There are many sources which say that a human cannot survive under the abrupt exposure to vacuum. What would happen if the exposure is not abrupt? Can a regularly clothed human survive in a vacuum chamber if we gradually lower the air pressure in the chamber to vacuum values for several hours of decompression and if he has a breathing mask with pure oxygen covering his eyes, nose, mouth and ears? The oxigen pressure in the mask is kept at the level of 1/10 of normal atmospheric air pressure in the end of decompression hours. The exhaled carbon dioxide is removed from the mask e.g. by using an outbreathing valve and CO2 absorbing substances.