[bjpete]

Listen to what Jon said, If you haven't taken a basic SCUBA course, then you probably haven't heard of the different gas laws, simply stated it's this: increased pressure (increase in depth), a given volume of air will be reduced, decreased pressure (rising to the surface) a given volume of air will expand. If you have your lungs full of air at depth and ascend then air in your lungs will expand which could be bad news. In SCUBA diving we train our students never to hold their beath while using compressed air, you must always be breathing (both in and out).