Oceangate

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.