What are the arc and electrical hazards?
Where the harm comes from in AGL work, why an arc needs no contact, and what removes the hazard before anyone gets close.
An arc is current jumping across a gap in air, and it can cause severe burns, eye damage, a pressure blast and flying molten metal without anyone touching a live part. In AGL work the commonest way to create one is to open a connector or cable on a live series circuit: the CCR keeps trying to drive the set current, the voltage at the break rises, and the gap can arc. The CCR’s open-circuit protection shuts the output down, but only after the break has happened, so it is never relied on as a safeguard. Failed connectors, water ingress, damaged insulation and poor terminations can also arc on their own. Opening the secondary of an isolating transformer while the circuit is live is also unsafe, because the voltage across the open secondary can rise to hazardous levels.
The hazard is not always gone when the CCR is off, and dark lamps are not proof that a circuit is dead. A long cable can hold stored charge or pick up induced voltage from nearby energised cables or lightning, and a circuit can be re-energised by mistake, including by remote control, so the circuit is isolated, locked out, proved dead, discharged and earthed as the procedure requires. Arc-rated PPE, face protection and a safe distance reduce the harm if something goes wrong, but they never replace de-energising. The airport’s risk assessment sets the PPE and the approach distances.
Frequently Asked Questions
Q1What is an electrical arc and why is it dangerous?
An arc is current jumping through air or vapour across a gap, for example where a live conductor or connector is pulled apart or an insulation fails. It produces intense heat, bright light and a pressure wave, and can throw molten metal. It can burn skin, damage eyes and start fires even without any contact with a live part.
Q2Why can opening a live series circuit cause an arc?
The CCR works to keep the set current flowing. If the loop is broken while current flows, the voltage at the break rises and can sustain an arc across the opening. Open-circuit protection in the CCR shuts the output down, but only after the break has happened, so it is not a safeguard. The CCR is switched off and the circuit isolated before any connector or cable in the loop is opened.
Q3Can a cable still be hazardous after the CCR is switched off?
Yes. A long cable can hold stored charge, particularly after insulation testing, and can pick up induced voltage from nearby energised cables or lightning. A circuit can also be re-energised by mistake, including by remote control, and dark lamps do not prove it is dead. After isolation the circuit is proved dead, discharged and earthed as the test and isolation procedure requires, and the isolation is secured with lock-out tag-out.
Q4Is arc-rated PPE enough protection?
No. PPE only reduces the harm if an arc happens. Isolation and proving dead remove the hazard, and safe working distance, closed enclosures and trained people limit it. The airport’s risk assessment sets the PPE and the approach distances, and PPE never replaces isolating the circuit.
Q5What are common causes of arcs on airfield lighting systems?
Opening a connector or cable on a live circuit, a failed or water-ingress connector or splice, damaged cable insulation, a loose or contaminated termination, and switching or racking equipment in the CCR room or substation with an existing fault. Poor maintenance and moisture raise the risk.
Q6What should be done if a flash, smell of burning or unusual sound is noticed?
Stay clear, do not touch the equipment, and report it so the circuit can be made safe by trained and authorised personnel following the airport emergency procedure. Anyone injured is given first aid and medical help as the site emergency arrangements require.
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