I would say when I went on my second certification dive in open water would have to be my worst one to date. We dove down to the platform where evryone was meeting up to perform the tasks given for the 2nd open water dive. All of a sudden some bubbles started to come from my spare 2nd stage. I got one of the dive masters attention so he could see what was going on. First he tapped on it, then hit it, then pushed purge button. All of a sudden, WOOSH both of my 2nd stages started free flowing like all hell! The buddy 2nd stage whipped out of his hands and started slamming the hellout of me and I was biting down on the corner of my primary trying to keep it next to my mouth so I could breath from the bubbles. Meanwhile that divemaster FROZE I mean just dumb founded. I had to keep signaling to share his air but he was temporarily froze. Then I signalled that I was surfacing no matter what...running the hell out of air fast! When I started to ascend he finaly gave me his other 2nd stage and we started to surface. But when I started using his air, it allowed my reg. to whip around and wham wham.. both hitting me. Slowly surfaced, whole time both my regulators smacking me. When we get to the surface, everyone was looking on to see what they called "a HUGE surge of bubbles" from the water. Man was that a little embarrassing and quite scary. I was so glad I payed attention during the pool dives. Come to find out, the ceramic valve thingy(I ain't no expert at the terms) in the 1st stage shattered. Man those reg.'s got like jet propulsion when they free flow on their own. Well thats my bad experience so for! What a time for something like that to happen, during certification, SCARY!! Didn't deter me though, I actually got more dives in than anyone else in the class cause the instructor felt horrible(was his equip. that I everyone was using) Anyone else gone through this experience??