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So if the runway had been swept before Concorde's departure, the accident would not have happened. Which leads me to ask:
1 - what is the normal frequency of take off / landings before runways are swept.
2 - would the runway normally be swept anyway in advance of a Concorde take off / landing given its known vulnerability of tyre damage."
The above seems to be focused on the initiating events. This is normally reserved to lawyers attempting to assign blame among multiple imperfections they care little about understanding.
There are hundreds of initiating events that occur each day in commercial flights yet almost none result in a catastrophic result such as a crash. This is because the design of the product has considered that these events will occur, even with multiple interactions, and that some consequences will result. The design intent was to minimize the number of likely interactions and to mitigate or apply barriers such that the consequential result will not be catastrophic to the passengers. It was therefore assumed that planes using runways would leave parts behind occasionally. If you have ever walked in the grass beside a runway, you would find enough parts to build an aircraft someday.
It was also assumed that some of these parts would cause cut tyres and even flat tyres. After all this data has been documented and recorded on all types of aircraft for years. However, the frequency of a blown tyre causing a fuel tank rupture is extremely rare indeed, no doubt due to the robustness of the fuel tank structure to the more hazardous (size number and release speed of) uncontained engine fragment.
Then after the aircraft was certified under these assumptions, new data became available which raised issues ,not about the initiating event (debris on the runway), but the consequential assumptions of energetic tyre ruptures that could/would puncture fuel tank skins. Some of these lessons were recognized and reinforcing and better understanding of these lessons has now been brought home with the recertification of the aircraft after the unexpected catastrophic accident. What is now being dealt with is a key part of the accident causal chain that will be most practical to interrupt.
Anybody who thinks that the can eliminate the initiating part of the causal chain is kidding themselves.