Earlier statistics compiled for 1985 1994 by FEMA  showed very similar results: electrical distribution was the fifth-ranked cause of fires, the fourth-ranked cause of fire fatalities, and the second-ranked cause of property loss.The electrical distribution causes [ The high losses sustained due to electrical distribution fires do not imply that the systems are unreliable.Furthermore, if the insulation had previously been preheated to 200 300C, then ignitions occurred when the preheated insulation was raised to only very mild temperatures during the voltage testfrom room temperature to 40Cwere found sufficient (] conducted laboratory studies on arcing faults (parallel arcing) of electrical cords.They identified that the process typically proceeds in a repetitive, but irregular fashion.
Another mechanism involves the combined effects of moisture and pollutants on the surface.
Thus, an over-current protection device cannot be expected to respond.
In 120 VAC circuits, it is not difficult to cause sustained arcing if there is a carbonized conductive path. The mechanism has been known in electrical engineering for a very long time .
There are about 270 million people in the US, occupying about 100 million housing units, with the average housing unit having 5.4 rooms [ = 2.16 billion.
A certain percentage should be subtracted for receptacles not in use.
Subtracting out the switch fires, 3290 fires per year are due to receptacles/outlets.