Fires destroy lives, livelihoods, and businesses. There are hundreds of thousands every year. It is estimated that France alone numbers between 250,000 and 300,000. They claim around 400 lives and 10,000 casualties. Statistics over the world tell the same story in countries that record and analyze fires.
Electrics – the main cause of home fires
Worldwide, electrics are the cause of 25% of all fires – and 80% of fires in dwellings in both apartment blocks and houses. In fact, electrical fires kill three times more than electrocution. Dwelling fires in the UK in 2011-2012 accounted for nearly 300 fatalities and over 11,000 injuries.
Yet there is far less awareness of electrical fires than of electrocution.
How do electrical fires start?
Short circuits, overloads, and ground fault currents are widely known to trigger fires. Circuit breakers prevent overload or short-circuits in home installations from turning into fires. Similarly, 300-mA-rated residual current devices prevent ground fault currents from heating and igniting construction materials.
But there is another, little known, fire hazard – dangerous electric arcs.
What is an electric arc fault?
Electric arc faults occur when an electric current quits its intended path and travels through damaged insulation.
There are two kinds of arc fault:
- Parallel arc faults: the current flows through damaged insulation from one conductor to another causing a short circuit that is too weak to be detected by a circuit breaker. The current, known as the leakage current, travels in arcs to ease its passage through the insulation.
- Series arc faults: when a single wire is too badly damaged to withstand the current, the current arcs across gaps in the conductor and into the insulation.
How do electric arc faults actually form?
Each arc heats and gradually carbonizes the insulation. Eventually the arcs ignite the carbonized insulation.
Burnt, or carbonized, insulation acts in effect like fuel that is ignited by electric arcs and a fast-accelerating chain reaction takes place. The leakage current generates arcs that carbonize the insulation. And the carbon deposits that form on the insulation are an extremely good conducting path. The cycle of arcing and carbon conduction gathers pace and intensity until the carbonized insulation spontaneously combusts.
What are the causes of an electric arc fault?
Loose wiring, ageing installations, overloaded plug outlets and faulty appliances are the main culprits.
Damaged or aged insulation between conductors is also a common cause. So, too, are damaged conductors. An extension cord may be squashed by a piece of furniture or twisted under a carpet, for example, or rodents may gnaw away at wires.
And with the rise in the number of home electric and electronic devices – often connected 24/7 – the risk of damaged insulation causing arc faults rises, too. Sub-standard multiway adapters and ageing installations are also serious risk factors.
Damaged to conductors may be caused by damp or the heat generated by electrical currents which loosens wiring. Both are gradual processes that unfold unseen over time – until it’s too late.
Do you have experience of electrical fires caused by arc faults? If you do, please share. And please post any suggestions on effective prevention.