From the article:
When a submarine hull collapses, it moves inward at about 1,500mph (2,414km/h) - that’s 2,200ft (671m) per second, says Dave Corley, a former US nuclear submarine officer.
The time required for complete collapse is about one millisecond, or one thousandth of a second.
A human brain responds instinctually to a stimulus at about 25 milliseconds, Mr Corley says. Human rational response - from sensing to acting - is believed to be at best 150 milliseconds.
The air inside a sub has a fairly high concentration of hydrocarbon vapours.
When the hull collapses, the air auto-ignites and an explosion follows the initial rapid implosion, Mr Corley says.
Human bodies incinerate and are turned to ash and dust instantly.
I believe they sent out a message that they had heard a loud pop and were aborting the mission? So the people on the support ship were basically waiting for them to emerge, and the worrying only really started when they took too long.