AODC035 - Safe use of electricity underwater.pdf

IMCA

The Interna

Carlyle HouseTel: +44 (0) 20 7931 8171 Fax: +4

Guidance Note No: AODC 035

This Code was reviewed in 1993 and Its content therefore rem

The information contained herein is givFor the avoidance of doubt no legal liability shall

Code of Practice for

The Safe Use of Electricity Under Watertional Marine Contractors AssociationIncorporating AODC and DPVOA

, 235 Vauxhall Bridge Road, London, SW1V 1EJ, UK4 (0) 20 7931 8935 E-mail: [email protected] Website: http://www.imca-int.com

September 1985

again in 1996 and no amendments were considered necessary. ains as relevant now as when it was first published

en for guidance only and endeavours to reflect best industry practice.attach to any guidance and/or recommendation and/or statement herein contained.

Recognition

This Code:

has been "Accepted by the United Kingdom Department of Energy for Use inUnderwater Operations".

has been "Accepted by the United Kingdom Department of Transport for Usein Underwater Operations".

is regarded "As a Recommended Standard for the Safe Use of ElectricityUnderwater" by the Norwegian Petroleum Directorate.

is "Acceptable to the Canada Oil and Gas Lands Administration for Use inUnderwater Operations".

has been "Recognised by the Industrial Inspectorate of the Department ofLabour in Ireland for Use in Underwater Operations".

Every reasonable effort has been made to ensure that the guidance given in this document isbased on the best knowledge available at the time of finalising the text. However, noresponsibility of any kind for any injury, delay, loss, damage or cost whatsoever, howevercaused, resulting from the use of the document can be accepted by AODC or any of theCompanies. Organisations or individuals involved with its preparation or publication.Any person or organisation using the information within the document should satisfy itself thatthe guidance is directly applicable to their specific situation and should seek specialisedelectrical advice if any doubt exists.

AODC 035 September 1985 Page 3

Code of Practice for the Safe Use of Electricity Under Water

Contents

Foreword 3Scope 5Introduction 6Discussion 7

GLOSSARY 11

SECTION 1 - APPLICATIONS OF ELECTRICITY UNDER WATER 14

1.0 Introduction 141.1 Deck Compression Chamber (DCC) and Hyperbaric Evacuation System 171.2 Transfer Chamber, Submersible Compression Chamber (SCC) and

Diver Lock-Out Submersible 181.3 Diver Heating (Electrical) 201.4 Hand Held Equipment 211.5 Habitat 221.6 Wet Welding and Cutting 241.7 Sea Bed Equipment 251.8 Impressed Current Systems 261.9 Remotely Operated Vehicle (ROV) 271.10 Manned Submersible 281.11 Umbilicals 291.12 High Power Equipment 301.13 Surface Electrical Distribution 311.14 Fresh Water 321.15 Explosives 33

Summary Table of Active Protection Practices 34

SECTION 2 - INSTALLATION AND USE OF EQUIPMENT 38

2.0 Introduction 382.0.1 Protection Against Electric Shock 382.0.2 Passive Protection 38

2.0.2.1 Insulation 382.0.2.2 Fixed Barrier 392.0.2.3 Protective Clothing 392.0.2.4 Shielding 392.0.2.5 Suitability of Earthing 40

2.0.3 Active Protection 402.0.3.1 Residual Current Devices 402.0.3.2 Line Insulation Devices 42

2.0.4 Toxicity of Materials 422.0.5 Installation Practice 422.0.6 Batteries 43

AODC 035 September 1985

2.1 Deck Compression Chamber (DCC) And Hyperbaric Evacuation System 462.2 Transfer Chamber, Submersible Compression Chamber (SCC) and

Diver Lock-Out Submersible 482.3 Diver Heating (Electrical) 492.4 Hand Held Equipment 502.5 Habitat 522.6 Wet Welding And Cutting 542.7 Sea Bed Equipment 572.8 Impressed Current Systems 592.9 Remotely Operated Vehicle (ROV) 612.10 Manned Submersible 632.11 Umbilicals 632.12 High Power Equipment 632.13 Surface Electrical Distribution 632.14 Fresh Water 642.15 Explosives 64

SECTION 3 - SYSTEM DESIGN

3.0 Introduction 653.1 New Techniques 653.2 Reduction In Toxicity Hazard 65

3.2.1 Selection Of Insulating Material 653.2.2 Terminal Blocks And Circuit Boards 663.2.3 Quantity Limitation 663.2.4 System Design 66

3.3 Protection Against Explosion And Fire Risk 66

APPENDICES

Appendix A: Bibliography 69

Section 1: Some Relevant Codes Of Practice, Recommendations, Standards 69

Section 2: Some Technical Reference Papers 71

Appendix B: Useful Formulae 73

Appendix C: Detailed Graph Of Allowable A.C. Current In The Body 75

Appendix D: Earth Fault Current Restriction 77


FOREWORD

In September 1982 the UK Department of Energy published a 'Code of Practice for theSafe Use of Electricity Under Water'. This was intended as general guidance on thesafe use of electricity under water and not as a mandatory or contractual document.

The Department of Energy funded a number of research projects which formed part ofthe background to the 1982 code. Other projects were still in hand at the time ofpublication, and various assumptions and safety factors were built into that code.Subsequent experimental results and work carried out elsewhere, showed that someof these were unnecessarily conservative, and early in 1983 the Department of Energyinvited industry to take over responsibility for development of the code, taking intoaccount new material and experience of working with the 1982 document. AODCaccepted this invitation.

This new Code is based on the earlier document but its format has been altered tomake it more readily usable by designers, manufacturers, users and others. Itincorporates the latest information available from known research projects and theexperience of a wide cross section of interested organisations.

The preparation of this code was overseen by a steering group comprisingrepresentatives from a wide cross section of interested organisations. These were:

T. A. Hollobone ChairmanC. W. Logan Association of Offshore Diving ContractorsL. E. Virr Admiralty Research Establishment/

Experimental Diving UnitR. M. Mavin Department of Energy, Diving InspectorateT.D. White Department of Energy, Electrical InspectorateM. Robertson Department of Transport (Marine Directorate)L. A. Mollinder/ J.F. Wilson Det Norske Veritas (representing the certifying authorities)F. D. S. McCrudden Institution of Electrical EngineersR. J. Moulton MaTSU/UKAEAW. B. Norton NIFOB. A. Mathisen Norwegian Petroleum DirectorateR. W. Barrett Underwater Engineering GroupD. L. Judd UKOOA, Engineering and Development CommitteeJ. E. Hendrick UKOOA, Diving Advisory Committee

The first draft of this code was prepared by a working party made up of representativesfrom AODC member companies assisted by a number of steering group members.The working party included (at various times):

I. J. Murray Thalassa (Chairman)C. W. Logan Technical Secretary, AODCM. D. Collar Comex Houlder DivingD Beedie, A W Bissett Oceaneering InternationalT. E. Shore OSELJ. Malone Sub Sea OffshoreP. Downs ThalassaJ. Low UDI GroupA. D. Lamont, K. J. Gill, Wharton Williams TaylorA. J. Cameron

This working party continued to provide input into various drafts as the code wasdeveloped, based on their practical experience.


Meetings of the steering group were held between November 1983 and October1984, and several drafts of the new code were considered. Copies of the final draftwere sent to over fifty organisations for detailed review and comment in July 1984and comments received were considered by the steering group. Set out below is a listof those organisation (in addition to steering group members) who submittedcomments.

BEAMA (Federation of British Electrotechnical and Allied Manufacturers Associations)

British Rig Owners Association Clinical Research Centre

Department of Transport

ERA Technology Limited

General Council of British Shipping

Health and Safety Executive

Institution of Electrical Engineers

Institute of Marine Engineers

Lloyd's Register of Shipping

Nautical Institute

NUTEC

Royal Institution of Naval Architects

Shell UK Exploration and Production

UDI Group Limited

UK Offshore Operators' Association Limited

University of Manchester, Department of Occupational Health

The new code is based on the 1982 code, the most recent research work in the field,and a wealth of experience provided by the Working Party, the Steering Group, andthose who submitted comments on the final draft. Sincere thanks are extended to allof these, but in particular to Professor W. R. Lee of the University of Manchester andDr. H L. Green of the Clinical Research Centre for their advice on basic electricalsafety and physiological criteria: Ian Murray for chairing the Working Party; DavidJudd of UKOOA; Bob Moulton of MaTSU; Frank McCrudden of the Institution ofElectrical Engineers and Crawford Logan, Technical Secretary of AODC, for theirsupport throughout the project and in particular in assessing detailed technicalcomments on the final draft and ensuring that the code incorporates in a meaningfulway all those that were agreed by the steering group.

Finally, thanks are due to the Department of Energy and MaTSU for arranging for theproduction of the final drawings and circuit diagrams.

The new code should provide sound guidance to all concerned with the use ofelectricity under water whether designer, manufacturer or user. It will be reviewed asa result of experience gained in its use and future research.


SCOPE

This Code deals with the various hazards which may arise from the use of electricityunder water. The most obvious of these is electric shock. In addition, degradation ofelectrical insulating material by heat can result in the emission of toxic or explosiveproducts, and hot surfaces or electric arcs from faulty equipment or switching devicescan ignite some gas mixtures. All these hazards are included in the Code. All otherrisks associated with the use of electric power under water (mechanical risks, non-electric burns, ionising radiation, and generation of sound, ultra-sound and shockwaves) are excluded.

The Code covers all types of electrical equipment used by the diver or submersiblepilot or employed for his benefit and under his control or that of his support team. Inaddition, it covers some electrical equipment unrelated to the underwater operationbut capable of creating a risk to the diver or submersible pilot.

The Code considers the risks arising from the various environments encountered. Itmakes recommendations for the selection, installation and maintenance of electricalapparatus used to enable an adequate level of safety to be achieved.

The Code does not address electrical safety above water. This subject is adequatelycovered in other documents (see sections 1.13 and 2.13 for references) howeverpersonnel involved in maintenance or modification of surface equipment used inconnection with electricity under water should remember that the measures outlinedin this Code are designed to protect man under water and may not on their ownprovide adequate protection for surface crew. The question of surface back-upsupplies and levels of redundancy is also not covered.

The limits set on insulation material are based on information relating to thedecomposition of materials and the physiological effect of the decomposition productsat normal atmospheric pressures. The effect of higher pressure on these processes isnot yet fully known and when further information becomes available the Code maybe amended.

The recommendations apply to underwater operations in sea water, but thedifferences which exist in fresh water are also addressed to a limited extent.


INTRODUCTION

This Code of Practice is in three sections. Section 1 gives an overview of the use ofelectricity in an underwater environment. Section 2 is aimed at the installer and userwith particular reference to present day standards and practices. It also covers theselection and installation of equipment, the provision of protective systems and thecorrect selection of materials. Section 3 gives guidance to the system designer andwhen read in conjunction with Sections 1 and 2 provides the designer with an overallunderstanding of the environmental constraints and details of current practice.

The Code describes practices aimed at minimising the risk associated with the use ofelectricity under water whilst at the same time allowing maximum flexibility in thesupply and use of electric power.

The Code addresses the environments met in the various applications of electricityunder water.

The values used in the Code are based mainly upon the values contained in documentIEC 479 : 1974 (International Electrotechnical Commission) which are usedinternationally in many industries. Pertinent information from work carried out by ERATechnology Limited and the Clinical Research Centre under contract for the U.K.Department of Energy (D.En) specific to diving has also been incorporated. In additiona wide range of published literature and technical papers have been consulted.

The response of living tissue to electric shock, on land, has been well researched. Thisdata has been applied to the special conditions of divers working under water.


DISCUSSION

Electrical Safety - Derivation Of Values

Research over many years has been aimed at determining the levels of safety forelectricity in contact with humans.

A number of different levels of electric shock have been established causingrespectively, Sensation (or Perception), Pain, Involuntary Contraction of Muscles andVentricular Fibrillation (when the heart pumping muscles become out ofsynchronisation). Electric shock can be fatal and the different levels often overlap. Insome circumstances Involuntary Contraction alone can cause death.

Individuals exhibit different reactions to electricity, and an electric shock which isonly just perceptible to one person can cause pain to another. For this reasonresearchers have used as large a number of subjects as possible, in order to arrive ataverage values and safety levels have been set to allow for the most susceptible. Thefactors causing these levels of shock are variable, for example, the duration of theshock is critical.

The most widely accepted international standard on the effect of electricity on thehuman body is report number 479 of the International Electrotechnical commissionpublished in 1974 (IEC 479). This document gives values for effective resistance of anindividual for various contact paths and also values of current which can flow safelythrough the body in different circumstances. These values are intended for use onland and, when they have been applied under water, arbitrary safety factors have beenapplied to the IEC values to allow for possible unknown effects such as pressure.

IEC 479 was based on experimental work by many researchers, including ProfessorLee in the U.K., Professor Dalziel in the U.S.A., and Professor Biegelmeier in Austria.Doctor Green of the Clinical Research Centre in London, has shown that many of thevalues in IEC 479 can confidently be applied to the underwater situation directlywithout the need to add safety factors (Appendix A Sect. 2 ref. 18). AdditionalResearch has demonstrated certain areas in which the values in IEC 479 can beextended although some of the values in the document may need to be reviewed(Appendix C).

This Code takes full account of all the experimental work and its effect on the valuesof current given in IEC 479, particularly the fact that the hyperbaric condition does notaffect the fibrillation level, and uses IEC 479 as the basis of the figures given.

Ohm's Law can be used to calculate the 'safe' voltage in any situation if the currentwhich is acceptable to flow through the body can be established and the current routeresistance is known. This can be applied to the underwater situation using thefollowing.

Current Route Resistance (This is the resistance offered by the diver's body).

In the past, because of uncertainty of the facts relating to underwater use, a value of500 ohms has been used for a typical, worst case, limb to limb contact irrespective ofvoltage. More recent research has shown that while this value is correct for highvoltages it is conservative for lower voltages, where resistances of over 1000 ohms


have been demonstrated. Although work remains to be done on exact values in theunderwater situation, the value of current route resistance for low voltages can safelybe raised in this Code to 750 ohms for voltages up to 50 volts. The value of 500 ohmsis retained for voltages over 50 volts. Both these values are conservative and are basedon the latest evidence.

The only exception to these values is where there is a possibility of a front to back ofthe chest contact path, when a resistance of 100 ohms has been used because of thepossible larger area of skin in electrical contact than in the limb to limb case.

Similarly, although resistance in a "dry" environment, such as a Habitat or a DeckCompression Chamber, should be much higher, it was felt that realistic situationswould involve significant levels of humidity and thus the "wet" values were also used.

Safe Body Current

It is important to differentiate between fault current and allowable current passingthrough the body. Based on the maximum fault current the resulting voltage gradientin the surrounding water can be calculated using the conductivity of the sea water,which can in turn be used to estimate the current likely in the divers body, assumingthe worst case. IEC 479 gives the relationship between shock duration and allowablecurrent passing through the body, in the form of two graphs, one for 50/60 Hz a.c.current and the other for d.c. current. These curves start at a short duration shock of10 ms and become constant for shocks lasting more than 10 seconds.

(Note: Higher frequencies of a.c. current are safer on long shock durations but are notin common use. No figures are therefore given for higher frequencies, although dataare available (Appendix A Section 2 Ref. 16 & 20).

The curves were drawn as a composite of three separate effects. If the shock is short,the only limiting value necessary is the level of current likely to cause heartfibrillation. As the shock duration increases, levels of current, well below that causingfibrillation, will induce involuntary muscle contraction and in particular severebreathing difficulties and the curves used these lower values. When the shockduration exceeds 10 seconds, an even lower value of current will produce thephenomenon in which a person cannot let go of an electrical conductor due tolocalised involuntary muscle contraction in the forearm. At this current level mostpeople suffer no other short term ill effects, as it is less than half that necessary tocause fibrillation or breathing difficulties.

Improved understanding of the "safe" current flowing through the body has allowedthese curves to be modified as follows:

D.C. Current

The d.c. curve (Figure 1) is unaltered for shock durations of 200 ms up to the straightline section over 10 seconds at a value of 40 m.A., although the section from 200 to500 ms is dotted to indicate reservations in fully endorsing it. The curve stops at 200ms as in shorter shocks than this there is little significant difference between a.c. andd.c. The single point value of 570 m.A. at 20 ms is included, however, as it is awidely used reference value which is considered safe and is only slightly higher thanthe equivalent a.c. value.


A.C. Current

The a.c. curve (Figure 1) has not been altered for durations greater than 20 ms.Experimental work subsequent to the publication of the curve, particularly by Dr. H.Green of the Clinical Research Centre in London, has however shown that atdurations less than 20 ms the IEC curve comes close to levels which can causefibrillation, and thus a horizontal line has been drawn at the value of 500 m.A. Dr.Green's work has also demonstrated 'safe' values for extremely short shock durationsand these are shown on the graph as 'provisional extension'. This modified graph,including some relevant experimental findings, is shown as Figure 13 in theAppendices.

These values have been proved to be applicable to the underwater situation withoutany further modification (See Appendix C for references).

Preparation of this Code has involved a number of assumptions, such as 20 ms beinga typical tripping time for actively protected circuits. It is possible to carry out thespecific calculations for any given situation using Fig 1 to establish the acceptablecurrent in the body and then applying the appropriate resistance value to give themaximum safe voltage.


GLOSSARY

Active Protection

The provision of protection against electric shock by a system which detects an actualor potential shock condition, and responds by actuating a protective device.

Constant-current Source

A source of electric power which supplies a current that is independent of the loadwithin a specified working range.

Constant-voltage Source

A source of electric power which supplies a voltage that is independent of the loadwithin a specified working range.

Deck Compression Chamber (DCC)

A pressure vessel consisting of one or more compartments, not suitable for immersionin the water, in which divers slowly return from the pressure of their dive to surfacepressure, or in which they live under pressure during saturation diving operations.

Differential Transformer

A current transformer which delivers an output current proportional to the vector sumof the input current in two or more conductors.

Diver Lock-out Submersible

A diver lock-out submersible is a submersible craft capable of deploying divers from aseparate lock-out compartment.

Explosive Mixture

A mixture of flammable gas or vapour and an atmosphere containing oxygen inproportions which, after ignition, will lead to rapid combustion spreading throughoutthe unconsumed mixture.

Flammable Material

A substance which can react continuously with oxygen which may therefore sustainfire when such a reaction is initiated by a suitable spark, static discharge, hot surfaceor adiabatic compression.

Fully-Protective Diving Suit

A diving suit which is fully insulating or fully conductive, or may incorporate bothinsulating and conductive layers, thus providing protection from shock arising fromvoltage gradients in the water.

Habitat

This refers to a structure which is located around or over the area to be worked onand inside which there is a substantially dry but humid gaseous atmosphere atambient sea water pressure.


Hyperbaric Evacuation System

A system by which divers can be evacuated under pressure in an emergency. It iscommonly based upon a pressure vessel which may or may not be housed in aseagoing hull.

Involuntary Contraction

In the context of this Code it refers to the phenomenon whereby an electric shockapplied to the hand or forearm causes the muscles of the forearm to contractinvoluntarily such that the victim cannot let go of the object giving the electric shock.

Isolating Transformer

A transformer, the input and output windings of which are electrically separated tolimit hazards due to accidental simultaneous contact with earth and live parts or metalparts which may become live in the event of an insulation fault.

Isolation

In electrical terms this refers to total disconnection from the supply.

Isolator : Optically Coupled

A coupling unit for communications, data or control signals, which incorporates anoptical link to provide electrical isolation between the input and output.

Isolator : Transformer Coupled

A coupling unit, for communications, data or control signals, which incorporates atransformer to provide electrical isolation between the input and output.

Line-Insulation Monitor (LIM)

An active device which continuously monitors the integrity of the insulation betweenlive conductors and the earth return circuit, and provides a read-out of the insulationlevel which can be used to trigger either an alarm or a tripping device.

If the LIM is contained in one unit with a circuit breaker then it is known as a LINEINSULATION CIRCUIT BREAKER (LICB).

Ohms' Law

This states that if a voltage of magnitude V is applied across a resistor R then thecurrent I through the resistor is related to V by the equation V = IR.

Partial Pressure

The partial pressure of a gas in a mixture of gases is that pressure which the gas wouldexert if it occupied the same volume alone at the same temperature.

Passive Protection

The provision of protection against electric shock by a system which inherentlyreduces the possibility of the occurrence of any shock condition.

Residual Current Device (RCD)

(Formerly known as an Earth Leakage Circuit Breaker).

An active protection device which detects earth-leakage current as a differencebetween the supply and load currents, and responds by tripping a circuit breakerwhich interrupts the supply.


Current-operated RCD An RCD connected directly, or through a differentialtransformer, to the supply circuit and responding toleakage current.

Voltage-operating RCD on RCD connected to the screen of a screened andearthed system and responding to voltage on thescreen.

Type 1 RCD An RCD which uses a differential transformer todetect the out-of-balance current in the conductorsconnecting the supply network to the load.

Type 2 RCD An RCD which detects leakage current to earth,being directly connected between supply and earth.

Current-Sensitive RCD A Type 1 or Type 2 RCD which responds to current.

Voltage-Sensitive RCD A Type 1 or Type 2 RCD which responds to voltage

NB: The term RCD, as used in this document, covers all fault operated circuitbreakers.

Safe Distance

The distance beyond which the voltage gradient in the water presents no hazard to thediver.

Submersible Compression chamber (SCC) - also known as a Diving Bell

A manned pressure vessel used under water to support divers.

Transfer chamber

A Transfer Chamber is a chamber connected to the Deck Compression Chamber bymeans of which divers under pressure can transfer from a Submersible CompressionChamber or Diver Lock-out Submersible to the Deck Compression Chamber or viceversa whilst maintaining pressure.

Trip Device

This refers to any device (RCD, LIM with trip facility etc.) which can interrupt theelectrical supply on detection of a fault. In this Code an overall system operating timeof 20 ms has been assumed in deriving the values given in the various tables.

Voltage Clipper (or Limiter)

A component which prevents the voltage in the circuit from rising above apredetermined level by drawing off the excess current at voltages reaching that level.


SECTION 1 - APPLICATION OF ELECTRICITY UNDER WATER

1.0 INTRODUCTION

The application of electricity during a diving operation has been sub-divided as shownin Fig. 2. Each of these sub-divisions reflects the relevant environment and the specificprotection requirements. The sub-divisions are :

1. Deck Compression Chamber (DCC) and Hyperbaric Evacuation System2. Transfer Chamber, Submersible Compression Chamber (SCC), and Diver

Lockout Submersible.

3. Diver Heating (Electrical). 4. Hand Held Equipment.5. Habitat.6. Wet Welding and Cutting. 7. Sea Bed Equipment.8. Impressed Current Systems.9. Remotely Operated Vehicle (ROV). 10. Manned Submersibles.11. Umbilicals.12. High Power Equipment.13. Surface Electrical Distribution. 14. Fresh Water.15. Explosives.

For each application, specific acceptable values are given. Their derivation isexplained in the DISCUSSION. The values given in this section are based on 20msmaximum shock duration. Total resistance values are also chosen as explained in theDISCUSSION.

Reference to the DISCUSSION will allow specific situations to be assessed, forexample, the use of active protection devices with reaction times other than 20ms.

In this Section three paragraphs are given for each sub-division. Paragraph a) gives abrief definition to allow full identification, paragraph b) identifies the environmentwhich the electrical equipment may encounter and paragraph c) lists acceptable activeprotection practices. This last section is in tabular form with four headings.

RECOMMENDATION

This summarises the manner in which electricity can be used safely. If none of thesemethods is possible then the electrical equipment should not be used or elsealternative arrangements should be made to ensure safety. Where a trip device isspecified, it is based on an overall operating time of 2Oms.


SAFE BODY CURRENT

This is the maximum current which can be allowed to flow through the diver's bodysafely, and has been derived from IEC 479: 1974. It is NOT the current flowing in theelectrical equipment.

CURRENT ROUTE RESISTANCE

This is the resistance offered by the diver's body. The values are based onexperimental data and are for limb to limb contact, except in the case of diver heatingwhere front to back of the chest was chosen.

VOLTAGE

This is the voltage derived from the maximum current allowable through the diver'sbody and the route resistance. It is expressed as a maximum value which should neverbe exceeded and also as a commonly used nominal value. The voltages stated are thevalues to which the diver may be subjected without serious physical harm.

Note:

1. Where d.c. is referred to, it is assumed that the ripple content is not more than5%, otherwise it should be treated as a.c. (Appendix A, Section 2 Ref 19).

2. Where a.c. is referred to, the voltage is RMS.3. All pressures given in this code are gauge pressures. This means that O Bar is the

pressure at sea level, otherwise known as atmospheric pressure.


1.1 Deck Compression Chamber : Hyperbaric Evacuation System

a. A Deck Compression Chamber is a pressure vessel consisting of one or morecompartments, (not suitable for immersion in the water) in which diversslowly return from the pressure of their dive to surface pressure, or in whichthey live at pressure during Saturation Diving Operations.

A Hyperbaric Evacuation System is a system by which divers can be evacuatedunder pressure in an emergency. It is commonly based upon a pressure vesselwhich may or may not be housed in a seagoing hull.

b. Internal pressure can vary between O and 50 bar but is commonly in therange 0 - 25 and can change at various rates. The atmosphere is normallycompressed air in the range O to 5 bar or a mixture of oxygen and helium upto 25% 02 or 0. 5 bar ppO2 whichever is the lower. Higher oxygenconcentrations may be encountered in special circumstances. Occupants arelikely to be lightly clad with no electrical protection from their clothing. Theinternal temperature range is normally 25C to 35C in a saturation chamberand 5C to 25C in an air chamber. Humidity in such chambers is normally inthe range 50 - 75%, but can exceptionally rise to 100%.

c. The acceptable practices are:

Recommendation Safe BodyCurrent X

mA

CurrentRouteResistance OHMS

= Voltage

Maximum V Nominal V

a.c. with Trip Device (1) 500 500 250 220d.c. with Trip Device 570 500 285 250a.c. without Trip Device 10 750 7.5 6d.c. without Trip Device 40 750 30 24

Note

1. Significantly higher frequencies of a.c. current provide higher safety levels.The advantage of using higher supply frequencies rapidly decreases forshorter duration shocks and no change in the safe level is recommended inthe region where most trip devices operate. For long duration shocks, alimit is set by the internal heat generated (Appendix A, Section 2 Ref. 16 &19).


1.2 Transfer Chamber, Submersible Compression Chamber (SCC) andDiver Lock-Out Submersible

a. A Transfer Chamber is a chamber connected to the Deck Compressionchamber (DCC) by means of which divers under pressure can transfer from aSubmersible Compression Chamber (SCC) or Lock-Out Submersible to theDCC or vice versa whilst maintaining pressure. It usually contains washingand toilet facilities during saturation diving.

A Submersible Compression Chamber (SCC), or a Diving Bell, is a mannedpressure vessel used under water to support divers.

A Diver Lock-Out Submersible (DLO) is a submersible craft capable ofdeploying divers from a separate lock-out compartment.

b. Transfer Chambers, Submersible Compression Chambers and Diver Lock-OutSubmersibles are very similar in their electrical requirements and are thereforeconsidered together.

Submersible Compression Chambers and Diver Lock-Out Submersibles maybe subjected to rough handling during launch and recovery and will also beimmersed for a long time in sea water.

Internal pressures will be in the range of 0 to 50 bar but normally 0 to 25 bar.This pressure could be subject to rapid change. Externally the TransferChamber will be subject only to atmospheric pressure but the SubmersibleCompression Chamber and Diver Lock-Out Submersible will be subject to seawater pressure according to the depth, which will be in the range of 0 to 50bar, but normally 0 to 25 bar.

The internal atmosphere is either compressed air at a pressure of 0 - 5 bar oran oxygen and helium mix at a pressure of 0 to 50 bar. The oxygenconcentration will normally be 25 % by volume or 0.5 bar ppO2, whichever islower.

Divers in Submersible Compression Chambers and Diver Lock-OutSubmersibles will normally wear divers' rubber suits, but in TransferChambers they could be lightly clad with no electrical protection from theirclothing.

The temperature inside all vessels will lie in the range of 25C to 35C, butcould drop to 10C in exceptional circumstances. External temperatures willvary from 0C to 30C but will normally be between 5C and 15C.

There will always be a high humidity internally and equipment mountedinside Transfer Chambers, Submersible Compression Chambers and DiverLock-Out Submersibles will be subject to exposure to sea water splash, andpossible total immersion in the case of Submersible Compression Chambersand Diver Lock-Out Submersibles.




mA


= Voltage

Maximum V Nominal V

a.c. with Trip Device 500 500 250 220d.c. with Trip Device 570 500 285 250a.c. without Trip Device 10 750 7.5 6d.c. without Trip Device 40 750 30 24

N.B. If Trip Devices are used then they should be able to be reset by theDiving Supervisor after necessary safety checks. They should have an overridefacility which may only subsequently be operated by the Diving Supervisor ifhe considers the danger to the diver as a result of loss of power to be greaterthan the possible electrical hazard.


1.3 Diver Heating (Electrical)

a. This refers to electrically heated undersuits where the current flows over alarge area close to the diver's body.

b. Electrical Diver Heating is not in common use within commercial diving,although it has been used in the past and may be used again in the future.

An electrically heated diver's suit will be exposed to the same environment asthe diver, a pressure range of 0 to 50 bar although normally 0 to 25 bar. Thispressure is not likely to change rapidly.

The ambient environment when energised will normally be seawater but forbrief periods during exit from or entry to a diving bell, the environment couldbe compressed air at a pressure of 0 to 5 bar or an oxygen and helium mixtureat a pressure from 0 to 50 bar. In the case of surface supported diving this briefperiod could be at 0 bar in air while the diver enters or leaves the surface ofthe sea.

A diver's clothing would always include a rubber suit but normally worn ontop of the electrically heated garment.

The temperature of the water surrounding the diver will normally be in therange of 5 to 15C.



mA


= Voltage

Maximum V Nominal V

a.c. with Trip Device (3) 200 100 20 18d.c. with Trip Device 228 100 22.8 18

N.B. The heating element in a suit or gas heater should be completelyenclosed in an earthed conducting screen.

d.c. without Trip Device (2) 70 100 7 6

Notes

1. These values have been divided by 2.5 to allow for the concentration ofcurrent in the region of the heart, in this case in the ratio of 2.5 to 1.(Appendix A Section 2 Ref. 19).

2. This is based on the level of shock leading to involuntary contraction ofbreathing muscles and not to the level causing forearm contraction whichis the basis for the figures in other cases without trip devices.

3. Significantly higher frequencies of a.c. current provide higher safety levels.The advantage of using higher supply frequencies rapidly decreases forshorter duration shocks and no change in the safe level is recommended inthe region where most trip devices operate. For long duration shocks, alimit is set by the internal heat generated. (Appendix A Section 2 Ref. 16 &19).

(1)


1.4 Hand Held Equipment

a. This refers to equipment held by the diver during routine operations, such ascameras, small hand tools and NDT equipment.

b. Hand held equipment for subsea use must be extremely robust to withstandnormal rough handling.

It will be exposed to a pressure equivalent to the depth at which it is to beused. This will be in the range 0 to 50 bar but normally 0 to 25 bar. Thispressure can be subject to very rapid change.

Its surroundings will include total immersion in sea water but it may also betaken into the gaseous environment of a diving bell or habitat, when it wouldbe in an atmosphere of compressed air at a pressure of up to 5 bar or anoxygen helium mix at a pressure of up to 50 bar.

The diver's clothing while the unit is energised will normally be a rubber suit.

The temperature range to which the equipment will be exposed is 0C to30C.



MA


= Voltage

Maximum V Nominal V



1.5 Habitat

a. This refers to a structure which is located around or over the area to beworked on and inside which there is a substantially dry but. humid gaseousatmosphere at ambient sea water pressure. The commonest use of such itemsis to provide facilities for hyperbaric welding.

b. Welding habitats are by their very nature subject to wide extremes ofenvironment.

During operations, equipment within a habitat will be subject to internalpressure varying between 0 to 50 bar but normally in the range of 0 to 25 bar.This pressure could be subject to rapid change.

The atmosphere is either compressed air at a pressure of 0 to 5 bar or anoxygen and helium mix at a pressure of 0 to 50 bar. The oxygen concentrationwill normally be the lower of 25% by volume or 0.5 bar ppO2

Occupants' clothing will be divers' rubber suits, conventional weldingclothing or even fire resistant boiler suits.

The internal temperature will vary from 5C up to 40C and exceptionally,particularly in very small habitats, could rise to 60C.

During the deployment phase, the habitat may be flooded and any electricalequipment must be capable of withstanding total immersion in salt water atambient pressure. During operations the humidity level will vary from 70-100%.



(Note For welding practices in habitats see Section 1.6)


MA


= Voltage

Maximum V Nominal V


A supply fed from an a.c.isolating transformer with non-earthed secondary. Using a lineinsulation monitor with circuitbreaker.

- - In this case, a single faultdoes not present ahazard and thus nomaximum voltage needbe stipulated providedthe protective devicesare able to prevent theoccurrence of a secondfault constituting ahazard.

A supply fed from an a.c.isolating transformer with thesecondary earthed through animpedance to limit fault currentto 1A, and trip device.

- - No voltage limit is statedas the diver is protectedby the fault current limitand the associated tripdevice.

Note

If Trip Devices are used then they should be able to be reset by the DivingSupervisor after necessary safety checks.

They should have an override facility which may only subsequently beoperated by the Diving Supervisor if he considers the danger to the diver as aresult of loss of power to be greater than the possible electrical hazard.


1.6 Wet Welding And Cutting

a. This covers any welding, burning or cutting operation where both the diverand the workpiece are totally immersed in water.

b. The environment is considered to be seawater. The pressure range will be 0 to50 bar but normally 0 to 25 bar.

The temperature could be in the range 0C to 30C but normally 5C to15C.

The diver will normally be wearing a rubber suit and heavy rubber gloves,over a pair of light rubber gloves. The gloves in particular will give a measureof electrical protection where the voltage gradient is highest.



mA


= Voltage

Maximum V Nominal V

d.c. without Trip Device 40 750 30 24

It is recognised that 30V dc is not a high enough voltage to be practical inmany circumstances. In such cases it is recognised that it would be difficult toprovide active protection to ensure that the diver is safe from electric shock atall times.

Safety is achieved by rigid adherence to good operational procedures. Adescription of the necessary operational practices is given in Section 2.6.


1.7 Sea Bed Equipment

a. This covers large items of equipment such as pumps or power packs used toprovide power on the sea bed for a variety of tools.

b. The environment is considered to be seawater. The pressure range will be 0 to50 bar but normally 0 to 25 bar.

The temperature range will be 0C to 30C but normally 5C to 15C.

The diver will normally be wearing a rubber suit.



mA


= Voltage

Maximum V Nominal V


- - In this case a single faultdoes not present ahazard and thus nomaximum voltage needbe stipulated providedthe protective devicesare able to prevent theoccurrence of a secondfault constituting ahazard.

A supply fed from an a.c.isolating transformer with thesecondary earthed through animpedance to limit fault currentto 1A and trip device.


Note

In all cases, such equipment should have a suitable seawater earth as outlinedin section 2.0.2.5.


1.8 Impressed Current Systems

a. These are systems installed to protect vessels or structures from corrosion bymeans of electrically supplied anodes in the sea which protect the parentstructure. The protective effect takes some hours or days to establish and theyare therefore rarely switched off unless special circumstances require.

b. Impressed current anodes are considered as surrounded by seawater at apressure dependent on the depth but normally 0 to 30 bar. The watertemperature is likely to be in the range 0C to 30C but normally 5C to15C.

Divers who may approach impressed current anodes will be swimming in seawater and normally wearing a rubber suit.



mA


= Voltage

Maximum V Nominal V


Physical barrier at suitabledistance to prevent diver enteringarea of potential hazard.

- - No maximum voltage isstated as the safe voltagewill depend on thedistance of the physicalbarrier. Appendix B,Section 2 gives moredetail.


1.9 Remotely Operated Vehicle (ROV)

a. These vehicles are controlled from the surface by an operator who has visualcontrol by means of a camera mounted on the ROV. The vehicles are linkedto the surface by an umbilical.

b. As ROVs are launched and recovered through the air/sea interface electricalcomponents must be robust to withstand the inevitable rough handling.

Once totally immersed, the pressure on the ROV is that of the surroundingwater, ranging from 0 to 100 bar but normally 0 to 30 bar. This pressure willchange rapidly during raising and lowering. The water temperature varies from0C to 30C.

Any diver who may come in contact with an ROV can normally be assumedto be wearing a rubber suit.



mA


= Voltage

Maximum V Nominal V


- - In this case a single faultdoes not present ahazard and thus nomaximum voltage needbe stipulated providedthe protective devicesare able to prevent theoccurrence of a secondfault constituting ahazard.



Note

Trip Devices should be able to be reset by the Diving Supervisor afternecessary safety checks. They should have an override facility which may onlysubsequently be operated by the Diving Supervisor if he considers the dangerto the diver as a result of loss of power to be greater than the possibleelectrical hazard.


1 .10 Manned Submersible

a. A manned free swimming submersible craft is designed to maintain some orall of its occupants at or near atmospheric pressure and carries all of itselectrical power onboard.

A one man tethered submersible is a small submersible craft tethered to thesurface and designed to maintain the occupant at or near atmosphericpressure. Electrical power is normally fed from the surface through theumbilical.

b. The environment within a one man tethered submersible and within the pilot'scompartment of a free swimming submersible is normally air at atmosphericpressure, although in extreme circumstances the oxygen concentration mayrise above 25% by volume. Care should be taken with electrical equipmentwhich may cause a fire in these circumstances.

The internal pressure will remain at 0 bar although exceptionally it may riseby a few millibar. External pressure due to depth of sea water could be up to100 bar.

Occupants will normally be lightly clad with no electrical protection fromtheir clothing.

Internal temperature will normally be in the range of 10C to 25C althoughthis could drop to 2C or rise to 35C for short periods. External temperaturewill be that of the sea water that is 0C to 30C.

There will always be high humidity levels.

c. The acceptable practices both for the internal occupant and for any externalelectrical equipment which may be in contact with a diver are:


MA


= Voltage

Maximum V Nominal V



1.11 Umbilicals

a. These are any cable or bundle of cables connected between the underwaterwork site and the surface or between two underwater work sites (butexcluding equipment described in section 1.12).

b. An umbilical is normally connected at the surface to an electrical source andat its lower end to the electrical load.

The environment to which the umbilical is exposed varies from the dryatmosphere, through the surface of the sea where pressure is still atmospheric(but with splashing or immersion) to its extreme in sea water at pressures up to50 bar.

The umbilical is likely to receive rough handling and to be exposed to watertemperatures from 0C to 30C, and, for its exposed length between thesurface of the sea and its topside connection, at temperatures well below 0Cor up to 50C. It will be subjected to regular flexural stresses and may also beexposed to tensile stress.

Any diver exposed to an electrical hazard from the umbilical can normally beassumed to be wearing a rubber suit.



mA


= Voltage

Maximum V Nominal V







1.12 High Power Equipment

a. Such equipment is not normally deployed by, or under the control of, theDiving Contractor but may need to be worked on by divers, a mannedsubmersible craft or an ROV. It includes subsea wellhead control devices andpower cables.

b. Such equipment will be considered to be in contact with, or at the surfaceinterface to be immersed in, sea water at a pressure equivalent to its depth andnormally in the range 0 to 50 bar.

The water temperature is likely to be in the range 0C to 30C.

Divers who may be at risk from high power equipment can normally beassumed to be wearing a rubber suit.

c. It should be recognized that power cables exist which cannot readily bedisconnected. Detailed investigation and assessment of possible hazardsshould be carried out before diving operations commence and the necessarysafety protections provided.

The acceptable practices are:


mA


= Voltage

Maximum V Nominal VPhysical barrier at suitabledistance to prevent diver enteringarea of potential hazard.

- - No maximum voltage isstated as the safe voltagewill depend on thedistance of the physicalbarrier. Appendix B,Section 2 gives moredetail.






1.13 Surface Electrical Distribution

a. This includes all equipment on the surface (support vessel or similar) which isunder the control of the Diving Contractor and necessary for the underwateroperation.

b. The environment will vary from the dry, warm and air conditionedaccommodation of a fixed platform to the exposed after deck of a ship wherewind, rain, vibration and sea-spray may be encountered.

The area in which the equipment is to be installed should be studied todetermine the likely environment.

c. It is not within the scope of this Code to specify protection practices forSurface Electrical Distribution as it is concerned only with the use of electricityunder water. There are adequate guidelines available through national andinternational standards. In particular the "Institution of Electrical EngineersRecommendations for the Electrical and Electronic Equipment of Mobile andFixed Offshore Installations", First Edition 1983; and "Regulations for Electricaland Electronic Equipment of Ships", Fifth Edition with recommended practicefor their implementation published by the Institution of Electrical Engineerswith amendments 1 to 4 give sound advice.

All electrical supplies for use under water should be electrically isolated fromthe distribution system of the ship or installation by, for example, the use ofisolating transformers or a separate generation source.

Personnel involved in maintenance or modification of equipment used inconnection with electricity under water should remember that the measuresoutlined in this Code are designed to protect man under water and may not,on their own, provide adequate protection for surface crew.

The question of surface back-up supplies and levels of redundancy is also notcovered.


1.14 Fresh Water

a. This covers any operation carried out in water which is not seawater.

b. Fresh water is normally much shallower than seawater and the pressure towhich equipment is likely to be subjected is 0 to 5 bar although in exceptionalcircumstances this could be as high as 25 bar.

The temperature of fresh water will be 0C to 30C.

c. This Code does not specify practices for use in fresh water due to theconsiderable difference in its conductivity, compared to salt water, and thegreater hazard in fresh water. It is recommended that for any application infresh water a calculation be carried out from first principles for each specificapplication and if any doubt exists, expert advice should be obtained.

Active protection values of voltage will remain the same as for seawater butother practices may be different.

In particular the protective effect provided by seawater providing earthing willbe reduced and any recommendation in this Code relying on this will notapply in fresh water.

Provided the conductivity of the fresh water is known then this Code providesenough basic data to assess any particular situation.


1.15 Explosives

a. This refers to any explosive charge or device which is initiated by electricalmeans.

b. The environment to which any electrical device used to initiate an explosionwill be subjected is considered to be sea water at a pressure of 0 to 50 bar, butnormally 0 to 25 bar.

The water temperature will vary from 0C to 30C.

c. In normal explosive operations, the electrical device will only be energisedwhen the explosive is to be detonated, and divers or submersible craft shouldnot be in the vicinity at this time. Therefore it is not necessary to specifyprotective practices against electrical hazard.

However it must be remembered that, unless specially designed detonatorsare used, the energy from radio frequency transmissions may initiate anelectric detonator.


SECTION 1 APPLICATION OF ELECTRICITY UNDER WATER

Summary Table Of Acceptable Practices

(Numbers in Brackets refer to explanatory notes at the end of this table)

Application (1) Recommendation (2) (3) Safe BodyCurrent X

mA (4)

CurrentRouteResistance OHMS (5)

= Voltage(6)

Maximum Nominala.c. with Trip Device (8) 500 500 250 220d.c. with Trip Device 570 500 285 250a.c. without Trip Device 10 750 7.5 6

1.0 Deck Compression Chamber(DCC) and HyperbaricEvacuation System

d.c. without Trip Device 40 750 30 24a.c. with Trip Device (7) 500 500 250 220d.c. with Trip Device (7) 570 500 285 250a.c. without Trip Device 10 750 7.5 6

2.0 Transfer ChamberSubmersible CompressionChamber (SCC) and DiverLockout Submersible d.c. without Trip Device 40 750 30 24

a.c. with Trip Device (8) 200 100 20 18d.c. with Trip Device 228 100 22.8 18N.B. The heating element in a suit or gas heater should be completely enclosed in anearthed conducting screen.


d.c. without Trip Device (10) 70 100 7 6a.c. with Trip Device 500 500 250 220d.c. with Trip Device 570 500 285 250a.c. without Trip Device 10 750 7.5 6


d.c. without Trip Device 40 750 30 24a.c. with Trip Device (7) 500 500 250 220d.c. with Trip Device (7) 570 500 285 250a.c. without Trip Device 10 750 7.5 6d.c. without Trip Device 40 750 30 24A supply fed from an a.c.isolating transformer with non-earthed secondary. Using a lineinsulation monitor with circuitbreaker (7)

- - (11)

5.0 Habitat

A supply fed from an a.c.isolating transformer with thesecondary earthed through animpedance to limit fault currentto 1A, and trip device (7)

- - (12)

6.0 Wet Welding And Cutting d.c. without Trip Device 40 750 30 24N.B. As this d.c. voltage will not be high enough in most cases it is clear that theprocess cannot be made safe electrically.Refer to sections 1.6 and 2.6 for detailed advice.

(9)



mA (4)


= Voltage(6)

Maximum NominalA supply fed from an a.c.isolating transformer with non-earthed secondary. Using a lineinsulation monitor with circuitbreaker

- - (11)7.0 Sea Bed Equipment (13)


- - (12)

d.c. without Trip Device 40 750 30 248.0 Impressed Current SystemPhysical barrier at suitabledistance to prevent diver enteringarea of potential hazard.

- - (14)

A supply fed from an a.c.isolating transformer with non-earthed secondary. Using a lineinsulation monitor with circuitbreaker (7).

- - (11)9.0 Remotely Operated Vehicle

A supply fed from an a.c.isolating transformer with thesecondary earthed through animpedance to limit fault currentto 1A and trip device. (7)

- - (12)

a.c. with Trip Device 500 500 250 220d.c. with Trip Device 570 500 285 250a.c. without Trip Device 10 750 7.5 6

10.0 Manned Submersible




mA (4)


= Voltage(6)

Maximum Nominala.c. with Trip Device 500 500 250 220d.c. with Trip Device 570 500 285 250a.c. without Trip Device 10 750 7.5 6d.c. without Trip Device 40 750 30 24A supply fed from an a.c.isolating transformer with non-earthed secondary. Using a lineinsulation monitor with circuitbreaker

- - (11)

11.0 Umbilicals

A supply fed from an a.c.isolating transformer with thesecondary earthed through animpedance to limit fault currentto 1A, and trip device

- - (12)

Physical barrier at suitabledistance to prevent diver enteringarea of potential hazard.

- - (14)

A supply fed from an a.c.isolating transformer with non-earthed secondary. Using a lineinsulation monitor with circuitbreaker

- - (11)

12.0 High Power Equipment

A supply fed from an a.c.isolating transformer with thesecondary earthed through animpedance to limit fault currentto 1A, and trip device

- - (12)

13.0 Surface ElectricalDistribution

Refer to text

14.0 Fresh Water Refer to text15.0 Explosives Refer to text


Notes1. APPLICATION This is the item of equipment in which the electricity is to be used.2. RECOMMENDATION

This summarises the manner in which electricity can be used safely. If none thesemethods is possible then the electrical equipment should not be used or elsealternative arrangements should be made to ensure safety. Where a trip device isspecified it is based on an overall operating time of 20 ms.

3. Where d.c. is referred to it is assumed that the ripple content is not more than 5%otherwise it should be treated as a.c. (Appendix A. Section 2 Ref 19). Where a.c. isreferred to the voltage is RMS.

4. SAFE BODY CURRENTThis is the maximum current which can be allowed to flow through the diver'sbody safely which has been derived from IEC 479: 1974. It is NOT the currentflowing in the electrical equipment.

5. CURRENT ROUTE RESISTANCEThis is the resistance offered by the diver's body. The values are based onexperimental data and are for limb to limb contact except in the case of diverheating where front to back of the chest was chosen.

6. VOLTAGEThis is the voltage derived from the maximum current allowable through thediver's body and the route resistance. It is expressed as a maximum value whichshould never be exceeded and also as a commonly used nominal value. Thevoltages stated are maximum values to which the diver may be subjected withoutserious physical harm.

7. Trip Devices should be able to be reset by the Diving Supervisor after necessarysafety checks. They should have an override facility which may onlysubsequently be operated by the Diving Supervisor if he considers the danger tothe diver as a result of the loss of power to be greater than the possible electricalhazard.

8. Significantly higher frequencies of a.c. current provide ids higher safety levels. Theadvantage of using higher supply frequencies rapidly decreases for shorterduration shocks and no change in the safe level is recommended in the regionwhere most trip devices operate. For long duration shocks a limit is set by theinternal heat generated (Appendix A Section 2 Ref 16 & 20).

9. These values have been divided by 2.5 to allow for the concentration of current inthe region of the heart, in this case in the ratio of 2.5 to I.

10. This is based on the level of shock leading to involuntary contraction of breathingmuscles and not to the level causing forearm contraction which is the basis for thefigures in other cases without trip devices.

11. In this case a single fault does not present a hazard and thus no maximum voltageneed be stipulated provided the protective devices are able to prevent theoccurrence of a second fault constituting a hazard.

12. No voltage limit is stated as the diver is protected by the fault current limit and theassociated trip device.

13. In all cases such equipment should have a suitable sea water earth as outlined insection 2.0.2.5.

14. No maximum voltage is stated as the safe voltage will depend on the distance ofthe physical barrier. Appendix B Section 2 gives details.


SECTION 2 - INSTALLATION AND USE OF EQUIPMENT

2.0 INTRODUCTION

This section has been laid out under the same headings as Section 1 to identify therelevant environmental and specific protection requirements.

For each application, where practical, a simple block diagram is given showing typicalpresent day practice, using the techniques identified in section 1, in order to achieve a'safe' system (where necessary the main electrical considerations are explained in asubsequent paragraph).

It must be stressed that the block diagram shows a typical circuit only and alternativecircuits would be acceptable provided the level of protection is at least that requiredby this Code and any relevant legislation.

2.0.1 Protection Against Electric Shock

Available methods of protection against electric shock fall into two groups,passive and active. Passive methods (insulation, screening and earthing)constitute a first line of defence against shock, and one or more of themshould always be used.

When a passive method fails, due for example to water ingress or deteriorationof earthing connections, the system may be in an undetected dangerouscondition and constitute a shock risk. Consequently, a passive method alonemay be inadequate where a high level of protection is needed and the use ofactive protection in addition, such as a residual current device, should beconsidered.

2.0.2 Passive Protection

There are five ways of providing passive protection.

2.0.2.1 Insulation

The primary means of providing passive protection against shock is byinsulation of the power system and the appliance it serves. Insulation is lesseffective under water than on dry land, because a defect at any point mightallow current to flow in the water and part of this current may be interceptedby the diver or submersible craft.

The effectiveness of insulation as a means of protection may be improved byusing two layers of insulation with a conducting screen in between. Twodefects are then needed to constitute a risk. The first defect can be detected bycontinuously monitoring the insulation level between the conducting screenand the load, and between the screen and the outer casing. Entry of watercould cause simultaneous failure of both sections of insulation; consequentlysealing arrangements (such as 'O'-rings and pressure balance terminations)should be incorporated if double insulation is to be more effective than singleinsulation.


Insulation should be further improved by supplying the load via an isolatingtransformer, the whole of the electrical system (including the transformersecondary winding and all the appliances) thus being insulated from earth. It isthen possible to make contact with any point on the secondary circuit withoutreceiving a shock. This prevents, for example, contact with a crane wire fromthe surface, the leg of a steel platform or a ship's hull from forming an earthreturn path and thereby creating a hazard.

If a first defect is not rectified, contact with the circuit or the occurrence of asecond defect may then cause current to flow through the diver. However, thiscan be avoided by incorporating an active protection device for detecting thefirst defect. The whole of the circuit (transformer, secondary winding,connected cable and the load) should have a high insulation resistance toearth. It is also necessary to restrict the capacitance of the circuit to earth.

In practice, the capacitance usually imposes a limit on the maximum length ofcable connecting the transformer secondary winding to the load - (SeeAppendix B.1).

2.0.2.2 Fixed Barrier

When electrical equipment requires direct contact with sea water to functioncorrectly (e.g. an impressed current anode) a fixed barrier can be installed tokeep the diver a specific safe distance away from it. This barrier should benon-metallic and non-conducting if possible.

In addition to such equipment, high-power fixed installations (e.g. cables andmotors) can feed large currents into the water if a fault occurs. Again fixedbarriers can be used to keep the diver at a safe distance - (See Appendix B.2).

The safe distance can be reduced by incorporating an impedance in the starpoint to earth line of the supply to limit the fault current. Care should be takento ensure that all protective devices will function at the low level. A faultcurrent limit of 1 A is recommended.

2.0.2.3 Protective Clothing

Any practice which limits the flow of current through the diver is beneficial.

Rubber gloves should be worn, particularly during welding, and should have acuff to give the wrist area some degree of protection.

The degree of protection offered by existing diving suits varies and they shouldnot be relied upon for protection.

2.0.2.4 Shielding

The electrical equipment may be enclosed within a conducting shield toprevent current from flowing into the water. Where a shield is fitted it shouldbe suitably connected to earth, to prevent a dangerous voltage by an internalfault.

Protective screens should be constructed from high-conductivity material andhave low-resistance joints, otherwise a fault current flowing in the screen can


produce a dangerous voltage gradient over its external surface. However, thisdeficiency can be greatly reduced by the use of a double screen. Theconducting screen (the external screen in double-screened systems) shouldalso be in contact with the water to restrict the voltage difference between thescreen and the surrounding water.

2.0.2.5 Suitability of Earthing

On any unit which operates at a voltage which is higher than the unprotected safelimit (30V d.c. maximum or 7.5V a.c. maximum) then the conductive structure orframe should be connected to earth to dissipate any fault current. The connectionshould have a low impedance to minimise any rise of voltage on the conductivestructure or frame, and sufficient mechanical strength to prevent accidentalbreakage when the equipment is operated within the stated limits. The connectionshould be through purpose-designed conductors in the power cables. The earthreturn path can be augmented by an area of bare metal (even corroded steel) incontact with the water; such an arrangement can be many times more effectivethan normal earth leads.

2.0.3 Active Protection

In addition to passive protection, and wherever practicable, the system should provideactive protection against shock resulting from direct contact with the live circuit of theequipment and indirect contact via the structure or the sea. Active protection may beprovided by a residual current device (RCD) or a line insulation monitor (LIM)coupled to a circuit breaker device.

2.0.3.1 Residual Current Devices (RCDs)

Commonly used RCDs have a typical operating time of 15 to 25 ms. The tripcurrents of RCDs should be selected to be as low as possible consistent withfreedom from accidental tripping which is inconvenient and can bedangerous. A trip current of 30 mA at 20 ms has been found to be suitable.


Two alternative types may be used; one uses a differential transformer todetect out-ofbalance current and the other is connected between an isolatedsupply and earth.

For d.c. systems, Differential Transformer RCDs are not applicable, andisolated supply RCDs should be designed for use in d.c. circuits.

Because of practical limitations in their design, differential transformers mayhave an upper limit on the rated value of the line current. Isolated supplyRCDs are not subject to any limits of load current.

2.0.3.2 Line Insulation Devices

A line-insulation monitor (LIM) may be used to monitor the insulation level of anumbilical cable as it enters or leaves the water and any developing electricalleakage. A read-out of insulation level should be provided with warnings of lowlevels if appropriate.

In order to use a LIM as part of an active protection device it should be connectedto a circuit breaker to give suitable overall system operating characteristics.

2.0.4 Toxicity Of Materials

In the event of a fire or even serious overheating, many commonly used electricalmaterials give off noxious and toxic fumes. As a diver or submersible pilot isconfined within his environment and unable to escape from any fumes, it isimportant always to use low-toxicity cables and other materials.

Full guidance on selection of such materials is given in section 3.2.

2.0.5 Installation Practice

To maintain the integrity of all forms of protection, portable and fixedelectrical equipment should be regularly inspected by competent staff. Onlysuch staff should carry out installation or rewiring, and any temporaryelectrical equipment used should be to the standard described in this Code.

Contractors responsible for underwater electrical equipment should authorisestaff in writing as competent for specific functions.

Competent staff should be familiar with proper installation procedures and beaware of the hazards and problems particular to underwater work.

Frequent inspections should be made for signs of mechanical damage oncables and for any general deterioration of equipment.

The following measures should be adopted for the installation, modificationand repair of electrical equipment for use under water.

1. All conductors should be adequately protected by suitable fuses and/orcircuit-breakers.

2. Conductors should have an adequate cross section, based, not only on fullload current and voltage drop along its length, but also on sustained


overload current if applicable, and the fault current which can flow for thetime taken for any protective devices to operate.

3. A minimum number of joints should be used in a circuit to reduce thepossible number of poor connections.

4. Terminal connections of proven integrity should be used, and conductor'tails' should be supported to avoid fatigue failures.

5. Wiring should be spaced to avoid cross-circuit breakdown or tracking.6. Conductors should be routed clear of areas where they may be liable to

mechanical damage, or else provided with some form of mechanicalprotection. Fixed cables should be positioned so that they do not form aconvenient hand grip.

7. Terminal chambers should be sealed against entry of moisture.8. Common power return circuits should not be used. Each circuit should

function independently. Similarly each protected circuit should beseparate so that a fault on one cannot interact with a second circuit.

9. Identification sleeving is potentially toxic when heated and should befitted at a distance from the termination.

10. A good tracking index material should be used and adequate trackingdistance should be incorporated in the design of plugs, sockets,connections and printed circuit boards to make allowance for any saltwhich may be present on the surface. Penetrators, where continuedtracking erosion can cause failure of the pressure seal, are particularlyvulnerable.

11. Solder should not be used on stranded or flexible cables, unless the wiringis fully supported to avoid any stress or fatigue at the joints resulting fromvibration.

12. Records should be maintained to ensure that the design safety standardsare met.

13. Records should be kept of maintenance carried out and any modificationsmade to equipment.

14. Records should be kept of routine testing of active protection devices.

2.0.6 Batteries

In the past, batteries have usually been considered to be electrically 'safe'. Asin many cases they are not used as a primary power source, but rather as areserve or back-up, they are frequently omitted from electrical safetyassessments.

In practice batteries can present very real hazards and considerable careshould be taken when using them.

Primary cells (Non-Rechargeable Batteries) have a limited life and whendischarged are notorious for producing corrosion products.

Short-circuiting of primary cells can be potentially hazardous and adequateshort-circuit protection should be provided.


Secondary cells (Rechargeable Batteries) are normally of higher power thanprimary cells, so the same basic recommendations apply. In addition,however, there is an explosive hazard from hydrogen gases produced duringrecharging and discharge.

Secondary cells should normally be recharged out on the surface in a properlyventilated area. (Further information on this subject may be found in section14 of the "Institution of Electrical Engineers Recommendations for theElectrical and Electronic Equipment of Mobile and Fixed OffshoreInstallations", First Edition 1983). If fixed installations are required to havesubmerged recharging facilities, the charge should be limited to a level belowthe gassing voltage; as a result, extra cells may be required to attain theworking voltage and the required battery capacity.

Where devices are provided for the recombination of free hydrogen andoxygen, care should he taken to prevent overcharging which may lead tocarry-over of the electrolyte and malfunction of the device.

If water enters a battery compartment, an explosive or toxic gas mixture maybe produced. Battery compartments should be completely watertight.

Fuses should be fitted in the battery compartment as close as possible to thebatteries and should be encapsulated to prevent a blown fuse from igniting thepossible hydrogen atmosphere in the compartment.

The state of batteries in battery-powered equipment should be checked beforeuse.

Batteries should be handled with caution. Since a battery cannot be turned off,it constitutes, even in a low charge state, a shock risk and also a burn risk, ifaccidentally short-circuited by metal tools. Electrolyte spillage or carry-overcan also provide a leakage path from a high potential terminal.

Where there is any possibility of relative movement between batteries, thenflexible electrical connections should be used.


2.1 Deck Compression Chamber (DCC) And Hyperbaric EvacuationSystem

Figure 4 shows a typical DCC electrical installation including a wide range ofchamber equipment. In this particular installation only supplies of up to 24v d.c. areused in the chamber.

Primary power is derived from a 440v 3 phase supply and is stepped down, isolatedand rectified to give the protected 24v d.c. for use with the chamber.

Instrumentation operates from a basic 220v a.c. supply. The excitation voltages for thevarious sensors are never greater than 10v d.c. at low currents, typically 15 mA.Regulation within the instrument associated with the sensor provides protection forthese supplies.


2.2 Transfer Chamber Submersible Compression Chamber (SCC) andDiver Lock-Out Submersible

Figure 5 shows the electrical arrangement of a typical mixed gas diving bell (SCC).The following points are worth noting:

All primary power is supplied via a main isolation transformer on the surface. Thecentre point of the secondary winding of this transformer is earthed through a suitableimpedance to limit the fault current to a maximum of 1A. An RCD is fitted to thecircuit with an overall response time of 20 ms.

Power inside the diving bell is entirely 24V dc with no active protection, and issupplied by transforming and rectifying the power supplied from the surface inside apressure proof container mounted on the outside of the bell.

The 220V a.c. which is used externally to power the underwater lights is protected bybeing fed from the isolation transfer with the fault current limited and activeprotection provided by the RCD.



As electrical diver heating is not presently used in commercial diving it is not possibleto provide a typical example of a suitable circuit.



Figure 6 shows the electrical installation of a typical hand held tool, in this case anNDT unit.

Primary power is derived from a 440V 3 phase system stepped down through anisolating transformer to supply 110V a.c.. The secondary winding of the isolatingtransformer is earthed through an impedance which limits the fault current to 1A andan RCD is fitted with a response time of 20 ms.


2.5 Habitat

Figure 7 shows the electrical arrangement of a typical welding habitat. The followingpoints are worth noting:

All primary power is supplied via a main isolation transformer on the surface. Allvoltages in the habitat are derived from additional isolation transformers on thehabitat.

Umbilical lines from the surface are continuously monitored for insulation breakdownusing line insulation monitors. Critical power supplies within the habitat, such as pre-heat power and power for hand-held tools, are also monitored continuously usingLIMs. The LIMs monitor leakage resistance by a d.c. injection method and can bearranged to provide shut-down of an affected circuit at any pre-set level of leakage.They also provide a continuous read-out to monitor progressive deterioration of circuitinsulation.


2.6 Wet Welding and Cutting

Figure 8 represents a typical electrical system for underwater welding and cutting. Thefollowing points are worth noting:

a. The welding unit should be grounded to the vessel and the ground lead should besecurely grounded to the work.

b. No part of the torch or the submerged sections of the power cables should be leftun-insulated.

c. The power source for welding under water is a d.c. welding generator or rectifierof a least 300A capacity.

d. Rubber gloves should be worn by the diver to provide additional protection.e. The return connection from the workpiece should be made as close to the work

area as possible.

f. A high-quality two-pole knife switch or a contactor, rated for breaking d.c., shouldbe included in the welding circuit as a means of positive disconnection in order tosafeguard the diver. It is important that the switch:

- can be seen to be open if a contactor is used, a visual indication of the contactposition should be provided.

- should be fixed so as to be readily to the hand of the person controlling thewelding equipment.

- cannot be knocked or vibrated to the 'on' position (it should fall to the 'off'position) and that a slotted cover is used to prevent accidental contact with thefixed live terminals.

g. Welding cables of adequate cross section should be used, connected in parallel ifnecessary, particularly with longer lengths, to avoid excessive voltage drop in thecable.

h. Lengths of cable should be kept to a minimum, consistent with operationalrequirements, to limit circuit inductance.

i. Cables should be arranged with positive and negative close together and tied atintervals to reduce the inductive effect.

j. Cables connected in parallel should be arranged with leads of the same polaritydiagonally opposite to reduce the inductive effect.

k. Welding cable should have a protective sleeve at the point of entry to connectorsto reduce flexing and prevent cable damage.

l. The welding cable should comprise two fully-insulated conductors, one of whichconnects the negative terminal of the welding (or cutting) set to the torch, whilethe other bonds the positive terminal of the set to the workpiece. Welding cablesof adequate cross-section should be used; guidance is contained in "BS 638:1979,Arc welding power sources, equipment and accessories, Part 4: Specifications forwelding cables". All joints in the cable should be fully insulated.

m. The electrode holder for an oxy-arc cutting system should be so designed that theoxygen valve is at all times insulated from the electrode.

n. The electrode should have an electrically insulating coating which is as resistant aspossible to chipping and to deterioration caused by prolonged immersion in seawater.


Note

In the past a device known as an open circuit voltage reducer has been used to reduceto a safe level the voltage on the electrode when there is no arc. When used underwater there have been many problems with these units and they should not be used asthe primary means of ensuring safety.Since safety of the diver cannot always be guaranteed by electrical protection alone itis necessary to adhere to pre-arranged operational safety procedures, including:

1. Since the tip of the welding or cutting electrode cannot be insulated from thewater, it should be at a safe distance from the diver's hand. The electrode shouldnot be consumed beyond a safe minimum length such that the distance from thehand to the tip of the electrode is at least 100 mm.

2. All welding and cutting equipment (including cables and connectors) should bechecked by a competent person before use to ensure that it is in a serviceablecondition.

3. A clear command system with return confirmation should be established forswitching supplies on and off.

4. Before lowering or raising of the workpiece, clamp or welding torch, a checkshould be made to ensure that the welding circuit is dead and that there is nowelding rod in the welding torch.

5. An electrode with an unchipped insulating coating should be used. Electrodeswhich have been in the water for a long time should be rejected in case thecoating has absorbed water.

6. Before welding or cutting begins, it is essential to check that there are nocombustible solids, liquids or gases adjacent to, on or within the workpiece.

7. A check should be made that there are no gas entrapment spaces above the workarea. Cutting or welding operations should never be carried out directlyunderneath a diving bell (SCC).

8. The welding circuit should only be switched on when:a. the diver is in position to start welding or cutting: this position must be as

stable as possible.

b. the workpiece clamp is securely fastened.c. the welding rod is fitted securely into the welding torch, is pointing away from

the diver, and is as near to the workpiece as practicable.

d. neither the diver nor any of the diver's equipment is between the weldingtorch and the workpiece.

e. the diver confirms that he is ready.9. Care should be taken with large loose metallic items carried by a diver (eg

wrenches and backpacks) to prevent electrical contact with a live electrode.

10. Electrodes should not be changed with the supply switched on.11. The welding torch should not be put down or carried with the power on.12. Welding or cutting equipment should never be taken into a diving bell (SCC) or

lock-out submersible. If any problem occurs with the welding/cutting gear, itshould be returned to the surface for attention.

13. Whenever practical, a second diver, or the person controlling the divingoperation, should be

Documents

AODC035 - Safe use of electricity underwater.pdf