Search for lost submersible near Titanic expands due to low oxygen levels.

The search area for the missing submersible, Titan, has doubled in size as rescuers rush more ships and vessels to the area, hoping to narrow their search with underwater sounds detected for a second straight day. The submersible disappeared on its way to the Titanic wreckage site, and authorities are still holding out hope of saving the five passengers onboard. The search is being conducted in an extremely challenging environment, and many obstacles remain, including pinpointing the vessel's location, reaching it with rescue equipment, and bringing it to the surface before the passengers' oxygen supply runs out. Newly uncovered allegations suggest there had been significant warnings made about vessel safety during the submersible's development.