Issued under the authority of the Home Office (Fire and Emergency Planning Directorate)

Fire Service Manual

FIRE SERVICE COLLEGE Volume 2 LIBRARY & INFORMAnON RESOURCE CENTRE

RETURN OR RENEW ON, OR BEFORE, THE LAST Fire Service Operations DATE STAMPED BELOW (2 RENEWALS MAX.) FINES ARE PAYABLE ON ANY ITEMS RETURNED LATE

,jl\lJ~\!U 10 I Electricity -11fFB JIJlI~

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FIRE SERVICE COLLEGE LIBRARY MORETON-IN MARSH GLOUCESTERSHIRE GL560RH

(01608) 650831 Exl.2338 [email protected] ~\\ ~-'\ \." 2.'f- The Fire Service College I

* 0 0 0 7 902 8 Q *

HM Fire Service Inspectorate Publications Section London: The Stationery Office •

E ectr·city

© Crown Copyright 1998 Published with the permission of the Home Office Preface on behalf of the Controller of Her Majesty's Stationery Office

Applications for reproduction should be made in writing to The Copyright Unit, Her Majesty's Stationery Office, St. Clements House, 2-16 Co]egate, Norwich, NR3 1BQ

ISBN 0 11 341112 X Electricity is one hazard which firefighters will encounter in many and varied operational circum­ stances.

Cover photograph: Northern Ireland Fire Brigade Its presence, or possible presence, must always be Half-title page photograph: West Midlands Fire Brigade taken into account when making an initial opera­ tional risk assessment at an incident.

A knowledge of the basic theory, potential hazards, types of equipment used and procedures to adopt set out this book will assist in the safe conduct of such incidents.

This book replaces:

The Manual of Firemanship Part 6b, Chapter 3 ­ Electricity and the Fire Service;

Technical Bulletin] /1978; and

Dear Chief Officer Letters: 5/1989 item C, Annex A and B; ] 1/1987 item C; and 16/1978.

The Home Office is indebted to all those who have helped, in particular the Electricity Association and its member companies, in the preparation of this work.

Printed in the United Kingdom for The Stationery Office 136269 1/98 C50

Electricity III Electricity

Contents

Introduction ix Structure of the Electricity Indu try Chapter 1 Electricity 1 1.1 Electrical Units 1 1.2 The Resistance of a Circuit 1 1.3 Conductors and Insulators 1 1.4 Short Circuits 3 1.5 Protective Devices 4 Chapter 2 Generation, tran mi ion and di tribution 7 2.1 Generation 7 2.2 Transmission and Distribution Systems 11 2.3 Substations 14 2.4 Methods of Transmission 20 2.5 Methods of Distribution 25

Chapter 3 Internal Di tribution 27 3.1 Single-phase Low Voltage Systems 27 3.2 Three-phase Low Voltage Systems 29 3.3 Three-phase High Voltage Systems 31 3.4 Protection Against Earth Leakage 31 3.5 Wiring Systems for Consumer Installations 33 3.6 Electric Lighting 35 Chapter 4 Electrical Hazards and Safeguard 37 4.1 Static Electricity 38 4.2 Electric Shock 38 4.3 Safe Approach Distances 39 4.4 Use of Rubber Gloves 43 4.5 Removing Persons from Electrical Contact 43 Chapter 5 Fire-Fighting Procedure 49 General 49 5.1 Fires in Generating Stations 50 5.2 Fires in Transformers 52 5.3 Fires On or Near Overhead Power Lines 56 5.4 Fires in Substations 57 5.5 Fires in Cable Boxes 58

Electricity V Electricity

5.6 Fires in Industrial Premises 59 5.7 Fires in Private Dwellings 59 5.8 Fires Involving Storage Batteries 60 5.9 Fires Involving Un-interruptible Power Supplies (UPS) 61 5.10 Fires in Motor Vehicles 63 Appendices 65 Al Case Study: Transformer fire, Novembel' 1997 67 A2 Electrical fire statistics 74 A3 Map showing areas covered by Regional Electricity Companies 75 A4 Electricity Association-Member Companies' Useful Addresses and Telephone Numbers 76

VI Fire Service Manual Electricity

Introduction

The presence of an electrical installation at, or At an incident involving electrical equipment near, a fire presents an added risk to firefighters. If which is owned or controlled by some other organ­ the supply can be cut off quickly firefighting can isation (e.g., a privately owned sub-station in a proceed normally, but, if this cannot be done large factory) then someone from the company immediately, non-conducting extinguishants usu­ with the relevant specialist knowledge should be ally have to be used. sought.

It was once considered that 'electrical fires' consti­ tuted a separate 'fire class' but a little thought will 'SAFE APPROACH' ­ show that any fire involving or started by electrical Training Video equipment must be either Class A, B, C or D. In 1994 the Electricity Association in conjunction In this book electrical theory is touched upon, but with HM Fire Service Inspectorate, the Fire the subject is better dealt with in a textbook spe­ Service College and the Fire Service, produced a cially written for it, and firefighters wishing to be training video 'SAFE APPROACH'. better informed should pursue their studies in that direction. This video should be seen as a part of an overall training package consisting of the Fire Service Electricity distribution and electrical apparatus are Manual, the video and I (i)(d) visits. discussed and also some types of electrical inci­ dents and how best to tackle them. Incidents Enquiries regarding the cost of, and how to obtain, involving electricity on railways are, at the time of the video 'SAFE APPROACH' should be directed publication of this book, dealt with in the Manual to: of Firemanship, Book 4, Part 3. This is to be replaced by a new book, 'Incidents involving The Production Unit Railways', in Volume 2 of the Fire Service Manual. The Fire Service College Moreton-in-Marsh Reference will be found in the text to an Gloucestershire GL56 ORH 'Authorised Person'. An 'Authorised Person' is someone from an electrical company witlYspecial­ ist responsibilities related to procedures with live electrical equipment.

At an incident involving electrical equipment which is owned or controlled by an electrical com­ pany an 'Authorised Person' is the only person who can confirm that electrical equipment is safe to approach. It is important to liaise with and take the advice of that person at the earliest opportunity.

Electricity IX •

Electricity

Structure of the Electricity Industry

England and Wale Scottish Hydro-Electric are responsible for the dis­ tribution of electricity in Scotland, the third com­ As a result of the privatisation of the electricity pany Scottish Nuclear, later merged with Nuclear industry in England and Wales, the Central Power to form British Energy. Electricity Generating Board's (CEGB) businesses were transferred to four companies. Three of these - National Power plc, PowerGen plc and Nuclear In addition to the major electricity companies there Power plc (the latter later merged with Scottish are, throughout the country, a number of smaller Nuclear to form British Energy) are engaged main­ generation businesses, for example, industrial ly in generation. The fourth company, National companies with on-site generation, rail and tram Grid Company plc is mainly involved in operating operators, local combined heat and power the transmission network. schemes, and some privately owned renewable energy schemes. Electricit. upply Companies It should be remembered thar the structure of the There are twelve major Electricity Supply electricity industry is likely to be subject to Companies (which are largely regionally based) change; with changes in both the names and the which jointly own the National Grid Company numbers of companies involved in the industry. (NGC). The Electricity Supply Companies operate See Appendices 3 and 4 for details of the major their own distribution networks which connect electricity companies. consumers in their areas to the National Grid or to local power stations. They buy electricity both from the major electricity generators and indepen­ dent power producers on the spot market and sell t it to their customers over these distribution net­ works.

orthern Ireland

As a result of privatisation three main electricity generating companies were formed which must The individual Electricity sell their output to Northern Ireland Electricity plc which has the monopoly of transmission and dis­ Companies MUST be regarded tribution in Northern Ireland. as the source of authoritative Scotland advice in relation to ALL relevant activities within As a result of the privatisation of the electricity their areas industry in Scotland three main electricity compa­ nies were formed of which two. ScottishPower and

t Electricity Xl Electricity Chapter

Chapter 1 - Electricity

1.1 Electrical Units This can be expressed mathematically by the fol­ lowing equations: Electricity, when flowing along a wire (known as a R-~ conductor) is called a current, and this is a measure -A or V = AR of the number of electrons passing a particular point in a conductor. This rate of flow is measured 1.2 The Resistance 0 a Circuit in units called amperes (symbol A). Pressure must be provided to cause the electrons to flow and this The resistance of a circuit, which is measured in pressure, which may be derived from a number of Ohms, depends on a number of factors, namely: sources, is termed the applied voltage or electro­ motive force (EMF). This is measured in volts (i) The length of a conductor. (symbol V); the greater the applied voltage, the An increase in length results in an increase in greater the current flowing. resistance. An analogy can be drawn between electricity (ii) The cross-sectional area of the conductor. flowing in a circuit and water flowing through a pipe. In hydraulics, the pipe offers a resistance to The greater the cross-sectional area, the the flow of water and this resistance to the pas­ lower the resistance. sage of water is proportional to the diameter of the pipe. (iii) The conductivity of the material used. Some materials are better conductors than Similarly with electricity, the conductor offers a others resistance to the flow of electrons; the greater the (e.g., silver is a better conductor than copper). size (diameter) of the conductor the lower the resistance. The resistance of a conductor is mea­ (iv) Temperature. sured in ohms (symbol R). For most materials, the hotter the material, There is a direct relationship between voltage, cur­ the greater its resistance. rent and resistance. For example, if a circuit has a resistance (R) of 1 ohm and a voltage (V) of 1 volt 1.3 Conductors and sulator is applied at its end, a current (A) of 1 ampere will flow. This fundamental principle is known as Electricity is always trying to find a path to earth, Ohm's Law which states: that is, to escape from its conductor and reach the ground or a conducting path which is connected to 'the value of a current passing through the ground. Some materials offer such a high resis­ a conductor is directly proportional to tance to the flow of electricity that the current can­ the potential difference between the not force its way along them; they are then said to ends of the conductor, and inversely act as insulators. Other materials offer little resis­ proportional to the resistance of the tance and are said to be good conductors; copper , conductor' . and aluminium are two examples of good conduc-

Electricity 1 Figure 1.1 11 kV pole Figure /.3 Range ofpvc showing detail of insulated insulated 6001/000 volt discs. armoured power cables (Photo: Eh:'Clrio(.1 Associmion)

Figure 1.2 Range ofpaper insulated IkVand IIkV distriblllion cables. (Plwru: £Iee/rid/,' A~\oci(l[iOIl) A mineral powder (generally magnesium oxide) within a copper sheathing is also used as an insu­ lating medium for cables which are laid in hot places, such as near furnaces or boilers or in situa­ tions where circuit integrity is vital e.g., alarms. These cables are known as MICS (mineral insulat­ ed copper-sheathed) or alternatively MICC (min­ eral insulated copper-clad) cables and are also used in general situations where extra physical protection is required.

When conductors form overhead lines or switch­ board connections then insulation is often neither desirable nor appropriate. In such cases arrange­ ments must be made to stop the cables coming into contact with their supporting structures and with tors and so are used extensively for electric cables. paper were the materials used for insulating, often each other. This is achieved by the use of insula­ Water is also a good conductor when impure, so a with lead sheathing and wire-armouring for pro­ tors which are usually made of porcelain or glass. firefighter with wet clothing or holding wet hose tection and moisture proofing, these are now like­ who touches a li ve conductor could form an elec­ ly to be found only in older buildings. 1.4 Short Circuits trical path to earth and receive a shock which could be fatal. Most insulated cable nowadays is, however, insu­ Figure /.4 JJ kV XLPE insulated distribution cable. Whilst air and most other gases are good insula­ lated by either an oil impregnated paper or by PVC rPholO: EleClricil.'r AssociaTion) tors, electric current can, if the insulation becomes In most instances the use of bare wire is impossi­ (polyvinyl chloride) or other plastics such as PCP faulty, leak between two conductors or between ble and the conductor must be continuously insu­ (polychloroprene) or CSP (chloro-sulphonated one conductor and ealth. The amount of CUITent lated to prevent electrocution on contact. Cables polyethylene). These plastics are extremely leaking depends, among other things, on the volt­ must, in many cases, also have additional cover­ durable and, whilst not strictly non-flammable, It should be kept in mind that burning plastic cov­ age, the condition of the insulating material and ings to prevent damage to this insulation. For will only burn whilst a source of heat such as a ered wire will give off toxic fumes and gases. the distance between the conductors. many years vulcanised rubber and oil impregnated naked flame is continuously applied.

2 Fire Service Manual Electricity 3 Figure 1.5 Miniature melt at a much lower temperature than that which Circuit Breaker. would result in a dangerous temperature rise in the WARNING -' (Photo: HM Fire Sen:ice II1SpeClOrrllc) THIS UNIT SHOULD BE SWlTCHEO OFF ~ ~ rest of the circuit, the fuse will act as the weak link ~ DURING SUPPLY WlR G INSULATlON TESTS !O in a chain. ~~~= ~;~~:V~AMAGE TO THE ~ ~ IlCD PIlO1ECTED SOClCET IT IS NOT NECESSARY TO 1;,l\ OlSCONN [eT THe UM1T. ~ I • REF4200 (b) Circuit breakers 13A. 'DJ/2¥N. M; MY 38 mA. TIW' CURRENT In the modern consumer unit, fuses may be replaced by miniature circuit breakers (MCB's) which look like an ordinary switch or a push but­ TEST REGUlARlY ton. They automatically interrupt the circuit if it •1 __1III1lII • B~__•1III1lII becomes overloaded or if a fault occurs. Once the B.-rllR'. cause of the fault or overload has been identified n FIIGIIIDCD""'aur .. and conected the MCB can be re-closed and the -- circuit brought back into service.

In installations of a greater power, the use of fuses and MCB's is impracticable for technical reasons, If a breakdown occurs in the insulation separating If a breakdown of insulation occurs, excessive cur­ and automatic circuit breakers, which operate adjacent conductors or a conductor from the earth, rent will probably flow through the faul t and. if the when the cunent rises to a dangerous level, are what is known as a short circuit takes place. That fuse or circuit breaker fails to operate, overheating installed. Such circuit breakers are designed to is, the cunent. instead of following its normal path, will result. For a fire to occur in such circum­ operate automatically if a fault occurs. They can be finds a quicker return path. The electrical resis­ stances, it is only necessary that there should be opened manually if necessary, for example to test tance in such a case is generally negligible, where­ combustible material in close proximity to an the mechanism. They are often closed manually or upon a heavy current will flow and cause intense over-heated wire or a hot spark. Fire can readily be automatically if they open due to a fault, to ascer­ local heating combined with overloading of the started through a short circuit whether or not a tain whether the overload was of a momentary cables. They may then become dangerously over­ cable is insulated. nature only. heated unless the circuit is broken. 1.5 Protective Devices If a line has been accidentally brought down and is Such a breakdown in the insulation may take place lying on the ground, it may not be making suffi­ in many ways. Insulating material will deteriorate When an electric current passes along a conductor cient contact with the ground to operate the circuit with age or from other causes, and a condition may it generates heat. If the maximum cunent the con­ breaker. Furthermore, the circuit breaker may be be reached where their insulating properties are ductor is designed to carry is exceeded, either closed automatically several times after a period of insufficient to prevent a short circuit. The perish­ because of excessive load placed on the circuit, or time to test whether the fault has cleared. This is ing of rubber, is a good example of this, and is one because of a short circuit, overheating will occur known as auto-re-closing (see page 14). of the reasons PVC has superseded rubber as an and the conductor may become hot enough to • insulating medium. Cables or wiring may be sub­ ignite the combustible insulation with which it is jected to mechanical stress through vibration covered. To prevent this, an electric circuit is fitted Therefore, it should never be caused by external influences, whilst dampness is with a fuse or circuit breaker to break the circuit in a frequent cause of the breakdown in insulating the event of an overload. assumed that a circuit is dead properties. even when a circuit breaker (a) Fuses Alternatively, excessive heat through external has operated. causes e.g., steam pipes, industrial processes for In its most basic form, a fuse is a short length of which the system has not been designed, will also wire having a low melting point and forming part lead to rapid deterioration. Furthermore, insulation of a circuit, the size of the fuse wire being calcu­ is often destroyed by nails driven into walls and lated for the normal expected load. If that load is penetrating the wiring; workers picks, pneumatic greatly exceeded the passage of the extra cunent drills etc., striking cable runs; abrasion and causes the temperature to rise and the fuse wire to (although rarely) rodents. melt, breaking the circuit. Because the fuse will

Y ••••4•••F.i".e.s.e.rv.i.ce.M.a.n.u.al•• ~..•••R E.le.c.tr.ic.i.t_.5 f Electricity hapt r

Chapter 2 - Transmission and distribution systems

2.1 Generation a rapid change (or alternation) in the direction of flow which occurs many times a second. The num­ A generator is a machine which produces electricity. ber of changes per second is called the frequency and is expressed in so many Hertz (Hz) (cycles per Electricity is generated, transmitted and distrib­ second); this is standardised at 50 Hz in the U.K. uted as alternating current and can be converted to direct current for specific purposes. Direct current Alternating current is generally used for transmis­ flows from the positive to the negative terminal of sion as the voltage can be increased or decreased the conductor. But, with alternating current there is according to the requirements by means of appara-

•

Figure 2.1 Turbine at Eggborough Power Station. (Photo: Nmiunal Power)

Electricit)' 7

n tus called a transformer. Alternating current is schemes) may also be used in some power stations. Figure 2.3 Pulverised coal particularly suitable for transmission over very The main generating stations are linked together fuel mills at Didcot power long distances for which very high voltages are and to the main centres of consumption by a net­ stalion. required. This is because if the voltage is work of high voltage overhead lines and under­ increased, the current is reduced and so the equiv­ ground cables generaJly known as "the grid". alent resistance for any given length of conductor passing the same amount of power is less, so (b) Power stations enabling smaller conductors to be used. Power stations may have outputs as high as 3,890 Electricity is also distributed almost entirely in the Megawatts (MW) while individual alternators vary form of alternating current which can, if necessary, in size between about I MW and 660 MW. be converted (or rectified) into direct current for Generally their energy sources are either hydro any specialised use. (water), fossil fuels (coal, oil or gas), or nuclear fission (uranium). (a) Alternators The main components of nuclear and fossil fuel Alternating current generators are called alterna­ power stations are fuel storage, steam raising (boil­ tors, which in the U.K. are generally driven by er or reactor) turbo alternators, water cooling, steam turbines, although gas turbine, diesel waste disposal, transformation and connection of engines or water turbines (in hydro-electric electricity to the national grid.

Figure 2.4 Hinkley Point nuclear power station, Somerset. Reactor pile cap.

These are unique to Cl nuclear power station. LI is highly unLikely Ihat fire­ fighters wouLd be called 10 an incident involving a reactor pile cap. Nuclear power slalions have especially sophisticated emergency plans. (Photo: Nuclear Eleclnc)

Figure 2.2 Drax Power Station. All power stations should have an emergency plan drawn up which the locaL Fire Brigade shouLd be aware of (Photo: Na/lOllal Power)

8 Fire Service ManuaL ELectriciry 9 I

------.....:iIlS...-. ~ To reduce fire hazard, areas such as control rooms, on the national grid. Factories and commercial particular voltage and yet be operating at a lower switch and transformer rooms, etc., are usually buildings etc., may have small gas turbine or diesel one. The majority of overhead transmission lines separated from other plant by walls of fire resisting engine alternators. A number of stations using are double circuit, i.e., a separate circuit is carried construction and may be equipped with automatic Combined Cycle Gas Turbines (CCGT) have also on each side of the tower or pylon and these may fire extinguishing systems. been built. These stations consist essentially of be energised from separate sources. natural gas and/or oil fired commercial or aero The type of building construction varies enor­ engine generators with the exhaust gases being (b) Transmission Systems mously but modern power stations are generally utilised in conventional steam boilers or, for exam­ fire resisting and consist of a steel frame with rein­ ple, in district heating systems. Most power stations in the United Kingdom feed forced concrete walls at low level and metal panel into the national grid system and the majority of walls above. Roofs are usually of an aluminium 2.2 Transmission and Distribution power transmission is by overhead lines. These construction with bitumen over, and they will usu­ Systems lines operate at 275 kV and 400 kY. The grid sys­ ally burn through and partially vent major fires. tem in England and Wales is under the control of (a) Transmission and Distribution Network the National Grid Company. In Scotland the grid Considerable quantities of insulating oil are pre­ system is under the control of Scottish Power and sent in electrical equipment, together with lubri­ Figure 2.7 shows the transmission and distribution Scottish Hydro-electric, whilst in Northern Ireland cating oil used on turbines and generators which is network in diagrammatic form. It should be noted the grid system is under the control of Northern also stored in large quantities. Most present day that transmission lines may be designed for one Ireland Electricity. stations use hydrogen in closed circuit for cooling the alternators and have hydrogen generating plant, or hydrogen storage in cylinders or banks. Electricity Regional electricity companies Sulphur Hexafluoride (SF6) Generating Companies To towns villages, This gas is used as an insulating and interrupting _ -l------: Final distribution medium in many types of electrical apparatus industrial _.'-.'_ (Secondary) substations areas throughout the voltage range. The types of equip­ 11,000 ment within which SF6 may be found varies from volts large gas-filled enclosures where entry by person­ nel is possible, to small items where access to the 33,000 volts gas-filled enclosure is not possible, even during Power station maintenance. Because it is heavier than air and Primary substation will not disperse easily it -can be a hazard in con­ fined or low lying areas as it is an asphyxiant. SF-;; Filled National Under fault conditions toxic and corrosive by­ Equipment Grid products can be produced, both as a gas and as 230 volts powdery products. Under catastrophic failure, this

powder can be blown over and contaminate the Substation Supply Electrical immediate area. Substation rail Figure 2.5 and 2.6 Sulphure Hexafluoride (SF6) filled I equipment warning signs. BA and full protective equip­ [I'

10 Fire Service Manual Electricity 11 Figure 2.8 For high voltage systems (1 kY upwards) there are PelhamlWaltham Cross Voltages over 50 volts a.c. normally three conductors or lines between the 400kV transmission line generator and the transformer. High voltage distri­ showing tension and sus­ and currents in excess of bution systems may have three wire or two wire pension towers. 5 milli-amps are considered arrangements. When the current is finally reduced (PhulO: Nnuonal Grid Compwly LId! dangerous. below I kY a common return conductor (neutral) is introduced.

The voltage between the three phase lines is 400 volts, but the voltage between each phase line and the neutral is 230 volts. Distribution systems are owned by, and under the control of the Electricity Companies within whose These two voltages are the national declared volt­ boundaries the systems are situated. ages for normal consumer use.

The loading of the transmission system is carried (e) Safety procedures out from Grid Control Centres located in various parts of the country with overall co-ordination at a The operation and maintenance of the Transmission National Grid Centre. Switching is carried out and Distribution lines is subject to detailed safety from the Grid Control Centres. Control of the dis­ procedures and rules. These Safety Rules precisely tribution systems varies from company to compa­ define who is permitted to work on the system. This ny, but, in general, each Company has centre con­ authorisation may only relate to a specific part of trol arrangements supported by local control. the system, outside of which that person may not be considered to be 'competent' e.g. only 'Authorised (d) Three-phase system Persons' may isolate lines etc.

Alternating current is normally generated by what is The basic principle is that all current-carrying known as the three-phase system, that is, a system parts of the system are treated as 'live' until they in which the current flowing is in three interdepen­ are isolated from the rest of the system, and con­ dent circuits, which are mutually displaced in phase. firmed to be 'dead' by approved procedures which

Figure 2.9 The reduction ofhigh voltage to low Red Phase .---- -...... -:.:-.-.------,j'--+-r-'------'­ (400/230) voltages in .' , , the three-phase system , , shown in diagrammatic ,, 400V 230V , form. ,, (c) Distribution Systems • Low voltage - greater than 50 volts but not , Yellow Phase , exceeding 1000 volts ac or 1500 volts dc. ,, Although high voltages are used to transmit large ,, 400V I NeU1ral I quantities of power from one part of the country to • High voltage - anything greater than low I I another, it is necessary to convert to lower voltages voltage i.e., greater than 1000 volts ac or ,, , 400V before the power can be used by consumers. This \ 1500 volts dc. \ is done in stages by means of transformers. Higher , Blue Phase 11 kV supply \ , ,, ,, voltages are generally reduced to 132 kY, and from Firefighters should appreciate that even low volt­ ,, ,, , , , , 132 kY to 33 kY or 11 kY for large industrial cus­ age systems such as those used in domestic prop­ , '. tomers and to 'Iow voltage' at 230/400 volts for erty are high enough to cause severe shock or even ------=-...... __._.' commercial and domestic customers. death if live conductors are touched. Furthermore,

flashovers resulting from insulation failure and/or Local Transformer Yoltages are classified as either low voltage or short circuit can result in severe arcing and burn high voltage. The classifications are: injuries.

Electricity 13 12 Fire Service Manual ~

•• ---..J~tr...... 11 include efficient earthing either at the points of iso­ When working on or near a tower or structure car­ Figure 2./0 Pole Mounted lation or at either side of the point of work. This rying live conductors, the minimum safe working Transformer. High voltage ~ confinnation will be given by an 'Authorised distances, as set out on page 42 (see Figure 4.2) lines are positioned hori­ IHigh voltage Person' from the electricity company. apply. zontally. Low voltage lines are posi­ In nonnal circumstances no work is allowed until a (I) System control tioned vertically. 'Safety Document' has been issued which clearly states the precautions which must be taken and the Irrespective of the voltage involved, every part of area within which work is permitted. In an emer­ the system is under control. Within the control net­ gency situation an 'Authorised Person' on site may work, access to the other control points is usually issue verbal instructions which MUST be followed. direct and rapid via telephone or radio. Thus the transmission and the distribution networks are These precautions are of the utmost importance always under the control of a 'Control Person', but when it is appreciated that: local lines at lower voltages may be under the con­ trol of local staff on telephone standby in homes (i) many lines are automatically controlled and and offices. It is vital that there be liaison between can be switched on remotely; the Brigade and the local 'Control Person'. Also, it is important that the fire brigade personnel should (ii) many lines have automatic re-closers so that have quick access to the control system. To enable they are re-energised automatically after a this to be done contact telephone numbers are fault; available at all sub-stations and on some structures or pieces of equipment belonging to the Electricity Figure 2.11 Outdoor (iii) an isolated line parallel to a live line may, if Companies, and certain ex-directory telephone Distribution 33 kV Primary not efficiently earthed, carry a lethal charge; numbers are available at brigade controls for this Substation. and purpose. These are, of course, only for use in an Vnmanned substations emergency. should not he entered (iv) single circuit isolated lines may be charged unless an 'Authorised due to atmospheric effects and carry lethal 2.3 Substation Person' is preselll EXCEPT voltages. If carrying out a rescue at (a) Types ground level. Electricity Company personnel who are permitted (PhOIO: Nafional Cnd Cumpany Lld) to climb towers or structures carrying live conduc­ The point where electricity is transformed from tors, receive extensive training and are subject to one voltage to another is known as a substation, strict safety rules which prohibit work within spec­ and these can vary greatly in size and type. An out­ ified distances of conductors. Any person working door distribution substation, for example, may on a tower or structure must also be under contin­ only occupy a space about 1.8 x 1.8 m, whereas a ual observation by another person on the ground. 400 kV switching and transforming substation could cover up to several hectares.

Pole-mounted substations

A pole-mounted rural distribution substation Fire Brigade personnel should (Figure 2.10) does not usually exceed I1 kV, has a transformer with exposed high voltage terminals Outdoor Distribution Substations gear with no accessible live parts, and a low NEVER climb overhead line and open or enclosed low voltage terminals. voltage (LV) distribution unit (Figure 2.12). supports without the approval of These substations are either one of two types i.e., The high voltage supply may be fed to the trans­ (i) Primary substations (132 kV/33 kV or 11 kV) Secondary substations, which are the most com­ an 'AUTHORISED PERSON' former from overhead or underground cables, and which may have exposed live conductors mon type of substation, are used to distribute elec­ from an Electricity Company the low voltage local distribution may also be (Figure 2. I I) or, tricity at 230/400 volts to domestic, commercial either overhead or underground. (ii) Secondary substations (11 kV/400v) which and light industrial premises. generally consist of a transfonner and switch

14 Fire Service Manual Electricity 15 - Figure 2.12 Ourdoor Indoor Distribution Substations Indoor 'grid' substations Distribution 11 kV Secondary Substation, These usually take the form of separate buildings or These are usually found in cities and large developed showing (left to right) HV rooms within or on the roof of larger buildings. areas where space is difficult to find. They are, in SWitchgear. LV Fuse They will contain one or more transformers, switch effect more compact versions of the outdoor 'grid' Cabinet and 11 kV/400 V gear and LV distribution units. Voltages do not nor­ substations and may contain enclosed or open type lramforma mally exceed 33 kY. switchgear and bare conductors. (Photo: Hlt4 rIn: St!n'lCe ImpnlOmfeJ

Outdoor 'grid' substations (b) Transformers

These substations (Figure 2.13) vary from single The more usual type of transformer consists of insu­ transformer units connected to a single overhead lated copper conductors wound round iron cores, transmission line, to multi-transformer units with which may be immersed in oil in a tank. In some trans­ several transmission lines. The larger sites may formers the oil may be contaminated with Polychlori­ include a control building and voltages may be up nated Biphenyl (PCB), and can pose a health and to 400 kY. environmental hazard if released (see page 55).

Figure 2.13 Outdoor Grid 400kV Transmission Substation. ,PholO Nallonol G,",d Comp"", Ltdl Figure 2.14 'Enclosed'transformers are generally used in urban areas. rP/WIG Nallonal Pn"erJ

16 Fire Service Manual Electricity 17 s In the larger types [Figure 2.151 e.g., those used for radiators and rely on natural air circulation for cool­ compound through a flame trap. Some large trans­ voltages down to 33 kV, separate radiators are pro­ ing. The quantity of oil depends on the size of the fonners, mainly in urban areas and at power stations, vided for cooling the large quantities of oil. transformer and in a large transformer may be as are provided with water spray extinguishing systems much as 136,000 litres. which automatically operate in the event of ftre. When the warm oil has risen to the top of the tank, it flows down the radiator, and the cool oil is then Should a transformer sustain damage, either through It should always be kept in mind thal, although the returned to the bottom of the tank. Pumps are an internal electrical fault or through some external power to the transformer on fire has been cut off, sometimes used to assist oil circulation and forced cause, the oil may be released, possibly at a high adjacent transformers could still be 'live' and care ventilation through the radiators may also be temperature or even on ftre. Transformers have been should be taken to keep water away from them. found. In these cases the pumps for oil and air cir­ known to explode. To prevent escaping oil flowing culation are automatically operated when the tem­ around other transfonners nearby, many modern (c) Switchgear and circuit breakers perature of the apparatus reaches a predetermined substations are constructed so that each unit is bund­ level. ed in a separate compound. Some bunds are filled High voltage with shingle to a sufficient depth to take the full Smaller transformers e.g., 11 kV and below, have quantity of oil which could be released. Provision When a switch is opened there is a tendency for the cooling tubes on the outside of the tank instead of may also be made for draining away the oil from the current to arc across the gap and, at high voltages, the distance the arc will jump is considerable. Consequently, high voltage switch gear used for transformers and feeders (see below) are, usually, either filled with oil to quench the arc when the Figure 2.16 llkV1400V Distribution Transformer. switch is opened or are of the 'Air Blast' type (PhOlo. HAt Fire Service InspeCl0raleJ (Figure 2.17). Some switches are automatic in

Figure 2.15 Typical 'Grid'transformer. showing separate radiators (on right hand side). Note the blind wall. (Photo: National Grid Company Lld) Figure 2.17 Air blast circuit breaker (switch). (Photo: Norional Grid Company LId)

18 Fire Service Manual Electricity 19 operation, others are manual and are operated Air-blast circuit-breakers operate at pressures up to Figure 2.18 Notice on when it is necessary to open or close a circuit. 60 bar. and when they 'break' they do so with explo­ pylon gives details of owning company. emer­ sive force and produce an extremely loud bang. gency telephone number A circuit breaker is a special type of switch which and lOwer identification is normally designed to operate automatically to number: These signs are protect a circuit against overloads or faults. (d) Ventilation of substations situated above the aJ1li­ climbing guard. Those on high voltage circuits which have their When substations are situated in buildings, venti­ (PI/UfO: Elrcrriotf Assnriatirm} contacts immersed in a tank of oil, operate when lation is necessary as a considerable amount of the current reaches a predetermined level. A very heat is generated by transformers, particularly high pressure is set up in the oil when the circuit when working at full load. Where forced ventila­ breaker opens. and the tanks are robustly con­ tion is provided, means also exist for shutting off structed. A gas vent is also provided to release any the ventilation in the event of fire. With modern explosive gas generated. Gases, such as acetylene. switchgear and protection, the risk is not great, but can be produced under fault conditions. If the where oil is used for cooling there is the possibili­ amount of gas produced is in excess of the ty that this may become ignited. designed ventilation provision there can be an explosion risk. 2.4 Methods of Transmission

Low voltage The transmission system, both overhead and under­ ground, operates mainly at 400 kV and 275 kY. It The distlibution side of a transformer which sup­ transports electricity from power stations to .the plies low voltage CUITent to consumers is connect­ distribution systems of the Electricity Companies ed to a distribution board. This is a fuse board con­ and other suppliers to meet the needs of consumers. taining four busbars, one for each of the three The transmission system is interconnected with phases and one for the neutral. The board is nor­ France by the cross-channel submarine cable mally contained in a locked metal case if outdoors, link. but may be open if inside a substation building. (a) Overhead Lines The switching arrangement for isolating trans­ formers from the distribution board is normally Transmission overhead lines at 400 kY and 275 kV through isolating link switches, but sometimes a are supported on large galvanised steel towers and circuit breaker is connected between the trans­ consist of un-insulated aluminium/steel or alu­ former and the busbars. Cartridge type fuses are minium alloy stranded conductors. The conductors generally inserted between the busbars and the dis­ are insulated from the towers by porcelain or glass tribution cables and used to isolate them. insulators. Figure 2.19 Detail of Feeder cable switchgear Most towers carry two circuits with the three phas­ Tower identification signs. es of each circuit installed in a vertical formation Note the emergencr tele­ The high voltage cables used to connect one sub­ on opposite sides of the towers. An additional con­ phone call number and the tower identification station to another are known as HV feeders. and ductor, which is an earth wire, connects the peaks number: three types of switch may be employed, namely: of the towers together. Depending on the power (Phoro: £Icetrinr" Association) transfer of each circuit the phases may have single, (i) the automatic oil circuit breaker; twin or quadruple sub-conductors.

(ii) an isolator (which is a manually operat­ Each tower has a unique identification number ed oil-immersed switch); or which is displayed on a notice mounted above an anti-climbing guard which is installed to pre­ (iii) an air break isolator (which is normally vent unauthorised access to the upper sections mounted outdoors on a pole or gantry of the tower. Each circuit also has a unique cir­ and operated at ground level). cuit identi fication which is a combination of

Electricity 21 20 Fire Service Manual Figure 2.20 Pylon. Note Figure 2.21 Wood poles the anti-climbing guard and carrying High Voltage lines the circuit identification carry a danger sign. Low colour code. voltage poles do not carry (PhUTO: ElectriciTy Associalion) a warning sign. (PhOfO: Midlnlld.~ EleclriciryJ

colours or symbols and these are displayed on (b) Cables To maintain the integrity of the insulation the heat which is dissipated into the backfill and plates fixed at various points on the legs of the majority are oil filled under pressure; some are gas ground around the cables. To maintain the design tower. Transmission cables can be up to 150 mm in filled with nitrogen or even contained in a welded rating, some circuits have cooling pipes laid in the diameter and may be laid single phase or three steel pipe which is itself filled with nitrogen under ground with the cables. These pipes contain water Wood pole lines operate from low voltage up to phase according to design. If they are single pressure. from either an open pumping system which 132 kV high voltage. Only high voltage poles are phase they will be laid in the ground in groups extracts and returns water to rivers, lakes, etc., or a fitted with a danger notice. of three. The power transfer capabilities of transmission closed system with towns mains water containing cables can give rise to a considerable amount of chemicals to prevent con'osion of the water pipes.

22 Fire Service Manual Electricity 23

> Figure 2.22a and 2.22h The cables are often laid in the public highways or Underground systems Underground cable link pavements and on some designs, at specific inter­ box. 4001230V. vals throughout the route, link boxes or pillars will The cables which run from the distribution units (Photo: HM Fire Service Inspecrorate) be installed. Link boxes in the carriage-ways are in the substation are called distributors and each protected by heavy pit covers. On oil-filled cable cable either consists of four conductors - one for routes, pressurised oil tanks may also be buried each of the three phases and one for the neutral, adjacent to the cables. or three conductors - one for each of the three phases. Transmission cables are usually buried at a depth of approximately I metre and are protected by rein­ Sometimes there is a fifth conductor in order to forced concrete cable covers imprinted with the provide a separate control wire for public street words "Danger electricity'. If the cables are mod­ lighting. ern exposed cables with PVC sheaths they will have "Electricity ... volts" imprinted in the sheath. Underground cables are continuously insulated and in some cases will be armoured. Cables are often used to interconnect equipment within substations and at larger urban sites these Overhead systems cables may be installed in a network of tunnels, often running for several kilometres under the site. Overhead electric lines are normally un-insulated, (it should always be assumed that all wires are un­ Fires in these tunnels present several hazards i.e., insulated unless specifically informed otherwise toxic fumes and thick smoke from burning insula­ by an Electricity Company official) and they are tion, cramped conditions, obstructions caused by mostly used in rural or semi-rural areas. cables and cable mounts and the presence of large numbers of HV cables. some of which could be The cables run from the distribution units in the exposed and live. substation to poles carrying the lines or conductors at the start of the overhead distribution system. The phases and the neutral of the cables are con­ Entry to these tunnels nected to the overhead lines or conductors at the and/or firefighting should top of the pole and consumers' services are tapped at the nearest pole to the premises concerned. NOT be undertaken without the presence of, and in Junction or link boxes consultation with, an At intervals on underground cables, link boxes (or ~Authorised Person'. feeder pillars) may be constructed to interconnect feeders and distributors to smaller cables, to enable cables to be tested and to facilitate inter-connect­ Cables are also installed in ducts or tunnels under ing or isolating of connections. major roads, motorways and rivers and in disused railway tunnels. These boxes are set in a brick pit below the ground with a cover at pavement or road level for access. 2.5 Methods of Distribution There may be several cables entering the box, and they will be connected to one side of a link for At a distribution substation, voltage is reduced to each phase. The other side of the link is connected its final level of 230/400 volts for use in shops, to a busbar, in the same way as in a distribution commercial premises, homes, etc. unit. The box is filled with a bituminous com­ pound, with only the contacts exposed. From the substation, electricity is distributed to the consumer either by overhead lines, underground In some areas, above-ground kiosks are used cables or by a combination of the two. instead of under-ground boxes. These kiosks take

24 Fire Service Manual Electricity 25 Electricity ap r

the form of steel or glass reinforced fibre (grf) feeder pillars and are used as feeder, disconnection or distribution boxes.

Only 'Authorised Persons' on the staff of the elec­ tricity companies, or their authorised agents are Chapter 3 - Internal Distribution permitted to have access to link boxes, feeder pil­ lars or above ground kiosks.

Service cables 3.1 ingle-pha e Low Voltage the neutral conductor would become discontinuous From the street distributors, service cables are Sy tems and it would be possible for a dangerously high taken to supply each individual consumer and ter­ voltage to appear on the consumer's installation. minate at a main fuse, or cut out, at the consumers' (a) The service termination premises. Apart from the main fuse and meter, the Finally, from the cut-out, two insulated and installation is the property of the consumer and Small consumers, such as domestic premises, are sheathed conductors are connected to a meter. therefore varies considerably in type and layout. supplied by the Electricity Company with a single There may be more than one meter if different tar­ Details of the wiring of consumers' premises are phase and earth system. iffs operate in a particular consumer's premises. discussed in Section 3. For new supplies, the electricity companies prefer (b) Internal distribution after the meter to install their service terminal equipment in cabi­ nets which are accessible from outside the build­ For the typical small-consumer type of installation ing. The supply to their cabinet is often through an the incoming cables from the meters are connected underground cable, even when the distribution sys­ to one or more consumer units which comprise a tem is on overhead lines. However, underground double pole main switch and a number of fuses or service cables may also be installed through sealed miniature circuit-breakers. Operation of the main ducts to service terminal equipment, often called switch will disconnect the installation from the the meter position, within the building. electricity company's supply system, but it must be remembered that the incoming supply from the In older overhead supply situations two service distribution system will remain live. The fuses or lines are secured to insulators attached to the miniature circuit-breakers control the lighting and building, and from these, short lengths of insulated power circuits in the building. cables are run to the service terminal equipment inside the building. Modern systems use an insu­ Socket outlets for power supplies are normally lated cable with two concentric cores from the connected to ring circuits in which the conductors overhead line to the point where it is attached to are looped from one socket outlet to the next. Both the building and on to the service terminal equip­ ends of the live conductor loop are connected to ment. the same fuse in the consumer unit. Similarly, both ends of the neutral conductor loop and the circuit The electricity company's service terminal equip­ protective conductor loop are connected to the ment should be mounted on fire resistant boards. neutral and earth blocks respectively. It is common Both underground and overhead service cables are for one ring circuit or main to serve one floor with connected to a cut-out. This consists of a fuse in each subsequent floor being served by a further the live, or phase, conductor to protect the supply circuit. In addition it is also common for a further cables if severe overloading occurs, and a solid circuit to serve a kitchen area. connection (sometimes through a link) in the neu­ tral conductor. The neutral conductor is not fused Occasionally, old installations may be found with because it is connected to earth on the electricity fused neutrals and similarly in older installations it company's system and, under normal conditions, may be found that each socket outlet is fed inde­ is always at, or near, earth potential. If a fuse had pendently with its own phase and neutral wire been installed in the neutral, and it had operated, from the final distribution fuse board.

26 Fire Service Manual Electricity 27 Figure 3.1 A typical 3.2 Three-phase Low VoJtage meter by four single core insulated and sheathed external electricity meter y terns conductors. After the meter the supply is fed cabinet. through a three-phase main switch to a distribution (PhOfO: Efer'/ricltI, AssociallOlr) (a) CommerciallIndustrial fuse board. In larger installations the main switch may be connected to a bus-bar chamber from The electrical demand of commercial or small which separate single-phase or three-phase circuits industrial premises may be such that the electrici­ controlled by their own switches may be taken to ty company has to provide a three-phase supply. distribution fuse boards at remote parts of the The connection from the distribution system will premises. be similar to a single phase supply, except that the service cable has either three cores and a concen­ (b) Residential tric neutral, or, on older installations, four separate cores encased in a lead sheath. A cut-out with fuses A block of flats is often supplied by a single three­ in all three line conductors and a solid neutral is phase service cable which terminates in a 'multi­ installed. The cut-out is connected to a three-phase way' cut-out or fuse board (Figures 3.2 and 3.3). A

Figure 3.2 Single 3-phase Riser ducts with service cable terminating in removable covers a Multi-way distribution board. 4th floor

D--:; M.", ,"obe"•• I

Cables routed on cable tray with steel conduits to meter cupboards on floors above and below

.,. "•• ~'., Z',,",;'" '~':'\':" . 2nd floor

D ":..; , ;'. . , .~ ".- . :. " . ~ 1st floor

Multiway distribution board

Cooker, immersion heater and shower circuits are There will be great vanatlOns in internal wIrIng separately run and fused in the consumer unit. arrangements and therefore no wiring convention Lighting circuits also operate on the loop system should be accepted as standard. but are more complex because of the need to pro­ vide a switch at a point remote from the light fitting.

28 Fire Service Manual Electricity 29 Figure 3.3 Earthing In both cases the rising mains will be in service heat or corrosion, and precautions have to be taken arrangements. ducts and will outwardly appear the same but it to protect personnel and installations against con­ should be remembered that in some large buildings sequent damage. Insulation failures could result in some of the distribution cabling may be three-phase. severe or fatal shock, or equipment overheating to a sufficient degree to constitute a fire risk. 4th floor For either system the internal distribution for each of the flats will be as previously described. Electrical systems are designed to provide two Meter cupboards lines of defence against electrical shock. The first 3.3 Three-phase High Voltage step is to give protection to the user during the nor­ Systems mal working of the installation (e.g., by insulation) and then, in the event of a failure of the first stage, Where the demand for power is high the electrici­ to give protection by automatic disconnection of ty company may supply power at high voltage the supply and earthing. (typically I1 kY) to a substation on the consumers' premises. For a medium sized customer a trans­ (a) Earthing former may be installed at this point to supply a normal three-phase low voltage installation, that is Earthing is the usual safeguard provided to give a three-phase four-wire bus-bar with separate sub­ protection against electric shock. An 'earth' is an 2nd floor circuits connected to it. electrical connection between a piece of equipment and the general mass of earth such that a fault on Some customers may require a high voltage supply that equipment will cause sufficient current to flow at remote points on the premises. In this case the to operate the circuit protective devices and, if the electricity company will install a high voltage equipment has a metal enclosure, to prevent a dan­ metering circuit-breaker and connect it to the cus­ gerously high voltage appearing on the casing. tomer's high voltage bus-bar. The customer will 1st floor then install their own high voltage switchgear to (b) Earthing Arrangements control each high voltage sub-main. Transformer substations are connected to the ends of the sub­ Fig 3.4 shows four examples of providing an earth mains to give a three-phase low voltage system. connection for electrical circuits (1-4) and an example of providing shock protection by a resid­ Because the operation of high-voltage switch gear ual current device (RCD) (5); must only be carried out by properly trained, com­ petent personnel, the electricity company will (1) Water pipe earthing: Because of the extensive often provide an emergency trip switch to isolate use of plastic piping, this method is now for­ the customer's high voltage system from the elec­ bidden as the sole means of earthing in the tricity company's distribution system. This fre­ Institution of Electrical Engineers' (lEE) quently takes the form of a 'fire alarm' type of Wiring Regulations. switch situated adjacent to the main intake substa­ tion or some other conspicuous position: breaking (2) Local earthing (other than water mains pipe): the glass on that switch automatically operates the In this system plates, rods or steel frames of electricity company's metering circuit-breaker. buildings are used.

number of separate fuses (usually not more than In some larger blocks there may be more than one 3.4 Protection Again t Earth (3) Cable sheathing and/or armouring: This is the eight) are connected to each line conductor and service cable. The first three-phase cable may ter­ Leakage most reliable system available and is used single-phase 'rising mains' taken to each flat. If minate on the ground floor and single-phase rising wherever possible, unless the system of sup­ meters are installed in the individual flats the ris­ mains will service the flats on that floor and the Electricity can only be safely used if the conduc­ ply is as provided in (4) below. ing main may terminate in another cut-out or a next few floors above. Another three-phase cable tors, or windings of apparatus which carry it, are main switch. Alternatively, the meters may all be will be terminated at a higher level to service the insulated, not only against contact with other con­ (4) Protective multiple earthing: 10 this system the installed at a single meter position adjacent to the flats on that level and the next few floors above, ductors, but also against contact with any metal in earth-continuity conductor connecting all service terminal equipment and the rising main ter­ and so on. which they are encased. Insulation may fail as a exposed metal work ofthe electrical installation minates in the consumer unit for each flat. result of ageing, moisture. mechanical damage, is itself connected to the local supply neutral.

30 Fire Service Manual Electricity 31 .~ ______...... JI (5) Residual Current Devices (RCD): These are Lead-alloy sheathed cables are sometimes to be Circuit fittings designed to help prevent electric found, but are no longer used for new work. Protective shock due to faulty electrical appliances or E N Conductor ..E .. L .. wiring. An RCD can detect changes in the Mineral-insulated copper-clad cables (MICC) or proper flow of electric current and when it mineral-insulated copper-sheathed cables (MICS) does so it disconnects the power supply in are used where resistance to fire, damp and •... milliseconds. This protects against electrocu­ mechanical damage is important. . : .. .. : • tion and other possible damage. • Under the lEE Wiring Regulations both power and • (c) Fires caused by earth faults lighting circuits require a separate earth-continuity conductor (known as the protective conductor) and C!3 Due to some high impedance in the circuit, the cur­ this often takes the form of a bare wire inserted rent may take an alternative route which can set up between two insulated conductors within the arcing which in turn may lead to ignition of adja­ cable. cent flammable material. In MICC or MICS the copper cladding or sheath 1. Water Pipe 2. Rod or plate 3. Cable Sheath The following are some examples of circum­ forms the earth-continuity conductor. stances where there is a high impedance which prevents the protective gear from operating: (b) Wiring systems and methods

LN Circuit • Failure of insulation allowing a leakage to Most cables can be laid directly and permanently .. Protective : Conductor occur between a phase conductor and an under plaster, but some installations employ con­ r-r--t---;.-..., Test earthing conductor or earthed metal-work, duits through which insulated single-core cables Button e.g., persistent arcing between a conductor can be threaded. Conduit-carried wiring is often and a conduit; found surface-fixed, especially if the wiring is done after the building is constructed. If non­ Nb An RCD operates • Local overheating at a point of high resis­ metallic conduit is used, an earth-continuity con­ when an out of balence is detected between tance in the earth fault path itself, e.g., at ductor is needed. L & W ego when a fault loose or corroded joints in the earth-continu­ to the Earth occurs. It does not require any ity conductor; Another system employs cable trunkjng, in which o separate connection large section metal or plastic trunkjng is used instead to Earth From O/H or • An earth fault current, unable to dissipate due of conduit to accommodate large numbers of cables UlG service Mains Supply to high impedance in the earth fault loop, of all types. This is usually a surface system so as to which finds an alternative path to earth by give easy access to cabling for re-arrangement. 4. Protective Multiple 5. Residual Current Earthing ( P.M.E) tracking or arcing to adjacent metal-work, Device e.g., arcing between an earthed conductor In many factories and workshops the plant layout (conduit) and a composite gas pipe. This is often subject to modification and such cases the could puncture the gas pipe and cause the required flexibility of electrical installation is met L. Line Conductor N. Neutral Conductor escape and ignition of gas. by cable or busbar trunking systems. These are N. Neutral Conductor CPC Circuit Protective generally mounted overhead in a steel trunking, Conductors and tapped to serve a machine or other apparatus; E. Earthing Lead 3.5 Wiring Systems for Consumer Installation a lead is taken from the fuse box (or tapping box) to each machine. (a) Cables used for wiring Note: The introduction of whole floors given over to All Earthing Lead Connections at the Earth Electrode must be fitted with a permanent Cables used for wiring can be either single or computer suites has led to special raised floors label indelibly marked with the words multi-cored. Modern single cables are PVC cov­ being designed in some new buildings. Cables for SAFETY, ELECTRICAL EARTH· DO NOT REMOVE ered for general use, but vulcanised rubber instal­ the electronic equipment are laid either in chan­ lations with tape and braid reinforcement may still nelling or directly under the floor and floor mount­ Figure 3.4 Four methods ofproviding an earth connection for electrical circuits and be found in old premises. ed sockets, access panels etc., are fitted to enable an example ofproviding shock protection by a Residual Current Device (RCD). the systems to be extended, maintained, etc.

32 Fire Service Manual Electricity 33 (c) Flexible wiring tained in a gas-filled quartz tube enclosed in an Typical Standard 13 amp Plug. evacuated glass bulb. When the current is turned The most common type of flex consists of two or on, the mercury or sodium is heated, vaporises and Illustration depicts an exploded view of a standard rewirableplug three separate conductors, each with one or two the current passing through the vapour causes it to AFTER DISCONNECTION FROM THE ELECTRICAL SUPPLY layers of coloured rubber or PVC insulation, fin­ glow. The colour of the light depends on the mate­ ished off with either a PVC or rubber sheath, or in rials used; mercury gives a bluish-green light and The following points should be visually checked: older installations, with silk or cotton. sodium an orange-yellow light.

Prior to November 1970 the colour coding for Normal voltages can be employed for these lamps, L Live (Brown) electric flex had been: but each must be fitted with a choke and capacitor N Neutral (Blue) to limit the current passing. The choke and capac­ E Earth (Green! Yellow) red - live conductor; itor are usually integral with or close to the lamp­ holder. Fuse RatIng black - neutral; and 3,5 OJ13amp A modified form of mercury vapour lamp is the appropriate to appliance green - earth. fluorescent tube, which is in wide use for lighting purposes. In it, ultra-violet light emitted by the The current UK colour coding for flexible cables mercury vapour strikes a thin layer of fluorescent connecting domestic appliances is: material deposited on the inside of the tube and 1. The Plug carcas 2. All three Pins are not (and plug top)to be excessivly loose and causes it to emit light. intact and not chipped, are not blackened or brown - for the live conductor; cracked or broken eaten away by Arcing (c) Luminous discharge lamps (if the later is evident, blue - for the neutral; and also visually inspect any mating socket for When a high voltage current is passed through a 3. Check Plug top screw similar signs of Arcing) green and yellow - for the earth tube containing certain gases at very low pres­ is secure and tight but (the protective conductor). sures, the gas becomes luminous and emits a not excessively so wavelength of a colour which depends on the gas 3.6 Electric Lighting In use.

There are three main types of electric lighting in For example, neon gives a red light, carbon diox­ use: ide white and hydrogen green. Because the tubes can be bent into a variety of shapes, they are wide­ (i) incandescent lamps; ly used for advertising purposes on the front of buildings and in shop windows. 4. Cable clamp apparartus (ii) vapour lamps; secure (yet must grip the These tubes work at 3,000 volts, or more, depend­ outer sheath of the supply (iii) luminous discharge lamps. ing on the length of the tube, transformers being cable properly). employed to step-up the voltage to the required 5. Any flexible cable or (a) Incandescent lamps figure. The wiring therefore constitutes a serious lead is not burnt or 7. Old Plug pins may not frayed and has no hazard to firefighters, since it may run in many necessarily be shouded, internal wiring showing The incandescent lamp is the most commonly used directions over the face of a building against which if the current plug is form of electric lighting. The current passes it may be necessary to pitch a ladder. The trans­ replaced by a new unit 6. Record the fact of through a fine high-resistance wire filament, rais­ formers, which are usually about 30Q-380mm ensure replacement plug visual inspection has shrouded terminal pins if appropriate. ing it to white heat. The filament is enclosed in a square, are mounted close to the discharge tubes glass bulb which is generally filled with an inert and may be in considerable numbers, depending gas. on the length of tubing to be lit. Thus, the average IF ANY DOUBT ABOUT ANY ITEM, DO NOT RE- CONNECT TO ELECTRICAL SUPPLY, sign for a cinema or theatre may require twenty or INFORM USER OF DEFECT. MARK UP EQUIPMENT AS UNSAFE AND REPORT FACTS TO LINE MANAGEMENT IMEOIATELY (b) Vapour lamps more such transformers.

These lamps do not have a filament but instead Figure 3.5 Typical standard 13 amp plug with suggested safety check list. have a small quantity of mercury or sodium con-

34 Fire Service Manual Electricity 35 E ectricity h- pt r

Figure 3.6 'Fireman's switch' .

(Photo: Crou'!1 copyr(f!/a)

Chapter 4 - Electrical Hazards and Safeguards

(a) Electrical Causes of fire (iv) regular preventive maintenance utilising good working practices. The majority of fires of electrical origin occur due to poor installation, poor or lack of maintenance or The 'Regulations of Electrical Installations' pub­ the mis-use of electrical systems and apparatus. lished by the Institution of Electrical Engineers is Electricity is capable of igniting insulation or other the code of practice for the majority of installa­ combustible material if the power is misused, tions operating at 230 and 400 volts in the V.K. equipment or cables are overloaded or are not properly insulated and maintained. The most com­ The design and maintenance of systems operating at mon electrical causes of fires are: higher voltage should only be carried out by organisa­ tions having the necessary knowledge and expertise. (i) short circuits caused by insulation failure or during work on an installation; A number of British Standard Codes of Practice have been published which deal with the mainte­ (ii) overheating of cables and equipment due to nance of switchgear from low voltages to the high­ overloading, Jack of adequate ventilation or est voltages found on the Grid System. high resistance joints; (d) 'Fireman's switch' For an interior installation the switch will normal­ (c) Preventive measures in or near ly be in the main entrance to the building. (iii) the ignition of flammable gases, vapours or Flammable Gases or Vapours The lEE Wiring Regulations (which are also dusts by sparks or heat generated by electrical issued as British Standard BS 7671) require that all The switch is installed in the low voltage circuit equipment; Where flammable gases or vapours may be present such installations either inside or outside a build­ and cuts off the supply to the transformer(s). particular care is necessary in the selection, installa­ ing must be provided with an isolation switch for Before pitching a ladder against a building on (iv) the ignition of combustible substances by tion and maintenance of electrical equipment. A use by firefighters. In the regulations this isolation which luminous discharge signs are fitted or work­ electro-static discharges. number of types of protection have been developed switch is called a 'fireman's switch'. (Figure 3.6) ing in the vicinity of such signs, either inside or both for electrical equipment and tools used in areas outside a building, the circuits should be isolated (b) Prevention of Electrical Causes of Fire where flammable gases and vapours may be present. For an exterior installation the switch will normal­ by pushing the switch upwards. These are: ly be mounted: There is always a possibility that fires will occur due to accidents whilst people are working on (i) Intrinsically safe equipment; • on the fascia of the building out of reach of the electrical systems. With the exception of such inci­ public but accessible to the fire brigade; or dents the incidence of fires of electrical origin can (ii) Flameproof equipment; be reduced by: • clearly distinguishable notices will identify (iii) Increased safety equipment; the location of the switch and the equipment (i) the correct choice of equipment; it controls. (iv) Pressurised equipment;

(ii) a well engineered design, with particular Note: In the lEE Wiring Regulations installations (v) Non-sparking equipment; attention paid to the electrical protection sys­ in arcades and malls are considered to be exterior. tems provided; (vi) Oil or sand filled equipment;

(iii) good installation practice; (vii) Specially protected equipment.

36 Fire Service Manual Electricity 37 wet exterior, tends to provide a path for a CUITent To assist in deciding which type or types of equip­ ready cause of static electricity. For practical pur­ It cannot be too strongly emphasised that if it is through the body. ment should be used, the areas where flammable poses, it is usually associated with substances known, or suspected, that an unconscious per­ gases or vapours may be present have been divid­ which, whilst non-conductors, are also flammable. son has suffered an electric shock, resuscitation Risk of injury due to touching live wiring or elec­ ed into zones. The safe use of electrical equipment Thus, if petrol (a non-conducting liquid) is should always be applied, and will often be suc­ trical material may be greatly reduced by observ­ in potentially flammable atmospheres depends not allowed to emerge as a jet from a nozzle, the noz­ cessful. ing the following simple precautions: only on the COITect choice of equipment for the zle can rapidly become charged with static elec­ zonal classification concerned, but also on the way tricity and, unless a path is provided to conduct the The effect of electricity on the human body can • It is dangerous to attempt to touch any wires it is installed, the type of cabling system used and charge to earth, a point is reached where the insu­ vary greatly in different persons and depends upon or electrical equipment except with the nec­ its maintenance. lating propel1y of the surrounding air breaks down a number of factors including for example, the essary safeguards, e.g., suitably rated rubber and a spark occurs which could ignite the petrol voltage of the supply and the path it takes through gloves, until it is certain that the circuit has At an incident, as far as firefighters are concerned, vapour. the body. been rendered dead. the zonal classification is not an important issue. Any indication of flammable gases or vapours will In the case of road tankers, conductive rubber tyres The immediate effect of an alternating CUITent is to • All switches in a building which has been demand the use of intrinsically safe and non-spark­ are normally fitted and special arrangements are cause the muscles to contract involuntarily. If an damaged should be treated with caution. It is ing equipment and tools. made to provide a path to earth when loading or a.c. conductor is, inadvertently, grasped it may be always wise to operate them with an insulat­ unloading. impossible to let go until the current is switched ed, dry object. (d) Dusts off. Non-flammable liquids and vapours will also build • If it is necessary to touch anything in a dam­ Combustible dusts may be ignited not only by up charges of static electricity under suitable con­ Although at the same current d.c. will have a less aged building, initially, only the back of the sparks from electrical equipment but also from hot ditions. For example, escaping steam from a frac­ severe effect than a.c. it must always be remem­ hand should be used. If it is live, the shock surfaces on such equipment. Overheating can also tured line or oil refining processes could build up bered that both direct current and alternating cur­ will then throw the hand clear. be caused by the heat insulating properties of the a charge on the plant itself, and special precautions rent can be fatal. dust. The selection of suitable electrical equip­ are taken to prevent this charge accumulating. In proximity to electrified railways, or any other ment, together with good 'housekeeping' practices Under appropriate conditions a static charge can Irrespective of whether a.c. or d.c. current is equipment using electricity, firefighters should will reduce the likelihood of electrical equipment be built up on vehicles or equipment fitted with involved in an incident, there is also the possibili­ remember that fire damage to cables and subse­ causing a dust explosion. rubber tyres e.g., a number of fires in hospital ty of indirect effects; for example, a shock quent use of water or foam has been known to operating theatres have been caused by static elec­ received by a person when climbing a ladder may leave an electrically charged path some distance When firefighters are working in dust laden atmos­ tricity, generated by the movement of the rubber cause them to fall and sustain injury. from the equipment. pheres precautions should be taken to remove the tyres on theatre trolleys, igniting ether or other As stated above it is not necessary to touch one of possibility of sparks igniting the dust. Non-spark­ flammable gases present. Either conducting rubber 4.3 Safe Approach Distances ing equipment and tools will remove the likelihood tyres, a trailing chain or conducting floors are used the conductors of a circuit to receive a shock as of ignition by sparking. In addition, the use of light to lessen the danger. Oxygen enriched atmos­ electricity can 'jump' across a gap if the clearance Whenever people are in the vicinity of bare, live water sprays will help to settle airborne dust and pheres which occur, for example, in hospitals and is not great enough and any conductive material, electrical equipment there is a risk of shock and/or their use should be considered with the obvious some industrial plants and/or processes, will also even though not in direct contact, may be electri­ arcing from the equipment to those people, or from thought being paid to the possible water damage increase the risk of fire posed by static electricity. fied. This distance will vary depending upon volt­ any conductive equipment they may be in contact which could occur. age and weather conditions. with. To minimise this risk it is always desirable to In industry the passage of belting over pulleys is a maintain the maximum practicable distance at all 4.1 Static Electricity frequent cause of static electricity. Where there is The principal dangers to a firefighter lie: times between any person and any item of live no possibility of fire risk, such charges may be electrical equipment. Static electricity is probably best known for its allowed to dissipate naturally but, where there is a (i) in unwittingly, in the dark or smoke, touching appearance as lightning which has been known to possibility of flammable vapours or dust, efficient a conductor which has been displaced by the Under normal circumstances the presence of cause a number of fires each year. It is probable that means of earthing should be provided. fire or which has electrified other conducting fences and/or baITiers, or the suspension of live some fires are also due to other forms of static elec­ material; and conductors on wooden or metal towers (having a tricity. It is impossible to prevent the formation of 4.2 Electric Shock ground clearances of about 5-7 metres), provides static electricity, but it presents no problems if it is (ii) in directing a jet of water or foam on to live adequate clearance to ensure that electric shock or conducted to earth before it has time to build up a If a firefighter comes into proximity with a live electrical equipment. arcing do not occur. charge sufficient to cause sparking. Precautions circuit, (direct contact is not necessary as electric­ taken against static electricity are normally based ity can 'jump') they may receive an electric shock When standing in water the danger from touching However, it is often necessary for firefighters to on this principle. which could be fatal. Other dangerous effects an electrical circuit is greatly increased. Even work, or use equipment under conditions which are which may occur are paralysis, fibrillation of the when wearing a non-conductive helmet, damp and abnormal, in the vicinity of electrical equipment. Friction between two non-conducting surfaces is a heart and cardiac arrest. perspiration under the helmet, combined with its

Electricity 39 38 Fire Service Manual In such circumstances additional safety precau­ Due allowance should be made for the knuckle on involving smoke with a Jarge carbon content e.g., tive than a solid jet and therefore sprays are tions/considerations are necessary. HP's. rubber tyres, certain types of plastics, forest and safer than jets. heath fires. Any actions which reduce the normal safety dis­ Firefighters should bear in mind that in high wind It has already been pointed out that it is not possi­ tances between personneJ, or any equipment they conditions, both the cables and the fire service The f1ashover hazard applies particularly to higher ble for a firefighter to positively identify the volt­ are using, and live electrical equipment should equipment may be oscillating and allowances voltages e.g., 400 kY, 275 kY and 132 kV over­ age rating of a conductor. In the absence of infor­ only be carried out following close liaison with an shouJd be made for that and the safe approach dis­ head power lines. However, as it is often not mation and advice from an "Authorised Person" "Authorised Person" of the Electricity Company. tance increased as necessary. possible to positively identify the voltage carried all high voltage conductors should be assumed to by a conductor, all high voltage overhead lines be live at the maximum voltage i.e., 400 kY. (a) Using Ladders and Aerial Appliances Training should be assumed to be capable of creating this Substations flashover situation. A corridor of 20 metres either side oL or around, When training and using ladders or aerial appli­ the live conductor should be maintained and no ances, then the safe approach distance should be In conditions of dense smoke or when flames are hand-held firefighting branch should be allowed Such items of equipment should NEVER be used doubled to 20 metres. approaching the conductors, firefighters should within that corridor. in or adjacent to Power or Sub Stations without an avoid positioning themselves or their equipment assurance from an "Authorised Person" of the (b) Working in Dense Smoke anywhere within a 'corridor' 10 metres either side If ground monitors or aerial appliances are in use Electricity Company that it is safe to do so. of the overhead power line (measured along the with large diameter nozzles (i.e., greater than A further possibJe hazard to firefighters exists Overhead lines ground). 20mm) then a corridor of 30 metres either side or when operating under, or in the near vicinity of, around the conductor should be maintained and no overhead power lines and dealing with a fire pro­ It is also possible for this flashover hazard to be such large diameter nozzle should be allowed There will be other occasions when, as part of ftre­ ducing dense smoke or with flames rising close to present with ground or near ground installations within that corridor. fighting or rescue operations, it is necessary to use lad­ the conductors. and in the absence of definite information and ders or aerial appliances in the vicinity of overhead advice from an "Authorised Person" of the (d) The Use of Foam lines. In such circumstances unless the Jine can be Under such circumstances there is a danger of an Electricity Company, the same clear 10 metre definitely identified as low voltage it must be assumed electrical flash-over from a conductor to earth! corridor should be maintained around any live There is little practical information on the conduc­ to be high voltage (i.e., over 1OOOY and up to 400kY) ground or adjacent structures, trees or Fire Brigade conductor. tivity of foam jets and sprays. and no part of any ladder, person or aerial appliance equipment. This phenomenon can occur in both should ever be closer than 10 metres to the line. urban and rural areas and particularly from fires (c) The Use of Water In the absence of specific data, foam should be applied with caution and the same minimum Water is a conductor of electricity and there are approach distances should be employed wherever OVERHEAD LINE HAZARDS specific safety considerations related to the use of possible. water or foam in the vicinity of live electrical equipment. (e) Explosion Risk

I I Experimental work has been done to establish the Oil filled transformers and switch gear have a fur­ leakage current which passes along a jet of water ther additional hazard of a possible catastrophic from a live conductor to the branch fitted with a explosive failure with the resultant release of hot variety of sizes of nozzle. or burning oil over a considerable distance.

The results of the experiments produced a series of The safe approach distances specified will help to theoretical distances (between a live conductor and avoid injury to firefighters should such a failure a nozzle) at which a pre-determined current would occur. pass along the water stream to the firefighter hold­ ing the branch. The variations in the distances The following points should always be kept in mind: determined, produced two important facts for the 400/275kV 132kV 33kV 11kV LV firefighter: • Water or foam should never be directly aimed minimum minimum onto live electrical equipment. clearance clearance minimum 7-7.3m • The risk of electric shock increases with the 6.7m clearance 5.2m increase in nozzle size (at the same distance). • When working near to electricity, sprays are safer than jets and smaller nozzle sizes are Figure 4.1 Overhead line hazards: transmissions lowers (pylons), poles and cables - minimum ground clearances. • Water in the form of droplets is less conduc- safer than large nozzle sizes.

40 Fire Service Manual Electricitv 41 - Minimum Safe Approach Distances NOTE: Minimum Safe Approach Distances shock. In such cases it is necessary to ensure that (for the electricity supply industry) on Railways the system voltage does not exceed the safe work­ ing limit of the gloves (normally rated at 3300Y). Rescues Because of differing operating circumstances to This means that for most purposes gloves can only Minimum safe approach distance the electricity industry RailTrack recommend that, be used on domestic low voltage cables and equip­ When carrying out a rescue in the vicinity of overhead lines 5 metres except for rescue purposes, no part of a firefight­ ment or appliances using domestic voltages. substations and other electrical equipment belonging to the ' er's body, tools or water jets should come within electricity supply industry 2.5m of the overhead line equipment (aLE) or Where system voltages exceed 3300Y, or it is not anything in contact with it, nor should a firefighter possible to verify the actual value, the only safe Other Operational Incidents go above the top window level of a carriage or course of action is to ensure that the supply is cut above the sides of other rolling stock (when the off and declared safe to touch. Not using hose Minimum safe approach distance train is on the track) until advised by a responsible railway official that the current has been cut off. Rubber gloves are generally stowed in waterproof When using ladders/aerial appliances or 10 metres tall equipment containers and should be kept in sealed plastic or 20 metres in training Rescues bags following testing. It is necessary to ensure In dense smoke or flames approaching 10 metre corridor good maintenance as any dampness or damage, conductor If carrying out a rescue firefighters must not touch including quite small holes, will reduce the insula­ Using hose an injured person if this means that they would tion effect of the gloves. have to come within one metre of live aLE or if When using hand-held jets 20 metre corridor the person is lying that close. On a conductor rail All rubber gloves should be regularly tested and system, not exceeding 750Y dc, a person in con­ when they are in use then every effort should be When using monitors (ground or aerial) 30 metre corridor tact with the live rail should not be touched. made to keep them dry Firefighters should normally wait for the current to • If crossing under overhead lines with ladders or tall equipment be cut off in either case. If this cannot be done 4.5 Removing Persons rom the equipment should be kept horizontal and as near to the without undue delay, a dry rope or wooden pole Electrical Contact ground as possible. may be used to push, or pull, an injured person away from live apparatus. (a) General

4.4 Use of Rubber Glove The human body has a relatively low resistance and therefore acts as a conductor of electricity, a The special electrical rubber gloves or gauntlets condition which is greatly increased if the skin is (rated at 3300Y) carried on many fire brigade wet. Therefore, if a person is in contact with live appliances have their greatest use in dealing with electric wiring, their body will form part of the 20m In low voltage systems normally found in business, circuit and any attempt to touch them is equiva­ I ~; Training industrial and private premises. They should be lent to touching the circuit. The same precautions worn when removing persons from contact with must be taken as if it were necessary to touch the electric wiring, for moving electric wiring which wtrlng. may prove a danger to operations and other work of a similar nature. For low voltage it is always preferable to isolate the supply and where high voltage above 3300Y is It should be noted that electricity regulations do involved this is ESSENTIAL. not permit any person to be engaged in any work activity on or near any bare live conductor unless At low voltages or at voltages known to be less

I special precautions are taken. than 3300Y rescue from live conductors is possi­ ble using rubber gloves and/or insulating items 20 m hand .I 10 m Because of the increased danger of high voltage, it such as a dry line, dry wooden stick or a length of held hose OperatIonal working is not generally advisable to undertake any work dry hose. Care must be taken to ensure that any Monitor without near or approach any live conductors or damaged item used is free of metallic strips along its length 30m hose insulated cables. However, there may be some cir­ and that any metallic attachment such as a hose cumstances where the use of appropriate electrical coupling, does not make contact with live conduc­ Figure 4.2 Minimum safe approach distances. rubber gloves may provide protection from electric tors and cause electrical flash-over or explosion.

42 Fire Service Manual Electricity 43 Figure 4.3 Dealh can Identification of the tower structure concerned is In the case of trespassers in proximity to live occur ifyou touch a of the utmost importance, and any identification Electricity Supply Industry (ESI) plant, immediate conductor or a person or markings on tower structures must be given if pos­ action is not necessary if the persons at risk can be object in cot/tact with a sible. A plate is fixed on the side of tower struc­ persuaded to remain where they are until the conduClOl: tures normally facing the nearest road, giving the arrival of ESI staff. Where conductors have fallen (Photo: £/c("u";or)' A.rsnc/llliOIl) route letter and tower number. to the ground, all that is usually necessary is for people to be kept as far away as is reasonably prac­ Circuit colours are also shown on colour plates ticable until the arrival of ESI staff. fixed to an adjacent side of the structure and these are easily visible from ground level. Tower struc­ A particular rescue problem arises where overhead tures in the immediate vicinity of a fire need not be transmission lines have fallen on to vehicles, or a approached because information taken from adja­ vehicle is in contact with them. Ground clearances cent structures is usually adequate for identifica­ of lines are sometimes as low as Sm at mid-span tion purposes. and this may be further reduced by ice or snow

Figure 4.4 Recommended actions 10 be taken when an overhead line is in contact with a vehicle.

• As a general rule, no tower structure or pole Firefighters must ensure that should be climbed without authorisation and they DO NOT TOUCH any a clear indication from an 'authorised per­ son' ofthe owning electricity company ofthe IF DRIVER IS INJURED, conductor, or any person NOT ABLE TO ESCAPE: dangers and ofthe minimum distance neces­ • INJURED DRIVER SHOULD .wryfor safety. NOT BE MOVED UNTIL or object in contact with ELECTRICAL HAZARDS ARE REMOVED.

a conductor • MAINTAIN SAFE APPROACH • In particular, no rescue of persons on live DISTANCE high voltage conductors should be attempt­ ed until full clearance has been obtained On normal household lighting and power circuits, from an engineer of the owning electricity it will suffice if several thicknesses of a dry non­ company. conducting material, such as sheets of dry news­ paper, a coat, rug, rubber gloves, etc., are used. • Unless under conditions closely controlled by an 'authorised person', the manoeuvring, Immediately a person has been removed from an or use ofmetal, or metal reinforced, ladders electric current, even though signs of life may be or other metal objects in the vicinity of tow­ absent, resuscitation should be carried out and ers or transmission lines should never be only discontinued when the patient revives or a allowed. doctor pronounces them dead. Occasions wiJl undoubtedly arise where circum­ (b) Overhead lines stances demand action by firefighters without technical supervision, and it is impossible to set It is extremely dangerous to climb tower structures out in detail the precautions necessary to ensure or poles carrying high voltage lines, and even more electrical safety in all instances. Initial action so when additional equipment, such as transform­ should ALWAYS be to contact the appropriate ers, switchgear or boosters, are mounted on them. control centre at least to obtain verbal advice.

44 Fire Service Manual Electricity 45

• f loading conductors. Clearances can be reduced by a vehicle attempts to leave it and makes contact If it is necessary for the driver or passenger(s) to IF J1': DOUBT TREAT AS HIGH VOLT GE earthworks or tipping without the knowledge of with the ground and any part of the vehicle at the leave a vehicle they should jump well clear of the D TAY WELL CLEAR the Electricity Company. Any vehicle in contact same time. vehicle ensuring that they do NOT touch the vehi­ with power lines should be treated as 'live' even cle and ground at the same time and land with both In some instances transmission lines can still be though the lines may appear to be dead. Generally, Provided that there is no hazard to the vehicle e.g., feet together. (See Figure 4.5) live with one conductor on the ground. In other any person within a vehicle is quite safe from elec­ fire, leaking hazardous load, ete., they should stay cases, it is possible for a line to be re-energised trocution as long as they stay within the vehicle. in the vehicle until an Electricity Company official They should then either jump away with both feet whilst the conductors are being moved. Electrocution may take place if any person inside confirms the line to be safe. (See Figure 4.4) together or hop away with only one foot in contact with the ground at the same time. This is to avoid the danger of receiving a shock through the feet in the area where a voltage gradient in the ground is If any part of the vehicle touches an overhead line the driver/passenger/s should: present because of direct, or indirect, contact • STAY IN THE VEHICLE, OR TRY TO DRIVE CLEAR between an overhead line and the ground. If not possible or if the vehicle catches fire Power lines found lying on the ground, even those • JUMP WELL CLEAR WITH BOTH FEET TOGETHER· DON'T CLIMB DOWN The metalwork of the vehicle may be LIVE apparently for low voltage, should NOT be approached until it has either been confirmed by • NEVER TOUCH THE VEHICLE ONCE THEY ARE ON THE GROUND an 'Authorised Person' that it safe to do so, or • RUN WELL CLEAR WITH LEAPING STRIDES AND STAY WELL CLEAR unless rescue from a line which has been positive­ A number of fatal accidents have resulted from people returning to the vehicle. ly identified as LOW VOLTAGE is involved.

Low voltage lines can be identified as:

(i) lines going into domestic premises.

(ii) generally, low voltage lines are on wooden poles and uninsulated.

However, it MUST be remembered that many wooden poles carry High Voltage lines. All poles carrying High Voltage lines SHOULD carry an appropriate warning sign (see Figure 4.6).

DO NOT take the lack of a warning sign on a single pole as sufficient evidence that it is a low voltage line. Other nearby wooden poles should also be checked for warning signs.

(iii) conductors are in vertical formation. (usuaJJy between 2-6 conductors).

If the overhead line has been identified as low voltage, rescue of a person who it is reasonably thought to be alive can be undertaken provided that the procedures set out in 4.5(a) above are com­ plied with. Overhead low voltage lines SHOULD

If anyone is unable to jump or is trapped in the vehicle they should be left there NOT be moved as it can cause arcing, which may Figure 4.6 Wood pole carrying High Voltage overhead until an Electricity Company Official confirms the line to be dead or earthed. bum a person if the conductor is touching them or lines. Only HV poles carry a warning sign. ignite any petrol vapours in the area. (Photo: £0$1 Midlands £/eClriciry) Figure 4.5 Recommended actions to be taken if unijured driver or passengers have to leave the vehicle.

46 Fire Service Manual Electricity 47

• I E ectricity Ch pt r

It should be remembered that in some circum­ Control centre giving the following information: stances overhead lines may, often, not be required to be isolated, to permit access without appreciable (i) Location; delay. The sudden interruption of electricity sup­ plies may itself endanger life: hospitals, lifts and (ii) Voltage; cranes are typical examples. and the interruption of Chapter 5 - Fire-fighting procedures an important connection between the system and a (iii) Route letters and tower number; and power station, for instance, may affect whole areas of the country. (iv) Circuit numbers.

In the light of the above, requests for switching out A circuit cannot be switched off immediately and General Emergency procedures should be detelmined with of circuits should only be made by the Officer-in­ may have to be earthed. The Officer-in-Charge of the site staff and the fire service. The procedures Charge of the incident who should have assessed: the incident should wait until the Grid Control (a) Liaison should be documented for reference both during an Engineer or Company Engineer has confirmed, incident and during training sessions. • the degree of danger at the scene of the inci­ either directly or through the respective Fire Incidents involving electricity will present particu­ dent; and Brigade Control, that the circuits have been taken lar hazards which require pre-training and plan­ (b) Equipment isolation out of service before it can be assumed safe to ning if they are to be tackled successfully. • the alternative solution ofkeeping firefighters work on, or in the vicinity of, the lines. In all cases involving electrical apparatus the first and equipment clear of possible risk. There should be close liaison both before and dur­ essential is to ensure that the apparatus is electri­ ing an incident. Pre-planning visits and on-site cally isolated and safe to approach. In large instal­ If it is felt justified to switch out the circuit then a training exercises should be arranged to ensure lations this will be carried out by an 'Authorised .request should be made to the appropriate Grid that proper risk assessments are carried out and Person' of the electricity company or, in a smaller personnel are familiar with plant and processes installation, by an employee of the operator at the Figure 4.7 Rescue Flow before an incident occurs. premises concerned. RESCUE FLOW CHART Chart showing the risk assessments that should be Figure 5.1 Close liaison To attempt the rescue of a person injured by, or in the vicinity of, made when attempting a between the Brigade and electricity follow the chart below. rescue in the I'icinity of local Electricity Company, electricity. hoth before and during an Keep yourself and others at incident, is VITAL. NO least 5 metres away from the (Pho!O.' Electricity Associatiun) electrical conductor or anything NO/DON'T KNOW touching it and await advice from the Electricity Company Has it•been confirmed that the power has been turned off? NO/DON'T KNOW

NO/DON'T KNOW Is it less than 1,000 volts? Is the casualty• more than NO (Iow voltage) YES 5 metres from the electrical conductor or anything touching it ? YES

YES• J Pull casualty clear with non- conducting • gloves or other material

48 Fire Service Manual Electricity 49 • protect firefighters against electric shock. This will need for partial or total evacuation depending on When dealing with incidents which may involve Elect."ical or associated also help to guard against a continued supply caus­ the scale and location of the incident. such substances then appropriate chemical protec­ ing re-ignition. tion and breathing apparatus should be employed. equipment should NOT be (d) Fuels touched or even approached 5.1 Fires in Generating Stations (g) Firefighting systems unless it is confirmed to be It is likely that various types of fuel will be present (a) General in a power station e.g., Generating stations are usually equipped with isolated and safe. fixed fire protection systems which cover most In nearly all cases, generating stations are continu­ heavy fuel oil, gas turbine oil, diesel oil, plants and equipment. Private hydrants will usual­ ously staffed at night although some small gas tur­ liquid petroleum gas, natural gas and coal ly be available. bine stations may be remotely controlled. Usually, are common. therefore a fire is likely to be discovered in its ini­ The type, location and working detail of any fixed (c) Extinguishing media tial stages and dealt with by the station fire team. Some fuel oils may be pre-heated to make them installations should be established during pre­ more fluid and easier to ignite in boilers. Such pre­ planning. Once electrical equipment is confirmed to be iso­ The generating station will have a fire emergency heating also makes these oils more susceptible to lated and safe then the appropriate extinguishing plan and, although similar in content, these plans accidental ignition where a spill and free flow of When an incident occurs it should be quickly estab­ media for the material involved in fire can be used. may vary according to location. Fire brigade per­ fuel has occurred. lished whether or not any fixed installation system sonnel should make themselves aware of the pro­ has operated. If a fixed installation system has not If the power supply cannot be isolated then the fire cedure to be observed in each instance through Pre-planning should take account of what fuels are operated it may be desirable to operate the system must be attacked in a way which will not cause regular liaison, pre-planning meetings and on-site available at the site, what quantities, their location manually to assist in bringing a fire under control. In danger to the firefighter, i.e., by the use of non­ training exercises. and what arrangements there are for protecting or either case consideration should be given to the pos­ conducting extinguishing media. Carbon dioxide, moving fuel stocks in emergencies. sibility of additional protection being needed for vaporising liquid, powder, dry sand, ashes, etc., are In all instances the PDA should be escorted from firefighters e.g., breathing apparatus. the substances normally used. Extinguishers or the gatehouse to the incident and should not stray When an incident occurs the pre-planned informa­ supplies of these materials will usually be found in un-escorted to any other parts of the site. tion in respect of the fuels on site should be used In the vicinity of the turbo alternators and boilers larger premises where electricity is generated or Generating station sites are large and it is recom­ to ensure that fuel stocks are protected from the there is usually a high pressure hydrant fed by consumed and their location and availability mended that rendezvous points and vehicle mar­ possibility of any fire spread. pumps for the high velocity water-spray protection. should be noted during pre-planning. shalling areas should be established with good These high pressure mains should not be used for radio communications to ensure the safe deploy­ (e) Hazardous substances firefighting unless specifically agreed with the gen­ Foam can be used for fires involving oil, provided ment of appliances at a large incident. erating company. Usually there is a lower pressure that there is no danger of the stream reaching appa­ Bulk storage of hazardous substances such as hydrant system available within the turbine hall for ratus which is still live. Once foam has been (b) Incident controllers methanol, propane, hydrogen, methane, chlorine general firefighting use and additional water mains applied it should be monitored to ensure that it and oxygen may also be found. will usually be available outside the building. does not flow and come into contact with live The generating station will have an "incident con­ equipment. troller" and it is essential for the safety of the on­ The pre-planning arrangements should ensure that The pumps supplying water mains within the site operatives and LAFB fire-fighters that the fire procedures for dealing with such substances are power station site may not start automatically and Carbon dioxide or vaporising liquids do not dam­ brigade officer and incident controller should established prior to an incident. it may be necessary to have them started manually. age electrical equipment. This is an extremely establish and maintain effective lines of communi­ important factor when dealing with incidents cation. If hazardous substances are encountered which The use of water in some areas of a generating sta­ involving delicate and complex apparatus such as have not been planned for in the pre-planning tion may not be safe, and areas where water may be that found in switchboards in generating stations, This liaison is vital and should be established arrangements then normal liaison with the station used should have been decided beforehand in con­ substations, telephone exchanges, or other elec­ immediately upon arrival. management should take place and chemical infor­ sultation with the Electricity Company Engineer. tronic equipment such as computers. Sand should mation sought in the usual way. only be used where it will cause little or no dam­ (c) Roll call (h) Cable racksfnmnels age, such as on cables, and never on machinery (t) PVC insulation with moving parts. As with any emergency incident the prime consid­ Cable racks, especially in large ducts and tunnels, eration should be the risk to life of people either Large quantities of cables will be found in generat­ will be found at generating stations and will pre­ In order to protect firefighters when extinguishing involved or likely to be involved. If evacuation has ing stations. The cable insulation is usually PVC sent their own specific problems of access. a fire known to have been started through an elec­ already taken place then an immediate roll call and any propagation of a fire involving that insula­ Guidance on dealing with incidents in tunnels can trical fault, the power supply must always be should be carried out. If evacuation has not taken tion can produce large volumes of toxic and irritant be found in Technical Bulletin 1/1993 which switched off before tackling the fire in order to place then consideration should be given to the smoke which will contain hydrogen-chloride gas. should be consulted at the pre-planning stage.

50 Fire Service Manual Electricity 51

p Figure 5.2 Cable rack and firefighting system.

(Ph01": HM Fire St'ITice ImpC:C10raleJ

5.2 Fires in Tran formers It is vital, therefore, to carry out flfefighting from a distance, taking advantage of available protection (a) General and the use ofground monitors should be considered. Figure 5.3 Burning transformers may explode and spray burning oil over a considerable distance. Most fires involving transformers are caused by an A firefighting attack should only be made when (Photo: West Midlands Fire Service) electric arc under transformer oil. Such an arc may the extinguishing or controlling media to be used be caused by an internal transformer fault and can has been established and there are sufficient stocks (b) Automatic protection should be given to manual operation to assist in fire­ produce hydrogen, acetylene and methane. Any to sustain the operation. fighting operations. explosive gases produced may ignite and the resul­ Transformers at power stations usually have tant violent explosion will rupture the transformer automatically actuated, high velocity, water-spray Remote transformers in substations are not usually tank and cause burning oil to flow or even be protection and at a fire incident it should have oper­ protected, in this way, except in some inner city sprayed over a considerable distance. ated. If the system has not operated consideration areas.

52 Fire Service Manual Electricity 53

ftp (c) Firefighting explosion this should be done from as far away as therefore, should be aware of this possibility and a below the permissible level of 50 ppm (0.005%), practicable and taking advantage of available pro­ working "corridor" with a minimum distance as leaching from the insulation and core, during ser­ The operating temperature of a transformer at the tection if possible. set out in Figure 4.2, page 42 should be maintained vice, can mean that the PCB level will rise again outbreak of fire may be quite high (100°C) and, as either side of overhead lines. above the permissible level. a consequence, the spread of fire can be rapid. The transformer oil cooler banks, if they are free standing, may collapse, and the porcelain insula­ As with any overhead line, ladders and other long Firefighters should be aware of this leaching The situation may be worsened due to the likely tors may shatter if they come in contact with fire or items of equipment should not be used in the area. process and, until expert monitoring shows oth­ delay in the start of fire-fighting operations which water jets. Ifporcelain bushings or insulators do erwise, regard an oil filled transformer or oil will be necessary to ensure isolation and earthing shatter, hot pieces of porcelain, which may be (e) Oil-filled switchgear filled switchgear as dangerous and requiring of the affected transformer. razor sharp, can be thrown over considerable full protection procedure including the wearing distances. High voltage switchgear, if oil-filled, is often cov­ of breathing apparatus. (It can be safely assumed Whilst awaiting an assurance that isolation of the ered by a system which automatically operates to that transformers and switch gear belonging to transformer has been carried out steps should be (d) Ionisation extinguish or control a fire. If such a system is member companies of the Electricity Association, taken to protect surrounding property and water installed but not operated then consideration i.e., the National Grid, the Generating Companies and foam supplies gathered and made ready. Where transformers, which are involved in fire, should be given to manually operate it to assist in and the Electricity Companies, do not contain are fed from overhead transmission lines, the heat firefighting. PCB's or are retrofilied. It is only in industrial and If the transformer is not separately bunded, burn­ and smoke may cause ionisation of the air sur­ commercial premises, and some railway premises ing oil could flow around others in the group, or rounding the conductors. This has the effect of Where such a system is not fitted, once it is certain and rolling stock, that equipment which still con­ 'bank', and rapidly involve them also. In such cir­ increasing the electrical conductance of air to the that the supply is switched off and the equipment tains PCB's and/or has been retra-filled may be cumstances it will be essential to lay and maintain point where it will allow electricity to flash from is earthed, fires involving oil can be extinguished found.) a foam blanket over the affected area as soon as phase to phase, phase to earth or to adjacent struc­ by the use of foam or, where appropriate, water possible. Bearing in mind the possibility of an tures, trees or fire brigade equipment. Firefighters, fog. Heating or burning of PCB's greatly increases the hazards as the production ofhighly toxic gases and As with transformers, oil-filled switch-gear, may, smoke can occur which could result in soil and if a short circuit occurs, violently explode and surface contamination. At such incidents, there­ spray burning oil over a considerable distance fore, as well as protecting firefighters with full and this should be borne in mind when position­ protective clothing and breathing apparatus, ing firefighting personnel and equipment. consideration should also be given to evacuat­ ing the area covered, or likely to be covered, by (0 Polychlorinated Biphenyl's (peB's) the resulting smoke/gas cloud.

PCB's, which are used in some transformers and Shict precautions should be taken to ensure that any other electrical equipment as an insulating liquid, spillage does not enter sewage systems or water are highly toxic and have harmful environmental courses. All spillage, including water used for effects if released, as they are not biodegradable. decontamination purposes, should be contained for specialist disposal as PCB's are not biodegradable. Since 1971 all new transformers must, if they con­ tain PCB's, indicate clearly that they do so. The appropriate authority should be notified where Transformers built prior to that date were not there is any likelihood of products from a fire, required to be so labelled and some, though not all, which involves PCB's, entering water courses. have been retrospectively labelled. Some owners, with transformers on their properties, are unaware If PCB's are spilled or leaked, the Officer-in­ that they contain PCB's, and this can mean some Charge of the incident should request the Local LAFBs have not been given advance warning of Authority to arrange disposal of the PCB's and any the presence of PCB's and are unaware of the need material which they may have contaminated. to take special precautions against them when attending transformer fires. FiI'efighters must NOT attempt Changing the liquid in a transformer from PCB to an alternative coolant fluid is known as retra-fill­ disposal themselves.

Figure 5.4 400 kV SF6 Gas Insulated Switchgear (GIS). IPho!U HM Fir. SElTic.lnspecJornte) ing. Although this can reduce the PCB level to

54 Fire Service Manual Electricity 55 .. (g) Residual charges Fires, especially those involving smoke with a These exceptions are: large carbon content, e.g., rubber tyres, certain The recommended safe Switching off the current to a high voltage instal­ types of plastic, forest and heath fires etc., (i) if a fire is at ground level; or lation, such as a cable, transformer or switch-gear beneath or near overhead transmission lines, may approach distances quoted in does not necessarily render it safe as a residual cause ionisation of the surrounding air and allow 4.3. 'Safe Approach Distances' (ii) if a person is lying on the ground inside the substation and apparently injured. charge of electricity may be present in the appara­ arcing to take place (see 5.2(d) above). In addi­ should be observed. tus. This charge is sufficiently powerful to cause tion heat from large fires in the vicinity of over­ electrocution. head transmission lines may cause the lines to The reason for this is that live open high voltage stretch and sag. If there is any doubt about the bushings are seldom located less than 2.5 m For this reason electrical equipment must always safety of the lines then the electricity company 5.4 Fires·n Substations above ground level. When this is not possible, be 'earthed' before it is safe to touch. This earthing should be notified. protective screens are provided round the equip­ is a separate physical technique and should only be (a) Grid substations ment for safety. carried out by an 'Authorised Person'. There are two further major hazards to be consid­ ered when using hose near to overhead power On the grid system, substations are generally of the However, once inside, (h) Entering protected premises lines: outdoor type, but some may, occasionally, be indoor or even underground. Firefighters lIlust NOT Where transformers, switchgear, etc., are protected (i) A high pressure jet playing on an overhead by fixed carbon dioxide or vaporising liquid instal­ line with horizontal conductors may cause the Because the voltages employed range from 6,600 climb equipment lations and the installation has operated, conductors to clash and produce arcing. This to 400,000 volts, it is essential that firefighters do • could lead to a breakage of the conductor not enter the substation, or attack any fires which use ladders resulting in live conductors falling to the might occur in them, until they have received noti­ • ground; and fication from an 'Authorised Person' of the direct any jet or spray The electricity company's Electricity Company that entry and tackling the • above ground 01" beyond 'Authorised Person' should be (ii) A water jet playing directly on to overhead fire can be safely carried out. consulted before any entry to conductors can result in earth leakage cur­ any titted safety screens. Not many sub-stations are permanently staffed and the enclosul-e is attempted. rents through the water jet stream to ground. This may cause the branch to become live a sub-station attendant will not, usually, be autho­ rised to allow entry for firefighting. with potentially fatal consequences. It should be understood that the statutory rights of entry to substations only apply to fire incidents. There are many factors governing the amount of The LAFB should, by co-operation with earth leakage current flowing down a jet stream, Electricity Company officials, know the status of al1 sub-stations in its area and the correct proce­ Should a person be seen lying on top of a trans­ Any firefighter entering such but it is not practicable to take all of them into former, switch, or, anywhere else above ground dure to take for each one. enclosures SHOULD be wear­ account when fighting a fire. level, they must NOT be touched until word is received from an 'Authorised Person' of the ) (b) Rescue ing breathing apparatus. Therefore, to minimise the risk of danger from Electricity Company that it is safe for rescue these hazards: As a general safety rule, work to be carried out.

Care should be taken when attempting to move Water or foam should injured people, even if they are lying on the 5.3 ires On or Near Overhead No grid substation should be ground away from a live power line as either the Power Lines NEVER be spraycd on cntered until an assurance has surrounding ground or the person could have a any electrical apparatus, residual charge of several thousand volts. Apart from transformers and switchgear, or appa­ been received from 3n ratus containing oil, there is little fire risk involved or ~lI1Y apparatus which has •Authorised Person' that this (c) Firefighting where transmission and distribution is carried out not been declared to be dead can be safely done. by means of overhead lines, although where the b)' an 'Authorised Person'. Many substations in rural areas are situated at a lines are carried on wood pole supports, and the considerable distance from water mains, or any route lies across scrub, heathland or similar coun­ static supplies. Fires involving large transformers try, there is some slight risk of scrub fires setting There are, however, two exceptions when entry will require large quantities of water and foam the wood pole supports alight and bringing the concentrate. Planning pre-determined attendances cables down. can be considered.

EleClricity 56 Fire Service Manual 57 for such a risk should therefore take account of the Similar precautions must be taken on industrial gas generated during the development of the fault a positive assurance that the supply is isolated and possible need for extra pumps for water relaying premises containing substations operated by the or if an external source of ignition is introduced safe to approach. and a foam tender and/or the availability of foam factory occupier. without first venting the box. stocks. If an assurance cannot be obtained from an on-site 5.5 Fires in Cable Boxe Should a fire occur in an underground cable result­ engineer or there is any doubt about the status of (d) Other substations ing in the street box cover being lifted and fire is the equipment then the supply should be assumed Where the transmission or distribution of electric­ actually visible, then C02 or Dry Powder should to be live and assistance should be sought from the Substations, other than grid substations, are of var­ ity is carried out by cables laid underground, the normally be used. local electricity company. ious types, and those which the firefighter is most chances of fire occurring are remote except at a likely to meet are located on commercial or indus­ cable or link box, or a feeder pillar where the main Another option is to use a small quantity of dry From the substation or switch-room the supply, trial premises, where they may be either be indoors cables may divide into a number of circuits. sand (damp sand MUST NOT be used) to extin­ which is then usually at 230/400 volts (although or outdoors. guish any fire in a cable box. In some power sta­ some equipment such as motors may operate up to Incidents caused by gas generated by faulty equip­ tions and sub-stations dry sand is available. 11 kV), generally passes through a local switch These substations operate at high voltages, and ment are rare, the most common cause of gas However, in the case of street boxes it should be and fuse board before it is conveyed to the indi­ they should be treated as highly dangerous until ingress is leakage from gas mains. A fire may be remembered that as burning cable insulation gives vidual apparatus. information has been received from an caused by an explosion which may blow off the off dense fumes which can fill the cable ducts, and 'Authorised Person' of the ElectIicity Company cover of the cable or link box. This can occur if a street box is filled with sand, the duct may In the case of a small fire, it may only be necessary that the electricity supply has been isolated and the through a fault in the cable with the consequent become sealed. The heated, expanding gases could to isolate circuits near the fire, and this should be installation is safe to approach. formation of an arc which ignites any flammable either blowout the sand or, more likely, cause the done by the plant engineer. fumes and fire to travel along the duct to other boxes, worsening the situation. 5.7 Fires in Private Dwellings

Firefighters should protect any exposed property The majority of fires of electrical origin which adjacent to the street box and await the arrival of occur in private houses are caused by faulty elec­ representatives of the electricity undertaking, who trical appliances or circuits, or by carelessness. should have been notified. Where incidents involving electrical equipment All personnel, and the public, should be warned to and appliances occur, the switch on any apparatus keep away from adjacent street boxes, whether should not be relied upon for isolating the appara­ above or below ground, in case further explosions tus. Instead the apparatus should be switched off at take place. the wall socket. For complete safety the plug should be removed from the socket. Underground cable or link boxes (Figure 2.22) and feeder pi llars are generally located sufficiently far Supply voltages in private houses do not normally t from a building for any risk of fire spread to be exceed 230Y. There are however some domestic unlikely but of course such an eventuality should not properties where the demand for electrical power be discounted. is high e.g., where there is an extensive use of night storage heaters, and the property may be 5.6 Fires in Industrial Premise served by more than one phase and so voltages of 400V could be encountered. Due to a high demand for electrical power, some industrial premises have a substation on their Care should be taken when dealing with a fire premises which often contains a transformer and involving the meter and fuse installation of a pri­ switchgear. The supply is invariably alternating vate house as it is generally mounted on a wooden current, although, if direct current is required, the board which may fall away from the wall when it substation will also contain converting plant. burns through; the ends of the service cable may then be exposed. In both cases, it should be assumed that the incom­ ing supply is at high voltage and, before attacking The correct action at a fire of this type is to extin­ the fire, it is most important that liaison is set up guish the flames and, as soon as possible, isolate Figure 5.5 JJkV Distribution Sub-Station transformer. (Phow Elerll'lcil.l' Assoe;c,,;o,,) with an engineer from the premises who can give the supply. At any fire involving electric cables

58 Fire Service Manual Electricity 59 should be considered. Nickel-iron batteries which ucts needed to sustain the fire are contained with­ use alkaline electrolyte are free of this danger. in the battery. If a fire does occur it may burn for up to 2 hours. If a fire has been caused by a short circuit, the cir­ cuit should be broken, if possible, by opening the To protect firefighters against the toxic fumes switch or disconnecting the leads, otherwise the breathing apparatus and protective clothing conditions which caused the fire will persist until should be worn and all others should be evacu­ the battery is fully discharged. The fire should, ated to at least 10 metres of the incident. preferably, be tackled with a hose-reel fog or spray, not because of the risk of shock, but because need­ The fire should be controlled and the surrounding less damage may be caused if a high pressure jet is area protected using water spray. Halon or Carbon allowed to strike the cells. Water should be kept Dioxide should NOT be used. away from cells which are not involved in the fire, because it will adversely affect the electrolyte. Any (c) Sodium Nickel Chloride Batteries electrolyte which has been released by the failure -~- of a cell should be diluted with a stream of water. At the time of writing (1997) it is believed that this type of battery will not produce corrosive products (b) Sodium Sulphur Batteries or generate high pressures.

This type of battery, if involved in fire, will give 5.9 Fires involving niterruptible off toxic Sulphur Dioxide and Hydrogen Sulphide Power Supplies (UPS) fumes. A fire originating inside this type of battery can take up to 30 minutes to become apparent and An Uninterruptible Power Supply (UPS) is a be very difficult to extinguish as the reactive prod- device that cleans up mains power and also pro-

Figure 5.6 230v overhead domestic line service. (PholO: HM Fire Service lospeclOral<') Figure 5.7 An 'individual' UPS serving just a single piece ofelectronic conditions under which they are sometimes re­ and installation, the Electricity Company should equipmenl. be notified, and the occupier advised not to charged can frequently lead to a fire. (Photo: GreYfJoifl/ Markermg Lle/J approach or use the installation until it has been DAKERI tested and rendered safe. Hydrogen is released during the charging process and concentration levels of only 4% are sufficient 5.8 Fire Involving Storage to create an explosive atmosphere. If a source of Batteries ignition is introduced into a battery charging area, and the conditions are suitable, there is a risk of an The traditional type of storage batteries are usual­ explosion. ly of the lead-acid or nickel-iron type and will be found in many electricity company and commer­ If batteries are involved in fIre then the products of cial premises and are also used in motor vehicles. combustion will contain droplets of electrolyte (dilute Newer types of batteries, especially for use in sulphuric acid) which is both corrosive and poisonous. vehicles are in the research stage and use sub­ stances such as sodium sulphur, sodium nickel Salt water should NOT be used on fires in which chloride. Other substances which are now used in lead-acid type batteries are involved since, under batteries are zinc and lithium. certain conditions, free chlorine may be generated.

(a) Lead AcidlNickel Iron Batteries Because of the possibility of the presence of corro­ sive and poisonous electrolyte and/or chlorine when When correctly installed and maintained, these dealing with fires involving lead acid batteries the batteries present little fire risk, but the unsuitable use of breathing apparatus and protective clothing

60 Fire Sen'ice Manual Electricity 61 I • I Figure 5.8 Large UPSs can ing. These vary in size from a medium sized refrig­ ., possible, one of the main leads from the battery . serve all electronic equip­ erator to a large wardrobe and have power outputs should be disconnected to prevent the fault contin­ ment in a building. of up to 100 kVA for the largest models. (Figures uing. The fire can then be dealt with using any (Photo: Merlin Gerin Lid) 5.7 and 5.8) appropriate extinguishing medium.

Hazards In modern engines it is common to have compo­ nents at dangerously high currents even when the One of the hazards posed by UPSs is that they pro­ engine is not operating. Although it will be safe to vide back-up power in an emergency. Firefighters carry out normal firefighting with extinguishers or may go into a room expecting all electrical/elec­ hose-reels etc., it is unwise to tamper with any tronic equipment to be "dead" because the mains electrical components within the engine compart­ power is off. But, because the equipment is linked ment. Unless firefighters are fully conversant with to an UPS they may discover that the equipment engine components and their function then actions is "live". should be limited to battery dis-connection and firefighting only and other specialist equipment, In the case of the larger UPSs which provide back­ including airbags, should not be interfered with. up for a whole building there should be a "cut-off' switch for it near the "cut-off' switch for the mains Electric powered vehicles power and thus it should not pose a problem. However, the smaller individual UPSs can pose a Largely because of environmental concerns, con­ particular hazard as they will stay "live" until their siderable effort is being put into the development own individual on/off switches are operated. of electric powered vehicles. Because the tradi­ tional lead acid battery cannot provide sufficient Firefighters shou Id therefore treat all electrical/ power, prototype Sodium Sulphur and Sodium electronic equipment, especially personal comput­ Nickel Chloride batteries (see Chapter 5.8) are ers, as potentially being "live" and not deliberate­ being trialed in electric vehicles. If these trials are ly direct water upon them or come into contact successful, these types of batteries (and other types with damaged or suspect equipment unless they in the research stage) may become common on the have been assured that the item does not have an road presenting different problems from those UPS or that, if it has, it has been turned off. posed by the traditional lead acid type of battery.

It should be remembered that an UPS system is installed to safeguard the electrical supply of vital or even life saving equipment and its dis-connec­ tion could have serious consequences. If possible, therefore, advice should be sought before such a system is switched off.

S.10 Fire in Motor Vehicle vides back-up power from its battery to a comput­ top models', which typically have a power output Many fires in motor vehicles are caused by electri­ er or other electrical equipment e.g., telecommuni­ of about 150/300 VA, are approximately the size of cal faults. They normally result from short circuits cations or medical equipment, during a power a large shoe box or, for 'slim line models', the size caused by damage to, or deterioration of, the elec­ blackout. of an attache case. Standing floor models vary in trical wiring system. size from a small suitcase to models the size of a There are two main types of UPS. small refrigerator with, typically, power outputs of Parts of the circuit may be overloaded by the between 5-20 kVA. attachment of additional equipment. As the wiring One type is used for individual pieces of electri­ is normally permanently connected to the battery caVelectronic equipment and are commonly found The other type is linked to a number of pieces of without a master switch, such fires may occur at associated with computers, especially personal equipment in a room or, in the case of the very any time and not only when the vehicle is in use. If computers. They vary in size considerably. 'Desk largest types, to all the equipment in a whole build-

62 Fire Service Manual Electricity 63 Electricity ~LJ,ul:ndi e

Appendices

A1 Case Study: Transformer fire, November 1997

A2 Electrical fire statistics

I A3 Map showing areas covered by Regonial Electricity Companies

A4 Electricity Association-Member Companies' Useful Addresses and Telephone Numbers

Electricity 65 ase Study APPENDIX 1 Tran fornler fire: ovember 1997

Electricity 67 - APPE DIX 1 APPE DIX 1

The following series of photographs is of an inci­ 1814 Stop message sent. dent which occurred in an electricity substation in Belfast on 4th November 1997. After the 'stop' message, foam was used intermittently as well as cooling jets. The incident was not terrorist-related and serves to highlight the duration and logistics involved in deal­ 1146 on 5th November 1997 ing with a fire of this type. Last pump returned to Station.

On receipt of the call at 0625 the predetermined A total of 20,500 litres of 3% Fluoroprotein attendance of 2 water tender ladders were mobilised, Foam compound was used as well as a small the electricity board informed and they confirmed quantity of High Expansion foam. 100 tons that an engineer would meet the appliances. of sand was also used. -

On arrival, it was found that a large transformer Appliances attending: within the substation was well alight and requests 11 Pumps were made to boost water supplies. 2 Foam tenders 1 Foam Trailer Pumps were increased to 8 and a foam tender, emer­ 1 Emergency Tender gency tender and water tankers requested. The fol­ 1 Control Unit lowing extracts show the subsequent development. 3 Water Tankers

0756 Informative message stated that '20,000 gallons of cooling oil involved. Preparing for foam attack. Awaiting isolation of electrical supply.'

A similar type of transformer to that involved in the fire. (All photographs in Appendix I: Northern Ireland Fire Brigade) 0818 Firefighting commenced. Breathing apparatus wearers with 5 x 4501/m foam branches. Department of the Environment requested to attend regarding potential for contamination of water courses.

0834 Make pumps 10 for personnel.

Pumps were subsequently made 11 and lorry loads of sand requested.

1126 An informative message reported 4 foam jets in use (4501/m), 10,000 litres of foam compound used. Pumping water from 500 metres away. Fire under control. Foam attack continuing.

1258 Informative - Foam attack stopped, 5 jets for cooling in use. 3,500 litres of foam compound on site, 12,500 litres foam compound used.

68 Fire Service Manual Electricity 69 APPE DIX 1 APPE DIX 1

70 Fire Service Manual Electricity 71 APPENDIX] APPE DJ 1

The transformer after the fire.

72 Fire Service Manual Electricity 73 J ------_....._------APPENDIX 2 Electrical Fires Statistics Map showing areas covered by APPENDIX 3 Regonia Electricity Companies

Shown below are some of the statistics relating to fires of electrical origin in 1994 (at the time of Em Electricity Association writing the latest year for which statistics are avail­ able). These figures are taken from:

Summary Fire Statistics - United Kingdom 1994 Home Office Statistical Bulletin lIE Scottish•••Power • Total number of fires in dwellings and other buildings: approximately 107,000 NORW=B

• Faulty electrical appliances and leads NORTHERN caused approximately 8,100 fires ELECTRIC (approximately 7.5% of all fires) which ElllUf ...... resulted in: 16 fatal casualties (approximately 4% of fatalities);

and 1,036 non-fatal casualties (approximately 10% of non-fatal casualties)

A fuller study of fires of electrical origin can be found in the Fire Statistics Research Paper -I "Accidental fires of electrical origin attended by local authority fire brigades in the United Kingdom, 1981-1988" published by the Home Office, October 1991.

SEEBOARD

@SWALEC SOUTHERN~- FIRST HYDRO ELECTRIC

~ BrItish Energy POWERGEN

~GU.m••y ~ @~ICITY E/«!TIcIty ....v AUlllORITY

Electricity 75 74 Fire Service Manual APPENDIX 4 Electricity Association-Member Companies' Useful Addresses and Telephone Numbers I

Em Electricity Association

MEMBER COMPANIES' USEFUL ADDRESSES

British Energy Chubu Electric Puwer Colllp;tIl~' East Midlands Elcctricin' Eostern Electricirv 10 Lodl';hk PI.Kl' :"Il.:,hlllll.!.1k Ht)II''':. 6;::' C:llf/,tm \trn·r Cnr!,,,,.,lll· o "rtl"l· , PO Ro.\ 4·4'1 PO Bm 40" \\'hn.'I't".Id P.l!"!. Fdinhurc,h EH 12 l)J)l­ 1);11,1')11'\\"1 \ 71'1;, \\·llll.l\llll,:-.... IIIIlll,.:.h,II11:"l,1'lII-:I. \\·hn'I".ld, [1"\\1(11 [P91 ..\W 'I'd 10) ~ I, ,27 2000 ld.IOI7114(]~ 0142 '1,·1 (011;;' l)U 1 IlIOI 1,,1. d1l47.~J ()xg6Kg ~.l:\ (Ol.~l) ~27 2277 r.l\ (0171 J4lJ;.l OHOI l-.".l\ (011:» 901 :-C!ClO 1-.1\. ilJ1473) ()OI036

Electricity Supply Board ESKOM Jntcrn:J.tional First Hydro Compall~ Guernscv Elcctricitv 27 L"wCf FllL\\"ilh,1l11 Strn:l 6,h H'lor, Rr,'tr'·llh.llll HOll'\' B.11.l HllU"', l."kl.:'hk )\Il,'IIh":-' \·IIl.\L:'· PO Rm. 4: r,k..:tn.:U\ HOll ....:. :"orth ~lIk Duhllll 2. E,rl' 1_"":,"(,·1 1'1,,\,1'. LOlldoll \\,e2l: 7l;\: '" ]).l\·id'~ r.u'\.... bdll': CH'; .~Xl . \',,1\. l,IKTn'l·' c..;Y·1 .i.~1) r( I I '1'1.'1' (00 ~;;.~l) 076 5:-01 r,·1 (Ol7]1 240 OOHS Id. (1112441 :il02.H Id dH 4,"l I J 4(1(j.~1 b,' {OO 35~ll661 5376 \',1\ 101711240 7S711 l-.l\· (012-4-1) ;,10()t)7 r.\\ (IH4XI) 46tJoi2

Hydro·Electric 1VO Energy }crsty Electricity London Elcctricitv 10 DlInkcld Road II11 \\,it.:,l1ltl1"\·:-'rr(·..:r PO Rn", 4;'" Qll'·l"l" Rn.h! 'I ,.III l'l.1r HlHI'<:, ~1'~7 HI~ll H,dhlrJl r ... nh rH I SW1'\. Lon,llll; \\'\ H \) ..~B -"I Ht:IIl:I" kr-n )l-A x\:\ ((.1 ) Llll1dllll \\,('1\' o:-\L" 1'''''1 (01 nl'J 4:;5040 '1\·1: Wl711 fll() I ~UO "1",,1 (OI~,Hl :;O;:;tl(H) I"d (OI71)242IJO;;O F:n (Oln~) 4:;:;045 ]-"l\' (U171 ) (116 IS I S )-.l\ (01 :;::4l :;o;() I) ~·.1\:(OI71)242 2X!;i

M3gnOX Electric Manweb Manx Electricity Authority Midl:mds Elcctricitv lh'rkdc"\' Cc:ntrc ~I.\ll\\d.., Hll\I~\', NlIL:5Ii\·ld Court PO 110\ 177" ])0;1 d,l' . ,\lu,klll\\ HIli, HJ.k·,\',\\l·l\ rkrkl.'k~· GU3 'JP« l'h":~ll'r Rlt~il\l.:~ P.uk: ('h\·,,\I.:r ("Hi I)IU­ j,k(,f.\l.ml,\tl)t)IP\ \\\::-1 ,\lid!.lIlJ<. Rc.2 XIH' Td (014:;3) 810451 ·Id.•0.'4,1112211 Td: (01624, 6S76S7 I'd (()121)423 234S F,\~. (014S~) ~12:;2l) "'J.\" (ll197xj R.U162 ....\\ (0 I ()2'1l 6S7611 1-.\\,1(J12114223311

National Grid National Power Northern Electric Northern Ireland Elcctricir\' :".11101\.,1 Gnd Hnu~\' Wil\,llllill Hill 1111:-1Il\":' P.uk C..lr!ln] Hml<.;;, ,\I"lrkl·I.'llr",·( 12U M.1I0I1l: Rn.)d ' Nrl:w Com,r Road. CO\ClHr\, (V4 HI\ \\'hll..:hlll W.H, ~\\ llldlJll S:"S 6pn \:,"\\·,·J:-I1...' lljlllll j\.I\,' :"EI Cl:"}­ Iklt,l" HT9 SHT .,-,,·'(0,20,;,42,000 . 1"1·1 (()17tJ3)·H77777 1,·1. (OI9!) 210 lOOO 'kl WIB2) ()61100 F.I\:: (01203) 4B67~ F.l\· (OI79.i) S92~2;, ....1\ (0191) 210 200\ ....\\. (012.\2) ()(1.~:;71J

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76 Fire Service Manual