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7 Reasonable Measures for Working near Overhead Electricity Lines
The reasonable measures to ensure a safe system of work for works near O/H lines involve implementing safety precautions on site to ensure that works are always carried out at a safe working distance. These precautions include erecting suitable ground level barriers, creating safe passageways (with goal posts, gateways and warning signs), assigning a signaller and fitting physical restraining devices to equipment .
7.1 General safety practices
7.2 Where no works are carried out underneath the O/H lines
7.3 Where there will be plant or equipment passing underneath
the O/H lines in the course of works
7.4 Where works are carried out underneath the O/H lines
7.5 Safe working practices for blasting works
7.1.1 Any O/H lines found in the vicinity of the proposed works must be assumed to be LIVE unless the O/H lines concerned are confirmed dead by the electricity supplier.
7.1.2 The working party shall ensure that all necessary safety precautions have been taken and all site personnel are fully conversant with safety precautions implemented on site.
7.1.3 No works shall be carried out in the vicinity of O/H lines unless a safe working distance is always maintained in such a way that damage to O/H lines can be prevented and personal safety can be safeguarded.
7.2 Where no works are carried out underneath the O/H lines
7.2.1 Ground level barriers parallel to the O/H lines should be erected at a horizontal distance of at least 6m from the outermost conductor of the O/H lines to prevent any part of the plant or equipment approaching too close to the lines.
7.2.2 If lifting and earth moving equipment (e.g. lorry crane, mobile crane or tower crane) are to be used or site personnel may carry steel bars, ladders or other conducting objects, the barriers shall be erected further from the O/H lines so that a minimum 6m horizontal distance is always maintained between any part of the crane (including loaded material) or hand-carried material and the outermost conductor of the O/H lines.
7.2.3 If an O/H line crosses a works site in which works are to be conducted on either side of the line, barriers on both sides of the line are required.
7.2.4 The electricity supplier or the Director may vary the minimum clearance required based on the type of works and plant or equipment used, voltage and spans of the O/H line, etc. If barriers cannot be erected to meet the clearance requirement due to the constraints of the site, the electricity supplier shall be consulted before commencement of works.
7.2.5 Ground level barriers should be set up such that they are stable when subject to strong wind or any human force. Typically, these barriers could be:
(a) a rail fence;
(b) a plastic/nylon rope fence with stout posts planted in between;
(c) an electrically earthed wire fence under tension to be set up in consultation with the relevant electricity supplier;
(d) an earth bank boundary of at least 1m in height, marked by sign posts to stop vehicles from entering; or
(e) a properly spaced array of large steel or plastic drums filled with rubble, timber balks or concrete blocks.
7.2.6 The barriers should be clearly visible for the benefit of the plant equipment operators. This could be achieved by putting up cloth flags (i.e. bunting) suspended vertically above ground between 3m and 5m on top of the barriers, or by applying paint stripes with distinctive colours on drums. To warn personnel of the nearby O/H lines, warning notices should be attached to or displayed on the barriers at intervals of not less than 2m. Care must be exercised when erecting the bunting to avoid becoming too near to the conductors of the O/H lines.
7.2.7 No materials whether or not to be used in relation to the works should be stored, even for a short duration, in the area between the O/H lines and the ground level barrier without first consulting the electricity supplier.
7.3 Where there will be plant or equipment passing underneath the O/H lines in the course of works
7.3.1 Allowing the passage of plant or equipment under the O/H lines increases the danger and should only be considered if reasonable alternative routes are not available. In order to minimize the danger areas, the number of the passageways for plant or equipment should be minimized. For safest crossing, the passageway, if provided, should be at right angle to the alignment of the O/H lines wherever possible.
7.3.2 In general, the precautions to be taken when making provisions for the passageway are as follows:
(a) Gateways to the passageway should be set up at both sides of the entrance by erecting goal posts. Similar to the barriers, the route of the passageway should be clearly fenced.
(b) The goal posts and crossbars should be rigid and of non-electrically conductive materials and be marked with distinctive colour stripes. If metallic goal posts or crossbars are used, they must be adequately earthed.
(c) Clearly marked warning notices should be placed at both gateways of the passageway indicating the potential electrical danger and ground clearance of the cross bar and advising that no part of the plant or equipment shall exceed this ground clearance when passing the fenced passageway.
(d) The passageway shall be sited, as far as practicable, on level ground and its surface must be adequately compacted, flattened and maintained to prevent the plant equipment and the loads being carried from undue tilting or bouncing when moving.
(e) Adequate lighting for the notices, signs, passageway and its gateways should be provided if movement of plant or equipment is to take place after dark. Light fittings for illumination of the O/H line conductors immediately above the passageway should be sited at ground level projecting light upwards towards the conductors.
(f) Warning notices should be erected on all approaches to the crossing.
(g) A signaller who is able to assess the clearance between the plant or equipment and the goal post shall be assigned to guide the movement of plant or equipment underneath the O/H lines. The signaller shall agree with the operator on suitable hand signals or flag signals to be adopted during moving.
7.3.3 Due consideration should be given to the speed, stopping distance, size and manoeuvrability of any plant or equipment when deciding the location of the goal posts and form of warning notices to be used. The gateway should be erected far enough away from the O/H lines such that the plant/equipment does not stop underneath the lines if it hits the goal post or crossbar.
7.3.4 If it is not possible to place a rigid crossbar on top of the goal posts due to the width of the passageway (e.g. the construction of carriageways underneath the O/H lines), a string of strong non-metallic rope under tension or an electronic detection beam could be used as a height limiter. The distance between the height limiter used in a gateway and the outermost O/H line conductor should be at least 12m.
7.4 Where works are carried out underneath the O/H lines
7.4.1 In addition to the use of ground level barriers, gateways and warning notices mentioned in Section 7.2 and 7.3, additional precautions are required for works carried out within a 6m horizontal distance from the O/H lines, particularly where upward movements of plant or equipment (e.g. cranes, loader arms, excavator buckets), or construction works could encroach on the safe working distance, resulting in damage to O/H lines and/or personal injury.
7.4.2 The following additional precautions shall be exercised when ground level works underneath an O/H line are undertaken (e.g. pipe laying, road construction/maintenance, etc.):
(a) Based on the minimum safe working distance advised by the electricity supplier, the working party shall assess its works underneath the O/H line to determine whether any tools, equipment and part of plant or equipment could encroach on the minimum safe working distance.
(b) No tools, plant or equipment shall be used if they could encroach beyond the minimum safe working distance when operated underneath the O/H line.
(c) Suitable physical restraining devices should be fitted to plant or equipment to inhibit any of its moving parts (e.g. derricks, cranes, jibs, hoists, etc.) from reaching beyond the safe working distance.
(d) A signaller shall be assigned to direct the operator in maintaining sufficient safe working distance when plant or equipment is operated underneath O/H lines. Depending on the site situation, the signaller should be provided with red and green flags or suitable communication equipment to maintain dialogue with the operator.
7.4.3 Site personnel should observe any warning notices in the vicinity of the O/H lines and never disturb any earthing conductors connecting the O/H line poles/towers to the ground. These conductors are normally buried.
7.4.4 The electricity supplier must be informed immediately of any damage, however slight, or interference to an O/H line. The working party shall keep people well clear of the area until the electricity supplier attends the site and gives further safety advice. No attempt should be made to remove any objects or retract any mobile crane which is in contact with the O/H line conductor unless the line is confirmed dead by the electricity supplier. This also applies in the case of an injured person who is still in contact with the O/H line conductor.
7.4.5 Stacking of goods and containers, erection of buildings and structures, etc. underneath an O/H line should be avoided as the distance between the line conductor and the top of the object is reduced and the chance of an object encroaching on the safe working distance is higher.
7.4.6 If there is genuine need to work directly underneath an O/H line but the safe working distance cannot be maintained at all times by all appropriate means, the working party should request that the electricity supplier de-energizes the O/H line for a certain period at a suitable time agreed between them.
7.5 Safe working practices for blasting works
7.5.1 Blasting works should be kept well away from an O/H line in order to prevent damage to the line and its supporting structure from flying debris. The following precautions should be taken if blasting works need to be carried out in the vicinity of an O/H line:
(a) The maximum particle velocity caused by the blasting shall be restricted to 25 mm/sec at the O/H line footing;
(b) Mechanical detonators should be used whenever possible. If an electric detonator is used, the suppliers of the explosives and detonating system should be consulted about their suitability. In general, electric detonators should only be used at least 60m from the nearest conductor of the line;
(c) Damping mats should be erected to reduce the effect of flying debris; and
(d) The requirements of the Buildings Department and Civil Engineering and Development Department in relation to blasting works should be followed.
