hsg39-Compressed air safety.pdf

7/27/2019 hsg39-Compressed air safety.pdf

1/50 Page1of50

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 HSEs current printed version.

Youcanbuythebookatwww.hsebooks.co.ukandmostgoodbookshops.

ISBN 978 0 7176 1531 5

Price 7.50

Thisbookaimstopromotethesafeuseofcompressedairanddescribesthemany

waysinwhichcompressedaircanbedangerousaswellashowtominimisethe

riskofsuchdangersoccurring.

Itisaimedatdesigners,manufacturers,installers,usersandothersconcernedwith

orresponsibleforhealthandsafetyatwork.

HSE Books


2/50Page2of50

Health and Safety

Executive

Crown copyright 1998

Firstpublished1990

ISBN9780717615315

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.


3/50Compressedairsafety Page3of50

Health and Safety

Executive

ContentsINTRODUCTION 5

COMPRESSOR PLANT 6

Groups of compressors 6

Hazards 6

General information and advice 6

Precautions 7

Safetyvalves 7

Pressureindication 7

Thermalprotection 7

Coolantprotection 8

Lubricantprotection 8

Explosionprotection 8

Airinlet/outletmonitoring 8 Otherinstrumentation 8

Airinlet/outletcontrol 9

AIR RECEIVERS 11

Statutory requirements 11

Hazards 12


Precautions 12

COOLERS 13

Hazards 13

General information and advice 13Precautions 13

AIR DRYERS 14

Hazards 14


Refrigerant 14

Dessicant 14

Precautions 14

INSTALLATION OF COMPRESSORS 16

Precautions 16

Smallcompressors 16

Mediumandlargecompressors 16Noise 16

MAIN LINE SYSTEMS 18

Hazards 18


Precautions 18

Pipe-runs 18

Filters,traps,separatorsandlubricators 21

Pressureregulators 22

PORTABLE PNEUMATIC EQUIPMENT 23

Statutory requirements 23Hazards 23


Precautions 24

Flexiblehoses 24



Health and Safety

Executive

Blowguns 24

Portabletools 25

PNEUMATIC POWERED MACHINERY 26

Hazards 26


Precautions 26

ACTUATORS 28

Hazards 28


Precautions 28

INTERLOCKING METHODS AND CIRCUIT DESIGN 31


Interlocking systems 31

Singlecontrolsysteminterlocking 31Dual control system interlocking 32

Power interlocking 40

Circuit design 41

Pistonarrest 41

Pistonarrestandhold 41

Overridinglockedposition 41

Predeterminedposition 41

INSPECTION AND MAINTENANCE 42


Hazards 42

General information and advice 42Maintenance of compressors and ancillary plant 42

Supervisionandprocedures 42

Daily 43

Checks mainly directed to reciprocating compressors 43

Weekly 43

600hours 43

Six-monthly 43

2000hrsorannually 44

Precautions 44

Maintenance of air powered equipment 44

Supervisionandprocedures 44

Daily 44

Weekly 45Monthly 45

Threemonthly 45

Sixmonthly 45

Precautions 45

TRAINING 46


Hazards 46

Precautions 46

Further information 46

British standards 47

Health & Safety Executive publications 48Legal requirements 49

FURTHER INFORMATION 50



Health and Safety

Executive

Introduction1 Thisguidancebookletaimstopromotethesafeuseofcompressedair

bygivingadvicetodesigners,manufacturers,installers,usersandothers

concernedwithorresponsibleforhealthandsafetyatwork.Itwasoriginally

producedin1990duringarapidlychangingsituationinEuropearisingfrom

thepreparationforthesinglemarketandwasfurtherrevisedunderthe

ReviewofRegulationsandGuidanceundertakenbytheHealthandSafety

Executive(HSE)in1996.

2 Therearemanywaysinwhichcompressedaircanbedangerous,for

example:

(a) itcanenterbodyorificessuchasthemouth,earsandanus,causing

severeandoftenfatalinjuries;

(b) athighpressureitcanpenetratetheskin; (c) particlesoroilcarriedinanairjetcandamagetheeyes;

(d) oil-cokedepositsinasystemcanspontaneouslyigniteandcausean

explosion;

(e) vesselscontainingcompressedair,evenatcomparativelylowpressure,

canexplodeviolentlyoncetheirintegrityislost;and

(f) dirtyorwetaircanleadtocorrosionandblockedvalveswhichmay

makethesystemunsafe.

3 Thisbookletexplainshowtominimisethelikelihoodofsuchproblems,

butitdoesnotgivespecificadviceonairseparationplant,thepneumatic

transportationofmaterialsthroughpipelinesorthesupplyofrespirableair.

Referenceinthisguidancebooklettoaparticularstandarddoesnotprecludeusinganequallyeffectivealternativestandard.



Health and Safety

Executive

Compressor plant

Groups of compressors

4 Forthepurposesofthisbookletcompressorsaredividedintothreegroups:

small,mediumandlarge.

5 Asmallcompressordeliversupto40litrespersecondoffreeairand/orhas

apowerinputofnomorethan15kW.Suchcompressorsmaybemobileor

fixedandmaybesuppliedaspackagedunits.Atypicalonewouldcomprise

areciprocatingcompressordrivenbyanelectricmotorontopoforalongside

anairreceiver.

6 Amediumcompressordeliversbetween40and300litrespersecondoffree

airand/orhasapowerinputofbetween15and100kW.

7 Alargecompressordeliversmorethan300litrespersecondoffreeairand/

orhasapowerinputofmorethan100kW.

8 Manymediumandlargecompressorsaresuppliedaspackagedunits.A

typicalonewouldcompriseacompressor,airintakefilter,motorandair

cooler,allonacommonbedframewithfactory-connectedpipingand

factory-installedelectricalcontrolsandwiring.Itcouldbeenclosedinasheet

metalhousingtreatedwithsoundproofingmaterialtoreducenoiselevels.

9 Usingapackagedunithasanumberofadvantages;itsimplifiesfoundation

work,reducesinstallationtimeandprovidesaproperlyengineeredand

adequatelyguardedassemblyofcomponentsinacompactspace.However,

theuserisstillresponsibleforsitingthesystemsothatincomingairisasdry

andfreefromcontaminantsassiteconditionsallow.Boththeairenteringthe

compressorplantandthedeliveredairmustbeasdry,cleanandcoolas

possible.Adviceonsitingisgiveninparagraphs60to67.

Hazards

10 Themajorhazardassociatedwithcompressorsisoverpressurisation,which

mayarisefrom:

(a) ablockedoutletorsomeotherrestrictiontoflow; (b) failureofautomaticcontrolscombinedwithlowairconsumption;

(c) compressormalfunction,egoverspeeding;

(d) anexternalfirenearthepressuresystem;and

(e) overheatingandthebuild-upofcarbonaceousdeposits,bothofwhich

canleadtofiresorexplosions.Althoughtheyarerare,firesand

explosionscanalsooccurasaresultofoiloroilvapourbeingignitedin

thepressuresystem.

11 Dirtyorwetaircancauseasystemtofailegbycausingfineparticlesof

debristoagglomerate,blockingsafetyrelatedvalves.

General information and advice

12 Standardsforthesafedesign,construction,installationandoperationof

manytypesofstationarycompressoraresetoutinBS6244Code of practice



Health and Safety

Executive

for stationary air compressors.Itspecifiesrequirementstohelpminimise

compressoraccidentsanddefinesgeneralsafetypractices.BSEN1012

Parts1&2coverCompressors and vacuum pump safety requirements.

NOTE: It is important that records are amended following

modifications to plant and pipework.

Precautions

13 TransmissionmachineryegVbelts,pulleysandotherdangerousparts,

shouldbeguardedtopreventaccess,seeBS5304Code of Practice for

Safety of machinery.

Safety valves

14 Onallmediumorlargemulti-stagepositivedisplacementcompressorsa

safetyvalveshouldbefittedbetweeneachstageand,whereappropriate,in

theinteroraftercoolercircuit.

15 Whereanisolatingvalveisinstalledinthedischargepipeworkbetweenthe

compressorandreceiver,thepipeworkonthecompressorsideofthevalve

shouldbeprotectedbyasuitablesafetyvalvethatcomplieswithBS6759,

Part2Specification for safety valves for compressed air or inert gasesand

isinstalledtoBS6244,clause21,unlessthesystemhasbeendesigned

towithstandthemaximumpressurethatcanbegenerated.(Thisvalveisin

additiontotheairreceiversafetyvalve.)Onsmallfixedandsmallandmedium

transportablecompressorunits,wheretheoutletofthecompressorisdirectly

connectedwithoutshut-offornon-returnvalvestoanairreceivertowhichno

othersourceofpressureisattached,onesafetyvalveontheairreceiveris

sufficient.

Pressure indication

16 Anaccuratelycalibratedairpressuregaugewithareadilyvisibleappropriate

scale-readingshouldbeprovidedaftereachstageofcompression.However,

onsmalltwo-stagecompressorsthisisnotrequiredafterthefirststage

ofcompression,butasuitabletappingtoenableatestdevicetobefitted

shouldbeprovided.GaugesshouldbeconstructedtocomplywithBSEN

837-1Part1-Bourdon tube pressure gauges- Dimensions, metrology,

requirements and testing andinstalledtocomplywithBSEN837-1Part2

Selection and installation recommendations for pressure gauges.

17 Onmediumandlargereciprocatingcompressorswithforcedfeedlubrication

systemsitisimportantthatagaugeisprovidedintheappropriatepositiontoindicateoilpressure.

Thermal protection

18 Tominimisetheriskofoverheating,largecompressorsshouldbeprovided

withasuitablethermalprotectivedeviceasnearaspracticabletothelast

stagedischargevalveor,wherethereismorethanonevalve,atacommon

pointofdischargewhichwouldautomaticallyshutdownthecompressor

whenapredeterminedtemperatureisexceeded.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-stagecompressorsathermalprotectivedeviceshouldalso

beprovidedasnearaspossibletothefirst-stagedischargevalve.Large

compressorswiththreeormorestageswouldrequireaseparatedevicefor

eachstage.



Health and Safety

Executive

20 Formediumandlargeair-cooledcompressorsprotectivedevicesshouldbe

providedtomonitorgeneralcompressoroverheatingwhichmaybecaused

bycooling-fanfailureorthefoulingofcoolingsurfaces.

21 Oil-floodedrotarycompressorsshouldhaveanautomaticshut-downdevice

topreventthetemperatureofthecompressedairfromexceedingasafelimit.

Coolant protection

22 Ifthecompressoriswatercooled,athermostatshouldbeprovidedtothe

coolingwateroutletorwaterreturntotheradiatorheadertanktoshutdown

thecompressorwhenthewatertemperatureexceedsthemanufacturers

recommendedmaximum.Wherethethermostatdevicedoesnotgiveno

waterornoflowprotection,awaterflowdetectiondeviceshouldalsobe

provided.Sufficientgoodqualitycoolingwaterisrequiredtocoolallparts

ofthesystemandinhibitblockagesandcorrosion.Thesupplymayrequire

protectionagainstfreezinginlowtemperatures.

Lubricant protection

23 Onmediumandlargecompressorsapressure-sensingdeviceshouldbe

providedtoshutdownthecompressorandactivatevisibleandaudible

alarmsifthelubricatingoilpressuredropsbelowthemanufacturers

recommendedminimum.Gravity-feedlubricationsystemsshouldbefitted

withalevelsensingdevice.Athermalsensingdeviceshouldbefittedtoset

offanalarmandshutdownthecompressoriftheoilinthecrankcase,sump

orscavengesystemsexceedsthetemperaturespecifiedbythelubricant

manufacturer.Therecanbesafetyadvantagestousingsyntheticester-based

oilsforlubricatingcompressors.

Explosion protection24 Ifcomponentsrunhot,oroilcokedepositsspontaneouslyignite,theremay

beanexplosion.BS6244describesthechemistryofsuchconditionsand

explainshowoilcokedepositscanbeprevented.Toreducetheexplosion

riskonmediumandlargecompressors,afusibleplugcanbefittedonthe

undersideofthepipebetweenthecompressorandthereceiverascloseasis

practicabletothecompressor.Whenorderingsuchaplug,userswillneedto

providethefollowinginformationforthemanufacturer:

(a) maximumdesignworkingpressure;

(b) makerandgrade,orclosedflashpointoftheoilusedforcylinder

lubrication;

(c) maximumdesignoutlettemperatureofair;and

(d) boreofoutletpipefromcompressor.

25 Fusibleplugsaregenerallyavailableforpressureupto340bar(5000psi).

Asanadditionalprecautionregularinspectionsofthecompressorshouldbe

carriedout(seeparagraphs142to170).

Air inlet/outlet monitoring

26 Awatermanometerorotherpressure-indicatingdeviceshouldbefittedto

eachinletairfilteronlargecompressors.Thedevicemeasuresthepressure

dropacrossthefilter,indicatinghowcleanitis.Itisrecommended,whereit

isreasonablypracticabletodoso,thatsuchdevicesbefittedtosmalland

mediumcompressors.

Other instrumentation

27 Onmediumandlargecompressorsconsiderationshouldbegiventofitting

temperaturereadingorrecordinginstrumentstoindicate:



Health and Safety

Executive

(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 control

28 Theinletvalvecaneitherbedesignedsothatitcannotbeusedinapartially

openposition,orbefittedwithvisibleandaudiblewarningsthatindicate

whetherthevalveisfullyopenorclosedduringplantoperation.Thevalve

operationisnormallyautomaticexceptwhenrequiredforstartingupthe

compressor.Oil-floodedrotarycompressorshavebuilt-inself-regulatinginlet

throttles.Constantspeedcompressorsshouldbeprovidedwithsuitable

controlgearsothattheamountofairdeliveredcanbecontrolledtosuit

demand.

29 Figure1showsanillustrationofalargecompressorinstallationandthe

positionsatwhichsafeguardsarerequiredorrecommended.Itisunlikelythat

anyinstallationwillrequireallthesafeguardsindicated.Thefinalrequirement

willdependonrelevantstatutoryrequirements,thedegreeofsupervisionthe

installationwillreceiveandthelocalenvironment.



Health and Safety

Executive

Figure 1 Illustrationofalargecompressorinstallationshowingthepositionatwhichsafeguardsare

requiredorrecommended

Thermal protective device to

monitor air-cooled

compressor general

overheating

Stopvalve

Receiver

identification

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

G

H

I

L

J

K

A

B

C

D

EF

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 flow

I

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

I

B

D

E

G

I

I

B

I

H

B



Health and Safety

Executive

Air receivers

Statutory requirements

30 Bothmanufacturersandusersshouldbefamiliarwiththestatutory

requirementsapplyingtocompressedairsystemsandairreceivers.These

areprincipallycontainedinthePressureSystemsandTransportableGas

ContainersRegulations1989.Additionalrecommendationsaregiveninthe

ApprovedCodeofPracticeSafety of pressure systems.

31 Inpremiseswheretheairreceiversmustbecleanedandexaminedat

regularintervalsandforairreceiverswithavalueofpressuretimesvolume

greaterthan250barlitres,thenatureandfrequencyoftheexaminationmust

becontainedinawrittenschemeofexamination.Thewrittenschemeof

examinationdrawnuporcertifiedbyacompetentpersonwillnormallyspecifyaperiodbetweenexaminationsof24to48months.

32 Whenconnectedtoanaircompressingplantareceivershouldeitherbe

constructedtowithstandthecompressorsmaximumpressuresafely,or

befittedwithasafetyvalveandapressure-reducingvalvetopreventthe

receiverssafeworkingpressurefrombeingexceeded.Whenproviding

asafetyvalveandpressuregaugeforasetofairreceiversthatare

interconnectedandcollectivelysuppliedthroughasinglepipe,theymaybe

treatedasonereceiver,providedthat:

(a)anyreducingvalveorothersuitableapplianceisprovidedinthesingle

supplypipe;and

(b)thereisnomeansofisolatinganyinterconnectingpipework.

33 ThereceivershouldbefittedwithasuitablesafetyvalvecomplyingwithBS

6759,Part2orsimilarequivalentstandardandadjustedsothatairisallowed

toescapeassoonasthesafeworkingpressurehasbeenexceeded.Itis

essentialthatthevalveiscapableofdischargingmoreairthanthesystem

cansupplytothereceiver.

34 Thereceivershouldbefittedwithacorrectpressuregaugecomplyingwith

BS1780orsimilarequivalentstandardandwhichindicatespressureinbar,

lbf/sqin,orothersuitableunits.

35 Thereshouldbeasuitableappliance,eithermanualorautomatic,fordrainingthereceiver.Itisrecommendedthatmanualdrainvalvesshouldbefullbore

andstraightthrough,tominimiseanybuild-upofdebriswhichcouldprevent

tightshutoff.Automaticdrainvalvesshouldhaveadequatecapacityfor

liquiddischarge,bedesignedtominimisedebrisbuild-upandhaveamanual

overridetocheckperformance.Astrainerpositionedimmediatelyupstream

ofthevalvewillhelppreventdebrisbuild-up.Protectionagainstfreezingof

valveswillberequiredininlowtemperatureconditions.

36 Areceivershouldhaveasuitablemanhole,handholeorothermeans(as

determinedbytherelevantstandards,forexampleBSEN286-1Specification

for simple unfired pressure vessels designed to contain air or nitrogenandBS

5169Specification for fusion welded steel air receivers)toenabletheinteriortobethoroughlycleanedandinspected.



Health and Safety

Executive

37 Areceivershouldbeclearlymarked,inaconspicuousposition,withitssafe

workingpressureandotherrelevantinformationrequiredbythePressure

SystemsandTransportableGasContainersRegulations1989.Thedetails

shouldbeclearlyvisibleonthevesseloraplateattachedtoit.

38 Areceivershouldbereadilydistinguishable.Thiscanbeachievedbypainting

onidentificationmarkingsorbyaffixingamanufacturersplate,givingthe

nameofthemanufacturer,serialnumberetc.

Hazards

39 Themainhazardisthatthevesselmayexplodebecauseitssafeworking

pressurehasbeenexceededorbecauseitsabilitytowithstandpressurehas

beenreducedthroughcorrosionfatigueorinternalcokefiresforexample.


40 AllnewairreceiversshouldconformtoBSEN286-1orBS5169,where

applicable,ortoastandardprovidingequalintegrity.

Precautions

41 Todeterminetherequiredcapacity,thecompressoroutputanddemand

patternneedtobetakenintoaccount.Asaguide,thiswillbebetweensix

andtentimesthefreeairoutputofthecompressoratnormalpressure(litres/

second).Manyuserstrytosaveoninitialcostandmakethemistakeofbuyingareceiverthatistoosmall.

42 Thedrainvalve,safetyvalve,examinationholesandmanholesneedtobe

accessible.

43 Thescaleofanygaugesneedstobeclearlyvisible.

44 Onlargecompressorsystemstheairreceivershouldbefittedwithafusible

plugconformingtoBS1123,Part1.Ifafirebreaksoutnearby,theplugwill

helptopreventanexplosionbyguardingagainst:

(a) theairtemperaturerisingtothecompressorlubricatingoilflashpoint;or

(b)anexplosionoccurringbelowthedesignedworkingpressurebecauseof lostintegrityowingtoheat.

45 Welded-onbracketsareoftenusedtomountcompressor-motor

combinationsontoairreceivers.Wherethisisthecase,weldingshouldbeto

thespecificationandapprovaloftheairreceivermanufacturer.Itshouldnot

becarriedoutindiscriminatelybecausetheweldermayunwittinglyweaken

thereceiver.Mountingbracketsshouldbedesignedandfittedinaccordance

withtheapplicableairreceiverstandard.Itisgoodpracticetoweldmounting

bracketsontointermediatereinforcingplatesratherthandirectlytotheair

receiver.



Health and Safety

Executive

Coolers

Hazards

46 Manyaftercoolersarepressurevesselsandtheassociatedhazardsare

similartothoseofairreceivers(seeparagraph39).


47 Coolingplaysanimportantpartinthesupplyofgoodqualitycompressedair.

Intercoolersandaftercoolerslowerthetemperatureofthecompressedair.

Thesecoolersareusuallywateroratmosphericaircooled.Withverysmallair

compressorsthefunctionoftheaftercooler(ietheloweringofthedewpoint

ofthecompressedair)isperformedbytheairreceiver.Forothercasesaseparateaftercoolerwillnormallybenecessary.

Precautions

48 Air-cooledcoolersusuallyrelyonagoodcirculationofexternalairoverthe

heatexchangersurfacetoensureeffectivetransferofheat.Thereshouldbe

adequatespaceavailablearoundtheseheatexchangerstoalloweffective

cleaningofallsurfaces.Thecoolingairinletsandoutletsshouldnotbe

obstructedbylooseequipment,materialsetcorbyanysubsequentlyerected

building.Wherepossibletheairinletshouldbesitedonthenorthsideofthe

building.

49 Itisrecommended,particularlyatmediumandlargecompressors,that

aftercoolersarefittedtothedischargesideimmediatelyafterthecompressor.

Thesearefrequentlyprovidedwithseparatorstoremoveoilandmoisture

fromtheair.

50 Acondensateseparatorwithanautomaticdrainvalveshouldbeprovided

atasuitabledrainagepointatthecoolerscompressedairoutlet.Protection

againstfreezingofthevalvewillberequiredinlowtemperatureconditions.

51 Whereafluidisusedasthecoolingmedium,acoolantdrainvalveshouldbe

fittedandthecoolingcircuitprotectedagainstcorrosion.Thereshouldbe

somewayofmeasuringtheinletandoutlettemperaturesofthecompressedairandofthecoolant.



Health and Safety

Executive

Air dryers

Hazards

52 Thehazardsassociatedwiththeshellsoflargedryersdesignedonthe

tube-in-shellprinciplearesimilartothoseofanairreceiver(forinformation

onhazardsseeparagraph39).Asecondaryhazard,shouldanairdryernot

functionproperly,isthatmoisture-ladenaircancauseasafetysystemtofail.


53 Airdryersaresometimesdesirablewherepiperunshavetoberoutedoutside

buildingsorwherethecompressedairisusedoutsidebuildingsegfor

operatingvalves.Whereexceptionallydryairisneeded,egforpurgingdoubleglazingunits,airdryersareessential.Therearetwomaintypes:refrigerant

anddesiccant.FurtherclassificationcanbefoundinBS6754Specifications

and testing of compressed air dryers.

Refrigerant

54 Refrigerantairdryerscanusuallyreducethedewpointofthecompressed

airto2C.Thispreventscondensationfromforminginthedistributionpipes

wheretheambienttemperatureexceeds2C.Thismaybesuitableeven

whereshortrunsofpipeareroutedintheopenair,providedtheyareproperly

insulated.

Dessicant55 Desiccantdryerscanreducethepressuredewpointofthecompressedairto

verylowlevels,exceptionally,aslowas-100Cbutnormally,between-20C

and-40C.Thereductioninthepressuredewpointofcompressedairshould

becloselyrelatedtotherequirementsoftheplantorequipmentinstalled.

Adesiccantdryernormallyconsistsoftwochambersthatbothcontain

desiccant-oneonstream,theotherbeingregenerated.Anautomaticinlet

valvedirectsairfromthecompressortoeachchamberinturn,thusensuring

aconstantsupplyofdryair.

56 Positioningoftheairdryerwilldependonthecustomersparticular

requirements,butwillbeeitherimmediatelybetweentheaftercoolerand

receiver(wherefitted)orimmediatelyafterthereceiver.Wheretheneed

forexceptionallydryairrepresentsonlyasmallpercentageofthetotalcompressedairused,adryermaybelocatedimmediatelyupstreamofthe

particularplantwherethedryairisneeded.

Precautions

57 Thechambersofairdryersarepressurevesselsandshouldconformwith

BS5500Specifications for unfired fusion- welded pressure vesselsortoa

standardprovidingequalintegrity.Ifmeansareprovidedforisolatingthe

dryer(anditisgoodpracticetoprovidemeansofisolationforallequipment),

eitherthechambersshouldbeconstructedtowithstandthemaximum

pressurethatcanbegeneratedbythecompressororasuitablepressurereducingvalveandasafetyvalveshouldbefittedtopreventthesafeworking

pressureofthechambersfrombeingexceeded.



Health and Safety

Executive

58 Wherethereisnomeansofisolatingthedryerfromasuitablesafetyvalve,eg

onthereceiver,andwherenon-returnvalvesarefittedtothedryeroutlet(to

protectitfromstoredenergyinthesystem),nosafetyvalvesareneeded.

59 Somedryersregeneratethedesiccantsimplybypassingaproportionof

thedrierairthroughit.Othersuseheatercoilsembeddedinthedesiccant.

Thislattertypeshouldbeequippedwithathermalprotectivedevicethat

candetectanytemperatureriseabovethethermostatsetting.Excessive

temperaturerisesduetothermostatfailureshavebeenknowntoleadtooil

mistexplosions.



Health and Safety

Executive

Installation of compressors

60 Smallcompressorinstallationsmayeasilybeoverlooked,especiallyifsited

inaseparateenclosureoutsidetheworkingarea,andconsequentlymay

notreceivepropermaintenance(seeparagraph146-158).Thedesignof

largeinstallationswillneedtoincorporateadequateaccessandsuitable

liftingequipmenttofacilitatemaintenance.Ifnormallightingislikelyto

beinadequate,locallightingshouldbeprovidedsothattheworking

areaisadequatelylit.Considerationshouldalsobegiventocompressor

specificationsiftheyaretobeinstalledinpossiblehazardousareas,e.g.in

garagepitswhereaflammableatmospheremaybepresent.

Precautions

Small compressors

61 Wherepossiblethecompressorunitshouldbemountedatgroundleveland/

orinanareabigenoughtoallowforinspectionandmaintenance.

62 Anyplatformusedforaccessorasaplaceofworkshouldbebigenoughfor

apersontostandsafelyonit,andhaveguardrailsandtoeboards.

63 Theunitshouldnotbemountedonaplantstructurewherethereisexcessive

vibration.

64 Smallunitsusedtosupplyworkshopsandsimilarinstallationsshouldbesited

wheretheyareaccessibleandphysicallyprotectedagainstdamagefrommaterial,toolsandequipment.Wheretheriskofdamageishightheyshould,

wherepossible,beinstalledinseparateroomsadjacenttothemainbuilding

(seeparagraphs60and67).

Medium and large compressors

65 Whereusersareresponsibleforon-sitesystemdesignandinstallationthey

shouldfollowthemanufacturersinstructionscarefully.Mediumandlarge

compressorsshouldbelocatedinaposition(usuallypermanent)bestsuited

forthepurposeandwithaccessforeaseofmaintenance.Thismeansthat

thecompressor,includingitsprimemover,airreceiver,cooleretc.shouldbe:

(a) nearthecentreoftheloadtominimisepiperuns;

(b) housedinabuildingthatisinsulatedorheatedtokeeptheambient temperatureabovefreezing;

(c) providedwithadequateventilatingairtopreventoverheating,andsited

sothattheintakeofmoistureisminimised;and

(d) sitedawayfromdustyatmospheresandprovidedwithadequatefacilities

fordrainingofcondensate.

66 Thereshouldbesomemeansofcontrollingairbornedustandcontaminants

inthevicinityofthecompressor.Theairintakeshouldbeprovidedwithan

efficientfilter.

Noise

67 Compressornoiseisoneofthemostcommonnoiseproblemsassociated

withtheworkplaceandispotentiallydamaging.Referenceshouldbemade

tothePreventionofDamagetoHearingfromNoiseatWorkRegulations,



Health and Safety

Executive

enactedon1January1990,andtheassociatedguides1and2and3to

8.Wherenoisefromcompressorsislikelytocauseexposuretohazardous

levelsofnoise,thisshouldbeincludedinthenoiseassessment(required

undertheNoiseatWorkRegulations1989)andtheassessmentshould

indicatethedegreeofnoisereductionrequiredtoreducetheexposureto

safelevels.Compressorsshouldbesuppliedwithnoiseemissioninformation.

Ifthisisnotthecase,purchasersshouldrequestthisinformationwhichcan

beusedintheassessment.Noisecontrolmeasures,ifrequired,includethe

following:

(a) sitingthecompressorawayfromworkareas;

(b) providingthecompressorwithanacousticenclosure(theneedfor

accessandremovalformaintenancewillneedtobeaddressed);

(c) providinganti-vibrationmountings;

(d) thefittingoforimprovingtheperformanceofsilencers;

(e) accesstoenclosuresprovidedforcompressorsshouldonlybe

permittedtopersonswearingsuitableandeffectiveearprotection.

68 HSE Guidance note PM 56givesinformationandadviceaboutnozzledesign

toreducenoise.



Health and Safety

Executive

Main line systems

69 Thissectiondealswiththesystemofpipes,valvesandfittingsfromthe

sourceofthesupplytothepointofapplicationorcontrol.

Hazards

70 Inadequatelysizedanddesignedsystemscanleadtotheoperatingunits

beingstarvedofair,causingmachinemalfunction.Repeatedmalfunctions

maytemptoperatorstoadoptunsafepracticestoovercomeanyproblems.

Badlydesignedpiperunsandlackofisolationvalvesmayexpose

maintenancestafftounnecessaryrisks.Somegradesofplasticpipeworkare

notrecommendedforuseincompressedairinstallationsanddesignersare

advisedtoconsultmanufacturerswhenselectingmaterials.

71 Incorrectmaintenanceofnon-metallicbowlsusedonfilters,traps,

separatorsandlubricatorscanleadtoexplosions.Itisimportanttoensure

thatalllubricantsusedtoreplenishlubricatorsarecompatiblewiththe

lubricatorbowlandtheequipmenttobelubricated.Attentionisdrawnto

BS6005Specification for moulded transparent polycarbonate bowls used

in compressed air filters and lubricators,regardinginstallation,useand

maintenanceofunitsfittedwithpolycarbonatebowls.


72 Compressedairsystemsinvariablygrow.Itisimportanttotakeintoaccount

anyforeseeableexpansionofthesystem,andgenerousallowanceshouldbe

madeonthesizeofpipingprovided.Thecostofinstallinga50mmdiameter

pipeislittlemorethana25mmone,anydifferencebeinginthecostof

material.However,flowcapacityofa50mmpipeisfourtimesthatofa25

mmoneandusingthelargersizeensuresbetterperformanceandfacilitates

futureadditionstothesystematlittleextracost.Asageneralguidethepipe

sizewouldbesuchthatthepressuredropbetweenthereceiverandthemost

remotetakeoffpointswouldnotexceed5%oftherequiredsupplypressure

withamaximumof0.3bar(4psi).Thepipesizeforinitialmainrunsinany

systemwouldnotnormallybelessthantheoutputportofthecompressor.

73 Therearetwomaintypesofcompressedairsystem;singlelineandringmain.Figures2and3showtypicallayouts,withpositionsindicatedfor

variousvalves,drains,filters,airlinelubricatorsandpressuregauges.

74 Usersshouldkeepaschematicdrawingoftheairsystemshowingpipe

runs,intendeddirectionofairflow,andthepositionsoffittingssuchas

valves,drains,etc.Thedrawingsshouldbeamendedwhenmodificationsor

additionsaremadetothesystem.Anygraphicsymbolsusedshouldcomply

withBSISO1219Fluid power systems and components. Graphic symbols

and circuit diagrams.

Precautions

Pipe-runs

75 Therouteofthepiperunandthepositionofvalvesandoperatingpoints

shouldbesafeandconvenientforthosewhowilluseandmaintainthe

system.



Health and Safety

Executive

76 Thepiperouteitselfshouldnotpresentahazardorobstructaccessand

shouldberoutedawayfromanyareaswhereitmaybevulnerableto

mechanicaldamage.

77 Thereshouldbeadequateandsufficientaccessways,workingplatforms

andclearancespaceprovidedtoenablethecompressedairsystemtobe

operatedandmaintainedwithoutexposinganyonetounnecessaryrisk.

78 Piperunsshouldhaveaslightfallinthedirectionofairflow,anddrainage

valvesshouldbefittedatthelowestpoint,insuchawaythatmoistureand

aircanbedischargedsafely.Adrainvalveshouldbefittedatthebottomof

verticalpiperuns.Sectionsofpipeandvalvesthatmayhavewaterinthem

andmaybeexposedtofrostshouldbesuitablyinsulated.Note: receiver

drains generally have a heavier duty than normal pipe run drains-see

paragraph 35.

79 Piperunsshouldbesecuredbybracketsorothersupportsinstalledatappropriateintervalstosupportthepipesystemsuchthateachremovable

sectionisself-supportingandtheremainingpipeisstableafterremoval.To

allowforexpansion,particularlyatthecompressor/receiverdischargeor

onstraightrunsexposedtosunlightorheatfromtheprocess,suitableand

adequateexpansiondevicesshouldbefitted;egbellows,loopbends,flexible

pipes.BS3974:Parts1-3Specification for pipe supportsgivesdetailsof

suitablemethods.

Figure 2 Singlelinesystem-typicallayout

Symbols Description

Shut-off valve

Manual drain (water trap)

Automatic draining valve

Lubricator

Pipe fall in direction of air flow

Filter, 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

Air

vent

Bin gate

operation

DO NOT CROSS-CONNECT AIRLINES

IN A SINGLE LINE SYSTEM



Health and Safety

Executive

Figure 3 Ringmainsystem-typicallayout

80 Pipingandassociatedfittingsconnectedbetweenthecompressorand

airreceivershouldbeeasytoclean.Ifcarbondepositsbuildupinsuch

pipeworktheremaybeanexplosion(seeparagraph24).

81 Alloutletpointsshould,wherepracticable,betakenfromthetopofthe

piperun,andastopvalveorself-ventingballvalve(wherenecessary

completewithhandle)shouldbeprovidedadjacenttotheconnectionpoint.

Theconnectionpointatanyoutletshouldbearrangedhorizontallyorfacedownwards;upwardfacingconnectionpointsinvariablyfillwithdirtand

promptthebadpracticeofblowingoutbeforeuse.Outletpointsshould

beprovidedatconvenientplacesforallroutineactivitieswhichrequire

compressedair.Theyshouldbepositionedsothathosesattachedtothem

willnotcrossorobstructthenormalaccesstotheworkplace,andcanbe

connectedwithouttheneedforclimbing.

82 Piperunsshouldbeidentifiedbypaintingthepipelightblue(BScolour

reference20.E.51)inaccordancewithBS1710.Whereapplicabletheriskof

couplinguptothewrongcompressedgassupplycanbefurtherreducedby

theuseofnon-interchangeableconnections(seealsoparagraph100).

83 Stopvalvesshouldbeprovidedandpositionedsothatthecomplete

pipeworksystemcanbeisolatedfromthecompressedairsupply.Allbranch

linesofsubsectionsofthesystemshouldalsohavestopvalvesfittedtoallow

separateisolation.Whereappropriateeachvalveshouldhaveafacilitytobe

lockedintheclosedposition.

Symbols Description

Shut-off valve

Manual drain (water trap)

Automatic draining valve

Lubricator

Pipe fall in direction of air flow

Filter, pressure regulatorpressure gauge, lubricator

Filter with manual control

Control valve

Pressure gauge

Air cylinder (spring return)

KEY

B

A

Control

point

To

drain

Air

pump

Air

point

Chute

operation

Maintenance area

Air

grinder

Compressor

installation

Compressor

installation

Bin gate



Health and Safety

Executive

84 Forringmainsorsystemswithdualsupply,stopvalvesmustbeprovided

whichenableeachindividualairsupplytobeisolatedfromthepipework

system.Thisarrangementofstopvalveswillallowsafeoperatingprocedures

tobeadoptedduringmaintenanceofthesystemandancillaryequipment.

85 Whereaircannotbeventedfromthesystemoranypartofthesystem

throughthenormaloutlets,valvesshouldbefittedforthispurpose.The

valvesspecifiedshouldbesuitablefortheapplication.Inmostcasesthree-

portvalvesorself-ventingballvalvesarethemostsuitabletypeforisolating

andventing;thesevalvesshouldbearrangedsothatwhenthesupplyisshut

off,thedownstreampartoftheairsystemisventedthroughtheexhaustport

ofthevalveandprovisionmadetolockthevalveinthisposition.

86 Wherevalvesaregrouped,orwherethepurposeorlocationofthevalve

isnotobvious,anoticeshouldbeprovidedindicatingthepositionand/or

purposeofthevalve.

87 Leveroperatedstopvalvescanbeinadvertentlymovedtotheopenposition.

Duringmaintenancetheyshouldbeeitherlockedintheclosedpositionorthe

leverhandleshouldberemoved.

Filters, traps, separators and lubricators

88 Filtrationandlubricationtoastandardofcleanlinessappropriatetoend

usagearenecessary.Airlinelubricatorsshouldbeprovidedforoperations

whichinvolveairtools,aircylindersoraircontrolvalves;theyshouldbe

positionedafterthestopvalveandafteranyfilterorseparator.Inbothcases

itisessentialthatfiltersandlubricatorsarepositionedafterandadjacenttoa

stopvalvetoallowsafeserviceandmaintenance.Theyshouldnotbefitted

intoringmainswherethedirectionofairflowisnotcontrolledbutintothebranchlinesleadingfromthem.Highstandardsoffiltrationwillberequiredfor

instrumentcontrolorintheelectronicsindustry.Ultra-highefficiencyfiltration

willberequiredinhospitalsandthepharmaceutical,foodstuffspreparation

andbrewingindustries,andappropriatefilters,trapsorseparatorsshould

befitted.Whereextremelycleanorsterileairisrequiredspecialistequipment

suppliersshouldbeconsulted.Precautionsshouldbetakenagainstthe

ingressofdirtandothercontaminantsfromthesurroundingareathrough

carefulsitingofthecompressor.Theuseofexhaustportfiltersshouldbe

considered.

89 Inmostcasesthesecomponentswillhaveeithermetallicortransparent

plasticbowls(usuallypolycarbonateorpolyamide),whichhavegood

impactstrength.Thepropertiesofthematerialsmayhoweverbeadverselyaffectedbysolvents,alcohols,cleaningsolutionsorsyntheticlubricants

andmaintenanceinaccordancewithmanufacturersrecommendationsis

essential.(NBUsefulguidanceforpolycarbonatebowlsisprovidedinBS

6005Specification for moulded transparent polycarbonate bowls used in

compressed air filters and lubricators.)Itisthereforeessentialthatcleaningof

polycarbonatebowlsiscarriedoutwithcleanrags,andthatmateriallikelyto

becontaminatedwithdilutedsolubleoilsshouldbeavoided.Wherepossible,

filters,separatorsandlubricatorsshouldbepositionedsothattheriskof

accidentaldamagetoanynon-metallicbowlsisminimised.Evensubsequent

minorknocksmayleadtodamagedbowlsexploding.Itisgoodpracticeto

shieldallnon-metallicbowlsandmanufacturersshouldensurethatsuch

bowlscanbeshielded.Specificrequirementsforfilters,traps,separatorsandlubricatorsarediscussedinparagraphs104,105and109.



Health and Safety

Executive

Pressure regulators

90 Whereitisnecessarytoprotectequipmentfromoverpressurisation,

pressureregulatorsshouldbeprovidedandsettomaintainaconstantsafe

downstreampressure.Anairpressuregaugeshouldbeprovidedonthe

outletside.Dependingonthelevelofriskcreatedbyoverpressurisationall

adjustablecontrolsshouldhavesomeformoftamper-resistantprotection.

Wheretheriskislow,asimplesnapactionlockshouldsuffice.Astherisk

increases,greatersecurityagainstunauthorisedadjustmentisneeded.

Considerationshouldbegiventousingmodelsincorporatingpositiveinternal

stopsorpositivemeansoflocking.Forveryhighrisks,non-adjustablemodels

maybethebestanswer;alternativelytheadjustableitemsmaybesitedin

lockableenclosureswiththekeykeptbyaresponsibleperson.

91 Apressurereliefvalve(safetyvalve)orothersuitableoverpressureprotective

deviceshouldbefittedandsettorelieveifthesafeworkingpressureofthe

equipmentorvesselisexceeded.Thereliefvalveshouldbepositionedso

thatifthevalvedischarges,therisktopersonnelisminimised.



Health and Safety

Executive

Portable pneumatic equipment


92 ThePressureSystemsandTransportableGasContainersRegulations1989

andtheProvisionandUseofWorkEquipmentRegulations1992setoutthe

dutiesofusersandownersofportablepneumaticequipment.

93 ThePersonalProtectiveEquipmentatWorkRegulations1992setoutwhat

eyeprotectionisneededforcertainprocessesusingcompressedair.

94 UndertheManagementofHealthandSafetyRegulations1992andthe

HealthandSafetyatWorkAct1974employershavearesponsibilitytotrain

theirstaff.Furtheradviceontrainingisgiveninparagraphs171to173.

Hazards

95 Bothblowgunsandhandheldtoolsareusuallyconnectedtoalengthof

flexiblehosewhichduringthecourseofitslifewillbesubjecttomechanical

damageandconsiderableflexing.Thisdamageand/orflexingparticularlyat

connectionpointscancausethehosetorupture.Thiscanleadtosudden

dischargesofcompressedairandmaycauseunsupportedlengthsofhoseto

whipandsnakedangerously.

96 Thepracticeofusingblowgunsforremovingswarf,powderedmaterialsetc

fromcomponentsandfrommachineryiswidespreadthroughoutindustry.

Thereareanumberofhazardsconnectedwiththeuseofblowguns

including:

(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,dryairsupplyshould

besafelygeneratedanddistributedtoalloutletpoints.Thetypeofequipmenttobeconnectedtotheoutletpointwilldeterminewhatextraprecautions,if

any,willberequired.Themostcommonrangeofdeviceswillbeairorblow

guns,portabletoolsorpneumaticpoweredmachinery.Eachhasitsown

particularrequirements.



Health and Safety

Executive

Precautions

Flexible hoses

98 Whenselectingaflexiblehose,usersshouldtakeintoaccountthesite

conditions,includingtemperatures,oilsandpressurestowhichitwillbe

subjected.Wherelubricatingoilispresentinpipelines,agradeofhose

resistanttothatparticularoilmustbeused.Asyntheticbasedgradeofhose

shouldbeusedformineraloilsandanaturalbasedgradeforvegetableoil.

Wherefireandexplosionrisksmaybepresent,theuseoffire-resistantanti-

static(FRAS)hosesshouldbeconsidered.Themanufacturersadviceshould

alwaysbefollowed.

99 Heavy,mediumandlightgradesofhoseareavailable.Wherehosesareused

forsemi-permanentdistributionofcompressedair,forexampleinquarries,

constructionsites,shipyards,farmyards,garageforecourtsetc,heavygrades

shouldbeused.Mediumandlightgradesareusedforgeneralpurposessuch

asfixedpneumaticmachineryandpneumaticcylinders,smallpowertoolsandportableequipment.Hosesusedwithhand-heldpowertoolsshouldbe

lightandflexible(butsuitablefortheduty).

100 Tubesandhosesusedtoconnectcylinderstotheircontrolvalvesare

availableinavarietyofcolourstomakefaultfindingandmaintenanceeasier

(seeparagraph143).Theyshouldbeneatlyrunandadequatelysecured.

Ifthefailureofaflexiblehosewouldbehazardousitshouldbefurther

restrainedorshielded.

101 Couplingaportabletooltotheoutletpointisusuallyachievedbyuseofa

quick-actingconnector.Theconnectorshouldbedesignedsothatwhen

disconnecteditautomaticallysealstheairpressureontheupstreamsideandslowlyventstheairpressureonthedownstreamside.Forallhosesabove10

mmbore,morethan10mlongorsubjecttoapressureexceeding7bar,the

connectorshouldhaveaself-ventingsocketwhichreleasesthedownstream

pressurebeforedisconnectionispossible.Alternatively,aplugwitha

controlledventingactionshouldbeused.Thesesafetyfeaturesprevent

inadvertenttooloperationanduncontrolledwhippingofthehosewhenits

inletendisuncoupledfromthesocket.Anotherwayofreducingwhippingor

snakingistofitemergencyshut-offvalves,hoserupturevalvesorairfuses

ascloseaspracticabletotheconnector.Thevalveswillcloseorreduceflow

toaverylowlevelintheeventofexcessiveair-flowconditionscausedbya

failureofthehose(seealsoparagraph83aboutfittingofisolationvalves).The

samerequirementcouldbenecessarywhenusingplastictubing.

102 Similarrequirementsforquick-actingconnectorsapplytomostpercussive

andvibratingairtools,whichmaybefixedorhandheld.Ifaquick-acting

couplingsocketisfittedatthehoseendadjacenttothetool,theplugshould

notbescreweddirectlyintotheinletportbutshouldbefittedontoashort

isolationhose(0.5to1.5mlong),thusisolatingtheplugandsocketfromthe

toolvibrations.

103 Wherehosesareusedtosuspendtools,theloadstrengthofhoseand

couplingsshouldbeatleastfivetimesthesuspendedload.

Blow guns

104 Blowgunsconsistingsimplyofareducedorificeindirectlinewiththesupplyhosecanbeextremelydangerous,unlesspreceededbyapre-settamper-

proofpressureregulatorsetatareducedpressurefromthenormal80psi

airlinesupply.Modelsareavailablecommerciallywhichincorporateanair

curtaindesignedtoprovideaprotectiveshroudaroundthenozzle.Although



Health and Safety

Executive

notcompletelysafe,thesedesignssignificantlyreducetheriskofeyeinjury

andthedangersfromcloseskincontact.Ifdesignedcorrectlysuchnozzles

canoftenhelptopreventtheoperatorfrombeingsubjectedtoexcessive

noise.Becauseairisventeddirectlyintotheatmosphere,cleandryair

isessentialandlubricatorsshouldnotbeused.Blowgunscanexhaust

significantquantitiesofairandplaceextraloadingonthecompressor

system.Inviewofthisandtheattendantriskarisingfromuseofblowguns,

theiruseshouldbeconsideredcarefullywithaviewtousingalternative

meansforcleaningdownmachineryorcomponents.

Portable tools

105 Pressureregulatorsshouldbeusedtoreducethepressuretotheoptimum

valueforthesafeandefficientuseoftheequipment.Thisvalueshouldbe

clearlymarkedonthetool.Filtersandlubricatorsshouldbefittedinthe

supplypipeasshownatAinFigure3.Topreventover-speeding,tools

withairmotorsshouldincorporateagovernororthrottle.Thereshouldbe

availableaneasilyaccessiblemeansofisolatingtheairsupplyfromthetool.EuropeanStandardprEN792Hand-held non electric power tools-Safety

coversdesignofdrills,grinders,nibblers,polishersetc.Itispoorpracticeto

pullportabletoolsusingthehoseoruseitasameansofaccessbyclimbing

ontosuspendedhose.Olddamagedhoseshouldnotbeusedtomakeup

freshhoseassemblies.



Health and Safety

Executive

Pneumatic powered machinery

Hazards

106 Thehazardsnormallyassociatedwithpoweredmachineryareequally

applicabletopneumaticpoweredmachineryandsuitablesafeguardsare

necessaryasdescribedinBSEN982Safety requirements for fluid power

systems and their components-PneumaticsandBS5304CodeofPractice

Safety of machinery.

107 Unlikeliquidfluidpowermedia,compressedairiselastic(compressible),

andbecauseofthis,additionalhazardscanarisefromstoredenergyand

actuatorsunderload(seeparagraphs138to141).Thishazardrequires

particularconsiderationwhenthemachineryisfittedwithinterlockingguards.Interlockingsystemsarecoveredinparagraphs129to137ofthisbooklet.


108 Wherepneumaticallypoweredmachineryisconnectedtotheoutletpoint

thisshouldbebymeansofconventionalconnectors,egcompressionor

push-in,push-onconnectorswithashut-offvalve.Plastictubingmade

fromPVCornyloniswidelyused,inparticularforpipinguppneumatically

operatedmachinesemployingpneumaticcylindersandvalves.Compression

orpush-in,push-on,connectorsofvarioustypescanbeusedwiththetubing

whichissuitableforconnectingtovibratingandmovingpartsbyforming

loopswhichabsorbthevibrationormovement,but,asforflexiblehoses

(Para98)itisalwaysnecessarytoconsidersiteconditionswhenapplying

plastictubing.ThespecificationfornylontubingisgiveninBS5409,Part

1.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,pressuregauge

andlubricatorset,asshownatPartBofFigure3.Withthisarrangement,

optimumconditionsfortheoperationoftheparticularmachinecanbeset

withoutaffectinganyotherequipmentconnectedtothesupply.Ifthefilter,

pressureregulator,pressuregaugeandlubricatorsetareproperlymaintained

(seeparagraphs160to170),wearonsealsinactuatorsandvalveswillbelimitedandthemachineryshouldperformcorrectlyandefficiently.The

likelihoodofmalfunctions,whichcouldleadtounintendedoperation,willalso

bereduced.

Precautions

110 Toalargeextentthedesignfeaturesneededwilldependonhowthe

machinewillbeused.However,paragraphs111to141outlinesomebasic

requirementsformachineandcircuitdesign.

111 Allcomponentsusedinthemachinedesign,includingconnectinghoses,shouldbeabletowithstandsafelythemaximumpossibleairmainpressure.

Themaximumsafeworkingpressureofthemachineshouldbeclearly,

prominentlyandpermanentlymarkedonthemachine.



Health and Safety

Executive

112 Allcomponentsshouldbeprotectedagainstover-pressurisationbythe

provisionofpressurereliefvalvesunlessthecomponentscanwithstandthe

compressorsmaximumpressureandwillnotbesubjectedtounacceptable

pressurebuildupduetohighexternalloads.

113 Themachineshouldbedesignedandconstructedsothatanycomponents

whichrequireadjustmentorregularmaintenanceareeasilyandsafely

accessible.

114 Supplyorcontrolsystemfailureshouldnotcauseahazard.Toensurethat

suchapossibilityisminimised,theeffectsofgravity,impactorvibration

shouldbeconsidered.Forthisreason,valvescontrollingactuatorsshouldbe

mountedwiththemainspoolhorizontal.Inaddition,anyactuatorsthathave

toadoptaspecificpositionforsafetyifthesupplyorcontrolsystemfails

shouldbecontrolledbyavalvewhichisspringbiased(mono-stable)tothe

safeposition.

115 Ifthemachineistobeprovidedwithanemergencycontrolitshould,without

delay,stoporsetmovingpartstowhicheverpositionprovidesmaximum

safety.Theemergencycontrolshouldbeofthemushroomheadtype,

colouredred,prominentlylocatedandreadilyaccessibletotheoperator.

Whereanoperatorhastoworkfrommorethanonepositionitmaybe

necessarytoprovideadditionalemergencycontrols.Operationofthe

emergencycontrolshouldnotofitselfcreateahazard.

116 Whereairisdischargedtotheatmosphereduringthenormalcourseof

operationofthemachine,andthiscausesworkerstobeexposedtohigh

levelsofnoise,somemethodofreducingtheworkersexposureshouldbe

considered.Componentsshouldbelocated,orshielded,sothatoperatorsarenotsubjectedtoairblastfromexhaustports.Ifsilencersarefitted,

theseshouldbedesignedtocreateminimumbackpressureandshould

becompatiblewithwaterandanylubricantsused.Alternativelyanexhaust

hosecanbefittedsothattheairisdischargedwellawayfromworkers,for

exampleunderafactoryroof(seeHSEGuidanceNotePM56Noise from

pneumatic systems).



Health and Safety

Executive

Actuators

Hazards

117 Wherelinearactuatorsareused,specialattentionshouldbegiventostroke

length,loadingandthemethodsofmountingthecylindertoavoidbuckling

ofthepistonrodandexcessivesideloadingwhichcouldleadtopistonrod

bearingandsealwear.Whereshearforcesonfixingscrewsarelikelyto

beexcessive,thecylindermountingshouldalsobekeyedordowelledin

position.Alternatively,fittedboltsmaybeused.

118 Repeatedshockloadsoncylinderendcapscaneventuallycauseeitherthe

cylinderorthepistonrodassemblytofail,whichcouldleadtoseriousinjury.

Mostcylindermanufacturerscansupplycylinderswithbuilt-incushioning

designedtoreducespeedatstrokeextremities,thusbringingthemachinecomponenttoashocklessstop.Equallyhazardousisthepotentialforpiston

androdtoseparate.Cylindermanufacturersshouldensurethatpistonsare

positivelylockedtothepistonrod.


119 Thefunctionoftheactuatordeterminestheprecautionsnecessaryfora

safedesign.Ifthepurposeistoimpartmotiontoaloadwhichisotherwise

supported,theproblemwillbedifferentfromthoseforanactuatordesigned

toliftorloweraload.Cylindersdesignedtoclampposeyetanotherproblem.

Precautions

120 Foranyactuatorsimpartingmotion,smoothactionispreferableand

cushioningisdesirable.Ifthecylindersaredouble-actingtheremaybe

occasions,egatstart-uporfollowinganemergency,whenthecylinderis

pre-exhausted,causingtheactuatortoacceleraterapidlywhenairisfirst

introducedtothecylinder.Wherethisislikelytocauseahazardasoftstart

arrangementshouldbeintroducedinthesupplylinetothemachine.Thiswill

initiallyrestricttheflowrateuntilacertainpredeterminedpressurehasbeen

reached.

121 Linearactuatorswithmagneticpistonsandintegralmountedreedswitchesorproximityswitchesforsignallingcontrolvalvesarenowpopular.This

islargelyduetothecomparativecheapnessofusingelectricormicro-

electroniccontroltogetherwithcostandspacesavingsfromnotneedingto

installindependentmechanicallyactuatedtrips.Safeguardingpneumatically

poweredmachineswherethecontrolcircuitiselectricalrequiresextracaution

toensurethattheriskofinjuryisminimisedifeithertheelectricorpneumatic

powersupplyfails.Reedswitchesmaymalfunctioninareassubjectedtohigh

vibrationlevelsorelectromagneticfields.

122 Actuatorsdesignedforliftingorsupportingloadsmaycollapsedangerously

ifthesupplyfails.Themachineshouldhavespring-appliedmechanical

scotchestosupporttheloadwhenevermovementisnotrequired.Incertaininstancesmechanicalscotchesmaybeimpracticable.Asasafetybackup

anormallyclosed,airtoopen,springreturnvalveinthecylindersupplyline

couldbeused.



Health and Safety

Executive

123 Supplyfailuretoclampingcylinderscanleadtoahazardbyreleasingthe

componentprematurely.Thiscanbeovercomebyusingsingleacting

cylinderswherethereturnspringappliestheclampingforce(seeparagraph

127),ortheuseoftwocontrolvalveswilltemporarilykeepthecylinder

pressurised(seefigures4and5).Butcareshouldbetakeninusingthis

designasevenasmallleakcouldaffecttheintegrityofthesystem.

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 Machinesincorporatingseveralactuatorsmayrequirethemtobesetina

certainpositionbeforethemachineisfirstused,andsubsequently,afterthe

emergencycontrolorinterlockingguardshavebeenoperated.Re-positioningmaybepossiblewithoutre-establishingthepneumaticsupply,butthese

caseswillbeintheminority.Inallothercasesre-positioningisbestachieved

byprovidingmanualoverridecontrols.Suchcontrolsshouldbeofthetwo

handtypeiedesignedsothatthetwocontrolsareplaced,separatedand

protectedtopreventspanningwithonehandonly,beingoperatedwithone

handandanotherpartofthebody,orbeingreadilybridged.Itshouldnotbe

possibletosettheactuatorsinmotionunlessthetwocontrolsareoperated

withinapproximately0.5secondsofeachother.Movementoftheactuators

shouldbearrested,orwhereappropriatereturned,immediatelyoneor

bothcontrolsarereleased.BSEN574Two Hand Control Devicescovers

functionalaspectsandprinciplesfordesignofthistypeofcontrol.

Cylinder

Stop

valve

Guard

(a) Interlocking

valves(b) Control

valves

(c) Power control valve(Air operated)


30/50



Health and Safety

Executive

Interlocking methods and circuit

designGeneral information and advice

125 Themethodusedforinterlockingshouldbecommensuratewiththerisk.The

highertheriskthehighertheintegrityoftheinterlockingsystemshouldbe.

126 Principlesfordesignandselectionofinterlockingdevicesassociatedwith

guardsaregiveninEN1088andBS5304.Generalprinciplesforapplication

aregiveninBSEN983Safety of Machinery-Safety requirements for fluid

power systems and their components-Pneumatics.

127 Onpneumaticmachinery,becausethepowermediumiscompressible

andnormallyexhaustedtoatmosphere,thesafetycircuitdesignisnot

straightforwardasforotherpowermedia.However,thebasicaimsfor

interlockingremainthesameand,wherepossible,thepowersupplyshould

beinterruptedbytheguardoperatedinterlockingdeviceandanyresidual

systempressureexhaustedtoatmosphere.Inthisconditionanycylinders

willbepre-exhaustedandalternativearrangementsinthesystemdesignwill

benecessarywhereanycylindersarerequiredtobeunderconstantload

(seeparagraph122).Inaddition,particularprecautionsmaybenecessary

whenreinstatingthesupplytopre-exhaustedcylindersifrapidacceleration

isundesirable.Toavoidtheneedtomaintainsupplypressuretocylinders

requiredtobeunderconstantload,suchasthoseoperatingclampsor

supports,alternativefeaturesshouldbeconsidered,suchassingle-acting

cylinders,orspringappliedmechanicalscotches.Cylindersfittedwithrod

locks,thelockingactionofwhichistriggeredbylossofairsupply,mayalso

beusedtopreventuncontrolledmovement.

128 Signalairlinesshouldbekepttoaminimumlengthtofacilitaterapidexhaust

pressuredecay.Wherethisisnotpracticableandpilotsignalsexhausting

totheatmosphereretainsufficientpressurelevelstooperatemaincontrol

valves(evenafteraguardhasbeenopened),additionalinterlockingdevices

shouldbeprovidedwhichpreventopeningoftheguarduntilitissafetodo

so.When3-positionvalvesareusedinsafetycircuits,wherepracticablethe

centrepositionshouldprovideasupply-sealed-onlycondition(outletsvented)

becauseanall-ports-sealedcentrepositioncanresultinstoredenergyintheactuator,leadingtounintendedmovementifpipingisdisconnected.

Interlocking systems

Single control system interlocking

129 Thebasicelementsofsinglecontrolsysteminterlocking(seeFigures4and5)

are:

(a) aninterlockingvalveorpositionswitchoperatedbytheguard;

(b) interposedcontrolvalves,electromechanicalrelaysand/orsolid-state

switchingdevices,ifany;and (c) anairoperated,solenoidoperatedorsolenoidactuatedairoperated

valve,controllingpowertothedrive.



Health and Safety

Executive

130 Anyoftheseelements,orthepipingorwiringinterconnectingthem,can

failandcausedanger,sotheyshouldbechosentoprovidethemaximum

degreeofreliability.Thegreaterthenumberofdevicesincorporatedinthe

system,theloweritsinherentreliability,sointerposingdevicesshouldbe

avoidedifpossible.

Dual control system interlocking

131 Thebasicelementsaresimilartothoseemployedinsinglecontrolsystem

interlocking.Wherethepossibilityofcommonmodefailureneedstobe

minimiseddifferentcontrolpowermediashouldbeusedandkeptseparate

exceptfornecessaryinterconnectionsforcrossmonitoring(whereprovided),

andconnectiontothesupply.

132 Suchsystemscanbeentirelypneumatic(seeFigures15and16),orhybrid

forexampleonesystem,pneumaticandonesystem,electric(seeFigures17and18).Thislatterarrangementmaybeparticularlyappropriatewhere

cylinderswithmagneticpistonsandintegralreedswitchesorproximity

switchesareused.Inbothsystemstheoutputofthepowercontrolling

devicesshouldbeconnectedsothateithercanstophazardousmovement

ofthemachinery,irrespectiveoftheconditionoftheother.Wherethecircuit

issuchthatasinglefailureisnotself-revealingegtheactuatorcontinuesto

operate,theintegrityofthedualcontrolsystemcanbeimprovedbycross

monitoring(shownalsoinFigures17and18).

Figure 6 Singlecontrolsysteminterlockingwithpistonarrest(guardopen)

Cylinder

Guard

(a) Interlocking

valves

(b) Controlvalves


Note:

Manual reprositioning of thecylinder is possible with thistype of control valve.



Health and Safety

Executive

Figure 7 Singlecontrolsysteminterlockingwithpistonarrestandhold(guardclosed)

Figure 8 Useofanequalisingvalve-controlinterlocking(guardopen)

Cylinder

Guard

(a) Interlockingvalves

(c) Power control valve

(Air operated)

(b) Equalisingvalve

Cylinder

Guard

(a) Interlocking

valves

(b) Control

valves


(Air operated)



Health and Safety

Executive

Figure 9 Useofanequalisingvalve-controlinterlocking(guardclosed)

Figure 10 Useofanequalisingvalve-powerlocking(guardopen)

Cylinder

Guard

(a) Interlocking

valves


(b) Equalisingvalve

Cylinder

Equalising valve

(with power interlocking)

Guard

Control valve

(Air operated)



Health and Safety

Executive

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)

Interposedcontrol

valvesPower

interlocking

valves

Note

Cylinder returnsto instroke

position wheneverguard is open



Health and Safety

Executive

Figure 13 Useofareservoir-powerinterlocking(guardclosed)

CylinderGuard

Reservoir

Power control valve(Solenoid operated)

Interposed

control

valves Power

interlocking

valves



Health and Safety

Executive

Figure 14 Controlsysteminterlockingfromcomplexsequence

A B

D

C

Guard

Toclose

Springreturn

To portsmarked

Sequence

Closed guard

A+B+

C+ D+

A-

C- D-B-

Open guard



Health and Safety

Executive

Figure 15 Dualcontrolsysteminterlockingwithoutcross-monitoring,bothchannelspneumatic

(guardopen)

Figure 16 Dualcontrolsysteminterlockingwithoutcross-monitoring,bothchannelspneumatic

(guardclosed)

Guard openCylinder

(a) Interlocking

valves


(b) Interposed

control valves

Guard closedCylinder

(a) Interlocking

valves


(Air operated)

(b) Interposed

control valves



Health and Safety

Executive

Figure 17 Dualcontrolinterlocking,onecontrolchannelpneumaticandoneelectric,withelectriccross

monitoring(guardopen)

Figure 18 Dualcontrolinterlocking,onecontrolchannelpneumaticandoneelectric,withelectriccross

monitoring(guardclosed)

Cylinder Guard open

Interlockingswitch

(electric)

Interlocking

valve(Pneumatic)

Monitor

Control

valves

A B

Power

controlvalve

2nd channelinterposed powercontrol valve

Sol A

Monitor C

Cylinder Guard closed

Interlockingswitch

(electric)Interlocking

valve(Pneumatic)

Monitors

Controlvalves

A B

Powercontrol

valve

2nd channelinterposed powercontrol valve

Sol A

Monitor C



Health and Safety

Executive

Figure 19 Guardoperatedpowerinterlockingwithscotchtopreventdrillfallingundergravity.Alsofitted

withguardlocktopreventinadvertentopening

Power interlocking

133 Powerinterlockingisachievedbydirectmechanicalactionofavalveinthe

mainairsupplyinserieswiththeactuator.Themechanicalactionmaybe

directfromguardmovement(seeFigures10and11)viaalinkage,bya

captivekeyoratrappedkey.

134 Interlockingbymeansofairisolationandexhaustmaycausedifficultieson

machinerywhichreliesontheairsupplytokeepheavyarticlessuspended

orcomponentsclampedinposition.Similarly,wherecomplexmachinery

isdesignedtoperformaseriesoffunctionsinsequenceautomatically(see

Figure14),airisolationandexhaustinterlockingcouldleadtotheneedforpotentiallydangerous,extensivemanualre-settingofactuatorsand

sequencingvalves.Forthesereasons,powersystemmethodsofinterlocking

arenotnormallypracticableforcomplexairoperatedmachineryandhence

controlsysteminterlockingofthepilotsignalshastobeused.

135 Wherepracticable,however,powersysteminterlockingofcomplexsystems

isbetterthansinglecontrolsysteminterlocking,providedthepower

interlockingvalveandthearrangementsbetweentheguardandvalveareof

similarorhigherintegritythanthecontrolsysteminterlocking.Inaddition,any

machinerypartswhicharesupportedbycompressedairandwhichwouldfall

undergravitywhentheairisisolatedandexhaustedshouldbeautomatically

scotchedwhiletheguardisopen.

136 SuchprecautionsareshowninFigure19,thelayoutofwhichisinlinewith

BSISO1219-2recommendations.HazardsarisefromactuatorsAl,A2,

A3andA5,whichneedsafeguarding.Also,A3operatesverticallyandwill

V3

V2

V1

Run

Singlecycle

Clamp

A1

B11 Clamp

A2

B22 B21

Drill

A3

ScotchA4

B31

Drill

A5B52 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 V2

Guard locks(A7+)A1+A2+A3+A5+

A2 - A3 - A5.

Guard unlocks (A7 -)A61 & A62 -

Machine stopsOpen guardScotch engages (A4+)



Health and Safety

Executive

fallundergravitywhenairsupply,throughtheguardoperatedinterlocking

valve,isexhausted.Thecircuithasthusbeenarrangedsothat,withthe

guardopen,A3isscotchedusingasingleactingcylinder.Oncetheguardis

closedthescotchwithdrawsandtheguardislockedsothatthesequence

cannotbebrokenbyinadvertentlyopeningtheguard.Thecompletesingle

cyclesequenceisindicatedinFigure19,whereitcanbeseenthattheguard

unlockstoallowmanualfeedingifnecessary.Continuouscyclingcanbe

effectedbyoperatingthevalvelabelledrun.If,duringuse,amalfunction

occursrequiringtheguardtobeopened,thiscanonlybeachievedby

shuttingthestopvalveinthemainairsupplyline.

137 Alltheseproblemshighlighttheneedforthemachinedesignerto

considercarefullytheoverallsystemdesigntoensurethattheinterlocking

arrangementsareeffective.Althoughinmanycasesinterlockingthepilot

signalsratherthanthepowersupplymaybetheonlypracticalsolution(see

Figure14),thisshouldbealastresortonly.

Circuit design

Piston arrest

138 Whereitisnecessaryjusttoarrestthemovementofapistonwhenaguard

isopen,thiscanbeachievedbyusingeithertwothree-port,two-position

valves(seeFigures6and7)oranequalisingvalve(seeFigures8to11).Ifan

equalisingvalveisusedthepistonmaynotstopimmediately,butitwillseek

anequilibriumpositionwherebyforcesonbothsidesofthepistonareequal.

ThecircuitinFigure6willallowmanualrepositioningofthepistonwithout

disconnectingpipes(dependingonthefrictioninthesystem).Neitherofthese

techniquesissuitableforclampingorsupportingapplications.

Piston arrest and hold

139 Where,forsafetyreasons,thepistonmustbearrestedandheldinposition,

twotwo-portcontrolvalvescanbeused(seeFigures4and5).Thepistonwill

seekanequilibriumpositionbeforecomingtorest.However,ahazardcould

ariseifconnectionstothecylinderarebrokentosubsequentlyoverridethe

lockedposition.Airexhaustingthroughthebrokenconnectioncouldallowair

underpressureontheoppositesideofthepistontoexpand,therebycausing

movementwhichcouldleadtoinjury.

Overriding locked position

140 Wherethelockedconditionmustbeoverriddenwhiletheguardisopen,a

two-portstopvalvecanbeaddedtothecircuit(seeFigures4and5).Thiswouldnormallyhaveblockedportsbutbydepressingthestopvalveboth

sidesofthecylinderareopenedtoatmosphere,enablingthepistontobe

movedmanually.

Predetermined position

141 Itmaybenecessarytoensurethatpistonsadoptapredeterminedsafe

positionintheeventofpowersupplyfailing.Againtheuseofsingleacting

cylindersmaybepossiblebutanalternativeistouseareservoirand

nonreturnvalvearrangement(seeFigures12and13).Itisimportantto

ensurethatwherereservoirsareusedtheyareofsufficientcapacitytoensure

thatthepistondoesnotstallinanunsafeposition.



Health and Safety

Executive

Inspection and maintenance


142 Therearespecificstatutoryrequirementsfortheexaminationand

maintenanceofpressuresystemsincludingairreceivers(seeparagraph

30).Inadditiontothespecificrequirements,generalrequirementsareset

outinSection2(2)(a)oftheHSWActandPUWER:employersmustprovide

andmaintainplantandsystemsofworkthatare,sofarasisreasonably

practicable,safeandwithoutriskstohealth.Thefollowingadviceisaimedat

assistingemployerstocarryoutthisduty.

Hazards

143 Faultfindingonpneumaticmachinerycanbehazardousifitisnotproperly

planned.Themachinedesignshouldincorporatemeansofminimisingthe

needfortrialanderrormethodsoflocatingafault.Furtherassistancecanbe

giventofaultfindingbyincorporatingdiagnostictechniqueswhichindicate

theareaofafault(seealsoparagraph100).


144 Theefficientsaferunningofacompressedairsystemreliesoncleanliness,

filtration,coolingandlubrication.Thebestwayofachievingthesefour

conditionsistooperatetheplantinaccordancewiththeoperatorsmanual

andtodrawupandfollowawrittenscheduleofmaintenanceworkwhichcan

berevisedinthelightofexperience.Thisisaformofsafesystemofwork.

Thewrittenscheduleshouldidentifyareasforattention,howoftenattention

shouldbegivenandtheresponsibilitiesofthosewhocarryoutandsupervise

thework(seeparagraphs146and147).

145 Thefrequencyofinspectiondependsverylargelyonthecircumstancesand

environmentinwhichtheplantisused.ThefrequencystatedinthisBooklet

shouldthereforebetakenasaguideonlyandadjustedtosuitparticular

installationsinthelightofoperationalexperience.

Maintenance of compressors and ancillary plant

Supervision and procedures

146 Smallcompressorunitsareeasilyoverlooked,especiallyifsitedinaseparate

enclosureoutsidetheworkingarea.Particularcareisneededtoseethat

regularmaintenance,inspectionandtestingiscarriedout.Proceduresshould

belaiddownandrecordskept.

147 Theusershouldnominatearesponsiblepersontosupervisetheproper

operationandmaintenanceofthecompressorplantinlinewiththe

manufacturersinstructions.

148 Thispersonshouldregularlycheckthatallinstructionsregardingoperationandmaintenanceareproperlyfollowedandthatthecompressor,its

accessoriesandsafetydevicesarekeptingoodworkingorder.The

responsiblepersonshouldalsomakesurethatmaintenanceworkiscarried

outonlybyadequatelytrainedstaff.



Health and Safety

Executive

149 Althoughtherearestatutoryrequirementscoveringsomeaspectsof

maintenance,thefollowingadditionalmaintenanceproceduresare

recommendedtominimisethelikelihoodofhazardsoccurring.

Daily

150 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

Weekly

152 Eachweekthesafetyvalves(wheredesignallows)shouldbecheckedby

easingthembyhand.

600 hours

153 Aftereach600hoursofrunning:

(a) thequalityofoilinthecrankcaseshouldbecheckedand,accordingto

themanufacturersrecommendations,replacedifnecessary;and

(b) theconditionoftheinletairfiltersshouldbecheckedandthoroughly cleanedorreplaced.Theintervalbetweensuccessivereplacements

willbedeterminedbylocalcircumstancesbutis,toacertainextent,

controlledbythecapacityofthefilterandthecleanlinessofthe

atmosphereinthevicinity.Whereoilwettedviscousfiltersareused,

spareunitsshouldbeprovidedandexcessoilshouldbedrained

fromthefilterunitsforatleastfourtoeighthoursbeforetheunitsare

replaced,exceptwherethemanufactureradvisesotherwise.

Six-monthly

154 Whereoilcokedepositsareliabletooccur,theexplosionriskcanbereduced

bycarryingoutsix-monthlyinspectionsofthedeliveryportsandpipework

andcleaningasrequired.Theperiodbetweeninspectionscanbemodifiedinthelightofexperiencegainedfromoperatingaparticularinstallation.



Health and Safety

Executive

2000 hrs or annually

155 Aftereach2000hoursofrunningorannually(whicheveristhesooner):

(a) inthecaseofoillubricatedcompressors,thedeliveryvalves,portsand

allthepipework,vesselsandfittingsbetweenthedeliveryportandthat

pointinthesystem

atwhichtheairtemperaturecanbeconfidentlyexpectedtobebelow

80C,shouldbeinspected.Anycarbonaceousdepositshouldbe

effectivelyremoved;

(b) fusiblepelletsorcompleteplugsshouldbereplaced;

(c) theconditionofprotectivedevicesshouldbecheckedandtestedto

determinethattheyoperatecorrectly;

(d) theintercoolerandaftercoolersectionsshouldbecleaned;

(e) theradiatorshouldbedrainedandwashedout;

(f) theoutputcontrolgearshouldbecleanedandinspected;and

(g) theairreceivershouldbethoroughlycleanedandexaminedinternally.

Precautions

156 Allmaintenancework,otherthanroutinecheckstofiltersdesignedfor

cleaningin-service,shouldbeundertakenonlywhenthecompressorhas

beenstopped,disconnectedandlockedofffromthepowersupplyandall

internalpressuredissipated.Otherprecautionsmayalsobenecessary:for

example,thecompressormayhavetobescotchedtopreventmovementof

themechanism.

157 Undernocircumstancesshouldflammableliquidsbyusedforcleaning.

Appropriatesafetyprecautionsshouldbetakenagainstanytoxicvapours

liberatedduringusageofanycleaningordegreasingliquids.

158 Anopenflameshouldneverbeusedforinspectingtheinteriorofa

compressor,pressurevesselorpipework.

Maintenance of air powered equipment

159 Dirtyandwetairandworncomponentsareamongthemostcommon

causesofhazardsassociatedwithairpoweredequipment.

Supervision and procedures

160 Theusershouldnominatearesponsiblepersontosupervisetheregular

inspectionandmaintenanceoftheequipment.Wheretheequipmentisextensive,someformofwrittensystemofplannedmaintenanceshouldbe

usedandrecordsoftests,repairsandmodificationskept.

161 Inadditiontoanymaintenancerequiredbystatutoryrequirements,the

followingmaintenanceproceduresarerecommended.

Daily

162 Thesystemshouldbecheckedforleaksandrepairscarriedoutas

necessary.

163 Attheendofeachdayanyaccumulationofwatershouldbedrainedfromthe

drainpoints.Thedrainvalvesshouldbeinspectedtomakesurethattheyarenotchokedwithsediment.



Health and Safety

Executive

Weekly

164 Attheendofeachweek,airlinelubricatorsshouldbetoppedupas

necessarywiththecorrectgradeofoilandcheckedtoensurethattheyare

providingadequatebutnotexcessivelubrication.Filtersshouldbechecked

andthosethatarecloggedorcausingunacceptableflowrestrictionsshould

bereplaced.

165 Similarly,onmachineswhichrequirepressureregulationbelowmains

pressure,thepressureregulatorshouldbecheckedtomakesurethatithas

notbeentamperedwithandthatthecorrectpressureismaintained.

Monthly

166 Allhoseswhicharesubjecttoflexingand/ormechanicaldamageshouldbe

inspectedforsignsofcrackingordeteriorationandreplacedasnecessary.

Particularattentionshouldbepaidtoareasadjacenttocouplings.

Three monthly167 Everythreemonthsmachineswithinterlockingguardsshouldbechecked

tomakesurethatallinterlockingvalvesarefirmlysecuredandoperated

positivelybytheircams.Checkthatwearinanylinkagesorvalveoperating

mechanismsisnotsoexcessivethatthevalveisindangerofmalfunctioning.

Six monthly

168 Everysixmonthsallstopvalvesshouldbechecked.Checkthataccessto

thevalvehasbeenmaintained,thatthehandleisinposition,thatitwillshut

offtheairsupplyandthatitwillopenfullyandoperatefreely.

Precautions

169 Beforeanypressurisedcomponentsaredismantledtheyshouldbeeffectively

isolatedfromallpressuresourcesandcompletelyventedtoatmosphere.

Precautionsshouldalsobetakentoguardagainstthepossibilityofinjury

throughsuddenreleaseoftrappedsprings.

170 Whencomponents,especiallyvalves,arefoundtobewornandservicekits

ofsealsareusedtorebuildthem,careshouldbetakentocheckthoroughly

thefunctionoftherebuiltvalvebeforeplacingitintheequipment.For

convenience,manufacturersofservicekitsoftenincludeenoughsealsto

servicearangeorfamilyofvalves,althoughnotallthesealsinthekitare

requiredforeachvalve.Incorrectsealreplacementcancompletelyalterthe

valvesfunctionandifreplacedintheequipmentcouldpresentaserioushazard.Manufacturersshouldsupplyclearinstructionsonhowtousesuch

servicekitsproperlyandsupervisorsshouldensurethatthisinformationis

passedontothepersoncarryingoutthemaintenance.



Health and Safety

Executive

Training


171 Section2(2)(c)oftheHSWActandManagement Regulations and

Regulations 8 & 9 of the Provision and Use of Work Equipment Regulations

(PUWER)requireseveryemployertoprovidesuchinformation,instruction,

trainingandsupervisionasisnecessarytoensure,sofarasisreasonably

practicable,thehealthandsafetyatworkoftheiremployees.Sections7and

8oftheHSWActplaceresponsibilitiesonemployeestotakereasonablecare

toco-operatewithemployersandnottointerferewithormisuseanything

providedfortheirsafety.

Hazards

172 Allthosewho,inthecourseoftheirwork,needtousecompressedair

mustbeproperlytrained.Manyaccidentswouldbeavoidedifadequate

trainingwasprovided.Itisprobablybecausecompressedairsuppliesare

socommonplace,beingfoundatmostgarageforecourts,forexample,that

employersfalselybelievethattrainingintheiruseisunnecessary.

Precautions

173 Supervisorsandworkersincludingmaintenancepersonnelmustbegiven

propertraininginsafeworkingpractices.Thetrainingshouldstressthe

hazardsassociatedwithcompressedair(seeparagraph2)andshould

highlightthefollowingpoints:

(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

ThefollowingfivepublicationsareproducedbytheEuropeanCommitteeon

ManufacturersofCompressors,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



Health and Safety

Executive

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,4theditionISBN090560802Xand

A guide to compressor noise reductionLondon,underrevision

EuropeanOilHydraulicandPneumaticsCommittee(CETOP)Hydraulic and

pneumatic systems circuit diagramsLondon

(PNEUROP,BCASandCETOPpublicationsareavailablefromtheBritish

CompressedAirSociety,33/34DevonshireStreet,LONDONW1N1RF)

RoyalSocietyforthePreventionofAccidents(ROSPA)Beware compressedairBirmingham,(IS303)(availablefrom:ROSPA,CannonHouse,ThePriory,

Queensway,BIRMINGHAMB46BF)

BritishAggregateConstructionMaterialsIndustryCompressed Air SafetyLondon

(availablefrom:BritishAggregateConstructionMaterialsIndustry,25Lower

hsg39-Compressed air safety.pdf

Documents

Transcript of hsg39-Compressed air safety.pdf