The optimization of today's switching technologies as well as the development of new switching technologies require a deep understanding of the physical processes during the current interruption process. Optical measurement methods – in this contribution the background-oriented schlieren method (BOS) – allow a quantitative determination of the physical properties gas density and temperature around current zero. By this method optical measurements of the switching arc in a circuit breaker model are performed with current amplitudes of Î = 3.5 kA in air at ambient pressure with exposure times down to 200 ns. Recordings are taken either from one or from two viewing directions and density profiles are reconstructed by filtered back-projection. Characteristic changes in the flow structure, e.g., the position of the Mach disc before and after current zero are, identified. The results of CFD-simulations (computational fluid dynamics) are found to be in agreement with the measurements.