Test data on impulse and 60-cycle voltage breakdown strength for compressed air with various electrode configurations are reported. The tests were made with rod-to-plane electrodes with spacings up to 8 inches and pressures to 250 psig (pounds per square inch gage). Breakdown phenomena of air insulation encountered in the development of an air insulated air-blast circuit breaker1 are reported. The methods used in locating, analyzing, and correcting the breakdown are discussed. The use of solid insulating material in conjunction with high-pressure air is discussed. Applications in barrier form, and as support members stressed in creepage, are covered briefly.