PRODUCED BY THE ENGINEERING DIRECTORATE OF THE ENERGY NETWORKS ASSOCIATION Engineering Recommendation G55/2 Issue 2 - September 2008 Safe Tree Working.

PRODUCED BY THE ENGINEERING DIRECTORATE OF THE ENERGY NETWORKS ASSOCIATION

Engineering RecommendationG55/2

Issue 2 - September 2008

Safe Tree Working in Proximity to Overhead Electric Lines

www.energynetworks.org

© 2008 Energy Networks Association

All rights reserved. No part of this publication may be reproduced,stored in a retrieval system or transmitted in any

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Energy Networks Association. Specific enquiries concerning thisdocument should be addressed to:

Engineering DirectorateEnergy Networks Association

6th FloorDean Bradley House52 Horseferry Road

LondonSW1P 2AF

This document has been prepared for use by members of theEnergy Networks Association to take account of the conditions

which apply to them. Advice should be taken from anappropriately qualified engineer on the suitability of this

document for any other purpose.

Engineering Recommendation G55/2Page 1 September 2008

CONTENTS Page

1 INTRODUCTION 2

1.1 Purpose 2

1.2 Background 3

1.3 Scope 3

1.4 Basic Principles 3

1.5 Definitions 4

2 ADVICE TO THIRD PARTIES 6

3 MANAGEMENT ACTION FOR NETWORK OPERATOR WORK 6

3.1 Competence and Authorisation of Persons 6

3.2 Standards of Arboricultural Work 7

3.2.1 Planning Stage 7

3.2.2 Execution Stage 8

3.2.3 Measure and Correct Stage 8

4 RISK ASSESSMENT REQUIREMENTS FOR NETWORK OPERATOR WORK 9

4.1 Generic Risk Assessment Principles 9

4.2 Site Specific Risk Assessment Principles 9

5 SAFE EXECUTION OF NETWORK OPERATOR WORK 11

5.1 Working Within the Proximity Zone 11

5.2 Work Planning Principles 11

5.3 Conditions Required for Working with the Line Live 12

5.4 Categories of Tree Work and Procedures to Control Risk 12

5.5 Effectively Insulated Conductors 19

5.6 Use of Machinery 19

5.7 Tidy-up Operations 19

5.8 Emergency Procedures 20

5.9 Performance Monitoring 20

5.10 Review of Procedures 20


1 INTRODUCTION

1.1 Purpose

The purpose of this Engineering Recommendation (ER) is to provide a common basis forsafe working practices for tree work in Proximity to any Network Operator’s equipment. Itsets out to differentiate between works carried out by or on behalf of Network Operators andworks carried out by third parties not in their employ. The primary focus of this document isto provide detailed advice to ENA member companies. Third parties will be steered towardsexisting publications for guidance.

Where relevant, this ER supports the standards and guidance set out in the followingpublications:

• Electricity at Work Regulations 1989 (EAWR)

• HSE Guidance Booklet HSG 85 ‘Electricity at Work - safe working practices’

• The Electricity, Safety, Quality and Continuity Regulations 2002 as amended 2006(ESQCR)

• BS EN 50110 - 1 :1997: ‘Operation of Electrical Installations’

• HSE Guidance Booklet HSG 47 ‘Avoiding danger from underground services’

• HSE Guidance Note GS6 ‘Avoidance of Danger from Overhead Electric Lines’

• Arboriculture and Forestry Advisory Group (AFAG) guide 804 ‘Electricity at Work:Forestry and Arboriculture’

• ENA ETR 136 (Vegetation Management Near Electricity Equipment - Principles of GoodPractice)

• ENA SHE Standard 04 - G55/1 Live Zone LV Distances

This ER also provides guidance in the establishment and use of management procedures toachieve the safest possible working practices.

Revision Note

The ER has been revised to take in to account the development in a maturing vegetationmanagement industry and to avoid any confusion in relating to the above documents.


1.2 Background

Working in Proximity to live overhead electric lines and underground electric cables isresponsible for many incidents every year. These incidents frequently result in the seriousinjury of people, damage to equipment and disruption of electricity supplies. Some of theseincidents are related to tree work in Proximity to live electrical equipment.

The risk of injury associated with any task may be minimised with a work plan based onrisk assessment, the use of Competent staff, the provision of suitable equipment and theapplication of safe work procedures. These are the actions that should be taken when preparingto work on trees in Proximity to all types of electrical equipment to ensure that the risk of anincident is minimised.

Tree work in Proximity to live overhead electric lines and other equipment is subject to theprovisions of the Electricity at Work Regulations (EAWR). This ER sets out to comply withthese provisions.

1.3 Scope

The approach set out in this ER is recommended for all tree work carried out in Proximity toany Network Operator’s live electrical equipment.

The management procedures established by this ER should be applied to work initiated by theNetwork Operator. Any work initiated by Third Parties should refer to Section 2.

Where the staff of any other employers are working in Proximity to live electrical equipmentthen the Network Operator will provide guidance to assist those employers to meet theirresponsibilities to provide a safe place of work. For tree work and related activities, theprinciples on which that guidance is to be founded are set down in this ER.

This ER gives recommendations for tree work with specific regard to the electrical hazard anddoes not seek to give guidance on managing the non-electrical hazards.

1.4 Basic Principles

To allow tree work in Proximity to live electrical equipment to be carried out safely it isrecommended that the following principles are followed.

All tree work is carried out:

• in accordance with this ER

• in accordance with appropriate working procedures established by the NetworkOperator concerned

• by appropriately qualified and Competent persons


1.5 Definitions

For the purposes of this ER the following definitions will apply:

Approved A tool including attachments approved by the Network Operator asInsulated Tool being insulated and fit for purpose to the extent that it may be used in

close proximity to live electrical equipment without presenting a dangerto the operator or network. The tools must be suitable for the voltagethat they are being used for.

Circuit Conductor An electrical conductor arranged to be electrically connected to anetwork.

Competent A suitably trained person, who is recognised as having sufficienttechnical knowledge, experience and ability to enable him or her toavoid danger in respect of the electrical overhead line network; isauthorised by the Network Operator and engaged to work on itsbehalf.

In the case of a tree cutter an example of this would be to have beenawarded the appropriate NPTC competency certificates and beauthorised by the Network Operator.

Effectively A line conductor which is insulated for continuous phase to phaseInsulated or phase to earth contact and is protected, so far as is reasonablyConductor practicable, against mechanical damage or interference having regard

to its accessibility.

Note: The implication here is that Effectively Insulated Conductors(such as low voltage aerial bundled conductors but not high voltagecovered conductors) may be placed such that they are ordinarilyaccessible, providing they are safe in the particular circumstances.

For the purposes of this ER all other conductors shall be treatedas non-insulated.

Live Zone The zone around an exposed live Circuit Conductor or supportinginsulators where there is a danger of burn or electric shock if any partof a person’s body or non-insulated tool they are using enters theZone. For HV and EHV circuit conductors this is related to the “SafetyDistance” as described by the Network Operator. The distances,which depend on voltage, are shown in Table 1.

Network Operator The organisation that owns and/or operates a distribution networkand is responsible for keeping vegetation clear of overhead lines. ANetwork Operator might also be referred to as a Distribution NetworkOperator (DNO) or Transmission Systems Operator (TSO).


Proximity Close enough to electrical equipment to present a danger. Dependingon the type of operation, the definition of Proximity is split in toProximity Zone 1 and Proximity Zone 2:

Proximity Zone 1 In the case of felling works then this includes all trees that are within twotree lengths of any live equipment. This will be measured horizontallyfrom a point directly beneath the nearest conductor to the base of thetree.

Proximity Zone 2 Includes all trees that are to be dismantled, pruned or have otherarboricultural work carried out on them that are within:

• 9m of any live equipment up to and including 66kV

• 15m of any live equipment greater than 66kV

Note that if there is any doubt about the voltage then the advice of theNetwork Operator should be sought.

This distance will be measured horizontally from a point directlybeneath the nearest conductor to a point directly under the nearestpoint of the canopy of the tree.

Where mechanical plant is being used e.g. harvesters or forwarders,then the stated distances will be measured to the nearest point to theline that any part of the machine or load can reach.

Third Party A person or organisation that needs to carry out tree works inProximity to a Network Operator’s electrical equipment for their ownpurposes.

Vicinity Zone The zone around an exposed live Circuit Conductor , which ifmaintained will ensure that the danger of burn or electric shock isprevented because the Live Zone is not breached. The Live Zone isincluded within the measurement of the Vicinity Zone. The distances,which depend on Voltage, are shown in Table 1. (Do not use “Workingand Access Clearances”, as described by some Network Operators,for the Vicinity Zone as they have different values.)

Table 1 Live and Vicinity Zone Distances

System Voltage Live Zone Vicinity Zone

Up to and including 1 kV 0.3m* 1m

Up to and including 11 kV 0.8m 2m

Up to and including 33 kV 0.8m 2.5m


Up to and including 132 kV 1.4m 3.5m



*see reference - ENA SHE Standard 04 - G55 Live Zone LV Distances


2 ADVICE TO THIRD PARTIES

Any Third Party not in the employ of the Network Operator wishing to carry out tree work inProximity (see Section 1.5, Definitions) to the Network Operator’s live electrical equipment

should consult the following documents:

• HSE Guidance Note GS6 ‘Avoidance of Danger from Overhead Electric Lines’

• Arboriculture and Forestry Advisory Group (AFAG) Guide 804 ‘Electricity at Work:Forestry and arboriculture’

• Energy Networks Association Public Safety Leaflet: ‘Safe Tree Working in Proximity toOverhead Lines’

These documents will direct the Third Party to consult with the Network Operator beforeproceeding.

For advice telephone your local Network Operator. The telephone number is in the telephonebook under Electricity.

Further guidance on public safety can be found on the Energy Networks AssociationWebsite:

http://www.energynetworks.org

3 MANAGEMENT ACTION FOR NETWORK OPERATOR WORK

It is recommended that Network Operators ensure that their procedures meet the requirementsof this ER. Although it is outside the scope of this ER, it must be remembered that non electricalhazards in connection with surveying, gaining consents and clearing vegetation must beadequately taken in to account in line with ENA ETR 136 (Vegetation Management NearElectricity Equipment - Principles of Good Practice).

3.1 Competence and Authorisation of Persons

The Network Operator should ensure that all staff involved in tree work in Proximity totheir overhead lines are Competent for both tree work and for working in Proximity to theirelectrical network.

Competence in tree work should be demonstrated through training, assessment and qualificationunder a nationally recognised utility arboricultural training scheme, or the Network Operator’sown tree working training scheme.

For Network electrical competence the Network Operator will ensure that training, assessmentand authorisation awarded to staff engaged meet the individual Network Operator’srequirements.

In the light of this revised Engineering Recommendation it is possible that certain certificates ofcompetence may not reflect best practice. There may then be a delay until these competencyunits are updated and personnel retrained and reassessed. It will be the responsibility of eachNetwork Operator to ensure that in the interim period they have robust systems in place toensure that personnel are adequately inducted and are deemed to be Competent to carry outworks in accordance with the best practice outlined in this document.

Trainees may be involved in site work only when they are subject to appropriate supervision,limitations and control, as determined by the Network Operator. Where trainees are engaged


in works adjacent to power lines then adequate arrangements for their supervision must beagreed with the Network Operator. It is recommended that these arrangements be recordedon the site risk assessment with specific reference to:

• the operative(s) being supervised;

• the supervisor(s); and,

• the level of supervision.

3.2Standards of Arboricultural Work

The standards referenced in this section address ‘good practice’ principles of work associatedwith safe tree work in Proximity to overhead electric lines.

The key safety management factors that should be applied by the Network Operator may begrouped within the recognised and accepted management process stages represented as:

PLAN - EXECUTE - MEASURE - CORRECT

3.2.1 Planning Stage

The following should be considered:

• Training and qualification in utility arboriculture practice (as referenced in section 3.1)

• The Network Operator will ensure that where relevant, project planning adopts the principlesof the following Engineering Technical Reports to ensure a safe and effective proceduralframework for the delivery of site specific requirements:

º ENA ETR 132 (Improving Network Performance Under Abnormal Weather Conditionsby Use of a Risk Based Approach to Vegetation Management Near Electric OverheadLines)

º ENA ETR 136 (Vegetation Management Near Electricity Equipment - Principles ofGood Practice)

• Surveys of the assets and associated vegetation to capture the data that will provide theinformation for the risk assessment.

• Vehicle and plant access with regard to the electrical hazard.

• Reference should be made to the geographical and electrical location of the work site.

• Defined asset to vegetation clearance objectives designed to maintain the statutoryclearance requirements.

• Specific methods of delivery such as a system outage or working in Proximity to the liveequipment.

• Site specific public safety risk control procedures; and the delivery and maintenance ofsurvey data to enable compliance with the relevant ESQCR requirements. Record of thevegetation condition identified as non compliant will require prioritisation e.g. accessibleassets via vegetation in a publicly utilised area.

• The asset condition risk and the site environment condition risk assessment are specificto the project location. The information/data recorded will be essential to facilitate safedelivery activities. Example of the items referenced may be asset conductor and fittingcondition, New Roads and Street Works Acts requirements (traffic management) otherenvironmental impact and risk such as water courses.


• The vegetative material risk should be assessed specific to the project location. Theinformation/data recorded will be essential to facilitate safe delivery activities. Example ofthe items referenced may be species specific regarding projected growth, individual treestructure condition, and the consequential risk of the works such as ‘wind blow effect.’

• Selection of appropriate plant, equipment and vehicles for the work to be carried out.

3.2.2 Execution Stage

During the Execution stage it must be ensured that:

• Critical customer/landowner details enable safe delivery of the planned works e.g. accessand egress routes.

• Robust site specific planning processes are demonstrated. All the required information willbe collated into a site specific document/file. Sound process will ensure the information isclear, concise and relevant. The information will be communicated to those staff associatedwith the physical delivery of the work. Site specific planning will ensure sufficient resourcefor the works. The relevant safety and environmental control information will be sharedwith all customers and stakeholders as necessary to ensure safe working and acceptableconduct.

• Equipment utilised for the delivery and execution of the work is fit for purpose. Items willconform to the basic requirements of being tested, certified, registered and maintained tothe approved Network Operator procedures.

• Guidance on suitable PPE to be worn is given in the AFAG guides relevant to each treerelated task. In addition the requirements of individual Network Operator proceduresmust be adhered to.

3.2.3 Measure and Correct Stage

During the Measure and Correct stage it must be ensured that:

• Safety event reporting and recording will be sufficiently robust to enable the NetworkOperator to identify all tree related incidents and ensure that they are reported both locallyand nationally via recognised electricity industry channels.

• Compliance measurement is ensured via audit activity. Checks and assessment arerecommended regarding:

º Quality of tree work

º Safety practice compliance

º Clearance from vegetation to assets achieved

º Clearance sustainability

º Compliance with environmental constraints

º Customer communication, understanding and satisfaction.

• Processes will be sufficiently flexible to accommodate modification required as a result ofnon compliances identified within the audit check cycle.


4 RISK ASSESSMENT REQUIREMENTS FOR NETWORK OPERATOR WORK

The Network Operator should ensure the principles of Risk Assessment are embedded in theprocess from project conception through to the delivery and execution phase of the work

The risk assessments will be available to all staff and associated stakeholders (as appropriate)involved in the works.

Network Operators should ensure that a suite of generic risk assessments covering allactivities involved in this type of work is available to all.

4.1 Generic Risk Assessment Principles

The generic risk assessment should include the following (the list is for example and notexhaustive):

• Procedures for live working (and its avoidance)

• Working at height (and its avoidance); the provision and use of Mobile Elevating WorkPlatforms (MEWPs), ladders and fall protection equipment.

• Plant and machinery e.g. wood chippers, stump grinders, MEWPs.

All tools and equipment to be used should be agreed with the Network Operator.

All tools and equipment must be serviceable, fit for purpose and properly used, maintainedand inspected. All tools and equipment must be used in accordance with any specificinstructions within Network Operator procedures.

• Arboricultural cutting equipment e.g. chain saws, pruning shears, chainsaw pole prunersand mechanical plant e.g. harvesters.

4.2Site Specific Risk Assessment Principles

The risk assessment will then be subject to and complimented by site specific riskassessment.

It is essential that the risk assessment process deals separately and adequately with both theelectrical and tree related hazards.

The site specific risk assessment will be available to all staff and associated stakeholdersinvolved in the works.

The site specific risk assessment should contain the following (the list is for example and notexhaustive):

• Justification for any live working proposed

• Evaluation of the risks regarding the planned work environment should be detailed.Consideration will be made regarding the location of Network Operator equipment inrelation to highways and roads, weather and ground conditions.

• The planned work methodology should be referenced regarding the electrical hazards,namely the category of the works as defined in Section 5.4. Access methods should bedetailed e.g. MEWPs, tree climbing, rope ascent, ladders. Consideration should also bemade and referenced to the management of materials produced as a result of the workse.g. moving and stacking of timber and waste.

• The physical condition of the vegetation involved in the works should be assessed from a


risk control perspective. Previous survey and condition data may be used to support thepre-work on site assessment.

• Public safety should be assessed regarding provision for overall site management andspecifically public exclusion (as appropriate), safe passage through the site if ‘rights ofway’ exist, prevention of damage to property leading to compromising safety e.g. damagingfences containing animals.

• Emergency procedures specific to the site should include the geographical and electricallocation, phone signal coverage, hospital locations, provision of communication with theNetwork Operator control centre, site ‘safe area’ for staff welfare and maintenance.Section 5.8 gives more guidance.

All staff allocated to undertake the works should be informed sufficiently to recognise andunderstand the risks and the control measures to be applied and it is suggested that a formalsign-off should be obtained. It is expected that all staff involved should record their acceptanceof the risk assessment and the control measures detailed e.g. tailboard conference. In theevent that any member of the working party identifies safety concerns that are not adequatelyaddressed then work should not continue unless suitable control measures can be agreed andimplemented.

It is a fundamental requirement that the on site risk assessment is updated and amendedto take account of any changes in conditions that take place during the execution of theworks e.g. a designated access/egress route may be altered. The change of risk state shouldalways prompt a review and as appropriate, action to control the situation e.g. a change in theweather.

Anyone visiting the site of work or joining the work team should be briefed on the risk assessmentprocess and the control measures in place.


5 SAFE EXECUTION OF NETWORK OPERATOR WORK

5.1Working within the Proximity Zone

All felling works carried out within Proximity Zone 1 or pruning and dismantling work inProximity Zone 2 should be carried out in accordance with the approved procedures of theNetwork Operator. Particular care should be taken to ensure that vehicles and plant on siteare considered and that their use complies with these procedures.

5.2 Work Planning Principles

All tree works must be planned in advance to ensure that the most appropriate method of workis adopted.

If branches breach the Vicinity Zone or there is any potential to breach the Vicinity Zone then,in line with regulation 14 of the Electricity at Work Regulations (see section 5.3), considerationshould firstly be given to whether or not an interruption to supply is already planned for thesection of overhead line concerned.

Once the justification process has confirmed the need to work with the line live, then the treesshould be assessed and categorised in terms of their position in relation to the overhead line(see Section 5.4 Procedures to Control Risks).

The guidance given in Section 5.4 will then allow the correct methods to be chosen. As workscontinue on more complex sites then the remaining trees should be continually assessed andwork methods revised accordingly.

In summary the process will be as follows:-

Consider if an interruption to supply has beenplanned for this section of line

Assess trees(See section 5.4)

Assign category of tree work

Establish work methods(See section 5.4)

If works are to be carried out live, thendocument justification (see section 5.3)

Cut trees and continually re-assess theremaining trees


5.3 Conditions Required for Working with the Line Live

All tree cutting shall be carried out where reasonably practicable with the line dead.

However, the Electricity at Work Regulations (EAWR) allow for situations where isolating anelectrical supply raises the risks to the customer or staff to a high level. Regulation 14 of theEAWR permits operations to take place provided that the following conditions prevail:

• It is unreasonable in all circumstances for the line to be dead; and

• It is reasonable in all circumstances for a person to work on or near the line while it is live;and

• Suitable precautions (including where necessary the provision of suitable protectiveequipment) are taken to prevent injury.

In addition to these conditions each Network Operator should have in place an approvedmethod of carrying out the work safely that is fully understood by the staff and includes detailsof the authorisation levels, supervision, assessment and appropriate equipment to be used.

Provided that the Network Operator has an approved method of work which includes ajustification process then trees can be cut with the line live using only trained, Competent andauthorised staff. This justification must be recorded as part of the risk assessment process(see also Section 4.2).

5.4 Categories of Tree Work and Procedures to Control Risk

The risks associated with each work site with respect to the electrical hazard must be assessedto determine the correct methods to be used to remove or prune the trees. The findings mustbe recorded as part of the risk assessment process detailed in Section 4.

A tree will be categorised in terms of the position of its branches relative to any conductors orelectrical equipment. The assessment will not take into account any work methods thatmay be intended to be used. The assessment shall be made immediately prior to workstaking place. The control methods to be used will then be determined as directed later in thissection.

There are four categories A, B, C and D with A generally being the most hazardous and D theleast. Where there is any doubt as to the category, default to the safer option.

In general a work site should be categorised as a whole and the most hazardous tree(s)will determine the category. If a work site is complex, requiring various work methods thenconsideration should be given to breaking it down in to more manageable sections.

Particular care should be taken when assessing climbing plants such as ivy on poles. It canbe difficult to determine exactly where the vegetation stops and in these cases again alwaysdefault to the safer option.

Having determined the category of the work site then the appropriate method(s) shouldbe decided and recorded. Work can then progress until the work site is completed or thecategory of the work site has reduced and different control methods can be adopted. Followinga re-assessment, in this way a logical sequence of work can be developed where the mosthazardous trees are removed first with higher levels of control. The removal of the mosthazardous categories of trees first will lessen the likelihood of reduced levels of control beingused inappropriately.


There will be occasions when this sequence can not be strictly adhered to if, for example, lesshazardous trees (Category D) need to be cleared to allow access to others (Category A), theseworks need to be carefully planned with all on site fully briefed on the hazards. Considerationshould be made on work sites like this to indicate clearly those trees that must not be workedon with the reduced control measures.

It must be noted that although a work site may have been categorised in advance it mustalways be re-assessed on the day of the works to take in to account any site changes, recentgrowth or temperature variations causing changes in line sag. This process must be repeatedif works continue on subsequent days.

The preferred method to control the electrical hazard is to carry out the work with the networkisolated and earthed in accordance with the Network Operator’s Safety Rules.

Where a decision making process has taken place in line with Section 5.3 and the works areto be carried out with the line live, then:

• For non-insulated conductors the control measures to be used should be determined bychoosing the most appropriate from those available under the following diagrams for eachcategory. However, the following will always apply for all categories of tree:

º No part of any person’s body shall ever breach the Vicinity Zone.

ºNo tools or equipment (except Approved Insulated Tools) shall breach the VicinityZone.

º No person shall work above any live conductor.

•For Effectively Insulated Conductors see Section 5.5.

In the event that works are not carried out in accordance with the recommended controls thenit should be ensured that the works are carried out with further supervision and a methodstatement approved by the Network Operator must be in place.

The Tree Category Decision Flowchart is given on the following page.


Tree Category Decision Flowchart

Is any part of thetree in the Vicinity

Zone?

Yes

Are branchesabove the

height of theconductors?

No

No

Yes Is the tree Nocapable of

breaching theVicinity Zone?

Category A Yes

Category B

Category C

Category D

A more detailed explanation of the four categories and recommended control measures isgiven on the following pages.


Category A

Within the Vicinity Zone (including the Live Zone), at or above the level of conductors orequipment. All of the trees illustrated below in Figures 1 and 2 are Category A trees.

V Z

L Z V Z

L Z

Figure 1 Figure 2

With the line live the method of work should be established by incorporating the followingcontrol measures:

• Where the voltage is greater than 33kV then the works will be carried out dead.The only exception to this will be where no branches breach the Live Zone and there

is further supervision and a method statement approved by the Network Operator thatensures there is no breach of the Live Zone.

•Branches can be reduced by using Approved Insulated Tools.•Approved Insulated Tools may only be allowed to be used in the Live Zone where a

procedure approved by the Network Operator is in place.• Trees with branches in the Live Zone must not be climbed. Trees with branches in the

Vicinity Zone but not in the Live Zone should only be climbed where a procedure approvedby the Network Operator is in place.

• If branches protrude through the Vicinity Zone and up above the height of the VicinityZone and overhang the extent of the Live Zone then the works will be carried out dead.

• Where Approved Insulated Tools or any cut materials have the potential to cause aphase to phase or phase to earth flashover then this work must be carried out dead.

• The length of cut section must be determined by risk assessment and recorded, particularlytaking in to account distances between phases

• A dedicated lookout groundsman capable of stopping work will be required to ensure thatthe required control measures are being adhered to.

• Works must be planned such that contact with electrical equipment is avoided.• The saw head should not be used in the Live Zone or on thin branches less than 25mm

diameter that protrude into the Live Zone; this prevents excessive movement andunintentional contact of branches with conductors.


Category B

Outside (but capable of breaching) the Vicinity Zone including the Live Zone, adjacent toconductors or equipment (see figures 3 & 4). All of the trees illustrated below in Figures 3 and

4 are Category B trees.

V Z

L ZV Z

L Z

Figure 3 Figure 4


• In the particular circumstance where branches are overhanging the Live Zone on HV asshown in Figure 4 then the works shall be carried out dead.

The only exception to this will be where there is further supervision and a method statementapproved by the Network Operator. This must incorporate further controls that ensure nobreach of the Live Zone and may incorporate the use of hand held sections, lowering

equipment or rope assisted felling. Full account of the weather conditions must be taken.• Control measures should, where necessary, include preparatory work to remove branches

in a logical manner to avoid the risk of small branches cut higher up in the crown outsidethe Vicinity Zone bouncing or cart-wheeling onto the line.

• If branches have the potential to breach the Vicinity Zone then Approved InsulatedTools must be used.

• If branches have the potential to breach the Live Zone then only small sections shouldbe removed to avoid a phase to phase contact or damage to the network. The maximumlength of cut section should be recorded on the risk assessment.

• These trees can be climbed and dismantled with suitable control measures, it must beensured that in the event of a fall or swing there is no possibility of a climber breaching theVicinity Zone.

• A dedicated groundsman capable of stopping work must be used to maintain clearances ifa climber or MEWP is above the level of conductors.

• Straight fell trees away with appropriate control measures (such as the use of two ropes)to ensure no breach of the Vicinity Zone. Suitable procedures must be approved by theNetwork Operator.


Category C

Within the Vicinity Zone (including the Live Zone), beneath the level of conductors orequipment. All of the trees illustrated below in Figures 5 to 8 are Category C trees.

V Z V Z

L Z L Z

V Z

L Z

Figure 5 Figure 6

V Z

L Z

V

Z

L Z

L Z

V Z

Figure 7 Figure 8


•Remove branches in the Live Zone with Approved Insulated Tools• If the trees are below the level of the Live Zone, with no possibility of breaching the

Live Zone (such as the trees shown in Figure 6) then they may be felled or pruned withnon-insulated tools such as a chainsaw.

• If the tree to be felled is below the level of the Live Zone with a possibility of breaching theLive Zone (such as the tree shown in Figure 7) then remove the branches with ApprovedInsulated Tools prior to felling.

• If the trees are below the level of the Live Zone then they may be climbed ensuringthat no part of the climber’s body, tools or equipment can breach the Vicinity Zone andthat branches are not caused to breach the Live Zone. A dedicated lookout groundsmancapable of stopping work should be used in this instance.


Category D

Within Proximity of the overhead electric line but not capable of breaching the Vicinity Zone.All of the trees illustrated below in Figure 9 are Category D trees.

V Z

L Z

Figure 9With the line live the method of work should be established by incorporating the followingcontrol measures:

• Use non-insulated tools and avoid any breach of the Vicinity Zone by operatives, tools orequipment

• Wherever possible trees should be felled away from conductors.• Trees must be felled into a cleared area to avoid the risk of a ‘domino’ effect with other

trees.


5.5 Effectively Insulated Conductors

Provided that the conductors are deemed to be Effectively Insulated Conductors by theNetwork Operator, the insulation is intact and the Network Operator’s Procedures allow,then it is acceptable to clear vegetation with the line live using conventional non-insulatedtools, ensuring that there is no breach of the Live Zone by persons, tools or equipment.

However, it must be borne in mind that where trees are present and have been touchingconductors then there will be a strong possibility that abrasion has caused damage to theinsulation. Older insulation may be subject to degradation and may not offer full insulation.Thorough inspection and constant vigilance is required. Where there is any doubt then theconductors must be treated as non-insulated.

To ensure that works are carried out safely the following controls should be adhered to:

• The Network Operator must deem the conductor type to be Effectively InsulatedConductors.

• Inspect the insulation to ensure that it is intact, if there is any doubt; assume the insulationis not effective.

• Inspect the network for non-insulated joints or jumper connections, if these are found thenthe control measures for non-insulated conductors (section 5.4) apply.

• Ensure that there is no breach of the Live Zone by persons, tools or equipment.

It must be noted that even where cable guards are fitted around cables on poles that extremecaution must be used when using any cutting equipment, but particularly with chainsaws andbrush cutters.

5.6 Use of Machinery

The use of mechanical equipment such as harvesters, front, side, and rear flails and timberforwarders are increasingly being used during clearance operations in Proximity to overheadlines.

All timber harvesting equipment should only be used in accordance with a method statementapproved by the Network Operator and in accordance with the control measures outlined inSection 5.4. This must incorporate measures for the safe access of machinery with respect tooverhead equipment.

5.7 Tidy-up Operations

On completion of works in Proximity to power lines then consideration must be given toany subsequent tidy up operations and to the safety of the general public. In particular thefollowing should be considered:

• Stacking branches or timber directly underneath the conductors should be avoided wherethere is any potential fire hazard or possibility of reducing ground clearances to belowminimum levels.

• Any long branches must be reduced in length where there is any possibility of them beinglifted to give access to conductors or electrical equipment.

• Timber and branches must not be stacked where it could give access to substations orelectrical equipment or where it is known that mechanical plant would be required to beused within minimum safety distances of overhead lines, as defined in HSE GuidanceNote GS6 ‘Avoidance of Danger from Overhead Electric Lines’.


5.8 Emergency Procedures

All staff must be trained in dealing with emergency situations. In the event of an incidentthen the emergency procedures detailed below should be followed. On no account should anattempt be made to remove a tree or a branch that has landed on and remains in contact withthe conductors.

The sequence of actions will depend on the type and severity of incident and the number ofpeople on site:

• If a vehicle comes in contact with an overhead line stay in the vehicle if it is safe to do soor follow the procedure for safe exit.

• Stop all work and make site safe.

• Contact the appropriate Network Control Centre as specified by the Network Operator.

• Keep everyone away from live conductors, fences or equipment and vegetation in contactwith conductors

• Call emergency services if necessary, give exact location and access details.

• Carry out aerial rescue only if safe to do so.

• Carry out First Aid if necessary or take the casualty to the nearest Accident and Emergencydepartment.

• Contact a supervisor to report the incident.

• Do nothing else until instructed by a suitably authorised person representing the NetworkOperator.

5.9 Performance Monitoring

Network Operators should have suitable monitoring systems that ensure that the standardsset out in this ER are achieved.

To achieve this, competent assessors must carry out regular assessments of a representativesample of tree work.

• These should cover working practices and equipment.

• It is the responsibility of the Network Operator to adjust the frequency of the safety checksin line with the findings.

• Take prompt and appropriate corrective action if performance standards are not beingmet.

It is recommended that every Manager/Supervisor maintains a record showing how thismonitoring is carried out in respect of the staff under his control.

5.10 Review of Procedures

It is recommended that the operation of all procedures established to meet the requirementsof this ER should be regularly reviewed in respect of their effectiveness in ensuring that allthose carrying out tree work on behalf of the Network Operator enjoy a safe, healthy workingenvironment and incident free operations. These reviews should lead to appropriate timelyaction.

PRODUCED BY THE ENGINEERING DIRECTORATE OF THE ENERGY NETWORKS ASSOCIATION Engineering Recommendation G55/2 Issue 2 - September 2008 Safe Tree Working.

Documents

work safe working practices

work regulations

engineering recommendation

safe tree

categories of tree work

network operator work9

network operator work6

work planning principles11