rescuers think there may still be survivors in that sunken ferry. we have word south korean crews are pumping oxygen into the ship just in case. while it seems like a desperate effort, it is possible to survive such a catastrophe, even if the ship has gone under water. more now from brian todd. >> reporter: rescuers in south korea are in a calculated but furious scramble. they're working under the assumption some passengers aboard the sunken ferry may still be alive. past accidents tell us it's very possible. november last year, an overcrowded double decker ferry sank off thailand. about 200 people were rescued. february 2006, an egyptian passenger ferry sank in the red sea, more than 300 were rescued there. there were even underwater russ cues after the "costa concordia"