The very high endurance originates in the minimum wear of the gas and of the contacts which are little stressed because of the low energy of the arc; this is due to: - the intrinsic qualities of the gas, - the limited arcing time, - smaller arc length, - the instability of the arc roots thanks to the use of hollow tungsten alloy arcing contacts, - full separation of arcing contacts and current carrying contacts. Safety The FP circuit breakers operate under low pressure. The internal pressure rise, due to gas compression and heating upon switching remains low. A safety membrane vents any excessive pressure that might arise, however improbable. At the atmospheric pressure, the circuit- breaker maintains sufficient dielectric characteristics and ensures safe load switching. The rapid gas recombination and the injection of fresh gas into the inter-electrode space ensures perfect breaking at TRV values amply higher than those recommended by the applicable IEC standard.