African Dude
Liquid Oxygen does NOT burn, but, if given a suitable source of heat (droplets falling in air can get it), it will vaporize. The density of liquid Oxygen at boiling point at ambient pressure (Temp=90K, or -183°C or -297 F) is slightly below the density of liquid water, whereas gaseous oxygen is slightly heavier than air. This gives us an expansion factor of the order of 1000 at ambient temperature and pressure. At 500 hPa, this factor is 2000. Liquid hydrogen is found at even lower temperatures (BP =20K or -253°C or -423F), and is much less dense (leading to those huge tanks, where liquid oxygen takes only a small volume), but the order of magnitude would be in the same range (too lazy to do the math)
Both liquid oxygen and liquid hydrogen tanks are pressurized, both for structural and thermodynamic reason, about which I will not elaborate. If the tanks get punctured or break apart, without combustion taking place, you will very quickly get a cloud of liquid droplets vaporizing and expanding very quickly, but this not enough to generate an explosion in the open.
Combustion of hydrogen with oxygen occur only in the gaseous phase, but as soon as it has started, the heat of combustion is sufficient to vaporize droplets. In that case, the mixture is very likely to explode (inflamation of hydrogen in air at ambient pressure is between 4% and 75% volume fraction, this range widens when you increase oxygen concentration, but I do not have exact figures at hand).
Lu
If combustion takes place (be it in air or oxygen-enriched air), it will produce huge amounts of heat and water vapor, which means that the water will not necessarily condense down to solid state. Beacuse of said heat, the flow in the cloud will be turbulent which will give you a cumlus-like cloud, even if you have ice forming. Moreover, in the case of an explosion, the flame is in the center and the cloud expands radially, hiding the flame from sight.
Last edited by Bre901; 5th Feb 2003 at 15:54.