

36 Areceivershouldhaveasuitablemanhole,handholeorothermeans(asdeterminedbytherelevantstandards,forexampleBSEN286-1Specification for simple unfired pressure vessels designed to contain air or nitrogenandBS5169Specification for fusion welded steel air receivers)toenabletheinteriortobethoroughlycleanedandinspected.



37 Areceivershouldbeclearlymarked,inaconspicuousposition,withitssafeworkingpressureandotherrelevantinformationrequiredbythePressureSystemsandTransportableGasContainersRegulations1989.Thedetailsshouldbeclearlyvisibleonthevesseloraplateattachedtoit.

38 Areceivershouldbereadilydistinguishable.Thiscanbeachievedbypaintingonidentificationmarkingsorbyaffixingamanufacturer’splate,givingthenameofthemanufacturer,serialnumberetc.

Hazards

39 Themainhazardisthatthevesselmayexplodebecauseitssafeworkingpressurehasbeenexceededorbecauseitsabilitytowithstandpressurehasbeenreducedthroughcorrosionfatigueorinternalcokefiresforexample.


40 AllnewairreceiversshouldconformtoBSEN286-1orBS5169,whereapplicable,ortoastandardprovidingequalintegrity.

Precautions

41 Todeterminetherequiredcapacity,thecompressoroutputanddemandpatternneedtobetakenintoaccount.Asaguide,thiswillbebetweensixandtentimesthefreeairoutputofthecompressoratnormalpressure(litres/second).Manyuserstrytosaveoninitialcostandmakethemistakeofbuyingareceiverthatistoosmall.

42 Thedrainvalve,safetyvalve,examinationholesandmanholesneedtobeaccessible.

43 Thescaleofanygaugesneedstobeclearlyvisible.

44 OnlargecompressorsystemstheairreceivershouldbefittedwithafusibleplugconformingtoBS1123,Part1.Ifafirebreaksoutnearby,theplugwillhelptopreventanexplosionbyguardingagainst:

(a) theairtemperaturerisingtothecompressorlubricatingoilflashpoint;or (b)anexplosionoccurringbelowthedesignedworkingpressurebecauseof

lostintegrityowingtoheat.

45 Welded-onbracketsareoftenusedtomountcompressor-motorcombinationsontoairreceivers.Wherethisisthecase,weldingshouldbetothespecificationandapprovaloftheairreceivermanufacturer.Itshouldnotbecarriedoutindiscriminatelybecausetheweldermayunwittinglyweakenthereceiver.Mountingbracketsshouldbedesignedandfittedinaccordancewiththeapplicableairreceiverstandard.Itisgoodpracticetoweldmountingbracketsontointermediatereinforcingplatesratherthandirectlytotheairreceiver.



Coolers Hazards

46 Manyaftercoolersarepressurevesselsandtheassociatedhazardsaresimilartothoseofairreceivers(seeparagraph39).


47 Coolingplaysanimportantpartinthesupplyofgoodqualitycompressedair.Intercoolersandaftercoolerslowerthetemperatureofthecompressedair.Thesecoolersareusuallywateroratmosphericaircooled.Withverysmallaircompressorsthefunctionoftheaftercooler(ietheloweringofthedewpointofthecompressedair)isperformedbytheairreceiver.Forothercasesaseparateaftercoolerwillnormallybenecessary.

Precautions

48 Air-cooledcoolersusuallyrelyonagoodcirculationofexternalairovertheheatexchangersurfacetoensureeffectivetransferofheat.Thereshouldbeadequatespaceavailablearoundtheseheatexchangerstoalloweffectivecleaningofallsurfaces.Thecoolingairinletsandoutletsshouldnotbeobstructedbylooseequipment,materialsetcorbyanysubsequentlyerectedbuilding.Wherepossibletheairinletshouldbesitedonthenorthsideofthebuilding.

49 Itisrecommended,particularlyatmediumandlargecompressors,thataftercoolersarefittedtothedischargesideimmediatelyafterthecompressor.Thesearefrequentlyprovidedwithseparatorstoremoveoilandmoisturefromtheair.

50 Acondensateseparatorwithanautomaticdrainvalveshouldbeprovidedatasuitabledrainagepointatthecooler’scompressedairoutlet.Protectionagainstfreezingofthevalvewillberequiredinlowtemperatureconditions.

51 Whereafluidisusedasthecoolingmedium,acoolantdrainvalveshouldbefittedandthecoolingcircuitprotectedagainstcorrosion.Thereshouldbesomewayofmeasuringtheinletandoutlettemperaturesofthecompressedairandofthecoolant.



Air dryers Hazards

52 Thehazardsassociatedwiththeshellsoflargedryersdesignedonthetube-in-shellprinciplearesimilartothoseofanairreceiver(forinformationonhazardsseeparagraph39).Asecondaryhazard,shouldanairdryernotfunctionproperly,isthatmoisture-ladenaircancauseasafetysystemtofail.


53 Airdryersaresometimesdesirablewherepiperunshavetoberoutedoutsidebuildingsorwherethecompressedairisusedoutsidebuildingsegforoperatingvalves.Whereexceptionallydryairisneeded,egforpurgingdoubleglazingunits,airdryersareessential.Therearetwomaintypes:refrigerantanddesiccant.FurtherclassificationcanbefoundinBS6754Specifications and testing of compressed air dryers.

Refrigerant54 Refrigerantairdryerscanusuallyreducethedewpointofthecompressed

airto2°C.Thispreventscondensationfromforminginthedistributionpipeswheretheambienttemperatureexceeds2°C.Thismaybesuitableevenwhereshortrunsofpipeareroutedintheopenair,providedtheyareproperlyinsulated.

Dessicant55 Desiccantdryerscanreducethepressuredewpointofthecompressedairto

verylowlevels,exceptionally,aslowas-100°Cbutnormally,between-20°Cand-40°C.Thereductioninthepressuredewpointofcompressedairshouldbecloselyrelatedtotherequirementsoftheplantorequipmentinstalled.Adesiccantdryernormallyconsistsoftwochambersthatbothcontaindesiccant-oneonstream,theotherbeingregenerated.Anautomaticinletvalvedirectsairfromthecompressortoeachchamberinturn,thusensuringaconstantsupplyofdryair.

56 Positioningoftheairdryerwilldependonthecustomer’sparticularrequirements,butwillbeeitherimmediatelybetweentheaftercoolerandreceiver(wherefitted)orimmediatelyafterthereceiver.Wheretheneedforexceptionallydryairrepresentsonlyasmallpercentageofthetotalcompressedairused,adryermaybelocatedimmediatelyupstreamoftheparticularplantwherethedryairisneeded.

Precautions

57 ThechambersofairdryersarepressurevesselsandshouldconformwithBS5500Specifications for unfired fusion- welded pressure vesselsortoastandardprovidingequalintegrity.Ifmeansareprovidedforisolatingthedryer(anditisgoodpracticetoprovidemeansofisolationforallequipment),eitherthechambersshouldbeconstructedtowithstandthemaximumpressurethatcanbegeneratedbythecompressororasuitablepressurereducingvalveandasafetyvalveshouldbefittedtopreventthesafeworkingpressureofthechambersfrombeingexceeded.



58 Wherethereisnomeansofisolatingthedryerfromasuitablesafetyvalve,egonthereceiver,andwherenon-returnvalvesarefittedtothedryeroutlet(toprotectitfromstoredenergyinthesystem),nosafetyvalvesareneeded.

59 Somedryersregeneratethedesiccantsimplybypassingaproportionofthedrierairthroughit.Othersuseheatercoilsembeddedinthedesiccant.Thislattertypeshouldbeequippedwithathermalprotectivedevicethatcandetectanytemperatureriseabovethethermostatsetting.Excessivetemperaturerisesduetothermostatfailureshavebeenknowntoleadtooilmistexplosions.



Installation of compressors60 Smallcompressorinstallationsmayeasilybeoverlooked,especiallyifsited

inaseparateenclosureoutsidetheworkingarea,andconsequentlymaynotreceivepropermaintenance(seeparagraph146-158).Thedesignoflargeinstallationswillneedtoincorporateadequateaccessandsuitableliftingequipmenttofacilitatemaintenance.Ifnormallightingislikelytobeinadequate,locallightingshouldbeprovidedsothattheworkingareaisadequatelylit.Considerationshouldalsobegiventocompressorspecificationsiftheyaretobeinstalledinpossiblehazardousareas,e.g.ingaragepitswhereaflammableatmospheremaybepresent.

Precautions

Small compressors61 Wherepossiblethecompressorunitshouldbemountedatgroundleveland/

orinanareabigenoughtoallowforinspectionandmaintenance.

62 Anyplatformusedforaccessorasaplaceofworkshouldbebigenoughforapersontostandsafelyonit,andhaveguardrailsandtoeboards.

63 Theunitshouldnotbemountedonaplantstructurewherethereisexcessivevibration.

64 Smallunitsusedtosupplyworkshopsandsimilarinstallationsshouldbesitedwheretheyareaccessibleandphysicallyprotectedagainstdamagefrommaterial,toolsandequipment.Wheretheriskofdamageishightheyshould,wherepossible,beinstalledinseparateroomsadjacenttothemainbuilding(seeparagraphs60and67).

Medium and large compressors65 Whereusersareresponsibleforon-sitesystemdesignandinstallationthey

shouldfollowthemanufacturer’sinstructionscarefully.Mediumandlargecompressorsshouldbelocatedinaposition(usuallypermanent)bestsuitedforthepurposeandwithaccessforeaseofmaintenance.Thismeansthatthecompressor,includingitsprimemover,airreceiver,cooleretc.shouldbe:

(a) nearthecentreoftheloadtominimisepiperuns; (b) housedinabuildingthatisinsulatedorheatedtokeeptheambient

temperatureabovefreezing; (c) providedwithadequateventilatingairtopreventoverheating,andsited

sothattheintakeofmoistureisminimised;and (d) sitedawayfromdustyatmospheresandprovidedwithadequatefacilities

fordrainingofcondensate.

66 Thereshouldbesomemeansofcontrollingairbornedustandcontaminantsinthevicinityofthecompressor.Theairintakeshouldbeprovidedwithanefficientfilter.

Noise

67 Compressornoiseisoneofthemostcommonnoiseproblemsassociatedwiththeworkplaceandispotentiallydamaging.ReferenceshouldbemadetothePreventionofDamagetoHearingfromNoiseatWorkRegulations,



enactedon1January1990,andtheassociatedguides1and2and3to8.Wherenoisefromcompressorsislikelytocauseexposuretohazardouslevelsofnoise,thisshouldbeincludedinthenoiseassessment(requiredundertheNoiseatWorkRegulations1989)andtheassessmentshouldindicatethedegreeofnoisereductionrequiredtoreducetheexposuretosafelevels.Compressorsshouldbesuppliedwithnoiseemissioninformation.Ifthisisnotthecase,purchasersshouldrequestthisinformationwhichcanbeusedintheassessment.Noisecontrolmeasures,ifrequired,includethefollowing:

(a) sitingthecompressorawayfromworkareas; (b) providingthecompressorwithanacousticenclosure(theneedfor

accessandremovalformaintenancewillneedtobeaddressed); (c) providinganti-vibrationmountings; (d) thefittingoforimprovingtheperformanceofsilencers; (e) accesstoenclosuresprovidedforcompressorsshouldonlybe

permittedtopersonswearingsuitableandeffectiveearprotection.

68 HSE Guidance note PM 56givesinformationandadviceaboutnozzledesigntoreducenoise.



Main line systems69 Thissectiondealswiththesystemofpipes,valvesandfittingsfromthe

sourceofthesupplytothepointofapplicationorcontrol.

Hazards

70 Inadequatelysizedanddesignedsystemscanleadtotheoperatingunitsbeingstarvedofair,causingmachinemalfunction.Repeatedmalfunctionsmaytemptoperatorstoadoptunsafepracticestoovercomeanyproblems.Badlydesignedpiperunsandlackofisolationvalvesmayexposemaintenancestafftounnecessaryrisks.Somegradesofplasticpipeworkarenotrecommendedforuseincompressedairinstallationsanddesignersareadvisedtoconsultmanufacturerswhenselectingmaterials.

71 Incorrectmaintenanceofnon-metallicbowlsusedonfilters,traps,separatorsandlubricatorscanleadtoexplosions.Itisimportanttoensurethatalllubricantsusedtoreplenishlubricatorsarecompatiblewiththelubricatorbowlandtheequipmenttobelubricated.AttentionisdrawntoBS6005Specification for moulded transparent polycarbonate bowls used in compressed air filters and lubricators,regardinginstallation,useandmaintenanceofunitsfittedwithpolycarbonatebowls.


72 Compressedairsystemsinvariablygrow.Itisimportanttotakeintoaccountanyforeseeableexpansionofthesystem,andgenerousallowanceshouldbemadeonthesizeofpipingprovided.Thecostofinstallinga50mmdiameterpipeislittlemorethana25mmone,anydifferencebeinginthecostofmaterial.However,flowcapacityofa50mmpipeisfourtimesthatofa25mmoneandusingthelargersizeensuresbetterperformanceandfacilitatesfutureadditionstothesystematlittleextracost.Asageneralguidethepipesizewouldbesuchthatthepressuredropbetweenthereceiverandthemostremotetakeoffpointswouldnotexceed5%oftherequiredsupplypressurewithamaximumof0.3bar(4psi).Thepipesizeforinitialmainrunsinanysystemwouldnotnormallybelessthantheoutputportofthecompressor.

73 Therearetwomaintypesofcompressedairsystem;singlelineandringmain.Figures2and3showtypicallayouts,withpositionsindicatedforvariousvalves,drains,filters,airlinelubricatorsandpressuregauges.

74 Usersshouldkeepaschematicdrawingoftheairsystemshowingpiperuns,intendeddirectionofairflow,andthepositionsoffittingssuchasvalves,drains,etc.Thedrawingsshouldbeamendedwhenmodificationsoradditionsaremadetothesystem.AnygraphicsymbolsusedshouldcomplywithBSISO1219Fluid power systems and components. Graphic symbols and circuit diagrams.

Precautions

Pipe-runs 75 Therouteofthepiperunandthepositionofvalvesandoperatingpoints

shouldbesafeandconvenientforthosewhowilluseandmaintainthesystem.



76 Thepiperouteitselfshouldnotpresentahazardorobstructaccessandshouldberoutedawayfromanyareaswhereitmaybevulnerabletomechanicaldamage.

77 Thereshouldbeadequateandsufficientaccessways,workingplatformsandclearancespaceprovidedtoenablethecompressedairsystemtobeoperatedandmaintainedwithoutexposinganyonetounnecessaryrisk.

78 Piperunsshouldhaveaslightfallinthedirectionofairflow,anddrainagevalvesshouldbefittedatthelowestpoint,insuchawaythatmoistureandaircanbedischargedsafely.Adrainvalveshouldbefittedatthebottomofverticalpiperuns.Sectionsofpipeandvalvesthatmayhavewaterinthemandmaybeexposedtofrostshouldbesuitablyinsulated.Note: receiver drains generally have a heavier duty than normal pipe run drains-see paragraph 35.

79 Piperunsshouldbesecuredbybracketsorothersupportsinstalledatappropriateintervalstosupportthepipesystemsuchthateachremovablesectionisself-supportingandtheremainingpipeisstableafterremoval.Toallowforexpansion,particularlyatthecompressor/receiverdischargeoronstraightrunsexposedtosunlightorheatfromtheprocess,suitableandadequateexpansiondevicesshouldbefitted;egbellows,loopbends,flexiblepipes.BS3974:Parts1-3Specification for pipe supportsgivesdetailsofsuitablemethods.

Figure 2 Singlelinesystem-typicallayout

Symbols DescriptionShut-off valve

Manual drain (water trap)

Automatic draining valve

Lubricator

Pipe fall in direction of air flowFilter, pressure regulatorpressure gauge, lubricator

Filter with manual control

Control valve

Pressure gauge

Air cylinder(spring return)

KEY

Chuteoperation

Maintenance area

Airgrinder

Compressorinstallation

Airpoint

Todrain

Todrain

To drain

Airvent

Bin gateoperation

DO NOT CROSS-CONNECT AIRLINESIN A SINGLE LINE SYSTEM



Figure 3 Ringmainsystem-typicallayout

80 Pipingandassociatedfittingsconnectedbetweenthecompressorandairreceivershouldbeeasytoclean.Ifcarbondepositsbuildupinsuchpipeworktheremaybeanexplosion(seeparagraph24).

81 Alloutletpointsshould,wherepracticable,betakenfromthetopofthepiperun,andastopvalveorself-ventingballvalve(wherenecessarycompletewithhandle)shouldbeprovidedadjacenttotheconnectionpoint.Theconnectionpointatanyoutletshouldbearrangedhorizontallyorfacedownwards;upwardfacingconnectionpointsinvariablyfillwithdirtandpromptthebadpracticeofblowingoutbeforeuse.Outletpointsshouldbeprovidedatconvenientplacesforallroutineactivitieswhichrequirecompressedair.Theyshouldbepositionedsothathosesattachedtothemwillnotcrossorobstructthenormalaccesstotheworkplace,andcanbeconnectedwithouttheneedforclimbing.

82 Piperunsshouldbeidentifiedbypaintingthepipelightblue(BScolourreference20.E.51)inaccordancewithBS1710.Whereapplicabletheriskofcouplinguptothewrongcompressedgassupplycanbefurtherreducedbytheuseofnon-interchangeableconnections(seealsoparagraph100).

83 Stopvalvesshouldbeprovidedandpositionedsothatthecompletepipeworksystemcanbeisolatedfromthecompressedairsupply.Allbranchlinesofsubsectionsofthesystemshouldalsohavestopvalvesfittedtoallowseparateisolation.Whereappropriateeachvalveshouldhaveafacilitytobelockedintheclosedposition.

Symbols DescriptionShut-off valve

Manual drain (water trap)

Automatic draining valve

Lubricator

Pipe fall in direction of air flowFilter, pressure regulatorpressure gauge, lubricator

Filter with manual control

Control valve

Pressure gauge

Air cylinder (spring return)

KEY

B

A

Controlpoint

Todrain

Airpump

Airpoint

Chuteoperation

Maintenance area

Airgrinder



Bin gate



84 Forringmainsorsystemswithdualsupply,stopvalvesmustbeprovidedwhichenableeachindividualairsupplytobeisolatedfromthepipeworksystem.Thisarrangementofstopvalveswillallowsafeoperatingprocedurestobeadoptedduringmaintenanceofthesystemandancillaryequipment.

85 Whereaircannotbeventedfromthesystemoranypartofthesystemthroughthenormaloutlets,valvesshouldbefittedforthispurpose.Thevalvesspecifiedshouldbesuitablefortheapplication.Inmostcasesthree-portvalvesorself-ventingballvalvesarethemostsuitabletypeforisolatingandventing;thesevalvesshouldbearrangedsothatwhenthesupplyisshutoff,thedownstreampartoftheairsystemisventedthroughtheexhaustportofthevalveandprovisionmadetolockthevalveinthisposition.

86 Wherevalvesaregrouped,orwherethepurposeorlocationofthevalveisnotobvious,anoticeshouldbeprovidedindicatingthepositionand/orpurposeofthevalve.

87 Leveroperatedstopvalvescanbeinadvertentlymovedtotheopenposition.Duringmaintenancetheyshouldbeeitherlockedintheclosedpositionortheleverhandleshouldberemoved.

Filters, traps, separators and lubricators88 Filtrationandlubricationtoastandardofcleanlinessappropriatetoend

usagearenecessary.Airlinelubricatorsshouldbeprovidedforoperationswhichinvolveairtools,aircylindersoraircontrolvalves;theyshouldbepositionedafterthestopvalveandafteranyfilterorseparator.Inbothcasesitisessentialthatfiltersandlubricatorsarepositionedafterandadjacenttoastopvalvetoallowsafeserviceandmaintenance.Theyshouldnotbefittedintoringmainswherethedirectionofairflowisnotcontrolledbutintothebranchlinesleadingfromthem.Highstandardsoffiltrationwillberequiredforinstrumentcontrolorintheelectronicsindustry.Ultra-highefficiencyfiltrationwillberequiredinhospitalsandthepharmaceutical,foodstuffspreparationandbrewingindustries,andappropriatefilters,trapsorseparatorsshouldbefitted.Whereextremelycleanorsterileairisrequiredspecialistequipmentsuppliersshouldbeconsulted.Precautionsshouldbetakenagainsttheingressofdirtandothercontaminantsfromthesurroundingareathroughcarefulsitingofthecompressor.Theuseofexhaustportfiltersshouldbeconsidered.

89 Inmostcasesthesecomponentswillhaveeithermetallicortransparentplasticbowls(usuallypolycarbonateorpolyamide),whichhavegoodimpactstrength.Thepropertiesofthematerialsmayhoweverbeadverselyaffectedbysolvents,alcohols,cleaningsolutionsorsyntheticlubricantsandmaintenanceinaccordancewithmanufacturers’recommendationsisessential.(NBUsefulguidanceforpolycarbonatebowlsisprovidedinBS6005Specification for moulded transparent polycarbonate bowls used in compressed air filters and lubricators.)Itisthereforeessentialthatcleaningofpolycarbonatebowlsiscarriedoutwithcleanrags,andthatmateriallikelytobecontaminatedwithdilutedsolubleoilsshouldbeavoided.Wherepossible,filters,separatorsandlubricatorsshouldbepositionedsothattheriskofaccidentaldamagetoanynon-metallicbowlsisminimised.Evensubsequentminorknocksmayleadtodamagedbowlsexploding.Itisgoodpracticetoshieldallnon-metallicbowlsandmanufacturersshouldensurethatsuch

bowlscanbeshielded.Specificrequirementsforfilters,traps,separatorsandlubricatorsarediscussedinparagraphs104,105and109.



Pressure regulators90 Whereitisnecessarytoprotectequipmentfromoverpressurisation,

pressureregulatorsshouldbeprovidedandsettomaintainaconstantsafedownstreampressure.Anairpressuregaugeshouldbeprovidedontheoutletside.Dependingonthelevelofriskcreatedbyoverpressurisationalladjustablecontrolsshouldhavesomeformoftamper-resistantprotection.Wheretheriskislow,asimplesnapactionlockshouldsuffice.Astheriskincreases,greatersecurityagainstunauthorisedadjustmentisneeded.Considerationshouldbegiventousingmodelsincorporatingpositiveinternalstopsorpositivemeansoflocking.Forveryhighrisks,non-adjustablemodelsmaybethebestanswer;alternativelytheadjustableitemsmaybesitedinlockableenclosureswiththekeykeptbyaresponsibleperson.

91 Apressurereliefvalve(safetyvalve)orothersuitableoverpressureprotectivedeviceshouldbefittedandsettorelieveifthesafeworkingpressureoftheequipmentorvesselisexceeded.Thereliefvalveshouldbepositionedsothatifthevalvedischarges,therisktopersonnelisminimised.



Portable pneumatic equipment Statutory requirements

92 ThePressureSystemsandTransportableGasContainersRegulations1989andtheProvisionandUseofWorkEquipmentRegulations1992setoutthedutiesofusersandownersofportablepneumaticequipment.

93 ThePersonalProtectiveEquipmentatWorkRegulations1992setoutwhateyeprotectionisneededforcertainprocessesusingcompressedair.

94 UndertheManagementofHealthandSafetyRegulations1992andtheHealthandSafetyatWorkAct1974employershavearesponsibilitytotraintheirstaff.Furtheradviceontrainingisgiveninparagraphs171to173.

Hazards

95 Bothblowgunsandhandheldtoolsareusuallyconnectedtoalengthofflexiblehosewhichduringthecourseofitslifewillbesubjecttomechanicaldamageandconsiderableflexing.Thisdamageand/orflexingparticularlyatconnectionpointscancausethehosetorupture.Thiscanleadtosuddendischargesofcompressedairandmaycauseunsupportedlengthsofhoseto‘whip’and‘snake’dangerously.

96 Thepracticeofusingblowgunsforremovingswarf,powderedmaterialsetcfromcomponentsandfrommachineryiswidespreadthroughoutindustry.Thereareanumberofhazardsconnectedwiththeuseofblowgunsincluding:

(a) eye injuries-atairlinepressurestheaircausesswarforotherparticles tomoveathighvelocitycreatingaserioushazardtotheeyesofthe operatororanyonenearby;

(b) other injuries-injurieshavebeencausedbydischarginggunswiththe nozzleheldclosetotheskin.Veryseriousinjuries,sometimesfatal,have occurredwhenthenozzleofthegunhasbeenpointedtowardsthe anus,evenatsomedistancefromit.Manyoftheinjuriesoccurwhen clothingisdusteddownandbecauseofthiscompressedairshould neverbeusedforcleaningclothing;insteadvacuumcleanerswithbrush typeheadsarerecommended.Othersaretheresultofhorseplay(see alsoparagraphs172and173);

(c) dust explosions-therehasbeenatleastoneseriousexplosionofadust cloudwhenablowgunwasusedtoremoveflammabledust;

(d) toxic hazards-theuseofcompressedairforcleaningtoxicmaterialcan resultinthedispersalofthematerialintotheair;

(e) noise-blowgunsfrequentlyproducehighnoiselevels.


97 Byfollowingtheadviceintheprevioussectionsaclean,dryairsupplyshouldbesafelygeneratedanddistributedtoalloutletpoints.Thetypeofequipmenttobeconnectedtotheoutletpointwilldeterminewhatextraprecautions,ifany,willberequired.Themostcommonrangeofdeviceswillbeairorblowguns,portabletoolsorpneumaticpoweredmachinery.Eachhasitsownparticularrequirements.



Precautions Flexible hoses98 Whenselectingaflexiblehose,usersshouldtakeintoaccountthesite

conditions,includingtemperatures,oilsandpressurestowhichitwillbesubjected.Wherelubricatingoilispresentinpipelines,agradeofhoseresistanttothatparticularoilmustbeused.Asyntheticbasedgradeofhoseshouldbeusedformineraloilsandanaturalbasedgradeforvegetableoil.Wherefireandexplosionrisksmaybepresent,theuseoffire-resistantanti-static(FRAS)hosesshouldbeconsidered.Themanufacturer’sadviceshouldalwaysbefollowed.

99 Heavy,mediumandlightgradesofhoseareavailable.Wherehosesareusedforsemi-permanentdistributionofcompressedair,forexampleinquarries,constructionsites,shipyards,farmyards,garageforecourtsetc,heavygradesshouldbeused.Mediumandlightgradesareusedforgeneralpurposessuchasfixedpneumaticmachineryandpneumaticcylinders,smallpowertoolsandportableequipment.Hosesusedwithhand-heldpowertoolsshouldbelightandflexible(butsuitablefortheduty).

100 Tubesandhosesusedtoconnectcylinderstotheircontrolvalvesareavailableinavarietyofcolourstomakefaultfindingandmaintenanceeasier(seeparagraph143).Theyshouldbeneatlyrunandadequatelysecured.Ifthefailureofaflexiblehosewouldbehazardousitshouldbefurtherrestrainedorshielded.

101 Couplingaportabletooltotheoutletpointisusuallyachievedbyuseofaquick-actingconnector.Theconnectorshouldbedesignedsothatwhendisconnecteditautomaticallysealstheairpressureontheupstreamsideandslowlyventstheairpressureonthedownstreamside.Forallhosesabove10mmbore,morethan10mlongorsubjecttoapressureexceeding7bar,theconnectorshouldhaveaself-ventingsocketwhichreleasesthedownstreampressurebeforedisconnectionispossible.Alternatively,aplugwithacontrolledventingactionshouldbeused.Thesesafetyfeaturespreventinadvertenttooloperationanduncontrolledwhippingofthehosewhenitsinletendisuncoupledfromthesocket.Anotherwayofreducing‘whipping’or‘snaking’istofitemergencyshut-offvalves,hoserupturevalvesorairfusesascloseaspracticabletotheconnector.Thevalveswillcloseorreduceflowtoaverylowlevelintheeventofexcessiveair-flowconditionscausedbyafailureofthehose(seealsoparagraph83aboutfittingofisolationvalves).Thesamerequirementcouldbenecessarywhenusingplastictubing.

102 Similarrequirementsforquick-actingconnectorsapplytomostpercussiveandvibratingairtools,whichmaybefixedorhandheld.Ifaquick-actingcouplingsocketisfittedatthehoseendadjacenttothetool,theplugshouldnotbescreweddirectlyintotheinletportbutshouldbefittedontoashortisolationhose(0.5to1.5mlong),thusisolatingtheplugandsocketfromthetoolvibrations.

103 Wherehosesareusedtosuspendtools,theloadstrengthofhoseandcouplingsshouldbeatleastfivetimesthesuspendedload.

Blow guns104 Blowgunsconsistingsimplyofareducedorificeindirectlinewiththesupply

hosecanbeextremelydangerous,unlesspreceededbyapre-settamper-proofpressureregulatorsetatareducedpressurefromthenormal80psiairlinesupply.Modelsareavailablecommerciallywhichincorporateanaircurtaindesignedtoprovideaprotectiveshroudaroundthenozzle.Although



notcompletelysafe,thesedesignssignificantlyreducetheriskofeyeinjuryandthedangersfromcloseskincontact.Ifdesignedcorrectlysuchnozzlescanoftenhelptopreventtheoperatorfrombeingsubjectedtoexcessivenoise.Becauseairisventeddirectlyintotheatmosphere,cleandryairisessentialandlubricatorsshouldnotbeused.Blowgunscanexhaustsignificantquantitiesofairandplaceextraloadingonthecompressorsystem.Inviewofthisandtheattendantriskarisingfromuseofblowguns,theiruseshouldbeconsideredcarefullywithaviewtousingalternativemeansforcleaningdownmachineryorcomponents.

Portable tools105 Pressureregulatorsshouldbeusedtoreducethepressuretotheoptimum

valueforthesafeandefficientuseoftheequipment.Thisvalueshouldbeclearlymarkedonthetool.Filtersandlubricatorsshouldbefittedinthesupplypipeasshownat‘A’inFigure3.Topreventover-speeding,toolswithairmotorsshouldincorporateagovernororthrottle.Thereshouldbeavailableaneasilyaccessiblemeansofisolatingtheairsupplyfromthetool.EuropeanStandardprEN792Hand-held non electric power tools-Safetycoversdesignofdrills,grinders,nibblers,polishersetc.Itispoorpracticetopullportabletoolsusingthehoseoruseitasameansofaccessbyclimbingontosuspendedhose.Olddamagedhoseshouldnotbeusedtomakeupfreshhoseassemblies.



Pneumatic powered machinery Hazards

106 ThehazardsnormallyassociatedwithpoweredmachineryareequallyapplicabletopneumaticpoweredmachineryandsuitablesafeguardsarenecessaryasdescribedinBSEN982Safety requirements for fluid power systems and their components-PneumaticsandBS5304CodeofPractice Safety of machinery.

107 Unlikeliquidfluidpowermedia,compressedairiselastic(compressible),andbecauseofthis,additionalhazardscanarisefromstoredenergyandactuatorsunderload(seeparagraphs138to141).Thishazardrequiresparticularconsiderationwhenthemachineryisfittedwithinterlockingguards.Interlockingsystemsarecoveredinparagraphs129to137ofthisbooklet.


108 Wherepneumaticallypoweredmachineryisconnectedtotheoutletpointthisshouldbebymeansofconventionalconnectors,egcompressionorpush-in,push-onconnectorswithashut-offvalve.PlastictubingmadefromPVCornyloniswidelyused,inparticularforpipinguppneumaticallyoperatedmachinesemployingpneumaticcylindersandvalves.Compressionorpush-in,push-on,connectorsofvarioustypescanbeusedwiththetubingwhichissuitableforconnectingtovibratingandmovingpartsbyformingloopswhichabsorbthevibrationormovement,but,asforflexiblehoses(Para98)itisalwaysnecessarytoconsidersiteconditionswhenapplyingplastictubing.ThespecificationfornylontubingisgiveninBS5409,Part1.Note: To prevent errors during installation and maintenance, all component parts should be clearly identified. The identification should correspond to the data on the circuit diagram.

109 Themachineshouldhaveitsownfilter,pressureregulator,pressuregaugeandlubricatorset,asshownatPartBofFigure3.Withthisarrangement,optimumconditionsfortheoperationoftheparticularmachinecanbesetwithoutaffectinganyotherequipmentconnectedtothesupply.Ifthefilter,pressureregulator,pressuregaugeandlubricatorsetareproperlymaintained(seeparagraphs160to170),wearonsealsinactuatorsandvalveswillbelimitedandthemachineryshouldperformcorrectlyandefficiently.Thelikelihoodofmalfunctions,whichcouldleadtounintendedoperation,willalsobereduced.

Precautions

110 Toalargeextentthedesignfeaturesneededwilldependonhowthemachinewillbeused.However,paragraphs111to141outlinesomebasicrequirementsformachineandcircuitdesign.

111 Allcomponentsusedinthemachinedesign,includingconnectinghoses,shouldbeabletowithstandsafelythemaximumpossibleairmainpressure.Themaximumsafeworkingpressureofthemachineshouldbeclearly,prominentlyandpermanentlymarkedonthemachine.



112 Allcomponentsshouldbeprotectedagainstover-pressurisationbytheprovisionofpressurereliefvalvesunlessthecomponentscanwithstandthecompressor’smaximumpressureandwillnotbesubjectedtounacceptablepressurebuildupduetohighexternalloads.

113 Themachineshouldbedesignedandconstructedsothatanycomponentswhichrequireadjustmentorregularmaintenanceareeasilyandsafelyaccessible.

114 Supplyorcontrolsystemfailureshouldnotcauseahazard.Toensurethatsuchapossibilityisminimised,theeffectsofgravity,impactorvibrationshouldbeconsidered.Forthisreason,valvescontrollingactuatorsshouldbemountedwiththemainspoolhorizontal.Inaddition,anyactuatorsthathavetoadoptaspecificpositionforsafetyifthesupplyorcontrolsystemfails

shouldbecontrolledbyavalvewhichisspringbiased(mono-stable)tothesafeposition.

115 Ifthemachineistobeprovidedwithanemergencycontrolitshould,withoutdelay,stoporsetmovingpartstowhicheverpositionprovidesmaximumsafety.Theemergencycontrolshouldbeofthemushroomheadtype,colouredred,prominentlylocatedandreadilyaccessibletotheoperator.Whereanoperatorhastoworkfrommorethanonepositionitmaybenecessarytoprovideadditionalemergencycontrols.Operationoftheemergencycontrolshouldnotofitselfcreateahazard.

116 Whereairisdischargedtotheatmosphereduringthenormalcourseofoperationofthemachine,andthiscausesworkerstobeexposedtohighlevelsofnoise,somemethodofreducingtheworker’sexposureshouldbeconsidered.Componentsshouldbelocated,orshielded,sothatoperatorsarenotsubjectedtoairblastfromexhaustports.Ifsilencersarefitted,theseshouldbedesignedtocreateminimumbackpressureandshouldbecompatiblewithwaterandanylubricantsused.Alternativelyanexhausthosecanbefittedsothattheairisdischargedwellawayfromworkers,forexampleunderafactoryroof(seeHSEGuidanceNotePM56Noise from pneumatic systems).



Actuators Hazards

117 Wherelinearactuatorsareused,specialattentionshouldbegiventostrokelength,loadingandthemethodsofmountingthecylindertoavoidbucklingofthepistonrodandexcessivesideloadingwhichcouldleadtopistonrodbearingandsealwear.Whereshearforcesonfixingscrewsarelikelytobeexcessive,thecylindermountingshouldalsobekeyedordowelledinposition.Alternatively,fittedboltsmaybeused.

118 Repeatedshockloadsoncylinderendcapscaneventuallycauseeitherthe

cylinderorthepistonrodassemblytofail,whichcouldleadtoseriousinjury.Mostcylindermanufacturerscansupplycylinderswithbuilt-incushioningdesignedtoreducespeedatstrokeextremities,thusbringingthemachinecomponenttoashocklessstop.Equallyhazardousisthepotentialforpistonandrodtoseparate.Cylindermanufacturersshouldensurethatpistonsarepositivelylockedtothepistonrod.


119 Thefunctionoftheactuatordeterminestheprecautionsnecessaryforasafedesign.Ifthepurposeistoimpartmotiontoaloadwhichisotherwisesupported,theproblemwillbedifferentfromthoseforanactuatordesignedtoliftorloweraload.Cylindersdesignedtoclampposeyetanotherproblem.

Precautions

120 Foranyactuatorsimpartingmotion,smoothactionispreferableandcushioningisdesirable.Ifthecylindersaredouble-actingtheremaybeoccasions,egatstart-uporfollowinganemergency,whenthecylinderispre-exhausted,causingtheactuatortoacceleraterapidlywhenairisfirstintroducedtothecylinder.Wherethisislikelytocauseahazardasoftstartarrangementshouldbeintroducedinthesupplylinetothemachine.Thiswill

initiallyrestricttheflowrateuntilacertainpredeterminedpressurehasbeenreached.

121 Linearactuatorswithmagneticpistonsandintegralmountedreedswitchesorproximityswitchesforsignallingcontrolvalvesarenowpopular.Thisislargelyduetothecomparativecheapnessofusingelectricormicro-electroniccontroltogetherwithcostandspacesavingsfromnotneedingtoinstallindependentmechanicallyactuatedtrips.Safeguardingpneumaticallypoweredmachineswherethecontrolcircuitiselectricalrequiresextracautiontoensurethattheriskofinjuryisminimisedifeithertheelectricorpneumaticpowersupplyfails.Reedswitchesmaymalfunctioninareassubjectedtohighvibrationlevelsorelectromagneticfields.

122 Actuatorsdesignedforliftingorsupportingloadsmaycollapsedangerouslyifthesupplyfails.Themachineshouldhavespring-appliedmechanicalscotchestosupporttheloadwhenevermovementisnotrequired.Incertaininstancesmechanicalscotchesmaybeimpracticable.Asasafetybackupanormallyclosed,airtoopen,springreturnvalveinthecylindersupplylinecouldbeused.



123 Supplyfailuretoclampingcylinderscanleadtoahazardbyreleasingthecomponentprematurely.Thiscanbeovercomebyusingsingleactingcylinderswherethereturnspringappliestheclampingforce(seeparagraph127),ortheuseoftwocontrolvalveswilltemporarilykeepthecylinderpressurised(seefigures4and5).Butcareshouldbetakeninusingthisdesignasevenasmallleakcouldaffecttheintegrityofthesystem.

Figure 4 Singlecontrolsysteminterlockingwithpistonarrestandhold(guardopen)

Note:Figures 4 - 19 illustrate principles only, and they are not intended to provide all the

information needed to construct a safe working system.

124 Machinesincorporatingseveralactuatorsmayrequirethemtobesetinacertainpositionbeforethemachineisfirstused,andsubsequently,aftertheemergencycontrolorinterlockingguardshavebeenoperated.Re-positioningmaybepossiblewithoutre-establishingthepneumaticsupply,butthesecaseswillbeintheminority.Inallothercasesre-positioningisbestachievedbyprovidingmanualoverridecontrols.Suchcontrolsshouldbeofthetwohandtypeiedesignedsothatthetwocontrolsareplaced,separatedandprotectedtopreventspanningwithonehandonly,beingoperatedwithonehandandanotherpartofthebody,orbeingreadilybridged.Itshouldnotbepossibletosettheactuatorsinmotionunlessthetwocontrolsareoperatedwithinapproximately0.5secondsofeachother.Movementoftheactuatorsshouldbearrested,orwhereappropriatereturned,immediatelyoneorbothcontrolsarereleased.BSEN574Two Hand Control Devicescoversfunctionalaspectsandprinciplesfordesignofthistypeofcontrol.

Cylinder

Stopvalve

Guard

(a) Interlockingvalves(b) Control

valves

(c) Power control valve(Air operated)



Figure 5 Singlecontrolsysteminterlockingwithpistonarrestandhold(guardclosed)

Cylinder

Stopvalve

Guard

(a) Interlockingvalves(b) Control

valves




Interlocking methods and circuit design General information and advice

125 Themethodusedforinterlockingshouldbecommensuratewiththerisk.Thehighertheriskthehighertheintegrityoftheinterlockingsystemshouldbe.

126 PrinciplesfordesignandselectionofinterlockingdevicesassociatedwithguardsaregiveninEN1088andBS5304.GeneralprinciplesforapplicationaregiveninBSEN983Safety of Machinery-Safety requirements for fluid power systems and their components-Pneumatics.

127 Onpneumaticmachinery,becausethepowermediumiscompressibleandnormallyexhaustedtoatmosphere,thesafetycircuitdesignisnotstraightforwardasforotherpowermedia.However,thebasicaimsforinterlockingremainthesameand,wherepossible,thepowersupplyshouldbeinterruptedbytheguardoperatedinterlockingdeviceandanyresidualsystempressureexhaustedtoatmosphere.Inthisconditionanycylinderswillbepre-exhaustedandalternativearrangementsinthesystemdesignwillbenecessarywhereanycylindersarerequiredtobeunderconstantload(seeparagraph122).Inaddition,particularprecautionsmaybenecessarywhenreinstatingthesupplytopre-exhaustedcylindersifrapidaccelerationisundesirable.Toavoidtheneedtomaintainsupplypressuretocylindersrequiredtobeunderconstantload,suchasthoseoperatingclampsorsupports,alternativefeaturesshouldbeconsidered,suchassingle-actingcylinders,orspringappliedmechanicalscotches.Cylindersfittedwithrodlocks,thelockingactionofwhichistriggeredbylossofairsupply,mayalsobeusedtopreventuncontrolledmovement.

128 Signalairlinesshouldbekepttoaminimumlengthtofacilitaterapidexhaustpressuredecay.Wherethisisnotpracticableandpilotsignalsexhaustingtotheatmosphereretainsufficientpressurelevelstooperatemaincontrolvalves(evenafteraguardhasbeenopened),additionalinterlockingdevicesshouldbeprovidedwhichpreventopeningoftheguarduntilitissafetodoso.When3-positionvalvesareusedinsafetycircuits,wherepracticablethecentrepositionshouldprovideasupply-sealed-onlycondition(outletsvented)becauseanall-ports-sealedcentrepositioncanresultinstoredenergyintheactuator,leadingtounintendedmovementifpipingisdisconnected.

Interlocking systems

Single control system interlocking129 Thebasicelementsofsinglecontrolsysteminterlocking(seeFigures4and5)

are:

(a) aninterlockingvalveorpositionswitchoperatedbytheguard; (b) interposedcontrolvalves,electromechanicalrelaysand/orsolid-state

switchingdevices,ifany;and (c) anairoperated,solenoidoperatedorsolenoidactuatedairoperated

valve,controllingpowertothedrive.



130 Anyoftheseelements,orthepipingorwiringinterconnectingthem,canfailandcausedanger,sotheyshouldbechosentoprovidethemaximumdegreeofreliability.Thegreaterthenumberofdevicesincorporatedinthesystem,theloweritsinherentreliability,sointerposingdevicesshouldbeavoidedifpossible.

Dual control system interlocking

131 Thebasicelementsaresimilartothoseemployedinsinglecontrolsysteminterlocking.Wherethepossibilityofcommonmodefailureneedstobeminimiseddifferentcontrolpowermediashouldbeusedandkeptseparateexceptfornecessaryinterconnectionsforcrossmonitoring(whereprovided),andconnectiontothesupply.

132 Suchsystemscanbeentirelypneumatic(seeFigures15and16),orhybridforexampleonesystem,pneumaticandonesystem,electric(seeFigures17and18).Thislatterarrangementmaybeparticularlyappropriatewherecylinderswithmagneticpistonsandintegralreedswitchesorproximityswitchesareused.Inbothsystemstheoutputofthepowercontrollingdevicesshouldbeconnectedsothateithercanstophazardousmovementofthemachinery,irrespectiveoftheconditionoftheother.Wherethecircuitissuchthatasinglefailureisnotself-revealingegtheactuatorcontinuestooperate,theintegrityofthedualcontrolsystemcanbeimprovedbycrossmonitoring(shownalsoinFigures17and18).

Figure 6 Singlecontrolsysteminterlockingwithpistonarrest(guardopen)

Cylinder

Guard

(a) Interlockingvalves

(b) Controlvalves


Note:Manual reprositioning of the cylinder is possible with this type of control valve.



Figure 7 Singlecontrolsysteminterlockingwithpistonarrestandhold(guardclosed)

Figure 8 Useofanequalisingvalve-controlinterlocking(guardopen)

Cylinder

Guard



(b) Equalisingvalve

Cylinder

Guard


(b) Controlvalves




Figure 9 Useofanequalisingvalve-controlinterlocking(guardclosed)

Figure 10 Useofanequalisingvalve-powerlocking(guardopen)

Cylinder

Guard



(b) Equalisingvalve

Cylinder

Equalising valve(with power interlocking)

Guard

Control valve(Air operated)



Figure 11 Useofanequalisingvalve-powerlocking(guardclosed)

Figure 12 Useofareservoir-powerinterlocking(guardopen)

Cylinder

Equalising valve(with power interlocking)

Control valve(air operated)

Guard

Cylinder Guard

Reservoir

Power control valve(Solenoid operated)

Interposedcontrolvalves Power

interlockingvalves

NoteCylinder returnsto instrokeposition wheneverguard is open



Figure 13 Useofareservoir-powerinterlocking(guardclosed)

Cylinder Guard

Reservoir

Power control valve(Solenoid operated)

Interposedcontrolvalves Power

interlockingvalves



Figure 14 Controlsysteminterlockingfromcomplexsequence

A B

D

C

Guard

TocloseSpring

return

To portsmarked

Sequence

Closed guardA+B+C+ D+

A-C- D-B-Open guard



Figure 15 Dualcontrolsysteminterlockingwithoutcross-monitoring,bothchannelspneumatic

(guardopen)

Figure 16 Dualcontrolsysteminterlockingwithoutcross-monitoring,bothchannelspneumatic

(guardclosed)

Guard openCylinder


(c) Power control valve (Air operated)

(b) Interposed control valves

Guard closedCylinder


(c) Power control valve (Air operated)

(b) Interposed control valves



Figure 17 Dualcontrolinterlocking,onecontrolchannelpneumaticandoneelectric,withelectriccross

monitoring(guardopen)

Figure 18 Dualcontrolinterlocking,onecontrolchannelpneumaticandoneelectric,withelectriccross

monitoring(guardclosed)

Cylinder Guard open

Interlockingswitch

(electric)Interlocking

valve(Pneumatic)

Monitor

Controlvalves

A B

Powercontrol

valve

2nd channelinterposed powercontrol valve

Sol AMonitor C

Cylinder Guard closed

Interlockingswitch

(electric)Interlocking

valve(Pneumatic)

Monitors

Controlvalves

A B

Powercontrol

valve

2nd channelinterposed powercontrol valve

Sol AMonitor C



Figure 19 Guardoperatedpowerinterlockingwithscotchtopreventdrillfallingundergravity.Alsofitted

withguardlocktopreventinadvertentopening

Power interlocking133 Powerinterlockingisachievedbydirectmechanicalactionofavalveinthe

mainairsupplyinserieswiththeactuator.Themechanicalactionmaybedirectfromguardmovement(seeFigures10and11)viaalinkage,byacaptivekeyoratrappedkey.

134 Interlockingbymeansofairisolationandexhaustmaycausedifficultiesonmachinerywhichreliesontheairsupplytokeepheavyarticlessuspendedorcomponentsclampedinposition.Similarly,wherecomplexmachineryisdesignedtoperformaseriesoffunctionsinsequenceautomatically(seeFigure14),airisolationandexhaustinterlockingcouldleadtotheneedforpotentiallydangerous,extensivemanualre-settingofactuatorsandsequencingvalves.Forthesereasons,powersystemmethodsofinterlockingarenotnormallypracticableforcomplexairoperatedmachineryandhencecontrolsysteminterlockingofthepilotsignalshastobeused.

135 Wherepracticable,however,powersysteminterlockingofcomplexsystemsisbetterthansinglecontrolsysteminterlocking,providedthepowerinterlockingvalveandthearrangementsbetweentheguardandvalveareofsimilarorhigherintegritythanthecontrolsysteminterlocking.Inaddition,anymachinerypartswhicharesupportedbycompressedairandwhichwouldfallundergravitywhentheairisisolatedandexhaustedshouldbeautomaticallyscotchedwhiletheguardisopen.

136 SuchprecautionsareshowninFigure19,thelayoutofwhichisinlinewithBSISO1219-2recommendations.HazardsarisefromactuatorsAl,A2,A3andA5,whichneedsafeguarding.Also,A3operatesverticallyandwill

V3

V2

V1

Run

Singlecycle

ClampA1

B11 ClampA2

B22 B21

DrillA3

ScotchA4

B31

DrillA5

B52 B51

FeedA61

A62B62 B61

C6 C7C5C1 C2 C3

B72

B62B52 B11 B21 B31 B22

Guardlock A7

B72

Interlockingvalve

Guard

Toclose

To lock

A7

B61 B51

Single cycle sequence

Close guardScotch withdraws (A4 - )Operate V2Guard locks(A7+)A1+A2+A3+A5+A2 - A3 - A5.

Guard unlocks (A7 -)A61 & A62 -Machine stopsOpen guardScotch engages (A4+)



fallundergravitywhenairsupply,throughtheguardoperatedinterlockingvalve,isexhausted.Thecircuithasthusbeenarrangedsothat,withtheguardopen,A3isscotchedusingasingleactingcylinder.Oncetheguardisclosedthescotchwithdrawsandtheguardislockedsothatthesequencecannotbebrokenbyinadvertentlyopeningtheguard.ThecompletesinglecyclesequenceisindicatedinFigure19,whereitcanbeseenthattheguardunlockstoallowmanualfeedingifnecessary.Continuouscyclingcanbeeffectedbyoperatingthevalvelabelled‘run’.If,duringuse,amalfunctionoccursrequiringtheguardtobeopened,thiscanonlybeachievedbyshuttingthestopvalveinthemainairsupplyline.

137 Alltheseproblemshighlighttheneedforthemachinedesignertoconsidercarefullytheoverallsystemdesigntoensurethattheinterlockingarrangementsareeffective.Althoughinmanycasesinterlockingthepilotsignalsratherthanthepowersupplymaybetheonlypracticalsolution(seeFigure14),thisshouldbealastresortonly.

Circuit design

Piston arrest138 Whereitisnecessaryjusttoarrestthemovementofapistonwhenaguard

isopen,thiscanbeachievedbyusingeithertwothree-port,two-positionvalves(seeFigures6and7)oranequalisingvalve(seeFigures8to11).Ifanequalisingvalveisusedthepistonmaynotstopimmediately,butitwillseekanequilibriumpositionwherebyforcesonbothsidesofthepistonareequal.ThecircuitinFigure6willallowmanualrepositioningofthepistonwithoutdisconnectingpipes(dependingonthefrictioninthesystem).Neitherofthesetechniquesissuitableforclampingorsupportingapplications.

Piston arrest and hold139 Where,forsafetyreasons,thepistonmustbearrestedandheldinposition,

twotwo-portcontrolvalvescanbeused(seeFigures4and5).Thepistonwillseekanequilibriumpositionbeforecomingtorest.However,ahazardcouldariseifconnectionstothecylinderarebrokentosubsequentlyoverridethelockedposition.Airexhaustingthroughthebrokenconnectioncouldallowairunderpressureontheoppositesideofthepistontoexpand,therebycausingmovementwhichcouldleadtoinjury.

Overriding locked position140 Wherethelockedconditionmustbeoverriddenwhiletheguardisopen,a

two-portstopvalvecanbeaddedtothecircuit(seeFigures4and5).Thiswouldnormallyhaveblockedportsbutbydepressingthestopvalvebothsidesofthecylinderareopenedtoatmosphere,enablingthepistontobemovedmanually.

Predetermined position141 Itmaybenecessarytoensurethatpistonsadoptapredeterminedsafe

positionintheeventofpowersupplyfailing.Againtheuseofsingleactingcylindersmaybepossiblebutanalternativeistouseareservoirandnonreturnvalvearrangement(seeFigures12and13).Itisimportantto

ensurethatwherereservoirsareusedtheyareofsufficientcapacitytoensurethatthepistondoesnotstallinanunsafeposition.



Inspection and maintenance Statutory requirements

142 Therearespecificstatutoryrequirementsfortheexaminationandmaintenanceofpressuresystemsincludingairreceivers(seeparagraph30).Inadditiontothespecificrequirements,generalrequirementsaresetoutinSection2(2)(a)oftheHSWActandPUWER:employersmustprovideandmaintainplantandsystemsofworkthatare,sofarasisreasonablypracticable,safeandwithoutriskstohealth.Thefollowingadviceisaimedatassistingemployerstocarryoutthisduty.

Hazards

143 Faultfindingonpneumaticmachinerycanbehazardousifitisnotproperlyplanned.Themachinedesignshouldincorporatemeansofminimisingtheneedfortrialanderrormethodsoflocatingafault.Furtherassistancecanbegiventofaultfindingbyincorporatingdiagnostictechniqueswhichindicatetheareaofafault(seealsoparagraph100).


144 Theefficientsaferunningofacompressedairsystemreliesoncleanliness,filtration,coolingandlubrication.Thebestwayofachievingthesefourconditionsistooperatetheplantinaccordancewiththeoperator’smanualandtodrawupandfollowawrittenscheduleofmaintenanceworkwhichcanberevisedinthelightofexperience.Thisisaformofsafesystemofwork.Thewrittenscheduleshouldidentifyareasforattention,howoftenattentionshouldbegivenandtheresponsibilitiesofthosewhocarryoutandsupervisethework(seeparagraphs146and147).

145 Thefrequencyofinspectiondependsverylargelyonthecircumstancesandenvironmentinwhichtheplantisused.ThefrequencystatedinthisBookletshouldthereforebetakenasaguideonlyandadjustedtosuitparticularinstallationsinthelightofoperationalexperience.

Maintenance of compressors and ancillary plant

Supervision and procedures146 Smallcompressorunitsareeasilyoverlooked,especiallyifsitedinaseparate

enclosureoutsidetheworkingarea.Particularcareisneededtoseethatregularmaintenance,inspectionandtestingiscarriedout.Proceduresshouldbelaiddownandrecordskept.

147 Theusershouldnominatearesponsiblepersontosupervisetheproperoperationandmaintenanceofthecompressorplantinlinewiththemanufacturer’sinstructions.

148 Thispersonshouldregularlycheckthatallinstructionsregardingoperationandmaintenanceareproperlyfollowedandthatthecompressor,itsaccessoriesandsafetydevicesarekeptingoodworkingorder.Theresponsiblepersonshouldalsomakesurethatmaintenanceworkiscarriedoutonlybyadequatelytrainedstaff.



149 Althoughtherearestatutoryrequirementscoveringsomeaspectsofmaintenance,thefollowingadditionalmaintenanceproceduresarerecommendedtominimisethelikelihoodofhazardsoccurring.

Daily150 Thecompressingplantshouldbekeptascleanandfreefromoildepositsas

possible.

151 Adailyroutinecheckshouldbecarriedoutonreciprocatingcompressors.Thecheckshould,whereapplicable,includethefollowing:

(a) thecoolingwatershouldbevisuallycheckedtomakesurethatitis circulatingproperlybyobservingtheflowoutletorflowindicator;

(b) theleveloftheoilinthecrankchambershouldbecheckedusinga dipstick,levelgaugeorotherdevice.Anyexcessiveusageoflubricating oilshouldbeinvestigated;

(c) theoilpressureshouldbechecked; (d) theoilfeedtothecylindersshouldbecheckedtomakesurethatit

isadequatebutnotexcessive.Oilconsumptionshouldberecorded, asexcessiveconsumptioncanoftenleadtoexplosionsdownstreamof thecompressor;

(e) theoutletairpressureandtemperatureshouldbechecked; (f) thecompressorperformanceshouldbecheckedegbylisteningforany

unusualnoisesduringrunning; (g) anydefectsfoundshouldberectifiedandarecordkept;and (h) attheendofeachdayanyaccumulationofoilandwatershouldbe

drainedfromtheairreceiver,theintercooler,theaftercoolerandmain supplypipes.

Checks mainly directed to reciprocating compressors

Weekly152 Eachweekthesafetyvalves(wheredesignallows)shouldbecheckedby

easingthembyhand.

600 hours153 Aftereach600hoursofrunning:

(a) thequalityofoilinthecrankcaseshouldbecheckedand,accordingto themanufacturer’srecommendations,replacedifnecessary;and

(b) theconditionoftheinletairfiltersshouldbecheckedandthoroughly cleanedorreplaced.Theintervalbetweensuccessivereplacements willbedeterminedbylocalcircumstancesbutis,toacertainextent, controlledbythecapacityofthefilterandthecleanlinessofthe atmosphereinthevicinity.Whereoilwettedviscousfiltersareused, spareunitsshouldbeprovidedandexcessoilshouldbedrained fromthefilterunitsforatleastfourtoeighthoursbeforetheunitsare replaced,exceptwherethemanufactureradvisesotherwise.

Six-monthly154 Whereoilcokedepositsareliabletooccur,theexplosionriskcanbereduced

bycarryingoutsix-monthlyinspectionsofthedeliveryportsandpipeworkandcleaningasrequired.Theperiodbetweeninspectionscanbemodifiedinthelightofexperiencegainedfromoperatingaparticularinstallation.



2000 hrs or annually155 Aftereach2000hoursofrunningorannually(whicheveristhesooner): (a) inthecaseofoillubricatedcompressors,thedeliveryvalves,portsand

allthepipework,vesselsandfittingsbetweenthedeliveryportandthat pointinthesystem

atwhichtheairtemperaturecanbeconfidentlyexpectedtobebelow 80°C,shouldbeinspected.Anycarbonaceousdepositshouldbe effectivelyremoved;

(b) fusiblepelletsorcompleteplugsshouldbereplaced; (c) theconditionofprotectivedevicesshouldbecheckedandtestedto

determinethattheyoperatecorrectly; (d) theintercoolerandaftercoolersectionsshouldbecleaned; (e) theradiatorshouldbedrainedandwashedout; (f) theoutputcontrolgearshouldbecleanedandinspected;and (g) theairreceivershouldbethoroughlycleanedandexaminedinternally.

Precautions

156 Allmaintenancework,otherthanroutinecheckstofiltersdesignedforcleaningin-service,shouldbeundertakenonlywhenthecompressorhasbeenstopped,disconnectedandlockedofffromthepowersupplyandallinternalpressuredissipated.Otherprecautionsmayalsobenecessary:forexample,thecompressormayhavetobescotchedtopreventmovementofthemechanism.

157 Undernocircumstancesshouldflammableliquidsbyusedforcleaning.Appropriatesafetyprecautionsshouldbetakenagainstanytoxicvapoursliberatedduringusageofanycleaningordegreasingliquids.

158 Anopenflameshouldneverbeusedforinspectingtheinteriorofacompressor,pressurevesselorpipework.

Maintenance of air powered equipment

159 Dirtyand‘wet’airandworncomponentsareamongthemostcommoncausesofhazardsassociatedwithairpoweredequipment.

Supervision and procedures160 Theusershouldnominatearesponsiblepersontosupervisetheregular

inspectionandmaintenanceoftheequipment.Wheretheequipmentisextensive,someformofwrittensystemofplannedmaintenanceshouldbeusedandrecordsoftests,repairsandmodificationskept.

161 Inadditiontoanymaintenancerequiredbystatutoryrequirements,thefollowingmaintenanceproceduresarerecommended.

Daily162 Thesystemshouldbecheckedforleaksandrepairscarriedoutas

necessary.

163 Attheendofeachdayanyaccumulationofwatershouldbedrainedfromthedrainpoints.Thedrainvalvesshouldbeinspectedtomakesurethattheyarenotchokedwithsediment.



Weekly164 Attheendofeachweek,airlinelubricatorsshouldbetoppedupas

necessarywiththecorrectgradeofoilandcheckedtoensurethattheyareprovidingadequatebutnotexcessivelubrication.Filtersshouldbecheckedandthosethatarecloggedorcausingunacceptableflowrestrictionsshouldbereplaced.

165 Similarly,onmachineswhichrequirepressureregulationbelowmainspressure,thepressureregulatorshouldbecheckedtomakesurethatithasnotbeentamperedwithandthatthecorrectpressureismaintained.

Monthly166 Allhoseswhicharesubjecttoflexingand/ormechanicaldamageshouldbe

inspectedforsignsofcrackingordeteriorationandreplacedasnecessary.Particularattentionshouldbepaidtoareasadjacenttocouplings.

Three monthly167 Everythreemonthsmachineswithinterlockingguardsshouldbechecked

tomakesurethatallinterlockingvalvesarefirmlysecuredandoperatedpositivelybytheircams.Checkthatwearinanylinkagesorvalveoperatingmechanismsisnotsoexcessivethatthevalveisindangerofmalfunctioning.

Six monthly168 Everysixmonthsallstopvalvesshouldbechecked.Checkthataccessto

thevalvehasbeenmaintained,thatthehandleisinposition,thatitwillshutofftheairsupplyandthatitwillopenfullyandoperatefreely.

Precautions

169 Beforeanypressurisedcomponentsaredismantledtheyshouldbeeffectivelyisolatedfromallpressuresourcesandcompletelyventedtoatmosphere.Precautionsshouldalsobetakentoguardagainstthepossibilityofinjurythroughsuddenreleaseoftrappedsprings.

170 Whencomponents,especiallyvalves,arefoundtobewornandservicekitsofsealsareusedtorebuildthem,careshouldbetakentocheckthoroughlythefunctionoftherebuiltvalvebeforeplacingitintheequipment.Forconvenience,manufacturersofservicekitsoftenincludeenoughsealstoservicearangeorfamilyofvalves,althoughnotallthesealsinthekitarerequiredforeachvalve.Incorrectsealreplacementcancompletelyalterthevalve’sfunctionandifreplacedintheequipmentcouldpresentaserioushazard.Manufacturersshouldsupplyclearinstructionsonhowtousesuchservicekitsproperlyandsupervisorsshouldensurethatthisinformationispassedontothepersoncarryingoutthemaintenance.



Training Statutory requirements

171 Section2(2)(c)oftheHSWActandManagement Regulations and Regulations 8 & 9 of the Provision and Use of Work Equipment Regulations (PUWER)requireseveryemployertoprovidesuchinformation,instruction,trainingandsupervisionasisnecessarytoensure,sofarasisreasonablypracticable,thehealthandsafetyatworkoftheiremployees.Sections7and8oftheHSWActplaceresponsibilitiesonemployeestotakereasonablecaretoco-operatewithemployersandnottointerferewithormisuseanythingprovidedfortheirsafety.

Hazards

172 Allthosewho,inthecourseoftheirwork,needtousecompressedairmustbeproperlytrained.Manyaccidentswouldbeavoidedifadequatetrainingwasprovided.Itisprobablybecausecompressedairsuppliesaresocommonplace,beingfoundatmostgarageforecourts,forexample,thatemployersfalselybelievethattrainingintheiruseisunnecessary.

Precautions

173 Supervisorsandworkersincludingmaintenancepersonnelmustbegivenpropertraininginsafeworkingpractices.Thetrainingshouldstressthehazardsassociatedwithcompressedair(seeparagraph2)andshouldhighlightthefollowingpoints:

(a) compressedairshouldneverbeusedforcleaningclothing;vacuum cleanerswithbrushtypeheadsarepermissible.Forothercleaning operationsspecialnozzlesdesignedtoprovidelowpressure,high volumemaybeusedwithcare(seeparagraphs96band104);

(b) horseplaywithcompressedairisextremelydangerousandisstrictly forbidden.Employersshouldnotethatyoungpeopleinparticularmay requirespecialsupervisiontomakesurethattheybehaveproperly;

(c) whenusingcompressedairtoolstheexhaustingairshouldbedirected awayfromthebody;

(d) compressedairshouldneverbeusednearanakedflame; (e) anydefectsinequipmentshouldbereportedatonce;and (f) safetyandmonitoringdevicesshouldneverbemisusedorabused.

Further information

ThefollowingfivepublicationsareproducedbytheEuropeanCommitteeonManufacturersofCompressors,VacuumPumpsandPneumaticTools(PNEUROP):

Safety recommendations for the use and operation of portable air compressors London

Safety recommendations for the use and operation of stationary air compressors London

Pneumatic tools - safety in operationLondon



Safety recommendations for the use and operation of portable pneumatic tools London

Recommendations for the proper use of hand held and hand operated pneumatic toolsLondon1986

BritishCompressedAirSociety(BCAS)produces:Guide to the selection and the installation of compressed air servicesLondon,4theditionISBN090560802XandA guide to compressor noise reductionLondon,underrevision

EuropeanOilHydraulicandPneumaticsCommittee(CETOP)Hydraulic and pneumatic systems circuit diagramsLondon(PNEUROP,BCASandCETOPpublicationsareavailablefromtheBritishCompressedAirSociety,33/34DevonshireStreet,LONDONW1N1RF)

RoyalSocietyforthePreventionofAccidents(ROSPA)Beware compressed airBirmingham,(IS303)(availablefrom:ROSPA,CannonHouse,ThePriory,Queensway,BIRMINGHAMB46BF)

BritishAggregateConstructionMaterialsIndustryCompressed Air SafetyLondon(availablefrom:BritishAggregateConstructionMaterialsIndustry,25LowerBelgraveStreet,LONDONSW1OLS)

BritishCoalReciprocalaircompressors(surfaceandunderground)(NCBcodesandrulesseries)Doncaster(availablefrom:BritishCoal,HQMiningDepartment,TheLodge,SouthParade,DoncasterDN12DX)

British and European Standards

BS1041: Temperature measurementBS1041: Part2Expansion thermometers(insevenparts)BS1041 Section2.1:1992Guide to selection and use of liquid-in-glass

thermometersBS1041: Part3:1969Industrial resistance thermometryBS1041: Part4:1992ThermocouplesBS1041: Part5:1992Radiation pyrometersBS1041: Part7:1988Guide to selection and use of temperatureltime

indicatorsBS1123: Part1:1987Safety valves, gauges, gas and fusible plugs for

compressed air or inert installations: code of practice for installationsBS1710: 1991Specification for identification of pipelines and services BS1704: 1992Specification for solid stem general purpose thermometersBS1780: 1992Specification for bourdon tube pressure and vacuum gaugesBS2917-1 1993/ ISO 1219-1 Specification for graphic symbols used on

diagrams for fluid power systems and componentsBS3974: Specification for pipe supports(inthreeparts)BS3974: Part1:1974Pipe hangers, slider and roller type supportsBS3974: Part2:1978Pipe clamps, cages, cantilevers, and attachments to

beamsBS3974: Part3:1980Large bore, high temperature marine and other

applicationsBSEN286 Part1:1991Specification for simple unfired pressure vessels

designed to contain air or nitrogenBSEN292 Part1:1991Safety of machinery: Basic concepts, general principles

for design. Basic terminology, methodology Part2:Technical principles of specifications



BSEN983 1996Safety of Machinery- Safety requirements for fluid power systems and their components-Pneumatics

BSEN1012-11997Compressors and vacuum pumps-Safety requirements Part 1 Compressors

BSEN1012-21997Compressors and vacuum pumps-Safety requirements Part 2 Vacuum pumps

BSEN837 Part1Bourdon tube pressure gauges-Dimensions, metrology,requirements and testing

Part2Selection and installation recommendations for pressure gauges

BSISO1219-1995Fluid power systems and components. Graphic Symbols and circuit diagrams

BS4575: 1987Part2:Code of practice for pneumatic equipment and systems 1988Part3:Fluid Power Transmission and Control SystemsBS4862: 1983Mounting dimensions of single rod double 10 bar pneumatic

cylindersBS4862: Part1:1983Specification for cylinders up to 25 ml boreBS5118: 1980Specification for general purpose rubber hoses for compressed

airBS5169: 1992Specification for fusion welded steel air receiversBS5304: 1988Code of practice. Safety of machineryBS5409: Specification for nylon tubing BS5409: Part1:1976Fully plasticized nylon tubing types 11&12 for use

primarily in pneumatic installationsBS5500: 1994Specification for unfired fusion welded pressure vesselsBS5791: Glossary of terms for compressors, pneumatic tools and machinesBS5791: Part11990GeneralBS5791: Part21990CompressorsBS5791: Part31990Pneumatic tools and machinesBS6005: 1997Specification for moulded transparent polycarbonate bowls used in compressed air filters and lubricatorsBS6066: 1986Specification for thermoplastics hoses for compressed airBS6244: 1982Code of practice for stationary air compressorsBS6754: 1986Specifications and testing of compressed air dryersBS6759: Safety valvesBS6759: Part1:1984Specification for safety valves for steam and hot waterBS6759: Part2:1984Specification for safety valves for compressed air or inert gasesBS7226: 1989Methods of test for performance of inlet air cleaning equipment for internal combustion engines and compressors

BritishStandardsareavailablefrom:BSISalesandCustomerServices389ChiswickHighRoadChiswickLondonW44ACTel01819967000Fax01819967001

Health & Safety Executive publications

Pneumatic nailing and stapling guns 1979,(Guidancenote,plantandmachinery/PM17),ISBN0118831925

Noise from pneumatic systems1985,(Guidancenote,plantandmachinery/PM56),ISBN0118835297



Safety in pressure testing1992(Guidancenote,generalseries/GS4)ISBN0717608115

Safety of pressure systems. Pressure Systems and Transportable Gas Containers Regulations 1989 Approved Code of Practice COP371990ISBN011885514X

A guide to the Pressure Systems and Transportable Gas Containers Regulations 1989 ISBN0118855166

Legal requirements

SupplyofMachinery(Safety)Regulations1992(asamended1994)ISBNS0-11-025719-7&0-11-045063-9

ProvisionandUseofWorkEquipmentRegulations1992(asamended1997)

ManagementofHealthandSafetyatWorkRegulations1992

MinesandQuarriesAct1954,HMSO,ISBN0108503895

PersonalProtectiveEquipmentRegulations1992

HealthandSafetyatWorketcAct1974,chapter37,HMSO,ISBN0105437743

ElectricityatWorkRegulations1989

ThePressureSystemsandTransportableGasContainersRegulations1989(SI1989No2169),HMSO,ISBN0110981693

The future availability and accuracy of the references listed in this publication cannot be guaranteed.

Further informationForinformationabouthealthandsafetyringHSE’sInfolineTel:08453450055Fax:08454089566Textphone:08454089577e-mail:[email protected],CaerphillyBusinessPark,CaerphillyCF833GG.

HSEpricedandfreepublicationscanbeviewedonlineororderedfromwww.hse.gov.ukorcontactHSEBooks,POBox1999,Sudbury,SuffolkCO102WATel:01787881165Fax:01787313995.HSEpricedpublicationsarealsoavailablefrombookshops.

BritishStandardscanbeobtainedinPDForhardcopyformatsfromtheBSIonlineshop:www.bsigroup.com/ShoporbycontactingBSICustomerServicesforhardcopiesonlyTel:02089969001e-mail:[email protected].

TheStationeryOfficepublicationsareavailablefromTheStationeryOffice,POBox29,NorwichNR31GNTel:08706005522Fax:08706005533e-mail:[email protected]:www.tso.co.uk(Theyarealsoavailablefrombookshops.)StatutoryInstrumentscanbeviewedfreeofchargeatwww.opsi.gov.uk.

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