"People were jumping out of the balloon from about the height of a seven-storey building, " Cherry Tohamy, an Egyptian who was in another balloon, told the BBC.

BBC: Egypt balloon crash: Two Britons and UK resident die

Unlike a conventional hot air balloon where the height is controlled by a burner, the gas balloons are filled with hydrogen and controlled by releasing gas to go down and throwing out ballast to go up.

BBC: Wiltshire

Finally, at a height of almost 19km, the balloon burst and the payload fell back to earth helped along by a parachute.

BBC: Giant weather balloon carries out its sky mission

If his fragile balloon were to tear and suddenly deflate below this height, there would not be enough time for the capsule to release itself and deploy a parachute.

BBC: A man on ledge, 23 miles up and no fear