tom775257
…I am interested what the ramifications of an explosive decompression in Concorde at cruise altitude would have been…
If by explosive decompression you mean a total and near-instantaneous decompression to 60,000 ft, then the ramifications would have been serious.
The sort of damage or failure necessary to have caused this would probably have brought with it a whole host of other problems, not the least of which may have been that the aircraft had ceased to be a viable flying machine - the early Comet accidents being a case in point.
However, in the overwhelming majority of decompressions, experienced over many years on all aircraft types, the aircraft did not explosively depressurise to ambient atmospheric pressure, even if it may have felt like it to the occupants.
Whether due to pressurisation system failure, discharge valve failure, a small hull breach, a door or window blow-out, or just plain human error, the cabin took time to decompress, often a considerable amount of it.
It was this time, the time the cabin took to climb which provided the flight crew with a safety margin, precious seconds in which to act to protect passengers and crew from extreme cabin altitudes.
On Concorde, this involved the crew in protecting themselves (pressurised O2 masks) analysing the situation (what warnings?, what cabin rate-of-climb?) rectifying if possible (re-instating packs, selecting alternate systems, closing errant valves manually) or, if control of the cabin had been irretrievably lost, initiating an emergency descent.
The cabin altitude on Concorde was typically around 5,000 ft in the cruise, and in common with most commercial aircraft, various flight deck warnings would occur as the cabin altitude rose through 10,000 ft, and again passing through 14,000 ft, to alert the crew to any problem, assuming their own eyes, ears, sinuses and lower intestines had not already done so!
There were also many protection devices fitted to Concorde to ensure that the cabin altitude never exceeded 14,000 ft, however, even had they all failed and the cabin had been climbing at 5,000 fpm, it would still have taken 36 seconds before the cabin altitude exceeded 8,000 ft.
It would have taken 108 seconds before it exceeded 14,000 ft and around 3 minutes for the cabin to exceed 20,000 ft, by which time the aircraft would have been well on its way down to safety in an emergency descent.
In most cases, the cabin altitude would never have got above 20,000 ft, and the overwhelming majority of these incidents, though alarming, would have been highly survivable for all occupants.
…would the passengers have all been unconscious pretty quickly due to the low pressures/ lack of forced pressure breathing?...
I hope I have shown that passengers being exposed to atmospheric pressure at FL600 was an extremely remote possibility for several reasons. It was something that never happened, or even came close to happening, during 27 years of commercial service.
However, to answer to your hypothetical question, if passengers were to remain exposed to atmospheric pressure at FL600 for any appreciable length of time, then a few seconds of useful consciousness, followed by a merciful lapse into unconsciousness, would be the probable outcome.
…Did a pilot/ both pilots always have to wear a mask during cruise?...
No.
The crew did not routinely wear O2 masks at any stage during the flight. All the O2 procedures were normal for long haul passenger aircraft operations, with the exception that the flight crew had a pressure breathing O2 system available.
…how fast could the Concorde get down to 10,000ft from cruise….
Starting from FL600, initially it would have been around 12,000 - 15,000 fpm, reducing on passing through FL500 and increasing again on passing through FL400.
On Concorde, once below FL500 an emergency descent also became a deceleration manoeuvre, which brought with it the necessity to move fuel forward rapidly to keep the CG within limits as the aircraft Mach number decreased.
Various emergency descent profiles were tried during test flying. The one that was finally adopted for line operations gave an average rate of descent of around 7,000 fpm, so the answer to your question would be around 5 – 7 minutes to 10,000 feet, depending on the aircraft altitude at the start of the descent.
Regards
Bellerophon