During a storm, when propagation field conditions are favorable, an OPR ESE air terminal will generate an upward leader. This upward leader from the OPR tip propagates towards the downward leader from the cloud at an average speed of 1 m/µs.
The emission of an early streamer to a lightning event delivers a beneficial triggering time compared to a single rod air terminal exposed to the same conditions. This in turn drives the enhanced performance and protective distance achievable by ESE devices.
The beneficial triggering time is determined as the average time gained at the moment of sparkover, with efficiency confirmed by high-voltage laboratory testing. All ESE tests are defined in Annex C of the French standard NF C 17-102 (2011 Version).
This beneficial triggering makes OPR air terminals especially effective for the protection of industrial sites, administrative or public buildings, monuments and open-air sites such as sports grounds.