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Why the oxygen timeline on sub may not be so fixed

Titanic sub: The latest in 70 seconds. Video, 00:01:10Titanic sub: The latest in 70 seconds

Sub rescuers expand search area as oxygen fears mount

Watch: Titanic sub passenger recalls losing contact. Video, 00:00:40Watch: Titanic sub passenger recalls losing contact

Inside Canada's search and rescue plane. Video, 00:00:39Inside Canada's search and rescue plane

What happens if the oxygen runs out. Video, 00:01:10What happens if the oxygen runs out

Sounds a glimmer of hope in sub search - but what next?

The location of search and rescue efforts. Video, 00:01:45The location of search and rescue efforts

Titanic sub: 'We have to remain optimistic and hopeful' Video, 00:00:58Titanic sub: 'We have to remain optimistic and hopeful'

Experts had warned about safety of missing sub

Adventurer who visited Titanic hopes for rescue

'No confirmation of what tapping sounds are' - Coast Guard. Video, 00:00:47'No confirmation of what tapping sounds are' - Coast Guard

How tapping sounds might reach rescue teams. Video, 00:01:33How tapping sounds might reach rescue teams

Scientist recalls near-fatal dive to Titanic wreck

Search for sub relocated after noises heard

Safety investigations launched into Titan sub deaths

Watch: The missing Titanic sub... in 77 seconds. Video, 00:01:17Watch: The missing Titanic sub... in 77 seconds

Titan sub: Narrow, dimly lit tube with curtained-off toilet

St John's hoping for missing sub's safe return. Video, 00:00:57St John's hoping for missing sub's safe return

Rescuers scan ocean for Titanic sub as clock ticks

Vehicle searching Titan's last known location - Coast Guard. Video, 00:00:43Vehicle searching Titan's last known location - Coast Guard