ita guideline high pressurized chamber

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ITA Working Group N5Health & Safety in Works

ITA REPORT N 010 / FEV 2012N ISBN: 978-2-9700776-4-0

G UIDELINES FOR GOOD WORKING PRACTICE IN HIGH PRESSURE COMPRESSED AIR


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ITA Report n 010 - Guidelines for good working practice in high pressure compressed air - N ISBN: 978-2-9700776-4-0 / FEV 2012

Layout : Longrine Avignon France www.longrine.fr

The International Tunnelling and Underground Space Association/Association Internationale des Tunnels et de lEspace Souterrain (ITA/AITES) publishes this report to, in accordance with itsstatutes, facilitate the exchange of information, in order: to encourage planning of the subsurface for the benet of the public, environment and sustainable development to promote advancesin planning, design, construction, maintenance and safety of tunnels and underground space, by bringing together information thereon and by studying questions related thereto. This reporthas been prepared by professionals with expertise within the actual subjects. The opinions and statements are based on sources believed to be reliable and in good faith. However, ITA/AITESaccepts no responsibility or liability whatsoever with regard to the material published in this report. This material is: information of a general nature only which is not intended to address the speciccircumstances of any particular individual or entity; not necessarily comprehensive, complete, accurate or up to date; This material is not professional or legal advice (if you need specic advice,you should always consult a suitably qualied professional).


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ITA Working Group N5Health & Safety in Works

PREPARED JOINTLY BY

INTERNATIONAL TUNNELLING ASSOCIATIONWORKING GROUP N5 - HEALTH & SAFETY IN WORKS

AND

BRITISH TUNNELLING SOCIETY COMPRESSED AIR WORKING GROUP

G UIDELINES FOR GOOD WORKING PRACTICE IN HIGH PRESSURE COMPRESSED AIR


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>> FOREWORD

4 GUIDELINES FOR GOOD WORKING PRACTICE IN HIGH PRESSURE COMPRESSED AIR

At its meeting in Vancouver in 2010, International Tunnelling Association

Working Group N 5, identied the need for guidance on the use of high

pressure compressed air. WG5 dened this as work in compressed air

at pressures above historical statutory limits, which in most countries are

between 3 and 4 bar (gauge), and which involves the use of breathing

mixtures other than compressed natural air and can involve the use of

saturation techniques.

High pressure compressed air working was a topic of interest which hadpreviously been addressed by the British Tunnelling Society Compressed

Air Working Group and which BTS CAWG had identied as a signicant

development in the use of hyperbaric techniques on site for which no

guidance existed.

Consequently the two organisations have come together to jointly produce

the rst edition of these guidelines for use by the international tunnelling

community.

This document will be reviewed and revised as necessary in the light of

practical experience of HPCA work on site. Comment and feedback is

welcomed and should be made to the ITA Secretariat through the website

www/ita-aites.org.


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>> T ABLE OF CONTENTS

5ITA WORKING GROUP N5 HEALTH & SAFETY IN WORKS

FOREWORD ..................... ......................... ......................... ........................ ............ 4

1. INTRODUCTION ......................... ........................ ......................... .................... 6

2. LEGISLATION, STANDARDS, GUIDANCE ETC ........................ .................... 7

3. NOTIFICATIONS, EXEMPTIONS AND APPROVALS ........................ ............ 8

4. ORGANISATION OF WORKS IN HPCA ......................... ........................ ...... 10

5. SAFE SYSTEM OF WORK AND OPERATIONAL PROCEDURES ............. 12

6. PLANT, EQUIPMENT AND GAS SUPPLY ...................... ......................... ..... 13

7. OCCUPATIONAL HEALTH ......................... ......................... ......................... . 18

8. HYPERBARIC PROCEDURES ...................... ......................... ...................... 19

9. RECORD KEEPING ........................ ......................... ........................ .............. 22

10. EMERGENCY PROCEDURES ....................... ......................... ...................... 22

11. INFORMATION, INSTRUCTION AND TRAINING ..................... .................. 23

12. ACKNOWLEDGEMENTS ...................... ......................... ......................... ..... 24

GLOSSARY OF TERMS AND ABBREVIATIONS ........................ ...................... 25


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2 >> S AFETY REQUIREMENTS IN ALL STAGES OF CONSTRUCTION

GUIDELINES FOR GOOD WORKING PRACTICE IN HIGH PRESSURE COMPRESSED AIR6

1 >> INTRODUCTION

1.1 BACKGROUND

In recent years several tunnels have beenbuilt which required the application of high pressure compressed air (HPCA) forinterventions in the head of the TunnelBoring Machine (TBM). This is a signicantdevelopment in hyperbaric activity intunnelling and has required the transferof hyperbaric technology, from the divingindustry to tunnelling.

1.2 SCOPE

These guidelines apply to the use of HPCA in tunnelling (including shaft sinking).

To date, such work has been mainlyassociated with TBM interventions formaintenance and repair. However it isforeseeable that conventional tunnellingoperations may have to be undertaken inHPCA.

The guidelines are intended for use byregulatory authorities, clients, designers,

contractors, insurers and others involved inHPCA work.Whilst this guidance is intended toapply to HPCA work as dened above,the guidance is equally applicable tointermediate pressure exposures above3.5 bar.

1.3 MINIMISING HYPERBARICEXPOSURE

It is implicit when undertaking HPCA work in accordance with these guidelines,that all reasonably practicable measuresshould be taken to minimise the numberof persons exposed along with thepressure and duration of each exposure,commensurate with minimising the overallrisk to the health and safety of thoseexposed.Note: there are measures such as remotewear detection and the use of CCTV whichcan be used alone or in conjunction withother ground stabilisation techniques(see Cl 1.7) to further reduce the need for HPCA interventions.

1.4 BALANCING MEDIUM

In the HPCA work covered by theseguidelines, the pressurising mediumenvisaged in the working chamber is

compressed natural air except wherestated otherwise. Non-air mixtures usedfor breathing are fed through a mask andunbilical.

1.5 CHOICE OF HYPERBARICTECHNIQUE

High pressure, non-sat exposures onlypermit short working periods becauseof the relatively lengthy decompressionrequirements required from suchpressures. Hence for exposures atpressures in excess of 5 bar, saturationworking should be considered. See Cl 8.1for further guidance.

1.6 EXISTING STATUTORY LIMITS ONPRESSURE

In many countries existing limits onexposure pressure do not appear to havechanged since work in compressed airwas rst regulated. Although there may notbe evidence to show how statutory limitswere derived, there is ample evidence thatthey were adequate for the requirementsof the tunnelling industry of the day asrecords show very few exposures to

pressures close to the limit. The inferenceis therefore that they were based on adegree of empiricism which reected boththe state of knowledge and the practicalworking limits which could be achievedwith air breathing in the early to mid 20 th century when most countries with statutorylimits set these limits. The pressures nowbeing considered for HPCA work are wellwithin the range of pressures routinelyexperienced in offshore commercial diving.Consequently it is concluded that there isnothing inherently unsafe about exposureto higher pressures per se , provided

appropriate safe systems of work areadopted.

1.7 OTHER GROUND STABILISATIONTECHNIQUES

Other ground stabilisation techniqueswhich are utilised in tunnelling includegrouting, ground treatment, groundfreezing and dewatering. These guidelinesdeliberately give no guidance on the oftencomplex issues around selection of anappropriate ground stabilisation technique.

The guidelines apply to the use of HPCA once the decision has been madeto use it.


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3 >> P LANNING FOR EMERGENCIES

ITA WORKING GROUP N5 HEALTH & SAFETY IN WORKS 7

2 >> LEGISLATION , STANDARDS , GUIDANCE ETC

2.1 NATIONAL LEGISLATION,STANDARDS AND GUIDANCE

These Guidelines are intended tocomplement existing national legislation,standards and guidance as appropriate.

As HPCA work is still a rarely used butdeveloping technique, few countries arelikely to have altered existing legislationand guidance to accomodate it.

These guidelines should be read inconjunction with the current version of theguidance documents listed in 2.3 and 2.4(and 2.5 where relevant).

2.2 ILO CONVENTION C167

The International Labour Organisationconvention C167 on Health and Safetyin Construction has been ratied by 24countries and requires through Article 21Work in compressed air:

out only in accordance with measuresprescribed by national laws or regulations.

carried out only by workers whosephysical aptitude for such work has beenestablished by a medical examination andwhen a competent person is present tosupervise the conduct of the operations.

2.3 RELEVANT GUIDANCE SOURCES -TUNNELLING

Although no comprehensive guidance

on HPCA has been identied, a numberof organisations provide highly relevantbackground guidance and information.

These Guidelines build extensively on theinformation which they provide.

2.3.1 ITA Report N001 The International Tunnelling AssociationReport N001 Guidelines for goodoccupational health and safety practicein tunnel construction was published in2008 and has a section covering work incompressed air. The report was draftedto apply within national statutory limits

and consequently does not have specicrequirements for HPCA work.

2.3.2 EN 12110 Tunnelling Machines Air Locks Safety RequirementsCEN/TC151/WG4 has conrmed thatEN 12110 would apply only to work incompressed air within national statutorylimits, assumed to be between 3 and4 bar. However WG4 recognised thatEN 12110 could be used to informrequirements for air locks for use in HPCA.Where reference is made to EN 12110, it isthe current version of the standard whichshould be used.Note: CEN/TC151/WG4 TunnellingMachinery is a working group of theEuropean Standard technical committeeCEN/TC151 Construction Machinery Safety. WG4 is responsible for EN 12336Tunnelling machines - Shield machines,thrust boring machines, auger boring

machines, lining erection equipment Safety requirements and EN 12110Tunnelling machines Air locks Safety

requirements. EN 12336 is currently being revised and will be harmonised as

EN 16191 Tunnelling machinery - Safety requirements.

2.3.3 British Tunnelling Society Guideto the Work in Compressed AirRegulations 1996.

The British Tunnelling Society (BTS)document Guide to the Work inCompressed Air Regulations 1996which was published in 2012, is a revisedand updated version of the guidancewhich was formerly published by theHealth and Safety Executive (HSE) aspublication L96. The BTS Guide primarily

covers work in compressed air within theexisting UK statutory limit of 3.45 bar.However the possibility of HPCA work had been foreseen when the Regulationswere drafted in 1996. Consequently theGuide to the Work in Compressed AirRegulations 1996 recognises the use of HPCA and provides extensive informationof fundamental relevance to HPCA work.

2.3.4 BS 6164:2011 CoP forhealth and safety in tunnelling in theconstruction industry

This British Standard has a sectiongiving guidance on work in compressedair. It complements the BTS Guide byaddressing the design of the tunnel/groundinterface, effects of compressed air on theground and air loss. It also gives guidanceon a range of emergency situations whichcould arise. The principles covered arerelevant to HPCA work.

2.4 RELEVANT GUIDANCE SOURCES DIVING

The hyperbaric techniques requiredfor HPCA are very similar to those fordiving at similar pressures but withoutbeing immersed in water. From the1970s onwards, diving technology andhyperbaric safety advanced greatly withthe exploitation of oil in the relatively deepwaters of the North Sea. Consequently

there is much relevant guidance to be hadfrom diving sources.

2.4.1 Classication societiesClassication societies are the majorinternational insurance companieswhich set detailed rules for the design,construction and testing of equipmentfor use in the marine environment. Thisincludes the hyperbaric systems used indiving and other underwater hyperbaricactivity. At least one classication societyhas already developed specic rules forthe tunnelling environment. Care should

be taken to ensure their application isappropriate, when transposing rulesintended for the marine environment to theunderground environment. The Contractorin Charge should be aware that theserules will most likely be applied to plantand equipment used in HPCA work as acondition of the insurance of the works.Reference is made to classication societyrules in these guidelines.


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2 >> LEGISLATION , STANDARDS , GUIDANCE ETC


2.4.2 Diving Medical Advisory Committee

The Diving Medical Advisory Committee(DMAC) (see www.dmac-diving-org) is aEuropean organisation comprising divingand hyperbaric medical experts fromcivilian, military and clinical backgroundswhich provides guidance on a range of issues relating to the medical aspects of hyperbaric exposure in diving. Even thoughthe much of its guidance is not relevant tothe environments in which the hyperbaricexposure occurs, some DMAC guidance isequally applicable to HPCA exposure.

2.4.3 HSE diving guidanceHSE publishes extensive guidance oncommercial diving, some of which isequally relevant to HPCA work.

2.5 ASME PVHO STANDARDS

The American Society of MechanicalEngineers produces standards for

pressure vessels for human occupancy(PVHO). Although reference can bemade to them as an alternative to EN12110 or Classication Society rulesas a source of guidance, any tunnellingspecic requirements in EN 12110 shouldbe adopted in addition to the ASMErequirements.

2.6 GUIDANCE FROM OTHERCOUNTRIES

2.6.1 Germany For non-saturation exposures, theDruckluftverordnung (Technical regulationfor compressed air application) applies.

This should be referred to along with theRAB 25 (Regeln zum Arbeitsschutz auf Baustellen Rules for occupational healthand safety on construction sites).

2.6.2 CanadaCanadian Standard Z275 .1-05Hyperbaric Facilities providescomprehensive guidance on requirementsfor hyperbaric chambers including thosefor saturation systems. Canadian StandardZ275.3-09 provides guidance on work incompressed air.


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3 >> X XXXX XXXXX


3 >> NOTIFICATIONS , EXEMPTIONS AND APPROVALS

3.1 NOTIFICATION OF REGULATORY AUTHORITY

In some countries it is a statutory requirementto notify the regulatory authority foroccupational health and safety or labourinspection of the intention to work incompressed air. Whether this is a requirementor not, it is strongly recommended that therelevant authority is notied and their advicesought.

3.2 EXEMPTIONS, VARIANCES AND APPROVALS

In countries where there are statutory limitson hyperbaric exposure, and/or prescribeddecompression procedures, it is likely thatHPCA work will require formal exemptionfrom or a variation in statutory requirementsprobably accompanied by a formal approvalof part or all of the exposure proceduresproposed. Similarly the use of non-airbreathing mixtures may require exemption,

variance or formal approval. As part of theapplication process a robust safety caseshould be prepared and submitted to theregulatory authorities setting out the technicalreasons dictating the need for HPCA interventions and justication of the hyperbaricprocedures being proposed.

In countries where there is no statutory powerof exemption etc, the advice of the nationalregulatory authority on how to proceed,should be sought at an early stage in planningthe project.

3.2.1 Technical justication A full technical justication of the proposeduse of HPCA should be made includinginformation on likely ground and ground waterconditions (see also Cl 5.2). It should includeinformation on proposed tunnel excavationand lining techniques along with informationon the airlocks and other plant and equipmentrequired for the hyperbaric interventions

3.2.2 Exemption The supporting evidence for an application foran exemption from regulations should include:

justication of why the exemption isconsidered necessary;

supporting the exemption.

exempted

3.2.3 Approval of alternative hyperbaricprocedures

The package of supporting evidence forapproval of alternative hyperbaric proceduresdecompression regime should includea description of the compression anddecompression procedures, exposure limitsand breathing mixtures. Where an alternativedecompression regime is proposed, thepackage of evidence should include:

approved;

evaluation or hyperbaric trials of the tables;

use using recognised measures of DCIincidence where available;

benets of the proposals;

supporting the application;

effectiveness of the hyperbaricprocedures throughout their use on site.Such a scheme should allow for post-

decompression physiological monitoring atthe level of individual exposed persons.

decompression illness and osteonecrosisusing the proposed procedures and acomparison of these risks with thoseoccurring from the use of the existingdecompression tables currently used in thecountry concerned.

3.2.4 VariancesIn some countries, the regulatory authoritygrants variances. These are formalpermissions to depart from or vary statutoryrequirements. Where there is no guidanceon how to apply for and issue a variance,the regulatory authority should treat them asexemptions and/or approvals as appropriate.

3.3 DEMONSTRATION OFEFFECTIVENESS OF DECOMPRESSIONREGIMES

On completion of all HPCA work, theContractor in Charge should prepare a reporton the effectiveness of the decompressionregimes used on the project. This should bebased on the statistical analysis of exposuredata and post-decompression physiologicalmonitoring of workers.

3.3.1 Derivation of the tables to be usedWhen relevant the submission should includedetails of the proposed compression and

decompression regime along with informationon how the decompression tables werederived and validated. This is not required fornationally recognised tables. However thechoice of such tables should be justied.

3.3.2 Mathematical modelling ofdecompression tablesPhysiological mathematical models of thehuman response to pressure exist and can beused as part of the process of demonstratingthe effectiveness of decompression regimes.

The models can be used to predict gas inblood levels and as part of the retrospective

analysis of exposure data. A relevant referenceis HSE Contract Research Report 201/1998Decompression risk factors in compressedair tunnelling: options for health risk reduction,Unimed Scientic Ltd, available from www.hse.gov.uk.


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3 >> NOTIFICATIONS, EXEMPTIONS AND APPROVALS / 4 >> ORGANISATION OF WORKS IN HPCA

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3.3.3 Statistical analysis A number of recognised parameters forreporting the results of statistical analysis of exposure data are available. Where sufcientdata exists it is recommended that singleexposure risk factors are used to calculatethe incidence of decompression illness andthe standardised bends ratio is used forcomparison between datasets. Both measuresare described by Lamont and Booth in Acutedecompression illness in UK tunnelling, ProcInst of Civil Engineers, London, Paper 14384,Nov 2006.

3.3.4 Details of personnel, expert advisersetc

The submission should include details of the qualications and expertise of the mainpersonnel to be used in overseeing HPCA work along with similar details for expertadvisers to the project

3.4 PROHIBITION ON THE USE OFOXYGEN AND NON-AIR BREATHING

MIXTURES

Where national regulations do not allowthe use of oxygen and/or non-air breathingmixtures, additional exemptions, approvals orvariances should be sought to cover their use.

The principles for such applications, set outelsewhere in this clause should be followed.

4.1 CONTRACTOR IN CHARGE

Experience has shown that there shouldbe a contractor with overall responsibilityfor the HPCA work the Contractor in

Charge. The Contractor in Charge shouldbe able to provide the senior personnelto manage the HPCA work from his ownresources. The Contractor in Chargeshould be responsible for ensuring that allplant and equipment necessary for HPCA work along with the personnel to operateand maintain that plant and equipment,are immediately available on site. Therecommendations in the BTS Guide,on personnel required and managementof work in compressed air, should befollowed.

4.2 NOTIFICATION OF PUBLICEMERGENCY SERVICES

The Contractor in Charge should notify thepublic emergency services for the area of the works, of the HPCA work. In additionany off-site facility operating a hyperbaricchamber to which HPCA workers mightbe taken in an emergency should benotied of the typical exposure regimesbeing operated on site, the decompressionbeing undertaken along with the breathingmixtures and gases used. There should bediscussions between the CMA along withthe contractors hyperbaric experts andthe hyperbaric facility over the maximumpressure capability of the facility andpossible treatment regimes which thatfacility could/should provide, to reectthe exposures being undertaken on site.

The facility should have contact details of a responsible person on site with whomcontact can be made at any time.

4.3 EMERGENCY PLANNING

Given the relative rarity of any compressedair tunnelling work, the local emergencyservices may have had no experienceof dealing with hyperbaric emergencies.

Therefore the Contractor in Chargeshould assist the services in planning theirresponse to an on-site emergency. Thatassistance should extend to the provisionof equipment and training facilities asnecessary. Where the emergency servicesare unable to respond, and this is likelyto be the norm, the Contractor in Charge

should make provision for emergencyresponse from within his own resources.

4.4 EMERGENCY EXERCISES

The Contractor in Charge should work withthe emergency services to allow them toundertake simulations and joint exercisesto improve their ability to respond toemergencies. Such exercises should beundertaken early in the works period andat intervals of not more than 12 monthsthereafter.

4.5 EXPERT HYPERBARIC ADVICE

The Contractor in Charge should haveaccess to expert hyperbaric advice. Likelytopics with which the hyperbaric expert(s)should be familiar include internationalpractice in hyperbaric exposure, plant andequipment, the availability and selectionof appropriate decompression regimes,gas and breathing mixtures, saturationand TUP techniques if appropriate andhuman physiology relevant to hyperbaricexposure.

4.6 ROLES TO BE DISCHARGED BY PERSONNEL

It is essential for the execution of HPCA work in a healthy and safe manner that a numberof personnel are nominated by the Contractorin Charge to take on various roles relating tothe management or undertaking of the work.

All those nominated should be competentand have had relevant previous experience

as appropriate, of managing, overseeing orundertaking work in compressed air or otherhigh pressure hyperbaric exposure alongwith knowledge of the tunnel environment.Given the rarity of HPCA work, it is likely(and could be desirable) that for thosemanaging or overseeing the work, part of that experience would have been gainedfrom a diving support role in the offshoresaturation diving industry. Those managing oroverseeing HPCA work do not need to holddiving qualications but should hold relevanthyperbaric support qualications (see the BTSguide).

It is recommended that the personnel and theroles set out in the BTS guide are adoptedfor HPCA work but with the changes notedbelow.

4.6.1 Hyperbaric supervisorFor HPCA work the role of the hyperbaricsupervisor as described in the BTS guideshould be extended to overall control andcoordination of both the hyperbaric andtunnelling aspects of each intervention. Thehyperbaric supervisor would effectively be adeputy to the person in charge. The personlling this demanding role should have hadexperience of HPCA work and also extensiveexperience of the tunnelling environment.

GUIDELINES FOR GOOD WORKING PRACTICE IN HIGH PRESSURE COMPRESSED AIR


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4 >> O RGANISATION OF WORKS IN HPCA


4.6.2 Gas attendantWhen deemed necessary by thehyperbaric supervisor, there should be aperson responsible for the organisation of gas supplies on site. Such a person shouldhave had experience of the managementof gas supplies in saturation diving aswell as an appreciation of the tunnelenvironment.

4.6.3 Lock attendant The lock attendants should have hadprevious experience of lock keeping atsimilar pressures to those to be usedon site. They should also have hadexperience of using exposure techniquesand breathing mixtures similar to those tobe used on site. This experience may havebeen gained in the diving industry howeverfamiliarity with the tunnelling environmentis also necessary. Lock attendants shouldalso control the hyperbaric aspects of TUPshuttle use.

4.6.4 Umbilical tenderWhen using line fed masks, there shouldbe a person in the manlock or intermediatechamber (see Cl 6.9) to tend the umbilicalsof those in the working chamber. Oneperson can tend no more than twoumbilicals simultaneously.

4.6.5 HPCA worker selection Those being exposed to HPCA should bemedically t. In addition they should beinstructed in and have sufcient knowledgeof the risks of hyperbaric exposure tobe able to work safely in a hyperbarictunnelling environment using non-airbreathing mixtures. They should preferablyhave had previous experience of workingin hyperbaric environments in tunnelling.Inevitably however, because of the rarity of HPCA work, they may come from a divingbackground. If so they should demonstratetheir ability to transfer their skills to HPCA in the tunnelling environment. There arelikely to be benets in HPCA work frombuilding a team of workers made up fromboth diving and tunnelling backgrounds.

4.6.6 Saturation workersBecause of the nature of saturationworking, its psychological and socialimpact requires special qualities in thosedoing the work. No-one should beconsidered for saturation working unlessthey can demonstrate having successfullyundertaken such work previously in eitherthe diving or tunnelling industry or haveundergone specic training and beenassessed as suitable. HPCA workersshould ideally hold an offshore commercialdiving qualication in saturationtechniques. Appropriate internationallyrecognised qualications are listed on theHSE website at http://www.hse.gov.uk/ diving/qualications/approved-list.pdf.


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5 >> S AFE SYSTEM OF WORK AND OPERATIONAL PROCEDURES

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5.1 SAFE SYSTEMS OF WORK

The requirements for safe systems of work set out in the BTS Guide are generallyapplicable to HPCA and should beadopted with modications as necessaryto reect the higher pressures. No work should be carried out on the TBM whichcould endanger those undergoing HPCA exposures whilst work in HPCA is beingundertaken. Additional requirements areset out in these guidelines.

5.2 FACE SUPPORT AND AIR LOSS

It is of fundamental importance to thesafe execution of HPCA work that thestability of the ground is maintained alongwith the structural integrity of the tunnellining. Calculations should be preparedto demonstrate that these requirementsare being met. Independent checking(Category 3) of the calculations shouldbe undertaken. In addition, it is important

to ensure that the correct air pressure ismaintained in the working chamber withoutexcessive air loss. The design input datashould be updated as actual data on watertable and the geological strata becomeavailable from site (see also Cl 1.3). Thecalculations should be submitted as partof the technical justication required underCl 3.2.1.

Additional sources of air loss such asaround the tailskin of the TBM shouldbe considered and appropriate remedialaction taken if required.

5.3 DUTY LOCK ATTENDANTS

There should be two lock attendantson duty at a hyperbaric control panelwhenever the health and safety of anyonein saturation or undergoing HPCA exposure is dependent on that panel.

5.4 FACE INTERVENTIONPROCEDURES

Before any face intervention takesplace, the stability of the ground and theavailability of suitable protective measuresnecessary to enhance stability should beconrmed.Before anyone enters the manlock to becompressed, the working chamber shouldhave been pressurised and air pressuremaintained for at least one hour. All valvesshould have been shown to be functionallyoperative.

5.4.1 Slurry TBMOn a slurry TBM, slurry in the excavationchamber should be allowed to seal theface to minimise air leakage, before anintervention takes place. Ensuring that thebentonite slurry, used prior to or for rellingthe excavation chamber during anintervention, has the correct properties andis subject to strict quality control of the

bentonite slurry is an essential aspect of the overall safety of the HPCA work.

5.4.2 EPB TBMIn permeable ground the excavatedmaterial in the excavation chamber shouldbe mixed with bentonite slurry during thelast advance cycle before entry to theexcavation chamber takes place.In cohesive ground the conditionedmuck in the excavation chamber can belowered without prior injection of additionalbentonite suspension.

5.5 REFILLING HEAD WITH SLURRY WHILST DECOMPRESSION STILLGOING ON

5.5.1 Slurry TBMOn a slurry TBM, the cutterhead should berelled with slurry as soon as possible afterHPCA work has been completed and theHPCA workers are sealed in the manlock,to maintain face support. This requirementmay conict slightly with requirements indocuments such as the BTS Guide or EN12336 regarding energising of equipment onthe TBM during hyperbaric interventions, butit is an essential precaution for HPCA work.

5.5.2 EPB TBMRestarting an EPB in a controlled mannerafter an intervention is a highly criticalactivity especially for larger diametermachines. Depending on the facepermeability two different proceduresare possible. If the face is permeable,bentonite suspension should be

pumped into the excavation chamberbefore restarting the advance. In lesspermeable soils, it is assumed that the

TBM will restart without the need to rellthe excavation chamber with bentonitesuspension.Note: Filling the chamber with bentonite

may produce a chamber ll that its too liquid to be discharged via the screw conveyor whilst maintaining full pressurecontrol. The restarting procedureeliminates any information about volume

loss or mass balance for a signicant amount of t ime and needs very stable face

conditions .

5.6 INCHING OF CUTTER HEAD

When designing a TBM for HPCA use,due account should be taken to ensurethe requirements in EN 12336 relating toaccess to the cutter head or excavationchamber and rotation of the cutter headin jog mode can be complied with whenaccess is by means of a manlock.



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5 >> SAFE SYSTEM OF WORK AND OPERATIONAL PROCEDURES/ 6 >> PLANT, EQUIPMENT AND GAS SUPPLY

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5.7 ACCESS IN CUTTER HEAD

The increased difculty in movingaround the cutter head and excavationchamber when wearing an umbilicalfed mask should be recognised duringmachine design and construction so thatappropriate access can be provided.

5.8 WELDING, CUTTING AND OTHERHOT WORK

Welding, burning and other hot work shallonly be carried out in HPCA in accordancewith a permit to work system. Thoseundertaking such work should normallywear outer garments made from a highlyame resistant material such as Nomexor equivalent. These garments shouldcompletely cover the head, neck and torsoas well as covering the shoes.Notes: There should be a person

immediately available and capable of responding to an outbreak of re during

hot work.It is important to ensure the correct dimensioning and installation of welding

supply cables as there have been incidents in the past in which hot cables have been a source of ignition.

5.9 USE OF EXPLOSIVES

Explosives should not be used underHPCA. Non-explosive techniques for rock bursting should be used instead.

5.10 CLAMPING OF BULKHEAD

DOORS

It should be possible to clamp shut thedoor between a manlock chamber and theworking chamber.

6.1 PLANT AND EQUIPMENT

6.1.1 All HPCA work The Contractor in Charge should ensure suitableand sufcient plant and equipment is availableon site, whenever needed, to undertake safelyand without risk to health, both the HPCA work,and any action which may be necessary in theevent of a reasonably foreseeable emergencyconnected with the HPCA work.

In the absence of national requirements,the plant and equipment shall meet therequirements of these guidelines alongwith the requirements in the BTS Guide,EN 12110 and relevant classicationsociety rules.

Assisting the Contractor in Chargein complying with this requirement isan important part of the hyperbaricsupervisors duties.

6.1.2 Saturation operationsIn addition to the requirements above,for saturation exposures a transfer underpressure shuttle, a saturation livingcomplex on the surface for storage of personnel under pressure and handlingequipment for the TUP shuttle shall beprovided.

6.2 RESTRICTIONS ON HPCA DUE TOTUNNELLING CONSIDERATIONS

In order to undertake HPCA work safely aconsiderable amount of space is requiredon the TBM. This is particularly relevantto TUP operations and hence saturationexposure. The geometrical constraints thispresents have a signicant bearing on theminimum diameter and type of TBM onwhich HPCA work can be undertaken.

It is suggested that geometrical constraintsmake TUP using the TBM airlock, andhence saturation working, impractical onEPB machines below 6 m in diameterbecause of conict with the screw

conveyor and erector and on slurry TBMsbelow 5 m in diameter because of conictwith the erector.

In smaller tunnels where it may not bepossible to use a TBM airlock, it will benecessary to install one or more bulkheadsin the tunnel. As much of the TBM backupequipment as possible should be movedback to allow the bulkhead(s) to bepositioned close to the rear of the TBMshield. In particular all hydraulic uid tanksand grease injection stations should beremoved. Major electrical installationsshould be de-energised.

Electrical power to essential services in theworking chamber should be supplied fromappropriate low voltage sources situatedoutside the working chamber.

6.3 ACCESS AND WORKING SPACEON TBM

The TBM should be designed andconstructed to provide adequate workingspace to access and operate the manlock safely. When HPCA operations are beingundertaken a working platform shouldextend for at least 2m on the free air sideof the manlock door to provide workingspace and to facilitate the removal of acasualty from the manlocks. The workingplatform should also accommodate theworkstation for the lock attendant and theair lock control panel.Note: if space on the TBM is limited, theworking platform may be a temporary

structure which is set up only for theduration of the HPCA work.

Likewise there should be a clear path topermit the passage of the TUP shuttle fromits transport vehicle to the manlock. Thisarea should be adequately lit.

6.4 MINIMUM LOCK DIMENSIONS

The dimensions of the manlocks shouldnot be less than those set out inEN 12110.

6.5 LOCATION OF LIVING HABITAT

The saturation living habitat should belocated on the surface in a purpose builtstructure and fully protected from adverseweather and temperature uctuations.

There should be a workstation for the lock attendants and the hyperbaric controlpanel.

The structure should be lit and heated/ cooled as necessary. The structure shouldbe protected by a water spray or highpressure water mist re extinguishingsystem.

ITA WORKING GROUP N5 HEALTH & SAFETY IN WORKS


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6 >> P LANT , EQUIPMENT AND GAS SUPPLY

14

6.6 SUITABILITY OF PLANT ANDEQUIPMENT

All plant and equipment should be suitablefor the maximum foreseeable workingpressure taking into account seasonalground water variations or tidal variationsas appropriate.

6.7 INSPECTION MAINTENANCE ANDTESTING

The Contractor in Charge should ensurethere are formal inspection maintenanceand testing procedures for the plantand equipment, taking account of themaximum foreseeable working pressure.

This should also take account of nationalrequirements for the inspection and testingof pressure systems. They should takeaccount of the requirements of the BTSGuide, EN 12110, relevant classicationsociety rules or the requirements of theinsurers of the Contractor in Charge

should be adopted. Full records should bekept of all inspection, maintenance andtesting.

6.8 EMERGENCY BREATHING SUPPLY

Where the working pressure is above5 bar, there should be the immediatecapability to supply an emergencybreathing mixture to each person underpressure in the working chamber. It shouldcomprise a suitable mask or helmet andindependent source of breathing mixture.

The quantity of emergency breathing

mixture available shall be at least sufcientto allow all persons under pressure toreturn to the manlock and to remain on theemergency supply until breathing from themasks in the manlock or from the manlock atmosphere itself, can be established witha reserve of at least 10 minutes (see Cl6.24).

6.9 UMBILICALS

Each person in the working chambershould have a single multiline umbilicalsupplying breathing mixture andcommunication lines to that person. Theumbilical casing should protect the linesfrom damage. Where there is a needfor an emergency supply of breathingmixture, a second breathing mixturesupply line should be provided in theumbilical. To permit rapid evacuation of the working chamber in an emergency,all umbilicals should originate in a placeof relative safety outside the workingchamber. This can be in the manlock orin an intermediate chamber which canbe securely isolated from the workingchamber. This intermediate chamber(motor chamber in the illustration below)can be considered as rst point of escapeor safe area but should not be consideredas manlock chamber for compression ordecompression purposes. There should

then be provision for transfer to themanlock chamber whilst still breathing theappropriate breathing mixture.

There should also be an on-board systemto supply breathing mixtures to those inthe TUP shuttle. It should be set up in away which will not impair the operation of the access door(s) between the man lock and the transfer shuttle.

6.10 COMMUNICATIONS

All masks or helmets for use in theworking chamber should be tted withan appropriate two way communicationssystem. For non-sat exposures, an integralcommunications system is requiredwhenever the mask or helmet has thepotential to interfere with normal verbalcommunication.

6.11 TUP SHUTTLE

The transfer under pressure shuttleshould be designed and constructedin accordance with relevant standardse.g. classication society rules andrelevant principles for airlocks. Its sizeshould reect the guidance on minimumdimensions in EN 12110. The TUP shuttleshould be of double chamber constructionas for manlocks. The shuttle shouldbe tted with all necessary life supportsystems including appropriate backup

capacity.

6.12 COUPLING

Pressurised systems should be ttedwith safety interlocks where necessary, toprevent any unintentional pressurisationor de-pressurisation, or uncontrolled lossof pressure. Particular attention should bepaid to chamber mating systems, and food


Example of typical intermediate chamber arrangement on slurry TBM


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15

and equipment locks. The requirements inthe BTS Guide and EN 12110 regardingthe opening of doors should be observed.

It should be possible to pressurise thetrunking with either air or breathingmixture.

It is imperative that it should be impossibleto open the mating clamp when thetrunking between the TUP shuttle andthe PVHO with which it is being mated,remains under pressure. The clampingmechanism should be equipped with aninterlock which makes it impossible torelease a clamping mechanism in the eventthat an undesirable drop in pressure wouldthen take place.

Appropriate performance criteria forcoupling systems including mating angescan be found in classication society rules.Germanischer Lloyd has a set of rulesspecically covering HPCA work.

Note: the term NATO ange seems to beused to denote a ange to STANAG 1079.There is no European or international

standard for mating anges and clamps.

The person operating the clampingmechanism must make sure that openingit will not cause an undesirable drop inpressure. There should be a clearly denedmethod for incrementally increasing ordecreasing trunking pressure as part of clamping procedures.

6.13 MOVEMENT OF TUP SHUTTLE

TO/FROM AND AROUND THE TBM

Transport of the TUP shuttle in thetunnel should be by a dedicated vehicle.

There should also be a standby vehicleavailable in the tunnel to move the shuttlein the event of breakdown. There shouldbe appropriate mechanical handlingequipment to facilitate the transfer of theshuttle between vehicles.

All vehicles involved in TUP transportshould have a xed, manually operated,on-board re protection system coveringmotor compartments, fuel tanks,switchgear, transmission systems, wheels

and tyres as relevant. A double shotsystem may be required to cover the tyresof rubber tyred vehicles to counter re-ignition of the tyres.

Movement of the shuttle should preferablybe by sliding or jacking. The movementpath should be designed avoid the need tolift the shuttle by crane whenever possible.Where craneage for TUP handling, isrequired, the crane must fully meetrecognised standards for personnel lifting.In the absence of national requirements atthe place of use, a factor of safety of 10should be applied to the hoist ropes.

All mechanized equipment for TUPhandling should be considered to be anessential service and meet the relevantrequirements for continuity of powersupply in EN 12336.

During all these movements, the lifesupport system for the shuttle should

remain under the direct control of a lock attendant . This can temporarily be theteam leader inside the capsule providedhe is competent to do so and the internalequipment of the capsule is properlydesigned to allow control to be exercisedfrom inside the capsule. At any time, alock attendant outside the shuttle shouldbe able to take over full control of the lifesupport system.

6.14 EMERGENCY TRANSFER FROMLOCK TO DEDICATED VEHICLE

There should be sufcient redundancyand/or diversity in the handling system,that a failure of one part of the systemdoes not prevent transfer of the TUPshuttle to the dedicated vehicle.

Tunnel workers involved in the shuttletransfer should have ready access to self rescuers.

6.15 EMERGENCY POWERCONTINUITY

All necessary steps should be takento ensure continuity of power to safetycritical equipment associated with the

hyperbaric operations for at least the timetaken to perform decompression or toremove those under pressure from thetunnel. Such equipment includes lightingand communications systems for the lock attendants station.

6.16 AIR AND GAS SUPPLY TO TUPSHUTTLE

The TUP shuttle should be mounted on asupport frame. The frame should have thecapability to carry an appropriate quantityof compressed air and breathing mixtureto maintain pressure in and life support tothe shuttle for at least 12 hours longer thanthe predicted journey time. The quantityof compressed air should as a minimumbe sufcient to pressurise the shuttle toworking pressure twice, from atmosphericpressure. There should be additional non-return valved ttings on to which additionalair and/or breathing mixture supplies canbe connected in an emergency.

6.17 SHUTTLE DOORS

Internal communicating doors in the TUPshuttle should be shut, and a seal shouldbe obtained when mating or unmatingto a manlock or the transfer of personnelor equipment is taking place. Thesedoors should not be opened again untilthe internal door between the transferchamber and the connecting tunnel hasbeen shut.

6.18 COLOUR CODING OF GAS

CYLINDERS AND PIPEWORK

Gas cylinders and pipework should becolour coded in accordance with nationalstandards in the country of use or whereno such standards exist, in accordancewith an internationally recognised colourcoding scheme such as EN 1089-3: 1997Transportable gas cylinders . Gas cylinderidentication (excluding LPG). Colourcoding using the colours for set out forgases used in diving. An alternativestandard is ISO 32:1977 gas cylinders formedical use marking for identication of content .



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6.19 MAN LOCK CONTROL PANEL

The TBM should be designed toincorporate a panel from which allhyperbaric operations on the TBM canbe controlled. It should be rememberedthat unlike in intermediate pressurecompressed air working, it may notbe safe to breath the high pressurecompressed air used as the pressurisingmedium because of the risk from nitrogennarcosis or oxygen toxicity. Accordingly,control of the HPCA work is a safety-critical operation.

During HPCA work, this panel, themanlocks and all services necessary fortheir safe operation should be consideredessential services (term as used in EN12336), on the TBM . It should be locatedclose to the manlocks on the TBM. Thepanel should be laid out according togood ergonomic principles and shouldincorporate the following:

valves;

stopwatch facilities;

direction of operation and function of allvalves and gauges;

mixtures;

storing exposure and decompression data;

manlock compartment;

compartment and the working chamber ;

The control panel should be provided withan un-interruptible power supply. Seatingfor the lock attendant at the panel shouldbe provided. The area should be lit to aminimum standard of 100 lux at workingsurface level. Emergency lighting with aminimum duration of 12 hours should beprovided.

The hyperbaric control panel should betted with sufcient air-line fed full facemasks to provide a supply of respirable air

to enable the lock attendant(s) on duty, tocontinue to operate the panel even whenthe tunnel atmosphere is irrespirable. Theair supply should have a minimum durationof 3 hours. In addition, there should be aself rescuers for each attendant on duty.

When not in use, the panel should beprotected from dirt ingress and damageeither by a lockable cover or by removingthe panel. If the panel is removed allservices to the panel should be securelycapped.

6.20 FACE PIECES - MASKS ORHELMETS

The most suitable mask for purpose,should be used, taking account of the need to provide security of t andto minimise inward leakage. Full facemasks or helmets should be used inthe working chamber for sat exposureswhere the pressurising gas is different

to the breathing mixture. The breathingresistance should meet diving industrystandards.

6.21 VOICE SCRAMBLING DUE TOUSE OF HELIUM

Some voice distortion can be expectedfrom helium based breathing mixtures andappropriate equipment should be providedto compensate for that distortion.

6.22 EXCAVATION CHAMBERTEMPERATURE

Steps should be taken to ensure that noone should enter the excavation chamberwhen the TBM has just stopped andthe temperature in it exceeds 28C. Theexcavation chamber temperature shouldbe displayed on the hyperbaric controlpanel.Note: a water spray cooling system for thecutterhead can reduce waiting time.

6.23 OXYGEN SAFETY

This is extensively covered in the BTSGuide.

6.24 GAS OR BREATHING MIXTUREQUANTITY

6.24.1. Primary gas supply The quantity of each breathing mixturerequired in the tunnel for the HPCA work including decompression, along withan allowance for leakage, wastage andcontingencies should be calculated.

6.24.2. Secondary gas supply A secondary gas supply of at least the gasvolume required for decompression plus1/3 the primary gas supply for the workingphase of the exposure should be providedin the tunnel.

6.24.3. Emergency gas supply For HPCA work at pressures above 5bar, an emergency gas supply equivalentin volume to the secondary supplyshould also be provided in the tunnel.

The emergency gas supply should beconnected to the spare gas line in the

umbilical.

6.25 SEPARATION OF OXYGENSUPPLY FROM BREATHING MIXTURESUPPLY

There should be separate supply linesfor oxygen and breathing mixtures alongwith separate masks, umbilicals andconnection manifolds.



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17

6.26 GAS OR BREATHING MIXTURESOURCING

Gas and breathing mixtures should besourced from a reputable supplier normallysupplying the medical or diving sectors.

The supplier should be able to demonstratethat control of gas purity and blending of breathing mixtures conforms to a qualityassurance scheme complying with aninternationally recognised standard suchas ISO 9001. Gas purity should complywith national standards in the countryof use or where there are none, with arecognised standard such as the currentversion of BS 8478 Breathing gases fordiving and hyperbaric applications or EN12021 Respiratory protective devices.Compressed air for breathing apparatus.

It is essential that all gas including thatused to form breathing mixtures, shouldbe of medical or diving quality. For routineHPCA operations only pre-mixed breathing

mixtures should be used.

6.27 SAMPLING AND TESTING

The Contractor in Charge should ensure allgas or breathing mixtures are sampled ondelivery to site and again immediately priorto use to conrm their composition is asintended. The Contractor in Charge shouldensure that on delivery to site, all gas orbreathing mixture cylinders are properlycolour coded. Where more than one gasor breathing mixture is used on site, theContractor in Charge should ensure that

proper arrangements are in place for theseparate identication, marking, storageand handling of each to prevent accidentalmisuse.

6.28 GAS MIXING

For sat exposures, it may be preferableto have a gas mixing and reclaim plant onsite when the quantity being processedis sufciently large to make it reasonableto do so. The gas mixing and reclaimoperation should be set up as a stand-alone operation separate from any HPCA activity and preferably run by a reputablegas supplier. The plant should operatein accordance with a quality assurancescheme certied as conforming with ISO9001.

Cylinders of gas to replenish the stocks onsite should have their purity conrmed onarrival at the gaz mixing and reclaim plant.

Before leaving the plant for re-use in HPCA work, every cylinder should be tested tocheck its composition and purity meet thedata marked on the cylinder.

All gas or breathing mixture supplied fromthe plant should be treated as being froman off-site supplier and subject to thesampling and testing in Cl 6.25. the persontesting the gas or breathing mixture ondelivery to the HPCA work should not bethe same person as tested that cylinderprior to dispatch from the mixing plant.

The Contractor in Charge should notpermit the piecemeal mixing of smallquantities of breathing mixture on an ad-hoc basis for use in HPCA exposures.

6.29 OXYGEN SAMPLING

For all exposures where the breathingmixture is supplied from cylinders, thereshould be direct sampling of the supplyto the masks immediately downstreamof the control panel to permit analysis of the oxygen content. Analysis should beto an accuracy of +/- 0.1% by volume.

An audible alarm should sound when theoxygen concentration deviates by morethan +/- 1% by volume from the requiredoxygen content.

6.30 PROVISION OF GAS IN THETUNNEL

The Hyperbaric Supervisor should conrmthat the volume of breathing mixturerequired for each supply is available inthe tunnel and on the TUP shuttle, if being used, before HPCA work begins.Immediately before use he should satisfyhimself that the composition of eachcylinder of breathing mixture is correct.He should do the same for any oxygenrequired for decompression purposes.

6.31 LOSS OF FLOW

Where more than one person is beingsupplied by umbilical from a singlepanel, severance or disconnection of one umbilical should not result in loss ordeprivation of supply to the others beingfed from that panel.

6.32 CLEANING AND DISINFECTION

OF MASKS

The cleaning and routine disinfection of masks is important to prevent the growthof micro-organisms including fungi,yeasts, bacteria and viruses. Fungi areone of the most likely contaminants andthese can produce large quantities of spores. Inhalation of these spores cancause an allergic reaction in the lungs,producing potentially life-threateningconditions, particularly in those individualswho may be predisposed to allergy.

The recommendations of HSE Diving

Information sheet N 12 Cleaning of divingequipment should be followed.

6.33 STORAGE OF MASKS

After cleaning, masks and helmetsshould be bagged and stored in a cleanenvironment.

ITA WG5 HEALTH & SAFETY IN WORKS


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7 >> O CCUPATIONAL HEALTH

18

7.1 PROVISION OF OCCUPATIONALHEALTH ADVICE

The Contractor in Charge should appointan occupational health doctor, theContract Medical Adviser (CMA), toadvise on all aspects of occupationalhealth arising from the HPCA work. Thatdoctor should hold a recognised specialistprofessional qualication in occupationalhealth and be familiar with the tunnelenvironment and competent in currentgood practice in hyperbaric medicinefor the pressures anticipated along withthe medical, social and psychologicalproblems of saturation working whereappropriate. The doctor should act as theprofessional leader for the medical aspectsof the HPCA work throughout its duration.

The CMA needs to be on call whenever anHPCA operation is in progress.

7.2 HEALTH ASSESSMENT

All those undergoing HPCA work shouldbe subject to a health assessment regimeappropriate to the pressures being used.Where appropriate national requirementsdo not exist, the regime should takethe form of a stringent annual medicalexanimation to establish tness forHPCA work coupled with periodic healthchecks throughout its duration, to ensurecontinuing tness for such work. The CMA should advise on the form and content of the examination and should undertake theexaminations unless national requirementsdictate otherwise. Reference can be made

to the BTS guide . The results of theexaminations should be recorded. Clinicalrecords should be retained by the CMA inhis archive in a secure fashion complyingwith recognised professional standards.

Anyone intending to enter saturationconditions should have a medical check within the 24 hours before enteringsaturation, to conrm their tness.

7.3 HEAT STRAIN IN THEHYPERBARIC ENVIRONMENT

Those undertaking heavy physical work in the hyperbaric environment are at risk from heat strain. Wearing the full facemasks required for efcient breathingpurposes can further increase the risk.

The risk arises from the reduction inbody cooling from sweat evaporation,due to the pressurised atmosphere. Thenormal indices by which heat strain risk is assessed, such as wet bulb globetemperature are for normobaric conditionsonly (including exposure to sunlight)and should not be applied to hyperbaricexposure without rst seeking expertadvice.

7.4 GENERAL HEALTH CARE FORTHOSE LIVING IN SATURATION

In addition to normal occupationalhealth provision, for saturation working

the Contractor in Charge has to makeprovision for the general physical andmental healthcare and dental healthcare of those living in saturation. The CMA shouldbe able to advise on this matter also.

7.5 FIRST AID

7.5.1 General requirements The Contractor in Charge should ensurethere is adequate availability of emergencymedical and rst aid facilities for thoseunder pressure. This should cover theworking chamber, airlocks, any TUP

facilities and the living accommodation if insaturation.

7.5.2 Non-sat exposures All persons undergoing non-sat exposuresshould have had basic rst aid training.

7.5.3 Sat exposures All personnel undergoing saturationexposure should have had basichyperbaric rst aid training. This trainingshould cover the use of common itemsof rst aid equipment including oxygenadministration systems. In the absenceof an appropriate hyperbaric rst aidqualication, a diving rst aid qualication

is an acceptable substitute. A minimum of two trained diver medicsshould be at pressure in the chambersystem. Fewer than two could result inthe situation where the only trained divermedic is the casualty.

7.6 BIOLOGICAL INFECTIONS

Bacterial and fungal infections can readilyoccur in saturation living. The guidancefrom the DMAC should be observed. Noone suffering from such infections or theear, nose or throat infections which arenormally a bar to entry into compressed airshould undertake saturation exposures.

7.7 PHYSIOLOGICAL MONITORING

7.7.1 Use of physiological monitoringIt is recommended that physiologicalmonitoring of tunnel workers post-decompression, should be adopted as atechnique for assessing the effectiveness

of decompression regimes in real time. The monitoring should be undertaken byrecognised specialists using standardprotocols. Techniques available includeDoppler monitoring and ultrasonicscanning. Research is ongoing toimprove the interpretation of the resultsin the context of tunnelling exposure.

The Contract Medical Adviser should becompetent to advise on the use of these techniques and other indicators of clinical decompression stress.

7.7.2 Monitoring frequency

For tables with no history of satisfactoryuse, all persons exposed should besubject to physiological monitoring aftereach exposure, until the effectiveness of the tables has been established. Thereaftera representative sample of exposuresshould be checked to conrm the ongoingeffectiveness of the tables

7.7.3 Doppler monitoringRelationships exist between bubble scoreand what is considered an unacceptablyhigh risk of DCI. Because of inter andintra-individual variation, no indication of the absolute risk to the individual can beinferred from personal Doppler scores.



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7 >> O CCUPATIONAL HEALTH

19

Based on the Kisman Masurel scale, itis recommended that continued use of a particular decompression schedule beassessed if more than 20% of individualsmonitored routinely have Doppler scoresof grade III or above. Whilst any grade IV score is considered an unacceptably highrisk of DCI, it is not per se a reason to givethat person a prophylactic recompressiontreatment.

7.8 MEDICAL EQUIPMENT TO BEHELD AT THE SITE

It should always be possible to undertakeemergency recompression on site withsuitable supporting medical equipmentavailable. In addition it should be possibleto monitor blood pressure, pulse rate alongwith the mood and state of confusion of a casualty. Blood pressure and pulse ratecan easily be monitored automatically.

Where sat exposures are being undertakenin a location without ready access topublic emergency medical services, themedical equipment and supplies set out inthe current edition of Medical Equipmentto be Held at the Site of an Offshore DivingOperation DMAC 15 should be availableon site.

7.9 ASSESSING FITNESS TORETURN TO HPCA WORK AFTERDECOMPRESSION ILLNESS

No one should be exposed to HPCA

following a decompression illness eventuntil declared t by the CMA.



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8 >> H YPERBARIC PROCEDURES


8.1 CHOICE OF ROUTINE EXPOSURETECHNIQUE

Routine non-sat exposures at highpressure allow for only short workingperiods (typically 45 minutes at 6 bar (g)).Such exposures permit inspection andlimited maintenance only to be undertaken.Where signicant working periods arerequired for major maintenance, saturationworking should be undertaken. Whenthe exposure pressure exceeds 6 barthe useful working period available withnon-sat exposures but still adhering tothe 2 hour decompression limit (see Cl8.8) becomes impracticably short andsaturation exposure should be considered.For safety reasons, saturation exposureshould always be undertaken at pressuresof 7 bar and over.

8.2 MINIMUM OXYGEN CONTENT INCYLINDERS

All gas cylinders delivered to site shouldcontain at least a sufcient concentrationof oxygen to support life were they to beused in error. Helium cylinders shouldcontain a minimum of 2% oxygen byvolume. Nitrogen cylinders should containa minimum of 16% oxygen by volume.

8.3 GAS PROPERTIES AND LIMITS OFEXPOSURE

The following properties of gases andexposure limits should be taken intoaccount when designing a breathing

mixture

8.3.1 OxygenOxygen is toxic at high partial pressures.Consequently any breathing mixture inroutine use should provide the user withoxygen at a partial pressure of between0.2 and 1.6 bar.

Excessive chronic or repeated exposureto hyperbaric oxygen is harmful to health.Such exposure can be measured inunits of pulmonary toxicity dose (UPTD)(sometimes referred to as oxygen toxicity

dose (OTD) or oxygen toxicity unit (OTU)).Limits should be placed on maximum dailyand weekly UPTD arising from hyperbaricexposure. Hyperbaric oxygen dose shouldbe kept as low as possible consistent withgood hyperbaric practice. Recommendedmaximum limits for routine exposure are400 UPTD daily and 2000 UPTD overany period of seven consecutive days. Itshould be noted that additional oxygenexposure will be incurred if therapeuticrecompression becomes necessary. Theongoing risk of oxygen toxicity should bereviewed regularly by the contract medicaladvisor.

8.3.2 NitrogenNitrogen is a narcotic gas at high partialpressures. It also has a high gas densitywhich makes the work of breathing morestrenuous. Exposure to compressednatural air at up to 5 bar is acceptedin some diving legislation. Howeverthe narcotic effect of nitrogen at such

pressures is considered to create anunsafe and inefcient working situation.

Compressed air or any breathing mixturein routine use containing nitrogen, shouldprovide the user with a partial pressure of nitrogen (PN 2 ) not exceeding 3.6 bar. Thislimit is equivalent to breathing air at 3.5bar (gauge). Due to the narcotic effects of nitrogen, caution should be exercised inbreathing air giving a partial pressure of nitrogen (PN 2 ) of 3 bar and over.

8.3.3 Helium

Helium is a relatively rare and henceexpensive gas. It has a low gas densitywhich facilitates breathing in HPCA athigh work rates. It also has a high thermalconductivity which can be benecial incountering the effects of heat strain. Somevoice distortion can be expected fromhelium based mixtures. Exposure to heliumat high pressure can lead to high pressurenervous syndrome. The threshold at whichthis occurs is not clearly dened but canbe around 15 bar.

Heliox is an alternative to trimix or nitroxfor saturation exposure.

8.4 TRIMIX

Trimix may be considered as an alternativeto heliox or nitrox for saturation exposures.

Trimix is probably the breathing mixture of choice for non-sat exposures at pressuresabove 3.5 bar because it reduces gasdensity and the narcotic effects of nitrogen.

8.5 NITROX

Nitrox may be use for exposures aroundthe interface between the intermediate andhigh pressure exposure range but is of littleuse in normal HPCA work because of therelatively limited range of pressures overwhich it can be used

8.6 BASIC PRINCIPLES IN SELECTINGBREATHING MIXTURES

There is considerable exibility whenselecting the proportions of each gas in

the mix but the following principles shouldbe adhered to:

sat exposures should never be less than16% and the PO 2 in the mix should neverexceed 1.6 bar in use. For sat exposuresthe PO 2 in storage should be between0.35 and 0.45 bar.

PN 2 of more then 3.6 bar in use.

mixture which reduces the gas density.

which satises the above.


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8.7 AIR BREATHING DURING NON-SATDECOMPRESSION

8.7.1 Air breaks during oxygendecompression.

Appropriate air breaks should beincorporated in the oxygen stages of thedecompression regime used.

The ratio should be around 20 to 30minutes oxygen breathing interspersedwith 5 minute breathing on air as requiredby the decompression schedule beingused.

8.7.2 Period without use of masks. Tables which include periods wherea mask is not required to be wornmay be advantageous as they permitcommunication, rehydration, andcomfort breaks for the workers as well asfacilitating medical monitoring.

8.8 EXPOSURE LIMITS - NON-SAT

EXPOSURE

For reasons of worker comfort andcontrol of hyperbaric exposure the moreconservative of the following criteria shouldbe adhered to:

as to require a decompression time inthe manlock of not more than 2 hours. If longer decompression is required it shouldtake place in a saturation habitat.

decompression time should not exceed 3hours

8.9 SHIFT PATTERNS NON-SATEXPOSURES

For non-sat exposures a shift patternof ve days on, two days off should beadopted.

8.10 DECOMPRESSION TABLES

The Contractor in Charge should selectthe decompression tables to be usedtaking account of the advice of his experthyperbaric advisers and the ContractMedical Adviser.

Tables with a proven history of effectiveness are to be preferred.Un-proven tables should be subject to astringent verication process before theyare put into routine site use.

8.11 TREATMENT TABLES, OMITTEDDECOMPRESSION TABLES, OVERRUNNING PERMITTED EXPOSUREPERIOD

As part of the safe system of work, theContractor in Charge should with theadvice of the CMA, identify appropriatetreatment tables for use in treating DCI.Similarly, the Contractor in Charge should

with the advice of the CMA identifyprocedures for dealing with omitteddecompression and extended exposureperiods.

Additionally, procedures for dealing withthe use of incorrect breathing mixturesduring exposure if relevant should bedrawn up.

8.12 LOSS OF OXYGEN SUPPLY DURING DECOMPRESSION

There should be procedures in place

including an appropriate air-onlydecompression table for use in the eventthe oxygen supply fails.

8.13 LIVING HABITAT FORSATURATION

In general the chambers in which workerslive whilst in storage should satisfy therelevant requirements of one of theclassication societies. They shouldnormally be sited on the surface.

8.14 LIVING HABITAT

The living habitat should meet therequirements of this document.

It is recommended that there is a minimumvertical clearance of 2 metres above theoor of the living chamber and a minimumvolume of at least 4 cubic metres peroccupant. Some classication societies setadditional requirements for living chamberscovering bed size and washing/toiletfacilities.

The layout of the living chambers andsystem of work (team size, shift patterns,etc) should allow occupants to have therequired periods of rest and not be wokenup by other occupants going to/from the

TUP shuttle.

8.15 LIVING IN SATURATIONCONDITIONS

For saturation working, the Contractor inCharge has to extend the safe systems of work to cover the welfare and well-beingof those in the living chambers betweenexcursions. This includes the provisionof food and drink, the maintenance of a comfortable living environment, theprovision of washing and toilet facilities,rst aid and medical provision. The normalstandards of the saturation diving industryshould be followed. 8.16 SATURATION SHIFT PATTERNS

In order to ensure safe and efcientoperations, HPCA personnel shouldwork within a time routine which allowsthem to develop a regular work and sleeppattern. The minimum rest period in theliving complex should be 12 hours (i.e. notworking or carrying out pre or post-work checks). Therefore, when operations arecarried out on a 24/7 basis only one work period per 24-hour period is recommended.



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8.17 DURATION OF SATURATIONEXPOSURES AND SURFACEINTERVALS

Where relevant national requirements donot exist, it is recommended that no onewho is an experienced saturation workershould experience a saturation exposureexceeding 28 days under pressure.Otherwise the exposure should not exceed14 days.

Thereafter that person should not undergoany further exposure to HPCA until at leastan equal interval of time at atmosphericpressure has elapsed.

A persons cumulative saturation exposureshould not exceed 13 weeks in any 26week period.

Prior to decompression a person shouldhave a 12 hour pressure stabilisationperiod in the living complex. An excursionat the pressure of the living complex can

be part of this 12 hour period.

8.18 WORKING PERIOD

The maximum working period is calculatedfrom initial lock-off until the nal lock-onto the living complex and personnel areready to transfer. No more than oneworking period per day is recommended.

The maximum working period away fromthe living complex shall be 8 hours in a 24hour period. The working periods set out inthese guidelines may need to be reducedfor very heavy work.

As personnel are involved in tiring physicalwork, the hyperbaric supervisor shouldappreciate that it may be appropriate forthem to return to the manlock periodicallyfor a short rest and to take refreshmentbefore nishing their task. In any case, thehyperbaric supervisor should ensure thatthe personnel have a refreshment break of at least 15 minutes, between 3 and 4hours into the working period.

8.19 HYPERBARIC OPERATIONS

During the transfer from shutle to chamberor living complex and back again everyeffort should be made to avoid changesin temperature, in the composition of themixture being breathed and physiologicaleffects including isobaric counterdiffusion.

For tunnelling, it is normally desirable toset the storage pressure to the workingpressure and thus avoid the need fordifferent breathing mixtures for excursions.Where it is likely that excursions will berequired for operational reasons, storagepressure should be selected to minimisepressure changes during excursions. Theexcursion procedure should be selected tominimise undesireable physiological effectsin those undertaking the excursion.

Final decompression to atmosphericpressure should not be started with anexcursion to a lower pressure in the working

chamber. There should be a 12 hour stopin the habitat before nal decompressionbegins unless there has been no excursioninvolving a working pressure different tostorage pressure in the preceding 12 hours

8.20 REMAINING ON SITE AFTERDECOMPRESSION

Personnel undergoing HPCA exposuresshould remain on site or its immediatevicinity, for 2 hours after decompressionfrom non-sat exposures and for 24 hoursfollowing sat exposures. This will allow

time for physiological monitoring to beundertaken.

8.21 ASCENT TO ALTITUDE

Personnel undergoing HPCA exposuresshould not y or otherwise ascend toaltitude in excess of 150 metres or 500feet e.g. mountaineering or driving over hillyterrain, for 24 hours after decompression.Where geographical or logistical conditionsrender this requirement un-acceptablerestrictive, Contract Medical Advisersshould produce local rules for travelinvolving ascent above this height.


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9 >> R ECORD KEEPING

23

9.1 RECORD KEEPING

Exposure records should be made in thelanguage of the jobsite on which the HPCA work is being undertaken. Records shouldbe held in electronic format using one of the internationally available ofce softwarepackages. Record keeping should generallybe as described in the BTS Guide alongwith any additional requirements of thenational regulatory authority. In additiona full record of the composition of allbreathing mixtures and gases used alongwith the times and pressures at which theywere used should be kept for each workingexposure and subsequent decompression.Gas purity records should also be kept.

9.2 RECORDS OF SATURATIONWORKING

For saturation exposures, a full recordfor each person exposed should be keptstarting at the point of initial compression

until the end of the nal decompression,including details of each excursion from thestorage habitat.

9.3 DISTRIBUTION OF RECORDS

On completion of the work, in addition tocopies of the records given to individualsand their employers, a copy of all records,in its ofcial language, should be offeredto the national regulatory authority foroccupational health and safety in thecountry where the work was undertaken.

9.4 RETENTION OF RECORDS

The Contractor in Charge should retainthe records in the company archives for aperiod of 40 years from the end of HPCA work.

9.5 INDIVIDUAL RECORDS

On termination of employment, each personexposed should be given a full record of hisexposures on the project, details of trainingreceived, results of medical surveillance,along with details of any decompressionillness events experienced and theirtreatment



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10 >> EMERGENCY PROCEDURES


10.1 EMERGENCY PROCEDURES ANDCASUALTY EVACUATION

The Contractor in Charge should drawup a comprehensive set of emergencyprocedures covering reasonablyforeseeable emergencies including thosewhich require the evacuation of personneland casualties to a place of safety on thesurface. The Contractor in Charge shouldensure that all necessary equipment andpersonnel identied in the proceduresis immediately available for deploymentand that a comprehensive test of theevacuation procedures is undertakenand recorded before any HPCA work begins. Procedures should be revised asnecessary during the course of the worksand further tests carried out.

Typical emergencies include but are notlimited to:

in the working chamber/manlock/TUP

shuttle.

other PVHO

otherwise no longer available

10.2 FIRE PROTECTION WITHIN AND AROUND THE TBM LOCK

The requirements of the BTS Guide andEN 12110 in respect of re precautionsapply and should be supplemented bythe outcome of a project-specic re risk assessment of the HPCA work beingundertaken and all relevant site conditions.No productive work or maintenance work should be undertaken elsewhere on the

TBM whilst HPCA work is underway.

10.3 FIRE PROTECTION FORSURFACE FACILITIES

The buildings housing the saturationliving complex should be tted with acomprehensive sprinkler system. Thesebuildings should be constructed fromincombustible materials wheneverpossible.

The control panel should be equipped with

at least one independent compressed airrespirator for the lock attendant.

In addition, there should be sufcientoxygen self rescuers at the control panelfor everyone normally working there

10.4 HYPERBARIC SELF RESCUERSIN THE WORKING CHAMBER

A compressed oxygen self rescuer for usein hyperbaric environments was shownto be feasible by HSE in the 1990s butits manufacturers never put it into mass

production. The concept has been shownto be technically feasible. There is norestriction by HSE, on others to developthe concept further.

10.5 FIRE PROTECTION FOR GASCYLINDERS

Gas cylinders on the surface should bestored in a well ventilated and secureenclosure. It should be physicallyseparated from other buildings orprotected by a suitable re wall.Cylinders in use should be protected by asprinkler system.


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11 >> INFORMATION , INSTRUCTION AND TRAINING

25

11.1 INFORMATION, INSTRUCTION AND TRAINING

All those undergoing HPCA exposuresshould be given appropriate training inthe risks from such work and how theserisks should be mitigated. Referenceshould be made to the BTS Guide for acomprehensive list of topics. The trainingshould take full account of site procedures.

The theoretical t raining modules of internationally recognised diver trainingqualications give an indication of the levelof hyperbaric knowledge required for non-sat and sat HPCA workers.

Most of the HPCA interventions to datehave been undertaken by personnelwith diving experience. However it isforeseeable that conventional tunnellingoperations may have to be undertakenin HPCA. Personnel for such work would require experience as miners inconventional tunnelling techniques. The

additional training required to make suchpersons competent to work under HPCA would be extensive and should reect therisks associated with the work to be done.



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12 >> A CKNOWLEDGEMENTS


In addition to the contributions from their respective members,ITA WG5 and BTS CAWG acknowledge the direct or indirect

contribution to the drafting of this document from AdvancedMarine Pte Ltd, Babendererde Engineers, Ballard Diving andSalvage, Herrenknecht, Germanischer Lloyd, Health and SafetyExecutive, Hyperbaric and Tunnel Safety Ltd, IHC Hytech, JCLPHyperbarie, Dr J King, Tony Ridley Hyperbaric Associates,CEN/TC151/WG4, Hyperbarie SARL, McNally Corporation,Dr W Sterk, Vinci and Washington State DoT.


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>> G LOSSARY OF TERMS AND ABBREVIATIONS

27

Breathing mixtureNon-air respirable mixture, such as oxygenand nitrogen (nitrox); oxygen and helium(heliox) or oxygen, nitrogen and helium(trimix) capable of supporting human lifeunder appropriate hyperbaric conditions.

BTS Guide The British Tunnelling Societys documentGuide to the Work in Compressed AirRegulations 1996.

Compressed air workerPerson working in compressed air.

Contract Medical Adviser (CMA)Medical practitioner qualied inoccupational health who is permittedto practice in the location at which theHPCA work is being undertaken and whois responsible for all medical aspects of HPCA work.

Contractor in Charge

Contractor with overall responsibility forthe HPCA work, and not necessarily themain tunnel conractor.

Decompression illness (DCI) A ill health conditions result ing fromdecompression following exposure topressure.

Diver medic An advanced hyperbaric rst aidqualication endorsed by the InternationalMarine Contractors Association (IMCA) ornational equivalent.

Excursion A period in saturation away from the livingcomplex, spent in the working chambernormally at a different pressure to thestorage pressure.

GasUsed in this document to mean eitheroxygen or a breathing mixture.

Gauge PressurePressure above atmospheric pressure asin normal tunnel practice.

High Pressure Compressed Air (HPCA)workWork in compressed air at pressuresabove historical statutory limits, which inmany countries are between 3 and 4 bar(gauge), and which involves the use of breathing mixtures other than compressednatural air and can involve the use of saturation techniques.Note: In the past it was customary in somecountries to describe exposure pressuresfrom which stage decompression was

not required as low pressure and todescribe exposure pressures from which

stage decompression was required ashigh pressure. It is now proposed that the latter be referred to as intermediate

pressure i.e. pressure between low pressure and the statutory limit.

Health and Safety Executive (HSE) The UK regulatory authority foroccupational health and safety.

Isobaric counterdiffusion The diffusion of gases in differentdirections without decompression andwithout changes in the environmentalpressure which leads to the formation of bubbles.

Non-saturation exposure (non-satexposure)

A short duration exposure comprisinga compression, a working period underpressure, followed by a decompression.It does not involve any storage time in ahyperbaric living complex.

OxygenUsed in this document to mean oxygen of medical or diving grade.

Partial pressure (of a gas) The pressure of a gas in a gas mixture thatthe gas would have if it alone occupiedthe gas lled space (Daltons Law). It isnormally stated in bar and is the productof the absolute pressure of the mixtureand the volume fraction of that gas in themixture. In this document partial pressureof a gas (e.g. oxygen) is shown as PO 2.

PressurePressures in this document are stated inbar (gauge).

Pressure vessel for human occupancy (PVHO)Manlocks and similar pressure vessels inwhich persons are exposed to pressure.

Quad Transportable gas storage consisting of multiple cylinder congurations connectedto a common manifold, within a protectiveframe.

Saturation exposure (sat exposure) A long duration exposure during whichthe person exposed lives under pressureand may make transfers into the workingchamber.

StorageMaintenance of persons at pressure in ahyperbaric living complex.

Transfer under pressure (TUP) The transfer of persons betweenpressurised habitats whilst maintainingthose persons under pressure.

Tunnel Boring Machine (TBM) A machine which in Europe would comewithin the scope of EN 12336 (referencesto EN 12336 in this document to becomereferences to EN 16191 on harmonisationof EN 16191).

Tunnelling

In this document tunnelling includes shaftsinking and caisson work.

Working period (sat exposures) The elapsed t ime from when a personleaves the living complex for the workingchamber until that person arrives back inthe living complex.



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l o n g r i n e 0 4

9 0

1 4

4 8

4 8

- ( 2 0 2 8 2

- 1 1 / 1 1

)

ita guideline high pressurized chamber

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