Need environmental science help with an atmospheric question

If a pressurized aircraft flying at high altitude suffers rapid decompression, a cloud can form in the cabin. Explain. Consider and aircraft with cabin pressure equal to atmospheric pressure at 5000ft and flying at 30,000ft. If the temperature of the cabin air is 20C and its relative humidity 20%, can a cloud form if there is rapid decompression? Below approximately what altitude would the air craft have to be flying such that a cloud could not form upon cabin decompression?