What might have happened to the Titanic exploration sub?

The search continues for a submersible that disappeared on a trip to view the wreckage of the Titanic. Five people are on board. The Coast Guard in Boston says the sub lost contact Sunday, about an hour and 45 minutes into its dive. Butch Hendrick is the president and founder of Lifeguard Systems, which conducts dive training for public safety officers. He joined CBS News to talk about the search.