CO2

[Observer]

Originally Posted by Kpt. Lehmann

To a degree I believe this is true!!! (Especially in boats that have made deep or prolonged dives...

In Iron Coffins there is a passage that stated a man opening the hatch upon surfacing had his cap sucked right off his head...

That could be an exaggeration but.... lets think about this for a moment.

The deeper you go... the more your hull is compressed... (What do you think all the creaking and groaning is about?)

Even if the pressure hull is compressed 1/4th of an inch overall... the air-pressure inside the boat must go up!!!

Upon rising to the surface there is no guarantee that the hull will regain that 1/4th inch. (Crushing a can of coke is much easier than popping it back into shape no?)

So the air stays compressed until the hatch is opened.

I suspect too, that in sinking boats, crewmen in some compartments would suffer ruptured ear-drums before death... due to the onrushing water compressing the remaining air very quickly.

No, no, no! You can believe what you want, but it would be fundamentally wrong on multiple levels!

As the boat submerges the hull does compress, but it has a negligible impact on atmospheric pressure inside the hull. Being inside a submarine is nothing like SCUBA because in order for a diver to inhale at depth the supply pressure must be greater than the current dive depth (44 lbs/100 ft or 1 atm/33 feet). All the physiological side effects aside due to the partial pressure of oxygen and nitrogen (Oxygen being more of a concern when breathing Nitrox), it's why the tank empties so fast at depth (roughly 50 lbs every breath when at 100 feet...that will empty a 80 cubic foot cylinder pretty quick).

Submarines on the other hand don't have this problem. The atmosphere is about 1 atmosphere or slightly higher. Interestingly the concentration of CO2 in a submarine (CO2 being the chemical trigger in the lungs to stimulate breathing) is about 50 - 100 times higher than atmospheric. The best way to minimize the effects from CO2 and CO is to increase the pressure in the boat. Submariners call it taking a pressure on the ship. 688s doe this using the low pressure blower. Uboats could use the diesels, but it would be a tricky evolution. In either case taking a pressure on the boat reduces the partial pressure of CO2 and therefore minimizes the negative effects (fatigue, lethargy, headache) of CO2.

Pressure in the boat can increase due to several other routine evolutions, but the most common is venting high pressure air inboard. This can happen, for example, when firing the torpedo tubes.

The fact that the sailor had his cap blown off indicates the pressure in the boat was greater than atmospheric, and when the bridge hatch was opened, the pressure equalized. There have been cases of sailors opening hatches before equalized to atmospheric that literally shot the sailor out of the boat in some cases severely injuring or killing the sailor.