From 70 meter it will be critical
Assuming the submarine hasn't imploded rapidly, killing or maiming you through shock-wave or flying splinters, the biggest hazard will be the air you breathe.
70 meters is the depth from which both components of the compressed air (having density 8 times bigger than on surface) pose a grave danger for you. Nitrogen is narcotic, causing disorientation, nausea, panic attacks or even hallucinations (if you go deeper, coma and death can occur). Oxygen becomes toxic, and can cause uncontrolled cramps or paralysis, which can occur suddenly and without any warning. Both effects are stronger with the time you are breathing compressed air. With every second your tissues will become more saturated with nitrogen, which can cripple or even kill you in case you make it alive to the surface.
So you have really limited time to reach any opening, take your last breath and make your way towards surface. With the full lungs you should be positive, but you need to constantly breathe out so that your lungs won't explode because of air expansion. This is not the only danger, the way is long! Trained freedivers manage it to resurface with the speed of over 1 meter pro second, but they are well trained and have fins (though, they need to fight gravity because their lungs are more empty you can imagine on those depths). If you got panic, you might loose consciousness, breath out, and sink back to the bottom and die.
Considering you've reached the surface intact, the bubbles of nitrogen can form in your blood or nerve system, crippling you or killing you on spot, because your blood saturated with nitrogen in the depth, which can't find it way out quickly enough.
You'd have to be extremely lucky to survive ascent from more than 100 meters. Many scuba divers have died in that depth from nitrogen narcosis trying to break records with pressed air.