Where does flashover collide?

In high-voltage engineering, flashover is a disruptive electrical discharge that arcs over the surface of, or through the air around, an insulator when the applied voltage exceeds the breakdown strength of that path, short-circuiting the gap the insulator was meant to hold. It is made worse by surface contamination, moisture, and transient over-voltages from lightning or switching, and the flashover voltage is a key rating for line and substation insulation. The referent is an insulation failure by arcing, which shares only the word with a room-engulfing fire.[1]

Unit

The flashover voltage at which the insulation arcs over

Recovery means

Not applicable

Measured by

Established by flashover-voltage tests under dry, wet, and polluted conditions

In fire dynamics, flashover is the rapid transition of a compartment fire from a growing, localised fire to full involvement of the room. Radiant heat from the hot smoke layer collecting at the ceiling raises every exposed combustible surface toward its ignition point, so they catch almost simultaneously, a change often associated with upper-layer temperatures of roughly 500 to 600 degrees Celsius. The referent is a thermal tipping point in an enclosure fire, unrelated to an insulator arcing over beyond the shared image of something suddenly jumping across.[2]

Unit

The upper-layer temperature or heat flux at the transition to full involvement

Recovery means

Not applicable

Measured by

Indicated by upper-layer temperature and floor-level heat flux reaching the threshold for simultaneous ignition