Below article provides instructions and guidance for working safely in the vicinity of overhead services, describing the precautions necessary to mitigate the associated risks.
Working close to or passing under overhead power lines without the correct control measures is the cause of serious personal injuries and accidents every year. Contact with overhead electric lines can be lethal whether they are carrying voltage as high as 400,000v or as low as 240v.
Overhead lines are not normally insulated and if contact or near contact is made with them by a crane jib, scaffold pole or other similar object an electrical current will discharge with a risk of causing fatal or severe shock and burns to any persons in the near vicinity.
Hazard Identification and Risk Assessment
HSE guidance details three broad categories when working on site, in particular:
i. Sites where there will be no work, or passage of plant under the lines, but plant will be in close proximity
ii. Sites where plant will pass under the lines
iii. Sites where work will be carried out beneath the lines
In any of these cases, sites should establish exactly the nature of the work/access required and notify the relevant electricity supplier.
The electricity supplier should be contacted before starting work to provide information on a safe working distance and height and limitation requirements.
From the data and information contained within this section a risk assessment should be produced specific to the works concerned.
Risk Checklist
- Cranes/piling rigs travelling under lines with jibs raised.
- Cranes slewing into lines.
- Tipper trucks travelling with tippers raised.
- Plant not following designated access routes (short cuts).
- Plant operators/banksmen guessing distances and height of lines must be sign posted.
- Increasing ground levels with spoil heaps.
- Erecting or carrying scaffold tubes and ladders in close proximity.
Control Measures While Working Near Overhead Services
No vehicle or plant should be allowed to approach or be worked in any position where it is liable to be within 15m of overhead lines suspended from steel towers, or 9m in the case of wood poles, unless the electricity suppliers representative has been approached for advice. Idiot Bars to be erected prior to making contact with source.
If the lines are not diverted or made dead, then precautions should be taken to comply with the regulations, if the lines are not diverted but can be made dead, arrangements can be made in consultation with the electricity suppliers, for the passage of tall plant or for work to be done at times when the lines are dead.
Sites where there will be no Work or Passage of Plant Under the Lines
a) Barriers should be erected at ground level parallel to the overhead lines.
b) These barriers should be an absolute minimum distance of 6m from the perpendicular of the line to prevent danger from any part of the plant encroaching. Where this minimum distance could be encroached by parts of mobile plant e.g. cranes, excavators or lorries, it is necessary for the plant operator to be given an additional indication by the provision of colored plastic flags or bunting 3-6m above the barrier to indicate the 6m distance.
c) Electricity suppliers may advise a safe separation distance greater than 6m, depending on the voltage of the lines.
d) Where site conditions permit and particularly where plant such as a mobile crane is used, the minimum distance of the ground level barriers should be a jib length plus 6m.
e) Measurements should only be made horizontally from underneath the nearest conductor – never take vertical measurements.
f) Where high voltage lines with long spans are involved, electricity suppliers may advise that allowances be made for lateral swing of the conductors to maintain the safe distance from barriers.
g) If access is only possible from one side, then a barrier is only required on that side, if not then barriers should be erected on both sides.
h) If there is a danger of men carrying metal scaffold tubes or ladders then the barrier should exclude them.
i) Ground level barriers should consist of:
- A start post and rail fence;
- A tension wire fence earthed at both ends, having flags on the wire.
- Large steel drums filled with rubble and placed at frequent intervals.
- An earth bank not less than 1m high and marked by posts to stop vehicles, or substantial timber bulks to act as wheel stops.
j) The barriers should be distinctively marked by either painting drums/fences red and white and alternate red and white plastic warning flags should be used on wire fences.
Sites where Plant will Pass Under the Lines
a) Where passage is required under overhead lines, this should be achieved by establishing designated access points.
b) These should be made as small as possible (10m max.) and should cross the line at right angles.
c) Goal posts should be constructed from rigid, non-conducting material and distinctively marked red and white.(Idiot Bars)
d) The electricity supplier will advise on the correct height to the cross bar.
e) The ground through the corridor should be level compacted and notices should be predominantly displayed indicating the height of the cross bar and instructing drivers to lower jibs and keep below this height until clear. If work will be carried out at night then the area should be illuminated.
f) When it is not possible to restrict the width of the opening, rigid non-conducting material will not suffice, then tensioned steel or plastic ropes may have to be used. These ropes should be sited at least 12m either side of the plumb of the outer most conductor to create an access corridor of 24m.
g) Where these ropes are used they should be earthed at both ends and highlighted accordingly.
Sites where Work will be Done Below the Line
a) If work below lines cannot be avoided then barriers, goal posts and warning notices should still be provided.
b) Work below lines should only be carried out after consultation with electricity suppliers and a permit to work system established.
c) To achieve this, plant such as cranes and excavators may need modification by the provision of restraining devices to prevent:
- Jibs being raised beyond the safe clearance level.
- Derricking or slewing beyond safe clearance level.
d) Access to plant and materials should be under direct control of a competent supervisor.
Erection of Buildings or Structures Below the Overhead Lines
In cases where the erection/refurbishment of buildings or structures are required and the line cannot be diverted or made dead then the following should be observed:
A safe system of working should be established prior to work commencing.
The electricity supplier should be consulted about the proposed works.
The use of tools or equipment e.g. scaffold poles, ladders which can reach sufficiently beyond the safe distance should be avoided.
A horizontal barrier of timber or other insulating material should be erected beneath the live conductor to form a roof over the construction area.
Note: The use of insulating guards and proximity devices are not accepted as complying with the Electricity at Work Regulations and should not be used.
Overhead Services Safety Checklist
a) Have all persons on site been informed of dangers associated with overhead lines?
b) Has local electricity supplier been contacted for advice?
c) Have barriers been erected, the required distance from the lines. (Idiot Bars)
d) Are barriers to the required standard?
e) If passage is required under lines, have goal posts been erected?
f) Are goal posts to the required standard?
g) Is the ground at pass under points level and compacted?
h) If work carries on after dark, is the area illuminated?
i) Where work has to be carried out under live lines, has a permit to work system been established?
j) Have warning notices been provided?
k) Has plant been fitted with restraining devices?
l) Where building or structures are to be erected under live lines has a safe system of working been established?
m) Has the area been checked by an competent person/electrician?
Other resources:
GENERAL GUIDE FOR WORKING IN THE VICINITY OF OVERHEAD AND UNDERGROUND ELECTRIC LINES