| rdfs:comment
| - When the porthole breaks, air will start to rush out into the sea, with some violence and a good deal of noise. The air pressure exceeds the water pressure at the porthole by an amount proportional to the height of the porthole above the moon pool water surface. This appears to be about 2.4 m (8 ft) and the overpressure will be 0.24 atmospheres (about 3.5 PSI). Even though Charlie has already closed the control room door, the air in the control room retains this overpressure until the porthole breaks. The air then rushes out into the sea and within a couple of seconds, its pressure reduces to match the water pressure at the porthole. The air will now escape more slowly in great big bubbles, and gulps of water will slosh in between bubbles, just as happens when you push an open empty bottle
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| abstract
| - When the porthole breaks, air will start to rush out into the sea, with some violence and a good deal of noise. The air pressure exceeds the water pressure at the porthole by an amount proportional to the height of the porthole above the moon pool water surface. This appears to be about 2.4 m (8 ft) and the overpressure will be 0.24 atmospheres (about 3.5 PSI). Even though Charlie has already closed the control room door, the air in the control room retains this overpressure until the porthole breaks. The air then rushes out into the sea and within a couple of seconds, its pressure reduces to match the water pressure at the porthole. The air will now escape more slowly in great big bubbles, and gulps of water will slosh in between bubbles, just as happens when you push an open empty bottle horizontally into a sink full of water. It will take more than just a few seconds for the room to fill up with water, but it can't fill above the top of the porthole. Charlie can stand on tip-toe or float up with the rising water and breathe the large pocket of air above it, which will last him maybe an hour, while Desmond works out how to get him out of there, assuming Charlie's not quite skinny enough to swim out through the broken porthole. It would seem intuitive that the weight of water in the control room would force the control room door open if Charlie undoes the latches on the inside. But the air pressure in the submarine port holding the door shut will still be greater than the pressure of the water on the inside, because the former is created by a greater total depth of water (i.e. depth of the moon pool surface below sea level). The pressure difference on either side of the door is proportional to the difference in height between the moon pool surface and the mid-point of the door, probably about 2 m (6 ft). It's equal to a 2 m / 6 ft head of water, which is quite a lot, and the two of them couldn't push and pull it open against that much pressure, which produces 2000 kg-force on the door if it's 1 square meter in area. If Charlie ducks underwater and undoes the latches and if Desmond can find something like a long length of strong steel pipe to use as lever, he may be able to lever open the door just a crack. A better solution is to use one of the firearms to shoot a hole in the door's porthole. Air will rush into the control room increasing the size of Charlie's air bubble up near the ceiling, then it will start bubbling out of the broken porthole again. The moon pool level will rise up and when it reaches half-way up the control room door, the pressure on either side of it balances and the door can swing open. Again, the water level in the main chamber can't rise higher than the top of the broken porthole. They have about a 12 foot space in the submarine port above this to breathe and prepare for the ascent. They need to get the diving gear, not only to assist with breathing on the swim out and the ascent, but because the Looking Glass is deep enough that, like divers, they ought to stop every 10 m on the ascent to clear nitrogen from the blood, or they risk suffering the bends.
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![[RDF Data]](/fct/images/sw-rdf-blue.png)