8.2 Overhead Power Lines & HSE GS6

Overhead Electrical Hazards & HSE GS6 Clearances

Quick Answer: Overhead power lines are among the most lethal MEWP hazards because electricity can arc across air gaps, so contact is not needed for electrocution. HSE guidance GS6 says the risk must be managed whenever work is planned within 10 m (horizontally, at ground level, from below the nearest wire). Options in order are: avoid the work, divert the line, have it switched off, or control the risk with 6 m barrier zones, non-conducting goalposts and the ENA exclusion zones (1 m LV, 3 m 11–33 kV, 6 m 132 kV, 7 m 275–400 kV) that no part of the machine may be able to reach. If contact occurs, stay in the platform where possible, move away from the line if it is safe to do so, call the emergency services, and keep everyone at least 10 m away until the line is confirmed isolated.

Electrocution and electrical flashover represent catastrophic risks on construction sites, civil engineering projects, utility maintenance, and tree surgery operations. IPAF's Global Safety Report 2026 found that electrocutions and electric shocks were the top cause of fatal and major incidents involving powered access in 2025. A clear understanding of electrical hazards, safe clearance distances, physical barriers and emergency procedures is vital for every MEWP operator.

---

Physics of Overhead Electrical Hazards: Arcing, Flashover & Electric Potentials

A common and fatal misconception among plant operators is believing that an overhead power cable must be physically touched by the machine to conduct electricity. In reality, the vast majority of overhead electricity distribution and transmission cables across the United Kingdom are completely uninsulated bare conductors suspended in free air.

1. High-Voltage Arcing & Flashover Dynamics

Air acts as an electrical insulator under normal conditions. However, every voltage level exerts an electric field stress across the surrounding air. When the electric field exceeds the dielectric breakdown strength of air (the dielectric threshold), the air atoms become ionised, transforming ambient air from an insulator into a highly conductive plasma path. This phenomenon is known as flashover or electrical arcing:

• Voltage and Arcing Distance: The higher the transmission voltage, the greater the distance electricity can jump across open air. While low-voltage 230 V / 400 V lines require very close proximity or contact to arc, high-voltage lines (11 kV, 33 kV, 132 kV, 275 kV, and 400 kV) can jump several metres across open air to an elevated metal boom or basket without warning.
• Atmospheric Degradation of Dielectric Strength: Humidity, rain, mist, dust and contamination reduce the insulating strength of air, so arcing becomes more likely in damp or dirty conditions.

2. Touch Potential ($V_{\text{touch}}$)

When a MEWP makes contact with an energised power line or an arc flashes over to the boom, the entire metallic structure—including the boom arm, slew ring, chassis, outriggers, and steel wheels—is instantly energised at the line voltage (e.g. 11,000 to 400,000 volts):

• The Mechanism: Touch potential is the potential difference (voltage drop) between the energised metal machine and the ground surface upon which a person is standing.
• The Fatality Pathway: If a person standing on the ground touches any part of the MEWP chassis, outrigger leg, tyre, or attached tool while the machine is energised, their body bridges this massive voltage difference. Electrical current enters through their hands, traverses their heart and thoracic cavity, and exits through their feet into the earth, causing instantaneous cardiac arrest, massive internal organ vaporisation, and fatal trauma.

3. Step Potential ($V_{\text{step}}$)

When high-voltage electrical current discharges through the MEWP tyres or outrigger feet into the ground, it does not instantly dissipate to zero volts. The electrical resistivity of the soil causes the voltage to radiate outward from the point of discharge in concentric circular contours (voltage rings), resembling ripples expanding on a pond:

$\text{Current Discharge to Ground} \implies \text{Radial Voltage Gradient in Soil}$

• The Mechanism: Step potential is the voltage difference between two points on the ground separated by a person's normal stride length (approximately 0.8 to 1.0 metre).
• The Fatality Pathway: Near the machine, the voltage gradient is exceptionally steep. The soil directly beneath the tyre might be at $11,000\text{ V}$, while the soil 1 metre away is at $7,000\text{ V}$. If a worker on the ground walks, runs, or takes a stride across this gradient, one foot touches ground at $11,000\text{ V}$ while the other touches ground at $7,000\text{ V}$:

$V_{\text{step}} = 11,000\text{ V} - 7,000\text{ V} = 4,000\text{ Volts}$

This $4,000\text{ V}$ potential difference forces lethal current up one leg, through the lower torso and pelvis, and down the other leg into the earth. Ground workers attempting to flee or run toward the machine can be killed by step potential without ever touching the equipment.

---

HSE GS6: Avoiding Danger from Overhead Power Lines

HSE guidance note GS6 (Avoiding danger from overhead power lines, 4th edition) explains how to manage work near overhead lines under the Health and Safety at Work etc. Act 1974 and the Electricity at Work Regulations 1989. It is guidance rather than law, but it describes what HSE expects. Its starting points are simple: always assume a line is live until its owner confirms it is dead, and remember that line owners (usually a distribution or transmission network operator) must advise you on controlling the risk when consulted.

Know the Line

• Supports: Most lines are carried on wooden poles (low-voltage, 11 kV and 33 kV distribution lines) or metal towers/pylons (132 kV, 275 kV and 400 kV transmission lines).
• Insulation: Treat every high-voltage line (over 1,000 V) as bare and uninsulated. Some low-voltage lines are covered, but old or damaged covering may not insulate, so treat it as bare if in doubt.
• Heights: GS6 gives the legal minimum heights as 5.2 m for low-voltage, 11 kV and 33 kV lines (5.8 m above roads), 6.7 m for 132 kV, 7 m for 275 kV and 7.3 m for 400 kV. Transformers and fuses on poles often sit lower. Almost any MEWP can reach these heights.
• Measuring: The height of the wires should be measured by a suitably trained person using non-contact measuring devices; sag changes with temperature and electrical load, so allow a margin and ask the line owner.

The Key Distances in GS6

         GS6 BARRIER SAFETY ZONE (work beside, not under, the line)

   Barrier                    Overhead line                    Barrier
     |<------- 6 m ------->|       (nearest wire)      |<------- 6 m ------->|
     |   no plant, no      |            *              |   no plant, no      |
     |   storage           |                           |   storage           |
   ==========================================================================  ground

The GS6 Hierarchy of Control

1. Remove the Risk

The most effective control is not to work where there is a risk of contact with, or close approach to, the wires. Can the task be redesigned or done from a position well away from the line?

2. Divert or Underground the Line

If the work cannot be moved, consult the line's owner about permanently diverting the line or replacing it with an underground cable. This is often impractical for short-duration work.

3. Switch It Off

Ask the owner whether the line can be temporarily switched off while the work is done. The owner needs time to plan this and may charge for it. Never accept a third party's word that a line is dead: confirmation must come from the line's owner.

4. Control the Risk

If the line cannot be diverted or switched off and there is no alternative, a site-specific risk assessment must decide whether the work can be done safely; if it cannot, it should not be done at all. The assessment covers the voltage and height of the wires, whether work is beside or under the line, the size and reach of the MEWP, the safe clearance distance (the owner can advise), site conditions and the competence and supervision of the team.

Barriers and Controlled Crossings

• Barriers: Where no work or plant movement will take place under the line, erect ground-level barriers (for example, rubble-filled drums, concrete blocks, earthed wire fencing with flags, or marked earth banks) to create the 6 m safety zone. Do not store materials or machinery in it, and make the barriers visible at night.
• Passageways and goalposts: If plant must pass under the line, keep the number of passageways to a minimum, fence the route, and erect goalposts made of rigid, non-conducting material (such as timber or plastic pipe) at each end, marked in red and white. The crossbar height is set so that plant passing under it stays clear of the safe clearance distance.
• Notices: Put warning notices on both approaches giving the crossbar clearance height and telling drivers to lower booms and keep below it. Illuminate them at night or in poor visibility.
• Darkness: Ideally, work should not take place close to or under a line in darkness or poor visibility; dazzle from lights can hide wires.
• Supervision: Work near lines should be directly supervised by someone familiar with the risks who can make sure the precautions are followed.

Life-Critical Emergency Response: Electrical Contact or Flashover Protocol

If a MEWP contacts an overhead power line or an electrical flashover occurs, the operator's immediate actions will determine whether the incident ends without injury or results in multiple fatalities.

                 ELECTRICAL CONTACT / FLASHOVER EVENT
                                  │
                                  ▼
                 ┌─────────────────────────────────┐
                 │       STAY IN THE BASKET        │
                 │   - Equipotential Zone Exists   │
                 │   - Do NOT Touch Basket & Earth │
                 └────────────────┬────────────────┘
                                  │
                                  ▼
                 ┌─────────────────────────────────┐
                 │   WARN ALL GROUND PERSONNEL     │
                 │   - Shout: "DANGER! STAY BACK!" │
                 │   - Keep at Least 10 m Clear    │
                 │   - NEVER Touch Ground Controls │
                 └────────────────┬────────────────┘
                                  │
                                  ▼
                 ┌─────────────────────────────────┐
                 │    ATTEMPT CONTROLLED REVERSAL  │
                 │   - Reverse Off Contact If Safe │
                 │   - If Intact, Drive Clear      │
                 └────────────────┬────────────────┘
                                  │
             ┌────────────────────┴────────────────────┐
             ▼                                         ▼
    [NO FIRE: MACHINE STABLE]               [UNCONTAINABLE FIRE]
             │                                         │
             ▼                                         ▼
┌───────────────────────────────┐       ┌───────────────────────────────┐
│      REMAIN IN BASKET         │       │        JUMP CLEAN CLEAR       │
│ - Call 999 and 105 (DNO)      │       │ - Zero Simultaneous Contact   │
│ - Wait Until Line Owner       │       │ - Land with Feet Together     │
│   Confirms It Is Isolated     │       │ - Hop / Shuffle 10 m+ Away    │
└───────────────────────────────┘       └───────────────────────────────┘

Step 1: STAY IN THE BASKET (The Equipotential Plane)

Unless an uncontrollable fire is consuming the machine, the safest place for the operator is inside the platform basket:

• Why Staying Put Helps: The platform, boom and chassis are all raised to roughly the same electrical potential. If you stay in the platform and touch nothing else, there is usually little potential difference across your body, which is why IPAF and GS6 advise staying in the machine. It is not a guarantee: IPAF notes that occupants may still receive a shock or be electrocuted, so the priority is to break contact and get the line isolated.
• Fatal Instinct: The natural human instinct is to panic and attempt to climb down the access ladder or jump onto a nearby roof. If the operator touches an external wall, steel scaffold, or steps onto the ground, they complete the circuit to earth and suffer fatal electrocution instantly.

Step 2: Warn Ground Personnel (Keep at Least 10 Metres Away)

The operator must immediately shout in a clear, commanding voice:

"DANGER! LIVE ELECTRICITY! DO NOT APPROACH! STAY BACK!"

• All site workers, banksmen and members of the public must keep at least 10 metres away from the machine, its outriggers and any fallen wires (IPAF's 2025 rescue guidance), and must not approach until the line owner confirms it is isolated.
• Strict Ground Control Prohibition: Ground personnel must NEVER attempt to operate the ground emergency lowering valves or controls. Touching the machine chassis while standing on the earth bridges the touch potential, causing instantaneous fatal electrocution.

Step 3: Attempt Controlled Movement Reversal

IPAF's guidance is that, if it is possible, the operator should move the platform away from the power line to a safe distance where electricity cannot jump or arc—for example by reversing the movement that caused the contact. If this is not possible, stay in the platform, call for help and wait.

Step 4: Emergency Services & DNO Notification

If the machine cannot be moved clear:

• The operator or ground personnel must immediately contact the emergency services by dialling 999 (specifying fire, rescue, and ambulance) and the UK National Power Emergency Number by dialling 105.
• State clearly: "A Mobile Elevating Work Platform has contacted live overhead power lines. The machine is energised with personnel on board. Urgent network isolation and earthing required."
• Provide the exact location using a site postal address, Ordnance Survey grid reference, or a what3words identifier.
• Remain in the platform until the line owner, through the emergency services, has confirmed that the line has been isolated. GS6 warns that a line which seems dead may be switched back on automatically after a few seconds, or remotely after minutes or hours, if the owner does not know it has been damaged.

---

Evacuation Under Fire Conditions: Mitigating Step Potential

The only scenario that justifies leaving the platform while the machine is in contact with live lines is an uncontainable, life-threatening machine fire (such as hydraulic fluid spraying over the arcing point, or tyres burning and exploding beneath the chassis).

If staying in the platform guarantees fatal burns or smoke inhalation, the operator must execute the life-saving emergency jumping evacuation:

1. Jump Cleanly Clear

• The operator must never climb down the boom or access ladder, and never step down one foot at a time.
• Jump as far away from the machine as possible. GS6 gives this advice for vehicles: it is only practicable from a cab, chassis or platform at or near ground level, never from height.
• Zero Simultaneous Contact: While jumping, ensure that no part of your body, clothing, harness, or trailing lanyard makes contact with the machine at the exact moment your feet touch the ground. If you touch the machine and the earth simultaneously, touch potential will kill you.

2. Land With Both Feet Firmly Together

• Land with both feet pressed tightly side-by-side at the exact same instant.
• Absorb the landing impact with bent knees, but do not stumble, fall over, or allow your hands to touch the ground.
• If a hand or knee touches the soil while feet are planted, you bridge a step potential gradient, resulting in severe electrical shock.

3. The "Bunny Hop" or "Shuffle" Technique

To escape through the concentric voltage rings radiating through the soil (mitigating step potential):

• The Bunny Hop: Keep both feet pressed tightly together, heel-to-heel and toe-to-toe. Take short, controlled hops, landing with both feet simultaneously. Never separate your feet.
• The Shuffle: Keep both feet flat on the ground pressed tightly against each other. Slide your feet forward slowly across the soil in tiny increments without lifting either foot from the earth, ensuring the heel of one foot never moves past the toes of the other foot.
• Continue hopping or shuffling until you are at least 10 metres clear of the machine and any fallen wires, and do not return to the machine until it is confirmed safe.

---

Industrial Overhead Obstructions: Travelling Cranes & Pipe Racks

Overhead hazards in industrial environments extend beyond electrical utilities to include overhead gantry equipment and process infrastructure.

1. Overhead Travelling Cranes (OTCs)

In factories, aircraft hangars, warehouses, and heavy fabrication workshops, Overhead Travelling Cranes (OTCs) operate on high-level gantry rails mounted beneath the roof structure. Fatal accidents occur when an overhead crane travels along its rails and collides with an elevated MEWP boom or crushes the basket against structural roof trusses.

• Lock-Out / Tag-Out (LOTO): Whenever a MEWP is deployed within the travel envelope of an OTC, the electrical power supply to the crane's gantry busbars must be isolated, locked out, and tagged out.
• Mechanical Rail Track Stops: Where the crane must remain available, physical rail stops or travel limits set by the crane's owner keep it out of the MEWP's working zone, even if someone tries to operate it.
• Liaison and Supervision: The user's supervisor must brief the factory crane supervisor, control the isolation keys, and station a dedicated spotter on the factory floor.

2. Overhead Process Pipe Racks & Structural Steelwork

Chemical manufacturing plants, oil refineries, and pharmaceutical facilities feature dense networks of elevated pipe racks carrying volatile liquids, high-pressure steam, natural gas, or toxic chemicals. Elevated MEWPs working near pipe racks must observe strict precautions:

• Elevating beneath or between pipe racks creates severe entrapment pinch points.
• Operators must never use pipe racks or structural steel as anchor points or push against them with the platform.
• Plan the platform position so that it cannot be trapped between pipework and the controls; approach slowly, one function at a time, with secondary guarding where the risk assessment calls for it.