This electrical switchgear has an interrupting chamber enclosing an interrupting gas (G) substantially devoid of SF6 and of CF4, and a first arcing contact (10) and a second arcing contact (18), the two arcing contacts moving causes an electric arc (26) to strike, while at least one irradiation wall (22) is provided that is suitable for being reached by the electric arc. At least two component materials that are part of at least one element selected from the interrupting gas, the first and second arcing contacts, and the or each irradiation wall, are suitable for decomposing under the effect of the electric arc, so as to form decomposed species (e1, e2) suitable for combining in the interrupting chamber, in order to form at least one new gaseous species (G1), before the electric arc is extinguished, the dielectric properties of said at least one new gaseous species being superior to the dielectric properties of said interrupting gas (G).